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 Report dateSiteEvent description
05000443/LER-2016-00126 April 2016Seabrook

On March 2, 2016 at 0253 while operating at 100% power, Seabrook Station experienced an automatic reactor trip due to a turbine trip.

A failure of inverter ED-I-11 caused a voltage transient in the power supplies for the Turbine Control System (TCS). The TCS is designed with redundant inverters so that the loss of one inverter will not cause a system failure. However, during this event, the inverter failure caused a voltage increase which exceeded the voltage limits of the TCS power supplies causing them to momentarily shut down. Loss of the TCS power supplies initiated an automatic turbine trip signal, which in turn actuated an automatic reactor trip as designed. Other plant equipment functioned as expected and no adverse consequences resulted from this event.

The direct cause of the event was a failure of inverter ED-I-11 which resulted in an overvoltage condition to the turbine control system.

At this time, the cause of the failure of the inverter has not been determined. If additional troubleshooting identifies a cause, this LER will be supplemented. Immediate corrective action was implementation of a temporary modification to energize the power panel normally fed by ED-I-11 to eliminate single point vulnerability. Planned corrective actions are to continue troubleshooting and repair of inverter ED-I-11, install overvoltage protection for the TCS cabinets and upgrade the TCS power supplies to higher voltage rated units.

FnRM 2RR (11-7015)

05000443/LER-2014-0027 August 2014Seabrook

On April 6, 2014, while the plant was in refueling outage sixteen, it was determined during surveillance testing that three of four reactor coolant pump (RCP) undervoltage (UV) reactor trip channels exceeded the Technical Specification (TS) channel response time acceptance criteria of 1.5 seconds for the RCP UV reactor trip function. The condition for the RCP UV time delay relays exceeding tolerance was experienced on all four channels; however, only three of the four channels did not meet their TS required response times. Since this condition involved multiple similar components, there is evidence indicating that this condition may have arisen over time and three channels of RCP UV were inoperable concurrently. This resulted in the plant operating in a condition prohibited by the TS.

The root cause was determined to be the revisions of the Design Control Manual in 1991 and earlier did not require a failure modes and effects analysis as part of the design change packages that installed the E7022PA relays. The RCP UV time delay setting was not identified as a critical attribute and the manufacturer's recommendations for applications requiring very precise time delay settings were overlooked and not incorporated into station procedures. Corrective actions already taken include the replacement of one relay and adjustment of all relays to acceptable response times.

Planned corrective actions are to revise procedures to energize relays for at least 3 hours before performing testing, to perform rechecks at 72 hours during outages and perform additional rechecks if adjustments were made.

05000443/LER-2014-00119 May 2014Seabrook

On April 1, 2014 at 00:26 while operating at approximately 15% power following turbine shutdown and removal of the main generator from service, Seabrook Station experienced an automatic reactor trip on reactor coolant two loop loss of flow. The loss of flow was the result of the unexpected closure of the main generator breaker (MGB) "B" phase resulting in 345KV bus 6 de-energizing to isolate the generator breaker. All buses transferred to the reserve auxiliary transformers as designed; however, a slight delay in the automatic transfer for bus 1 resulted in two reactor coolant pumps (RCP) tripping. The RCPs tripping resulted in an automatic reactor trip due to reactor coolant loop low flow. The emergency feedwater system actuated on low SG level, and plant equipment functioned as expected. No adverse consequences resulted from this event.

The root cause is inadequate procedural guidance as the procedure used for MGB operation lacked appropriate information regarding local/remote selector switch position, mitigating actions, and minimizing time with MGB protection defeated. Corrective action is to revise the procedure to add controls to communicate potential risk while switch is in the local position, ensure the use of guarded equipment controls, and minimize the time spent with the switch in local without breaker lock rods installed.

05000443/LER-2012-0054 February 2013Seabrook

On 12/7/12, with the plant in Mode 1 at 100% power, Service Water Cooling Tower level was discovered to be below the Technical Specification (TS) limit of 42.15 feet. Following discovery, a fast fill of the cooling tower was performed to restore water level above the TS limit. It was subsequently determined that cooling tower water level was below the TS limit for approximately 17 days.

adverse consequences resulted from this event and no safety system functional failure occurred since there was sufficient water in the cooling tower to maintain the cooling tower functional at all times.

