05000352/LER-1917-003, Regarding Condition Prohibited by TS Due to Inoperable RPIS
| ML17142A145 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 05/22/2017 |
| From: | Libra R Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LG-17-070 LER 17-003-00 | |
| Download: ML17142A145 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 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)(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)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 3521917003R00 - NRC Website | |
text
Exelon Generation LG-17-070 May 22, 2017 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Limerick Generating Station, Unit 1 Renewed Facility Operating License No. NPF-39 NRC Docket Nos. 50-352 10 CFR 50.73
Subject:
LER 2017-003-00, Condition Prohibited by TS Due to Inoperable RPIS Enclosed is a Licensee Event Report (LER) which addresses a condition prohibited by Technical Specifications (TS) at Limerick Generating Station (LGS) Unit 1. The condition occurred when a Rod Position Indication System (RPIS) power supply failed. The alternate indication used to satisfy the TS action was subsequently determined to be invalid, given the failed power supply.
The failure to meet the TS Action constituted a condition prohibited by TS. Therefore, this LER is being submitted pursuant to the requirements of 50.73(a)(2)(i)(B) for an Operation or Condition Prohibited by TS.
There are no commitments contained in this letter.
If you have any questions, please contact Robert 8. Dickinson at (610) 718-3400.
Respectf~ly, fZJl-~
Richard W. Libra Vice President - Limerick Generating Station Exelon Generation Company, LLC cc: Administrator Region I, USNRC USNRC Senior Resident Inspector, LGS
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- 3. PAGE Limerick Generating Station, Unit 1 05000352 1 OF 4
- 4. TITLE Condition Prohibited by TS Due to Inoperable RPIS
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED I
SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO MONTH DAV YEAR FACILITY NAME DOCKET NUMBER 03 22 17 2017 - 003
- - 00 05 22 17
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITIED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
D 20.2201 (bl D 20.2203(a)(3Hil D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A)
D 20.2201 (d)
D 20.2203(a)(3)(ii)
D 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B) 1 D 20.2203(a)(1 l D 20.2203(a)(4)
D so.13(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1 )(i)(A)
D 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
- 10. POWER LEVEL D 20.2203(a)(2)(iil D 50.36(c)(1 )(ii)(A)
D 50.73(a)(2)(v)(A)
D 13.11 (a)(4)
D 20.2203(a)(2)(iiil D so.36(c)(2l D 50.73(a)(2)(v)(B)
D 73.71 (a)(S)
D 20.2203(a)(2)(iv)
D so.46(a)(3)(iil D 50.73(a)(2)(v)(C)
D 13.11(a)(1 i 100 D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
D 50.73(a)(2)(v)(D)
D 13.77(a)(2)(il D 20.2203(a)(2)(vi)
[8J 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 13.11(a)(2)(iil D 50.73(a)(2)(i)(C)
D OTHER Specify in Abstract below or in SEQUENTIAL NUMBER 003 REV NO.
00 Following restoration of operability, it was identified that the failure of the power supply rendered the full core display incapable of updating in response to a position change for the affected control rods.
An additional 81 control rods had no position indication while the power supply was failed.
Therefore, it was determined that the TS required actions for the control rods had not been met following the power supply failure. TS 3.1.3.7 provides several options to either determine control rod position or insert the control rod within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> after discovery. If one of these options cannot be met within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, an action is entered to be in hot shutdown within the following 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The time between the initial power supply failure and replacement of the power supply was approximately 19.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> and exceeded the total 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br /> to complete the TS required shutdown.
Following restoration of RPIS indication it was confirmed that the control rods had remained at their original positions. Per TS Bases, the RPIS system must be operable in order to ensure that the control rod pattern can be followed and therefore other parameters maintained within their limits. Per the Updated Final Safety Analysis Report (UFSAR) Section 7.7.1.2, the Reactor Manual Control System and RPIS Subsystem are power generation systems and not safety related, nor required to fulfill a plant safety function associated with any design basis events or transients. The RPIS system is not included in the Probabilistic Risk Analysis (PRA) program. There was no control rod movement that occurred and none was required during the time that rod position was inoperable.
There was no safety consequence for this event.
IV.
Cause of the Event
A Corrective Action Program Evaluation (CAPE) was performed to determine the cause of the failure to identify a loss of control rod position. The evaluation concluded that procedural guidance was inadequate in identifying what indicators are available given failure of the power supply.
The lack of proceduralized guidance on which RPIS indicators are available to be used for RPIS operability and limitations on their use is the primary cause of this event. The procedures provide an incomplete list of indicators and no cautions or limitations on the "memory" within RPIS that could cause false indication. During this event, the procedure provided options to perform this via the Control Rod Position Report (preferred) or the Four Rod Display. The other potential indicators that provide control rod position were not addressed.
Based on this evaluation, it was determined that the cause of this event is inadequate procedural guidance regarding control rod position indicators available and limitations on their use. This includes which indicators can be used to satisfy surveillance requirements and how to confirm that the indicated position is updating with current data. A contributor to this event is that Operations personnel were not aware that some RPIS indicators are based on system memory.
V.
Corrective Actions Completed/Planned SEQUENTIAL NUMBER 003 REV NO.
00 The Operations procedures for RPIS indication will be revised to address all available indicators and methods to verify the indicators are accurate. The training program will be updated with information on the memory used for control rod position indication.
VI.
Previous Similar Occurrences On 5/27/2006, a Unit 2 power supply failed causing a loss of rod position indication on the Plant Monitoring System, the Four Rod Display, and the Rod Worth Minimizer (RWM). The Full Core Display was initially used to verify all rods full-in or full-out. Following review of the vendor manual, it was determined that the Full Core Display was showing position from memory and not current position based on the failure. The power supply was replaced within the LCO action window. This event had similar action taken by the operators in use of the Full Core Display. This was a lost opportunity to revise procedures to document the findings regarding the Full Core Display indication. Page _4_ of _4_