05000528/LER-2006-005
| Docket Number | |
| Event date: | 10-05-2006 |
|---|---|
| Report date: | 08-08-2008 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 5282006005R01 - NRC Website | |
All times are Mountain Standard Time and approximate unless otherwise indicated.
1. REPORTING REQUIREMENT(S):
This LER is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B) to report a condition prohibited by the Technical Specifications (TS).
Specifically, on October 5, 2006, at 1123 hours0.013 days <br />0.312 hours <br />0.00186 weeks <br />4.273015e-4 months <br /> operations personnel increased reactor coolant system (RCS)(EIIS: AB) pressure to greater than 1837 psia with the plant in Mode 3, Hot Standby. The TS requires two trains of emergency core cooling systems (ECCS)(EIIS:BP BQ) to be OPERABLE in this condition. However, safety injection check valve 1PSIEV134 (S1-134)(EllS: V) was not in its seated position at the time of the transition. Proper operation of the check valve is verified with RCS pressure greater than 1600 psia. The most recent successful test prior to this event was completed on October 8, 2005. Operations personnel were not aware of the status (and could not have known) of the check valve position until 1815 hours0.021 days <br />0.504 hours <br />0.003 weeks <br />6.906075e-4 months <br /> on October 5, nog,when testing of the check valve was conducted and revealed that the valve was not seated.
2. DESCRIPTION OF STRUCTURE(S), SYSTEM(S) AND COMPONENT(S):
The function of the ECCS is to provide core cooling and negative reactivity to ensure that the reactor core is protected after certain accidents. Two redundant, 100% capacity trains are provided. In MODES 1, 2, and 3, with pressurizer pressure (EIIS: PZR) greater than or equal to 1837 psia or with RCS cold leg temperature (Tc) greater than or equal to 485°F both trains are required to be OPERABLE with each train consisting of High Pressure Safety Injection (HPSI)(EIIS: BQ) and Low Pressure Safety Injection (LPSI)(EIIS: BP) subsystems. This ensures that 100% of the core cooling requirements can be provided in the event of a single active failure.
SI-134 is a Borg-Warner (B-W), Model 77790, 12 inch, 1500 lb, ASME Class 2, bonnet hung, swing check valve, located on the LPSI cold-leg injection piping inside containment on the 80 foot elevation. This check valve functions to protect from over pressurization of the LPSI piping during HPSI pump operation. The check valve opens to allow safety injection and shutdown cooling flow to the RCS, closes to prevent diversion of HPSI flow and to provide isolation/protection of the LPSI discharge piping.
This valve also functions as a containment isolation (EIIS: BD) valve that is open during certain accident conditions and is not required to be type C tested in accordance with the Containment Leakrate Testing Program (Appendix J Program).
3. INITIAL PLANT CONDITIONS:
On October 5, 2006, Unit 1 was in MODE 3 and activities were in progress to return the plant to power operation following a forced outage to repair pressurizer heaters (EIIS:
EHTR). There were no structures, systems, or components that were inoperable at the time of discovery that contributed to this condition.
4. EVENT DESCRIPTION:
On October 5, 2006, at 1708 hours0.0198 days <br />0.474 hours <br />0.00282 weeks <br />6.49894e-4 months <br /> Surveillance Test (ST) 73ST-9SI05, Leak Test of HPSI/LPSI Containment Isolation Check Valves, was being performed. During the performance of section 8.3 of the ST, check valve SI-134 failed to seal properly. This ST uses a high pressure safety injection (HPSI) pump to pressurize the piping downstream of SI-134 while monitoring leakage to piping upstream of the valve through a drain valve. During the test, the pressure and flow rate through the drain connection was unexpectedly high and the test conditions could not be established and a leak rate could not be determined.
At 1815 hours0.021 days <br />0.504 hours <br />0.003 weeks <br />6.906075e-4 months <br /> SI-134 was declared inoperable and control room personnel entered the applicable TS Required Actions for LCOs 3.0.3 (due to both HPSI trains inoperable), 3.5,3 conditions A and B (LPSI A train and HPSI A train inoperable), 3.6.3 condition A (SI-134 containment isolation function inoperable) and entered the required action for technical requirements manual (TRM) TLCO T3.5.201 condition A (shutdown cooling train A inoperable).
At 1852 hours0.0214 days <br />0.514 hours <br />0.00306 weeks <br />7.04686e-4 months <br /> TS LCOs 3.0.3 and 3.5.3 condition B (for the HPSI A train) were exited when motor operated containment isolation valve SIA-UV-635 (EIIS: INV) was deenergized in its closed position which isolated the piping upstream of SI-134. At 1859 hours0.0215 days <br />0.516 hours <br />0.00307 weeks <br />7.073495e-4 months <br /> TS LCO 3.5.3 condition B was exited for the HPSI B train system following system realignment.
Ultrasonic Test (UT) equipment was used to monitor SI-134 and indicated that the valve disc was in the closed orientation. The plant was cooled down and RCS pressure was decreased to exit the conditions that required two operable ECCS trains and to allow low pressure safety injection (LPSI) A train pump to flush the check valve seat. As forward flow through the check valve was established, UT confirmed that the disc opened and then closed when flow was secured. This verified that the disc was not caught under the valve seat, which had been a previous operating experience concern.
The UT did not confirm whether the disc was fully seated.
