ML20070K910
| ML20070K910 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 07/22/1994 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20070K907 | List: |
| References | |
| NUDOCS 9407280065 | |
| Download: ML20070K910 (3) | |
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NUCLEAR REGULATORY COMMISSION SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED T0, EXEMPTION FROM APPENDIX J TYPE C LOCAL LEAK RATE TESTING IN THE REVERSE DIRECTION FOR FOUR CONTAINMENT ISOLATION VALVES NEBRASKA PUBLIC POWER DISTRICT COOPER NUCLEAR STATION DOCKET NO. 50-298
1.0 INTRODUCTION
By letter dated June 29, 1994, the licensee requested permanent exemption from certain Type C (local leak rate) testing requirements of Appendix J to 10 CFR Part 50 for four containment isolation valves (CIVs).
The exemption would allow reverse-direction testing of the CIVs. Appendix J requires, in Section III.C.I., that Type C test pressure must be applied in the same direction as that which would exist when the' valve would be required to perform its safety function, unless it can be determined that the results from the tests for a pressure applied in a different (or reverse) direction will provide equivalent or more conservative results.
This generally means that valves must be pressurized on the side of the valve disc that is towards containment; this is often called " forward-direction" testing, in contrast to " reverse-direction" testing which means pressurizing from the side that is away from containment.
For the four valves being considered, the licensee wishes to test in the reverse direction, even though it might not give equivalent or conservative results.
2.0 EVALVATION The licensee is applying for permanent exemption for the following four valves: RHR-MOV-M0167A, RHR-MOV-M01678, RCIC-V-37, and HPCI-V-44. M0167A and M01678 are 1-inch diameter globe valves.
Valves RCIC-V-37 and HPCI-V-44 are stop-check globe valves, with 8-inch and 20-inch diameters, respectively. A stop-check globe valve disk is not connected to the valve stem. Normal flow comes from underneath the seat and pressure on the disk forces it off of the seat causing the valve to open.
The disk is guided by a disk skirt in the valve.
Under backflow conditions, the pressurization of the torus (during accident conditions), in conjunction with gravity, forces the disk into the seat and closes the valve.
The four valves are not currently testable in the accident direction due to the inability to isolate the valves from the containment and the lack of test connections.
In general, Type C testing of globe valves in the reverse 9407280065 940722 DR ADOCK 050002
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. direction is more conservative than testing in the accident direction with respect to seat leakage because the pressurization is under the seat, which tends to unseat the disk and increase leakage.
However, by testing in the reverse direction, the valve bonnet and stem packing are not exposed to the test pressure and possible leakage would not show up in the test results.
Whereas the testing from the reverse direction of these valves would provide more conservative seat leakage, it cannot quantitatively be demonstrated to provide equivalent or more conservative valve leakage testing results due to the potential for leakage through the packing and bonnet gasket.
Rather than Type C testing of the bonnet and packing boundaries which would require system modifications, the licensee offers several compensating factors, as follows:
(1) The bonnet and packing are exposed to the test pressure of each Type A Test (integrated leak rate test), currently conducted every three to four years. Although this does not provide an individual leak rate for the valve's boundaries, it assures that the total containment leak rate, which includes the bonnet and packing leakage, is within allowable limits.
(2) The licensee proposes that a soap bubble test be performed on the pressurized stem bonnet boundaries of the valves during the Type A test.
Using the acceptance criterion of zero bubbles for this test, this would provide a direct indication of the leak-tightness of the packing and the bonnet.
(3)
In between the Type A tests, the licensee will specifically observe valves RCIC-V-37 and HPCI-V-44 for indication of leakage through the insulation lagging during scheduled system surveillance tests which subject these valves to pressurization.
(4) An additional factor is specifically applicable to valves RCIC-V-37 and HPCI-V-44, which are Anchor stop-check globe valves.
During plant operation, the stem is in the raised position, which engages the backseat between the stem and the bonnet under the gland area, minimizing the potential leakage through the packing gland.
If the licensee were to make modifications in order to allow forward-direction testing of these valves, such as the addition of block valves and test connections, it would increase design complexity, create additional potential leakage paths, and increase loading on torus attached piping.
Considering that the disk seat is conservatively tested by reverse-direction testing and that the leak-tightness of the bonnet and packing boundaries is reasonably assured by other means as noted above, the staff finds that
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.o permanent exemption from the " equivalent or more conservative results" requirement of Appendix J is justified and, therefore, reverse-direction Type C testing of the four subject valves is acceptable.
3.0 CONCLUSION
Based on the above evaluation, the staff finds that permanent exemption from Appendix J to allow reverse-direction Type C testing of containment isolation valves RHR-MOV-M0167A, RHR-MOV-M0167B, RCIC-V-37, and HPCI-V-44 are acceptable.
Principal Contributor:
J. Pulsipher Date:
July 22, 1994
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