ML20135E492

Summary of 961220,970129-30 & 0219 Telcons W/W Re AP600 Adverse Sys Interaction Rept WCAP-14477.List of Participants Encl

ML20135E492
Person / Time
Site:	05200003
Issue date:	03/04/1997
From:	Huffman W NRC (Affiliation Not Assigned)
To:	NRC (Affiliation Not Assigned)
References
NUDOCS 9703070100
Download: ML20135E492 (14)

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p rro UNITED STATES

,j NUCLEAR REGULATORY COMMISSION

't WASHINGTON, D.C. 20666-0001

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March 4, 1997 APPLMANT: Westinghouse Electric Corporation PROJECT:

AP600

SUBJECT:

SupmARY OF TELEPHONE CONFERENCES TO DISCUSS WESTINGHOUSE RESPONSES TO AP600 ADVERSE SYSTEMS INTERACTION REPORT DISCUSSION ITEMS On December 20, 1996, and January 29, January 30, and February 19, 1997, members of the Nuclear Regulatory Commission (NRC) staff and Westinghouse (Attachment 1) conducted telephone conferences (telecons) concerning the AP600 Adverse Systems Interaction report, WCAP-14477. NRC discussion items on the report were provided to Westinghouse via NRC letter dated October 3, 1996.

Westinghouse provided responses to these questions via facsimiles sent to the NRC on December 19, 1996 and January 13, 1997. The first set of ASI discus-sion item responses from Westinghouse were documented in an NRC telecon summary dated January 8, 1997. The remaining ASI discussion item responses are provided in Attachment ? of this memorandum.

The following is a summary of actions and highlights from telecons on January 29, Jaauary 30, and February 19, 1997, concerning the Westinghouse ASI respon-ses:

Q#1 - The staff found the supplemental information on the DVI line break o

scenarios satisfactory.

Q#3 - Westinghouse agreed to modify its response to question #3 to include a discussion which addresses that PRHR heating of the IRWST water prior to IRWST injection has been accounted for in some of the Chapter 15 small break LOCA analyses.

Q#29 (b) - Although the staff had previously found this response satisfactory, the question was reopened due to a concern that inadver-tent full ADS depressurizaton during a SGTR may result in a boron dilution concern due to backleakage from the SG into the RCS. Westing-house agreed to consider this scenario and revise its response as necessary.

Q#7 - Westinghouse agreed to incorporate the table provided in the response to this question into the next revision of the ASI report. The report vould also be revised to clarify that the PMS will override any PLS failure mode signal.

Q#11 - Westinghouse will revise its response to this question to clarify that the timing of system actuations or sequential availability of defense-in-depth systems following a loss of offsite power (due to load sequencingontothestandbydieselgenerators)"!j will have no adverse interactions with the. safety related systems.

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9703070100 970304 PDR ADOCK 0520 3

. March 4, 1997 Q#12 - Westinghouse will clarify its response to determine if the tank will really rupture (as opposed to relieve pressure via a pressure relief valve or rupture disk.

If the tank can actually rupture, can it cause physical damage to any other systems located in its vicinity?

Q#31 - The staff found the Westinghouse response satisfactory.

Q#32 - Westinghouse agreed to modify its response to this question to state that interactions between secondary or other non-safety related systems have been assessed te the extent that these interactions do not increase the initiating event frequencies in the PRA.

Q#15 - The staff noted that, based on the testing program, there is a small potential for CMT refill following accumulator injection. CMT refill could result in operator confusion and lead to some error of commission due to uncertainty in the way the accident response was progressing. Westinghouse stated that CMT refill would have no effect on core cooling and as long as the critical safety functions are being maintained, it doesn't matter whether water is coming from the CMT or the IRWST. Assuming the operators followed their ERG's, there would be no problem with this condition. The staff accepted the Westinghouse i

response.

Q#16 - The staff found the Westinghouse response satisfactory.

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Q#17 - The staff requested Westinghouse to modify its response to this question to include consideration of the oscillations observed during OSU testing. The revised response will include a discussion regarding how the oscillations seen at OSU during non-LOCA transients or post-ADS injection and long term cooling would not be seen by the AP600 plant instrumentation or operator. The response would further explain that given the relatively small magnitude of these oscillations, there is no impact on plant safety.

Q#24 - The staff asked if any analyses had been performed on the PRHR heat exchanger as a function of tube uncovery. Westinghouse stated that some hand calculations had been made but that LOFTRAN had not been used for this type of analysis. Westinghouse noted that the shutdown evaluation report would provide more information on this concern.

