05000313/LER-2004-001-01, Arkansas Unit 1, on 04/29/2004, Operation Prohibited by Tech Specs Due to Undetected Inoperable Channel of Required Source Range Nuclear Instrumentation During Core Alterations Caused by a Signal Processing Unit Circuit Brea
| ML042380353 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 08/16/2004 |
| From: | James D Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 1CAN080404 LER 04-001-01 | |
| Download: ML042380353 (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)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3132004001R01 - NRC Website | |
text
-~ Entergy Entergy Operations, Inc.
1448 S. R. 333 Russellville, AR 72802 Tel 501 858 5000 1 CAN080404 August 16, 2004 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001
Subject:
Licensee Event Report 50-313/2004-001-01 Arkansas Nuclear One - Unit 1 Docket No. 50-313 License No. DPR-51
Dear Sir or Madam:
In accordance with 10CFR50.73(a)(2)(i)(B), enclosed is a supplement to the subject report concerning a condition prohibited by technical specifications due to an inoperable channel of source range nuclear instrumentation. The purpose of this supplement is to provide the results of the failure analysis.
This correspondence contains no new commitments.
Sincerely, Dae E. t~mes nag r, Licensing DEJ/f v Enclosure a
k::-,,
- h' 1CAN080404 Page 2 cc
Dr. Bruce S. Mallett Regional Administrator U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 NRC Senior Resident Inspector Arkansas Nuclear One P.O. Box 310 London, AR 72847 Institute of Nuclear Power Operations 700 Galleria Parkway Atlanta, GA 30339-5957 LEREvents@inpo.org
- -I NRC FORM 366 U.S. NUCLEAR REGULATORY APPROVED BY OMB NO. 3150-0104 EXPIRES 6-30-2001 (1.2001)
COMMISSION LICENSEE EVENT REPORT (LER)
Estimated burden per response to comply with this mandatory Information collection request 50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br />. Send comments regarding burden estimate to the Records Management Branch (T.6 E6), U.S.
Nuclear Regulatory Commission, Washington, DC 20555-0001, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202 (3150-0104), Office of Management and Budget, Washington, DC 20503.
FACILITY NAME (1) 1 DOCKET NUMBER (2)
PAGE (3)
Arkansas Nuclear One -
Unit 1 l
05000313 1 OF 4 TITLE (4) Operation Prohibited by Technical Specifications due to an Undetected Inoperable Channel of Required Source Range Nuclear Instrumentation During Core Alterations Caused by a Signal Processing Unit Circuit Breaker Failure.
EVENT DATE (5)
LER NUMBER (6) l REPORT DATE (7)
OTHER FACILITIES INVOLVED (8)
MO DAY YEAR SEQUENTIAL REV MO DAY YEAR FACILITY NAME DOCKET NUMBER NUMBER NO FACILITY FANIDOAM CKET NUMBER 04 29 2004 2004 001 01 08 16 2004 OPERATING 1 1
THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR: (Check one or more) (11) lMODE (9) 6 l
20.2201(b) 20.2203(a)(3)(i) l 50.73(a)(2)(i)(C) 50.73(a)(2)(vii)
POWER 1
1 20.2201(d) 20.2203(a)(3)(ii) l 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) lLE L0 I
0 l l 20.2203(a)(1) 20.2203(a)(4) l 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i) 50.36(c)(1)(i)(A) l 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A) 20.2203(a)(2)(ii) l 50.36(c)(1)(ii)(A) l 50.73(a)(2)(iv)(A) 50.73(a)(2)(x) 20.2203(a)(2)(iii) l_ 50.36(c)(2) 50.73(a)(2)(v)(A) 73.71(a)(4) 20.2203(a)(2)(iv) l 50.46(a)(3)(ii) l_
50.73a)(2)(v)(B) 73.71(a)(5) 20.2203(a)(2)(v) l 50.73(a)(2)(i)(A) l 50.73(a)(2)(v)(C)
OTHER 20.2203(a)(2)(vi)
X 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D)
Specify in Abstract
_____!_____1_1_1_1_1_
1_ or =
(17)
A.
Plant Status At the time this condition was discovered, Arkansas Nuclear One, Unit 1 was shutdown and in Mode 6 for refueling outage 1R18.
B.
Event Description
At 2251 on April 29, 2004, during the removal of inverter Y-28 [EF] from service for planned maintenance, the ANO-1 shift manager observed that the plant computer [ID] indication for the green train source range nuclear instrumentation [IG] did not exhibit the expected response when its power supply was de-energized.
