05000306/LER-2006-002
| Docket Numberrev | |
| Event date: | |
|---|---|
| Report date: | |
| 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 |
| 3062006002R00 - NRC Website | |
FACILITY NAME (1)� DOCKET NUMBER (2) LER NUMBER (6)� PAGE (3) 06 -- 02 --
EVENT DESCRIPTION
During the Unit 2 refueling outage, Nuclear Management Company, LLC (NMC) staff were inspecting the cables1 for Unit 2 neutron flux monitor2 channels 2N51 and 2N52 in response to an improper splice identified on the Unit 1 cables for neutron flux monitors earlier in 2006 (see Licensee Event Report (LER) 1-06-03). NMC staff found that neither 2N51 nor 2N52 had the required shim in the sleeves for the splice connection on their respective cables. The gap due to the missing shims could have exposed the associated connectors3 to accident environments and is an untested configuration for environmental qualification purposes. As a result of the improper Raychem splice installation, 2N51 was declared inoperable on November 27, 2006 and 2N52 was declared inoperable on November 28, 2006.
EVENT ANALYSIS
Technical Specification Limiting Condition for Operation (LCO) 3.3.3, EM (Event Monitoring) Instrumentation4, Table 3.3.3-1, requires the neutron flux monitors 2N51 and 2N52 to be operable.
LCO 3.3.3, Condition D, requires that if one or more functions with two required channels are inoperable, one channel is to be restored to operable status within seven days. Condition H requires the unit to be in Mode 3 within six hours if Condition D is not met. The potential exists that the subject splices were inoperable from the time they were installed (several years before) and that Unit 2 had been operating in a condition prohibited by Technical Specification LCO 3.3.3. Thus, this condition is reportable per 10 CFR 50.73(a)(2)(i)(B).
Impact on Safety System Functional Failure Performance Indicator The as-found condition did result in inoperability of 2N51 and 2N52. However, these neutron flux monitors are for post-accident indication only and provide no automatic safety function. They are Regulatory Guide 1.97 Type B, Category 1 variables. They are used only to warn the operator with no credit taken for them in any safety analysis. Therefore, this event does not represent a loss of safety function. Consequently, this event is not reportable per 10CFR 50.73(a)(2)(v).
1 EIIS Component Identifier: CAB 2 EIIS Component Identifier: MON 3 EIIS Component Identifier: CON 4 EIIS System Code: IP FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Prairie Island Nuclear Generating Plant Unit 20 05000306 YEAR 06 -- 02 -- 0
SAFETY SIGNIFICANCE
This event did not result in a loss of any automatic safety system function, since the neutron flux monitors are used for post-accident indication only. This event did not affect the health and safety of the public. Therefore, the safety significance of this event is considered minimal.
CAUSE
The cause of this condition is believed to be the same as that reported in LER 1-06-03, where 1N51 and 1N52 were found in the same condition. As noted in LER 1-06-03, historical work orders for 1N51 and 1N52 were reviewed. The work orders removed the Raychem splice and did not specify installation of the shim when reinstalling the splice.
CORRECTIVE ACTION
The subject splices were corrected prior to returning Unit 2 to Mode 2.
Extent of condition was reviewed for the condition reported in LER 1-06-03. This particular connector configuration is unique to the neutron flux monitors.
The technical manual for the neutron flux monitors will be revised to include the Raychem splice installation instructions provided by the vendor.
PREVIOUS SIMILAR EVENTS
LERs for Unit 1 and Unit 2 since 2003 found previous events related to operation or condition prohibited by Technical Specifications, but no other LERs were related to neutron flux monitors or improperly installed splices.