Q#26 - Westinghouse has committed to revise the ASI report to include the response to this discussion item. However, the staff was also interested in the possibility that cold leg thermal stratification could result in flashing in the CMT and actuation of ADS when it isn't necessary, particularly in a cool down event such as a main steam line break. Westinghouse agreed to modify its response to explain why inadvertent ADS was not a concern due to thermal stratification of the cold leg.

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. March 4, 1997 Q#28 - The staff noted that the response to this question was not consistent with the staff's understanding of the scope of the report.

Potential for adverse interactions in many beyond design basis areas are being considered. Westinghouse agreed that this response was incorrect and would revise it to be responsive to the question.

Q#38 - The staff found the Westinghouse response satisfactory.

Q#40 - The staff questioned whether the ADS vacuum breakers functioned in any capacity to prevent pressurizer refill that was observed in testing at OSU. Westinghouse stated that there was no concern that the pressurizer refill phenomenon seen at OSU would take place on an AP600 and that the vacuum breakers were not installed to protect against this condition. No credit for vacuum breakers is taken in SSAR Chapter 15 analysi;.

Q#41 - The staff asked if steam in the pressurizer relief lines could adversely impact the SRVs? Westinghouse said that it would not.

Q#42 - The staff found the Westinghouse response satisfactory.

I Q#47 - The staff questioned if there were any potential adverse boron dilution concerns from SGTR events. Westinghouse agreed to modify its 3

j response to address this question.

Q#48 - Westinghouse has agreed to incorporate this response into the next revision of the ASI report.

l Q#51 - The staff asked if there were any circumstance which would result j

in isolation of the CMTs from the RCS and require that the CMTs have i

safety relief capability? Westinghouse stated that if the CMTs were isolated from the RCS, there would be no mechanism for introducing l

energy or heat which would necessitate safety relief valves.

I It was noted that no additional comments have been received from the technical i

review staff on the Westinghouse responses to the ASI report discussion items and that completion of actions committed to during the telecons should l

satisfactorily resolve all issues on adverse systems interactions.

Based on i

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, March 4, 1997 the time involved in reviewing all the ASI responses, Westinghouse estimates that the response updates will be provided around March 14, 1997, and a revision to the ASI report by March 28, 1997.

The staff agreed that these dates are satisfactory.

original signed by:

William C. Huffman, Project Manager Standardization Project Directorate Division of Reactor Program Management Office of Nuclear Reactor Regulation Docket No.52-003 Attachments: As stated cc w/ attachments:

See next page DISTRIBUTION w/ attachments:

[ Docket File-PDST R/F TMartin PUBLIC TQuay BHuffman DTJackson TKenyon JSebrosky Alevin, 0-8 E23 JLyons, 0-8 E23 NSaltos, 0-10 E4 ACubbage, 0-8 E23 JBongarra, 0-9 H15 HWalker,0-8 D1 Cli, 0-8 D1 HLi, 0-8 H3 JRaval, 0-8 D1 EThrom, 0-8 H7 MSnodderly, 0-8 H7 DISTRIBUTION w/o attachments:

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SCollins,FMiraglia, 0-12 G18 AThadani, 0-12 G18 Dross, T-4 D18 WDean, 0-17 G21 JMoore, 0-15 B18 ACRS (11)

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DATE 03/7/97 03/4/97 0FFICIAL RECORD COPY

Westinghouse Electric Corporation Docket No.52-003 cc: Mr. Nicholas J. Liparulo, Manager Mr. Frank A. Ross Nuclear Safety and Regulatory Analysis U.S. Department of Energy, NE-42 Nuclear and Advanced Technology Division Office of LWR Safety and Technology Westinghouse Electric Corporation 19901 Germantown Road P.O. Box 355 Germantown, MD 20874 Pittsburgh, PA 15230 Mr. Ronald Simard, Director Mr. B. A. McIntyre Advanced Reactor Program Advanced Plant Safety & Licensing Nuclear Energy Institute Westinghouse Electric Corporation 1776 Eye Street, N.W.

