05000423/LER-2005-001

LER-2005-001,

Docket Number
Event date:	02-24-2005
Report date:	08-25-2005
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
4232005001R00 - NRC Website

1. Event Description On 2/24/05, with Unit 3 at 100% power, during the performance of a surveillance test (SP3613A.2-1) on the "A" Hydrogen Recombiner [BB], the system failed leak tightness causing the "A" Hydrogen Recombiner to be declared inoperable. Investigation revealed that a routine maintenance activity conducted on September 7, 2004 required a compression fitting in the system to be disassembled. This fitting was reassembled improperly.

Following the work, a post maintenance test was successfully completed. A surveillance test conducted on February 24, 2005, revealed the compression tubing fitting failure. It is hypothesized that the fitting began to leak when it was stressed (either mechanically or thermally) between the tests. The period when the "A" Hydrogen Recombiner was inoperable exceeded the Technical Specification (TS) Allowed Outage Time (AOT) of 30 days.

Additionally, the "B" Hydrogen Recombiner was taken out of service for routine maintenance on October 20, 2004 and January 11, 2005 causing a loss of safety function. This event/condition is being reported pursuant to 50.73(a)(2)(i)(B), related to operation in a condition prohibited by the Technical Specifications and 50.73(a)(2)(v)(D), related to a condition that could have prevented the fulfillment of the safety function of a system.

2. Cause The apparent cause was poor workmanship on September 7, 2004, resulting in a poorly assembled tubing compression fitting. The threaded connection was galled and not fully tightened onto the ferrule. When the fitting was being reassembled, the galling gave the impression that the fitting was tight when it was not. As a result, further tightening did not compress the fitting as desired.

3. Assessment of Safety Consequences This event is of very low safety significance. An NRC safety evaluation (SE) published September 25, 2003 (68 FR 55416), which identifies the minimal risk significance of Hydrogen Recombiners in large, dry containments, is applicable to Millstone Power Station Unit 3. Additionally, a probabilistic risk assessment (PRA) of the subject condition was performed to determine the impact on core damage and large early release risk.

The Hydrogen Recombiners are designed to prevent accumulation of combustible hydrogen in the Containment generated from radiolysis and chemical reactions following a loss-of-coolant accident (LOCA). The Hydrogen Recombiners at Millstone Power Station Unit 3 are not modeled in the PRA and are not considered a risk­ significant accident mitigating system. The Hydrogen Recombiners are not modeled in the Millstone Unit 3 PRA since: (1) the Hydrogen Recombiners do not prevent core damage, and (2) hydrogen generation in design basis accidents does not realistically challenge Containment integrity. Therefore, the risk to the public from an inoperable Hydrogen Recombiner is insignificant.

Additionally, a Technical Specification (TS) change request was submitted to the NRC on September 8, 2004, to delete the TS requirements associated with the Hydrogen Recombiners and Analyzers. The NRC subsequently issued this license amendment on June 29, 2005.

4. Corrective Action The compression joint was repaired (on February 28, 2005) via AWO M3-05-04144 and a post maintenance acceptance test was satisfactorily performed.

The maintenance department communicated compression fitting fit-up requirements and work practices to minimize the potential for a repeat event of this type. Additional corrective actions were included in the station's corrective action program.

5. Previous Occurrences Internal operating experience was reviewed and did not provide any additional information.

Energy Industry Identification System (EDS) codes are identified in the text as [XX].