05000305/LER-2008-001, Pressurizer PORV and Reactor Coolant System Vent Valves Appendix R Spurious Operation Concern
| ML083240089 | |
| Person / Time | |
|---|---|
| Site: | Kewaunee  |
| Issue date: | 11/07/2008 |
| From: | Scace S Dominion, Dominion Energy Kewaunee |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 08-0681 LER 08-001-00 | |
| Download: ML083240089 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3052008001R00 - NRC Website | |
text
z*XI"Donhinion Dominion Energy Kewaunee, Inc.
N490 Highway 42, Kewaunee, WI 54216-9511 NOV 0 7 2008 ATTN: Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555-0001 Serial No. 08-0681 LIC/RR/RO Docket No.: 50-305 License No.: DPR-43 DOMINION ENERGY KEWAUNEE, INC.
KEWAUNEE POWER STATION LICENSEE EVENT REPORT 2008-001-00 Pursuant to 10 CFR 50.73, Dominion Energy Kewaunee, Inc., hereby submits the following Licensee Event Report applicable to Kewaunee Power Station.
Report No. 50-305/2008-001 -00 This report has been reviewed by the Facility Safety Review Committee and will be forwarded to the Management Safety Review Committee for its review.
If you have any further questions, please contact Mr. Richard Repshas at (920) 388-8217.
Very truly yours,
/Ste h
SnEcace Site Vice President, Kewaunee Power Station Attachment(s)
Commitments made by this letter: NONE
- - It Z--
pA
Serial No. 08-0681 Page 2 of 2 cc:
Regional Administrator, Region III U.S. Nuclear Regulatory Commission 2443 Warrenville Road Suite 210 Lisle, IL 60532-4352 Mr. P. S. Tam Sr. Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08-H4A 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Kewaunee Power Station
NRC FORM 366 U.S. NUCLEAR REGULATORYCOMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2010 (9-2007)
, the NRC (See reverse for required number of may not conduct or sponsor, and a person is not required to respond to, the digits/characters for each block) information collection.
- 3. PAGE Kewaunee Power Station 05000305 1
OF 4
- 4. TITLE Pressurizer PORV and Reactor Coolant System Vent Valves Appendix R Spurious Operation Concern
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED I
FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR NUMBER NO 1
05000 FACILITY NAME 09 11 2008 2008 001 00 11 07 2008 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
EO 20.2201(b)
[I 20.2203(a)(3)(i)
EJ 50.73(a)(2)(i)(C)
[I 50.73(aX2)(vii)
N El 20.2201(d) 0 20.2203(a)(3)(ii) 0 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
Nl 20.2203(a)(1)
El 20.2203(a)(4) 0 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i)
[I 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
[:
50.73(a)(2)(ix)(A)
El 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A)
El 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
- 10. POWER LEVEL El 20.2203(a)(2)(iii)
El 50.36(c)(2)
El 50.73(a)(2)(v)(A) 0 73.71 (a)(4)
El 20.2203(aX2)(iv)
El 50.46(a)(3)(ii)
El 50.73(a)(2)(v)(B)
El 73.71(aX5) 100 El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
[I 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
==Event Description==Pressurizer and Reactor Head Vent Valves RC-33B, RC-45B, and RC-49 Valves PR-33B and RC-45B are each in series with RC-49, so a fire would need to cause spurious opening of RC-49 and one of the other valves in series. Similar to the pressurizer PORV, a fire in the relay room would require use of shutdown procedure AOP-FP-002, "Fire In Alternate Fire Zone." The valve circuits are either individually deenergized by removing fuses in RR-1 76, or RR-1 76 is completely deenergized by opening the Circuit 12 feed breaker from Train B DC distribution cabinet BRB-1 04.
The 125-VDC power cable from RR-1 76 that supplies all three of the subject vent valves is routed in a cable tray in the relay room. However, there are other 125-VDC cables in the tray. Spurious opening of PR-33B and RC-49 or RC-45B and RC-49 could be postulated as follows: Control cable for PR-33B or the control cable for RC-45B and the control cable for RC-49 experience fire damage resulting in an internal short.
between conductors (creates a closed circuit that can result in opening each valve if power is available) and external cable-to-cable hot shorts occur between the power cable and other energized DC conductors in the same cable tray (i.e., concurrent DC hot shorts of the proper polarity from the same battery on the control cable, affecting any two valves in series). The current procedural guidance does not deenergize all of the DC cables in the tray containing the power cable. Therefore, the pressurizer vent or reactor head vent high-low pressure interface could be spuriously breached due to a fire.
