05000271/LER-2007-001
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No N/A | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2712007001R00 - NRC Website | |
DESCRIPTION
On 04/06/2007, with the reactor at full power, Instrument & Control (I&C) Technicians were performing routine surveillance procedure OP 4361, High Pressure Coolant Injection (HPCI) System (EIIS = BQ) Isolation NB Logic Functional/Calibration Test. During performance of the surveillance, the as-found time delay for the "A" channel isolation logic relay (EIIS = RLY2), 23A-K49, was found to be actuating at 36.5 minutes. The required set-point is 30.0 minutes +/- 2.5 minutes (27.5 to 32.5 minutes) with an allowable as-found tolerance of +/- 4.0 minutes (26.0 to 34.0 minutes). The as-found value for this relay was greater than the allowable per the Technical Specification Table 3.2.2 requirement of less than or equal to 35 minutes. Three of the last four surveillances, performed once per operating cycle, also had as-found settings that were found to have exceeded the Technical Specification requirement. Therefore, due to the multiple test failures, this condition is being reported pursuant to 10CFR50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications.
The HPCI System auto-isolation instrumentation logic is designed to provide for isolation and shutdown of the HPCI System if leaks or ruptures of the steam lines occur. A steam leak is indicated by local temperature increases near the HPCI equipment or steam piping. A rupture of the steam piping would result in abnormally high steam line flows.
Therefore, the parameters monitored by the steam line break logic are: HPCI equipment space high temperature, main steam tunnel high temperature, and HPCI steam line high flow. Two separate auto-isolation logics are provided, both of which are tripped by the same parameters.
The subject relay affects the main steam tunnel high temperature HPCI time delay isolation logic only. Four temperature switches mounted near the HPCI steam supply piping in the main steam tunnel provide monitoring for this function. When the set-point is reached, each of these switches sends a signal to two identical one-out-of-two-taken-twice logics. Following a 30 minute time delay, as provided for by the HPCI 23A-K49 (A channel) and HPCI 23A-K48 (B channel) time delay relays, each logic sends a signal to one of the two auto-isolation logics, generating an isolation signal. The high temperature isolation signals for the HPCI steam lines in the steam tunnel employ timers (time delay relay) to allow the operator time to identify the leak and to take appropriate action.
The timers prevent immediate isolation of the HPCI System upon indication of a high temperature in the steam tunnel, thus providing core cooling and makeup capabilities until the valves close or until the leak is identified.
As part of the root cause analysis, an extent of condition review identified that the Reactor Core Isolation Cooling (RCIC) system had similar time delay relays. The data reviewed for the HPCI 23A-K48 relay and the RCIC relays revealed that since 1998, all relays tests were within the Technical Specification Requirements.
CAUSE
Root Cause:
The root cause of this condition was that the surveillance procedure was less than adequate. Specifically, prior to calibration methodology changes implemented during operation Cycle 25, based on historical performance, the procedure did not account for relevant manufacturer information regarding the unique characteristic of a long time delay'relay. After discussing this condition with the manufacturer, a recommendation was provided to implement a "cold" relay check and adjustment when necessary. A minimum two hour cool down period was also recommended following any adjustment and subsequent recheck.
Contributing Cause:
Design documentation provided by the manufacturer was determined to be inadequate. Specifically, relevant manufacturer's information presented in multiple documents associated with the calibration methodology for the same model relay was fragmented, conflicting and unclear.
ASSESSMENT OF SAFETY CONSEQUENCES
The HPCI system is designed to supply high pressure coolant to the reactor core, to prevent excessive fuel clad temperatures, in the event of a small-break loss of coolant accident (LOCA) that does not result in a rapid depressurization of the reactor vessel, and can supply reactor makeup during periods when the Feedwater System is isolated or otherwise unavailable. The condition described within this LER would not have prevented the HPCI system from performing the design safety functions listed above at any time.
The "B" channel HPCI isolation logic relay (23A-K48) successfully passed all calibration tests performed during the period when the "A" channel relay deficiencies existed. Due to the redundant design of the isolation logic, the HPCI Isolation Trip System would have ensured that a timely HPCI system isolation occurred if required, thereby maintaining the design function of the system. Because the "B" Trip System was fully operable, the HPCI system would have isolated within the Technical Specification limit of 35 minutes in the event of a main steam tunnel high temperature condition.
The delayed isolation safety analysis that evaluates the impact on other safety related' components assumes that the isolation occurs in 40 minutes. Therefore, since the actual isolation times are bounded by the time assumed in the analysis, these events did not have any increase in risk to the health and safety of the public.
CORRECTIVE ACTIONS
Immediate Actions
1)The condition described by this LER was entered into the Entergy Corrective Action Program and promptly shared with the Entergy Fleet and subsequently shared with the nuclear industry on 06/01/2007 through the Operating Experience Program processes.
2) Checked the HPCI 23A-K49 relay using improved methodology. Results were satisfactory.
3) Reviewed the manufacturer's (Agastat) literature for applicable models in use at VY to determine if similar information may have been overlooked as a result of a complex presentation for information regarding relay calibration methodology within the manufacturer's literature that may have impacted other VY components and/or procedures. No additional issues were identified Previously Implemented Actions 1)Revised the surveillance procedure for the HPCI isolation time delay relays (23A-K48 and 23A-K49) to implement the improved methodology in accordance with manufacturer recommendations during operation cycle 25.
2) Revised the surveillance procedure for the RCIC system isolation time delay relays (13A-K41 and 13A-K42) to implement the improved methodology in accordance with manufacturer recommendations during operation cycle 25.
Long Term Action Perform an additional check of the HPCI relay (23A-K49) during operation cycle 26 to confirm that actions taken have resolved the condition.
ADDITIONAL INFORMATION
No similar events have occurred at VY within the past ten years.