ML20206J407
| ML20206J407 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 11/21/1988 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20206J405 | List: |
| References | |
| NUDOCS 8811280182 | |
| Download: ML20206J407 (4) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION 3EQUEST FOR EXEMPTION FROM CONTAUTST "lTEC3AT 0 LEAKAGE RATE TEST - RETEST SCHEDULE SURRY POWER STATION, UNITS 1 AND 2 DOCKET N05. 50-280 AND 50-281
1.0 INTRODUCTION
By letter dated August 12, 1988, Virginia Electric and Power Company, the licensee for the Surry Power Station, requested 4 one-time exemption for Surry Unit 2 from the requirements of 10 CFR 50 Appendix J, Section III.A.6.(b) so that the normal retest schedule of Appendix J,Section III.0.1.(a) can be resumed. The normal schedule requires a Type A Containment Integrated Leakage Rate Test (CILRT) to be conducted three times during each 10-year servic::
period.Section III. A.6.(b) states that, if two consecutive Type A tests f ail to meet tne applicable acceptance criteria, a retest must be performed during each subsequent refueling outage or approximately every 18 months, whichever comes first, until two consecutive tests meet the acceptance criteria given in Section III.A.5.(b). Surry Unit 2 failaa the "as found" Type A tests that were conducted in 1983, 1985, and 1986, due to leakage rate additions ftom Type C testing (local leakage rate testing of containment isolation valves).
In each case, the leakage was associated with the normal containment sump isolation valves (TV-DA-100/200 A&B) and/or valves in systems that the licensee asserts dre normally filled with water and operating under pr,t-accident conditions.
If then leakage additions had not been necessary, the subject Type A tests would hve passed and the plant would not require an accelerated test schedule.
Therefore, the licensee identified two objectives in their submittal: 1) to demonstrate that the corrective action taken for the normal containment sump )
isolation valves for Unit 2 has elimineted the chronic leakage problem, and 2 to show, for Units 1 and 2, that the design of the "water-filled" penetrations is such that it precludes leakage of containment atmosphere through. the penetra-tions during an accident thus making it unnecessary to add the associated Type C leakage rates to the Type A leakage rate. The licensee stated that accomplishing these two objectives would justify the requested exemption.
The licensee addressed the first objective in its letter dated August 12, 1988.
The second objective was discussed with the licensee during an August 24-25, 1988 mieting at the plant site and was addressed in letters dated February 29, August 15, and August 31, 1988.
Section 6.2.2.2 of the f acility UFSAR also contained pertinent information.
The staff has reviewed these documents and our evalua-tion follows.
2.0 EVALUATION 1)
Normal Containment Sump Isolation Valves In order to establish the "as found" condition of integrat3d containment leakage, licensees would ideally conduct a Type A test near the beginning of a refueling outage, before making any repairs or adjustments to containment 83112801G2 881121 PDR ADOCK 0U000281 P
boundary components such as containment isolation valves.
However, for various p(e.g.tical reasons, most licensees 'nstead conduct local 'eakage rate tests, Type C) rac sary to reduce excessive leakage. The Type A te:t i: then performed near the end of the refueling outage.
In order to determine the "as found" integrated leakage rate under these conditions, the licensee performs Type C tests both before and af ter repairing a valve, and the difference in leakage rates is then added to the Type A leakage rate.
In this manner, an "as lef t" leakage rate (actually measured in the Type A test) and an "as found" leakage rate (Type A measurement plus Type C "penalties") is determined.
If either exceeds the test acceptance Criterion, a test f ailure is indicated and an increased Type A test f requency may be required in accordance with the requirements of Appendix J, Section Ill.A.6.
In the case of Surry Unit 2, Type C penalties (high leakage rates) f rom the normal containment sump isolation valves (TV-DA-100/200 A&B) have contributed to several "as found" Type A test f ailures (1983,1985,1986).
To correct this probleu, the licensee redesigned and replaced the valves in both Unit 1 and Unit 2 in 1986. The new valves were of a different type that was intended to be more resistant to wear caused by the frequent cycling open and closed that the valves experienced.
This cycling occurred because the valves served as process control valves by controlling the flow of water out of the normal con-toinment sump. When the valve replacement did not completely solve the problem, the licensee installed another valve (a check valve) in each line to serve as a process control valve. This allowed the containment isolation valves to remain open and not cycle during normal plant operation, thereby avoiding excessive wear. The most recent Type C testing results for both Units, as detailed in the licensee's letter dated August 12, 1988, indicate that the leakage problem has been largely eliminated and that these valves no longer exhibit excessive leakage.
The staff finds that this corrective action has been effective and supports the requested exemption.
