ML20087E045
| ML20087E045 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 01/09/1992 |
| From: | COMMONWEALTH EDISON CO. |
| To: | |
| Shared Package | |
| ML20087E043 | List: |
| References | |
| NUDOCS 9201210007 | |
| Download: ML20087E045 (35) | |
Text
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B.YRON.STAIlON UBS DESIGN BASIDBECONSIITMIlON EINALREEQBI JanuaryA_1992 EXECUTIVE
SUMMARY
I.
Histoneal Backgroundilntroduction 11.
UHS Reconstitutien Scope latroduction A.
Byron UHS Design Bases B.
Increase in Steady State Heat Load C.
Increase in LOCA Unit Containment Heat Load D.
Wet Bulb Temperature increase E.
Changes in Cooling Tower Flowrates Summary.oLEllectLotReconstitullon.Clianges Ill.
Methodology and Analyses latroduction A.
Scenario Development & Initial Assumptions / Conditions B.
Syctem Hydraulic Calculations C.
Containment Heat Load Calculations D.
Steady State Tower Performance Analyses E.
Time Dependent Basin Temperature Calculations IV.
Results/ Conclusions A.
UHS Operability Concerns 8.
Results of Analyces C.
Operability Assessment Recommendations / implementation V.
Attachments A.
References B.
UFSAR Changes C.
Remaining Open items D_
Figures i92012icco7 92o109 tPDR ADocK 0300o4s4
'F PDR ZNLD/1402/3
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SUMMARY
4 i
An Ultimate Heat Sink Design Bases Reconstitution effort and Operability Assessment process undertaken by Commonwealth Edison Company (CECO) has concluded the UHS meets all the applicable General Design Criteria of 10 CFR 50 Appendix A. The UHS design accident analyses and operation have been determined to be consistent with all relevant Regulatory Guides and design standards committed to in the Byron /Braidwood UFSAR. The capability of the UHS to perform its two princlole safety functions has been verified. These safety functions are: 1) dissipation of decay heat energy after reactor shutdown and 2) dissipation of decay heat energy and containment stored heat energy after an accident.
As a direct result of the review, administrative requirements have been imposed
)
until a Technical Specification amendment can be prepared and approved. The administrative limitations assure critical initial assumptions made in the accident analyses are observed in day to day plant operation. The process of reconciling descriptive UFSAR entries with the reconstitution efforts findings is underway.
Safety Evaluations will be performed for all permanent changes made to the UFSAR description.
The reconstitution and operability assessment efforts were carried out by a team i
of individuals which resulted in the integration of the operating oxperience of station personnel with accident analysis, engineering and licensing knowledge of pmsonnel from CECO's Corporate Offices / Architect Engineer's Staff. The analyses performed as part of the r9 constitution effort, as described in this report, have shown that SX cold water basin temperature does not exceed 98#F during normal and potential accident conditions. The evaluation did not result in the need for any hardware modifications to the plant. One minor setpoint value change was made for the high temperature auto closure interlock of the bypass
- valves to the Cooling Tower riser p ping. Improvements were made in the normal and emergency operating procedures to provide greater assurance of Essential Service Water Cooling Tower operation consistent with assumptions made in the accident analyses.
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I.
HISTORICAL BACKGROUND /
INTRODUCTION in October of 1980, the Essential Service Water Cooling Towers were preoperationally tested as part of the test arc 0 ram for Byron Unit 2. As a result of evaluation of the test data, Commonwealt1 Edison Company (CECO) determined that additional testing was necessary under more challenging conditions. In a letter to the Nuclear Regulatory Commission dated November 3,1986, CECO indicated that testing up to that time had demonstrated the capability of the system to handle design basis accident heat loads under limited ambient conditions. CECO proposed procedural restrictions to be in place until the additional tower performance testing could be completed and evaluated, in a
- January 14,1987 letter, CECO identified interim administrative controls to be put in place for plant operation unt!! an additional Ultimate Heat Sink (UHS) Cooling Tower Performance test could be completed in the summer of 1987. The letter I
also committed to providing an evaluation of the performance test. The Commission subsequentiv placed a License Condition in Attachment 1 to the Byron Unit 2 Full Power dperating License NPF 66 referencing the two previous letters. The License Condition stated that Byron shall comply with the schedular tesung commitments of those letters.
On March 24,1987 CECO submitted an application for amendment of Technical Specifications Section 3/4.7.5d The requested amendment would allow the 80 F Basin temperature limit to be exceeded without any cooling tower fans running during part of the pending cooling tower performance test.- On May 12,1987.
Amendment #8 to the Byron Technical Specifications was issued containing this allowance. On May 26,1987 CECO provided an analysis to the Commission which stated that previous analyses and oporating restdctions on cooling tower operation were overly restrictive Previous analyses assumed a steady state heat load on the cooling towers due to a Loss of Coolant Accident (LOCA) on one unit and the normal shutdown of the second unit, in actuality, tne LOCA heat load peaks at approximately 100 seconds into the transient and then rapidly tapers off to a lower values. If the transient nature of the LOCA heat toad and the heat abcorption capability of the water inventory in the Essential Service Water (SX) system are ta <en into account, then the administrative wet bulb temperatute restriction could be removed and replaced with a temporary operating limit of 90 F on the SX Pump discharge temperature. Upon completion of the Cooling Tower performance test the new administrative limit would be re evaluated.
On May 29,1987 two letters were issued to the Commission indicating 4 cooling tower fans were necessary v9rsus the previously indicated 3 fans, to accommodate the design basis accident at the design basis wet bulb temaerature. One of the two letters also transmitted the time dependent transient ena ysis, which supported the 90*F SX pump dischaige temperature limit, provided 4 fans are assumed ava'ilable for heat removal. A sconario leaving only 4 fans operable, while one unit is undergoing a LOCA/ LOOP and the second unit is proceeding to a sato shutdown, starts by having only the six fans required operable by Technical Specifications. A single active tallure of an Emergency Diesel Generator then caused two of the six remaining operable f ans to be non-functional. Therefore, only the four remaining fans were assumed to be available to remove the design basis heat load.
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From May 21 to June 4,1987 Byron Station personnel and Environmental Systems Corooration (ESC) conducted performance testing on the Byron mechanical draft coo ing towers. The results were evaluated and transmitted to the Commission on Februar 1,1988 as Revision 1 of the " Byron Nuclear Generating, Station Essential Service Nator Cooling Tower Thermal Performance Test Report. Our intent at that time was to submit a Technical Saecification amendment to the Commission to provide assurance beyond the ad ministrative controls already belop maintained, that Cooling Tower operation remain within the assumptions made.n the report. On April 24,1989 the Commission issued a Safety Evaluation Report and Technical Evaluation Report concluding that the Byron Essential Service Water Cooling Towers met the Commission s design cnteria.
On August 16,1990 CECO submitted an application for Amendment of the Byron Station Technical Specifications. The proposed amendment affected both Specifications 3.7.4 and 3.7.5. The proposed amendment did (cIlowing 1)
Changed the maximum basin temperaturo limit to a single limit of 88'F in combmation with additional fan operational requirements, 2) Separated the basin level switch omerability requirements from the Essential Service Water Makeup Pumps operaallity requirements, and 3) Proposed other minor changes of an administrative nature. A meeting was schedulod for March 18,1991 between CECO and NRR fo allow CECO to present the rationale and bases for the proposed Technical Specification Amendment. In preparation for the meeting / presentation CECO personnel met on March 11,1991.
