Resolution of Generic Safety Issues: Issue 54: Survey of Valve Operator-Related Events Occurring During 1978, 1979, and 1980 (Rev. 1) ( NUREG-0933, Main Report with Supplements 1–34 )
In December 1981, AEOD completed a survey of valve operator-related events that occurred during 1978, 1979, and 1980 and submitted a draft report707 to NRR for comment. In this study, AEOD established that motor-operator failures could be grouped into three principal categories: (1) torque switches; (2) limit switches; and (3) motor burn-out. On March 5, 1982, NRR comments708 on this draft report were forwarded to AEOD. Following issuance of the final AEOD report (AEOD/C203),709 additional comments were provided by NRR.509
Following receipt of comments from the various NRC Offices, AEOD provided an assessment of these comments.710,711 NRR then provided a response712 to this assessment in an effort to clarify certain matters related to this issue in terms of an expansion of an RES program (FIN A6367) to address features of this issue. Subsequently, AEOD issued a report (AEOD/E305)713 covering 8 LERs on the degradation of MOV assemblies and presented results that augmented the findings of AEOD/C203.709 In March 1984, the status of this issue was reported in an MEB memorandum.714 This issue is related to Item C-11 and TMI Action Plan Item II.E.6.
Degradation of motor-driven valve motors from thermal overloads may be occurring in repeated high-temperature cycles that is not detected in the present in-service testing programs. This may lead to premature motor burnout and subsequent unexpected unavailability of the valve during accident conditions. Moreover, torque switch settings and adjustments may be inadequate to ensure valve operability and qualification under accident conditions.
This issue would affect the design and operation of all existing and future nuclear plants for the lifetime of the plants.
The possible solutions are: (1) reassessment of the present guidance in Regulatory Guide 1.106 on bypassing thermal overload-protection devices for motors, (2) improvement of the methods and procedures for the setting of torque switches, and (3) the development of signature tracing technique(s) to be incorporated into the in-service testing programs in order to detect valve deterioration, aging effects, improper maintenance, and improper valve adjustments that are not presently detectable.
The principal concern in this issue is the operability of the motor-driven valves under accident, faulted, or emergency conditions. It is noted from the Action Plan715 for TMI Action Plan Item II.E.6.1 that the work scope includes verification of safety-related valve function under system emergency or faulted conditions, torque and limit switches settings and adjustments, motor burn-out resulting from improper cycling, and MOV operator signature tracing by evaluation, test, and analysis. Therefore, it is concluded that the objectives of Issue 54 will be met completely in TMI Action Plan Item II.E.6.1.