05000454/LER-2014-002
| Byron Station, Unit 1 | |
| Event date: | 02-19-2014 |
|---|---|
| Report date: | 04-21-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4542014002R00 - NRC Website | |
A. Plant Condition Prior to Event Event Date/Time: February 19, 2014 / 1200 hours0.0139 days <br />0.333 hours <br />0.00198 weeks <br />4.566e-4 months <br /> CST Unit 1 - Mode 1 - Power Operations, Reactor Power 100 percent Unit 2 - Mode 1 - Power Operations, Reactor Power 100 percent Reactor Coolant System [AB]: Normal operating temperature and pressure.
B. Description of Event
On February 19, 2014, it was determined that the Byron Station has not complied with Technical Specifications (TS) 3.4.3, °RCS Pressure and Temperature (P/T) Limits," between March 2011 and October 2013, during start-up of the plant following plant refueling outages. Byron TS 3.4.3 Limiting Condition for Operation (LCO) 3.4.3 states that °RCS pressure, RCS temperature, and RCS heatup and cooldown rates shall be maintained within the limits specified in the PTLR.° The applicability is "At all times". At Byron Station, the PTLR is contained in the Technical Requirements Manual (TRM) and not in the TS.
During previous Reactor Coolant System (RCS) vacuum fill operations at Byron Station Unit 1 and Unit 2, RCS pressure exceeded the Pressure and Temperature Limits Report (PTLR) P/T curve lower bound in that the P/T curve does not indicate a limit below 0 psig. The Byron PTLR for both units contains pa curves providing acceptable regions of reactor coolant system (RCS) operation. The lower pressure bound on the P/T curves is zero pounds per square inch gauge (psig) pressure. During RCS vacuum fill and vent operations, as allowed by Byron operating procedures, portions of the RCS have experienced vacuum conditions of up to negative 14 psig. This is outside the lower bound of the P/T curve and is not in compliance with the TS 3.4.3 requirement.
C. Cause of Event
The cause of operation outside of the P/T curve limits is the application of an inadequate operating procedure that allowed the P/T lower pressure bound to be exceeded during vacuum fill operations.
Contributing to this was an inadequate 10 CFR 50.59 evaluation performed in support of a 1998 revision to the same operating procedure to allow vacuum refill of the RCS.
D. Safety Significance
Westinghouse Engineering analysis concluded that vacuum refill of the RCS in Mode 5 does not violate the 10 CFR 50, Appendix G pressure and temperature requirements for the Reactor Vessel (RV). Furthermore, the NRC-approved methodologies contained in Westinghouse WCAP-14040 do not preclude the PIT limits from being revised to include a pressure less than 0 psig. Therefore, the PTLR can be revised to change the lowest pressure value in the P/T limit curve figures and data tables from 0 psig to either 0 psia or -14.7 psig (without considering instrument uncertainties) due to vacuum refill of the RCS. Therefore, the safety significance of this issue is considered low.
E. Corrective Actions
The Byron Unit 1 and Unit 2 PTLR documents have been revised and implemented in support of the Byron Unit 1 spring 2014 refueling outage and the Byron Unit 2 fall 2014 refueling outage.
F. Previous Occurrences
There have been no previous occurrences of this nature in the previous three years.
Byron Station, Unit 1 05000454