2)
"Water-Filled" PenetrationsSection III.A.1.(d) of Appendix J requires that during a Type A test, certain piping systems that penetrate containment must be vented to the atmosphere inside containment and drained of water, exposing the associated containment isolation valves to the containment atmosphere during the test and thus including them in the Type A test.
It is intended to simulate accident conditions for piping systems that might rupture or otherwise be open to the containment atmosphere during a LOCA.
As an alternative to venting and draining a system, Type C tests may be performed on the associated containment isolation valves and the measured leakage rates added to the Type A leakage rate.
Type C additions of this kind from certain valves in the safety injection and l
containment recirculation spray systems have contributed to the "as found" failures of the last three Type A tests at Surry Unit 2.
The licensee asserts that these "water-filled" penetrations are not potential containment atmosphere leak paths, and thus their Type C leakage rates should not be added to the Type A leakage rate.
i I
3-The containment penetrations in question are nos. 7, 15, 21, 23, 46, 60, 61 62, and 113 (various high head and low head safety injection pump discharge lines into containment), 68 and 69 (safety injection pump suction lines from the containment recirculation sump), and 66 and 67 (recirculation spray pump suction lines from the containment recirculation sump). The valves in these penetrations are currently Type C tested and will continued to be Type C tested.
Further, their leakage rates will continue to be added to the total of all local leakage rates. Total leakage must be less than 0.60 La in accordance with Appendix J, where La is the maximum allowable leakage rate for the contain-ment specified in the facility Technical Specifications. The licensee proposes only that the Type C leakage rates for the subject penetrations r.ot be added to the Type A leakage rate.
The high head and low head safety injection (HHSI and LHSI) systems and the recirculation spray system are Engineered Safety Feature, safety-related, and Seismic Category 1 systems. The HHSI has three redundant pumps whose discharge lines enter a connon header outside containment before splitting to the various containment penetrations. The LHSI has two redundant pumps whose discharge lines are connected outside containment by a crosstie line with locked open valves. Water is supplied to these systems from the containment sump for long term core cooling.
Therefore, the staff finds that the designs of these systems assure 1) a supply of high pressure water to penetrations 7, 15, 21, 23, 46, 60, 61, 62 and 113 for at least 30 days af ter the onset of a LOCA including in the event a worst-case single active failure (e.g., loss of a pump or diesel generator), dnd 2) a water seal of the subject valves thereby precluding containment atmosphere leakage through the closed valve disks. However, most of the subject valves are oriented in such a way that valve packing / stem leakage of each of the valves located outside containment is not precluded by this water seal, thus providing a potential leak path out of the containment.
For all of these valves except the one in penetration 60, a water leg (pipe loop) exists between the valve and its penetration.
For penetration 60, there is a horizontal run of pipe between the valve and its penetration which acts in a manner similar to a water leg. Considering 1) the presence of the water legs, 2) the fact that the periodic Type C tests on all of the valves of concern include the possible packing / stem leak paths so that such leakage will be maintained low, and 3) that the Surry subatmospheric containment is designed to reduce containment pressure below atmospheric pressure one hour after onset of a LOCA, significant packing / stem leakage for these valves is not likely.
Therefore, the staff finds that penetrations 7, 15, 21, 23, 46, 60, 61, 62 and 113 need not be vented and drained during Type A tests and the associated Type C leakage rates need not be added to the Type A leakage rate.
penetrations 66, 67, 68, and 69 are containment recirculation sump suction paths for the recirculation spray and safety injection pumps. The containment recirculation sump will be filled with water during a LOCA and will remain water filled throughout the accident.
Therefore, the staff finds that the recirculation sump penetrations are not potential containment atmosphere leak paths, and the associated Type C leakage rates need not be added to the Type A laakage rate.
3.0 CONCLUSION
Based on the above, the staf f concludes that "water-filled" containment pcr.etrations 7, 15, 21, 23, 46, 60, 61, 62, 66, 67, 68, 69, and 113 are sealed with water to the extent that they need not be vented or drained during Type A tests, and the associated Type C leakage rates need not be added to the Type A leakage rate. The staff further concludes that the t
original leak path of concern that has caused the recent Type A "as found" failures, the normal containment sump isolation valves (TV-DA-100/200 A & B),
has been corrected since these valves no longer exhibit excessive leakage.
Therefore, on the basis of the licensee's effective corrective action to reduce "as found" containment leakage, the staff concludes that a return to the normal Type A test schedule of Section Ill.D.1.(a) of Appendix J to 10 CFR Part 50 is justified, and the requested exemption for Surry, Unit 2 from the requirements of Section III. A.6.(b) for increased Type A containment leakage rate testing frequency should be granted.
Dated: November 21, 1988 Principal Contributor:
J. Pulsipher t.
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