05000237/LER-2012-001, Regarding One Division of APRM Neutron Flux-High Channels Inoperable as a Result of Power Maneuver
| ML123550019 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 12/06/2012 |
| From: | Czufin D Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| SVPLTR 12-0058 LER 12-001-00 | |
| Download: ML123550019 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 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)(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 |
| 2372012001R00 - NRC Website | |
text
Adm Dresden Nuclear Power Station 6500 North Dresden Road Exelon Generation, Morris, IL 60450 815 942 2920 Telephone www.exeloncorp.com 10 CFR 50.73 SVPLTR # 12-0058 December 6, 2012 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Dresden Nuclear Power Station, Unit 2 Renewed Facility Operating License No. DPR-19 NRC Docket No. 50-237
Subject:
Supplemental Licensee Event Report 237/2012-001-01, One Division of APRM Neutron Flux-High Channels Inoperable as a Result of Power Maneuver Enclosed is Supplemental Licensee Event Report 237/2012-001-01, One Division of APRM Neutron Flux-High Channels Inoperable as a Result of Power Maneuver. This is a final report which describes an event which is being reported in accordance with 10 CFR 50.73(a)(2)(v)(A),
any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to shutdown the reactor and maintain it in a safe shutdown condition.
There are no regulatory commitments contained in this submittal.
Should you have any questions concerning this letter, please contact Mr. Hal Dodd at (815) 416-2800.
Respectfully, David M. Czufi
)
Site Vice President Dresden Nuclear Power Station Enclosure cc:
Regional Administrator - NRC Region III NRC Senior Resident Inspector - Dresden Nuclear Power Station
NFRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (10°2010)
, 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 Dresden Nuclear Power Station, Unit 2 05000237 1 OF 4
- 4. TITLE One Division of APRM Neutron Flux-High Channels Inoperable as a Result of Power Maneuver
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER SEQUENTIAL REV MONTH DAY YEAR N/A 05000 MONTH DAY YEAR YEAR NUMBER NO.
FACILITY NAME DOCKET NUMBER 02 19 2012 2012 -
001 01 12 06 2012 N/A 05000
- 9. OPERATING MODE
- 11. THIS REPORTiS SUBMITFED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
[o 20.2201(b) 0 20.2203(a)(3)(i)
[I 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii) 1 El 20.2201(d)
[E 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A) 0l 20.2203(a)(1)
[I 20.2203(a)(4) 0l 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
[I 20.2203(a)(2)(i)
El 50.36(c)(1)(i)(A)
[I 50.73(a)(2)(iii)
[I 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL [I 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A)
[I 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
El 20.2203(a)(2)(iii)
El 50.36(c)(2)
ED 50.73(a)(2)(v)(A)
[1 73.71 (a)(4) 073 El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(a)(5)
El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
El OTHER El 20.2203(a)(2)(vi)
El 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specify in Abstract below or in This event is being reported in accordance with 10 CFR 50.73(a)(2)(v)(A), any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to shut down the reactor and maintain it is a safe shutdown condition. Although the channels did not meet the Technical Specifications surveillance requirement, it did not result in a condition that was prohibited by the plant's Technical Specifications.
C.
Cause of Event
During a planned down power, the night shift operating crew reduced reactor power to approximately seventy-three percent. As expected, the down power maneuvers affected the gain setting for the APRMs. However, the magnitude of the change to the gain settings was not anticipated. This resulted in all the gains on one of the two Divisions experiencing an out of tolerance concurrently during the evolution. The movement of control rods, which are adjacent (Groups 9 and 10) to Local Power Range Monitors (LPRM), have a definite affect on the power inputs being received by the APRMs. These local power inputs resulted in the Divisions 1 and 2 APRMs indicating conservatively and non-conservatively, respectively. This occurrence is inherent to boiling water reactors.
During the control rod sequence exchange, the Division 2 APRMs went non-conservative. The LPRMs that inputted into the Division 2 APRMs were located adjacent to control rods (Grp 10) that were inserted during the sequence exchange, which results in a non-conservative indication. The LPRMs that inputted to the Division 1 APRMs were adjacent to control rods (Grp 9) that were withdrawn. This resulted in the Division 1 APRMs indicating conservatively. This is the expected divisional APRM response based on control rod sequence exchanges using Grp 9 and Grp 10 rods during the existing fuel cycle.
D.
Safety Analysis
The safety significance of this condition is low. The Flow Biased Neutron Flux-High trip function was conservatively set and would have generated a trip signal at approximately 104 percent rated thermal power which is well below the specified Technical Specification Allowable Value of 122 percent rated thermal power. Due to the Flow Biased Neutron Flux scram signal being available, the minimum critical power safety limit was not adversely impacted. Although the Fixed Neutron Flux-High trip would have exceeded the Technical Specification Allowable Value, the trip would have occurred prior to the value that is assumed in the plant's fuel cycle transient analysis. Therefore the health and safety of the public and plant employees was not compromised as a result of this condition.
E.
Corrective Actions
The operations rounds were revised to include an hourly check of APRM gain settings when unit load maneuvers are anticipated or planned to occur during the shift. This would ensure that out of tolerance gain settings are corrected within the two-hour technical specification allowance.
Additionally, new computer alarms which annunciate on sustained non-conservative indications for an APRM have been implemented on both operating units.
F.
Previous Occurrences
A review of DNPS Licensee Event Reports (LERs) for the last three years did not reveal any similar reportable conditions.
G.
Component Failure Data
Not Applicable