During the review of March 11,it appeared there may be two assumations that were used in the calculations of the SX cooling tower heat removal capab lity that did not reflect actual conditions in certain accident scenarios, in addition, a number of questions remained unanswered regarding the UHS design bases and related analyses. As a result, CECO requested a delay of the NRC presentation. The CECO Nuclear Engineering Department (NED) began drafting an action plan to re-examine the design bases of the UHS and all assumptions of calculations supporting its heat romoval capability to ellmlnate any uncertainty, The next CECO meeting took place at Byron Station on March 27,1991. The draft action plan prepared by NED was discussed. Meeting participanto concluded that if there were inaccurate assumptions, the effect on the calculations would be offset by the margin available by the seasonal weather conditions, (i.e., the significantly lower wet bulb temperature conditions of early spring relative to the assumed 78'F calculation assumption). The other major oolnt of discussion was to identify the individual tasks of the NED action plan wh ch could be used in a more definKive operability assessment. An April 4th meeting concluded that execution of a design basis reconsutution and operability action plan would likely take until October 1, 1991 and require significant resources.
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On April 12,1991 a three stop UHS Operability Action Plan was decided upon to ensure safe and conservative operation of the SX cooling towers for the spring l
and summer of 1991 While the design bases reconstitution effort and final operability assessment were underway, two interim operability assessments were to be performed usin9 the NED operability determination procedure ENC-OE-40.1, prior to a final operability assessment determination.
The first ENC OE-40.1 assessment (Ref. 4 and 6), which was completed by NED on April 15th, addressed the two questionable assumptions made in the original analysis. This Interim operability assessment was to remain valid until June 1, 1991, by which time a more detailed operability assessment could be performed.
The next assessment would bound operatio' of the Byron units opring the time of the year which would present the greatest challenge to the cooling tower's heat removal capability under design basis accident :onditions. By letter dated April 23,1991, CECO withdrew its proposed amendment apalication to modify the UHS Technical Specifications, It was decided resubmittal o tne aroposed amendment should occur after the Design Basis Reconstfrution of tl J iS.
A second interim operabl'ity assessment was completed using ENC-QE 40.1 (Ref. 5 and 7), on June 1,1991. This assessment provided a basis for summer operation of the cooling towers. The Nuclear Engineering Department issued i
guidance to Byron Station as a part of this assessment to assure conservative operation of the SX system cooling towers during the summer until the final l
operability assessment could be performed in the fall of the year.
The final operability assessment (Ref.11) was completed on November 1,1991 and was subsequently onsite reviewed. It involved a com alete reconstitution of the inputs, assumptions and applicable design bases for tie UHS. As a result of this final assessment, long term administrative requirements were imposed and normal / emergency operating procedures were improved.
An inter-disciplinary team pertoimed each of the operability assessments subsequent to the mitial assessment, integrating the operating experience of station personnai with the accident analysis, engineering and licensing knowledge of personnel from CECO's Corporate Offices / Architect Engineer's Stah. The team generally met on a bi-wookly basis between May of 1991 cnd January of 1992.
l This report as produced by the team members and precedes a resubmittal of an applicatio-r amendment to the Technical Specificallons for the UHS.
To eri is reader of this report to more easily understand what follows, a brief desc of the Ultimate Heat Sink design is presented here. The Ultimate l
Hea; consists of two Essential Service Water Cooling Towers and the normal maks safety related makeup and badap makeup systems, Two simpilfied I
gener i _cangement drawings are provided as Figures 1 and 2 in Appendix D.
Thc d.awings depict the tower design and its interconnections with the rett of the Essential Service Water System. Each of the two safety related mechanical draft Cooling Towers consists of a water storage basin, four fans, four riser valves and two bypass valves. Normal makeup to the Cooling Towers is provided from the non safety-related Circulating Water system, w!!h the safety-related emergency supply of makeup water provided by tne Diesel. Driven SX Makeup Pumps located in the River Screen House. The Diesel Driven SX Makeup Pumps auto-start on a low level in the basins. Loss of both the normal and safety-related makeu;a pumps due to natural phenomena such as a tomado, flooding or loss of SX Maieup Pump suction (due to a selsmic event concurrent with low river flow) can be circumvented by use of the backup deep weli makeup pumps.
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l it.
UIIS RFCONSTITUTION SCOPE Introductiom The scope 01 the operability assessment and design basis reconsStution efforts was IMtlally limited to those facts about the UHS for which either the design basis was known to be incorrect or uncertain enough to warrant review.
However, the process remained flexible since the scope ol the review was allowed to broaden wh9n discrepant hems were identified.
As part of the '.901 reconstitution of the Ultimate Heat Sink design basis for Byron Station, several items were identitled as being indeterminate or different f rn those previously assumed in the UFSAR and design analyses. These items 9ct the calculated performance of the SX cooling towers during a postulated
, sign basis accident. Extensive design review and reanalysis was required to determine the cumulative effect of thelo!!owing five items on SX tower calculated cold water basin temperature.
1.
The first item is the veridication of the licensing desl n basis 0
requirements for the Byron Station UHS. The regulatory requirements were reviewed to determine the limit'ng design basis event and the lumbar and type of postulated equipment failures.
2.
The second item is an increase in the non-LOCA unit's calculated steady etate heat load, from the 3reviously assumed D
24 x 10 BTU /hr (24 MBTU/hr) cepicted in UFSAR Fi0uro 9.2 7 and derived from UFSAR Table 9.2-6 in previous UHS performance calculations.
3.
The third item is an increase in the calculated rate of energy transport from the I.OCA unit containment into the Essential Service Water (SX)
System via the Reactor Containment Fan Coolers and Containment Recirculation Sump /RH Heat Exchangers/CC Heat Exchangers as shown in UFSAR Table 9.2 6.
4.
The fourth item regards statements re;ating to the assumed worst case wet bulb temperature (Twb) for the cooling tower. UFSAR Section 9.2.5 refers to the design basis as 78*F Twb, while Byron UFSAR Section 2,3 states that 82*F Twb is the mcteorological design basis.
5.
The fifth item is that the Essential Service Water flows previously assumed are different from the operationally observed values. The flow ;seo in previous analyses assumed 48,000 gpm flowing to a single tower trom two SX pumps.
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r II.
A.
Byron 11HS DesignBaceo Design Be.quiremonta The Byron Ultimato Heat Sink (UHS) was desl ned to satisfy the 0
requirements of the following applicable General Design Critoria (GDC) of 10CFR 50, Appendix A:
2 Design bases for protection against natural phenomena 4 - Environmental and dynarnic effects design basis 5 - Sharing of structures, systems, and components 17 - Electric power systems 38 - Containment heat removal 44 - Coohng water 45 -Inspection of cooling water systems 46 - Testing of cooling water systems Since the Byron Ultimate Heat Sink is shared by the two units, the condition of both must be determined for the design basis event.