No The cause of the event was failure to use diverse means to validate the accuracy of a potentially inaccurate cooling tower level indicator. Corrective actions included restoring level in the Service Water Cooling Tower and increasing the use of operator fundamentals.

05000443/LER-2012-0028 November 2012Seabrook

On September 25, 2012 with the unit in a refueling outage and defueled, station personnel, while reviewing a design change for installation of new circuit boards in the solid state protection system, identified a deficiency in the procedure that performs response time testing of the reactor trip breakers (RTB). The RTB have two diverse trip methods: the undervoltage circuit and the shunt trip circuit. When a RTB is opened through the shunt trip circuit, two coils (STA and SH TR) must function in order to open the breaker. A review of the existing test method found that the shunt trip circuits for both RTB had not been adequately tested. Further, a review of previous revisions of the surveillance procedures concluded that the response time of the shunt trip circuit had never been adequately tested.

This event is similar to and has the same cause as the inadequate time response testing reported in LER 2012­ 001. The cause of both events was ineffective methods utilized in the mid 1980's to verify that surveillance test procedures ensured compliance with the TS. The corrective actions for this condition included revising the surveillance procedure and obtaining response times, which were found to be within acceptable limits. A review of the adequacy of time response testing is ongoing to address the extent of condition. No adverse consequences resulted from this event.

05000443/LER-2011-00314 February 2012Seabrook

On December 21, 2011, during operation at approximately 65% power, station personnel identified a condition that previously rendered one of the offsite AC power sources inoperable. The plant design includes two independent offsite AC sources: (1) one circuit through the unit auxiliary transformers (UAT) to both trains of emergency buses, and (2) a second source through the reserve auxiliary transformers (RAT) to both trains of emergency buses. Offsite power is normally provided through the UAT, and the RAT supply is in standby. Operability of the RAT supply is contingent on the ability of the system to perform a fast transfer to the RAT supply upon opening of a UAT supply breaker. A review of the system design determined that when the emergency diesel generator (EDG) is operating in parallel with offsite power, the fast transfer feature to the RAT supply is unavailable, rendering this offsite AC source inoperable. On at least two occasions, this previously unrecognized condition rendered the offsite AC source inoperable for a period longer than permitted by the technical specifications.

This event resulted from a failure to recognize the impact of EDG operation on the fast transfer feature.

Operations issued guidance that the offsite AC source is inoperable during parallel operation of an EDG. No adverse consequences resulted from the event.

05000443/LER-2011-0022 December 2011Seabrook

At approximately 1226 on October 6, 2011 with the plant operating in Mode 1 at 100% power, Seabrook experienced a plant trip on low steam generator water levels following loss of an operating main feed pump. The main feed pump tripped on low suction pressure while restoring a condensate pump to service following maintenance. During restoration of the pump, air entered the condensate system and caused a drop in condensate pump discharge pressure, which resulted in a low pressure condition at the suction of the main feed pump. The trip of the main feed pump on low suction pressure initiated a turbine setback; however, with reduced feedwater flow, steam generator levels decreased to the low level reactor trip setpoint. The automatic systems functioned as designed. The emergency feedwater system automatically actuated and recovered steam generator levels. No adverse consequences resulted from this event.

The cause of this event was the lack of a procedure for restoring a condensate pump to service during operation at power. The corrective action revised the operating procedure to provide instructions for filling and venting a condensate pump following maintenance.

