ML13333A472
| ML13333A472 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 01/15/1980 |
| From: | Baskin K Southern California Edison Co |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| TASK-06-04, TASK-6-4, TASK-RR NUDOCS 8001220388 | |
| Download: ML13333A472 (5) | |
Text
Southern California Edison Company P. 0.
BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD. CALIFORNIA 91770 January 15, 1980 Director of Nuclear Reactor Regulation Attention:
D. L. Ziemann, Chief Operating Reactors Branch #2 Division of Operating Reactors U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Gentlemen:
Subject:
Docket No. 50-206 Containment Purging and Venting San Onofre Nuclear Generating Station Unit 1 By letter dated December 14, 1979 a response was provided to the NRC's "Interim Position for Containment Purge and Vent Valve Operation Pending Resolution of Isolation Valve Operability," as described in the October 23, 1979 letter from D. L. Ziemann.
The enclosure to this letter reiterates our response and provides additional information concerning the containment purge and vent valves at San Onofre Unit 1.
If you have any questions concerning this matter, please let me know.
Subscribed on this
/f day of 1980 ByA K. P. Baskin Manager, Nuclear Engineering and Licensing Subscribed and sworn to before me this OFFICIAL SAL.
day of 1980.
AGNES CRABTREE/
NOTARY pUBLIC - CAUIFORNIA 0
PRINCIPAL OFFICE IN LOS ANGELIM COUNTY My CobbEDExp.Av&27.1l2 Notar Public in and for the County of L Angeles, State of California Enclosure 0o012 20 :38
ENCLOSURE Containment Purge and Vent Valve Operation San Onofre Unit 1 The purge valves at San Onofre Unit 1 are two Henry Pratt 24" butterfly valves designated POV 9 and 10.
POV 9 is located in the purge line and POV 10 is located in the exhaust line.
Both valves are outside containment.
The vent valves at San Onofre Unit 1 are two Fisher Controls 6" butterfly valves designated CV 10 and 116.
CV 10 is located in the sphere equalizing line outside containment and CV 116 is located in the sphere equalizing line inside containment. SCE's response to the NRC's "Interim Position for Containment Purge and Vent Valve Operation Pending Resolution of Isolation Valve Operability" as described in the enclosure to the October 23, 1979 letter is provided below.
- 1. NRC INTERIM POSITION Whenever the containment integrity is required, emphasis should be placed on operating the containment in a passive mode as much as possible and on limiting all purging and venting times to as low as achievable.
To justify venting or purging, there must be an established need to improve working conditions to perform a safety-related surveillance or safety-related maintenance procedure.
(Examples of improved working conditions would include deinerting, reducing temnperature*, humidity*, and airborne activity sufficiently to permit efficient performance or to significantly reduce occupational radiation exposures).
SCE RESPONSE Purge Valves At San Onofre Unit 1, the purge valves are normally closed during plant operation.
Previously, they have been opened during hot shutdown to purge the containment atmosphere for entry at cold shutdown.
To comply with the NRC's interim position, the purge valves will be maintained closed until the reactor is in a cold shutdown condition.
Vent Valves The vent valves at San Onofre Unit 1 are normally open. The purpose for this is to maintain the containment atmosphere at or below atmospheric pressure. This is necessary to satisfy the initial conditions of the containment pressure-temperature re-analysis which assumes the containment atmosphere to be at 0 psig.
Therefore, it is not possible to further limit the venting of the containment. Further discussion on the vent valves is provided in the SCE response to NRC Interim Position 2a. below.
- Only when temperature and humidity controls are not in the present design.
-2
- 2. NRC INTERIM POSITION Maintain the containment purge and vent isolation valves closed whenever the reactor is not in the cold shutdown or refueling mode until such time as you can show that:
- a. All isolation valves greater than 3" nominal diameter used for containment purge and venting operations are operable under the most severe design basis accident flow condition loading and can close within the time limit stated in your Technical Specificatilons, design criteria or operating procedures. The operability of butterfly valves may, on an interim basis, be demonstrated by limiting the valve to be no more than 300 to 500 open (900 being full open).
The maximum opening shall be determined in consultation with the valve supplier.
The valve opening must be such that the critical valve parts will not be damaged by DBA-LOCA loads and that the valve will tend to close when the fluid dynamic forces are introduced.
