05000446/LER-2011-001, Regarding Inoperability of ECCS Trains Due to Gas Void
| ML11188A085 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 06/27/2011 |
| From: | Madden F, Flores R Luminant Power, Luminant Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CP-201100762, TXX-11069 LER 11-001-00 | |
| Download: ML11188A085 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 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)(viii)(A) 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)(A), Loss of Safety Function - Shutdown the Reactor 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) |
| 4462011001R00 - NRC Website | |
text
Luminant Rafael Flores Senior Vice President
& Chief Nuclear Officer Rafael.flores@Luminant.com Luminant Power P 0 Box 1002 6322 North FM 56 Glen Rose, TX 76043 T 254 897 5550 C 817 559 0403 F 254 897 6652 CP-201100762 Log # TXX-11069 June 27, 2011 Ref. #
U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
SUBJECT:
COMANCHE PEAK NUCLEAR POWER PLANT DOCKET NO. 50-446 LICENSEE EVENT REPORT 446/11-001-00, INOPERABILITY OF ECCS TRAINS DUE TO GAS VOID
Dear Sir or Madam:
Enclosed is Licensee Event Report (LER) 446/11-001-00, "Inoperability of ECCS Trains Due to Gas Void,"
for Comanche Peak Nuclear Power Plant (CPNPP) Unit 2.
This letter contains no new regulatory commitments regarding CPNPP Units 1 and 2.
Should you have any questions concerning this submittal, please contact Mr. Tim Hope, Manager, Nuclear Licensing, at (254) 897-6370.
Sincerely, Luminant Generation Company LLC Rafael Flores By::______
Fred W. Madden Director, Oversight & Regulatory Affairs A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway - Comanche Peak - Diablo Canyon
- Palo Verde
- San Onofre South Texas Project
- Wolf Creek
U.S. Nuclear Regulatory Commission TXX-1 1069 Page 2 06/27/2011 Enclosure c -
E. E. Collins, Region IV B. K. Singal, NRR Resident Inspectors, Comanche Peak
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (10-2010)
, the NRC may d t/h ts for each block) not conduct or sponsor, and a person is not required to respond to, the gitscaraters information collection.
/3. PAGE Comanche Peak Nuclear Power Plant Unit 2 05000 446 1
OF 4
- 4. TITLE Inoperability of ECCS Trains Due to Gas Void
- 5. EVENT DATE
- 6. LER NUMBER
- - 7.
REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIALý REV MONTH DAY YEAR OC U
NUMBER NO.
05000 FACILITY NAME DOCKET NUMBER 04 26 2011 2011 1 -
0 06 27 2011 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) 2 20.2201(b)
[
20.2203(a)(3)(i)
E] 50.73(a)(2)(i)(C)
I] 50.73(a)(2)(vii)
El 20.2201(d)
El 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(A)
[
50.73(a)(2)(viii)(A)
[]
20.2203(a)(1)
[
20.2203(a)(4) 50.73(a)(2)(ii)(B)
[
50.73(a)(2)(viii)(B)
E] 20.2203(a)(2)(i)
E] 50.36(c)(1)(i)(A)
E] 50.73(a)(2)(iii)
E] 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
[
50.36(c)(1)(ii)(A)
E] 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x) 0 20.2203(a)(2)(iii) 5 50.36(c)(2)
F] 50.73(a)(2)(v)(A) 5 73.71(a)(4) 0 20.2203(a)(2)(iv) 5 50.46(a)(3)(ii) 5 50.73(a)(2)(v)(B) 5 73.71(a)(5) 5 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A) 5 50.73(a)(2)(v)(C)
E] OTHER E] 20.2203(a)(2)(vi)
[
50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify in Abstract below or in SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES CPNPP Unit 2 was performing a reactor power ascension from refueling outage 2RF12. Unit 2 entered Mode 2 at 1538, April 25, 2011, and was critical at 1754. At 0020, April 26, 2011, during post-outage void verification inspections, a 3.71 ft3 void was discovered in the high point piping run containing Refueling Water Storage Tank Isolation Valve 2SI-0047 [EIIS: (BQ)(TK)(ISV)] and vent valve 2SI-8978 [EIIS: (BQ)(V)]. Unit 2 entered Limiting Condition for Operation Action Requirement (LCOAR) A2-11-231 for LCO 3.0.3, Two Trains of Containment SprayIEIIS: (BE)], Safety Injection [EIIS: BQ)], and Residual Heat Removal [EIIS: (BP)j Inoperable.