- Appendix A of the UFSAR indicates commitment to Regulatory Guide 1.27, Rev. 2 - 1976 " Ultimate Heat Sink for Nuclear Power Plants" with no exceptions. It states in part,"Also, in the event of an accident in one unit, the sink should be able to dissipate heat for that accident safely, to permit the concurrent safe shutdown and cooldown of the remaining units, and to maintain all of them in a safe shutdown condition." Tho Standard Review Plan, NUREG 0800 Rev. 2 July,198f (Section 9.2.1
- Station Serv'ce Water System) states the NRC reviewers should conclude in their evaluation that, "The applicant has met the requirements of GDC 5 with respect to sharing of structures, systems, and components by demonstratinn, that such sharing does not significantly impair its safety function, including in the evont of an accident in one unit, an orderly shutdown and cooldown of the remain!ng units". GDC 5 itself uses nearly identical wording. Byron SER, Section 9.2.5 uses different wording referring to " safe shutdown" or " normal shutdown" of the non-accident unit in two separate instances, Lin11tinollesignBasis&entandRasis.forAsnumptions For design purposes the worst case accident scenario considered for the Byron Station UHS is a LOCA coincident with a Loss of Offslie Power (LOOP) on one unit, and the concurrent orderly shutdown and cooldown from maximum power to Mode 5 of the other unit using normal shutdown operating procedures. This scenario also includes a single active failure.
The choice of LOCA as a worst case accident is in compliance with the guidance provided in the Standard Review Plan (SRP) used in the evaluation of Byron Station design and is in agreement with NRC Reg Guide 1.27. Revision 2, which requires the removal of heat resulting from the limiting design basis event. The LOCA will produce the rnost limiting heat input to challenge the UHS heat dissipation capabilities.
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j 11.
A. - Byron..UbS DesigrtDases (Continued)
The coupling of mitiating event (LOCA) with a coincident loss of offsite powm on the LOCA unit only, is consistent with industry practice for mtm.. unit sites and ANSf/ANS 51,1 - 1983, " Nuclear Satety Criteria for the Design of Precsurized Water Reactor Plants", it is also consistent with GDC 17, which was utilizeo in the design of Byron Station systems.
The intent of the guidance given for the Ultimate Heat Sink heat dissipation capability design basis is to require a shutdown of the non-accident reactor by reducing power to zero, placing the reactor in a subcritical condition, and decreas ng coolant omperature to ultimately achieve Cold Shutdown a
conditions (Reactor Coolant System temperature <200*F). Additional heat load is placed on the SX system and UHS once Residual Heat Removal (RHR)is placed in operation at approximately 350'F, Under normal conditions the minimum time to reach this condition, assuming an orderly shutdown and cooldown from maximum power using normal operating procedures, would be a total of eight hours. It would take approximately four hours to place the unit in Hot Standby at 557*F from full power conditions, ar'd an extremoly conservative additional four hours to cooldown the RCS from 557 F to 350"F, Considering the likely initial time delay in Initiating a shutdown.of the non accident unit, compethion for human resources with the LOCA unit undergoing recovery and the relatively low orlority of cooling down the non accident unit from a stable Hot Standby bondition, it would be a reasonable assumption that the non accident un!!would not ach! eve Hot Shutdown Conditions of 350*F for 10 to 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
The selection of crediblo single failures was limited to single active
' failures. Tho selection of single active failures was based on guidance from IFEE Standards, the Byron Safety Evaluation Report 1982 (Section 9.2.5) and SRP Section 9,2,5, Section 9.2.5 of the SF1P specifies that the NRC reviewer verify the UHS cooling tower design mechanical systems (fans, pumps, and centrols) can withstand a single active failure in any of these systems, including failure of any auxiliary electric power source.
in summary, the limitinp design basis event for the Byron Station Ultimate Heat Sink is a Loss of doolant Accident coincident with a Loss of Offsite Power on one unit, in cejunction with the other unit proceeding to an orderly shutdown and soldown from maxlmum power to Mode 5 This UHS accident scenar., should also include the effect of a single active failure. This particular reries of initiating event, coincident event, and single active failure is consistent with regulatory requirements and with the design basis event presented to the NRD in a May 29,1987 letter from
. K.A. Ainger (CECO) to H.R. Denton (NRC).
.f e
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- _ - - - _ = _ = _.
ll.
B.
Incroalejrt Steady _ State.Heallo.ad The previous steady state heat load from two units was 07 MBTU/hr (24 MBTU/hr for the nun.LOCA Unit plus 43 MBTU/hr for the LOCA Unit L72 M). The new steady state heat !oad from two units is 103 MBTU/Hr BTU /hr for the non LOCA Unit plus 31 MBTU/hr for the LOCA Unit). This results in a greator domand on the SX Cooiing Towers.
The towers must accept and dissipale more steady stato energf than previously assumed. The steady stata heat load of 103 MBTU/1r was i
utilized in the calculations. Tho total unorgy rejection must be considered, clnce thic steady state alorgy is added as a baselino to the LOCA Unit ContainrAnt heat loud which is varies with tir.io, 11.
C.
loctoaca la LOCAUnitSontainmentlientload Soveral chan00s were made in the analysis assum ptions which resulted in an increa9ed rate of energy transport Inio the SX system from the LOCA Unit Contalnment. A review of the UFSAR contalnment intobrity calculations indicates that the highest heat loads occur for the RC Doublo Ended Pump Suction Break with maximum saroty injection.
Provlous analyses assa.,sd 3 RCFC's and 1 Containment Spray (CS)
Pump one ating, This was conservative in the sense that it combined this ont input f ailure assumption with a coinciderst loss of heat apability failuto of two SX fans to operate). No single dissipat i could re(sult in 3 RCFC's running and 2 disabled SX fans.
active fai In contrast, this reconstitution study maximized the accident unit containment heat load to the UHS by:
operating,g scenarios with 4 RCFC's and olther 1 or 2 CS pump (s)
Postulatin Assuming higher SX water flowrates to the RCFC's, Assursg hicher air flowrates to the RCFC's, and Assuming earlier switchover to Containment Rocirculation phase and correspondingly earlier RHR haat loads witn 2 CS Pumps operating, consistent with the design of ECCS recirculation.
i t
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l 11.
C.
Increatoja LOCA. Unit ContainmenLHeat Load (Continued)
The 4 HCFC's/2 CS pump case, in cornbination with the other changes above resulted in reater LOCA Unit Containment intocrated heat loads of approximaie! 25% for the first two hours after acc dont initiation and an increase i LOCA Unit Containment peak heat load i
from 513 to 830.8 MBTU/hr. These incroaced heat loads were used for conservatively evaluating UHS Tower performance and do not affect previous UFSAR Chaptor 6 containment analyses.
NOTE: The Total Heat Load = LOCA Unit Containment Heat Load +
Stoady State Heat Load (ex for the 4/2 Case 830.8 + 103 =
933.8 MBTU/hr)
The 4 ROFC's/1 CS pump case also resulted in greater LOCA Unit Containment integraied heat loads of aparoximately 25% and an increase in LOCA Unit Containment pea t heat load frnm 513 to 841.0 MBTU/hr. However, the 4/2 caso does result in a slightly higher integrated heat load than the 4/1 case.
As a result of increases in the total heat load to the towers, the analysis was also expanded to inc8.10 the effects of increased evaporation from the SX Towers.
o 11.
D.
WeLBu!blempemtumJac. tease
- 1. The design conditions for the UHS were specified in the Byron UFSAR Section 9.2.5 as 78'F Twb, but Secilon 2.3 states the meteorolo0lcal desl0n basis is 82*F Twb.
The UFSAR values of 78'F Twb and 82*F Twb are both correct in l
specific contexts. The actual" design operating" wet bulb temperaL:e of the UHS is 78'F (1% exceedance value) as supported by ASHRAE (Ref.16). The worst case meteorological wel bulb temperature for the Byron Station area is 82*F for a 3
- hour period, as deter nined in 11e UFSAR 30 year climatological record search.
