05000446/LER-2008-001, Re Reactor Trip Due to a Sheared Condenser Vacuum Instrument Sensing Line
| ML081420029 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 05/12/2008 |
| From: | Madden F Luminant Generation Co, Luminant Power |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CP-200800701, TXX-08071 LER 08-001-00 | |
| Download: ML081420029 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 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)(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)(i)(B), Prohibited by Technical Specifications |
| 4462008001R00 - NRC Website | |
text
Mike Blevins Executive Vice President
& Chief Nuclear Officer Mike.Blevins@ Luminani.com Luminant Power P O Box 1002 6322 North FM 56 Glen Rose, TX 76043 Luminant T 254 897 5209 C 817 5599085 F 254 897 6652 CP-200800701 Log # TXX-08071 Ref. #
50.73(a)(2)(iv)(A)
May 12, 2008 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
SUBJECT:
COMANCHE PEAK STEAM ELECTRIC STATION DOCKET NO. 50-446 ACTUATION OF REACTOR PROTECTION SYSTEM LICENSEE EVENT REPORT 446/08-001-00
REFERENCE:
Dear Sir or Madam:
Enclosed is Licensee Event Report (LER) 08-001-00 for Comanche Peak Steam Electric Station (herein referred to as Comanche Peak Nuclear Power Plant) Unit 2, "Reactor Trip Due to a Sheared Condenser Vacuum Instrument Sensing Line."
This communication contains no new licensing basis commitments regarding Comanche Peak Nuclear Power Plant (CPNPP) Unit 2.
A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway
- Comanche Peak
- Diablo Canyon
- Palo Verde
- South Texas Project
- Wolf Creek Ll-bep;z
U. S. Nuclear Regulatory Commission TXX-08071 Page 2 05/12/2008 Sincerely, Luminant Generation Company LLC Mike Blevins By:
"Fred W. Madden Director, Oversight & Regulatory Affairs Enclosure c -
E. E. Collins, Region IV B. K. Singal, NRR Resident Inspectors, Comanche Peak
Enclosure to TXX-08071 NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSIO APPROVED BY OMB NO. 3150-0104 EXPIRES: 8/31/2010 (9-2007)
, the NRC may digits/characters for each block) not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE COMANCHE PEAK NUCLEAR POWER PLANT UNIT 2
'05000446 1 OF4
- 4. TITLE Reactor Trip Due to a Sheared Condenser Vacuum Instrument Sensing Line
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR FACILITY NAME DOCUMENTNUMBER NUMBER NO.
N/A 05000 03 16 2008 12008 I 001 00 05 12 2008 FACILITY NAME DOCUMENT NUMBER 0
N/A 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
Mode 1
[
20.2201(b)
[]
20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii)
El 20.2201(d)
[
20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
[E 20.2203(a)(1)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
E] 50.73(a)(2)(viii)(B)
_1 20.2203(a)(2)(i)
E]
50.36(c)(1)(i)(A)
[
50.73(a)(2)(iii)
[] 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
[
50.36(c)(1)(ii)(A)
[]
50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x) 100%
[l 20.2203(a)(2)(iii)
El 50.36(c)(2)
El 50.73(a)(2)(v)(A)
[] 73.71 (a)(4)
El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
[]
50.73(a)(2)(v)(B)
[] 73.71(a)(5)
El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
[]
50.73(a)(2)(v)(C)
[]
OTHER El 20.2203(a)(2)(vi)
El 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
VOLUNTARY LER
- 12. LICENSEE CONTACT FOR THIS LER FACILITY NAME TELEPHONE NUMBER (Include Area Code)
Tim Hope - Nuclear Licensing Manager (254) 897-6370CAUSE SYSTEMWI COMPONENT MANU-REPORTABLE
CAUSE
SYSTEM COMPONENT MANU-REPORTABLE FACTURER TO EPIXE FACTURER TO EPIX
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED MONTH DAY YEAR El SUBMISSION YES (If yes, complete 15. EXPECTED SUBMISSION DATE)
W NO DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
On March 16, 2008, Comanche Peak Nuclear Power Plant (CPNPP) Unit 2 was in Mode 1 operating'at 100%
power. At 1137 hours0.0132 days <br />0.316 hours <br />0.00188 weeks <br />4.326285e-4 months <br />, the Unit 2 Main Turbine tripped due to a sensed loss of condenser vacuum and the Main Turbine trip caused an automatic reactor trip. All control rods fully inserted, and all three Auxiliary Feedwater pumps started as expected as a result of the reactor trip. All systems responded normally during and following the reactor trip.
