05000321/LER-2009-002
| Docket Numberyear Sequential Revmonth Day Year Month Day Yearnumber No. 05000 | |
| Event date: | 05-04-2009 |
|---|---|
| Report date: | 06-18-2009 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3212009002R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor Energy Industry Identification System codes appear in the text as (EIIS Code XX).
DESCRIPTION OF EVENT
On May 4, 2009 at 851 EDT, Unit 1 was in hot shutdown, Mode 3. Stroke time testing of the inboard Main Steam Line Isolation Valve (MSIV) (EIIS Code SB), 1B21-F022B, failed to meet both the procedural minimum limit, and the Technical Specification minimum limit of greater than or equal to three seconds. The valve closed in 1.53 seconds. A Work Order was initiated to identify and repair the cause of the failure. Once the failure mechanism was was performed. This inspection determined that a similar condition does not exist on any of the other MSIV's.
CAUSE OF EVENT
This event was caused by the loss of oil in the actuator due to a leak at a fitting on the actuator. The oil provides a dampening effect for the valve closure and the absence of oil allowed the valve to close faster than desired. The oil leak originated from a 3/4 inch NPT port on the dashpot cylinder. The cause of the leak is attributed to degradation of the Teflon tape applied as a thread sealant.
REPORTABILITY ANALYSIS AND SAFETY ASSESSMENT
This event is reportable per 10 CFR 50.73 (a)(2)(i)(B) because a condition prohibited by the Technical Specification existed. Specifically, the 'B' inboard MSIV closed faster than the limit established by the plant's Technical Specifications.
The MSIV's have a specific stoke time listed in the Technical Specification. This acceptable closing time range is intended to perform a duel function. First to close and perform a primary containment (EIIS Code NH) isolation function with a maximum closure time which limits the release of radiological products. Second the associated minimum closure time reduces vessel peak pressure and protects against fuel damage. In this event one MSIV closed faster than the minimum time stated in the Technical Specification. An evaluation of the effect of this quicker valve response was performed and is summarized below.
Hatch Core Analysis has performed an evaluation of the MSIV closure event for Hatch-1 Cycle 24 in which one MSIV closes faster than the minimum allowable time required by Technical Specification (TS) SR 3.6.1.3.6. The approach taken in this evaluation was to model one MSIV closing in the as-measured time of 1.53 seconds and the remaining valves closing in the minimum allowable Technical Specification time of 3.0 seconds, and then run applicable reload licensing calculations.
function of valve area versus time after the closure signal was weighted to reflect one valve closing faster than the remaining valves.
The MSIV fast closure with direct scram on valve position (MSIVD) and the MSIV fast closure with flux scram (MSIVF) events were analyzed. The assumptions listed below are common to both the MSIVD and MSIVF results.
1. 1 MSIV closes in 1.53 seconds and the remaining valves close in 3.0 seconds.
2. The smallest throat diameter (4.905 in) was used for all SRVs.
3. A conservative axial power shape was used for all test cases. This assumption results in a top-peaked power shape at the end of cycle which retards the effect of the reactor scram.
4. The reactor is operating at either 105% of rated core flow, which is the maximum allowable core flow at rated power, or at 92.9% of rated core flow, which is the minimum licensed core flow at rated power.
5. 1 of the 11 SRVs is assumed to be out of service.
The MSIVD event with all MSIVs closing in 3 seconds is classified as a non-limiting Anticipated Operational Occurrence (A00) in the FSAR, but it was analyzed to verify it did not become a limiting event due to the faster MSIV closure time. The MSIVD results presented in this document are based on the following additional assumptions:
1. The initial reactor dome pressure is at the nominal, rated value of 1045 psig.
2. The MSIV closure event occurs at 100% of rated thermal power.
3. All control rods insert at the COLR Option B scram speeds. Note: These scram speeds have always been met for Plant Hatch.
4. Credit is taken for the direct scram on the MSIV safety-grade valve position switches.
The MSIVF event is used to evaluate compliance with the 1325 psig Reactor Coolant System (El IS Code AD) Pressure Safety Limit (Technical Specification 2.1.2) during the worst anticipated reactor vessel over pressurization event. The Tech Spec Safety Limit is evaluated at the top of the reactor vessel in the steam dome and the value is conservatively selected to ensure the 1375 psig ASME Boiler and Pressure Vessel Code overpressure limit is not violated at the bottom of the reactor vessel. The following additional assumptions are made for the MSIVF event:
1. The direct scram from the valve position switches fails; therefore, the scram is delayed until the APRM system's high neutron flux scram signal is reached.
2. The initial reactor dome pressure is at the maximum value of 1058 psig as specified in Tech Spec SR 3.4.10.1.
3. The MSIV closure event occurs at a reactor power level (100.5%) which is slightly greater than rated power at the very end of cycle when there are no control rods in the Specified acceptable fuel design limits (SAFDLs) were checked for the MSIVD event since it is classified as an A00 in the Plant Hatch FSAR. The ACPR results were not calculated by ODYN for the MSIVD cases because the peak fuel surface heat flux does not rise above its initial value. Therefore, there was no effect on the Operating Limit MCPR values. Also, as a result of no increase in heat flux, the fuel rod thermal and mechanical overpowers were insignificant and well below the allowable limits.
The SAFDLs are not applicable to the MSIVF event because it is classified as a special event that is used to conservatively evaluate compliance with the ASME Boiler & Pressure Vessel over pressurization limit for the reactor pressure vessel.
Based on this analysis, the faster (1.53 sec) closure of one MSIV would have no discernable affect on the response of the fuel or peak pressure relative to the 3 second TS values. In fact, the peak pressures of the MSIVF cases were only marginally higher than the results of the Hatch-1 Cycle 24 reload licensing analysis (Table 2).
Table 1 — MSIV Transient Results Peak PeakFlow Peak Heat OLMCPR OLMCPR Dome Vessel MOEvent Conditio TOPFlux 13 A Pressure Pressure P n _ % initial ref (psig) (psig) MSIVD ICF 100.03 no effect no effect 1205.1 1244.9 0.0 7.6 MSIVD _ MELLLA 100.02 no effect no effect 1201.0 1236.3 0.2 0.2 MSIVF ICF 128.92 N/A N/A 1292.9 1329.3 N/A N/A MSIVF _ MELLLA 127.13 N/A N/A 1293.0 1326.2 N/A N/A OLMCPR : Operating Limit Minimum Critical Power Ratio (Option NB Scram Speeds) TOP�: Thermal Overpower MOP : Mechanical Overpower use of the Loctite 5772 sealant. In addition to improve reliability of all threaded fittings for the MSIV actuators the procedure has been revised to require cleaning and the application of new Loctite 5772 sealant any time threaded connections are removed from the actuator.
ADDITIONAL INFORMATION
Other Systems Affected: None Failed Components Information:
Master Parts List Number: 1B21-F022B EIIS System Code: SB Manufacturer: Atwood & Morrill Co. Reportable to EPIX: Yes Model Number: VPF279221 Root Cause Code: D Type: Valve, Shutoff EIIS Component Code: SHV Manufacturer Code: A585 Commitment Information: This report does not create any new permanent licensing commitments.
Previous Similar Events:
There are no similar events within the past two years in which an MSIV stroke time tested outside of the time specified in the Technical Specifications.