ML13326A643
| ML13326A643 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 10/24/1980 |
| From: | Noell P, Stilwell T Franklin Institute |
| To: | Polk P Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML13326A640 | List: |
| References | |
| CON-NRC-03-79-118, CON-NRC-3-79-118, TAC-43464 NUDOCS 8105010564, TER-C5257-253 | |
| Download: ML13326A643 (8) | |
Text
- ttachment 2
TECHNICAL EVALUATION REPORT PRIMARY COOLANT SYSTEM PRESSURE ISOLATION VALVES SOUTHERN CALIFORNIA EDISON COMPANY SAN ONOFRE UNIT 1 NRC DOCKET NO.
50-206 NRC TAC NO.
12920 FRC PROJECT C5257 NRC CONTRACT NO. NRC-03-79-118 FRC TASK 253 Prepared by Franklin Research Center Author: P. N. Noell The Parkway at Twentieth Street T. C. Stilwell Philadelphia, PA 19103 FRCGroupLeader:
P. N. Noell Prepared for Nuclear Regulatory Commission Washington, D.C. 20555 Lead NRC Engineer: P. J. Polk October 24, 1980 This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, or any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third party's use, or the results of such use, of any Information, apparatus, product or process disclosed in this report, or represents that its use by such third party would not Infringe privately owned rights.
Franklin Research Center 8 10501A Division of The Frankhn Insdtute The Beniamin Franklin Parkway Phila., Pa. 19103 (215) 448-1000
1.0 INTRODUCTION
The NRC has determined that certain isolation valve configurations in systems connecting the high-pressure Primary Coolant System (PCS) to lower pressure systems extending outside containment are potentially significant contributors to an intersystem loss-of-coolant accident (LOCA).
Such configu rations have been found to represent a significant factor in the risk computed for core melt accidents.
The sequence of events leading to the core melt is initiated by the con current failure of two in-series check valves to function as a pressure isola tion barrier between the high-pressure PCS and a lower-pressure system extend ing beyond containment. This failure can cause an overpressurization and rup ture of the low-pressure system, resulting in a LOCA that bypasses containment.
The NRC has determined that the probability of failure of these check valves as a pressure isolation barrier can be significantly reduced if the pressure at each valve is continuously monitored, or if each valve is periodi cally inspected by leakage testing, ultrasonic examination,.or radiographic inspection.
The NRC has established. a program to provide increased assurance that such multiple isolation barriers are in place in all operating Light Water Reactor plants designated by DOR Generic Implementation Activity B-45.
In a generic letter of February 23, 1980, the NRC requested all licensees to identify 'the following valve configurations which may exist in any of their plant systems communicating with the PCS: 1) two check valves in series or 2) two check valves in series with a motor-operated valve (MOV).
For plants in which valve configurations of. concern are found to exist, licensees were further.requested to indicate: 1) whether, to ensure integrity of the various pressure isolation check valves, continuous surveillance or periodic testing was currently being conducted, 2) whether any check valves of concern were known to lack integrity, and 3) whether plant procedures should be revised or plant modifications be made to increase reliability.
Franklin Research Center (FRC;)
was requested by the NRC to provide tech nical assistance to NRC's B-45 activity by reviewing each licensee's submittal against criteria provided by the NRC and by verifying the licensee's reported findings from plant system drawings.
This report documents FRC's technical review.
2.0 CRITERIA 2.1 Identification Criteria For a piping system to have a valve configuration of concern, the follow ing five items must be fulfilled:
- 1) The high-pressure system must be connected to the Primary Coolant System;
- 2) there must be a high-pressure/low-pressure interface present in the line;
- 3) this same piping must eventually lead outside containment;
- 4) the line must have one of the valve configurations shown in Figure 1; and
- 5) the pipe line must have a diameter greater than 1 inch.
PCs OiT HP
-LP Figure 1. Valve Configurations Designated by the NRC To Be Included in This Technical Evaluation
2.2 Periodic Testing Criteria For licensees whose plants have valve configurations of concern and choose to institute periodic valve leakage testing, the NRC has established criteria for frequency of testing, test conditions, and acceptable leakage rates.
These.criteria may be summarized as follows:
2.2.1 Frequency of Testing Periodic hydrostatic leakage testing* on each check valve shall be accom plished every time the plant is placed in the cold shutdown condition for refueling, each time the plant is placed in a cold shutdown condition for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> if testing has not been accomplished in. the preceding 9 months, each time any check valve may have moved from the fully closed position (ie., any time the differen-tial pressure across the valve is less than 100 psig), and prior to.returning the valve to service after maintenance, repair, or replacement work is performed.
2.2.2 Hydrostatic Pressure Criteria Leakage tests involving pressure differentials lower than function pres sure differentials are permitted in those types of valves in which service pressure will tend to diminish the overall leakage channel opening, as by pressing the disk into or onto.the seat with greater force. Gate valves, check valves, and globe-type valves, having function pressure differential applied over the seat, are examp'les of valve applications satisfying this requirement. When leakage tests are made in such cases using pressures lower than function maximum pressure differential, the observed leakage shall be adjusted to function maximum pressure differential value. This adjustment shall be made by calculation appropriate to the test media and the ratio between test and function pressure differential, assuming leak age to be directly proportional to the pressure differential to the one half power.
