05000416/LER-2017-004
| 07-13-2017 | On May 26, 2017, while performing the Automatic Depressurization System (ADS) quarterly surveillance, the time delay on the Trip System A (Division 1) ADS initiation timer relay was found outside of its Technical Specification (TS) Allowable Value of 5 115 seconds. Specifically, the ADS timer requirements in TS 3.3.5.1, Emergency Core Cooling System Instrumentation, Table 3.3.5.1-1, Emergency Core Cooling System Instrumentation, Function 4, Sub-function c. ADS Initiation Timer, Allowable Value was not met. The cause was determined to be inadequate preventive maintenance and review of the previous test results. This event is reportable as a license event report (LER) in accordance with 10CFR50.73(a)(2)(i)(B), as a "condition prohibited by Technical Specifications" because the same relay failed its previous test and could not be considered as OPERABLE during the full interval between tests. Corrective actions included replacement of the defective timer relay and planned actions to replace the corresponding timer relays in ADS and the Feedwater Control System. In addition, the applicable preventive maintenance procedures were revised. The event posed no threat to the health and safety of the general public or to nuclear safety as ADS would have performed as designed. No Technical Specification safety limits were challenged or violated.
APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020 366A U.S. NUCLEAR REGULATORY COMMISSION NRC FORM (4-2017)
(See NUREG-1022, R.3 for instruction and guidance for completing this form httplAwm.nrc.00vireadino-rm/doc-collections/nureas/staff/sr1022/r3/) 05000 416 ContentsDESCRIPTIONOn May 26, 2017, while performing Automatic Depressurization System (ADS) [AD][C23] quarterly surveillance, the time delay on the Trip System A ADS initiation timer relay [RLY2] was found outside of its Technical Specification (TS) Allowable Value of 115 seconds. Specifically, the ADS timer requirements that are specified in Technical Specifications 3.3.5.1, Emergency Core Cooling System (ECCS) Instrumentation, Table 3.3.5.1-1, Emergency Core Cooling System Instrumentation, Function 4, Sub-function c. ADS Initiation Timer, Allowable Value were not met. The failure mechanism is degradation of the timing function in the ADS initiation timer relay (Agastat Model TR14D3EC750) that delays initiation of ADS in order to allow time for high pressure injection to restore reactor water level. The TS Allowable Value for this timer is less than or equal to 115 seconds. The as found value was beyond this value. This surveillance is performed on a quarterly basis. This same condition was found during the last surveillance performed on February 23, 2017. This condition was not found during the surveillance performed prior to that on November 18, 2016. The Automatic Depressurization System is required in Modes 1, 2, and 3 with the reactor above 150 psig. Between November 18, 2016 and January 30, 2017, the plant was in Mode 4. Therefore this function was not required from November 18, 2016 to January 30, 2017, which is when the reactor reached 150 psig in Mode 2. The ADS was required to be Operable from January 30, 2017, until May 26, 2017. ADS initiation is accomplished by energization of either the Trip System A (Division 1) or Trip System B (Division 2) solenoids [FSW] associated with each of the ADS valves. The logic for each Trip System is separate and either trip system will cause all the ADS relief valves to open. Therefore, the automatic safety function would still be accomplished within the allowable time provided that the Trip System B was Operable. Trip System B initiation logic was taken out of service on March 10, 2017, to support performance of the quarterly ADS channel calibration surveillance procedure. An additional review was performed to determine if the Trip System A logic would have initiated within the allowable time during the period when the Trip System B logic was out of service. The average rate of change of the setpoint between surveillances was 0.402 seconds/day for the first interval (November 18, 2016 - February 23, 2017) and 0.424 seconds/day for the second interval (February 23, 2017 - May 26, 2017). Use of the larger rate of change is conservative, and therefore a rate of 0.424 seconds/day was assumed for the second interval. Linearly extrapolating from an as left condition of 104 seconds on February 23, 2017, it is concluded that the setpoint would have been approximately 110.4 seconds on March 10, 2017. This value is within the 115 second TS AV. Therefore, it is concluded that no loss of safety function occurred for this condition. REPORTABILITYThis event is reportable as a license event report (LER) in accordance with NUREG-1022, Section 3.2.2, and 10CFR50.73(a)(2)(i)(B), as a "condition prohibited by Technical Specifications" because the same relay failed its previous test and could not have been considered operable for the full interval between tests. The timer relay would have been considered inoperable for a time period such that the Technical Specification 3.3.5.1 completion time would not have been met. NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (6-2016) CONTINUATION SHEET(See NUREG-1022, R.3 for instruction and guidance for completing this form + a httplAvwt.v.nrc.covireadinci-rm/doc-collections/nureqs/staff/sr1022/r3I) APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020 Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the Information Services Branch (T- 2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555.0001, or by e-mail to InTocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection. 05000 416 CAUSEThe direct cause of the failure is the degradation of timing function for ADS initiation timer relay 1B21-K5A, most likely due to the electrolytic capacitor degradation. The cause of the failure was an inadequate preventive maintenance task and inadequate procedural guidance. The procedures did not require periodic replacement of the relay nor did they require an engineering review of the test results. CORRECTIVE ACTIONSImmediate: The defective timer relay in Trip System A was replaced. Completed: Preventive maintenance tasks were revised to require periodic replacement of the relays. Surveillance testing was revised to require timely engineering review of the completed quarterly surveillance tests. Planned: The corresponding relays in ADS and the Feedwater Control System will be replaced. This action has been entered in the corrective action program and may be modified in accordance with that program. SAFETY SIGNIFICANCEInitiation of the ADS is accomplished by energizing either the Trip System A or Trip System B solenoids associated with each of the ADS valves. Each separate trip system will cause all the ADS relief valves to open. Therefore, the automatic safety function would still be accomplished within the allowable time with Trip System A inoperable provided that Trip System B was Operable. Trip System B initiation logic was taken out of service on March 10, 2017, to support performance of the quarterly ADS Channel B calibration surveillance procedure. An additional review was performed to determine if the Trip System A logic would have initiated within the allowable time during the period when the Trip System B logic was out of service. The conclusion was that the "A" setpoint would have been approximately 110.4 seconds on March 10, 2017. This value is within the 115 second TS AV. Therefore, at least one division of ADS was always available to perform the safety function. In addition, manual actuation was available, and operators are trained on the conditions requiring manual actuation and the associated procedures. The ADS acts as a backup to High Pressure Core Spray System [BG] for a small break loss of coolant accident. The High Pressure Core Spray System was not impacted by the degraded condition of ADS. The event posed no threat to the health and safety of the general public or to nuclear safety as ADS would have performed as designed. No Technical Specification safety limits were challenged or violated. Industrial safety was not challenged, and there was no potential or actual radiological release during the event. PREVIOUS SIMILAR OCCURRENCESThe identified licensee event reports were attributed to inadequate maintenance procedures. The events were reviewed and it has been determined that the causes and corrective actions were sufficiently different that they could not have predicted or prevented the occurrence of this event. |
|---|
| Grand Gulf Nuclear Station, Unit 1 | |
| Event date: | 05-26-2017 |
|---|---|
| Report date: | 07-13-2017 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4162017004R01 - NRC Website | |
| ||||||||||||||||||||||