05000249/LER-2008-003, Regarding Unplanned Control Rod Withdrawals
| ML090090372 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 12/31/2008 |
| From: | Wozniak D Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| SVPLTR # 08-0067 LER 08-003-00 | |
| Download: ML090090372 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function 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)(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 |
| 2492008003R00 - NRC Website | |
text
Exelon Exelon Generation Company, LLC www.exeloncorp.com Nuclear Dresden Nuclear Power Station 6500 North Dresden Road Morris, IL 60450-9765 10 CFR 50.73 SVPLTR # 08-0067 December 31, 2008 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Dresden Nuclear Power Station, Unit 3 Renewed Facility Operating License No. DPR-25 NRC Docket No. 50-249
Subject:
Licensee Event Report 249/2008-003-00, "Unit 3 Unplanned Control Rod Withdrawals" Enclosed is Licensee Event Report 249/2008-003-00, "Unit 3 Unplanned Control Rod Withdrawals" for Dresden Nuclear Power Station, Unit 3. This event is being reported in accordance with 10 CFR 50.73(a)(2)(v)(D), "Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident." There are no regulatory commitments contained in this submittal.
Should you have any questions concerning this report, please contact Mr. Stephen Taylor, Regulatory Assurance Manager, at (815) 416-2800.
Respectfully, David B. Wozniak U
Site Vice President Dresden Nuclear Power Station Enclosure cc:
Regional Administrator - NRC Region III NRC Senior Resident Inspector - Dresden Nuclear Power Station
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2010 (9-2007)
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- 3. PAGE Dresden Nuclear Power Station, Unit 3 05000249 1 OF 4
- 4. TITLE Unit 3 Unplanned Control Rod Withdrawals
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE J
- 8. OTHER FACILITIES INVOLVED SEQUENTIAL REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO.
MONTH DAY YEAR N/A N/A lFACILITY NAME DOCKET NUMBER 11 03 2008 2008 - 003 00 12 31 2008 IN/A N/A
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
El 20.2201(b)
El 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii) 4 El 20.2201(d)
El 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
[I 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
El 20.2203(a)(2)(i)
[I 50.36(c)(1)(i)(A)
[I 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL El 20.2203(a)(2)(ii)
[I 50.36(c)(1)(ii)(A)
El 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
El 20.2203(a)(2)(iii)
El 50.36(c)(2)
E-50.73(a)(2)(v)(A)
[1 73.71(a)(4) 000 El 20.2203(a)(2)(iv) 0l 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 [E
20.2203(a)(2)(vi)
El 50.73(a)(2)(i)(B)
Z 50.73(a)(2)(v)(D)
Specify in Abstract below or in A Unit 2 start-up from an unscheduled mid-cycle forced outage in 2005 was delayed due to excessive nitrogen gas accumulation in HCU piping. This event prompted the development and issuance of Revision 4 to DOP 0500-05, which permitted isolation of any or all HCU accumulators by closing the HCU insert, and HCU withdraw valves to limit migration of nitrogen gas into HCU piping. The intended purpose was to shorten subsequent venting of drives after system restoration. The procedure did not contain any precautions, prerequisites, selection criteria or limitations for the quantity of HCUs to be isolated with an operating CRD pump. The root cause evaluation determined that the procedure lacked sufficient guidance for the intended use.
In 2007, the Institute of Nuclear Power Operations (INPO) issued SEN 264 that provided information based on recently reported historical events at several Boiling Water Reactors (BWRs) in Japan during outages, which occurred between 1978 and 2000. In each event, single or multiple control rods unexpectedly withdrew from the core without a deliberate command withdrawal signal. The SEN 264 stated in part:
"The unexpected rod withdrawals occurred during either isolation or restoration of multiple HCUs. With a CRD pump running and the majority of the HCUs isolated, CRD system pressures had increased sufficiently for some control rods to withdraw from the core when the associated HCU isolation valves were manipulated in a specific sequence."
"These events involved a scenario which was not well known within the industry, and other BWRs are potentially vulnerable if operated in a similar fashion without compensatory actions taken to address the anomalous operating conditions."
DNPS operations and engineering personnel reviewed the applicability of SEN 264 and concluded that although unlikely, the vulnerability exists at DNPS. Based on this conclusion, a procedure review was conducted in accordance with the requirements in procedure LS-AA-1 15, "Operating Experience Procedure," to identify procedures requiring revision to address the SEN 264 issue. The review identified procedures revisions were required to DOP 0300-08, "Control Rod Drive System Hydraulic Control Unit Isolation / Pump Isolation," DOP 0400-01, "Reactor Manual Control System Operation" and DGP 03-04, "Control Rod Movements." The procedure revisions made were considered adequate to address the SEN 264 issue and were completed in October 2007.
The RCR evaluation reviewed the cause of procedure DOP 0500-05 not being revised to address the SEN 264 issue and identified that the procedural requirements in LS-AA-1 15 to perform the procedure review provided insufficient guidance. LS-AA-1 15 did not require adequate technical rigor during the evaluation for effected procedures, did not require adequate documentation of the effected procedure evaluation, and lacked sufficient departmental, inter-departmental and cross-discipline reviews to ensure the issue under review is completely addressed.
D.
Safety Analysis
The safety significance of the event is minimal. A detailed risk assessment was performed for this event and concluded that the risk of core damage was judged to be negligible due to the reactor
remaining subcritical, no boiling in the core and redundant heat removal methods being available.
Reactor engineering calculations determined the core remained sub-critical by approximately 4.5 percent. Therefore, the consequences of this event had minimal impact on the health and safety of the public and reactor safety.
E.
Corrective Actions
All control rods were re-inserted per procedure to the full-in position by manually opening the associated HCU insert valve.
Procedure DOP 0500-05 was revised to provide administrative barriers to prevent unplanned control rod withdrawal as described in SEN 264.
Procedure LS-AA-1 15 will be revised to require sufficient rigor, departmental, inter-departmental and cross-discipline reviews for high significance / risk OPEX items.
Procedure OP-DR-108-101-1002, "Operations Department Standards and Expectations," will be revised to require if a knowledge-based procedure conditional statement shall be executed, in a non-emergency condition at the discretion of the supervisor, then a peer check by a second licensed operator shall be obtained.
F.
Previous Occurrences
A review of DNPS Licensee Event Reports (LERs) for the last three years did not identified any LERs associated with unplanned control rod withdrawal.
G.
Component Failure Data
N/APRINTED ON RECYCLED PAPERPRINTED ON RECYCLED PAPER