ML14133A571
| ML14133A571 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 08/03/1981 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | Dietch R SOUTHERN CALIFORNIA EDISON CO. |
| References | |
| TASK-05-11.A, TASK-5-11.A, TASK-RR LSO5-81-08-008, LSO5-81-8-8, NUDOCS 8108050091 | |
| Download: ML14133A571 (5) | |
Text
August 3, 1981 Docket No. 50-206 LSOS08-008 Mr. R. Dietch, Vice President Nuclear Engineering and Operations Southern California, Edison Company 2244 Walnut Grove Avenue Post Office Box 800 Rosemead, California 91770
Dear Mr. Dietch:
RE:
SEP TOPIC V-II.A; ELECTRICAL, INSTRUMENTATION AND CONTROL FEATURES FOR ISOLATION OF HIGH AND LOW PRESSURE SYSfEMS; SAFETY EVALUATION FOR SAN ONOFRE 1 The enclosed staff safety evaluation supplements our contractor's evaluation that has been made available to youpreviously, As a result of our safety evaluation of Topic V-II.A,.we areproposing modifications to the CVCS and LPSI valve control circuits.
The need to actually implement these changes will be determined during the integrated plant safety assessment. This topic assessment may be revised in the future if your facility design fs changed or if NRC criteria relating to this topic are modified before the integrated assessment is completed.
Sincerely, Dennis M. Crutchfield, Chief Operating Reactors Branch #5 Divis ion of Licensing
Enclosure:
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0a Mr. R. Dietch SAN ONOFRE 1 Docket No. 50-206 cc Charles R. Kocher, Assistant General Counsel James Beoletto, Esquire Southern California Edison Company Post Office Box 800 Rosemead, California 91770 David R. Pigott Chickering & Gregory Three Embarcadero Center Twenty-Third Floor San Francisco, California 94111 Harry B. Stoehr San Diego Gas & Electric Company P. 0. Box 1831 San Diego, California 92112 Resident Inspector/San Onofre NPS c/o U. S. NRC P. 0. Box 4329 San Clemente, California 92672 Mission Viejo Branch Library 24851 Chrisanta Drive Mission Viejo, California 92676 Mayor City of San Clemente San Clemente, California -92672 Chairman Board of Supervisors County of San Diego San Diego, California 92101 California Department of Health ATTN:
Chief, Environmental Radiation Control Unit Radiological Health Section 714 P Street, Room 498 Sacramento, California 95814 U. S.-Environmetal Protection Agency Region IX Office ATTN:
EIS COORDINATOR 215 Freemont Street San Francisco, California 94111
TOPIC: V-11.A REQUIREMENTS FOR ISOLATION OF HIGH AND LOW PRESSURE SYSTEMS
- 1. INTRODUCTION Several systems that have a relatively low design pressure are connect ed to the reactor coolant pressure boundary. The valves that form the interface between the high and low pressure systems must have suffici ent redundancy and interlocks to assure that the low pressure systems are not subjected to coolant pressures that exceed design limits. The problem is complicated since under certain operating modes (e.g., shut down cooling and ECCS injection) these valves must open to assure ade quate reactor safety.
II. REVIEW CRITERIA The review criteria are presented in Section 2 of EG&G Report 1345 F "Electrical, Instrumentation, and Control Features for Isolation of High and Low Pressure Systems".
III.
RELATED SAFETY TOPICS AND INTERFACES The scope of review for this topic was limited to avoid duplication of effort since some aspects of the review were performed under related topics, The related topics and the subject matter are identified be low. Each of the related topic reports contain the criteria and review guidance for its subject matter.
V-3 Overpressurization Protection V-10.B RHR Reliability VI-4 Containment Isolation Topic V-11.B is dependent on the present topic information for completion.
IV, REVIEW GUIDELINES The review guidelines are presented in Section 7.3 of the Standard Review Plan.
V. EVALUATION As noted in EG&G Report 1345 F, the San Onofre Nuclear Station Unit 1 has three systems with a lower design pressure rating than the RCS that are directly connected to the RCS. The CVCS, SIS, and RHR systems do not meet current licensing requirements for isolation of high and low pressure systems as specified below.
- 1) The CVCS isolation valves have no pressure-related interlocks as.
required by BTP EICSB-3
-2
- 2) The SIS and long-term recirculation system motor-operated isolation valves have no pressure-related interlocks required by SRP 6.3
- 3) None of the RHR system isolation valves automatically close if RCS pressure increases above RHR system oepration, and the outboard isolation valves have no pressure-related interlocks as required by BTP RSB-5-1. The interlocks for the inboard isolation valves are neither diverse nor independent.
The licensee has defended the present design by the following statements.
"1. The first paragraph on page 4 of the evaluation should be revised to read as follows:
"The long-term recirculation system uses the charging pumps in series with the recirculation pumps to provide water from the containment sump to each RCS cold leg. Isolation is provided by an MOV in each of the three branches. These MOVs are in series with the RCP Seal injection flow control valves. In addition, there is a check valve at the discharge of each of the charging pumps. The MOVs are opened using a manual switch and have no interlocks to prevent opening when RCS pressure is above SIS design pressure. The flow control valves are normally open during operation to provide seal injection to the RCPs. All lines are designed for full RCS pressure."
- 2. The purpose of this SEP topic is to ensure proper isolation of systems with a lower pressure rating than the RCS. As noted in comment 1 above, the recirculation path from the charging pump discharge is de signed to RCS pressure. In fact, during normal operation, these lines
- are pressurized to RCS pressure. Therefore, this system should not be included in the scope of this topic.
- 3. Although the description of the Chemical and Volume Control System (CVCS) on pages 4 and 5 of the evaluation is correct, the conclusions of the evaluation are not appropriate. The CVCS is operated contin uously during normal operations. As such, the piping is open to RCS pressure on a continuous basis. The letdown portion of the system is
- orificed inside containment. These orifices prevent RCS pressure from affecting the low pressure portions of the system. Moreover, downstream of the orifices is the pressure relief valve RV206 which relieves to the pressurizer relief tank inside containment. There is therefore, no need for pressure interlocks on the let down valves, since CVCS overpressurization is prevented by the system design.
The discharge of the CVCS is designed for RCS pressure. It is there fore, not a low pressure system and should not be addressed as part of this topic evaluation,"
-3 The staff does not agree with these statements because:
- 1) The charging path check valves are not tested and therefore, according to IEEE Std. 379, must be assumed to have failed in addition to the single rahdom-failure of a motor operated valve. Such an event would lead to overpressurization of the charging pump suction side pipes, and
- 2) Given an event that isolates the letdown system outside of containment coincident with a failure of the relief valve, overpressurization of the letdown system appears to be likely.
VI.
CONCLUSIONS Because of the severe consequences of a LOCA outside of containment, the staff proposes that San Onofre Unit 1 be modified as follows:
- 1) The SIS and long-term recirculation system motor operated isolation valves be modified to satisfy the review criteria of SRP 6.3 or an acceptable check valve test program be implemented.
- 2) The CVCS discharge isolation valves be modified to satisfy BTP EICSB-3 or a redundant relief valve be installed or demonstrate that a break in this line will not violate 10 CFR 100 limits.
The staff does not believe that the RHR system should be modified (if at all) until the low temperature overpressurization protection review (USI A-26) is completed.