It is at this 82 F wel bulb whic't Regulatory Guide 1.27 states the UHS must be capable of performing its cooiing function for the critical time aenod (i.e, during the c esign basis event LOCA/ LOOP on one unitdon LOCA Ualt Shutdown). The effect on the Cooling Tower's ability to reject ile design heat loads was considered for the reconstitution analyses utilizing the hl her wet bulb temperature of 82*F, The effect of raisin the wet bulb temperature was a resultant decrease in he cooling tower performance.
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- 2. In addition to the primary analysis cases, scenarios were developed with the Tower Bypass Valves assumed open.
The bypass valves are typically opened manually in cold weather.
For normal operation, the bypass valves auto open at 52*F decreasin0 femoerature and auto close at 70*F increasing temperature. T lose interlocks help protect the tower fill section
. Calculations performed for tower bypass operations from freezing' F Twb, corresponding to the tower bypass valve utilized a 70 interlock setpoint, ll.
E.
Changos.irtCooling TowerBowrates The revious analysis assumed 48,000 GPM flow from 2 SX pumps to
- c. si le tower with 4 cells operatin) and each cell receiving an equi lent share of the total flow.
n April,1991, Byron Station performed Special Procedure #91-008 (Ref. 2) to measure SX floes and ressures under 8 different system configurations. Sargent and Lun utilized this plant specific data to benchmark the SX FLO ERIES computer model(Ref.18). After the calibration was performed, the model was run to predict Individual tower cell flows and major SX branch ilows for each of the postulated single failure scenarios. The reconstitution calculations used these predicted flows (Ref.19) to account for the change in tower performance with respect to changes in flow.
Summary of Elfocts_oLBeconstitution. Changes Extensive evaluation was required to determine the cumulative effect of those five items on the SX tower cold water basin temperature. The analyses oorformed as part of the reconstitution effort, as described in Sectlon ll, have shown that GX cold water basin temperature does not exceed the Technical Specification value of 98'F durin0 normal and potential accident conditions.
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lli METHODOLOGY AND ANALYSES
==
Introduction:==
This section presents an overview of the methodology and analyses undertaken in the evaluation of the five identified items of concern as they relate to the performance of the UHS coolin towers under accident conditions. Starting with a LOCA and LOOI on one unit, accident scenarlos were constru::ted by invokin0 single active failures on critical systems or components that were olther part of, or interf aced with, the UHS /ESW system. For each scenario, system flows, total heat loads, and steady stato perframance for individual towers were determined. These inputs were t hen incorporated into a global time dependent model of the cooling towers which yloided a prediction of the basin temperature as a function of time.
Ill.
A.
Scenarlo Devolopment.and lottlat. Assumptions / Conditions.
The scenario 'Jovelopment was a team effort among several Commonwealth Edison Company departments including Operating, Technical Staff, Ro2ulato Assurance, Project Management, Nuclear Fuel Services, Nuclear En ineering (Systems and Mechanical / Structural) an iluclear Licensing. Sargent & l. undy
)
Engineers, Westinghouse Electric Corporation and a consultant also participated in the scenario development. The scenarios developed are consistent with the design basis described in Section ll.A ' Byron UHS Design Basis" of this report.
Various single f ailure scenarios were annlyzed. These scenarios each postulate a LOCA as the initiating event coincident with a LOOP on the LOCA unit plus a single active f ailure. In addition, the non accident unit proceeds to an orderly shutdown and cooldown from maximum power to mode 5 using normal shutdown operating procedures. Typically, two sets of initial conditions for each single
" allure scenario were analyzed since Technical Specification 3.7.5 and plant administrative controls require all available SX tower fans to be running in high speed when the SX tower cold water basin temperature is greater than 80*F. Below 80 F no fans are required to be operating in h10h speed.
TheJollowing conditions were_ considered foteach single _ active.f allure analyzed.atthe_Ilmit!ng 02:F_wot bulb temperature.
- 1. Initially the essential service water system was assumed to be aligned in the normal operating configuration of one pump operating per unit, the pump discharge train crosstle valves open, the unit crosstle valves closed and the return header crosstle valves open. The normally operating heat exchangers and coolers were assumed to receive flow.
- 2. Cooling tower cold water basin level was assumed to be at the Technical Specification minimum of 50% This provides the minimum available volume for the SX system to serve as a heat sink. Basin levels above 50% provide ar" litional volume that would increase the heat load capacity of the SX system and result in a lower peak basin temperature.
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lll.
A.
Scenario _ Development.and_lnitial Assumptions / Conditions _(Continued) i
- 3. Administrative controls for the UHS require unit shutdown if the tower cold water basin temperaturo is over 88'F. Thorofore, no analyses woro performed assuming inillal cold water basin temperatures above 88'F.
- 4. It was assumed that two cooling tower cells were inillally out of servico and the corresponding riser valves were closed sinco current requirements of Technical Specifications allow this.
Consistent with administrative controls, those cells were assumed to be powered from different units' power supplies. The scenarios considered either one cell out of service on each tower or two cells out of service on one tower, depending on whichover was the most limiting.
- 5. It was assumed that the tower bypass valves were closed initially.
G. Administrativo controls require at least six tower fans running on high speed when the basin tenaerature is greater than or equal to 80 F. In those scenarios, crediL for UHS hoat removal was credited immediately following the event since the remaining f ans would auto reenergize with the respective Diesel Generator output breaker auto-closure.
- 7. Administrative controls do not require any fans running on high speed when the basin temperature is less then 80*F. Therefore, the single failure scenarios were analyzed assuming an initial basin temperature of 80*F and assuming no fans were initially running.
These scenarios did not take credit for UHS ambient heat dissipation until post LOCA operator actions were initiated to open riser valves and start fans.
- 8. When operator actions were required in the Main Control Room, it was assumed these actions occurred 10 minutes following safeguards signals. This caused a ten minute delay before heat removal via the fans begins. The 10 minute delay allowed the Main Control Room operator to reach the applicable step in the Byron Emergency Procedures. This was a reasonable assumption, because all actions are achievable from within ino control room and no local operator action is required.
- 9. The two essential service water pumps on the accident unit were assumed to operate following the LOCA based on auto start sl nals, unless the single active failure prevented one pump from 0
starting. The non accident unit pump that was running initially was assumed to remain running, it was assumed that only one non accident unit SX pump was running in the post accident modes since the non running pump wou.. not receive an auto start signal.
- 10. All s lety related essential service water system heat exchangerr and coolers were assumed to be ali signals in the post LOCA condition,gned for service based on ESF Simitaconditions_wero_ considered lotcooLweatheLoperation.with_tbo following exceptions:
- 1. It was assumed that tower bypass valves are initially open for the cool weather scenarios.
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i lli.
A.
Scen:rlo_Q:vdopm:nt and.taltlalAssumptions/ConditionsjContinu:d)
- 2. When operator actions are required locally, it was assumed these
- actions can be initiated 30 minutes following safeguards signals.
While a wide variety of single active failures can be postulated, scenarios were constructed which f allinto one of three cate0orles:
- a. Heat input to the SX System affected
- b. Heat Removal by Cooling Tower affected c Heat input and Heat Removal affected The Individual scenarios, as documented in References 10 and 17 detailed the various initial flow alignments, fans out of service and single
- active failures. For each scenario an analysis case was developed. The analysis case dectihed the initial conditions, the flow distribution, the energy transport load set, and the available equipment.
