ML13330A077
| ML13330A077 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 08/08/1980 |
| From: | Haynes J SOUTHERN CALIFORNIA EDISON CO. |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| TAC-65149, NUDOCS 8008130485 | |
| Download: ML13330A077 (5) | |
Text
Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD. CALIFORNIA 91770 August 8, 1980 Director of Nuclear Reactor Regulation Attention: D. M. Crutchfield, Chief Operating Reactors Branch #5 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D.C. 20555 Gentlemen:
Subject:
Docket No. 50-206 Failure of the Salt Water Cooling System San Onofre Nuclear Generating Station Unit 1 By letter dated June 20, 1980, you requested four items of information concerning failure of the Salt Water Cooling System at San Onofre Unit 1. Our letter of July 24, 1980 transmitted the responses to Items 1, 2, and 3. The enclosure to this letter provides the response to Item 4 of the June 20, 1980 letter as agreed with Mr. T. Wambach of your staff during a telephone discussion of July 1, 1980.
Item 4 of your letter dated June 20, 1980, requests that we provide an analysis of the effect of the loss of the Salt Water Cooling System during the design basis loss of coolant accident (LOCA) or the main steam line break (MSLB) inside containment, whichever is more limiting with regard to heat load on the Component Cooling Water System (CCWS) and necessary operator actions.
As a result of our review of existing analyses, it was determined that the MSLB was the more limiting of the two accidents since the heat loads on the CCWS are greater, and therefore, the operator action requirements must be accomplished within a shorter interval of time to prevent exceeding CCWS design limits.
In response to your letter dated December 21, 1980, a reanalysis of the MSLB accident is being conducted as a part of the NRC requirements to provide actuation of the Auxiliary Feedwater System, which have resulted from the TMI-2 accident. The reanalysis is to be completed by October 1, 1980.
If the results of this reanalysis impact the response to Item 4 of your June 20, 1980 letter, we will advise you.
If you have any questions or desire additional information concerning the enclosure, please contact me.
Very truly yours, J. G. Haynes Chief of Nuclear Engineering Enclosure 8008130O' S
ENCLOSURE SALT WATER COOLING SYSTEM FAILURE Item 4:
Please provide an analysis of the effect of the loss of the Salt Water Cooling System during the design basis loss of coolant accident or the main steam line break inside containment, whichever is more limiting with regard to heat load on the Component Cooling System and necessary operator actions. No additional failures need be assumed.
Question:
A. Determine the time that it takes for the Component Cooling Water System to reach its design temperature limit with the heat load it will experience during the injection phase and recirculation phase, both with and without containment spray.
Response
Assuming that the Salt Water Cooling System fails at the same time as the LOCA or MSLB occurs, and no backup salt water cooling is available, it will take more than 17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br /> for the Component Cooling Water System to reach its design temperature limit. This 17-hour time is largely due to an unusual situation in which the spent fuel pool becomes a heat sink for the Component Cooling Water System. With the spent fuel pit heat exchangers not operating, as could be the case with loss of offsite power, it will take 'slightly more than 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> for the Component Cooling Water System to reach its design temperature limit.
The worst case LOCA situation considers failure of the Salt Water Cooling System at the time (approximately 25 hours2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br /> after LOCA) of peak temperature (250 0F) in the containment sump. Without the spent fuel pit heat exchangers operating, it will take 20 minutes for the Component Cooling Water System to reach its design tempera ture limit.
The discussion above is based on containment spray actuation at 44.1 seconds after LOCA. Without containment spray, sump temperature would exhibit a slower increase and a lower peak, resulting in a smaller maximum heat load for the Component Cooling Water System. The timing requirements for operator action are therefore based on the worst case assumption which includes containment spray.
For the worst case MSLB situation, it is conservatively assumed that the residual heat removal (RHR) system is placed in service 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> after shutdown to cool the reactor coolant from 350 0F to cold shutdown conditions. The heat load on the RHR heat exchanger in this case is greater than for the LOCA condition described above.
In fact, the heat load on the RHR heat exchanger during this worst case MSLB is similar to the heat load experienced during a cooldown from 350 0F under normal conditions. If failure of the Salt Water Cooling System occurs at this time, it will take approximately 5 minutes to reach the design temperature limit of the Component
-2 Cooling Water System, if no action is taken by the operators.
However, it would be expected that a loss of the Salt Water Cooling System would prompt operator action to cease operation of the Residual Heat Removal System and provide heat dissipation via the steam generators, thereby minimizing the heat load on the CCWS. In addition, steps would be taken to initiate backup salt water cooling to maintain CCWS temperature below the design limit.
