ML20009F181
| ML20009F181 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 07/13/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20009F180 | List: |
| References | |
| NUDOCS 8107300086 | |
| Download: ML20009F181 (8) | |
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SAFETY EVALUATION YANKEE ROWE NUCLEAR POWER ST/. TION DOCKET NO. 50-29 ADE00ACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES I'ITRODUCTION AND
SUMMARY
Yankee Atomic Electric Company (YAECO) was requested by NP.C letter dated August 8,1979 to review the electric power system at Yankee Row Nuclear Power Station. The review was to consist of:
a) Determining analytically the capacity and capability of the offsite power system and the onsite distribution system to automatically start as well as operate all required loads within their required voltage ratings in the event of 1) an anticipated transient, or 2) an accident (such cs LOCA) without tranual shedding of any electric loads.
b) Determining if there are any events or conditions which could resu;C in the simultaneous or,. consequential loss of both required circuits from the offsite network to the onsite electric distiibution system and thus violating the requirements of GDC 17.
The August 8,1979 letter included staff guidelines for performing the required voltage analysis and the licensee was further required to perfarm a test in order to verify the validity of the analytical results.
YAECO responded by letters dated February 27, 1980 and January 21,198'i. A detailed review'and technical evaluation of the submittal was performed by Lawrence Livermore Laboratory (LLL) under contract to NRC, and with general supervision by NRC staff. This work was reported in LLL Technical Evaluation Report (TER),
Adequacy of Station Electric Distribution System Voltages, Yankee Rowe Nuclear Power Station, dated May 29,1980 (attached). We have reviewed this l
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report and concur in the conclusions that the offsite power system and onsite distribution system are capable of providing acceptable. voltages for worst case station electric load and grid voltages.
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EVALUATION CRITERIA of-The criteria used by LLL in this technical evaluation of the analysis includes Gr>C 13 (" Instrumentation and Control"), GDC l' (" Electric Power Systems") of Appendix A to 10 CFR 50; IEEE Standard 308-1974 (" Class lE Power Sy. stems for Nuclear Pcwer Generating Stations"); ANSI C84.'-1977 (" Voltage Ratings for Electric Power Systems and Equipment-60HZ"); and the staff positions and guidelines in NRC letter to YAECO dated August 8,1979.
ANALYSIS AND TEST FFATURES YAECO c.1alyud each offsite power source to she ensite distribution system-under maximum and minimum load conditions with the offsite power sources at maximum and minimum voltage, ll7Kv and 109 Kv respectively. TN w 3/ sis included the effects on the Cla::s lE equipment when starting and running a large non-Class lE motor under conoitions with maximum load and minimum grid voltage.
It has been established that the emergency 480 volt loads would operate within allowable limits for the worst case conditions noted above.
During the minimum voltage transient experienced on the'~120 vac system, two valve monitoring sjstems (PORV and SV) may tolsely indicate that a normally closed valve has opened. The licensee states that this false indication can be verified by other system parameters and is, therefore, j
considered acceptable and of no safety significance.
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I The voltage analysis was verified by comparing actual bus voltages to voltages predicted by the computer program. Two verification tests were made for actual plant operating conditions. The comparison showed the calculated voltages for the Class lE buses are within - 0.85 and + 1.70 percent of the measured bus volt 35es.
This close correlation verifies the adequacy of the analysis submitted.
CONCLUSIONS We have reviewed the LLL Technical Evaluation Report and concur in the findings that:
1.
YAECO has provided verified voltage analyses to demonstrate that the Class 1E equipment termina' voltages remain within acceptable operating limits for the postulated worst case conditions.
2.
The tests to ver:ry tne analysis was valid and showed the analysis to be accurate.
3.
YAECO's reaffirmation of compliance with GDC 17 requirements is accep' table.
4 Upon the review and approval of the degraded grid protection modifications proposed by YAECO and currently being reviewed by LLL, there will be acceptable assurance that spurious tripping of offsite power to Class IE equipment will r.ot take place upon starting a large non-Class lE load.
TECHNICAL EVALUATION OF THE ADEQUACY OF STATION ELECTR(C DISTRIBUTION SYSTEM VOLTACES FOR THE YARKEE ROWE NUCLEAR POWER "TATION 9
(Docket No. 50-29)
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Lawrence Livermore National. Laboratory, Nevada of
1.
INTkODUCTION The Nuclear Regulatory _ Commission (NRC) by a letter dated.
August 8, 1979 [Ref. 1), expanded its generic review of the adequacy,of the station electric distribution systems for all operating nuclear pcwer facilities.
This review is to determine if the onsite distribution system, in conjunction with the offsite power sources, has sufficient capacity and capability to automatically start and operate all required safety loads within the equipment voltage ratings.
In addition, the NRC requested each licensee'to. follow suggested guidelines and to meet certcin requirements in the analysis.
These requirements are detailed in Section 5 of this report.
By letters dated February 27, 1980 [Ref. 2] and January 21, 1981
{Ref. 3], Yankee Atomic Electric Company (YAECO), the licensee, submitted th(ir analysis and conclusion regarding the adequacy of the electrical distri-bution system's voltages at the Yankee Rcwe Nuclear Power Station.