Event and Safety Consequence Analysis:
The originally accepted post-fire mitigating action was to deenergize the PORV and RCS vent valves via opening a breaker or pulling fuses. As an enhancement, the station made modifications to the PORV and vent valve cabling in design change, DCR 2055, for protection from a hot short by routing a portion of the circuit in dedicated conduit. However, a portion of the circuit in the relay room connecting to the control room was left in cable trays. The design change was developed by the original architect/engineer for the plant and implemented in the 1987 timeframe. From a review of the modification package, there is very little design information identified and no discussion as to why only a portion of the PORV and vent valve circuits were rerouted in dedicated conduit.
In the Station Appendix R analysis, PORV PR-2B is required to remain closed to control RCS pressure and inventory. A postulated spurious opening of the PORV due to a fire would have a significant adverse affect on the ability to control pressure and inventory. A risk assessment for potential spurious opening of the pressurizer PORV was performed. The conclusion, with conservatiye assumptions, shows that the condition of concern cannot be characterized as being a risk significant event (i.e., Incremental Core Damage Probability Deficit is significantly less than 1.OE-4).
Similarly, in the Appendix R analysis, the pressurizer and reactor head vent valves are required to remain closed to control RCS pressure and inventory. The vent lines contain a flow restriction orifice such that RCS flow from inadvertent actuation is less than the flow capacity of one charging pump. Therefore, the depressurization transient is expected to be bounded by the PORV PR-2B spurious opening. However, for RCS makeup, the Appendix R analysis assumes that the RCP seals leak at 44 gallons per minute and credits only charging pump C. Therefore, makeup from the charging pump cannot be assumed to mitigate the head vent discharge flow.
The Station fire protection program is based on a defense-in-depth philosophy. The primary combustible in the relay room is cable insulation. This cabling is qualified to IEEE 383 flame test requirements. Therefore, self-ignited cable fires are not postulated and the tendency to propagate fire is minimized. The room also has functional automatic fire detection, comprised of multi-sensor smoke detectors. This will permit detection of a fire in its early stages, such that manual actuation of the fixed C02 fire suppression system and fire brigade response can be effective in extinguishing the fire. The relay room also has restricted personnel access and administrative restrictions on transient combustibles and hot work. The current procedural guidance for deenergizing the PORV and the vent valves reduces the possibility of a spurious operation in the event of a fire that damages cables. External DC hot shorts of the proper polarity could cause the PORV or vent valves to spuriously open, which must be considered in the case of RCS high-low pressure interfaces. However, the NRC acknowledges in RIS 2004-03, Rev. 1 and Generic Letter 86-10 that a failure involving two concurrent, cable-to-cable, DC hot shorts of the proper polarity has a low probability of occurrence. The PORV and vent valve circuit protection inadequacy represents a degradation of the Appendix R safe shutdown capability.
However, it does not have a significant adverse affect on the Station fire protection program defense-in-depth philosophy.
Cause
The cause of this condition is believed to be an incorrect assumption that deenergizing the PORV and vent valve circuits alone would be sufficient to prevent spurious operation. Thus, the PORV and vent valve cable rerouting partially in conduit was viewed as a betterment item. The modification was developed by the original architect/engineer for the plant and originally implemented in the 1987 timeframe. Given the lack of detail in the modification information, no conclusive cause could be determined why only a portion of the PORV and vent valve circuits were rerouted in dedicated conduit.
Corrective Actions
Immediate actions were to post a fire watch for the relay room. The posting of a one-hour roving fire watch and the active detection system provides adequate compensatory measures to detect a fire in its incipient stage such that rapid extinguishment can occur prior to the spurious operation of PR-2B or a combination of RC-33B and RC-49 or RC-45B and RC-49.
Additional evaluations to determine if plant modifications, procedure changes, or a determination of acceptability of the condition, will be performed during the implementation of the NFPA 805 transition for Kewaunee Power Station.
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