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RO 80-001/01T:during Review of Steam Line Break Analysis, Incorrect Assumption Utilized in Zero or Low Power Steam Line Break Analysis Discovered.Cause Unstated.Necessary Mods to Be Implemented Prior to Startup| ML20126B434 |
| Person / Time |
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| Site: |
Maine Yankee |
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| Issue date: |
01/30/1980 |
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| From: |
Wood E
Maine Yankee |
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| To: |
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| References |
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| NUDOCS 8003120721 |
| Download: ML20126B434 (1) |
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~w.;g w w Juuuary 30, L980 ETnited States Nuclear Regulatory Comission Directorate of Regulatory Operations Region I 631 Park Avenue King of Prussia, PA 19/.06 Reference Licenne No. DPit-36 (Docire t No . 50-309)
Dear Sirs O/r
Subject:
Ma hm Yankee Reportable Occurrence #80-001/Ol M Pursuant to the roepsirements of Technical Specification S.9.1.6.h, the l 1
Maima Yankee Atomic Power Company hereby submits the following report.
In the course of reviewing the steam line break analysia in response to the concerne raised by the NRC with regard to automation of the auxiliary feedwater syscam, it was discovered that an incorrect assumption was utilised tu the sero or low-power steam line break analysis. The analysis had assumed that at low power levels, when ieedwater is being controlled by the feedwater regulating valve hypass valves, that these bypass valve.s would remain "as-is" throughout the transient. In reality, as a result of the low steam generator pressure reactor trip eignal, an override signal causes the feedwater bypass valves to ramp to an 80% open (5% full feedwater flow) position. A reanalysis of this event shown that this opaning of the feedvater bypass valves results ih an unacceptably high rate of feedwater addition to the af fected steam generator causing a rapid cooldown of the reactor coolant system and a return-to-power transient. A return to power following a seema line break is not permitted under the current design basis for Maina Yankee.
Ttie plant was in the refueling mode at the time this error was discovered and therefore no imumdiate corrective action was necessary. Modifi-cations necessary to correct this error shall be implemented prior to plant startup.
l Very truly yours. I MAINE YAIJKEE ATOMIC POWIUt COXPANY
_ ,1'1 'fl .
Edis tu C. Wood Plent Manager ECW/k af D** D *D"T a1_J1[3\
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