ML19260D575
| ML19260D575 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 01/30/1980 |
| From: | Wood E Maine Yankee |
| To: | |
| References | |
| NUDOCS 8002110443 | |
| Download: ML19260D575 (2) | |
Text
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Box 450. RFD 2 q
f Wiscusset. Maine 04678
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s%% _,2g Ja:.uary 30, 1980 United States Nuclear Regulatory Coc=ission Directorate of Regulatory Operations Region I 631 Park Avenue King of Prussia, Pennsylvania 19hC6
Reference:
license No. DFR-36 (Docket :;o. 50-309)
Dear Sir:
Subject:
Maine Yankee Reportable Occurrence #30-001/0lT-0 Pursuant to the requirements of Technical Specification 5 91.6.h, the Maine Yankee Atomic Power Company hereby suttits the following report.
In the course of reviewing the steam line break analysis in response to the concerns raised by the NRC with regard to automation of the auxiliary feedvater system, it was discovered that an incorrect assumption was utilized in the zero or low-power steam line break analysis. The analysis had assumed that at low power levels, when feedvater is being controlled by the feedvater regulating valve bypass valves, that these bypass valves vould remain "as-is" throughout the
- ansient.
In reality, as a result of the low steam generator pressure reactor trip signal, an override signal causes the feedvater bypass valves to ramp to an SC". open (5', full feedvater flow) position. A reanalysis of this event shows that this opening of the feedvater bypass valves results in an unacceptably high rate of feedvater addition to the affected stea= gen-erator causing a rapid cooldown of the reactor coolant system and a return-to-power transient.
The possible return to power vculd only occur during the last portion of the core operating cycle and with a coincident stuck rod of the highest worth.
Whereas the plant is operated in the near zero power mode very infrequently during the last part of each cycle, and very conservative (pessimistic) assump-tions are made in the analysis (eg. guillotine rupture of the :ain steam line, highest worth rod stuck, etc.) such an incident is highly unlikely. However, a return to power following a steam line break is not permitted under the current design basis for Maine Tankee.
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o CORRECTED COPY January 30, 1930 The plant was in the refueling mode at the time this error was discovered and therfore no i==ediate corrective action was necessary.
Modifications necessary to correct this error shall be i=ple=ented prior to plant startup.
Very truly yours, MAI:lE YXIKEE ATCMIC POWER COMPEIY
/giv.
[, _ Y Edvin C. ~4:od Plant.%neger EC*4/bev
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