05000400/LER-2007-004
| Docket Number Sequential Revmonth Day Year Year Month Day Year N/A 05000Number No. | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4002007004R00 - NRC Website | |
Energy Industry Identification System (EIIS) codes are identified in the text within brackets [ ].
I. DESCRIPTION OF EVENT
At 18:00 on October 19, 2007, while replacing connector assemblies in response to a Nuclear Industry Advisory (10 CFR Part 21) issued by PRIME Measurements LLC and Nuclear Regulatory Commission (NRC) Information Notice (IN) 2006-14, Harris Nuclear Plant (HNP) personnel identified bare conductors on the field side pigtail at the epoxy interface of the connector assembly associated with Barton transmitter LT-487 [LT], Steam Generator 'B' wide range level indication [JB]. At the time of the event, the plant was shutdown in mode 5 with a temperature band of 185-195 degrees and a pressure band of 325-350 psig. There was no other inoperable equipment that contributed to this event, and Barton transmitter LT-487 has not experienced a failure to date.
PRIME Measurements LLC ("PRIME"), formally Barton Instrument Systems & ITT Barton, manufactured model 763, 763A and 764 pressure and pressure differential transmitters that included an electrical connector assembly, welded to the bottom of the electronics housing. The external lead wires enter the electronics enclosure through a hermetic seal called a connector assembly. The external lead wires are soldered to the glass sealed pins of the hermetic seal. Epoxy potting is used to structurally support the soldered wire connections and establish a seal to protect the solder connections from shorting, which could be caused by an electrically conductive accident environment that results from an Environmental Qualification (EQ) Design Basis Accident that includes a pressure spike and steam.
PRIME identified that their model number 763, 763A and 764 transmitter electrical assembly pigtails (field side) could be configured with bare conductor exposed at the connector assembly wire/epoxy interface. This condition constitutes an unqualified (untested) configuration that could result in a conductor to conductor or conductor to ground short when exposed to a moisture environment. Upon identification of the potential for this unqualified configuration, PRIME issued an NIA to the nuclear industry and the NRC issued IN 2006-14.
Nuclear Condition Reports were written at HNP to investigate, evaluate and correct any unqualified connector assemblies. Engineering Change (EC) 66510 was developed to resolve the 10 CFR Part 21 issue concerning the defective Barton model transmitters assemblies and replace those located in the Reactor Containment Building (RCB) [NH]. Fourteen out of the scheduled eighteen transmitter connector assemblies were replaced during RFO-14. Only one of the fourteen replaced transmitters, LT-487, had this exposed wiring defect. The four remaining transmitters will be replaced at the next opportunity.
This is being reported as a condition prohibited by Technical Specifications in accordance with 10 CFR 50.73.
II. CAUSE OF EVENT
The cause of this issue was a defect in the manufacturing process of the transmitter connector assembly that was identified via the 10 CFR Part 21 process and impacts several nuclear utilities. The degradation was due to a fabrication deficiency at the vendor site. Specifically, the transmitter conductors were not imbedded sufficiently into the epoxy.
III. SAFETY SIGNIFICANCE
This event is not significant because the Steam Generator 'B' wide range level transmitter did. not fail. This event is reportable based on the fact that the transmitter was installed during initial plant construction and the HNP Technical Specifications require any inoperable wide range Steam Generator level transmitter channel to be restored to operable status within forty eight hours. As such, this issue is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications.
Actual Safety Consequences:
This condition is not considered a significant degradation of plant safety since there was not a Loss of Coolant Accident requiring Post Accident Monitoring [IP] of equipment during the time frame the transmitter connector assembly was installed.
Potential Safety Consequences:
This condition does not pose a significant degradation to plant safety. The wide range Post Accident Monitoring indication is defined as a Regulatory Guide (RG) 1.97, type 'D' variable. HNP specific RG 1.97 commitments state that the specific LT-487 design function may be supplemented by the redundant narrow range transmitters on Steam Generator 'B'. HNP has replaced all the connector assemblies associated with all Steam Generator 'B' narrow range transmitters. No bare conductors were identified on the removed connectors. Therefore, the Steam Generator 'B' narrow range transmitters were available as supplemental indication. The HNP specific RG 1.97 commitments also state that additional diversity to the LT-487 indication is available by use of steam line pressure and auxiliary water flow indications. Therefore, in the event that LT-487 indication was lost or provided inaccurate indication, plant operators would have had the stated supplemental / diverse means necessary to allow them to take any actions appropriate to maintain the plant in a safe condition.
IV. PREVIOUS SIMILAR EVENTS
This condition is historical and a one-time event identified via a 10 CFR Part 21 notification.
V. CORRECTIVE ACTIONS
The root cause of this issue is a defect in the manufacturing process of the transmitter connector assembly.
This was identified via the 10 CFR Part 21 process and impacts several nuclear utilities.
Actions taken at the HNP to mitigate the impact of the faulty manufacturing process included replacing fourteen of the eighteen identified faulty connectors during RFO-14. Deferral of the four remaining transmitters to RFO- 15 is not considered significant based on successful modification of fourteen transmitters. A minimum of three transmitters on each steam generator have been modified and all three pressurizer transmitters have been modified. Therefore, it is reasonable to expect that all Reactor trip or ESF actuations that are provided by the transmitters will be available during post accident conditions.
VI. COMMITMENTS
This document contains no new regulatory commitments.