- b. Modifications, as necessary, have been made to segregate the containment ventilation isolation signals to ensure that, as a minimum, at least one of the automatic safety injection actuation signals is uninhibited and operable to initiate valve closure when any other isolation signal may be blocked, reset, or overridden.
SCE RESPONSE
- a. The response to Interim Position 2a for the purge and vent valves is as follows:
Purge Valves In accordance with the above position the purge valves will be maintained closed except during cold shutdown and refueling. A temporary operating memorandum has been issued and will be in effect until qualification of the valves has been completed.
Vent Valves It is not possible to maintain the vent valves closed as discussed above. The valve vendor, Fisher Controls, has performed a preliminary analysis to determine the maximum opening for the valves. Based on this analysis, they have recommended a valve opening of 700. Details of the Fisher analysis are provided in the following discussion.
A calculation of allowable differential pressure across the valve for various openings was done. The analysis performed by Fisher utilized a containment temperature of 270 0F. Based on the design basis LOCA pressure-temperature re-analysis 1, this temperature would be reached approximately 40 seconds following the initiating event.
Table 1 indicates the results of the analysis:
1 Reference Case II in SCE letter to the NRC dated January 19, 1977, "Containment Post Accident Pressure Reanalysis, San Onofre Unit 1".
-3 TABLE 1 Angle Opening 10 20 30 40 50 60 70 80-90 (degrees)
Differential 188.1 185.8 192.1 164.7 138.2 83.3 59.7 35.5 Pressure (psi)
Actuator Torque Required (in-lb) 733.2 738.2 724.5 784.4 780.2 707.3 676.4 644.1 Following this calculation of the opening angles versus the maximum allowable differential pressure, the required actuation torque for an angle opening of 700 and 50 psi was determined.
The torque value was 592 in.-lb.
A maximum containment pressure of 49.41 psig was calculated as part of the pressure-temperature re-analysis for San Onofre Unit 1. At an angle opening of 700 the vent valves will close against an allowable differential pressure of 59.7 psi.
Therefore, under the maximum possible pressure of 49.4 psig, the calculations show that the valves will close with an angle opening of 700.
The valve vendor has also determined that the valve actuators are capable of handling the torque generated by the valve at any angle opening under the design basis LOCA conditions.
SCE and Fisher Controls have also looked at the ability of the vent valves to close from the fully open position.
As indicated in the pressure-temperature reanalysis 1, the peak post-accident pressure of 49.4 psig is reached at 62 seconds following the initiating event.
Assuming actuation of a containment isolation signal at 2 psig and conservatively assuming a valve closing time of 5 seconds as indicated by the valve vendor, the vent valves will be closed at about 5 seconds following the initiating event.
The differential pressure the valves would experience at 5 seconds is less than 35 psig.
Table 1 indicates that at an opening of 800_900, the vent valves will close against a differential pressure of 35.5 psig.
Notwithstanding the above conclusion that the vent valves will close from the full open position in the event of a design basis LOCA, and the Fisher Controls recommendation to limit the valve opening to 700, SCE will modify the valves to provide for a maximum opening of 500 to comply with the NRC interim position.
The equipment to modify the valves for a 500 opening has been ordered and will be available by the next plant shutdown.
Until the valves are modified they will be maintained in their full open position.
1 Reference Case II in SCE letter to the NRC dated January 19, 1977, "Containment Post Accident Pressure Reanalysis, San Onofre Unit 1".
- b. As indicated in prior submittals, the purge and vent valves will automatically close upon receipt of an isolation signal from any one of the following: (1) high containment pressure, (2) high contain ment radiation, or (3) safety injection actuation. Of the three actuation signals, only safety injection can be manually overridden.
This manual override is utilized during plant cooldown when reactor coolant pressure is below 1750 psig to prevent an inadvertent automatic actuation of the safety injection system. This override of the safety injection actuation signal is automatically disengaged when the reactor coolant pressure is above 1900 psig.
In the event containment isolation is required when the safety injection signal is overridden, isolation will be accomplished upon receipt of either a high containment pressure or a high containment radiation signal.
Therefore, the purge and vent valves would still close if the safety injection signal were not present.
Consequently, modification of the containment isolation signals to the purge and vent valves is not necessary at San Onofre Unit 1.