05000382/LER-2009-004

LER-2009-004, Condition prohibited by Technical Specification with Log Power Channel Inoperable

Docket Number
Event date:	07-05-2009
Report date:	12-11-2009
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
LER closed by
IR 05000382/2010005 ()
3822009004R00 - NRC Website

BACKGROUND

The Reactor Protective System (RPS) portion of the Plant Protection System (PPS) [JC] consists of sensors, calculators, logic, and other equipment necessary to monitor selected Nuclear Steam Supply System (NSSS) and containment conditions and to effect reliable and rapid Control Element Assembly (CEA) insertion (reactor trip) if any or a combination of the monitored conditions approach specified safety system settings.

The system's functions are to protect the core and Reactor Coolant System (RCS) [AB] pressure boundary for defined anticipated operational occurrences (AOOs) and also to provide assistance in limiting the consequences for certain postulated accidents. Manual reactor trip is also provided.

Some reactor trip signals are provided with operating bypasses that are required to allow reactor startup.

The High Logarithmic Power (HLP), High Local Power Density (LPD), Low Departure from. Nucleate Boiling Ratio (DNBR), and Low RCS Flow trips are allowed to be bypassed at prescribed Modes or power levels since these trips would otherwise generate an unnecessary trip signal during reactor startup and power increase. The LPD, DNBR, and RCS Flow Low operating bypasses are required to be automatically removed by the respective channel Log Power excore nuclear instrumentation (ENI) [IG] signal at 1E-4% power (increasing) to ensure the channel function is available to trip the reactor.

Technical Specification (TS) 3.3.1 requires a minimum of 3 out of the 4 Log Power trip channels to be OPERABLE when Log Power is below 1E-4% power in Mode 2, and also in Modes 3, 4 and 5 when CEAs are capable of withdrawal. However, the TS does not require the Log Power trip channels to be OPERABLE while in Mode 1 or above 1E-4% power, even though the DNBR, LPD, and RCS Flow Low trip channels with Log Power dependent operating bypasses are required to be OPERABLE in Modes 1 and 2.

TS 3.3.1, Table 3.3-1 note C requires the PPS operating bypasses for LPD, DNBR, and RCS Flow Low be automatically removed when at or above1E-4% power. This automatic function is dependent upon the Log Power output signal andassociated 1E-4% power bistables on the same PPS train. When the Log Power ENI is rendered inoperable, TS Table 3.3-1 note C is not met verbatim for LPD, DNBR, and RCS Flow Low on the same train, even though these operating bypasses are manually defeated by key switch, with their keys removed.

With one or two DNBR, LPD and/or RCS Flow trip channels inoperable, TS 3.3.1 Table 3.3-1 ACTIONs require the inoperable channel(s) to be placed in the bypassed or tripped condition within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />.

EVENT DESCRIPTION

On 8/20/09, the NRC Resident inspector challenged the Waterford 3 application of the TS 3.3.1 associated with the PPS operating bypasses when the Log Power channel (B) was considered inoperable while in Mode 1. At the time, PPS Log Power channel B was considered inoperable; however, DNBR, LPD, and RCS Flow Low were not considered inoperable based on the understanding that PPS Log Power channels were not required in Mode 1 and there was no reliance on Log Power channels for the automatic removal of operating bypasses since these operating bypasses were not being utilized and were secured in the unbypass position with keys removed from the keyswitches. In response, Waterford 3 applied literal TS 3.3.1 Table 3.3-1 note C wording, which required these operating bypasses to be "automatically removed", declared DNBR, LPD, and RCS Flow Low trip channels inoperable, entered TS 3.3.1 ACTION 2, and placed these trip channels in bypass.

Historical applications of TS 3.3.1 were the following:

The channel B PPS Log Power ENI had been declared inoperable 9/1/2008 since the previous reactor startup, due to elevated power indication at very low power levels due to external induced noise while significantly below power levels typical for approaching reactor criticality. Further evaluation resulted in determination that the Log Power channel B had been Operable, but degraded, fully capable of performing the'function to automatically remove the operating bypasses of LPD, DNBR, RCS Flow and Log Power PPS chalinels: The TS 3.3.1 ACTION 2 was exited, and the trip channels were restored.

On 10/15/09, while performing reviews of plant procedures and historical log entries, Waterford 3 plant personnel discovered Technical Specification (TS) 3.3.1 requirements of Table 3.3-1, note C, were not met during past maintenance testing. Specifically, on 7/5/09, during PPS channel C Log Power calibration test, DNBR and LPD trip channels on the associated channel being tested (C) were bypassed, however, the RCS Flow Low trip channel was not placed in bypass or in tripped condition, or otherwise declared inoperable.

