05000255/LER-2006-002

LER-2006-002,

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
2552006002R00 - NRC Website

U.S. NUCLEAR REGULATORY COMMISSION Palisades Nuclear Plant 05000-255 2006 -- 002 -- 00

EVENT DESCRIPTION

On March 26, 2006, with the plant in Mode 1, in-place testing of main steam safety valve RV-0710 [RV;SB] determined that the as-found lift pressure did not meet the acceptance band of +/- 3% of setpoint, as specified by Technical Specification Table 3.7.1-1, "Main Steam Safety Valve Lift Settings." The initial as-found lift pressure for RV-0710 was 6.73% above the specified lift setting.

This was the second unsatisfactory as-found lift pressure for a main steam safety valve, as in-place testing on March 25, 2006, had previously determined that RV-0707 had failed to meet the as- found acceptance band, with an initial as-found lift pressure of 6.75% above the specified lift setting.

Technical Specification LCO 3.7.1 requires a minimum of 23 out of 24 main steam safety valves to be operable in Modes 1, 2 and 3. Testing of main steam safety valves is performed one valve at a time, with each valve adjusted if necessary and returned to operable status before proceeding with the testing of another valve. In this manner, a maximum of one valve is known to be inoperable at any time during testing. However, since the cause of the two unsatisfactory as-found lift pressures may have arisen over a period of time, it is assumed that the required number of main steam safety valves was not operable during past plant operation. Therefore, this occurrence is considered reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by the plant's Technical Specifications.

CAUSE OF THE EVENT

The primary cause has been identified as Initial High Lift Phenomenon (IHLP) due to a combination of disc/seat and spindle guide bearing bonding. IHLP is characterized by the as-found lift pressure being 30 psig or higher than a second lift test with no adjustments or corrective measures taken.

Industry experience indicates that in most cases the second lift pressure will meet the initial as- found acceptance band of +/- 3% of setpoint. This was the case with RV-0707 and RV-0710 as both of the valves exhibited a significant reduction in lift pressure on a second test lift which was performed prior to any adjustment, with each valve meeting the as-found acceptance band of +/- 3% of setpoint.

From industry evaluation, IHLP is believed to be associated with in-place testing using an assist device and is not believed to be prevalent in off-site bench testing results or actual in-plant pressurization events.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Palisades Nuclear Plant 05000-255 2006 -- 002 -- 00

CORRECTIVE ACTIONS

Final lift pressures were established for both valves within the acceptance band of +1- 1% of setpoint. RV-0707 required adjustment to achieve the final acceptance band, while RV-0710 met the acceptance band without further adjustment.

An additional 6 main steam safety valves were removed and tested at an off-site testing facility. All 6 valves met the as-found lift pressure acceptance band of +1- 3% of setpoint on their initial lift test.

The spindle guide bearing clearances have been increased in 8 of the valves to reduce the potential for spindle guide bearing bonding. The remaining valves are planned to be similarly modified in future outages on an on-going basis.

SAFETY SIGNIFICANCE

The safety significance of this occurrence is considered minimal. A bounding analysis has been performed which demonstrates that design limits would not have been challenged with the as-found lift pressures for RV-0707 and RV-0710.

PREVIOUS SIMILAR EVENTS

Palisades Licensee Event Report 04-003, "Main Steam Safety Valves Exceeded Lift Setpoint Acceptance Band" Palisades Licensee Event Report 86-004, "Main Steam Relief Valves Fail To Meet 'As Found' Pressure Acceptance Criteria" Palisades Licensee Event Report 83-074, "Valves Failed To Meet 'As Found' Acceptance Criteria" Palisades Licensee Event Report 78-002, (not titled)