05000483/LER-2006-001
| Docket Numbersequential Revmonth Day Year Year Month Day Year None Number No. | |
| Event date: | 11-14-2005 |
|---|---|
| Report date: | 03-14-2006 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material |
| 4832006001R00 - NRC Website | |
I. DESCRIPTION OF THE REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION
This event is being reported criterion:
10CFR50.73(a)(2)(i)(B), an operation or condition prohibited by Technical Specifications.
B
- PLANT OPERATING CONDITIONS PRIOR TO THE EVENT Plant was in MODE 4 with temperature > 275 degrees F. at the time the stroke test was performed. The plant was in Mode 1 at the time the determination was made.
TS 3.4.12, Cold Overpressure Mitigating System (CONS) is applicable in Mode 4 with RCS temperature less than or equal to 275F, Mode 5 and Mode 6 with the head on the reactor vessel.
C
- STATUS OF STRUCTURES, SYSTEMS OR COMPONENTS THAT WERE
INOPERABLE AT THE START OF THE EVENT AND THAT CONTRIBUTED TO
THE EVENT
Not applicable for this event
- D
- NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND
APPROXIMATE TIMES
During testing on 11/14/2005 the pressurizer Power. Operated Relief Valves (PORV)s, BBPCV0455A and BBPCV0456A, initially closed slower than the maximum stroke time allowed (2 seconds) in the test procedure. The open stroke time for both valves were within procedure limits
- Subsequent review by engineering of the basis for the stroke time values indicated that the limits in the procedure were not conservative with respect to the maximum allowed stroke times credited in the Callaway Analyses of Record (AOR) for a Cold Overpressure Mitigating System (CONS) function.
The analyses for CONS assumes an opening time and delay time for the pressurizer PORVs
- Evaluations performed by Callaway engineering personnel have determined that PORV stroke times measured during surveillance testing did not account for all of the delay times credited in the Design Bases CONS Analyses of Record. Further reviews determined the allowed delay times could not be met by the control loop. This results in PORV stroke times which are non-conservative to the CONS AOR This was reported to the NRC on ENS* 42257 on 01/13/2006.
It was entered into the plant corrective action system as CAR 200509374.
The event was conservatively reported under 10CFR50.73(a)(2)(v), event or condition that could have prevented fulfillment of a safety function.
Specifically items (C) and (D) - control or radiation releases and mitigate the consequences of an accident. Further reviews (see below section�SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT) indicate there is reasonable expectation of fulfillment of the COMS function. Since it is reasonable that the function will be fulfilled and COMS is not considered in the FSAR chapter 15 accident analyses, we no longer consider this event reportable under 10CFR50.72(b)(v)(C), 10CFR50.72(b)(v)(D), or 10CFR50.73(a)(2)(v)(C) or 10CFR50.73(a)(2)(v)(D).
At the time the determination was made, the plant was in Mode 1. TS 3.4.12, COMS, is applicable in Mode 4 with RCS temperature less than or equal to 275F, Mode 5 and Mode 6 with the head on the reactor vessel.
To meet the COMS requirements, TS 3.4.12 allows using the pressurizer PORVs, Residual Heat Removal (RHR) system suction relief valves, a combination of PORVs and RHR suction relief valves, or the reactor coolant system (RCS)depressurized with a RCS vent >1= 2.0 square inches.
Based upon the non-conservative stroke time criteria contained in the test procedure, conservatively the pressurizer PORVs were not operable for COMS purposes during the timeframes listed below in section II.B., Duration Of Safety System Unavailability.
The preoperational test procedure for the pressurizer PORVs verified the PORV open stroke time. The stroke time requirement was seconds. In the 1983-1984 timeframe, Callaway Inservice Test Program (IST) established maximum allowable stroke time of 2 seconds. This stroke time was chosen based upon the Westinghouse/SNUPPS PIP (SNUPPS:
Standardized Nuclear Unit Power Plant System) (PIP: Project Information Package). The stroke time allowed in plant procedures has remained consistent since that time.
