ML19282B918
| ML19282B918 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 02/16/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19282B907 | List: |
| References | |
| NUDOCS 7903190028 | |
| Download: ML19282B918 (6) | |
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UNITED STATES l
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NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 s._...,
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMEllDMENT N0. 42 TO FACILITY OPERATING LICENSE N0. DPR-39 AND AMENDMEllT NO. 39 TO FACILITY OPERATING LICENSE NO. DPR-48 COMMONWEALTH EDISON COMPANY ZION STATION UNITS 1 AND 2 DOCKET NOS. 50-295 AND 50-304 Introduction 1
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By letter dated February 2 and supplemented February 9,1979, Commonwealth i
Edison Company (the licensee) reouested changes to the Technical Specifica-tions appended to Facility Operating Licenses DPR-39 and DPR-48 for Zion Station, Unit Nos.1 and 2, respectively. The proposed amendments would revise the Technical Specifications consistent with the r :sults of the licensee's ECCS reanalysis required by the Commission's Order for Modification of License of April 21, 1978.
Discussion On March 21, 1978 an error was discovered in the Westinghouse ECCS evaluation model. The error involved the calculated heat generation resulting from the Zr-water reactign and affected the calculated peak cladding temperatures after a LOCA.
Followir.g discovery of this error, the licensee administratively reduced the total peaking factor limits for Zion Units 1 and 2 from F =2.235 to F =1.90 and reinstated axial g
g power distribution monitoring system ( APDMS) surveillance fe. the power levels above 89.3 percent and 90.9 percent of rated power for Units 1 5
and 2 respectively, 6 This new value of FQ was intended to conservatively accommodate the Zr-water reaction error. On April 21, 1978, the Commission issued an Order for Modification of Licenses which amended Facility Operating Licenses DPR-39 and DPR-48 by modifying the Technical Specification limit for the total nuclear peaking factor Fn.
The new values of F0 allowed were 2.04 if the accumulator volumes Mere modified as specified in the licensee's letter of April 17,1978, or 1.9, if the accumulator volumes were not so modified.
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l The Order for Modification also included operating surveillance requirements with the Axial Power Distribution Monitoring System (APDMS) above certain j
specified power levels for both units. These surveillance requirements were necessary to ensure that the revised peaking factors identified in the Order would not be exceeded.
j in addition to the above, the Order required that the i n.ensee submit, as i
soon as possible, a reanalysis of ECCS cooling performance using an approved Westinghouse evaluation model. corrected for the above error. The licensee j
has completed that reanalysis, and has administratively irrposed a more i
stringent peaking factor limit, Fg, of 1.86, and has submitted proposed Technical Specification changes to reflect this lower allowable Fg limit.
In addition, the licensee has proposed revised operating limits that would j
allow base loaded operation with reduced requirements for APDMS provided j
this lower Fg limit is not exceeded.
Eva'uation I
By letter dated January 24, 1979, the licensee informed us that the preliminary results of the ECCS reanalysis for Zion Station had been completed and that a lower allowable total peaking factor, FQ, of 1.86 had been administratively imposed based on preliminary evaluation of the results of that reanalysis. This value is below the interim value t
specified in the Commission's Order of April 21, 1978. To assure this new FQ limit is not exceeded under any mode of operation (principally load following) the licensee administratively reduced power of Unit 1 by 5 to 7 percent and activated the APDMS for power levels above about 88 percent.
Unit 2 was already operating at reduced power (coastdown mode) in preparation for an upcoming refueling outage. The Unit 2 power level is low enough such that operation within the new Fo limit of 1.86 is assured without APDMS surveillance.
By letters dated February 2 and 9,1979, the licensee submitted the ECCS reanalysis required by the Order. The reanalysis was perfomed usjng the February 1978 version of the Westinghouse ECCS evaluation model which has been approved by the NRC. In addition to including the correction of the Zr-water reaction error and several code O
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maintenance and analytical improvements, the reanalysis contained the following changes:
(1) revised inputs to the containment code which include taking credit for the pair. ed surfaces, (2) a modified accumulator j
model, (3) steam dynamic cooling, and (4) En improved 15 x 15 FLECHT heat transfer correlation. The reanalysis used the following operating limitations or restraints:
- Limiting value of hot channel peaking factor of F =1.86, q
- One percent'of. steam generator tubes plugged,
- Accumulator water volume of 818 cu f t per accumulator, and
- Accumulator pressure of 615 psia With these restraints and limits, the peak cladding temperature and the local and total Zr-water reactions were claculated to be within the limits set forth in 10 CFR 50.46.
The calculated values of these parameters for Units 1 and 2 are:
- Peak Cladding Temperature:
2174*F
- Local Zr-Water Reaction:
6.98%
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- Total Zr-Water Reaction:
<0.3%
i We have reviewed the results of the licensee's revised LOCA analysis and have concluded that the safe operation of Units 1 and 2 with an Fg limit of 1.86 and with the other constraints listed above, has been adequately demonstrated. We concur, therefore, with the following proposed changes to the Technical Specifications:
(1) Total peaking factor, F for both units shall be reduced to a maximum limit of F =1.86, and (2) Accumulator water volume shall be reduced to 770 cu f t minimum and 818 cu ft maximum.