The unit was cooled down to Mode 4, Hot Shutdown, and on October 6 at 0731 hours0.00846 days <br />0.203 hours <br />0.00121 weeks <br />2.781455e-4 months <br /> TLCO T3.5.201 condition A was exited. Plant management decided to perform maintenance on SI-134 which required the plant to be placed in Mode 5, Cold Shutdown, which was achieved on October 6, 2006, at 1525 hours0.0177 days <br />0.424 hours <br />0.00252 weeks <br />5.802625e-4 months <br />. TS LCO 3.6.3 was exited at that time.
5. ASSESSMENT OF SAFETY CONSEQUENCES:
The condition in which SI-134 did not seal on October 5, 2006 did not result in any challenges to fission product barriers or in any offsite releases. Therefore, there were no actual adverse safety consequences as a result of the valve failure to seal properly.
With SI-134 not in its fully seated position, pressurization of the LPSI piping upstream of SI-134 could occur during accident conditions or an inadvertent safety injection actuation. An engineering calculation has concluded that the affected LPSI piping is qualified for an internal pressure of 1950 psig per the requirements of ASME Section III Appendix F. This pressure bounds the in-service discharge pressure test data of the Unit 1 HPSI pumps taken in both August 2006 and November 2006.
The following additional evaluations were conducted by engineering personnel:
1) The effect of HPSI pressure on LPSI MOV operation was considered and determined that the A train Shutdown Cooling Heat Exchanger (SDCHX) Inlet and Outlet Isolation MOVs (SI-685 and SI-686) could have been pressure locked in the closed position. The B train SDCHX valves were unaffected by the leaking CV.
2) LPSI train A piping, which could have been exposed to HPSI pressure during an event, was reviewed for other components that could have been damaged by the high pressure. The only components other than piping and valves in the subject section of piping are the LPSI Pump A Discharge Flow Transmitter, 1JSIAFT0306 (Rosemount Transmitter Model 1153DB) and Pressure Indicator, 1JSINPT0306 (Rosemount Transmitter Model 1152GP), both of which, per their Vendor Technical Documents, are hydrostatically tested at 150 percent of working pressure or 2000 psi, whichever is greater. In addition, there is a temperature element, installed in a thermal well, which equals or exceeds the piping pressure capabilities. Therefore, the over pressurization of the LPSI piping would not have catastrophically failed any components attached to the piping.
3) Pressurization of the LPSI discharge piping would have resulted in the lifting of thermal relief valves PSV-439 and PSV-161, which have a combined capacity flow of approximately 20 gpm. The effect of this 20 gpm flow into the Equipment Drain Tank (EDT) from LPSI relief valves was evaluated. The EDT volume is approximately 10,000 gallons and is equipped with a relief valve (CH-657) which is sized to pass 300 gpm when the tank is over pressurized. The EDT relief valve discharges to the non-ESF sump which is sufficiently sized to preclude flooding at inflows well in excess of 20 gpm. The EDT volume (even if starting half full) is considered to be adequate to provide Operators sufficient time to isolate the LPSI header. Therefore, Auxiliary Building flooding is not considered to be a significant issue.
4) The impact to HPSI injection flow rate was reviewed for diversion of 20 gpm of injection flow to the LPSI header relief valves with the check valve open. Calculation 13-MC-SI-0215 includes a 20 gpm margin, which bounds the injection flow loss while ensuring that the credited flow rates are delivered to maintain the core covered and to provide for long term cooling.
There were no other,failures that rendered a train of a safety system inoperable. The condition would not have prevented the fulfillment of the safety function, and the condition did not result in a safety system functional failure as defined by 10 CFR 50.73(a)(2)(v).
7. CORRECTIVE ACTIONS:
SI-134 was disassembled and inspected. A new bonnet/disc assembly was installed in the valve and the valve passed required testing. Additional actions were taken to preclude recurrence of this condition, including:
1)The check valve maintenance procedure 31MT-9ZZ17 was revised to incorporate B-W assembly information and component clearance information.
2)The check valve predictive maintenance program was revised to require verification of freedom of movement of the disc, to assess the operational readiness of the valve and, for B-W valves, to test that the disc closes on its own to verify operational readiness.
3)Disassembly, inspection and correction of Unit 1 and Unit 3 B-W swing arm check valves (>12" diameter) with known configuration discrepancies (or a lack of inspection data) relative to newly acquired B-W assembly information and clearances has been completed. These inspection activities for similar check valves in Unit 2 were completed during the most recent refueling outage (2R14).
4) The check valve predictive maintenance program inspection interval has been changed to a 12 year frequency for all 12" and larger B-W swing check valves (safety injection tank outlet check valves and RCS loop check valves). The valve affected by this event had not had preventive maintenance performed during its operating life in excess of 20 years.
8. PREVIOUS SIMILAR EVENTS:
TK) discharge check valve did not seat properly. The root cause of that event was reported as a lack of preventive maintenance (PM) activities for the SIT discharge check valves sufficient enough to prevent the unacceptable buildup of contaminants on the spherical bearings and hinge arm joint. Corrective actions from that event were to inspect the 14 inch ECCS check valves however SI-134 is a 12 inch check valve and was not included in the scope. In 2005 the 12 inch check valves were incorporated into the inspection schedule and SI-134 was scheduled to be inspected during the Unit 1 refueling outage scheduled for the spring of 2007.