ML13331A470
| ML13331A470 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 07/30/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML13331A469 | List: |
| References | |
| NUDOCS 9008030218 | |
| Download: ML13331A470 (6) | |
Text
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UNITED STATES 0
NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY-EVALUATION REPORT BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO A REQUEST FOR RELIEF FROM INSERVICE TESTING REQUIREMENTS PUMP RELIEF REQUEST NOS. 2, 4 AND 9 SOUTHERN CALIFORNIA EDISON COMPANY SAN ONOFRE NUCLEAR GENERATING STATION, UNIT 1 DOCKET NO. 50-206 INTRODUCTION Southern California Edison Company (the licensee) is required by the Code of Federal Regulations, 10 CFR 50.55a(g), to perform inservice testing (IST) of components in accordance with the ASME Boiler and Pressure Vessel Code Section XI to the extent practical.
10 CFR 50.55a(g) also specifies the ASME Code classification requirements for older plants, such as San Onofre Unit 1.
Components which are part of the reactor coolant pressure boundary and their supports shall meet the requirements applicable to components which are classified as ASME Code Class 1. Other safety-related pressure vessels, piping, pumps and valves shall meet the requirements applicable to components which are classified as ASME Code Class 2 or Class 3.
If the licensee determines that certain ASME Section XI Code requirements are impractical, the Code of Federal Regulations, 10 CFR 50.55a(g)(5), requires the licensee to submit information in support of that determination for NRC review.
As allowed by 10 CFR 50.55a(a)(3)(i) and 10 CFR 50.55a(g)(6)(i), the NRC may grant relief from the code requirements and may impose alternative requirements that are determined to be authorized by law, will not endanger life or property or the common defense and security, and are otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed. This Safety Evaluation Report (SER) contains the NRC staff findings with respect to granting or not granting relief from ASME Section XI Code requirements as part of the licensee's IST program.
The licensee's current IST program covers the third ten-year inspection interval from January 1, 1988 to January 1, 1998. The program is based on the require ments of Section XI of the ASME Code, 1983 Edition through the Summer of 1983 Addenda and remains in effect until January 1, 1998, unless the program is modified or changed prior to the ten year interval end date.
9--00:EK):3C1218 90-07:30 PDR AO0C2K 05OU 0 6 11:1 i=D :
-2 By letter dated November 30, 1989, the licensee provided its response to Generic Letter (GL) 89-04, "Guidance on Developing Acceptable Inservice Testing Programs." In its response, the licensee stated that it had revised its IST program to conform to the 11 positions stated in Attachment 1 of the GL.
Therefore, as allowed by the GL, specific NRC approval of the licensee's IST Program is not required. However, new relief requests and revisions to existing relief requests still require NRC review and approval if they are not addressed by the positions stated in Attachment 1 of GL 89-04.
As part of its response to GL 89-04, the licensee requested relief from IST requirements for certain components in accordance with the guidance provided by the GL. This Safety Evaluation specifically addresses the licensee's request for relief associated with pump relief request (PRR) numbers 2, 4 and 9.
Pump Relief Request No. 2 As part of its program for the third ten-year IST interval (January 1, 1988 to January 1, 1998), the licensee requested relief from measuring bearing temperature and vibration in accordance with ASME Code Section XI, Table IWP-3100-1, for diesel fuel transfer pumps G-74A, G-74B, G-75A and G-75B. As a basis for relief, the licensee stated that the diesel fuel transfer pumps are submergence type pumps located in the diesel fuel storage tanks and are not accessible. The licensee proposed to measure the pump motor thrust bearing vibration quarterly as an alternative. Because hardware modifications were required, the licensee proposed to begin the alternate testing following the Cycle 11 refueling outage (letter dated August 3, 1988).
In its response to GL 89-04, the licensee indicated that the alternate testing previously committed to for the diesel fuel transfer pumps would be delayed until the end of the Cycle 12 refueling outage. The licensee stated that the schedule delay was consistent with the Integrated Implementation Schedule (SCE letter dated November 16, 1989) and the schedule proposed for resolving Full Term Operating License (FTOL) open items (SCE letter dated October 2, 1989).