Energy Systems Business Unit Suite 300 Box 355 Washington, DC 20006-3706 Pittsburgh, PA 15230 Ms. Lynn Connor Ms. Cindy L. Haag Doc-Search Associates Advanced Plant Safety & Licensing Post Office Box 34 Westinghouse Electric Corporation Cabin John, MD 20818 Energy Systems Business Unit Box 355 Mr. James E. Quinn, Projects Manager Pittsburgh, PA 15230 LMR and SBWR Programs GE Nuclear Energy Mr. M. D. Beaumont 175 Curtner Avenue, M/C 165 Nuclear and Advanced Technology Division San Jose, CA 95125 Westinghouse Electric Corporation One Montrose Metro Mr. Robert H. Buchholz 11921 Rockville Pike GE Nuclear Energy Suite 350 175 Curtner Avenue, MC-781 Rockville, MD 20852 San Jose, CA 95125 Mr. Sterling Franks Barton Z. Cowan, Esq.

U.S. Department of Energy Eckert Seamans Cherin & Mellott NE-50 600 Grant Street 42nd Floor 19901 Germantown Road Pittsburgh, PA 15219 Germantown, MD 20874 Mr. Ed Rodwell, Manager Mr. S. M. Modro PWR Design Certification Nuclear Systems Analysis Technologies Electric Power Research Institute Lockheed Idaho Technologies Company 3412 Hillview Avenue Post Office Box 1625 Palo Alto, CA 94303 Idaho Falls, ID 83415 Mr. Charles Thompson, Nuclear Engineer AP600 Certification NE-50 19901 Germantown Road Germantown, MD 20874

WESTINGHOUSE /NRC AP600 ADVERSE SYSTEM INTERACTIONS TELECONFERENCE PARTICIPANTS i

JANUARY 29, 1997 HAME ORGANIZATION ROBIN NYDES WESTINGHOUSE MIKE CORLETTI WESTINGHOUSE SELIM SANCAKTAR WESTINGHOUSE LARRY CONWAY WESTINGHOUSE B0B KEMPER WESTINGHOUSE ALAN LEVIN NRC AMY CUBBAGE NRC BILL HUFFMAN NRC JAUNUARY 30, 1997 HAME ORGANIZATION ROBIN NYDES WESTINGHOUSE MIKE CORLETTI WESTINGHOUSE RICK WRIGHT WESTINGHOUSE LARRY CONWAY WESTINGHOUSE TERRRY SCHULZ WESTINGHOUSE CHUCK BROCK 0FF WESTINGHOUSE ALAN LEVIN NRC AMY CUBBAGE NRC BILL HUFFMAN NRC FEBRUARY 19, 1997 HAME ORGANIZATION ROBIN NYDES WESTINGHOUSE MIKE CORLETTI WESTINGHOUSE ALAN LEVIN NRC BILL HUFFMAN NRC Attachment I

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33. There are interactions noted that involve the spent fuel cooling system. One rationale given for a low level of concem is that " spent fuel pool accidents are not deemed to be of risk significance." It is not clear that this is consistent with our expressed concern with shutdown risks, or with the fecent technical issue on the SFP cooling system, which are still under discussion with Westinghouse.

Response

As discussed in section 2.2.19, many design features have been incorporated into the AP600 to avoid adverse system interactions involving the SFS and the safety related pools and tanks that it services. The statement quoted appears in Table 31 which is an assessment of adverse human commission errors. It is pointing out there is a possibility that, due to human errors of commission, the operators could cause the refueling cavity / transfer canal / spent fuel pool to be drained and cause a loss of spent fuel pool cooling, and whether this accident has been evaluated in the PRA. However, such fuel pool events have not historically been evaluated in PRA, and this has been the case for the AP600.

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38. Will spurious opening of the CMT discharge valves (not due to a CMT actuation signal), cause the RCPs to trip? ' For example, loss of air to the CMT discharge valve will result in them l

failing open - will this cause the RCPs to trip? If not, what adverse effects would this cause?

Response

Spurious openng of the CMT discharge valves will not cause the RCPs to trip. As described in the report, operation of the RCPs reduces the CMT tecirculation/ injection flow l

rate. Therfore, if the RCPs were running and a CMT valve or valves spuriously opened, j

the CMTs would either not inject, or inject at a low flow rate. Since no safety signal would have been actuated, the operator would be permitted to attempt to reclose the valves, or if necessary, bring the plant to an orderly shutdown. The effect of CMT recirculation would cause a cooling of the RCS and a reduction in RCS pressure. Depending on the

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recirculation rate, the low pressure reactor trip followed by a low RCS T. cold safeguards signal would actuate. This would cause the RCPs to trip, allowing full CMT flow. The results of such an event are bounded by the SSAR Chapter 15 analysis for spunous safeguards signal.

