ML20203E034
| ML20203E034 | |
| Person / Time | |
|---|---|
| Site: | Oconee, Mcguire, McGuire  |
| Issue date: | 04/16/1986 |
| From: | Ward D Advisory Committee on Reactor Safeguards |
| To: | Stello V NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| Shared Package | |
| ML20203E039 | List: |
| References | |
| ACRS-R-1190, NUDOCS 8604240065 | |
| Download: ML20203E034 (2) | |
Text
_ _ - _ _ _ _ _ _ _ _ _ _ _ _ __
[mie UNITho 3T=TEs d
f NOCLEAR REGULATORY COMMISSION ADVlsORY COMMITTEE ON REACTOR sAPEGUARDS 8
WASHINGTON, D. C. 20SSE April 16, 1986 Mr. Victor St.ello, Jr.
Executive Director for Operations U. S. Nuclear Regulatory Commission Washington, D. C. 20555
Dear Mr. Stello:
SUBJECT:
PROPOSAL BY DUKE POWER COMPANY TO OPERATE THE MCGUIRE NLCLEAR STATION, UNITS 1 AND 2. WITH0tJT UPPER HEAD INJECTION SYSTEMS During its 312th meeting, April 10-12, 1986, the Advisory Comittee on Reactor Safeguards reviewed the proposal by the Duke Power Company to operate the McGuire Nuclear StatHon, Units 1 and 2, without the upper head injection system (UHIS) portions of the emergency core eooling systems. The ECCS Subcomittee met to review this proposal on February 21, 1985 and March 26, 1986.
We heard presentations by the NRR Staff, which endorses the proposal, by Duke Power Company, and by Westinghouse Electric Corporatien, the designer of the McGuire Nuclear Steam Supply System.
The NRC Staff provided a preliminary Safety Evaluation Report on this topic. Their review bases were augmented during discussion with us at this meeting.
The UHIS was added to the McGuire units and later added to most PWRs with ice condenser containments to improve core cooling during hypothe-tical large break LOCAs.
The UHIS includes a pressurized accumulator which provices a high volume flow of water directly into the upper head if the reactor coolant pressure decreases below approximately 1000 psic as would be expected in an LB-LOCA.
This system supplements the ECC5 accumulator, which arovides high volume flow to the cold leg at lower pressure in most PbRs.
Thus, following an LB-LOCA, the core wf11 be refilled from top and bottom as opposed to only from the bottom as in most PWRs without the UHIS.
At the time of the McGuire operating license review, analyses of ECCS performance, using available " evaluation model (EM) codes, indicated that the more rapid reflooding provided by UHI5 was necessary to reduce calculated peak clad temperatures (PCTs).
The higher PCTs were the result of steam binding in parts of the reactor coolant system brought on by the lower containment back pressure typical of ice condenser containment performance during a hypothetical LB-LOCA.
Without the UHIS, it would have been necessary to operate the McGuire units with re-strictions on core power or core power peaking.
With the UHIS, permis-sible peaking factors were similar to those in other Westinghouse pl a nts.,
Duke Power's experience with the UNIS at McGuire has not been entirely satisfactory. While there has been no indication that the system would j
y/) 4p I
p l
Mr. Victor Stello, Jr. not perfom its function should an LB-LOCA occur, it h6 resulted in increased occupational radiation exposures and added to the complexity of plant operation and maintenance.
There is strong incentive for its removal if it can be shown to be unnecessary.
Since the time of McGuire's operating licensing review, codes used for analysis of ECCS performance have been improved.
This includes both EM codes and those used to make (more nearly) best estimate (BE) analyses.
I Recent analyses, using the improved codes, by both the licensee and its contractors and 'the NRC Staff and its contractors, indicate that the performance of the McGuire ECCS, without the UHIS, is better than was predicted by the codes of a decade ago.
The licensee claims, and the NRC Staff concurs, that the calculated performance is enough improved that the McGuire units can safely be operated without the UNIS and with normal core power l'mitations.
Using the improved EM codes has shown that licensing requirements can be met without the rdIS. There is also evidence, from the rather sketchy BE analyses comr'.eted, that the UHIS does provide some benefit and that operation without LHIS will reduce real PCT margins.
However, we are persuaded that there are certain safety benefits in removing the (MIS, chiefly by reducing both the complexity of plant operation and its vulnerability to certain reactor upsets.
We agree that the Duke Power Company proposal can be accepted.
However, we suggest that they con-sider maintaining the removal and disconnection of the UNIS on a re-versible basis until further calculations show that the core operating conservatisms of McGuire without UNIS are similar to non-UNIS units We believe our review of this matter points up the need to exp idite revision of both 10 CFR 50.46 and Appendix K.
The reliance on o 'erly conservative evaluation models as mandated by the above regula. ions adversely impacts nuclear power plant safety.
Mr. C. J. Wylie did not participate in the Comittee's review of this matter.
Sincerely.
k, David A. Ward Chaiman References Memorandum dated March 18, 1986 from C.
H.
Berlinger, NRh t
P.
Boehnert, ACRS St.aff,
Subject:
Draft SER for the Proposed Operati n of McGuire Units 1 and 2 Without Upper Head In.iection, with enclosures
,