On 11/28/07, during the channel (C) calibration test while D channel ENI Log Power was concurrently inoperable, DNBR and LPD trip channels on the associated channel being tested (C) were bypassed. LPD and DNBR was placed in the tripped condition on the associated channel already inoperable (D). However, RCS Flow Low trip channels were not placed in bypass or in tripped condition, or otherwise declared inoperable on either train (C or D). The Operations procedure for Plant Protection System provides requirements for testing Excore/CPC channel while another channel is already inoperable; however, this procedure does not address the RCS Flow Low trip channel.

Compliance was not met for TS 3.3.1 Table 3.3-1 Action 2, Action 3, nor TS 3.0.3.

CAUSAL FACTORS

NRC issuance of Amendment No. 40 (ADAMS Accession No. ML021760266) changed the Technical Specifications by removing the operability and surveillance requirements for Log Power Channels when reactor power is above 1E-4% of rated thermal power. The NRC Safety Evaluation Report explicitly stated that the operation of the Log Power Level Channels at power levels above 1E-4% of rated thermal power (RTP) is recognized to be inappropriate for technical specification requirements since on startup, the trips are bypassed. This led to the philosophy that above 1E-4% RTP with the DNBR, LPD, and RCS Flow trips enabled and able to perform their specified safety functions that a log power issue did not affect DNBR, LPD, and RCS Flow trip operability. The 1E-4% bistable which is actuated by log power has no adverse impact on DNBR, LPD, and RCS Flow trips above 1E-4% once the trips are enabled.

NRC issuance of Amendment No. 145 (ADAMS Accession No. ML0217904720) was intended to clarify the known TS Table 2.2-1 and 3.3-1 verbatim compliance issues associated with TS Table 3.3-1 log power. This change clarified the 1E-4% power level is associated with neutron power and not thermal power. This amendment did not change the NRC Amendment No. 40 philosophy.

The Maintenance Instrumentation procedures for Log Power testing and maintenance address the need to consider bypassing LPD and DNBR trip channel; however, the procedures do not specifically address the need to consider RCS Flow Low trip channel operability. The DNBR and LPD were included, not because their operability were believed to be affected, but as a conservative action because of the integrated circuitry could potentially cause an unnecessary DNBR and LPD bistable trip while performing test or maintenance activities on the associated Log Powel' channel. This requirement in TS Table 3.3-1 note C for operating bypasses to be automatically removed had been interpreted as being satisfied, not requiring the Log Power channel, when these operating bypasses are removed and disabled by their key switches removed.

CORRECTIVE ACTIONS

Operations Standing Order was put in place 8/31/09 to ensure that LPD, DNBR, and RCS Flow is bypassed or placed in trip condition when the associated Log Power channel is rendered inoperable in Modes 1 and 2, regardless if Log Power trip channel is required or if the operating bypasses are utilized.

A TS amendment request was submitted to NRC via Entergy Letter No. W3F1-2009-0045 (ADAMS Accession No. M L092990199) to clarify the TS related requirement of operating bypass to read, "shall be capable of automatic removal whenever the operating bypass is enabled and logarithmic power is above the 1E-4% bistable setpoint.

Changes to the maintenance procedures for Log Power are being finalized to address bypassing or placing RCS Flow Low in trip condition to ensure compliance with TS when the associated Log Power channel is rendered inoperable due to maintenance testing.

Changes to the PPS Operations procedure are being made to address bypassing or placing RCS Flow Low in trip condition to ensure compliance with TS when the associated Log Power channel is rendered inoperable due to maintenance testing while a second Log Power channel is already inoperable.

SAFETY SIGNIFICANCE

Four PPS measurement channels with electrical and physical separation are provided for each parameter used in the direct generation of trip signals. A two-out-of-four coincidence of like trip signals is required to generate a reactor trip signal. The fourth channel is provided as an installed spare and allows bypassing of one channel while maintaining a two-out-of-three logic protection system. In these cases, where RCS Flow channel was not bypassed or placed in trip condition, the operating bypasses were not utilized, but maintained locked in the un-bypassed condition with key removed, such that the trip function was not affected by the associated log power channel being inoperable. Accordingly, there were no safety consequences associated with this condition.

SIMILAR EVENTS

A review of previous events was performed to identify similar licensee events at Waterford 3 reported in the last three years. There were no similar licensee events identified.

ADDITIONAL INFORMATION

Energy industry identification system (EllS) codes are identified in the text within brackets [ ].