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39. The adverse effects of cold weather on the operation of the PCCS appears to merit some l

consideration. For instance, undw extremely cold temperature conditions, it is conceivable that the annulus floor drains at the bottom of the containment annulus could ice up. Actuation of the PCCS would result in cooling water not evaporated from the containment vessel water accumulating in the lower annulus. Enough water accumulation could eventually affect annulus l

air flow and degrade PCCS operation. In addition, icing of the distribution bucket and weirs could affect distribution of PCCS flow on containment.

Response

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AP600 18004

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l Lower annulus drains: he design of the lower annblus drains are such that they cannot be affected by cold external temperatures. De annulus drain within the floor is an open design such that any blockage within the storm drain system will not block water drainage l

from the annulus. There will be holes around the perimeter of the drain connection to the i

storm drain system such that any backup from the storm drain system will drain directly l

into the yard. The additional advantage of this configuration is that freezing within the l

storm drain system or the drain connection will not preclude drainage of water from the containment annulus. Two drains are provided, each with sufficient flow capacity via the storm drain system or directly to the yard to drain 100% of PCS flow rate.

1 Water distribution bucket and weirs: no water distribution bucket will fill very rapidly to j

operating level (less then 5 seconds). De enthalpy of the water and the high flow rates will prevent the water from Amering within the bucket. While the weirs will fill more t

i slowly, the initial water temperature and additional heat transfer from the shell will j-preclude significant icing within the weirs.

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40. The stage 1,2, and 3 ADS discharge lines have vacuum breakers to prevent water hammer l

following ADS actuation. What am the consequences of ADS actuation with the breakers.

unseated such that ADS discharge is diverted directly into containment rather than quenched in j

the IRWST? How is the position of the vacuum breakers determined and monitorod?

Response

ADS operation with a vacuum breaker unseated could potentially divert some blowdown j

flow from the spargers in the IRWST directly to containment. However, since this line is j.

very small compared to the IRWST line (3" compared to 16") and, even if the vacuum j

breaker was not seated, there still would be significant resistance in this line to restrict the steam blowdown, the amount of blowdown through this line will be insignificant. Even if d

the amount of blowdown was significant, the steam would be condensed on the containment shell and other passive heat sinks in containment and the condensate would be collected in either the containment sump (loop compartments) or the IRWST. There would l

be no effect on the performance of the passive safety systems as a result of this scenario.

1 dt. The pressurizer safety relief valve discharge lines appear to have a drain line connecthn to the i

1 ADS valve discharge lines. It would seem that actuation of the ADS valves could pressurize the safety relief valves discharge line and blow the rupture disk. What adverse efects would this i

have on system operations? In addition, if ADS 1 is used manually to depressurize, will the j

operator have to manually close the drain line isolation valve to the RCDT?

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Response

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ADS operation could result in the rupture disks being blown open. However, similar to the discussion for #40, this will have no effect on the performance of the passive safety systems. If manual ADS operation (without an $ signal) were to be ennployed, the operator should close the line to the RCDT for equipment protection. However, if he failed to do so, the line would be automatically isolated on high RCDT pressure, thereby preventing the tank from being damaged. Again, as stated in the report, this is an equipment protection concem and there will be no effect on the performance of the passive safety systems as a result of a failure to isolate the RCDT during ADS operation.

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42. In order for the IRWST to function properly, it must directly communicate with the containment atmosphere. Steam and pressure venting capabilities of the IRWST are discussed in the SSAR but there does not appear to be any description of the vacuum relief assurance for the IRWST.

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The staff assumes that the TRWST design will have a vacuum relief design sufficiently sized to permit required drain down. However, has the possibility of clogging or obstruction of the vacuum relief paths been considered along with any adverse effect this would have on IRWST draining? Westinghouse should consider including a discussion on this in the adverw systems j

interaction report and a description of the venting design in the $$AR. This concern would also i

be applicable to vacuum venting design and potential for clogging / obstructions for the PCCS j

tank.

l Resposse:

j The IRWST'is a closed tank that is not air-tight. However, several openings in the tank are l

provided that would prevent a negative pressure from developing inside the tank during i

IRWST draining. One IRWST vent (4 ft') is continuously open for purposes of preventing 8

i hydrogen buildup in the tank. In addition, two other vents (4 ft each) are provided to prevent a reverse pressurization across the tank walls due to a rapid pressurization of the l

containment which would result from a large mass and energy release. These vents contain louvers which open inward such that a vacuum would not develop in the IRWST. Other j'

openings include 26 vents (100 ft' total) that prevent pressurization of the IRWST. These vents also contain louvers that open outward and are not air tight. Finally, two 4" open l

pipes that connect the containment gutter to the IRWST are provided and these too would l

prevent reverse pressurization in the IRWST.

