05000333/LER-2012-002

LER-2012-002, High Pressure Coolant Injection Pressure Control Valve Failure

Docket Number
Event date:	08-30-2012
Report date:	02-14-2014
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
Initial Reporting
ENS 48258	10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
3332012002R01 - NRC Website

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BACKGROUND

On January 18, 1988, a design change was made that installed a larger inline filter in the pressure sensing line for the High Pressure Coolant Injection (HPCI) [EIIS System Identifier: BJ] booster pump P-1B recirculation pressure control valve (23PCV-50) [EIIS Component Identifier: PCV]. This change was made because of several instances where the 23PCV-50 filter or snubber would become blocked by debris thereby preventing the pressure control valve from controlling. A two year preventative maintenance (PM) activity was also established to clean, inspect, and replace the filter and snubber.

On April 30, 2012, a new revision of OP-15, “High Pressure Coolant Injection” was issued. This revision of OP- 15 added a new section, G.9, “Fill and Vent HPCI Suction Piping From Condensate Storage Tanks (CST),” to address a corrective action identified during the Nuclear Regulatory Commission (NRC) inspection on gas accumulation earlier in the year.

On June 8, 2012, a HPCI outage was conducted in order to perform PM on HPCI Booster Pump P-1B Suction From Suppression Pool Check Valve (23HPCI-61) [EIIS Component Identifier: V]. This required the HPCI system to be isolated and drained, including the pump and suction line piping. In addition, the filter and snubber on the pressure sensing line for 23PCV-50 were also replaced as required by the PM.

During restoration, a portion of the HPCI suction piping was filled and vented from the torus per OP-15, Section G.8, “Fill and Vent HPCI Suction Piping from Torus.” The remaining HPCI suction piping was filled and vented from the CSTs in accordance with OP-15, Section G.9. Post work and return to service testing was completed satisfactory three days later and operability was demonstrated by a successful completion of ST-4N, “HPCI Quick-Start, Inservice, and Transient Monitoring Test (IST).” EVENT DESCRIPTION & ANALYSIS On August 28, 2012, while running the HPCI turbine for ST-4N, several annunciators were received in the control room, indicating that the reactor building equipment sump “A” (20TK-69A) [EIIS Component Identifier:

TK] was being overflowed and water was running down into the floor sump. This condition was confirmed visually by an operator. At that time the source of the extra water was unknown. Since the volume of water entering 20TK-69A was greater than what was expected to come from the HPCI system. It was assumed that torus water was coming through a leaking check valve on the discharge of the reactor building equipment drain sump pump. At the time of discovery, torus water level was being lowered by pumping it to the radwaste system [EIIS System Identifier: WD] via the equipment drain discharge header.

On August 30, 2012, operators performed ST-4E, “HPCI and SGT Logic System Functional and Simulated Automatic Actuation Test.” The data collected during this surveillance revealed that while the HPCI turbine was in operation, there was approximately 75 gpm of water going into the “A” reactor building sump. The source of this water was determined to come from HPCI Booster Pump P-1B Recirculation Safety Valve (23SV-66) [EIIS Component Identifier: RV] which was lifting on high pressure. Troubleshooting determined that the cause of 23SV-66 to lift was a failure of 23PCV-50 to properly control pressure.

Control pressure for 23PCV-50 is 75 psia which is the design pressure for the HPCI lube oil cooler (23E-2) [EIIS Component Identifier: CLR] and gland seal condenser (23E-1) [COND]. However, data collected during the ST- 4E run on August 30, 2012, demonstrated that 23PCV-50 was not repositioning as expected. The increased down stream pressure caused 23SV-66 to lift, allowing CST water into the reactor building equipment sump.

The HPCI system is considered operable when it is aligned to one or both CSTs with power available to support automatic realignment to the suppression pool if required. This is based on the design of the CSTs and the accident analysis which credits the suppression pool for supplying the HPCI System. With an assumed leakage of 75 gpm of CST water being directed into 20TK-69A, HPCI may not have been able to meet its mission time without realigning its suction to the torus. If the HPCI suction source re-aligned to the torus, due to low CST levels, the water being discharged to 20TK-69A would be torus water; this condition would result in total leakage sources outside containment exceeding the 5 gpm limit established by the Final Safety Analysis Report (FSAR).

As a result, HPCI was declared inoperable on August 30, 2012. On September 2, 2012, after replacing the sensing line filter and snubber; flushing the system with clean CST water; and successfully performing return to service testing; HPCI was restored to operable status. This was reported to the NRC on August 30, 2012, via ENS #48258. It is being reported in this LER in accordance with 10 CFR 50.73(a)(2)(v)(D), any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.

The action that led to 23PCV-50 failing to control pressure was filling the HPCI pump suction from the torus during restoration from the June 2012 maintenance outage. That action introduced foreign material into the suction line that eventually fouled the filter in the 23PCV-50 sensing line. The date that 23PCV-50 was not capable of performing its function is indeterminate. The period of time from June 2012 to August 2012 is greater than the allowed outage time for HPCI (TS LCO 3.5.1), therefore this event is also being reported under 10 CFR 50.73(a)(2)(i)(B), any operation or condition which was prohibited by the plant's Technical Specifications.