2.2.3 Acceptable Leakage Rates:
- Leakage rates less than or equal to 1.0 gpm are considered accept able.
- Leakage rates greater than 1.0 gpm but less than or equal to 5.0 gpm are considered acceptable if the latest measured rate has not exceeded the rate determined by the previous test by an amount To satisfy ALARA requirements, leakage may be measured indirectly (as from the performance of pressure indicators) if accomplished in accordance with approved procedures and supported by computations showing that the method is capable of demonstrating valve compliance with the leakage criteria.
that reduces the margin between the measured leakage rate and the maximum permissible rate of 5.0 gpm by 50% or greater.
- Leakage rates greater than 1.0 gpm but less than or equal to 5.0 gpm are considered unacceptable if the latest measured rate ex ceeded the rate determined by the previous test by an amount that reduces the margin between measured leakage rate and the maximum permissible rate of 5.0 gpm by 50% or greater.
- Leakage rates greater than 5.0 gpm are considered unacceptable.
3.0 TECHNICAL EVALUATION
3.1 Licensee's Response to the Generic Letter In response to the NRC's generic letter (Ref. 11, the Southern California Edison Company (SCE) stated [Ref.
2] that, "No Event V isolation valve config uration as defined above exist at San Onofre Unit 1."
The licensee then described briefly eight valve configurations which do exist within the Class I boundary of the high-pressure piping connecting Reac tor Coolant System piping to low-pressure system piping.
Of these eight valve configurations itemized in Reference 2, the Safety Injection System cold-leg branches were determined by FRC to cootain a valve configuration of concern.
It is FRC's understanding that, with SCE's concurrence, the NRC will direct SCE to change its Plant Technical Specifications as necessary to ensure that periodic leakage testing (or equivalent testing) is conducted in accor dance with the criteria of Section 2.2.
3.2 FRC Review of Licensee's Response FRC has reviewedithe licensee's response against the plant-specific Piping and Instrumentation Diagrams (P&IDs)
[Ref. 3] that might have the valve con figurations of concern.
FRC has also reviewed the efficacy of instituting periodic testing for the check yalves involved in this particular application with respect to the re duction of the probability of an intersystem LOCA in the cold-leg branches of the Safety Injection System pipe lines.
In its review of the P&IDs [Ref. 31 for San Onofre Unit 1, FRC found the following piping system to be of concern:
The Safety Injection System, containing the valve configurations of concern, is composed of three piping branches, each connected to the cold-leg side of PCS Loops A, B, and C. Each cold-leg branch contains the single check valve in series with a motor-operated valve (MOV) configuration with the high-pressure/low-pressure inteface located at the upstream side of the MOV. The valves comprising this system of concern are listed below:
Safety Injection System Loop A, cold leg high-pressure check valve, 867A high-pressure MOV, 850A Loop B, cold leg high-pressure check valve, 867B high-pressure MOV, 850B Loop C, cold leg high-pressure check valve, 867C high-pressure MOV, 850C In accordance with the criteria of Section 2.0, FRC found no other valve configurations of concern existing in this plant.
FRC reviewed the effectiveness of instituting periodic leakage testing of the check valves in these lines as a means of reducing the probability of an intersystem LOCA occurring. FRC found that introducing a program of check valve leakage testing in accordance with the criteria summarized in Section 2.0 will be an effective measure in substantially reducing the probability of an intersystem LOCA occurring in these lines, and a means of increasing the probability that these lines will be able to perform their safety-related functions.
It is also a step toward achieving a corresponding reduction in the plant probability of an.intersystem LOCA in San Onofre Unit 1.
4.0 CONCLUSION
Based on the previously docketed information and drawings made available for FRC review, FRC found that the cold-leg branches of the Safety Injection System for San Onofre Unit 1 contain a valve configuration of concern (identi fied in Figure 1).
Thus, the valve configurations of concern existing in San Onofre Unit 1 incorporate the valves listed in Table 1.0.
If SCE modifies the Plant Technical Specifications for San Onofre Unit 1 to incorporate periodic testing (as delineated in Section 2.2) for the check valves itemized in Table 1.0, then FRC considers this an acceptable means of achieving plant compliance with the NRC staff objectives of Reference 1.
Table 1.0 Primary Coolant.System Pressure Isolation Valves System Check Valve No.
Allowable Leaka2ee Safety Injection Loop A, cold leg 867A Loop B, cold leg 867B Loop C, cold leg 867C "To. be provided by the licensee at a future date in accordance with Section 2.2.3.
5.0 REFERENCES
- 1.
Generic NRC letter, dated 2/23/80, from Mr.
D. C. Eisenhut, Department of Operating Reactors (DOR),
to Mr.
J. G. Haynes, Southern California Edison Company (SCE).
- 2.
Southern California Edison Company's response to NRC's.letter, dated 3/14/80, from Mr.
J. G. Haynes (SCE) to Mr. D. G. Eisenhut (DOR).
- 3.
List of examined P&IDs:
Southern California Edison Company Drawings of San Onofre Unit 1:
568766-15 568767-19 568768-15 568769-14 568776-21 568777-15