Various analyses, correspondence and design documents going back to 1983 have the following PORV stroke times for the COMS function: signal delay time of 0.85 seconds, valve opening time of 0.85 seconds. The valve closing time has varied in the range of 1.05 - 1.75 seconds.
Additional analyses were performed after the stroke times were measured on 11/14/2005. The analyses showed that no change would be needed to the COMS related PTLR curves if the following times could be met:
Open stroke time: 1.9 seconds (0.7 seconds delay, 1.2 seconds stroke) Close stroke time: 2.6 seconds (0.7 seconds delay, 1.9 seconds stroke) The neasured stroke times for the pressurizer PORVs on 11/14/2005 were:
BBPCV0455A Test 1: Open 1.2 seconds, Close 2.2 seconds BBPCV0455A Test 2: Open 1.6 seconds, Close 1.5 seconds BBPCV0455A Test 3: Open - seconds, Close 1.3 seconds BBPCV0456A Test 1: Open 0.5 seconds, Close 2.1 seconds BBPCV0456A Test 2: Open 0.6 seconds, Close 1.6 seconds BBPCV0456A Test 3: Open - seconds, Close 1.3 seconds Review of past test results for the past three years, show the final valve opening times were within 1.6 seconds and closure times were within 2.3 seconds.
E. METHOD OF DISCOVERY OF EACH COMPONENT, SYSTEM FAILURE, OR
PROCEDURAL ERROR
PORV stroke time was discovered by an inservice test program surveillance. The non-conservative test procedure stroke time criteria was discovered by engineering and vendor review of the COMS calculations.
II. EVENT DRIVEN INFORMATION
A. SAFETY SYSTEMS THAT RESPONDED
Not applicable for this event.
B. DURATION OF SAFETY SYSTEM INOPERABILITY
TS 3.4.12, COMS, is applicable in Mode 4 with RCS temperature less than or equal to 275F, Mode 5 and Mode 6 with the head on the reactor vessel. To meet the COMS requirements, TS 3.4.12 allows using the pressurizer PORVs, Residual Heat Removal (RHR) system suction relief valves, a combination of PORVs and RHR suction relief valves, or the reactor coolant system (RCS)depressurized with a RCS vent >/= 2.0 square inches.
The affected equipment is the pressurizer PORVs when used for COMS function. Their function at normal RCS operating conditions is not affected.
(3 year history) COMS TS Applicable Timeframes� Start�Stop Comment 10/23/2002 1452 10/28/2002 0720 Refuel 12 Cooldown 11/14/2002 1502 11/21/2002 0554 Refuel 12 Heatup 03/22/2003 0034 03/31/2003 0557 March 2003 outage 04/10/2004 1946 04/19/2004 0344 Refuel 13 Cooldown 05/16/2004 0312 06/07/2004 0514 Refuel 13 Heatup 09/17/2005 1635 09/22/2005 1713 Refuel 14 Cooldown 11/01/2005 0421 11/13/2005 1735 Refuel 14 Heatup Timeframes for potential non-compliance with TS 3.4.12:
Timeframe 10/23/2002 1452 - 10/26/2002 0206 11/17/2002 0042 - 11/19/2002 0116 11/19/2002 0153 - 11/21/2002 0244 11/21/2002 0244 - 11/21/2002 0544 03/22/2003 0034 - 03/24/2003 0022 03/27/2003 2210 - 03/31/2003 0557 04/10/2004 1946 - 04/19/2004 0344 05/23/2004 0052 - 05/24/2004 2308 05/24/2004 2308 - 05/26/2004 0007 05/26/2004 0007 - 05/28/2004 0919 05/28/2004 0919 - 05/28/2004 1025 05/28/2004 1025 - 05/29/2004 0143 06/01/2004 0025 - 06/06/2004 0514 09/17/2005 1635 09/18/2005 1737 11/08/2005 0433 11/09/2005 1143 - 09/18/2005 1737 - 09/22/2005 1713 - 11/09/2005 1143 - 11/09/2005 1502 11/09/2005 1502 - 11/13/2005 1735 COMS By 2 PZR PORVs 1 PZR PORV and 1 RHR suction relief 1 PZR PORV and 1 RHR suction relief 2 PZR PORVs 2 PZR PORVs 1 PZR PORV and 1 RHR suction relief 2 PZR PORVs 2 PZR PORVs 1 PZR PORV and 1 RHR suction relief 2 PZR PORVs 1 PZR PORV and 1 RHR suction relief 2 PZR PORVs 2 PZR PORVs 2 PZR PORVs 1 PZR PORV and 1 RHR suction relief 2 PZR PORVs 1 PZR PORV and 1 RHR suction relief 2 PZR PORVs The above dates and times were taken from control room narrative logs, watch relief checklists, plant computer data, and work control system data.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT.