Containment Sprayfumpfailure The single failure of a containment spray pump was chosen to maximize the peak heat load on the UHS This failure maximized the peak heat removal rate b the four o erating RCFC's, however, the UHS towers were not functionell affected b this failure.
CoolloglowetEanfalture The single failure of a tower fan affects the heat removal capability of a tower. This failure was considered in addition to the two cells that were
. assumed to be out of service initially. The accident unit containment heat load on the UHS for this failure corresponds to that generated from 4 RCFC's and 2 containment spray pumps operating.
DieseLGeneratoLEallute The single failure of an emergency diesel generator affects UHS heat load, system flows and tower function. The accident unit containment heat load
- on the UHS for this failure corresponds to that generated from 2 RCFCs and 1 containment spray pump operating. The SX system flows
. correspond to one SX pump operating on each unit. In addition to the 2 out of service cells,2 additional cells were affected by the diesel failure.
4 Essential.Semice_Waterfump Eallure The single failure of an accident unit essential service water pump reduces overall system and tower flow rates. The towers were not functionally affected by this failure, The accident unit containment heat load on the UHS for this failure corresponds to that generated from 4 RCFCs and 2
. containment spray pumps operating.
Other f ailures considered result in either lower _ heat input to the tower or did not affect tower heat transfer capability or were enveloped by the -
above limiting failures.
These scenarlos provided the basis for SX system flow and tower cell flow calculations, containment mass / energy release calculations, tower performance calculations and the overall basin temperature calculations summarized in the folio.ving sections.
lZNLD/1402/16
=
s-M_---------_-------,-a._--
.. ~
Ill.
B SystentHydraullc_Calculat!vns Scenario specific SX flows were calculated (Ref.19 and 20) for each particular set of postulated accident events (Ref,12 and 17) for summer and cool weather operation. CECO contracted Sargent and Lundy Engineers to utilize their FLOSERIES computer model (Ref.18) to delerm ne SX pump, total tower, and individual tower cell flow rates.
i The FLOSERIES model was calibrated to more accurately predict I
actual Essential Service hater system flow and pressure conditions, obtained du..og Byron Station Special Procedure SPP #91008. The FLOSERIES calibration was performed using the two SPP test cases that most closely represented a post LOCA SX system configuration.
The calibrated model was utilized to analytically predict flows for each of the remaining SPP test cases. The 3redicted flows were compared to SPP measured flows to confirm the LOSERIES analytical prediction accuracy, The calibrated FLOSERIES model was used as the basis for additional calculations to predict flows for various postulated accident scenarios.
The FLOSERIES computer runs yield the flows to the major components (RCFC's and CC Heat Exchangers) and flows through the Individual tower cells. The results of the computer runs for summer opera'lon show typical tower cell flowrates range from 7,000 to 16,000 ppm / cell. It should be noted that this range of predicted tower flows differs from the previously assumed value of 12,000 g am/ cell, which was derived from the total of 48,000 gpm evenly distriauted to four cells. For cool weather operation will the bypass valves open, tower cell flows ranged from zero to 11,400 gpm/ coll.
These predicted flows were then used by CECO as input to the UHS performance calculations.
i t
ZNLD/1402/17
Ill.
C.
Containmontlient Load Calculations The containment heat load calculations (Ref.14) examined the impact of containmont heat removal equipment availability and its impact on the ultimato heat sink, in parilcular, the Reactor Containment Fan Coolers (RCFC) formed a major portion of the duty of the huat sink durin0 postulated LOCA scenarios. The analysis examined various LOCA casos with respect to equipment availability to generato a series of RCFC hoat removal rates vorsus time data using the CONTEMPT 4/ MOD 5 code. This code has boon used extonsively thf oughout tho industry and is recommended for uso for containment analysis in the Standard Revie Plan.
The mass / energy release data used was for the Double Ended Pump Suction LOC A cases with maximum and rninimum sofoty in%ction capabilities as used in the containment Integrity calculations of the UFSAR. However, those analysos diffor frem the contalnment integrity cases given in Section G of the UFSAR in that the heat romoval ratos via the RCFCs and RHR systems woro rnaximized to prodlet a limiting heat load on the UHS. The RCFC periormanco was recalculated to bound maximum expected SX flow ratos and air flowrates. The mass and energy rotoase information was adjusted to incorporato RHR heat removal rates, calculated by Wostin0 ouso, h
(Ref. 21) durin0 the recirculation phase. The coollng loads generated wore used by NED to determine UHS periormance during LOCA conditions.
111.
D.
SteadyEtatelowedMormanceAnalyseo Cooling tower performance is dependent upon the three paramotors; ambient wet bulb temperature, hoat load, and wator/alr flow ratos, in turn, values for each of those are dictated by features of the specific accident scenario under ovaluation. This section describes the program undertaken by CECO to dolormine the periormance of the Byron UHS coolin0 towers under the postulated accidents discutsed above.
The heat transfer model used to evaluate and prodlet the performanco of those cooling towers was derived from the Morkoi theory developed in 1925, as modiflod by M.R. Lofovro in 1984 (Referenco 22). As l
water passos through the fill re0 on of the tower it is dispersed into a lar00 number of small droplets so as to maximize the heat transfer surf ace area. Merkel assumed that at a given olevation in the tower each water droplet has a uniform temperature and is surrounded by a film of fully saturated air at the same temperature. Heat is transferred from the water primarily by evaporation from the film into the air.
^ litionally, because 11e air is cooler than the water, some degrou of bansible heat transfer takes place as well. Using several approximations Merkel showod that the total rate of heat transfor was proporilonal to the droplot film to air enthaby difference. This relationship was then incorporated into an ntegral, referred to as the demand integral, which could be used directly to evaluate tower performance.
M. R. Lefevre's contributions improved upon the earlier approximations with the end result that more accurate and conservative predictions of tower performance woro achloved. Using these principles, the MRL Corporation develo aod a general computer program which was used extensively in the U lS reconstitution effort.
7.NLD/1402/18
lit.
D.
Steady _Stato_TowetPctiormance Analysos (continu:d)
Tho Byron UHS cooling tow:r t:st program wcs compl:t:d in 1987 characteristic, (Ref. 3). jective the determination of the tower and had as the main o3 A total of 33 so 3arato tests woro completod, with varying wet bulb temperatures, wauer flow ratos and hont loads.
Simultaneous measutomonts of the alt flow allowed for the relationship of air to water flow to be determined as well. The tower characteristle and air water curvo are required when predleting oorformance at conditions other than thoso directly measured. Thesa 3yron specific cooling tower functions woro then incorporated into the MRL computer program by Environmental Systems Corporation.
Before using a computer program for safety related applications it must first undergo a validation verlilcation arocess por CECO oroceduros. The validation plan utillzod a land calculation to ndependently verify the accuracy and reliability of the code (Ref. 23).
The results of this comparison are documonted in the validation report (Ref.15).
The hand calculation used the MRL heat transfer model, together with the Byron UHS tower characteristic and alr/ water flow relationship.
The only differences betwoon the hand calculation and the computer program methodology were as follows:
- 1) The MRL program used a multi-point Simpson's Rulo integration scheme to ovaluate the domand integral; the hand calculation used the alternate mothod of Gaussian Quadrature to completo this task, and
- 2) The program used an lloration scheme to dolormino the sensible and latent heat transfers so aarately,Instead of assuming fully saturated air upon en1ry into the tower, as was the case in the hand calculation.