Question:
B. Determine the time and manpower that it would take to align backup salt water cooling capability with and without off-site power available.
Response
Alignment of backup salt water cooling capability requires the actions of either one control room operator (CRO) who remains in the control room or one plant equipment operator (PEO) who leaves the control room to perform necessary manual actions, or both, depending on plant conditions. Backup cooling can be provided by the auxiliary salt water cooling pump within 5 minutes by CRO action only with or without offsite power for the worst case accidents analyzed if no additional failures are assumed. If additional problems arise and manual actions have to be performed by the PEO, the time for alignment of the auxiliary salt water cooling pump would increase to a maximum of 20 minutes. Since alignment of the screen wash pumps as backup for the Salt Water Cooling System always involves local manual actions, the time required in this case would be a maximum of 20 minutes with or without offsite power. Time requirements are assumed to begin from the time it is determined that the north and south salt water cooling pumps are inoperable and a backup system is required.
These times assume no additional failures, as stated in Item 4.
It should be noted at this point that the 20-minute figure given in the response to Question A assumes (1) a LOCA, (2) a loss of offsite power, and (3) failure of both loops of the Salt Water Cooling System at the same time as the peak temperature is reached in the containment sump. Similarly, the 5-minute figure given in the response to Question A assumes (1) a MSLB, (2) a loss of offsite.power, (3) failure of both loops of the Salt Water Cooling System at the same time that maximum heat load is placed on the RHR system, and (4) no operator action in response to a rapid increase in Component Cooling Water temperature.
Even under these highly unlikely conditions, assuming no additional failures, the initia tion of backup salt water cooling can be accomplished in time to prevent exceeding Component Cooling Water System design temperature limits. Further, as emphasized in our letter of July 24,
- 1980,
-3 preventive maintenance procedures for the Salt Water Cooling System are being formulated and will be implemented prior to resumption of operation following the current refueling outage. These preventive maintenance procedures will reduce the probability of simultaneous random failures going undetected and significantly improve the reliability of the Salt Water Cooling System.
Question:
C. Determine the time and manpower that is used for other manual actions required during this accident, such as shifting from injection to recirculation and any other operator actions required by your emergency procedures.
Response
In determining the time and manpower requirements for manual actions during this accident, it is assumed that a normal crew (one Watch Engineer, one Control Operator, one Assistant Control Operator and one Plant Equipment Operator) plus the auxiliary feedwater watch are on duty. It is assumed that the Watch Engineer and the auxiliary feedwater watch are unavailable for manual actions.
During the first 60 minutes following a LOCA or MSLB, the estimated time requirements for shift operators to perform manual actions are as follows:
Control Operator 20 minutes or less Asst. Control Operator 10 minutes or less Plant Equipment Operator 20 minutes or less The estimated time requirements for shift operators to perform all manual actions during the course of a LOCA or MSLB, until auxiliary systems are providing circulation through the reactor, are as.
follows:
Control Operator 40 minutes or less Asst. Control Operator 40 minutes or less Plant Equipment Operator 30 minutes or less Thus, ample operator time is available to initiate backup salt water cooling, since it takes four hours for the Component Cooling Water System to reach its design temperature limit for the case in which the Salt Water Cooling System failure is coincident with a LOCA or MSLB.
For the case in which failure of the Salt Water Cooling System occurs at the beginning of cooldown with the RHR heat exchanger, the operator(s) will be performing a routine cooldown procedure, requiring minimal manual actions for the operator(s).
Thus, the operator(s) will be available to initiate backup salt water cooling within the five minutes that it takes for the Component Cooling Water System to reach its design temperature limit.
e4 For the third case, 25 hours2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br /> after a LOCA, it takes 20 minutes for the Component Cooling Water System to reach its design temperature limit. At this time, the operator(s) are involved in the recirculation phase and manual actions are at a minimum, allowing prompt operator action to initiate backup salt water cooling.
Question:
D. Determine the heat removal capability of the backup salt water cooling provided and a comparison with the component cooling water heat load at the time.
Response
The heat loads on the Component Cooling System are variable with time, particularly the heat load from the recirculation heat exchanger. Additionally, the heat removal capability of the backup salt water cooling is strongly dependent upon temperature differen tial. Under all conditions following a LOCA or MSLB, the heat removal capability of the backup salt water cooling is sufficient to result in an equilibrium temperature of less than the 200OF design temperature in the Component Cooling Water System which will assure continued system operation within design limits.