ML13331A410
| ML13331A410 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 05/16/1990 |
| From: | Ray H SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML13331A411 | List: |
| References | |
| NUDOCS 9005230141 | |
| Download: ML13331A410 (4) | |
Text
Southern California Edison Company 23 PARKER STREET IRVINE, CALIFORNIA 92718 HAROLD B. RAY TELEPHONE VICE PRESIDENT 714 -458-4400 May 16, 1990 U. S. Nuclear Regulatory Commission Attention:
Document Control Desk Washington, D.C. 20555 Gentlemen:
Subject:
Docket No. 50-206 Amendment Application No. 182, Revised Spent Fuel Pool Cooling Decay Heat Removal Requirements San Onofre Nuclear Generating Station Unit 1
SUMMARY
During a review of administrative controls necessary for the full core off-load planned for the Cycle 11 outage, it was recognized that the actual heat loads on the Spent Fuel Pool (SFP) Cooling System will be greater than those reported in the Updated Final Safety Analysis Report (UFSAR).
This finding was reported to the Commission in accordance with 10 CFR 50.72 on April 24, 1990. The cause of this problem was that previously calculated maximum normal and abnormal heat loads described in the UFSAR were underestimated due to calculational error. This amendment application requests NRC review of a revision to the decay heat removal requirements of the SFP Cooling System as described in UFSAR Section 9.1.3.
Recent calculations conservatively predict that the maximum SFP heat load during the upcoming outage will be approximately 8.6 MBtu/h. Because this heat load is higher than the maximum specified in the UFSAR, NRC approval of the increased heat load is required before the defueling can be performed. As such, we respectfully request expedited review and approval of this amendment application and associated Proposed Change No. 224 by July 10, 1990.
Receipt of the Commission's approval by that date will allow us to maintain the current outage schedule.
The SFP Cooling System currently meets the temperature and time to boil limits indicated in the UFSAR since the actual heat load in the pool is currently far below those postulated. The system design currently includes one permanently installed pump and a spare pump which can be connected to the system if required. The spare pump will be permanently installed in the cooling system prior to the upcoming full core off-load. This modification will assure that the SFP will not boil given the maximum abnormal heat load and a worst case active component failure.
9005230141 900516(
PDR ADOCK 05000206 R
Porr:
Document Control Desk May 16, 1990 SFP COOLING SYSTEM PERFORMANCE We have conservatively recalculated the maximum heat loads, pool temperatures and times to boil upon loss of cooling for several plant conditions, on a preliminary basis, assuming a worst case active component failure. A comparison of the results of these preliminary calculations with the current UFSAR maximum abnormal heat load case is given in Table 1. We will provide formal confirmation of these results by May 31, 1990.
TABLE 1 SFP COOLING SYSTEM DECAY HEAT REMOVAL CAPABILITY COMPARED TO CURRENT UFSAR MAX. ABNORMAL HEAT LOAD*
Time to Boil Max. SFP Heat Max. SFP Upon Loss of Plant Condition Load (MBtu/h)
Temp (*F)
Cooling (hr)
Current UFSAR Max.
6.8 116 47 Abnormal Heat Load Fuel Cycle 10 0.5
<90 No Boiling (current SFP (By Observation) fuel inventory)
Cycle 11 Outage 8.6 138 21 Fuel Cycle 11 14.7 179 6
(with postulated emergency defueling)
Corrected UFSAR Max.
17.0 193 3
Abnormal Heat Load
- See PCN-224 for assumptions used in calculations.
SFP COOLING SYSTEM MODIFICATIONS We are proceeding to implement modifications to the SFP Cooling System to improve SFP cooling availability in light of the shortened time intervals to boiling upon loss of cooling during the infrequent high heat loads.
The modifications will reduce the time required to place the spare cooling pump in-service should the primary pump experience a failure. Since the spare pump is not presently connected to the system, up to 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> is now required to install the piping spool pieces and electrical connections so it can be utilized. While this time was considered adequate for the 47 hours5.439815e-4 days <br />0.0131 hours <br />7.771164e-5 weeks <br />1.78835e-5 months <br /> to boiling specified in the UFSAR, it does not provide adequate margin given the corrected 21 hours2.430556e-4 days <br />0.00583 hours <br />3.472222e-5 weeks <br />7.9905e-6 months <br /> to boiling conservatively calculated for the heat load projected during the upcoming outage.
Document Control Desk May 16, 1990 The following modifications are being completed so that the time to place the spare pump in-service is reduced to approximately 30 minutes whenever the pool high temperature alarm setpoint is exceeded:
Permanently connecting the spare SFP cooling pump to the SFP Cooling System. The additions to the system will be Seismic Category A and quality class safety-related.
Powering the spare pump from a separate electrical train.
Due to the extensive electrical system modification to be completed during the upcoming outage, a non-safety related construction power source that is fed directly from the San Diego Gas and Electric power grid, or is otherwise provided, will be the interim power source. The spare pump power supply will be upgraded to safety-related class prior to the Cycle 12 refueling.
Providing appropriate controls that are consistent with existing system requirements. Due to the extensive electrical modifications to be completed during the Cycle 11 refueling, non-safety related local manual controls will be provided. The controls will be upgraded to safety-related prior to the Cycle 12 refueling.
As a minimum, operation of the SFP Cooling System will be monitored once per shift during the full core off-load. Should the existing pool high temperature alarm of 125*F be exceeded, the alarm setpoint will be reset to 150*F or an individual will be assigned to monitor the system's performance.
If the pool temperature should ever exceed the 150*F limit, a dedicated individual will continuously monitor system operation. This is acceptable since at 150OF it would take at least 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> to reach pool boiling upon pump failure. The ability to quickly align and operate the spare pump within approximately 30 minutes of the discovery of a primary pump failure will assure that the maximum SFP heat loads can be reliably removed.
PROPOSED REVISION OF UFSAR SFP COOLING REQUIREMENTS We request NRC approval of the following revised SFP Cooling System decay heat removal requirements:
SFP temperature no greater than 150OF for the SFP maximum normal heat load case (including assumption of failure of one cooling pump).
No pool boiling for the SFP maximum abnormal heat load case (including assumption of failure of one cooling pump).
Pumps, piping, valves, electrical power sources, and connections will satisfy the existing system quality requirements.
The SFP cooling pumps will be powered and controlled from separate electrical trains.
Document Control Desk May 16, 1990 In recognition of our request for expedited review and approval of the above proposed revisions to the UFSAR SFP cooling requirements, we are prepared to support a meeting at your earliest convenience to discuss these issues. If you have any comments or questions regarding this amendment application, please call me.
Very truly yours, Enclosure cc: J. B. Martin, Regional Administrator, NRC Region V C. Caldwell, NRC Senior Resident Inspector, San Onofre Units 1, 2 and 3 J. H. Hickman, California Department of Health Services