The vents described above are located in the tank roof and are designed to discharge horizontally, six inches above the roof surface. This design prevents clogging from water or i

debris that could be found on the roof of the tank.

l With respect to the PCCS storage tank, two vent lines are provided to prevent drawing a vacuum i

in the tank during draining. These vent lines are 2" pipes that connect the tank air space to the j

valve room below the tank. These lines are sufficient to prevent drawing a vacuum in the tank.

43. Are there any adverse interactions or effects possible from ADS blowdown on the IRWST level l

instrumentation?

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Response

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The IRWST level instruments are used to provide signals to the PMS to actuate the i

containment recirculation valves on a low 1RWST water level. During ADS blowdown.

steem is condensed in the IRWST, causing the tank to heat up and to be slightly pressunzad. 'Ihe IRWST level instruments are DP transmitters with upper and lower taps connected to the tank such that pressurization effects will not affect their accuracy. In addition, since these transmitters are located inside containment, they are designed and i

qualified for harsh environments that could be experienced, including those that result from i

an ADS blowdown. Finally, tbs IRWST level setpoint that actuates contamment i

S recirculation is not reached until the IRWST is nearly empty. At that time, the blowdown 1

i via the ADS valves discharging to the IRWST is low and above the water level such that i

i the level transmitters will not be affected.

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47. Is it possible for a secondary side break or rupture (within containment) to cause and actuation of the ADS system? Under such circumstances, significant additional water inventory will be added to containment; are there any adverse conditions possible from such a scenario (such as boron dilution)?

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Response

As demonstrated in the SSAR Chapter 15 Analyses, there are no design basis secondary side breaks that would result in ADS actuation. As ADS actuation on secondary side

' breaks is clearly unacceptable for various reasons (degradation of RCS pressure boundary for Condition 11 events, increased mass and energy release for steamline breaks inside contsinment), the sets of assumptions considered in the SSAR analyses have been ulected to maximin the potential for ADS operation. In all cases, ADS actuation is not predicted for any design basis secondary side, break.

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49. 5xtensive effort is being placed on the humaa factors design of control room operator controls br ths / P600. For example, manual actuation of the ADS requires two separate operator

.stions. Experience indicates that many human factors related events are a result of errors during testing or maintenance ofl&C components. In the case of a spurious ADS signal.

Westinghouse states in Table 31 that the most likely human error may be related to testing or maintenance ofinstrumentation. Related specifically to the ADS-4 squib valves, what protection j

is provided by the design of the ADS-4 actuation circuitry to prevent an inadvertent discharge of a squib valve during surveillance testing, trouble shooting, or repairs being conducted inside the l

applicable I&C cabinets in the PMS system. For example, what measures would prevent a i

technician Dom accidently performing a continuity check on the electrical leads to a squib valve l

explosive charge (assuming that such a check could result in the firing of the charge)? Are there any other systems in which an inadvertent actuation due to maintenance or IAC could have significant adverse effects.

j Resposse:

ne protection logic cabinets of the Protection and Safety Montioring System (PMS) provide the !&C interface to the plant equipment or component which perfonns an engineered safety feature function. Dese protection logic cabinets include features which reduce the probability of inadvertent component actuation. As discussed in SSAR Section 7.1.2.10, component level logic is triple redundant. Component actuation commands from multiple logic processors are combined with the power interface cards in a twcrout-of-three voting logic. This prevents the failure of a single logic processor from causing spurious I

actuation or preventing a required actuation. On-line diagnostics and built-in automatic te.st capability eliminates the need for operator interactions and therfore reduces the probability of inadvertent operation due to operator error.

In addition to the features described above, the interface with the fourth stage ADS squib valves is accomplished in a manner which provides additional protection against inadvertent ADS-4 actuation. De fourth stage ADS squib valves are connected to two separate protection logic cabinets within a single division such that both protection logie cabinets must output an acmation signal to fire the squib. This eliminates the possibility that any single maintenance action within a protection cabinet could cause inadvertent opening of the squib valve.

A standard functional requirement for squib valve design ~ is the " fire current" and "no fire current" values. The fire current is the minimum current required to actuate the valve. De no-fire current is the maximum current that will not actuate the valve. The ADS stage 4 squib valve has a fire current of 5 amps (at 70*F) and a no-fire cunent of I amp for 5 minutes. De design value for continuity checks of the ADS-4 valves is conducted at.05 amps for 5 seconds.