Evaluation The licensee's plan to complete IST modifications during the Cycle 12 refueling outage constitutes a change to the alternate testing that was proposed for PRR No. 2 in its submittal for the third ten-year IST interval dated December 28, 1987, as supplemented by letter dated August 3, 1988. The licensee's IIS submittal does not satisfy the requirements of 10 CFR 50.55 a(g)(5) for re questing relief from ASME Section XI Code requirements and should not be viewed as a mechanism for obtaining NRC approval of changes to relief requests that were previously submitted. Therefore, the licensee's IIS submittal is not the proper vehicle for delaying IST modifications. Proposed delays to previously approved alternate testing schedules should be provided in the form of a revised relief request.
-3 The licensee's schedule for resolution of FTOL open items dated October 2, 1989, indicated that IST Modifications would be completed during the Cycle 12 refueling outage. The NRC staff approved the licensee's schedule for resolution of FTOL open items by Confirmatory Order dated January 2, 1990.
Therefore, the licensee's action to delay alternate testing of the diesel fuel transfer pumps until the end of the Cycle 12 refueling outage was approved by the Confirmatory Order and is acceptable.
Pump Relief Request No. 4 As part of its program for the second ten-year IST interval (January 1, 1978 to January 1, 1988), the licensee requested relief from testing the residual heat removal (RHR) pumps, G-14A and G-14B, quarterly as required by ASME Code Section XI, IWP-3400, except during periods of cold shutdown. By letter dated June 9, 1989, the NRC staff provided its evaluation of the licensee's second ten-year IST program and PRR No. 4 was determined to be acceptable.
In its submittal for the third ten-year IST interval dated December 28, 1987, PRR No. 4 remained unchanged from the previous IST submittal.
However, in its response to GL 89-04, the licensee identified that a recent change was made to the existing basis for PRR No. 4 and this PRR was resubmitted for NRC approval in accordance with the generic letter requirements.
The following alternate testing was originally proposed by the licensee in its submittal for the third ten-year IST interval for the RHR pumps and was not revised:
"Test the pumps within 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> of placing the RHR system in service if it has been more than 3 months since the pump's last inservice test.
Test frequency during cold shutdown periods will be quarterly."
Licensee's Basis for Requesting Relief The licensee originally stated the following basis for PRR No. 4:
"During normal plant operation, the low pressure RHR system is isolated from the RCS by motor operated valves MOV-813 and MOV-814 which are series valves on the suction side of RHR pumps G-14A and G-14B.
Additionally, MOV-833 and MOV-834, the first isolation valves at the RCS boundary, are interlocked with RCS pressure such that these valves may not be opened until RCS pressure has been reduced to 400 psig or less.
The pumps are provided with a 2 inch diameter bypass that is used for safety injection recirculation alternate path hot leg injection and a 3/4 inch diameter bypass that is used for system warmup. If the pump is run with the suction valves MOV-813 and MOV-814 closed, net positive suction head for the pumps would be provided by letdown pressure.
However, for this to be done the pressure control valve (PCV-1105) would have to be placed in the manual position and RCS letdown pressure would be controlled by the plant operators. Since this valve has a very slow response time, it could result in system overpressurization and the
V
-4 lifting of the RHR system relief valve RV-206, which has a setpoint of approximately 480 psig. Lifting of this relief valve has, historically, led to continued valve leakage and cause for having to perform difficult repairs in Mode 3.
If the RHR pumps are operated in this abnormal configuration, the total flow would be approximately 320 gpm, which is below the minimum flow required for pump hydraulic stability (380 gpm). Additionally, these pumps are located inside containment within the secondary shield in a high radiation area. Consequently, since they are inaccessible during plant operation, visible abnormalities and deterioration in RHR pump performance during the test would go undetected.
Testing the pumps without the RHR system in service would force system equipment to be operated in an abnormal manner and, therefore, increase the risk of unanticipated system transients. In addition, as stated previously, it would increase the risk of lifting the system pressure relief valve (RV-206) and possibly damage the pump due to its operation outside of its design conditions.
Past operating experience has demonstrated there is no indication that additional pump testing between plant shutdowns would increase pump reliability. There have been no pump failures during startup of the RHR system in the entire operating history at San Onofre Unit 1. As a result, the pumps should be tested quarterly only during cold shutdown."