The void was removed by aligning temporary tubing from 2SI-8978 to a drain and venting the system until a steady stream of water was observed flowing from 2SI-8978. Void elimination was then verified via ultrasonic inspection.
LCOAR A2-11-231 was exited at 0143, April 26, 2011.
Prior to the April 2011 2RF12 refueling outage, various sections of piping were ultrasonically tested to verify the absence of gas voiding. The high point piping containing 2SI-0047 and 2SI-8978 was verified free of gas voids on March 31, 2011.
Further analysis demonstrated that the declaration of inoperability was a conservative action, and RHR and SI would have fulfilled their respective safety functions and been operable. The analysis confirmed that one (1) train of containment spray was inoperable, however the containment spray safety function would have been fufilled with the remaining operable CT train.
E. THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE, OR PROCEDURAL PERSONNEL ERROR This condition was identified as a result of void verification inspections required by CPNPP procedure STA-698, "Gas Intrusion Program." The inspections are required to be conducted following the isolation of the Residual Heat Removal (RHR) system from the Reactor Coolant System (RCS).
- 11. 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 - Nocomponent 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.
Ill. 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 One (1) train of Containment Spray was inoperable upon Unit 2 entry into Mode 4 on April 24, 2011 at 0518 until the LCOAR was exited on April 26, 2011 at 0143.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT The primary function of the ECCS is to remove the stored and fission product decay heat from the reactor core during accident conditions. The analysis methodology used to determine system operability in this event conservatively postulates that the entirety of the discovered void would enter the suction of a single pump, thereby preventing the pump from performing its designated safety function. Further analysis demonstrated that the declaration of inoperability was a conservative action, and RHR and SI would have fulfilled their respective safety functions and been operable. This analysis is based on detailed study of the void transport and piping design. The analysis confirmed that one (1) train of containment spray was inoperable, however the containment spray safety function would have been fufilled with the remaining operable CT train.
Based on the above, it is concluded that the health and safety of the public were unaffected by this condition and this event has been evaluated to not meet the definition of a safety system functional failure per 10CFR50.73(a)(2)
(v).
IV. CAUSE OF THE EVENT
The direct cause of this event was the introduction, transport, and accumulation of gases in the vicinity of 2SI-0047, resulting in a void of sufficient size that very conservative analytical methods used at the time of discovery determined the Containment Spray, Safety Injection, and Residual Heat Removal systems were rendered inoperable.
The gas void was the result of the RHR system fill and vent evolution and subsequent RHR operation that transmitted the void to its final location. Contributing to this event was the fact that vent valve 2SI-8978 (located in the section of piping where the void was discovered) was not included in applicable venting procedures.
The cause of this event was the failure to identify a unique system configuration and the untimely identification and removal of a gas void that could have potentially rendered both trains of the Containment Spray, Safety Injection, and Residual Heat Removal systems inoperable.
V. CORRECTIVE ACTIONS
Immediate corrective action was the venting of the gas void and returning the ECCS systems to operability. After vent valve 2S1-8978 was discovered not to be in the applicable venting procedures, the Unit I vent valve counterparts were also reviewed. The review discovered Unit 1 vent valve 1SI-0240 was also not included in applicable venting procedures. Consequently, 2SI-8978 and 1SI-0240 will be incorporated into the appropriate venting procedures.
Subsequent corrective actions include revision of the post-outage void verification program to require the conduct of preliminary void verifications at locations where potentially dual-train operability-affecting voids may form after entry into Mode 5 but prior to entry into Mode 4 and revision of STA-698 to include a requirement to periodically review fill and vent procedures to ensure all known gas intrusion mechanisms (e.g., pressure damming) are considered.
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