05000353/LER-2007-001, Regarding Scram Discharge Volume Vent and Drain Valves Opened Due to Fuse Removal
| ML071300083 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 05/09/2007 |
| From: | Mudrick C Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Plant Licensing Branch III-2 |
| References | |
| LER 07-001-00 | |
| Download: ML071300083 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) 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)(i)(B), Prohibited by Technical Specifications |
| 3532007001R00 - NRC Website | |
text
10CFR50.73 May 9, 2007 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Limerick Generating Station, Unit 2 Facility Operating License No. NPF-85 NRC Docket No. 50-353 Subject: LER 2-07-001, Scram Discharge Volume Vent and Drain Valves Failed Open Due To Clearance Planning Error This Licensee Event Report (LER) addresses a condition that could have prevented fulfillment of the safety function for the primary containment system. This event was caused by a clearance planning error that resulted in removal of fuses to the back-up scram valves which caused the scram discharge volume vent and drain valves to open. This resulted in a breach of primary containment in Operational Condition 3 (Hot Shutdown).
Report Number:
2-07-001 Revision:
00 Event Date:
March 10, 2007 Discovered Date:
March 10, 2007 Report Date:
May 9, 2007 This LER is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(v)(C) and 10CFR50.73(a)(2)(vii)(C).
There are no commitments contained in this letter.
If you have any questions or require additional information, please do not hesitate to contact us.
Sincerely, Original signed by Christopher H. Mudrick Vice President - Limerick Exelon Generation Company, LLC cc: S. J. Collins, Administrator Region I, USNRC S. L. Hansell, USNRC Senior Resident Inspector, LGS
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (6-2004)
LICENSEE EVENT REPORT (LER)
(See reverse for required number of digits/characters for each block)
APPROVED BY OMB: NO. 3150-0104 EXPIRES: 06/30/2007
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 1. FACILITY NAME Limerick Generating Station, Unit 2
- 2. DOCKET NUMBER 05000353
- 3. PAGE 1 OF 4
- 4. TITLE Scram Discharge Volume Vent and Drain Valves Opened Due To Fuse Removal
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL NUMBER REV NO.
MONTH DAY YEAR FACILITY NAME DOCKET NUMBER 05000 03 10 2007 2007 - 001 - 0 05 09 2007 FACILITY NAME DOCKET NUMBER 05000
- 9. OPERATING MODE 3
- 10. POWER LEVEL 0
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply) 20.2201(b) 20.2203(a)(3)(i) 50.73(a)(2)(i)(C) 50.73(a)(2)(vii) 20.2201(d) 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) 20.2203(a)(2)(i) 50.36(c)(1)(i)(A) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A) 20.2203(a)(2)(ii) 50.36(c)(1)(ii)(A) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x) 20.2203(a)(2)(iii) 50.36(c)(2) 50.73(a)(2)(v)(A) 73.71(a)(4) 20.2203(a)(2)(iv) 50.46(a)(3)(ii) 50.73(a)(2)(v)(B) 73.71(a)(5) 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C)
OTHER 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D)
Specify in Abstract below or in (If more space is required, use additional copies of (If more space is required, use additional copies of NRC Form 366A) (17)
The RPS logic for the backup scram valves energizes the 125 VDC solenoids on the backup scram valves during a scram to block and vent the scram air header. The same circuit energizes a relay that is used to de-energize the SDV vent and drain valve pilot valves during a scram. The RPS logic is otherwise designed to de-energize the scram valve pilot valve solenoids on each hydraulic control unit (HCU) during a scram.
The safety function of the SDV vent and drain valves is to close on a scram to limit the amount of reactor coolant discharged so that adequate core cooling is maintained and offsite doses remain within the limits of 10CFR100. The valves open on scram reset to maintain the SDV vent and drain path open so that there is sufficient volume to accept the reactor coolant discharged during a scram. The discharge of reactor coolant to the SDV can be terminated by scram reset. For a bounding leakage case, the offsite doses are well within the limits of 10CFR100 and adequate core cooling is maintained.
Cause of the Event
The event was caused by a failure to anticipate the system response that occurs when the backup scram valve fuses are removed.
Corrective Action Completed A System Specific Tagging Guide was implemented for backup scram valve fuse removal. The guide requires closing the manual valves in the SDV vent and drain lines prior to removing the fuses.
Previous Similar Occurrences There were no previous similar occurrences of the SDV vent and drain valves causing a primary containment breach when primary containment was required to be operable.