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Metal Seated Valves
The metal seated valves did develop progressively greater leakage during the wear aging. The leakage of the Nicotef seats was higher than the standard constructions. However, the leakage was never enough to cause the cylinder port pressure, which was monitored during the leakage tests, to increase or decrease. ASCO notes that failure, as defined in ASCO nuclear qualification reports, involves a significant change in cylinder port pressure. Specifically, section 6.2.2 of AQR 67368 Appendix A states "All valves must not have a pressure increase at a cylinder port which is required to be vented or a pressure decrease at a cylinder port which is required to be pressurized in excess of 10% of the maximum operating pressure differential".
EFFECT ON QUALIFICATION:
Listed below is a summary of the various qualification phases. The impact on qualification due to the removal of lubricant is provided for each phase.
A. Thermal Aging Simulation:
This testing simulates the effect of time and elevated temperatures on the age sensitive components such as elastomers and coils. Elimination of the run-in oil and use of water as an o-ring assembly aid do not adversely affect valve response to this simulation. These lubricants do not enhance or detract from the age sensitive component's resistance to thermal aging. Therefore, removal of these lubricants would have no impact on the performance of these age sensitive components. The Nicotef coating is a proprietary blend of nickel and Teflon. The nickel is unaffected by thermal aging. Teflon is a high temperature material that is unaffected by the amount of thermal aging experienced by the Nicotef coating during this simulation. This conclusion is also supported by the results of the NS testing discussed in Appendix A. Current thermal aging results from the NP qualification program remain valid.
B. Wear Aging Simulation:
This testing subjects the valve to energized/de-energized cycling in order to simulate the wear that a valve would see during its service life. Elimination of the run-in oil and use of water as an o-ring assembly aid do not adversely affect valve response to this simulation. The effect of using the Nicotef was evaluated during the testing described above. Based on this testing and the NS testing outlined in Appendix A there is no impact on the qualification of the NP valves.
C. Pressurization Aging Simulation:
This testing simulates the effect pressurization of the power plant containment chamber has on valves in particular the external seals. Since none of these modifications affect any of the seals, current pressurization aging results are valid.