ML13331A424
| ML13331A424 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 05/25/1990 |
| From: | SOUTHERN CALIFORNIA EDISON CO. |
| To: | |
| Shared Package | |
| ML13331A423 | List: |
| References | |
| NUDOCS 9005310137 | |
| Download: ML13331A424 (1) | |
Text
Enclosure to letter of May 25, 1990 BASIS:
Opening of the containment ventilation and sphere equalization valves, CV-10 and CV-116, is limited to periodic containment pressure reduction, air circulation for ALARA considerations upon personnel entry, and for performing valve surveillances. These limitations will maximize the amount of time that the valves are closed during power operation. In the closed position, these valves serve as a pressure barrier to provide containment isolation in the event of a steam line break or loss of coolant accident. Although both of these valves have been proven capable of closing during an accident event, by keeping them both closed to the maximum extent practicable, it is more likely that they will already be closed in the event of an accident and not have to change position.
By maintaining CV-40 in the position in which it vents exhausted instrument air into the containment atmosphere, it is maintained in its isolated position.
The isolation valves of the Sphere Equalization Ventilation line CV-116 and CV-10 are mechanically limited to a maximum opening angle of 47 degrees and 53.5 degrees respectively. These valves have been demonstrated capable of closure from an angle of up to 70 degrees under the differential pressures generated by a design basis accident (),(2),
however, the opening angle has been limited to approximately 50 degrees for conservatism.
The isolation valves of the Sphere Purge Air Supply (POV-9) and Air Outlet (POV-10) lines have not been demonstrated capable of closure under the differential pressures generated by a design basis accident. For this reason, isolation in these lines shall be maintained. This shall be accomplished by locking closed the manual isolation valves CVS-301 and CVS-313. These valves shall remain locked closed during MODES 1, 2, 3, and 4 until POV-9 and POV-10 can be demonstrated capable of performing their containment isolation function under post accident conditions.
REFERENCE:
(1) SCE to NRC letter dated March 27, 1984, from M. 0. Medford to D. M. Crutchfield.
(2) NRC to SCE letter dated November 2, 1984, from J. A. Zwolinski to K. P. Baskin, Transmits NRC Safety Evaluation.
9005310137 900525 PDR ADOCK 05000206 S NPDC SAN ON0FRE - UNIT 1 3.6-10 AMENDMENT NO: