05000369/LER-2013-002
| Mcguire Nuclear Station, Unit 1 | |
| Event date: | 06-13-2013 |
|---|---|
| Report date: | 8-12-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3692013002R00 - NRC Website | |
BACKGROUND
The following information is provided to assist readers in understanding the event described in this LER.
Applicable Energy Industry Identification [EllS] system and component codes are enclosed within brackets.
McGuire Nuclear Station (MNS) unique system and component identifiers are contained within parentheses.
Auxiliary Feedwater System [BA](CA):
The purpose of the CA system is to provide an emergency feedwater supply to the Steam Generators [SG](SG) if the respective Unit's Condensate and Feedwater System [SJ](CF) is not available. The CA system is capable of transferring fission product decay heat and other residual heat loads from the Reactor Coolant System [AB] (NC) to a heat sink during both normal operation and accident conditions. Each Unit's CA system contains two Motor Driven pumps [P] (MDCAP) and one Turbine Driven Pump [P](TDCAP). The normal suction source of water for the MDCAPs and TDCAP is the CA Storage Tank [TK](CAST). The Nuclear Service Water System [BI](RN) provides the safety related assured suction source of water for the CA pumps when the normal suction supply from the CAST is not available. Pressure switch [PS] (PS) 1CAPS5390 actuates on a Unit 1 TDCAP suction pressure - low condition to align the safety related assured RN water source to this pump. When calibrating the actuation setpoint for this PS, compensation is made for differences between the reference elevation and the PS's mounting elevation and sensing line tap elevation. The applicable Technical Specification (TS) requirements are specified in TS 3.7.5, "Auxiliary Feedwater (AFW) System".
Engineered Safety Feature Actuation System Instrumentation [JE] (ESFAS):
The ESFAS system senses selected Unit parameters, determines whether or not predetermined safety limits are being exceeded and, if they are, sends actuation signals to the appropriate engineered safety features components whose aggregate function best serves the requirements of the accident. The applicable TS requirements are specified in TS 3.3.2, "Engineered Safety Feature Actuation System (ESFAS) Instrumentation".
TS Table 3.3.2-1, Function 6f, specifies the Nominal Trip Setpoint (3.5 psig) and Allowable Value (> 3 psig) for the CA pumps suction transfer to the safety related assured RN water source on suction pressure — low. Function 6f also indicates, for the TDCAP, four instrumentation channels are required to ensure suction transfer to the safety related assured water source. 1CAPS5390 is one of these required instrumentation channels.
EVENT DESCRIPTION
In August 1993, MNS implemented a modification which physically relocated Unit 1 PS 1CAPS5390. Prior to this relocation, the water leg applied in the calibration procedure for this PS was consistent with the actual water leg value in the field.
Following relocation, 1CAPS5390 was calibrated on September 2, 1993. The water leg applied in the calibration procedure was the value used prior to relocation of the PS. This value did not reflect the actual water leg value in the field.
On May 29, 2013, during a review of CA system PS setpoints, it was identified that the calibration procedure for 1CAPS5390 utilized an incorrect water leg value. Subsequent to this, 1CAPS5390 was declared inoperable pending further evaluation and the applicable Required Actions of TS 3.3.2 were implemented.
On May 30, 2013, 1CAPS5390 was calibrated using a water leg value consistent with the actual water leg value in the field.
On May 30, 2013, 1CAPS5390 was returned to an OPERABLE status.
REPORTABILITY DETERMINATION
On June 13, 2013, an evaluation concluded that the water leg error identified on May 29, 2013 effectively resulted in a 1CAPS5390 Nominal Trip Setpoint of 2.36 psig. This is a non-conservative trip setting with respect to the Nominal Trip Setpoint (3.5 psig) and Allowable Value Limit 3 psig) specified in TS Table 3.3.2-1, Function 6f.
Therefore, 1CAPS5390 was inoperable from September 2, 1993 until it was returned to an OPERABLE status on May 30, 2013 following calibration using the correct water leg value.
TS Table 3.2.2-1, function 6f, indicates, for the TDCAP, four instrumentation channels are required to ensure suction transfer to the safety related assured water source. 1CAPS5390 is one of these required instrumentation channels. With one or more channels of Auxiliary Feedwater Suction Pressure-Low inoperable in a Mode of Applicability, the applicable Required Actions of TS 3.3.2 require that the channel(s) be returned to an operable status or the associated CA pumps be declared inoperable within the specified Completion Times. While in a Mode of Applicability, TS 3.7.5 provides the Required Actions and specified Completion Times for an inoperable CA pump(s). If these TS actions and completion times are not met, additional Required Actions are specified by TSs. Since the inoperable condition with 1CAPS5390 was unknown, the applicable TS Required Actions were not completed within the specified Completion Times during the period of time this PS was inoperable while in a Mode of Applicability. This represented an operation or condition prohibited by TSs which is reportable to the NRC as per the requirements of 10 CFR 50.73(a)(2)(i)(B).
CAUSAL FACTORS
1. Investigation determined that program weaknesses exist for measuring and calculating water leg setpoint corrections.
MNS Water Leg Data Program procedural controls are not in place to ensure guidance is provided to individuals concerning calculation of water legs.
CORRECTIVE ACTIONS
Immediate:
1. Implemented a modification to correct the 1CAPS5390 setpoint based on actual waterleg reference values for this PS.
Completed:
1. Performed an extent of condition review with respect to operability of other TS related instruments.
Within the scope of this review, no additional items were found that resulted in inoperability of TS related instruments.
Planned:
1. Revise and formalize the MNS program for measuring and calculating water leg setpoint corrections and, after revision, revise applicable procedures as needed.
SAFETY ANALYSIS
Past as-found/as-left 1CAPS5390 calibration data was reviewed in conjunction with a review of analytical limits, TS values, and uncertainties associated with the 1CAPS5390 loop. This analysis determined that, worse case, the applicable analytical limits were not exceeded and therefore, with the subject condition, 1CAPS5390 would still have actuated and aligned the safety related assured water source to the Unit 1 TDCAP in time to support the pump's safety function. Therefore, this event was not safety significant.
ADDITIONAL INFORMATION
To determine if this event was recurring, a search of the McGuire Problem Identification Process (PIP) database was conducted for a time period covering five years prior to the date of this event. For those applicable events with a corresponding cause code, a thorough review concluded this was not a recurring event.