Since the new total nuclear peaking factor limit would ' remain below 2.32, the value for which the Westinghouse generic "18 case FAC" analysis applies, the licensee would still be' required to use APDMS surveillance above the " turn-on power fraction" defined as the ratio of the limiting F =1.86 and the maximum F for unrestricted load follow and base load g
0 m6 des of operation obtained from the "18 case FAC" analysis. Because of
, the uncertainties associated uith APDMS type surveillance technique, additional penalties have to be considered in calculating measured values of F.
The licensee has shown that in some instances this may lead to limiking the maximum allowed power to levels below the licensed power of the plant. For example, it was demonstrated for the present fuel cycle with Zion Unit 1 in the load following mode of operation, that this upper 1imit would be 93 to 95 percent of licensed power. For the future cycle in Zio.n Unit 2 this upper power limit is predicted to be even lower.
In order to avoid unnecessarily derating the plant during
.the present and future operations, the licensee has proposed to operate the plant in the base load mode of operation above critical power levels.
In this mode, with defined exceptions, APDMS is not required. The core power distribution in this mode would be monitored by full core flux maps, taken at monthly intervals, and the plant would be operated within a narrow AI target band of 13%. The licensee has proposed a Technical Specification procedure, as described below, for bringing the plant into the base load operation.
Prior to increasing the power above the limit where APDMS is now required for unrestricted operation, the plant would be operated at constant power within a 13% AI (a measure of axial flux imbalance)
I target band for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. A full core flux map would then be taken and analyzed.
If the calculated peaking factor, F, is within the prescribed limit, then " base load only" operat90n without APDMS at higher power would be permitted. After achieving base load operation, subsequent core flux maps would be taken af ter one week, two weeks, one month, and monthly thereafter. The unit would then be permitted to stay in base load operation without APDMS monitoring only if power is maintained within the 5 percent band below the maximum allowable power, or if it is above the limit determined by the APDMS surveillance setpoint (if the latter value is less restrictive) as long as the results of the flux maps demonstrate an acceptable F is n
being maintained and the plant does not revert to a load swing of load following mode or is not otherwise subjected to a sudden load change.
During base load operation, the axial power distributin would be maintained within a 13 percent AI target band.
Should any of these conditions not be met, the core power would be required to be reduced to below the APDMS turn-on power fraction and the entire procedure for bringing the unit back into base load operation without APDMS would then have to be repeated.
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l We have reviewed the supplemental procedures described above for l
operating the Zion units without APDMS surveillance in a base load only mode at high power levels and conclude that there is sufficient assurance that the reactor power distribution will stay within its specified limit.
Summary I
Based on our review of the licensee's ECCS reanalysis and the other
. referenced documents, we conclude that operation of Zion Units 1 and i
2 at a peaking factor limit of 1.86, with reduced accumulator water volume will be in conformance with the 10 CFR 50.46 criteria. We also conclude that the proposed Technical Spe:ification procedures for APDMS type surveillance and for base load operation will ensure that the new Fg value of 1.86 will be met and are therefore acceptable.
Environmental Considerations We have determined that these amendments do not authorize a change in effluent types or total amounts or an increase in power level and will not result in any significant environmental impact. Having made this deter-mination, we have further concluded that these amendments involve an action j
which is insignificant from the standpoint of environmental impact and, f
pursuant to 10 CFR 551.5(d)(4), that an environmental statement, or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance of these amendments.
Conclusion We have concluded, based on the considerations discussed above, that:
1 (1) because the amendments do not involve a significant increase in the probability or consequences of accidents previously considered and do I
not involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) such activities will be conducted in compliance with the Commission's regulations and the issuance of these amendments will not be inimical to the common defense and l
security or to the health and safety of the public.
l Date:
February 16, 1979 1
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1, I References 1.
Letter from Ccomonwealth Edison Company (C. Reed) to NRC (H. R. Denton),
dated February 2,1979.
2.
Letter from Ccmmonwealth Edison Company (C. Reed) to NRC (H. R. Denton),
dated February 9,1979.
3.
Letter from NRC (A'. Schwencer) to Commonwealth Edison (C. Reed), dated April 21, 1978, transmitting Order for Modification of License.
j 4.
Letter from Westinghouse Electric Corporation NS-CE-1751 (C. Eicheldinger),
to NRC (J. F. Stolz), dated April 7,1978, transmitting LOCA-ECCS Analysis with Zirc/ Water Reactor Correction.
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5.
Letter from Commonwealth Edison (C. Reed) to NRC ( A. Schwencer), dated i
April 7,1978.
6.
Letter from Commonwealth Edison (C. Reed) to NRC ( A. Schwencer), dated April.17,1978.
7.
WCAP-9220-P-A, Westinghouse ECCS Evaluation Model, February 1978 Version, February 1978.
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