Semantic search

At 10:18 EDT on October 26, 2012, at 100% power in Mode 1, during the monthly equipment swaps, primary shield fan S-2B-SB failed to remain secured after engaging the main control board (MCB) hand switch. The condition caused the “B” emergency diesel generator (EDG) to be inoperable, but licensed operators and other station personnel did not recognize the impact on EDG operability. On October 31, 2012 at 15:26, “B” EDG was returned to operable status.

The primary shield fan starting upon closure of the EDG output breaker had no significant adverse impact on the ability of the EDG to perform its safety function. The primary shield fan is a small load, and the EDG loading capability had sufficient margin to accept the small load upon closure of the output breaker.

The cause of the failure of the fan to remain secured was age-related failure of the 42 seal in contact.

The root cause of the failure to recognize the impact of the contact failure on the “B” EDG operability was that the Technical Specifications Bases do not provide adequate clarity regarding Surveillance Requirement applicability and the specific requirements associated with EDG Operability. Corrective actions include revising the Technical Specification Bases, procedure changes, and additional training.

On October 23, 2013, while operating at 100% power in mode 1, two main steam safety valve setpoints were found outside the +/- 1% tolerance of table 3.7-2 of technical specification 3/4.7.1.1. Three other valves were tested and setpoints were found to be within tolerance. Upon discovery of the out of tolerance conditions, the two setpoints were adjusted to within technical specification tolerances which restored compliance with the technical specifications. The cause was determined to be setpoint drift incompatible with analysis specified criteria. The corrective action will be implementation of a revised safety analysis that accommodates increased setpoint drift and supports revised technical specification setpoints.

Main steam safety valves are used to satisfy American Society of Mechanical Engineers code requirements for overpressure protection. The limiting accident analysis has more margin available than the measured deviation from setpoint, so the impact on safety is very minor.

Shearon Harris Nuclear Power Plant, Unit 1 05000400

On November 11, 2013, while in Mode 5, sample results of the 'C' waste gas decay tank (WGDT) were not properly evaluated in which hydrogen results should have been documented as greater than 4 percent and oxygen at 4.03 percent. Due to this condition, it was not recognized that the conditions of Technical Specification (TS) 3.11.2.5 were not met and required immediate suspension of all additions of waste gas to the system, reduction of oxygen to less than or equal to 4 percent by volume, then reduction of oxygen to less than or equal to 2 percent within 48 hours. HNP was in this condition for 30 calendar days until the oxygen concentration in the 'C' WGDT was reduced to below the TS limit on December 11, 2013.

The root cause was determined to be an inadequate understanding of the risks associated with degassing the waste gas system with inoperable analyzers. Corrective actions include revising procedures, training, and reinforcing expectations for procedural use and adherence. This event is considered to have no safety significance as an engineering evaluation determined that this condition did not generate any combination of explosive gases in the system.

On June 12, 2014, while operating at 100 percent power in Mode 1, Harris plant personnel determined that inadequate cable protection existed in control cables for the Turbine Emergency Oil Pump. The cables had no electrical protection devices (fuses) other than the circuit breaker. The control cables are routed through several fire areas, including the main control room, and under postulated conditions, could have created a common enclosure fire hazard situation. Compensatory measures (hourly fire watches) were implemented for affected areas of the plant to ensure continued public safety until electrical protection devices were installed.

The apparent cause was the historical installation of an unfused section of cable in the control circuit of the Turbine Emergency Oil Pump.

On March 12, 2015, while operating at 100% power in mode one, surveillance testing identified the lift setting of main steam (MS) safety valve (SV) 1MS-49 was outside of the technical specification (TS) allowed tolerance.

Testing of all other installed MSSVs identified four additional MSSVs that were also outside of the TS allowed tolerance. On April 9, 2015, while shutdown for a refueling outage, pressurizer SV 1RC-127 was found outside its TS allowable tolerance. The primary cause of the SV lift settings being outside of the TS allowed tolerance was setpoint drift incompatible with analysis specified criteria. 1RC-127 was also determined to have an operating history of being outside of tolerance when tested. The valve installed as 1RC-127 was removed from service, and all six valve lift settings have been restored to within the allowable tolerance. The 1% TS tolerance is more restrictive than the American Society of Mechanical Engineers code allowed tolerance of 3%. The primary corrective action to preclude recurrence will be implementation of a revised safety analysis that accommodates increased setpoint drift and supports revised technical specification setpoints. The condition is similar to that reported in licensee event report 2013-002-00. The small deviations beyond the allowable tolerance result in a very low safety significance.

On April 7, 2015, and April 9, 2015, the reactor vessel head penetration nozzles were being examined while the Harris Nuclear Plant was shut down for a scheduled refueling outage. Ultrasonic examinations identified indications that required repair in three head penetration nozzles. The indications were approximately 0.233, 0.260, and 0.297 inches long in nozzles 14, 18, and 23 respectively, and axial in orientation. The maximum through-wall extent was approximately 32%. An inspection of the exterior surfaces of the reactor head confirmed there was no leakage. The indications were repaired using the inside diameter temper bead welding process. The repairs restored compliance with the American Society of Mechanical Engineers code requirements.