05000443/LER-2011-00120 May 2011SeabrookOn March 24, 2011 during operation in mode 1 at 100% power, station personnel, while reviewing station documents, determined that one of the two containment gaseous radioactivity monitors did not meet the qualifications for a reactor coolant system leakage detection monitor required by the technical specifications (TS). The indication provided by the backup gaseous monitor did not meet the seismic requirements of Regulatory Guide (RG) 1.45, Reactor Coolant Pressure Boundary Leakage Detection Systems, and the monitor should not have been used to satisfy TS requirements. TS 3.4.6.1 requires a containment gaseous monitor and a particulate monitor. On several occasions, the plant operated with the normal particulate and gaseous monitors out of service and relied on the backup gaseous monitor to meet TS requirements. This situation resulted in a condition prohibited by the TS when plant operation continued with two inoperable leakage detection monitors for longer than the 6 hours permitted by the TS. No adverse consequences resulted from this event. The cause of the condition was the design change that installed the backup monitor in the early 1990's did not qualify the monitor's indication to seismic requirements in accordance with RG 1.45. The condition was corrected in April 2011 by a design change that upgraded the gaseous monitor indication to meet seismic requirements.
05000443/LER-2010-00114 May 2010Seabrook

On March 15, 2010 during operation in mode 1 at 100% power, both trains of the containment enclosure emergency air cleanup system (CEEACS) were rendered inoperable due to an opening in the ventilation area boundary. For approximately five hours on March 15 and approximately 4 hours on March 17, a door in the containment enclosure boundary (CEB) was opened to support planned maintenance activities in the positive displacement charging pump room. Under accident conditions, the CEEACS maintains a negative pressure in the enclosure surrounding the containment to prevent uncontrolled releases of radioactivity into the environment.

However, the breach in the CEB created by the open door would have prevented both trains of the CEEACS from establishing the minimum required negative pressure in the enclosure. This condition placed the plant in Technical Specification (TS) 3.0.3, although it was unrecognized at the time, and resulted in a loss of safety function for the CEEACS. The causes of the event included lack of programmatic controls to ensure the control room is notified prior to propping open a CEB door and historical guidance that led the operators to believe that only TS 3.6.5.2, Containment Enclosure Boundary Integrity, applied when a CEB door was open. The planned corrective actions will strengthen an existing program to address opening CEB doors and revise the TS.

05000443/LER-2003-00113 November 2003Seabrook

On June 10, 2003, due to a potential for a common mode failure found during preventive maintenance activities for the "A" Emergency Diesel Generator (EDG-1A), EDG-1B was started and run unloaded to satisfy the requirements of Technical Specification (TS) 3.8.1.1 action b.

A subsequent review conducted on June 18, 2003, determined that unloaded testing of EDG-1B did not adequately address the requirements of TS 3.8.1.1. EDG-1B was subsequently retested satisfactorily under loaded conditions.

Failure to complete the loaded run within the required action statement time constitutes noncompliance with the requirements of the action statement and is reportable as a condition prohibited by TS pursuant to 10 CFR 50.73(a)(2)(i)(B). LER 02-002-00 identified a condition where plant operators failed to start the operable EDG unit within 24 hours after discovery as required by TS 3.8.1.1 action b.

The cause of this event was the failure of Licensee personnel to understand the entire affect of a change to the Technical Specifications due to an inadequate license amendment review process and an inadequate response to TS 3.8.1.1 questions. Corrective actions include revising the TS change review process, and providing additional training for the Operations Department and personnel involved in the event.

There were no adverse safety consequences as a result of this event.

05000443/LER-2002-00126 July 2002Seabrook

On May 28, 2002, at 2:31 AM, with the plant in Mode 4, the Control Room Operator initiated a manual reactor trip due to the loss of indication for control rod L5 during control rod surveillance testing.

At the time of the event, control bank A was at 72 steps withdrawn; the other shutdown and control banks were fully inserted into the core. During the withdrawal of control bank A, a Digital Rod Position Indication (DRPI) urgent alarm was received indicating that the rod position indication for Control Bank A was invalid. Pursuant to Technical Specification 3.1.3.3, the reactor trip breakers were manually opened using the reactor trip switch. All rods fully inserted. All systems functioned as required. At the time of the event, reactor coolant temperature was approximately 276 degrees Fahrenheit and reactor coolant pressure was approximately 552 psig.

An eight-hour event notification to the Nuclear Regulatory Commission (NRC) was made pursuant to the requirements of 10CFR50.72(b)(3)(iv)(A). The event notification was 38947.

It was determined that DRPI rod L5 position indication card had failed in service. The failed card was replaced and the surveillance was completed satisfactorily.

This License Event Report is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(iv)(A).