ML20127C347
| ML20127C347 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 05/13/1992 |
| From: | Thadani A Office of Nuclear Reactor Regulation |
| To: | Varga S Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20127C350 | List: |
| References | |
| FOIA-92-276 NUDOCS 9205280221 | |
| Download: ML20127C347 (2) | |
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i xay 13, 1992 MEMORANDUM To:
Steven A. Varga, Director Division of Reactor Projects I/II Office of Nuclear Reactor Regulations FRCM:
Ashok C.
Thadani, Director Division of Systems Technology Office of Nuclear Reactor Regulations
SUBJECT:
MILLSTONE 1 ECCS ANALYSIS WITH OR WITHOUT FEEDWATER COOLANT INJECTION FAILURE The ;mactor Systems Branch reviewed the Emergency Core Cooling Sys*.en (ECOS) analysis for Millstone Unit No. 1 (MNPS-1) because ot qJestions raised about an apparent inconsistency between a licensee Technical Specification amendment request and the staff safety evaluation granting the amendment request.
This apparent inconsistency is concerned with whether or not the core would uncover during a LOCA event.
Our review confirmed our understanding that the core will uncover for the limiting small break with an assumed feedwater coolant injection (FWCI) failure.
Further, we also recognized that with FWCI operation'there will still exist break sizes for which core uncovery could occur.
uncovery was shown to occur in the updated Final Safety Core Analysis Report as well as the latest reload analysis dated December 20, 1990, that reconfirmed that MNPS-1 meets the criteria of 10 CFR 50.46.
In fact, the core is predicted to uncover over most of the break spectrum with the worst single failure assumed.
This worst single failure is the gas turbine which fails the FWCI and a train of low pressure core injection (LPCI) and low pressure core spray (LPCS).
The core is predicted to recover with the available-Automatic Depressurization System and the other trains of LPCI and LPCS.
Thus, the apparent inconsistency is not a safety concern because the staff recognized that core uncovery would occur and was considered during our review.
The licensee for MNPS-1 proposed a change to Technical
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in Amendment No. 45, dated June 18, 1990, to Specification 3.5.C, reduce the flow for the FWCI from 8000 gpm (original licensing The to 4000 gpm for loss of offsite power events only.
basis) reduction of the feedwater flow was accomplished by a setpoint change for switching the Feedwater Control System from Level 1
Control (normal configuration) to Flow Control with one Feedwater No hardware pump running at a minimum flow of 4000 gpm.
modifications, deletions, or additions were required.
This was the gas turbine from tripping due to an overload done to prevent q
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Steven A. Varga May 13, 1992 condition caused by feedwater pump runout.
The licensee proposed this change and the statf approved it because the limiting condition of'no FWCI operation (FWCI failure) was already analyzed in the design basis for the ECCS accidents (LOCA) over the entire break spectrum.
For a postulated LOCA with FWCI failure, the reactor water level will decrease causing the Automatic Depressurization System (ADS) to initiate to reduce pressure so the low pressure ECCS can recover and reflood the core and continue to meet the criteria of 10 CFR 50.46.
A statement made by the licensee in Basis C of the Technical Specifications (TS) 3.5.C for MNPS-1 reads, "For the pipe breaks for which the FWCI is intended to function, the core never-uncovers and is continuously cooled, thus no core damage occurs."
The specific meaning of this stat. ment is confusing and centers on the interpretation of the phrase, "for which FWCI is intended to function."
our safety evaluation report did not use or rely on this statement as a basis for our acceptance of the FWCI gas turbine modification.
Our latest review confirms our belief that there will be break sizes above which the loss of water through the break will be larger than the FWCI can replenish, and as a-result, the system will ultimately depressurize and core uncovery may occur.
However, the consequences of these breaks will meet all the criteria of 10 CFR 50.46 and is bounded by the original licensing basis of the plant.
The peak cladding temperature for the limiting small break is approximately 2150*F for no FWCI operation.
This is similar to Dresden Unit 2 which shows a PCT of approximately 1900*F with failed high pressure coolant injection (approximately 5000 gpm) for about the same break size.
We have discussed with the licensee our evaluation of the possible confusion which results from tne bases statement for the Technical Specification.
The licensee agrees with our assessment' and has agreed to amend the Technical Specification bases to state that core uncovery may occur _for a_ range.of break sizes, even with the FWCI operating as intended.
Ashok C.
Thadani, Director j
Division of Systems Technology cc:
T. Murley office of Nuclear Reactor Regulations W. Russell plSTRIBUTION l
Docket Files RFrahm JTaylor DJatts-AThadani l
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D:DS RFrahm/ Bah MRazzaque RJones A%hadani 4/29/92 4/29/92 4/30/92
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See previous concurrence i
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