05000454/LER-2011-001, For Byron Station Unit 1, Regarding Potential Loss of Residual Heat Removal System Safety Function in Mode 4 When Aligned for Shutdown Cooling Due to Potential for Flashing or Voiding Coolant During a Shutdown Loss of Coolant A
| ML110660223 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 03/07/2011 |
| From: | Tulon T Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Ltr: 2011-0042 LER 11-001-00 | |
| Download: ML110660223 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4542011001R00 - NRC Website | |
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1.10.0101 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Byron Station, Units 1 and 2 Facility Operating License Nos. NPF-37 and NPF-66 NRC Docket Nos. STN 50-454 and STN 50-455
Subject:
Licensee Event Report 2011-001-00 Potential Loss of Residual Heat Removal System Safety Function in Mode 4 When Aligned for Shutdown Cooling Due to Potential for Flashing or Voiding of Coolant During a Shutdown Loss of Coolant Accident The enclosed Licensee Event Report (LER) is being submitted in accordance with 10 CFR 50.73, Licensee event report system, paragraphs (a)(2)(i)(B), (a)(2)(v)(B), and (a)(2)(vii). This LER involves three occurrences where both residual heat removal (RH) trains were aligned for shutdown cooling with the reactor coolant system at a temperature that could potentially cause RH system voiding during a shutdown loss of coolant accident.
There are no regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact Mr. David Gudger, Regulatory Assurance Manager, at (815) 417-2800.
Respectfully, J. Tulon Vice President Byron Station
Enclosure:
LER 2011-001-00 Ti TJT/JEL,cy
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 10/31/2013 (10-2010)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the digits/characters for each block) information collection.
- 13. PAGE Byron Station, Unit 1 05000454 1 of 4
- 4. TITLE Potential Loss of Residual Heat Removal System Safety Function in Mode 4 When Aligned for Shutdown Cooling Due to Potential for Flashing or Voiding of Coolant During a Shutdown Loss of Coolant Accident
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEUAL REV MONTH DAY YEAR Byron Station Unit 2 05000455 FACILITY NAME DOCKET NUMBER 01 05 2011 2011 001 00 03 07 2011 N/A N/A
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REOUIREMENTS OF 10 CFR §: (Check all that apply)
LI 20.2201(b)
LI 20.2203(a)(3)(i)
LI 50.73(a)(2)(i)(C) 50.73(a)(2)(vii) 1 LI 20.2201(d)
LI 20.2203(a)(3)Oi)
LI 50.73(a)(2)(ii)(A)
LI 50.73(a)(2)(viU)(A)
LI 20.2203(a)(1)
LI 20.2203(a)(4)
LI 50.73(a)(2)(ii)(B)
LI 50.73(a)(2)(viii)(B)
LI 20.2203(a)(2)U)
LI 50.36(c)(1)(i)(A)
LI 50.73(a)(2)(iii)
LI 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL LI 20.2203(a)(2)(ii)
LI 50.36(c)(1)(ii)(A)
LI 50.73(a)(2)(iv)(A)
LI 50.73(a)(2)(x)
LI 20.2203(a)(2)(iii)
LI 50.36(c)(2)
LI 50,73(a)(2)(v)(A)
LI 73.71(a)(4)
LI 20.2203(a)(2)(iv)
LI 50.46(a)(3)(ii) 50.73(a)(2)(v)(B)
LI 73.71(a)(5)
LI 20.2203(a)(2)(v)
LI 50.73(a)(2)(i)(A)
LI 50.73(a)(2)(v)(C)
LI OTHER LI 20.2203(a)(2)(vi) 5O.73(a)(2))(B)
LI 50.73(a)(2)(v)(D)
Specify in Abstract below or in The following administrative controls were implemented to address the RH issue:
During RCS cooldown at least one train of RH will be aligned for injection until RCS temperature is < 200 degrees F. (Mode 5)
During RCS heatup at least one train, preferably both, will be aligned for injection prior to raising RCS temperature >/= 200 degrees F. (Mode 4)
On January 5, 2011, and in subsequent review of the past three years, three occurrences were identified where both RH trains were placed into operation prior to reaching Mode 5 (<1= 200 degrees F):
October 6, 2008, Unit 2 refueling outage. The second train of RH was placed in SDC at 0448; Mode 5 occurred at 0454 (2 trains in SDC for 6 mm with RCS > 200 degrees F).
September 14, 2009, Unit 1 refueling outage. The second train of RH was placed in SDC at 0542; Mode 5 occurred at 0603 (2 trains in SDC for 21 mm with RCS > 200 degrees F).
April 19, 2010, Unit 2 refueling outage. The second train of RH was placed in SDC at 0529, and Mode 5 occurred at 0536 (2 trains in SDC for 7 minutes with RCS > 200 degrees F).
These conditions represent an event or condition that could have prevented fulfillment of a safety function.
Therefore, this event is being reported pursuant to 10 CFR 50.73(a)(2)(i)(B), any operation or condition which was prohibited by Technical Specifications; 10 CFR 50.73(a)(2)(v)(B) as a condition that could have prevented the fulfillment of a systems safety function; and 10 CFR 50.73(a)(2)(vii), any event where a single cause or condition caused two independent trains to become inoperable in a single system.
C.
Cause of Event
The cause of this event was inadequate operating procedure temperature limits, which were based on a technical error in the vendor communication.
Byrons operating procedures were written and executed as intended; however, the limit of 260 degrees Fahrenheit was based on system operating guidance provided by the equipment manufacturer that did not consider all operating modes. The error went unrecognized in both the vendors and Byrons original review of NSAL-93-004 in 1994.
D.
Safety ConseQuences
There were no actual safety consequences impacting plant or public safety as a result of these events. This issue addressed the potential for the development of steam voiding in the RH pump suction shutdown cooling piping of the RH system if the RH system had to be transmtioned from shutdown cooling to the ECCS mode due to a LOCA occurring in Modes 3 or 4 at temperatures above 200 degrees F (Modes 3 and 4).
The potential exists for flashing/steam voiding of an RH system hot leg suction line if the RH system is aligned for ECCS recirculation, following termination of shutdown cooling with an RH temperature that exceeds 200 degrees F, and suction of the RH system is transferred to the ECCS recirculation sump during a LOCA. Therefore, this is considered a safety system functional failure.
In the event that the RH system became inoperable, abnormal and emergency procedures exist that provide guidance to immediately secure any RH pumps aligned for shutdown cooling to prevent pump damage, to restore core cooling through alignment of a high head safety injection pump in injection mode, and restoration of the medium head safety injection pumps if necessary. Existing procedures also include steps to vent and refill the RH loops if necessary.
In Modes 3 or 4, at least one charging (CV) pump is available and would be aligned to the RWST. Additionally, the steam generators would be available with auxiliary feedwater providing a heat sink to aid in decay heat removal.
E.
Corrective Actions
The corrective actions include:
Pending permanent procedure revisions, an Operations Department standing order was implemented for the RH system to establish controls that ensure at least one train of RH is aligned for injection when RCS temperature is > 200 degrees F.
Appropriate operating and emergency procedures will be revised to reflect the more restrictive 200 degrees F temperature limit for restoration/alignment of an RH Train for ECCS injection following termination of shutdown cooling.
Technical Specification Bases 3.5.3, ECCS Shutdown, will be revised to reflect the new temperature limit.
F.
Previous Occurrences
There have been no previous events identified at the Byron Station.