05000397/LER-2005-001
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3972005001R00 - NRC Website | |
SUBMISSION
- YES (If yes, complete 15. EXPECTED SUBMISSION DATE) Id NO DATE - ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) On 2/25/05, Energy Northwest reported (ref: Event Report 41442) a condition at Columbia Generating Station that was discovered while reviewing plant service water (TSW) [KG] system design documents.
Energy Northwest determined that seismic category II TSW piping in the turbine (TG) [NM] and radwaste (RW) [NE] buildings could rupture and drain during a seismic event. Draining of the loop seal in this piping.would xesultinaninoperable secondary.containment (SC) [NG].because two.TSW_system high_ _ point vent valves located within the secondary containment would automatically open resulting in direct communication between SC atmosphere and the TG/RW atmospheres. Such an occurrence would exceed the SC leakage rate assumed in Columbia's accident analysis. To prevent an excessive leakage rate during such an event, one of the two vent valves has been deactivated in the closed position.
Columbia's safety analysis does not postulate a release of radioactive material in excess of Part 100 limits for a Safe Shutdown Earthquake (SSE) that causes SC to become inoperable in this fashion.
Analysis shows that the SSE will not in itself cause a LOCA and it is beyond design and licensing bases to assume a LOCA coincident with a seismic event. In the event that the SSE made SC inoperable, the Technical Specifications (LCO 3.6.4.1.B) require that the plant be in mode 3 in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and in mode 4 in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. Since this is achievable it is reasonable to conclude that, in the event described in the report, plant shutdown can be accomplished without radiological release and within the completion time of the action required by the Technical Specifications. Although safe shutdown of the plant without radiological release is assured post SSE, SC would not be considered operable in the reported condition because seismic requirements were not met. Therefore this condition is reportable pursuant to 10 CFR 50.73(a)(2)(i)(B) because SC was inoperable for a greater period of time than allowed by Technical Specifications.
26158 R2 Plant Condition Plant operating conditions before the event were mode 1 and 100% power.
Event Description
On 2/25/05, Energy Northwest reported (ref: Event Report 41442) a condition at —Columbia-Generating-Station-thatwas-discovered-while reviewing plant service-water (TSW) [KG] system design documents. Energy Northwest determined that seismic category II TSW piping in the turbine (TG) [NM] and radwaste (RW) [NE] buildings could rupture and drain during a seismic event. Draining of the loop seal in this piping would result in an inoperable secondary containment (SC) [NG] because two TSW system high point vent valves located within the secondary containment would automatically open resulting in direct communication between SC atmosphere and the TG/RW atmospheres. Such an occurrence would exceed the SC leakage rate assumed in Columbia's accident analysis.
Immediate Corrective Action To reduce SC leakage rate to within the assumed value during the described event, one of the two TSW high point vent valves was deactivated in the closed position.
Cause
The cause of this deficiency in Columbia's design is that original design engineers did not incorporate an SC boundary within the TSW system that would withstand an SSE.
Further Corrective Action An extent of condition evaluation has determined no other condition exists that would present an additional SC breach pathway that would result in an inoperable SC. Additionally, as detailed in a letter submitted to NRC on September 30, 2004, (G02-04 -170, "License Amendment Request – Alternative Source Term), Energy Northwest has submitted analyses which demonstrate the ability of SC to perform its designed safety function with SC leakage in excess of that presented by the design deficiency described in this report.
Immediate corrective actions are adequate to rectify the condition until a permanent long term design solution is completed.
Assessment of Safety Consequences
There are two principal accidents in Columbia's safety analysis for which SC is credited as a mitigating system. These are the Loss Of Coolant Accident (LOCA) and the Fuel Handling Accident (FHA). The SC performs no active function in response to either of these limiting events, however, its leak tightness is required to ensure that the release of radioactive materials from the primary containment is restricted to those leakage paths and associated leakage rates assumed in the accident analysis, and that fission products entrapped within the SC structure will be treated prior to discharge to the environment.
Columbia's safety analysis does not postulate a release of radioactive material in excess of Part 100 limits for a Safe Shutdown Earthquake (SSE) that causes SC to become inoperable in this fashion. Analysis shows that the SSE will not in itself cause a LOCA and it is beyond design and licensing bases to assume a LOCA coincident with a seismic event. In the event that the SSE made SC inoperable, the Technical Specifications (LCO 3.6.4.1.B) require that the plant be in mode 3 in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and in mode 4 in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. Since this is achievable, it is reasonable to conclude that, in the event previously reported, plant shutdown can be accomplished without radiological release and within the completion time of the action required by :the Technical Specifications. Additionally, historical records show that during the last three years the high point vent valves were not opened during a time when SC was required to be operable.
Although safe shutdown of the plant without radiological release is assured post SSE, SC would not be considered operable in the reported condition because seismic requirements were not met. Therefore this condition is reportable pursuant to 10 CFR 50.73(a)(2)(i)(B) because SC was inoperable for a greater period of time than allowed by Technical Specifications.
There were no safety consequences associated with this condition.
Similar Events No previous events were identified where seismic category II piping outside SC was postulated to affect SC integrity as a result of an SSE.
Energy Industry Identification System Information codes from IEEE Standards 805 1984 and 803-1983 These are noted the first time they are used in the LER text as required by IEEE Standards.
26158 R2