A total of nineteen comparisons between the MRL program outputs and the hand calculations were mado, (Rof. 9). The main paramotora wore varied over the following ranges:
ambient wet bulb temperaturo: 50,70 and 82 'F Twb water flow por coll: 6000,8000,10000 and 16500 gpm
-cooling tower rango (AT): 4,20,23,30,38 and 40 'F Those broad parameter variations enveloped the conditions required for ovaluation of the accident scenarios.
The level of agreement between the MRL rogram predictions and the hand calculations was shown to be very hi h. Values of the predicted cold water basin tom )orature agrood to wit iln -0.40 to +0.02 F with an average difference o' 0.09'F. Additionally, fer all but three cases, the hand calculations yloided cold temperatures below those given by the program. The MRL program, then, as judged by the banc calculation, was seen to give conservatively high values of cold water temperatures over a wide spectrum of flows, cochng tower ranges and wet bulb temperatures.
la summary, this reanalysis of the porie:mance testing of the Byron cooling towers confirms the results obtained in 1987. Therefore, the tower characteristic and resultant arodicted performance remain unchanged from that given in the ESC test report (Ref. 3). Further, the successful validation of the Byron s )ecific MRL computer program allows for its use at conditions specifiec by each accident scenario.
ZNLD/1402/19
e Ill.
E.
IlmaDependent Dasinlemperature_ Calculations This calculation predicted the basin temperature using a time dependent two coolin0 towers model (Ref. 8). The basin temperature was the important result for it is the inlet temperature for the essential service water system. The calculations were aoriormed using as an input, the scenario document which ovaluatoc the various combinations of failures and plant inillal conditions as described in Section Ill. A.
The timo dependent feature of the model was developed to account for the translent nature of the LOCA heat load. The containtnent analysic as described in Section 111. C. showed a LOCA Unit containment peak heat load of 830.8 MRTU/hr at 45 seconds and an avera00 heat load of approximately 450 MBTU/hr for the first hour after the accident. At two hours into the LOCA the heat load has decreased to approximately 260 MBTU/hr and continued to decrease.
The calculations used the timo dependent total heat loads to dete mine the amount of heat added to the essential service water cystem.
The two cooling towero model was developed to orovido the capability to nodel differont flow and energy (heat load) go ng to each of the co9 ting towers. As discusnod in oection 111. B, the flow to each of the cooling towers could be c., Nicantly different under different accident scenarios. The model also '.ad the ability to account for non functional passive cells in a cooling tower. The fraction of flow to a tcwor was determined by dividing the flow to that tower by the total flows to both towers. The fraction of er.ergy to a tower was determined by dividing the flow through the LOCA unit RCFCs that is going to that tower by the total flow through the LOCA unit RCFCs.
De 3ending on the scenario, the energy transport also considered the distribution of miscellaneous heat loads. Cooling was assumed to occur only for cells with f ans running at high speed.
The calculation used the followin0 esign inputs:
d
- 1. The accident scenarios and initial assumptions woro as described in Section Ill. A.
- 2. The flows to the individual tower cells were determinad by the Sargent & Lundy (Ref.19 and 20). The flow data were developed based on the system alignments under different accident scenarios. The data was used to determine th6 amount of flow and energy going to each of the cooling towers.
ZNLD/1402/20
Ill.
E.
Ilme.DependenLBasin.Iemperature_ Calculations (continued)
- 3. The basin volume was assumed to be at the Technical Specificat$on minimum of 50%, corresponding to an SX system Inventory of 1,030,000 gallons (Reference 1).
- 4. The steady state heat loads of 31 MBTU/hr from the accident unit and 72 MBTU/hr for the other unit were used. These heat loads were from a Sargent & Lundy calculation (Ref.13). These steady state heat loads were added to the LOCA Unit conta!nment heat loads to obtain the total heat load on the UHS for the basin temperature calculation.
5 The LOCA energy profiles for various single failuro modes were obtained l rom the calculation performed by CECO Nuclear Funi Services Department (Ref.14). This calculation included different cases which evaluated the effects of various combinations of available RCFC's/CS pumps or the loss of an emergency diesel generator. The calculation also included a case which provided a
' benchmark' of the UFSAR analysis. The calculated heat loads were approximately 25% higher for the first 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> than the heat load reported in Figure 9.2 7 of the Byron /Braldwood UFSAR. As an example, Figure 3 graphically represents the transient UHS Total Heat Load for scenarios where 4 RCFC's and 1 CS pump are removing heat from containment.
- 6. A wet bulb temperature of 82 'F was utilized for the majority of the analyses cases. For cool weather operation, a wet bulb temperature of 70 *F was used.
- 7. The cooling tower performance curves generated by the MRL computer pro 0 ram, as described in Section Ill, D, were based on the average flow per cell to a cooling tower. In all of the cases, the cooling tower performance curves were generated using a flow slightly higher than the average tower flow. This method gave a conservative estimate of the cooling tower performance since the tower performance increases with decreasing flow.
Thirty separate calculallons (Ref.10 and 24) were performed to evaluate the time dependent basin temperature resoonses. These calculations also included sensitivity runs to evaluate the et"ect of varying the fractions of flow and energy to the towers by + 10% The results o' the calculations verified the basin temperature does not excerd 98 'F under the postulated accident scenarios.
i ZNLD/1402/21
111.
E.
IlmRDependent Dasialemperatuta_Calculat!ons (continued)
Several of the assumptions utilized in the calculations were inherently conservative. These conservatisms, while not being quantitatively analyzed, provide addillonal margin to the 100 'F SX system basin design temperature.
Some of the major conservatisms are:
ec minimum of
- 1. Besin level was asma ed to be at the Tech Sp% level which would 50% The basin is ra'ually maintained at 82 provide additional tower heat capacity.
- 2. No credit was taken for ambient heat dissipation in cooling tower passive cells (i.e. thoso cells with riser valves open but the fans off). Any coollng that occurn from these passive cells or from f ans running in low speed would provide more margin to the maximum basin temperature determination.
- 3. The 80'F basin temperature calculations assumed 10 minutes for operator action to turn on the f ans in high speed. The fans wouid typically be running In high speed eartler than the analys!s assumed when started in accordance with emergency operating procedures.
- 4. No credit was tanen for the cooling contribution from the makeup flow of the SX makeup system.
- 5. More fans than assumed are usually maintained functional.
It is certain that the calculated peak basin temperature would be lower li any of these conservatisms were removed.
ZNLD/1402/22
IV.
RESULTS/ CONCLUSIONS Introduction This section summarizes the results and conclusions of the Design Basis Reconstitution arogram for the Byron Ultimato Heat Sink. The original concerns are d scussed along with their resolutions as they were incorporatud into the final calculations. Finally, the recommendations from Nuclear Enginooring to Byron Station are addressed and itomized.
IV.
A.
UHS Oporability.concetns The UHS was designed for both normal operations and accident conditions such that the return temporature of the coolant supalled to essentialloads would always bu loss than or equal to 100*F. A va'uo of 98'F was used to maintain a EF margin to the 100'F SX system design temperature consistent with previous analysos. Questions relating to heat luads and flow and their potential impact on this limiting temperature ultimately resulted in an examination of the actual design basis of the UHS.
