05000445/LER-2014-002
| Comanche Peak Nuclear Power Plant (Cpnpp) Unit 1 | |
| Event date: | 02-04-2014 |
|---|---|
| Report date: | 04-03-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4452014002R00 - NRC Website | |
I. DESCRIPTION OF THE REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION:
During the past 3 years, a vacuum was drawn on the Unit 1 RCS during 1RF15 and 1RF16 using procedure SOP-101A, "Reactor Coolant System" and on the Unit 2 RCS during 2RF12 and 2RF13 using procedure SOP-101B, "Reactor Coolant System." LCO 3.4.3 requires the RCS pressure, temperature, and heatup and cooldown rates be maintained within the limits specified in the PTLR. The Applicability for LCO 3.4.3 is "At all times." The RCS heatup and cooldown limitations in the PTLR only specify a pressure to 0 psig.
Since the Applicability of TS 3.4.3 is "At all times," and the PTLR does not provide curves associated with a vacuum in the RCS, the plant was not operating in accordance with the TSs. Required Action C.1 requires initiating action to restore parameter(s) to within limits with a Completion Time of "Immediately." TS 1.3, "Completion Times," defines "Immediately" as "...pursued without delay and in a controlled manner." Action was not taken to restore parameter(s) immediately.
The events that occurred during 1RF15,1RF16, 2RF12, and 2RF13 are therefore reportable as an operation or condition prohibited by Technical Specifications pursuant to 10CFR50.73(a)(2)(i)(B).
B. PLANT CONDITION PRIOR TO EVENT:
At the time of discovery, both units were in Mode 1 (Power Operation) at 100 percent power.
C. STATUS OF STRUCTURES, SYSTEMS, OR COMPONENTS THAT WERE INOPERABLE AT THE
START OF THE EVENT AND THAT CONTRIBUTED TO THE EVENT
There were no structures, components or systems (SSC) that were inoperable at the start of the event and that contributed to the event.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES:
On February 4, 2014, Luminant Power recognized Operating Experience at another station to be potentially applicable to Comanche Peak Nuclear Power Plant (CPNPP). An NRC inspection report described a failure to comply with reactor coolant system (RCS) Pressure/Temperature (P/T) Limits when RCS pressure decreases below 0 pounds per square inch gauge (PSIG). At the time of discovery, CPNPP's Pressure Temperature Limit Report (PTLR) only described pressures equal to or greater than 0 PSIG. However, since early 1996, CPNPP's analyses and procedures allowed drawing a vacuum during RCS refill following refuelings. Therefore, Luminant Power is conservatively reporting RCS pressure below 0 PSIG as a violation of Technical Specification 3.4.3 "RCS Pressure and Temperature (P/T) Limits.
The coordination of the change in RCS operating conditions was less than adequate, in that the associated affected documents were not revised as a result of failing to correctly identify the documents and/or involve all applicable parties, as well as the subtlety of the PTLR pressure value discrepancy. The apparent mental model by licensed operations personnel was not aligned with the literal applicability of the PTLR curves, in that the curves are applicable during RCS vacuum fill conditions, and not limited to only heat-up, cool-down, and inservice leak/hydrostatic testing conditions. Luminant Power interpreted the PTLR to only apply to RCS pressure conditions above atmospheric pressure, and therefore did not consider it in conflict with the adoption of the vacuum refill analysis and procedure. Corrective actions included revising the PTLR to specify negative 14.7 pounds per square inch gage (PSIG) as the lower limit. The explicit PTLR compliance error during vacuum refill did not adversely affect the health and safety of the public or station personnel.
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE, OR PROCEDURAL
PERSONNEL ERROR
In accordance with procedure STA-426, "Industry Operating Experience Program" Luminant Power personnel screen various industry operating experience (OE) sources. This event was identified as a result of an informal review of NRC inspection reports by the NSSS Systems Manager. The NSSS Systems Manager recognized the generic implications of a unique violation in NRC Inspection Report 05000440/2013007 dated January 3, 2014, and created Condition Report CR-2014-000960.
During the last three years, RCS pressure was reduced below 0 PSIG during the vacuum refill process in CPNPP Units 1 and 2. Specifically, RCS pressure was reduced below 0 PSIG during 2RF12, 1RF15, 2RF13, and 1RF16.
II. COMPONENT OR SYSTEM FAILURES
A. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE
Not applicable - No component failures were identified during this event.
B. FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED COMPONENT
Not applicable - No component failures were identified during this event.
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY FAILURE OF COMPONENTS
WITH MULTIPLE FUNCTIONS
Not applicable - No component failures were identified during this event.
D. FAILED COMPONENT INFORMATION
Not applicable - No component failures were identified during this event.
III. ANALYSIS OF THE EVENT
A. SAFETY SYSTEM RESPONSES THAT OCCURRED
Not applicable - No safety system responses occurred as a result of this event.
B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY
Not applicable
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT
The design change implementing vacuum refill evaluated the physical effects of the sub-atmospheric RCS pressure to not adversely impact the reactor vessel and Reactor Coolant Pressure Boundary (RCPB) structural integrity. Vacuum refill was implemented under 10 CFR 50.59, which relied upon Westinghouse WCAP-14040.
The NRC Safety Evaluations are contained in Revision 2 and Revision 4 of the topical report approving them as acceptable P/T limits development methodologies.
CPNPP Operating Procedures SOP-101A, "Reactor Coolant System", for Unit 1, and SOP-101B, "Reactor Coolant System", for Unit 2, ensure sufficient RCS pressure to assure adequate net positive suction head (NPSH) for the RHR system, over an operating band of temperatures, pressures, and RHR flows.
Therefore, the explicit PTLR compliance error during vacuum refill did not adversely affect the health and safety of the public or station personnel.
IV. CAUSE OF THE EVENT
The coordination of change in RCS operating conditions was less than adequate, in that the associated affected documents were not revised as a result of failing to correctly identify the documents and/or involve all applicable parties, as well as the subtlety of the PTLR pressure value discrepancy. Luminant Power interpreted the PTLR to only apply to RCS pressure conditions above atmospheric pressure, and therefore did not consider it in conflict with the adoption of the vacuum refill analysis and procedure.
V. CORRECTIVE ACTIONS
On April 1, 2014, the Comanche Peak Nuclear Power Plant Pressure and Temperature Limits Report, Revision 3 became effective, which includes figures showing acceptable operation down to -14.7 PSIG.
VI. PREVIOUS SIMILAR EVENTS
There have been no previous similar reportable events at CPNPP in the last three years.
Comanche Peak Nuclear Power Plant