Derefore, continuity checks can be performed on the squib valves without actuating the valves.

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01/13/97 HON 11:55 FAI 412 374 5535 AP600

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51. Dere appears to be the possibility of adverse effiscts following the termination of an abnormal event. For example, the CMTs could be actuated during an event which is then successfully terminated abr a period of CMT recirculation. His would leave the CMTs full of hot water at elevated pressure. What potential interactions could occur as the CMTs are cooled? How are these interactions prevented or mitigated? In general, have interactions of this type (i.e.,

recovery from terminable sequences) been considered?

Response

Termination of CMT operation aAer successful mitigation of an event is accomplished by closing the two, parallel outlet isolation valves. The protection logic is such that, if conditions arose that required CMT operation subsequent to CMT isolation, automatic protection is provided. For example, if CMT termination criteria are met (RCS stable and i

subcooled, pressurizer water level recovered), the RCPs can be restarted and the CMTs isolated by closing the outlet valves. Subsequently, if pressurizer water level falls below the CMT actuation setpoint, the CMTs will be automatically re-actuated Furthermore, the ERGS direct the operator to monitor RCS subcooling and pressurizer water level and to manually re-initiate CMT operation if termination criteria can not be maintained.

Once the CMTs have been isolated (via the outlet isolation valves), a retum to power operation will not occur until the CMT temperature and boron concentrativn are retumed to their Tech Spec limits. This is accomplished by irdecting cold bcrated water into the CMTs via connections in the bottom of the CMT, using the CVS makeup pumps. The makeup pumps pump borated water at the proper boron concentration and the botter, less borated water is flushed back into the RCS via the open cold leg balance line. During the process of restoring ti.e CMT temperature i

and boron concentration, the CMTs can be actuated without problems.

Recovery from terminable events has been considered in the design of the AP600 systems and protection logic and is captured at a high level in the ERGS. Similar to terir.ination of the CMTs, termination of the PRHR is accomplished by isolation of the two, parallel outlet isolation i

valves. Re-actuation of these PRIR valves is accomplished automatically or manually if PRHR termination criteria are not met. Following PRHR operation, a return to power operation can not I

occur until the IRWST water temperature is returned to its Tech Spec limit of 120*F. This is accomplished by aligning the RNS to cool the IRWST.

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j Response to #1, coat'd p

For the DVI line break scenario, the issue of whether RNS iQwtion could affect the timing of l

the ADS valve opening was considered. For such a break, it was questioned whether RNS idection could slow down CMT idection, such that ADS actuation of the first stage and/or j

fourth stage valves would be delayed beyond what was shown in the SSAR analysis. However, as presented in the SSAR analysis of a DVI line break, it is shown that the CMT connected to i

the broken DVI line empties in the first ~200 seconds. During this time, the RCS pressure is above ~700 psig which is well above the RNS cut-in pressure (~100 psig). In this analysis, the i

first stage ADS valves are actuated at 216 seconds The first stage ADS actuation setpoint corresponds to a water level in either CMT of 67%, which occurs very early. The actuation time is delayed due to the assumed time delays of the PMS. De second and third stage valves open on a time delay from the first stage valve actuation. The fourth stage valves then open at 526 seconds, which is 310 seconds aRer first stage ADS. The fourth stage ADS actuation setpoint is based CMT level of 20% coincident with a time delay aRer first stage ADS actuation. As can be seen from this analysis, since the faulted CMT empties very fast, with very high RCS pressures (above RNS pump shutoff), operation of the RNS pumps will not affect the timing of the ADS valve actuation. Furthennore, considering that it would be practically impossible for j

the operators to align the RNS for idection mode in the first 200 seconds following a double-ended break of a DVI line, and therefore, cince the CMTs would be empty prior to RNS i

operation, there are no adverse interactions from operation of the RNS pumps that could j

adversely affect the timing of ADS for a DVI line break, i

For the DVI line break scenario, the issue of whether RNS purnp operation could cause a short.

circuiting of the containment sump recirculation flow during this phase of the accident was i

considered. However, during the containment sump recirculation phase, the RCS pressure is j

near atmospheric pressure, and the RNS, if operating, will provide a greater recirculation / injection flow than would be provided by gravity idection only. There are no scenaros where operation of the RNS pumps will provide less i$ection than if only PXS gravity

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injection was provided.

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