As delinoated earilor in this report, the UHS is required to satisfactorily diss!pato the heat loads trom both units operating initially at 100% power, where ono Unit experienctis a LOCA/ LOOP, and the other unit proceeds to an orderly shutdown. Concurrently, a single activo failure is postulated to occur. Those initial condillons, coupled w th ambiont weather conditions and operating requiroments, established the startin0 point for evaluation of all other concerns.
The ability of the UHS cooling towers to satisfy the 98'F Technical Specification temperature limit receives it greatest challengo in summer weather when the wet bulb temperature can be relatively high. As the wet bulb tem peraturo increases, the temperature to which water can be cooled by a coo ing tower also increases, With the exception of bypass operation, which only occurs during cool weather, the value of 82 F was used for the limiting wet bulb temperature for all calculations.
The questions concerning SX flows to the cooling towers were resolved in a two step process. Starting from the accident scenarios, the status of equipment and overall system lineup was establishod. The benchmarked FLOSERIES model for the SX system was used to determine flows, in particular those directed to Individual cells of each of the cooling towers.
As mentioned earlier, the water flow throu0h activa tower cells is one of the main factors affecting tower performance.
The finalitems of concern were the magnitudes of the heat loads from both units. The postulated accident scenarios again were used to quantify these loads which were separated into two cawgories. First, the steady state loads from both units were determined by IIsting the individual loads of all components assumed to be in service. More significantly, the transient LOCA unit heat loads were re-evaluated for each scenario. The loads were then summed and incorporated into the final calculations.
ZNLD/1402/23
l l'/.
B.
Results otAnalysis The ability of th9 UHS cooling towers to satisfy the design objective of maintaining a water return tem;wrature of loss than or equal to 98'F has been ovaluated under norm..
4 vcident conditions. Of most concom was the tower response to
%sts accident.
Accordingly, the ma ority of the reconstituvon offort was directed toward examining a} spectrum of pontulated single falluto scenarios.
The normal unit operatinj and shutdown loads are minimal when compared to accident heat loads. Thorofore, under those conditions the UHS cooling towers have ample capacity to maintain the basin tem >oratures well belew the Technical Specification limit of 98'F. At bas n temperatures above 80'F the plant is requlrod to have a minimum of six fans oaorating in high spood. Currently, an administrativo limit of 38 *F is employed, above which shutdown is required.
The accidents which woro evaluated woro derived directly by application of from the system design basos. With one unit experloncing a simultaneous LOCA/ LOOP and the other unit proceeding to a normal shutdown, four major accident scenarios woro developec by postulating single activo f ailures which could affect total heat loads and/or cooling tower capability. As allowed by Technical Specifications, two of the eight f ans were assumed to be out of service. This condition reduces the overall tower capability. Two calculations for each of the scenarios were completod, one at an inillal basin temperature of 80*F ( no fans until 10 mintuos), and the other at 88'F (fans automatically re-onergize). Finally, ihn most challenging weather condition was assumed, that of an ambient wot bulb temperature of 82*F.
ZNLD/1402/24
In summary, the results of the detalled calculations are as follows:
1.
Eallure.otit's Bigber_ Capacity _ContainmenLSprayf ump All other equhment was assumed to function properly. This case is of interest because It resulted in the highest peak heat load being supplied to the towers. The maximum basin temperature for this scenarlo was calculated to be 95.7 F.
2.
Failure of.a_CoolingTower Fan This accident scenarlo was important to evaluate because of the resultanilimited tower capability. Although it is known that some de0ree of cooling takes place in a aassive coll, the calculations conservat voly took no crediu for such heat removal. Figure 4 depicts the resultant temperature profile for this scenario for the cases starting from inillal basin temperatures of 80*F and 88*F. The maximum basin temperature was calculated to be 97'F for this scenario.
3.
Eni!u re_olonoImergency. Die seLGene rator This scenario resulted in the possibility of two failed tower fans. However, the accident heat loads were also signliicantly reduced due to the fact that only one train of RCFC's was removing heat from containment. Calculations for this scenario resulted in a maximum basin temperature of 06.2*F.
4.
Fallute_olan Acc.!dentJ)nlLSXEump The impact of overall reduced flow was evaluated in this scenario. Because tower performance generally increases with reduced how, this accident was not as great a challenge to the UHS cooling towers. The rnaximum basin temperature was determined to be 95'F.
Based on the above calculations and results, it has been demonstrated that for all accident scenarios the basin temperature never exceeds the limiting Technical Specification Bases value of 98'F. Further, as discussed in Section Ill.E. several conservative assumptions were used, which if removed, would result in lower values of maximum basin temperatures, in addition to the primary analysis cases, the effects of cool weather operational al!gnments were considered, The major change was that the ambient wet bulb ternperature and the Initial basin temperature were assumed to be 70*F consistent with the tower bypass valve interlock setpoint. The other major assumption is that if a bypass valve falls to close, there is a time delay of 30 minutes for local operator action. An examale of the temperature proflie for ene scenario of byaass operat on is shown in Figure 5. Maximum i
emperatures or the seven analyzed cases were all determined to be 1-c less than 91 F..
The analysis was expanded to include the effects of increased evaporation on the SX towers due to the increased heat loads. The analysis demonstrated that the existing SX make up systern can adequately maintain a water supply to the basins during a design basis LOCA under an oaverse set of assumptions (Ref. 25). These assumptions include low river level, SSE, and single active failure.
ZNLD/1402/25
Operability. Assessment Recommendations / Implementation
\\
IV.
C.
Nuclear Engineering Department made soveral recommer.dations to prosorve the assumptions used in the analyses.
BYRON STATION IMPLEMENTING NED RECOMMENDATION ACTION:
The OOS outago editor program and 1.
Maintain Riser station operating procedure Valve Closed BOP SX T2,"SX Tower Oooration when Fan is OOS Guidelines",were revised to couple riser closing to a fan cul of servico.
Station abnormal operations procedures 1/2 BOA PRI 7, "EssentialService 2.
Maintain Basin Temperatuto less Spoc LCOAR procedure OBOS 7.51aworo rev than or equal to 88 F Byron MCR Annunciator HosponsoProcedures. BA for actions to control basin temperature.
Procedures 1/2 BOA PRI 7 and BAR 3.
At least six f ans 1/2-2 B2 provido actions to have ALL running in High available f ans running in high speed Speed when 3asin at >80*F, LCOAR procedure EOS 7.5-j a Temp > 80'F toquires at least six f ans operable at >80*F.
Byron Operating proceduro OBOS 0.10,"Shittly and Daily 4.
Mainta,n Basin Operating Surveillance" maintains SX basin Level at or lovel above the 50% lovel(normally above 50%
. The Low maintained at or above 82%)% basin leve!
Level alarm setpoint is at 56 with auto makeup initioling at 53% level.
Byron Ernergency Procedures 1/2 BEP-0 5.
Stari SX Fans
" Reactor Trip or Sately injectioncontain in High Spood Unit 1/2" (Temporary Charge)igh within 10 minutes actions to start all SX f ans n h spood in the event containmuni pressuroexce of a Large Break LOCA accordance with Stop 14 "Rosponso Not Obtmned" column to ca~ e the action is accomplished withh.:io first 10 minutes.
20 psig in containment is indicative of either a lar0e break LOC A or a Secondary Break, in both casos a large heat load would exist in containment so it is imperative that SX tans be started. Additionally,1/2 BEP 1,
" Loss of Reactor or Secondary Coolant Unit 1/2" (Temporary Chango), addresses SX system operation during accidents other than a large break LOCA.
