ML20002A422
| ML20002A422 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 08/31/1972 |
| From: | Heider L YANKEE ATOMIC ELECTRIC CO. |
| To: | US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 8011170162 | |
| Download: ML20002A422 (3) | |
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TELE PH O N E 617 366-9011
. August 31, 1972
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United States Atomic Energy Commission Washington, D. C.
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Attention: Directorate of Licensing
Reference:
License No. DPR-3 (Docket No. 50-29)
Dear Sirs:
On April 14, 1972 the Atomic Energy Commission approved Change No. 97.
Included in this change was a modification to the low main coolant flow trip circuitry. The modification included changing the main coolant flow sensing initiating signal from differential pressure across the steam generator to undercurrent or overcurrent on the main coolant pump motors.
The Technical Specifications require that all conditions including low main coolant flow that cause reactor scram also cause a turbine trip.
The omission of this portion of the modification was discovered as a result of a routine study conducted following a reactor scram and turbine trip. On Sunday, August 27, 1972, a severe local thunderstorm caused actuation of the undercurrent relays on main coolant loop numbers 2 and 3 which resulted in a reactor scram and turbine trip. Upon completion of a complete system check out and determination as to the cause of the scram and trip, the plant was returned to service.
Subsequently, a detailed sequence of events study (conducted following all scrams and trips) revealed that the turbine trip was not initiated by the low main coolant flow trip signal that scrammed the reactor. Any one of several automatic-signals or the immediate action of the operator by manually reaffirming reactor scram'and turbine trip could have caused the resulting turbine trip'within seconds after the reactor scram.
Upon completion of the detailed sequence study, it was discovered that during engineering of the low main coolant flow trip circuitry, the turbine trip portion of Proposed Change No. 96 was inadvertently omitted. Therefore, the plant prepared a Plant Design Change Request to correct the omission.
The Plant Design Change Request was reviewed and approved by Westboro Nuclear Services Division Engineering and Operations Departments. Material procure-ment and the preparation of repair procedures were also initiated immediately.
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United States Atomic Energy Commission August 31, 1972 Attention: Directorate of Licensing Page 2.
The Nuclear Safety and Audit Review Committee Chairman was informed of the omission and the proposed corrective action. Upon contacting a majority of his Committee, the recommended corrective actions were approved.
On Wednesday, August 30, 1972, the plant was removed from service, the approved modification was completed and preoperationally tested in accordance with written approved procedures.
We trust you will find this information complete and satisfactory; however, should you desire additional information feel free to contact us.
Very truly yours, YANKEE ATOMIC ELECTRIC COMPANY 44 0 Louis H. Heider Manager of Operations GCA/smw cc: James O'Reilly r-
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CONTROL NO: 4874 (TEMPORARY FORM)
A FILE FROM: Yanxee, Atomic Euc. Co.
DATE OF DOC:
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Louie H. Heider ORIO CC OTHER SEIiT AEC r~uR V
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gFROPIIiF0 40 50-29 DESCRIP2IO:i: Ltr rpt a prok w on 6-27-/2 wne7 ENCLOSURES:
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