The purpose of this report is to evaluate the licensee's submittal
.ith respect to the NRC criteria and presenc the reviewer's conclusion on the aJequacy of the station electric distribution systems to mair tin the voltage within the design limits of the required Class IE equipmment for the worst case starting and load cunditions.
2.
DESICN BASIS CRITERIA The design basis criteria that were applied in determining the adequacy of station electric distribution syste:s voltages to start and operato all required safecy loads within their required voltage ratings are as follows:
(1) Ceneral Design Criterion 17 (CDC 17), " Electric Power
- Systems, of Appendix A, "Ceneral Design Criteria for Nuclear Power Plants," in the Code of Federal Regulations,
!ttle 10, Part 50 (10 CFR 50) [Ref. 4].
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FIGURE.1 - Y ANKEE ROWE ELECTRIC AL ONE - L!NE DIAGRAM i
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4.2 ANALYSIS RESULTS During the voltage analysis under the above condit,ons, a potential problem was discovered and reported as Licensee Event Report 50-29/79-26
[Ref. 7}.
With the generator of f line, the center buses tied to the outer buse, and the grid at the minimum expected value, the auxiliary poser system might not have the capacity to operate all Class 1E loa'ds upon a SIAS.
As a solution to this problem, voltage regulators were installed on the seconda.y side of the 115KV/2400-volt station service transformers.'
The regulators main-tain a regulated secondary voltage of + 20 volts with a variation in the primary voltage of + 15%.
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The worst case Class 1E eqpipment terminal voltages shown in Table 1 occur under the following conditioffi 4.2.1 Overvoltage s
Plant at cold shutdown, minimum plant load and grid at maximum expected voltage of 117KV.
4.2.2 Undervoltage Wo rs t case loading exists when an accident occurs without loss of offsite power and with the generator off line, grid at minimum expected voltage of 109 KV, 2400-volt bus No. 1 not tied to 2400-volt bus No. 2 (breaker 1224 open), 480-volt bus 4-1 tied to 480-volt bus No. 5-2 (breaker 4548 closed), offsite source is the 115KV Harriman line.
4.3 ANALYSIS VERIFICATION YAECO verified their computerited voltage analysis talculations by ecmparing actual.easured bus voltages to voittges predicted by the compute'r program.
Rather than performing the test with an actual degraded grid condi-tion, actual plant cperating conditions were selected.
The ccmputer program was used to predict bus voltages for the operating condition and then compared to actual measured bus voltages for the same plant condition.
Two verification tests were made.,The first verification test produced percent deviat.on errors l
of -0.85 to + 0.42 and the second test of -0.64 to + 1.70.
A plus percent Jeviation error indicates predicted values to be higher than measured values.
.a' 5.
EVALUATION
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The NRC generic letter [Ref. 1] stated several requirements that the plant must meet in their voltage analysis.
These requirements and an evaluation of the licensee's submittals are as follows:
(1) With the minimum expected grid voltage and maximum load condition, each offsite source and distribution system connection must be capable of starting and continuously operating all Class lE equipment within the equipment's voltage ratings.
The voltage analysis submitted by YAECO shows that aftet installation of voltage recilators, each offsite source, in conjunction with the 97 site distribution, has the capa-bility and capacity to automatically start and continue to operate all Class lE equipement within their design ratings with one exception.
During the minimum voltage tran'sient experienced on the 120VAC system, two valve monitoring systems (PORV and SV) may falsely indicate that a normally closed valve has opened.
The licensee states that this false indication can be verified by other system parameters and is, therefore, considered acceptable and of no safety significance.
(2) With the naximum expected of,f site grid voltage and miai=um load condition, each offsite source and distribution system connection must be capable of continuously operating the required Class lE equipment without exceeding the equipment's d
voltage ratings.
The voltage analysis submitted by YAECO shcus tnat after ins:allatien of voltage regulators, each effsite scurce at the maximum expected grid voltage with =inimum plant operating losis will supply adequate voltage to the Class 'I equipmcat 1
without exceeding their design ratings.
l ll (3) The analysis must show that there will be no spurious sepa-ration from the offsite power source to the Class 1E buses by the voltage protection relays when the grid is within the normal expected limits and the loading conditions established
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by the NRC are being met.
LLNL will verify in a separate report (TAC #10060) that the requirements of this pcsition are met, as, final designs and Technical Specifications have not been submitted..
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REFERENCES s.,
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1.
.NRC letter (W. Cammill) to all Power Reactor Licensees, dated August 8, 19 7.
2.
YAECO letter (J. A. Kay) to NRC (D. L. Ziemann), dated Februarv 27, 1980.
3.
YAECO. letter (J. A. Kay) to NRC (D. L. Ziemann), dat d March 11, 1980.
4 Code of Federal Reculations. Title 10,,Eart 50 -(10 CFR 50), Cereral Design Criterion 13 anc 17 of Appendix A for'* Nuclear Power Plents.
5.
ANSI C84.1-1977, " Voltage Ratind for Electric Power Systems and Equipment."
6.
IEEE Std. 308-1971, " Class IE Po*wer' Systems for Nuclear Power Genera' ting Stations."
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7.
YAECO letter to NRC, Licensee Evett Report 50-29/79-26, dated October!27, D79.
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