Left: NRC regulations supplement the testing requirements for MOVs by requiring licensees establish a programme to ensure that MOVs continue to perform their design- basis safety functions
The programme included tests performed by the
participating licensees at their plants over five years, to assess whether there was a potential for degradation of valve friction coefficients for various valve types and applications. Test results collected by participants are only applicable
to the implementation of the JOG programme, because of the limited amount of MOV test data and the different methods used by individual licensees to evaluate the test data. For example, valve friction coefficients determined for
MOVs as part of the JOG MOV Program do not represent a database of valve friction coefficients that can be applied in general to calculate the thrust and torque required to operate various MOVs under design-basis conditions. The NRC inspectors found that licensees did not always re-justify the qualifying basis for MOVs following extensive maintenance (such as disassembly) to determine whether the valves were susceptible to performance degradation as part of the JOG MOV Program.
New commitments The NRC regulations in 10 CFR 50.55a(b)(3)(ii) supplement the testing requirements for MOVs by requiring that licensees establish a programme to ensure that MOVs continue to be capable of performing their design-basis safety functions. Licensees committed to implementing the JOG MOV
Program are expected to follow suit. For example, the JOG MOV Program does not include
grace periods for JOG test intervals. Further, the JOG program schedule is specified in years rather than refueling outages. In addition, a change in the risk ranking of an MOV, or an adjustment to MOV capability margin based on performance data, can result in a different diagnostic testing interval under the JOG MOV Program. Some MOVs are outside the scope of the JOG MOV
Program, and are defined by JOG as Class D valves. Licensees are required to establish methods to periodically demonstrate the design-basis capability of their Class D valves
Testing
Among testing issues, the NRC inspectors found that: ● Licensees did not always ensure that POV tests were properly conducted, acceptance criteria for the POV testing applied the correct assumptions (such as actuator thrust limits), proper evaluations of test data were completed to demonstrate that the POVs can perform their safety functions, and records of evaluations were maintained in accordance with plant procedures.
The NRC staff discussed the above issues in detail with the applicable licensees during then POV inspections. The licensees took action to address any immediate concerns related to these issues identified by the NRC inspectors. In many instances, the issues were determined to be minor, because of the capability margin available for the specific POVs being evaluated at the applicable nuclear power plant. ■
www.neimagazine.com | March 2024 | 27
● Some POVs have specific limitations related to leakage past the valve disk when closed. MOVs can be set to fully close and meet their leakage limitations when controlled by the torque switch. The NRC inspectors found that licensees did not always have a valid test or analysis demonstrating that the limit switch control setting of the MOV under static conditions would achieve the required leaktight performance when the MOV is closed under dynamic conditions.
● Licensees did not always justify the qualification of POVs to perform their design-basis safety functions, including functional, environmental, and seismic capability. Some licensees lacked adequate justification to extend the life of installed POVs.
● The ASME Code requires that valves with remote position indicators be observed locally at least once every two years to verify that valve operation is accurately indicated. The NRC wants licensees to verify that valve operation is accurately indicated by supplementing valve position indicating lights with other indications, such as flow meters or other suitable instrumentation.
● Licensees did not always conduct a detailed evaluation of the effects of backseating on the valve bonnet and stem to verify structural integrity.
● Licensees did not always perform a complete verification and validation of POV computer software prior to implementation. These calculation methodologies need verification and validation for appropriate assumptions and data points. Further, stroke time might be calculated improperly when computer data are used to measure the MOV stroke time.
● Some licensees rely on the actuator handwheel to manually operate MOVs to perform important functions and licensees did not always evaluate the handwheel for proper sizing and good working condition.
● Licensees did not always determine a proper lubrication interval for each MOV stem to address potential lubrication grease degradation, which can adversely affect MOV operation.
● Licensees did not always follow their procedures for maintaining records associated with POV qualification, testing, operation, maintenance, and corrective action.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45