(Information was extracted from the root cause evaluation for CAR 200509374).
This issue has a low safety / risk significance. Stroke time for the Pressurizer PORVs is not modeled in the FSAR Chapter 15 analyses. The PRA analyses do not model the plant when Cold Overpressure Mitigation System (COMS) is required.
Westinghouse Letter SCP 88-111 provides pressure versus time data for the most limiting mass and heat injection events. During the time period just prior to PORV opening, pressure increases at an approximate rate of 22 psi/sec. The additional stroke time evaluated is less than 0.5 seconds, therefore an additional pressure increase of approximately eleven psi could have occurred.� Technical Specification Bases, B 3.4.12 states "Exceeding the RCS P/T limits by a significant amount could cause brittle cracking of the reactor vessel." Eleven psi is not considered significant.
The analysis includes assumptions which also qualitatively allow this potential pressure increase. These include:
- Safety Factor of 2 for primary stresses
- Assumes an initial flaw equal to 1/4 the reactor vessel wall thickness.
Actual NDE techniques detect smaller flaws.
- Conservative mass and heat injection rates.
III. CAUSE(S) OF THE EVENT AND CORRECTIVE ACTION(S)
(Information was extracted from the root cause evaluation for CAR 200509374).
The immediate action taken to address this issue was to declare BBPCV0455A and BBPCV0456A inoperable. A second surveillance test was performed on these valves and the closing stroke times were within the 2 second maximum stroke time. An analysis of the stroke time deviation was performed by engineering and the valves were determined to be operable per Technical Specification 5.5.8 related functions, but not for Technical Specification 3.4.12 COMS functions.
Engineering in conjunction with Westinghouse, will change the current stroke time analysis to allow Operations to use the PORVs for COMS per Technical Specification 3.4.12.
Two compensatory actions were implemented as part of the Operability Determination completed for CARS 200509374
- Administrative controls, in the form of a Night Order, were put in place to assure COMS credit is not taken for TS Limiting Condition of Operation (LCO) 3.4.12
- a and 3.4.12
- The second compensatory action was a revision to the Callaway Plant Emergency Operation Procedures (EOPs) that credit operation of COMS. These EOPs now include steps to ensure temperature is maintained above the COMS initiation temperature before RHR is placed into service
- These compensatory actions are not considered the solution to the issue of inadequate COMS setpoints and are therefore considered temporary until new COMS curves can be put into service
- The root cause of the event is inadequate communication between the Design Engineering and Inservice Test Engineering groups with regard to changes made to the curve book
- This breakdown of communications occurred several times in the period between Callaway Plant startup and the Replacement Steam Generator design review performed in 2003
- Engineering's procedures and the form for evaluating changes to the curve book will be revised to include instructions to communicate curve book changes with the affected groups and to communicate adequate controls to ensure impact on other plant programs and departments is considered.
PREVIOUS SIMILAR EVENTS IV.� None V
- � ADITIONAL INFORMATION None