ML20114B949
| ML20114B949 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 12/31/1984 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20114B941 | List: |
| References | |
| TAC-54432, NUDOCS 8501290653 | |
| Download: ML20114B949 (3) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION
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l SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO.105 TO FACILITY OPERATING LICENSE NO. DPR-57 GEORGIA POWER COMPANY OGLETHORPE POWER CORPORATION MUNICIPAL ELECTRIC AUTHORITY OF GEORGIA CITY OF DALTON, GEORGIA EDWIN I. HATCH NUCLEAR PLANT, UNIT NO. 1 DOCKET NO. 50-321 1.0 Introduction By application dated February 6,1984, Georgia Power Company (GPL or the licensee) requested an amendment to Appendix A of Facility Operating Licenses Nos. DPR-57 and NPF-5 for Edwin I. Hatch Nuclear Plant, Units 1 and 2, to reflect certain proposed plant ^ modifications related to the Average Power Range Monitor and Rod Block Monitor Instrumentation. We issued the requested changes for Unit 2 in Amendment No. 39.to Facility Operating License No. NPF-5 on July 13, 1984 At that time, the change for Unit I was held in abeyance.
The licensee, by letter dated September 6,1984, revised their original request to:
- 1) provide an additional restriction on plant operation during the limiting Condition for Operation with one recirculation loop out of service;
- 2) remove the one-hour time period allowed prior to blockage of control rod withdrawal with the plant in a Limiting Control Rod Pattern and both Rod Block Monitor channels inoperable; and 3) correct a typographical error in the February 6, 1984, submittal.
2.0 Evaluation The Average Power Range Monitor, Rod Block Nonitor, and Technical Specifica-tion Irrprovement (ARTS) Program for Edwin I. Hatch Nuclear Plant, Units 1 and 2, supporting document GE Licensing Report NEDC-30474-P and the associated d anges to the Technical Specifications were reviewed and approved in the supporting Safety Evaluation to Amendment 39 to Facility Operating License No. NPF-5 dated July 13, 1984. This evaluation addresses the balance of the changes requested by the licensee in their September 6, 1984, submittal.
2.1 Restricted Plant Operation With One Recirculation loop Out of Service The possibility of thennal-hydraulic instability in a BWR has been investicated in the startup of early BWRs.
For modern higher-power density reactors, pressure perturbation techniques were developed to measure core stability margins. Based on these tests and analytical models, it has been shown that the high power / low flow corner of the power / flow MAP is the region of least stability margin. This region is encountered during single
. loop and natural circulation operation of a BWR. The NRC staff has been 8501290653 841231 PDR ADOCK 05000321 P
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studying BWR thermal-hydraulic stability characteristics for several years.
To assure compliance with General Design Criteria 10 and 12, natural circulation operation has been prohibited and single loop operation has been l
restricted by Technical Specifications for most plants. GE recently presented the staff with stability test data which demonstrated the occurrence of limit cycle neutron flux oscillations at natural circulation and several percent above the rated rod line.
i The oscillations were observable on the APRM's and were suppressed with control rod insertion.
It was' predicted that-limit cycle oscillations would occur at the operating condition tested; however, the characteristics of the observed oscillations were different than those previously observed during other stability tests. Namely, the test data show that some LPRM indications oscillated out of phase with the APRM signal and at an amplitude as great as six times the core average. GE has prepared and released a Service Information Letter, SIL-380, to the licensees with measures to avoid and control abnormal neutron flux oscillations. The major action recommended by SIL-380 to be taken by utilities to avoid the regions of least stability following a recirculation pump (s) trip event is to reduce power by inserting control rods to or below the 80% rod line using-the plant's prescribed control rod shutdown insertion sequence.
In response to NRC staff concerns and to make the Technical Specifications consistent with the operating recommendations of SIL-380, GPC, in a-letter dated September 6, 1984, has proposed changes to the Edwin I. Hatch Unit 1 Technical Specifications.
The principal addition made to the Technical Specifications is the following:
When operatirig with one recirculation loop, the plant will initiate within 15 minutes an orderly reductton in themal power to less than a specified limit within 2 tours. This limit corresponds to a load line 1'
leading to 80% reactor power at rated core flow.
We have reviewed these proposed changes and have found that they result in a considerably more stable operating mode since the plant will be operating at a lower power / flow ratio which has been shown by testing and analysis to result in increased thermal-hydraulic stability. We find that these changes-are prudent and acceptably resolve our thermal-hydraulic-stability concerns for Hatch Unit I since long tem single loop operation is-not permitted and natural circulation operation is prohibited. Should such operation be requested in the future, we would reevaluate this Technical Specification to determine if additional changes are necessary.
2.2 Clarification of the Limiting Condition for Operation with a Limiting Control Rod Pattern As a part of the ARTS submittal of February 6, 1984, the licensee proposed cbc.ges to_ Section 3.3.F of the Technical Specifications, "O Limiting Control Rod Pattern (for Rod Withdrawal Error, RWE)peration with a The NRC staff and licensee discussed the proposed change and mutually agreed that the change to-
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. the paragraph was acceptable with the exception nf "within I hour" in sentence 3 of the para:;raph on operation with a Limiting Control Rod Pattern for RWE when core thermal power is 130%.
In order to clarify this issue, the licensee revised the sentence ty deleting the "within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />" in their submittal of September 6,1984 We have reviewed this change and find that it is acceptable since the charge makes it ciear that control rod withdrawal is not allowed without at least one ooerable RBM channel when a limiting control rod pattern exists.
2.3. Administrative Error - Technical Spccification Table 3.2-7 The licensee, in their submittal of September 6, 1984, identified that "g" was omitted for the trip setting for the Low Trip Setpoint (LTSP) in the February 6, 1984 submittal. The Technical Specification page was revised as a part of the September 6, 1984, submittal. We find the change acceptable.
3.0 Environmental Consideration An Environmental Assessment and Finding of No Significant Impact has been issued for this: amendment.
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4.0 Conclusion We have concluded, based on the considerations discussed above, that (1) there is reasonable assurance that the health and safety of the will not be endangered by operation in the proposed manner, and (2) public such activities will be conducted in compliance with the Connission's regulations and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.
Cated: Decenber 31, 1984 Principal Reviewers:
R. Kendall, G. Schwenk 1
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