The licensee provided the following revised basis for PRR No. 4:
"During normal plant operation, the low pressure RHR system is isolated from the RCS by motor operated valves MOV-813 and MOV-814 which are series valves on the suction side of RHR pumps G-14A and G-14B.
Additionally, MOV-813[833] and MOV-834, the first isolation valves at the RCS boundary, are interlocked with RCS pressure such that these valves may not be opened until RCS pressure has been reduced to 400 psig or less.
The pumps are provided with a 2-inch diameter bypass that is used for safety injection recirculation alternate path hot leg injection and a 3/4 inch diameter bypass that is used for system warmup. If the pump is run with the suction valves MOV-813 and MOV-814 closed, there is no practical way to provide adequate NPSH (net positive suction head).
Testing the pumps without the RHR system in service would force system equipment to be operated outside its design conditions.
Past operating experience has demonstrated there is no indication that additional pump testing between plant shutdowns would increase pump reliability. There have been no pump failures during startup of the RHR system in the entire operating history at San Onofre Unit 1. As a result, the pumps should be tested quarterly only during cold shutdown."
-5 Evaluation The licensee's revised basis states a stronger position than the original basis for requesting relief from the ASME Code Section XI requirements. There fore, the NRC staff's previous determination judging PRR No. 4 to be acceptable for the second ten-year IST interval remains valid and relief is granted from the Code requirements as requested pursuant to 10 CFR 50.55a(a)(3)(i).
Pump Relief Request No. 9 By letter dated November 30, 1989, the licensee requested relief from measuring pump bearing temperatures as required by ASME Code Section XI, Articles IWP-3300 and IWP-4310, for all pumps except the safety injection recirculation pumps (C-45A and G-45B) and the diesel fuel transfer pumps (G-74A, G-74B, G-75A and G-75B). The following alternative testing was proposed by the licensee:
"In lieu of measuring the bearing temperature for pumps in the Inservice Testing Program, substitute additional vibration monitoring. In addition to the Code required unfiltered displacement vibration measurements, test in units of velocity during each Inservice Test. Record these measurements and use them as a substitute for bearing temperature measurements.
The acceptance criteria for the vibration measurements, shall be those provided in OM-6, Inservice Testing of Pumps in Light-Water Reactor Power Plants, with Addenda through May 31, 1989."
Licensee's Basis for Requesting Relief "It is unlikely that bearing failure would be detected by a yearly test.
The Code does not require continuous monitoring of bearing temperature and this parameter is only indicative of impending pump bearing failure when it is continuously monitored. Annual bearing temperature measurement is required by the Code but if a bearing is failing temperature increases rapidly until bearing failure. Furthermore, this temperature increase is only seen for those bearings outside of the pumped fluid flow path (bearings in separate housings) and does not, therefore, afford reliable detection of bearing degradation for bearings submerged in and cooled by the pumped fluid.
As a result of this reasoning, OM-6 entitled "Inservice Testing of Pumps in Light Water Reactor Power Plants," does not require bearing temperature to be measured."
Evaluation The NRC staff agrees with the licensee's position that monitoring pump bearing temperature on an annual basis is not likely to predict impending bearing failure and that continuous temperature monitoring would be necessary for such trending to be meaningful. The licensee's proposal to measure pump vibration in units of velocity in addition to the quarterly Code required unfiltered
-6 displacement vibration measurements will provide more reliable indication of pump degradation than annual temperature monitoring in combination with displacement vibration measurements. Therefore, relief from the ASME Code Section XI requirement to measure pump bearing temperature annually as requested by the licensee is granted pursuant to 10 CFR 50.55a(a)(3)(i).
CONCLUSION Based on the foregoing evaluation, the NRC staff has determined that, pursuant to 10 CFR 50.55a(a)(3)(i) and 10 CFR 50.55a(g)(6)(i), relief is granted subject to the conditions described in this evaluation. This relief is authorized by law and will not endanger life or property or the common defense and security and is otherwise in the public interest giving due consideration to the burden placed upon the licensee if the requirements were imposed on the facility.
Principal Contributors: E. Sullivan J. Tatum Dated:
July 30, 1990