ML18081A375

Significant Deficiency Rept Re Containment Purge & pressure- Vacuum Relief Valves.Actuator Torque Values Were Insufficient to Move Valves from Open to Closed Positions W/ Design Differential Pressure of 60 Psi.Design Reviewed

ML18081A375
Person / Time
Site:	Salem
Issue date:	10/05/1979
From:	Public Service Enterprise Group
To:
Shared Package
ML18081A374	List: ML18081A373 ML18081A375
References
NUDOCS 7910190144
Download: ML18081A375 (2)

Text

i r

., _," ,,.,.._.~

SALEM NUCLEAR GENERATING STATION NO. 2 UNIT CONTAINMENT PURGE AND PRESSURE-VACUUM RELIEF VALVES

1. Background Information Four (4) 36 11 butterfly valves are used in the system to purge the containment. Two redundant valves in series (one insiGe and one outside the containment) are used in the purge inlet line and similarly two redundant valves are used in the purge exhaust line.

In addition, the system used during normal operation for pressure-vacuum relief contains two redundant 10 11 butterfly valves (one inside and one outside the containment).

The design allowed for these valves to be opened to perform their designated functions when the plant was in any opera-tional mode. They were also required to close, if in an open position during an incident (LOCA or steam line break) against the resulting containment pressure(s).

The maximum pressure inside the containment after an incident is calculated to be 43.2 psig. This will occur approximately twenty (20) seconds after the incident. It is estimated that the valves will start to close in about one to two seconds after the incident at which time the containment pressure is calculated to be 10 to 14 psig. The valve has a closure time of less than 2 seconds, therefore, the valve should be fully closed in three to four seconds after the incident. At that time, the containment pressure is calculated to be 18 to 24 psig. However, a more conservative design differential pressure of 60 psi was used to evaluate valve closing torques.

The NRC staff requested that the torque values required for closing the valves under incident conditions be verified.

2. Description of Deficiency During the verification of the original data, the vendor determined that the actuator torque values were not suffi-cient to move the valves from the full open (90°) position to the closed position (0°) with a design differential pressure of 60 psi. With a differential pressure of between 18 to 24 psi, which is the calculated actual differential, the actuator torque values were marginal.

( .

.~-

3. Effects on Safety If the valves had been open at the time of an incident and did not close, it would affect containment isolation.

4. Corrective Action Taken

,For~ the 36" purge valves, administrative controls will be implemented to keep the valves closed in all operating modes except modes 5 and 6 (cold shutdown and refueling).

The 10" valves will be modified by the vendor. The modifi-cation will consist of reworking the actuator and a realign-ment of the actuator and valve shaft such that the full open position will correspond to 60° open instead of the original 90° open. This will significantly reduce the required closing torque with a 60 psi differential to a value well below the available actuator torque. The new required closing torque with a 60 psi differential will be 4,572 in-lbs., whereas the actuator torque available will be 9,100 in-lbs., (spring force only, with no air assist).

In addition, a review of the valve design is being made in accordance with the NRC preliminary "Guidelines for Demonstra-tion of Operability of Purge and Vent Valves".

5, Schedule for Implementation The valves are to be shipped to the vendor for rework and are scheduled to be returned to the plant for installation on or about October 26, 1979.