I
\\
2 ZNLD/1402/26
Additional station actions to support NED's Final Operability Assessment include:
1.
Byron Station On Site Review #91 172 was conducted to evaluato and accept the operability assessment.
2.
Operating Dept. "Special Operating Order" #SO U1/U218 explained the final resolution of the UHS issues until the Toch Spoc Amendment is issued.
3.
Byron Station Tralning Department issued a " Required Listening /Roadin f 3ackage for all licensed operators explaining the resolution of the lh S items.
4.
Byron Station Training and CECO Production Training Department were requested to review the On Site Review and Operability Assessment to address potential changes or improvements in
- 1) Lesson Plans,2) simulator modeling changes for SX operations, and 3) Simulator operator responses on large break LOCA's.
The administrative controls in place to implement recommended engineering act!ons provide reasonable assurance that the maximum basin temperature limit of 98*F will not be exceeded. The safety function and capability of the UHS, as assumed in the Tech Specs and UFSAR, remain unchanged. The UFSAR and Tech Spec changes rec uned to clarify the UH' design and incorporate the adminlStrative contro s will be performed s
in accordance with Byron Station and Commonwealth Edison procedures including 10CFR50,59 reviews. A summary of the UHS UFSAR sections requiring significant revinion is provided in Attachment B.
Attachment C contains a list of the romalning open items which require further evaluation.
L 1
l l
ZNLD/1402/27
.-=
1 V.
ATTACHMENTS l
AttactimentA References
- 1. *Byion Station Essential Service Water Cooling Tower Performance Test Pronram, January,1989", Sargent & Lundy Letter to Mr. C.A. Moerke dated 1/f9/80, File No. 917, (DFB 70), Project No. 7500 92.
- 2. Byron S'asclal Procedure & SPP #91008,"SX Pressure Flow Data",
dated 5/3/9' Nuclear Generating Stat!on Essential S)ervice Water Cooing Tower 3. Env:
l Thermal Performance Test Report.
- 4. Interim Operability Assesstiient Pof ENC OE-40.1 dated 4/15/91
- (CHRON #166024).
5; Ope' rability Assessment Per ENC OE-40.1 dated 5/31/91 (CHRON
- 168014).
- 6. Calc. # NED O-MSD 2, dated 5/22/91: O orability Assessment of ESW L coo!ing Towers per ENC-OE-40.1 dated 4/1[/91.
- 7. Calc. # NED O MSD-5, dated 5/31/91: ESW Coeling Tower Transient l
l Model: Part 11 (Single Tower /One Basin Model)
- 8. Calc. # NED O MSD 6, dated 9/3/91; ESW Cooling Tower Trandent Model; Part lli (Two Tower /Onc Basin Model)
- 9. Calc # NED M MSD 8, dated 12/13/91: ESW Cooling Tower Pedormance Calculation: Part I, Rev.1 (CHRON # 177488)
. Cooling Tower Basin Temperature Calculation.yron Ultimate Heat Sink- (Tw
-10. Calc. # NED M MSD 9,' dated 10/24/91: B l-l Model) (CHRON # 174986)_-
(CHRON #175462) y Assessment Per ENC.OE 40.1, dated 11/1/91
- 11. Final Operabilit
~
l l
,12. Ultimate Heat Sink Design Basin LOCA Single Failure Scenarios, Sargent & Lundy calc. UHS 01, Rev. 2, dated 9/10/91. File _No. 9.17, Project No. 8893 38/39.
13.? Tabulation of UHS Heat Loads, Sargent & Lundy calc. UHS 02 Rev..
- O, dated 7/3/91. File No. 9.17, Project ho. 8893-38/39.
P i
ZNLD/1402/28 '
u
i
- 14. Byron Station Containment Rocponse for Ultimate Heat Sink Requirement, Commonwealth Edison Nuclect Fuel Services Department (CECO NFS) document RSA B 9103, dated 8/28/91.
- 15. ESC /MRL Cooling Tower Performance Program VO1 Sof tware Vorification and Validation Report SVVR-805, Rev.1. dated 11/94, CHRON # 177547.
- 16. American Society of Heating and Refrigeration Engineers (ASHRAE)
Handbook fundamentals,1989, IP odition, Pg. 24.7.
- 17. Sargent & Lundy Calculation UHS 04 "Ultimato Heat Sink Design Basis LOCA Single Fallure Scenarios for Cool Weather Operation",
Revision O dated 09 25 91.
- 18. Sargent & Lundy Calculation MAD 91-080 " Service Water Model Calibration", Revision 2 dated 10 04 91.
- 19. Sargent & Lundy Calculation MAD 91-121 " Cooling Tower Flows for UHS Analysis", Revision 1 dated 10 04-91.
- 20. Sargent & Lundy Calculation ATD-91-0142
- Cooling Tower Flows for UHS Cool Weather Analysis", Revision t dated 11-18 91.
- 21. " Commonwealth Edison Company Byron Station Nuclear Ultimate Heat Sink Studles", Westinghouse lotter, CAE 91221. B. Humphries (W5 to R. nienlewicz (CECO), f,ugust 8,1991.
- 22. Lefevre, M.R.," Eliminating the MerkelTheory Approximations Can it Replace the EmpiricM ' Temperature Correction Factor'?, "CTI Journal Vol.
8, No.1, Page 36, dated February 7,1984.
- 23. ESC /MRL Cooling Tower Performance Program Versions 01, Software Verification and Validation Plan SVVP-805, Rev. O dated 10/91 (CHRON
- 174759),
- 24. Calc. # NED M MSD 11, dated 12/17/91: Byron Ultimate Heat Sink Cooling Tower Basin Temperature Calculation (Bypass Operation)
(CHRON #177615).
- 25. Calc. # NED M MSD 14, dated 1/9/92, Byron Ultimate Heat Sink Cooling Tower Basin Makeup Calculation (CHRON #178429)
I ZNLD/1402/29 l
Attachment D SUMMAHY_OESIGNIFICANT UHS UESAR REVISIONS Subsection Summary.nf Reyblon 2.3.1.2.4 BY Revised to discuss the use of different wet-bulb temperatures in the SX Cooling Tower design.
9.2.5.1 BY, Revised for heat load values.
Table 9.2-6 Revised for heat load values.
Figuro 9.2. 7 Revised for heat load values.
9.2.5.2.1BY Added new description for analysis assumptions.
9.2.5.3BY Added paragraphs describing the new analysis.
Renumbered the remaining paragraphs into a different subsection.
ZNLD/1402130
REMMNING.OEENJIEMS DEEtHIEM DESCRIEIlON COMELEIlON DAIE UHS 9101 Affect on other SX londs due 3/31/92 to axcessive CC Hx flows with only one SX pump running on the respective unit.
An evaluation is presently underway to determine the maximum CC flow allowed such that other flows will not be affected. The analysis includes 4
sensitivity of different flows to changing CC flows.
UHS 9107 Braidwood analysis for Lake 3/31/92 Evaporation
/
avaluation is underway to document the higher expected containment heat loads on the
- cooling lake in the Braldwood analys s.
l UHS 91 11
" Station Blackout" impact on UHS 3/31/92 A meeting has been scheduled to discuss and review the most recent analyses and its impact (if any) on CECO's committments to SBO lasues 4
ZNLD/1402/31
y AttachmenLD Sgures o
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