The cause of the indications was attributed to primary water stress corrosion cracking. Per the requirement of 10 CFR 50.55a(g)(6)(ii)(D)(5), examinations are required to be performed on the reactor vessel head every refueling outage to identify flaws and ensure appropriate repairs are performed. This is similar to the conditions reported in Harris Licensee Event Reports 2013-001-00 and 2013-003-00.

On June 16, 2015, while Harris Nuclear Plant (HNP) was operating at 100% in mode 1, two doors between the Reactor Auxiliary Building (RAB) and Main Steam Tunnel (MST) were opened to support a maintenance activity. These doors are credited in the high energy line break (HELB) equipment qualification and internal flooding analyses for HNP; however the opening of these doors is not addressed in these analyses. If a HELB occurred in the MST during a time in which these doors are open, the Essential Services Chilled Water system could become inoperable.

The root cause of this event was determined to be that HNP Engineering failed to develop and implement control measures for hazard barriers credited for mitigating HELB events. Immediate corrective action was taken to close the doors and issue a Standing Instruction that prohibits these doors from being blocked open during modes 1 through 4. Corrective action is planned to develop and implement an engineering change that evaluates the required passive design features needed to support HELB analysis and overall licensing bases. This engineering change will identify required passive design features and establish the necessary process to ensure barriers are appropriately identified and controlled.

On July 22, 2016, the 'A' Essential Services Chilled Water (ESCW) chiller tripped due to low oil pressure and was declared inoperable.

The cause was oil leakage from a recently replaced brass tube fitting connecting the high-pressure side of an oil pressure differential sensing line to the lubrication system. An equivalent stainless steel fitting was installed in place of the brass, and the 'A' ESCW chiller was then declared operable.

This failed brass fitting was a recently installed like-for-like replacement component following a similar 'A' ESCW chiller trip on July 15, 2016, caused by low oil pressure as a result of leakage through the original brass tube fitting.

The cause of the failed tube fitting was fatigue crack growth resulting from vibration, with stress corrosion cracking having a secondary role. The material was replaced with stainless steel, and further analysis to address the vibration is ongoing.

On October 8, 2016, the Shearon Harris Nuclear Power Plant was reducing power to enter a planned refueling outage (RFO-20). The plant was at approximately 8 percent power in Mode 1 when the unit experienced an unplanned reactor trip with a safety injection (SI) and main steam line isolation (MSLI). A malfunction of the turbine controller during turbine mechanical overspeed trip testing caused an excessive draw of steam flow from the Steam Generators (SGs). This caused the Engineering Safety Features Actuation System instruments to detect a valid change in SG pressure and initiate a rate compensated Low Steam Line Pressure signal. This signal initiated a SI and MSLI, which in turn initiated reactor trip, turbine trip, feedwater isolation, and closed the main steam isolation valves.

Degraded equipment within the turbine controller resulted in excessive opening of the governor valves; this was caused by an inadequate supply of hydraulic oil to meet the increased system demand during testing. Insufficient hydraulic accumulator capacity was available to support system demand. One accumulator was known to be out-of-service; a second was discovered post-event. Also, a hydraulic oil pressure switch used for turbine control was not functioning properly. The equipment deficiencies have been corrected.

Changes have been made to the testing procedure to validate at least four accumulators are in service prior to testing. The Power Operation (Mode 2 to Mode 1) procedure will also be revised to validate at least four accumulators are in service. A new calibration procedure will be implemented for the deficient oil pressure switch to ensure better quality control over verifying switch function.

Between October 15 and October 19, 2016, the Shearon Harris Nuclear Power Plant (SHNPP) reactor vessel closure head penetrations were being examined. SHNPP was shut down for a scheduled refueling outage (RFO) for cycle 20 (RFO-20).

Nondestructive examinations identified four rejectable indications impacting four penetration nozzles. Indications associated with nozzles 30, 40, and 51 were indicative of primary water stress corrosion cracking (PWSCC), with the largest indication having an axial extent of 0.372 in. with a through-wall extent of 0.247 in. (39 percent). The fourth indication was identified on nozzle 23 by dye penetrant testing. This indication had a rounded profile indicative of a weld fabrication void, and was 0.307 in. on the major dimension.

The weld was fabricated during the previous outage, RFO-19. The void was originally identified during RFO-19 and was acceptable.

However, the void has since opened to unacceptable dimensions due to normal operating conditions.

A leak path assessment and a bare metal visual examination of the reactor vessel head top was completed, with no leakage identified.

The three PWSCC indications were repaired using the inside diameter temper bead weld method. The fabrication void was removed via localized grinding, with no additional welding necessary. All repairs were completed prior to exiting the refueling outage.