Specifically, operators anticipated that the indicated count rate would decrease when the inverter was shutdown; however, the indication did not change.
The control room staff began an investigation by reviewing historical trend data on the plant computer, the Safety Parameter Display System (SPDS) [ID], and operator log readings taken at 0835 and 1944 CDT.
Due to the extremely low readings, the operator logs did not provide conclusive evidence as to the time of failure of the affected instrument channel.
However, it was determined from the evaluation of the plant computer and SPDS data that the green train source range nuclear instrumentation channel had failed at 1052 CDT.
Additionally, the review determined that the redundant red train source range instrumentation was functioning normally.
During a portion of the time that one source range channel was inoperable, the failure had not yet been detected and transfer of fuel assemblies from the reactor vessel to the spent fuel pool continued. While such core alterations are in progress, ANO-1 technical specifications require that two source range neutron flux monitors shall be operable.
With one of the required channels inoperable, core alterations and any operations that would dilute RCS boron concentration to less than the technical specification limit must be immediately suspended. Contrary to this requirement, while one of the required monitors was inoperable, the transfer of fuel assemblies continued until the core off-load was complete.
This condition prohibited by technical specifications was present from 1052 until fuel off-loading activities were completed at 2159 on April 29, 2004.
Once core alterations were terminated, no fuel remained in the core and the technical specification requirement was no longer applicable.
(1 7)
C.
Root Cause An analysis has been performed to determine the specific cause of the failure of the source range instrumentation.
The results of the evaluation have determined that the probable event initiator was a random failure of the signal processor drawer circuit breaker (circuit breaker found open).
Technicians also observed that the breaker felt mechanically weak (i.e., moved easily from trip to close positions).
Although additional failed components were identified (i.e., power supply and pre-amplifiers), they were not event initiators, but were a consequence of weaker electronic components that were stressed when the system was re-energized to support troubleshooting and repair activities.
It has also been concluded that the configuration of the Gamma Metrics source range instrumentation does not provide sufficient continuous functional monitoring capability for detection and annunciation of a channel failure during core alterations; particularly when indicated count rates are at the extreme low end of the scale.
D.
Corrective Actions
Prior to resumption of core alterations for the core reload, the failed circuit breaker, the power supply, and two pre-amplifiers were replaced.
The instrumentation was then tested and operability was demonstrated by performing a Channel Operability verification in accordance with the Source Range Channel Calibration procedure.
This procedure is used to support compliance with technical specification surveillance requirements.
Test results were satisfactory and the green train source range monitoring channel was returned to operable status.
Planned corrective action includes development of a method for continuous functional monitoring of Gamma Metrics source range instrumentation to enable the timely detection of a failure of a required channel.
E.
Safety Significance
The basis for the requirement for an additional channel of source range neutron flux monitoring during core alterations is to ensure redundant monitoring capability when positive reactivity changes are being made to the core.
At the time of this event,4RY E (3)
INRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (1-2001)
LICENSEE EVENT REPORT (LER)
FACILITY NAME (1)
DOCKET (2)
LER NUMBER 6 PAGE (3)
YEAR I SEQUENTIAL REVISION I
- 1 NUMBER INUMBERI Arkansas Nuclear One -
Unit 1 05000313 2004 001 01 4 OF 4 NNIRRATIVE (17)
ANO-1 was in Mode 6 and a full core off-load of fuel assemblies from the reactor vessel to the spent fuel pool was in progress.
When the source range monitoring channel failure occurred, 36 of 177 fuel assemblies remained in the reactor vessel.
Transfer of fuel assemblies continued until all of the fuel had been removed from the reactor vessel and relocated to the spent fuel pool.
This was accomplished approximately 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br /> after the failure of the required green train source range monitor. Although this failure was not immediately detected, the redundant source range instrument channel was unaffected by this condition and remained operable throughout the remainder of the core off-load activity.
While the likelihood of positive core reactivity changes was diminished with the continued removal of the fuel assemblies, any unexpected changes in core reactivity would have been detected by the operable channel, and operators would have been alerted of a significant change in neutron flux.
The unavailability of one train of source range neutron flux monitoring instrumentation did not adversely impact the ability to perform required actions based on this parameter.
For these reasons, the safety significance of this condition was determined to be minimal.
F.
Basis for Reportability This report of a condition prohibited by technical specifications is submitted in accordance with 10CFR50.73(a)(2)(i)(B).
G.
Additional Information
There have been no previous similar events reported by ANO as Licensee Event Reports.
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].