The cause of this event was a sheared common vacuum instrument sensing line to the Main Condenser 2B due to the sensing line being designed and installed without adequate flexibility. The failure was ultimately the result of a combination of residual stress induced by condenser movement and cyclic stress due to vibration. Immediate corrective actions included repair of the sheared vacuum instrument sensing line and modification of the supports on the Unit 1 and 2 sensing lines. The passive single point failure vulnerability was removed on Unit 2 during the tenth refueling outage and it will be removed on Unit 1 during the next refueling outage.
All times in this report are approximate and Central Time unless noted otherwise.
NRC FORM 360 (9-2007)
PRINTED ON RECYCLED PAPER NRC FORM 366 (9-2007)
PRINTED ON RECYCLED PAPER
Enclosure to TXX-08071 (If rmore space is required, use additional copies of SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES On March 16, 2008, CPNPP Unit 2 was in Mode 1 operating at 100% power. At 1123 hours0.013 days <br />0.312 hours <br />0.00186 weeks <br />4.273015e-4 months <br />, Operators (utility, licensed);in the Unit 2 control room received alarms that indicated Main Condenser B vacuum [EIIS: (SH)(COND)]
was less ;than 24 inches on Channels 1, 2 and 3 and slowly trending down. By verifying alternate indications, the Operators found that condenser vacuum was actually stable at 28 inches. At 1137 hours0.0132 days <br />0.316 hours <br />0.00188 weeks <br />4.326285e-4 months <br />, Operators received an automatic "low vacuum" trip on the Main Turbine [EIIS: (TA)(TRB)]. The turbine trip initiated an automatic reactor trip. All c ontrol rods fully inserted, and all three Auxiliary Feedwater pumps [EIIS: (BA)(P)] started as expected as a result of the reactor trip. All systems responded normally during and following the reactor trip.
E.
THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE, OR PROCEDURAL OR PERSONNEL ERROR Operators (utility, licensed) in the Unit 2 Control Room received alarms that indicated Main Condenser B vacuum was less ithan 24 inches on Channels 1, 2 and 3 and trending down.
II. COMPONENT OR SYSTEM FAILURES A. FAILURE MODE, MECHANISM, AND EFFECT OF EACH FAILED COMPONENT Not applicable - there were no component failures associated with this event.
B. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE Not applicable - there were no component failures associated with this event.
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY FAILURE OF COMPONENTS WITH MULTIPLE FUNCTIONS Not applicable - there were no component failures associated with this event.
(If more space is required, use additional copies of (If more space is required, use additional copies of NRC Form 366A) (17)
V.
CORRECTIVE ACTIONS
Immediate corrective actions included repair of the sheared vacuum instrument sensing line and modification of the supports on the Unit 1 and 2 sensing lines to add flexibility to the lines. These support modifications reduced the bending moments, which in turn reduced the chronic stresses that led to the failure of the sensing line on
!March 16, 2008.
To reduce the probability of similar events occurring in the future, the passive single point failure vulnerability was addressed on Unit 2 during the tenth refueling outage by removing the common line and installing separate sensing lines to the transmitters. As a part of this modification, the condenser pipe segments were also modified to reduce vibration.
As a part of the CPNPP Corrective Action Program, a similar modification to remove the common line and install separate, sensing lines will also be performed on the Unit 1 Main Condensers during the next refueling outage.
Engineering will issue a lessons learned on this event and will also review other similar passive single point failure vulnerabilities in both units.
VI.
PREVIOUS SIMILAR EVENTS
There have been no previous similar reportable events at CPNPP in the last three years.PRINTED ON RECYCLED PAPER