CAUSE OF EVENT

Mechanistic The apparent cause of the event was determined to be material in the 23PCV-50 sensing line and filter. This was validated by physical inspection during troubleshooting. The material was a result of filling and venting the 23PCV-50 sensing line with torus water containing suspended solids.

Normally the 23PCV-50 sensing line is maintained full of water. With its short stroke, suspended solids don't make their way up the line and into the filter. However, during the HPCI LCO in June, both the HPCI system and the 23PCV-50 pressure sensing lines were drained at the same time. Therefore, when the HPCI suction piping was filled from the torus, the sensing line was also filled. This resulted in suspended solids from the torus water clogging the filter in the sensing line.

Programmatic The event was reviewed for organizational and programmatic deficiencies that may have caused or contributed to the event. It was determined that Operations Procedure, OP-15 had insufficient detail in its guidance for filling and venting from the torus. This had the unintended consequence of filling portions of the HPCI line, including the instrument line for 23PCV-50, with material from the torus.

An extent of condition review was performed for other PCVs subject to the same failure mode. The systems reviewed were HPCI, Reactor Core Isolation Cooling [EIIS System Identifier: BN], Residual Heat Removal [EIIS System Identifier: BO], and Core Spray [EIIS System Identifier: BM]. This review did not identify any other PCV that was applicable to the failure mode described in this LER.

FAILED COMPONENT IDENTIFICATION

Description: HPCI Booster Pump P-1B Recirc Pressure Control Valve Manufacturer: Masoneilan Intl, Inc.

Model/Part Number: 525 NPRDS Manufacturer Code: M120 FitzPatrick Component ID: 23PCV-50

CORRECTIVE ACTIONS

Completed The PCV in-line filter and snubber have been replaced.

The pressure sensing line for 23PCV-50 was flushed with clear water.

23PCV-50 was tested satisfactory.

All other components in the HPCI system have been evaluated for extent of condition, and are not susceptible to this failure mode.

HPCI system has been tested successfully per ST-4N.

Future Actions Revise OP-15 to add additional guidance for filling the HPCI suction piping.

Evaluate a design change to have 23SV-66 discharge into torus vice equipment sump.

Revise PM to fill sensing line using a clean water source.

ASSESSMENT OF SAFETY CONSEQUENCES

The HPCI System is designed to provide adequate core cooling to limit fuel clad temperatures in the event of a small break in the Reactor Coolant System piping with a loss of coolant that does not result in rapid depressurization of the reactor pressure vessel (RPV).

The significance of this condition is based on the safety function performed by the HPCI system. With 23PCV- 50 not controlling pressure, 23SV-66 would lift continuously with HPCI in operation. This would initially result in CST water being directed to 20TK-69A. If the HPCI suction source re-aligned to the torus, due to low CST levels, the water being discharged to 20TK-69A would be torus water; this condition would result in total leakage sources outside containment exceeding the 5 gpm limit established by the FSAR. An assessment of the potential risk contributions associated with this alignment was performed, and the result screened, per the criteria established in NRC IMC 0609, as very low safety significance with nominal risk.

Radiological & Industrial Safety There were no actual radiological or industrial safety consequences. The potential impact on radiological and industrial safety is minimal; Secondary Containment is required to be Operable in all applicable Modes of operation.

There was no actual or potential nuclear safety consequences associated with this condition. At all times HPCI was available to provide a source of RPV water inventory in the event of a loss of coolant accident. Additionally, the Automatic Depressurization System (ADS) in combination with the Low Pressure Coolant Injection system (LPCI) and the Core Spray system (CS) were available to provide core cooling during the period of HPCI inoperability. Secondary containment also remained OPERABLE during this period.

This deficiency did have a potential impact on the Primary Coolant Sources Outside Containment Program required by TS 5.5.2. This program is in place to ensure that leaks are tracked, assessed, and prioritized such that the potential to exceed post accident release rates are minimized. With respect to this program, it would only be impacted in the event that the HPCI suction was aligned to the torus.

The potential impact of this condition was minimized because during the course of this event, the HPCI system suction was aligned to the CST's. In addition, Emergency Operating Procedures (EOP) preferentially maintain the HPCI suction aligned to the CSTs and during accident conditions the EOPs do address high water levels in the reactor building sumps and crescents; actions include isolating systems discharging into the area, shutting down the reactor and depressurizing the reactor.

SIMILAR EVENTS

Internal operating experience (OE) was reviewed through Entergy's corrective action program. There were no relevant events found. Similarly, external industry OE was reviewed via INPO. Although there were several events that had some applicability to JAF, none of the events were relevant with regards to the event being reported in this LER. Insights from the OE search were incorporated into the corrective action plan.

REFERENCES

JAF Condition Reports: CR-JAF-2012-04994, CR-JAF-2012-04958, CR-JAF-2012-03015 JAF TS 3.5.1, ECCS – Operating, TS 5.5.2 – Primary Coolant Sources Outside Containment JAF Engineering Change 39479 JAF FSAR 6.4.1 High Pressure Coolant Injection System