05000482/LER-1917-003, Regarding ARV and MSSV Tornado Missile Vulnerabilities Result in Unanalyzed Condition
| ML17317A462 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 11/02/2017 |
| From: | Shawn Smith Wolf Creek |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| WO 17-0081 LER 17-003-00 | |
| Download: ML17317A462 (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)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 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)(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) |
| 4821917003R00 - NRC Website | |
text
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'NUCLEAR OPERATING CORPORATION Stephen L. Smith Plant Manager U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 November 2, 2017 WO 17-0081
Subject:
Docket No. 50-482:
Licensee Event Report 2017-003-00, "ARV and MSSV Tornado Missile Vulnerabilities Result in Unanalyzed Condition" To Whom It May Concern:
The enclosed Licensee Event Report (LER) 2017-003-00 is being submitted pursuant to 1 O CFR 50.73(a)(2)(i)(B), 10 CFR 50.73(a)(2)(ii)(B), 10 CFR 50.73(a)(2)(v)(A), and 10 CFR
- 50. 73(a)(2)(v)(B).
This letter contains no commitments. If you have any questions concerning this matter, please contact me at (620) 364-4093, or Cynthia R. Hafenstine at (620) 364-4204.
SLS/rlt Enclosure: LER 2017-003-00 cc:
K. M. Kennedy (NRC), w/e B. K. Singal (NRC), w/e N. H. Taylor (NRC), w/e Senior Resident Inspector (NRC), w/e Sincerely, P.O. Box 411 /Burlington, KS 66839 I Phone: (620) 364-8831 An Equal Opportunity Employer M/F/HCNET
NRC FORM366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2017) bllf;!:/lwww.nrc.gov/r!;l<idiog-rmfgoQ-colleQ!ionsfnur!;lg-;;fs!afff-;;r1022/r3l) the NRG may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Wolf Creek Generating Station 05000 482 I OF 4
- 4. TITLE ARV and MSSV Tornado Missile Vulnerabilities Result in Unanalyzed Condition
- 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 MONTH DAY YEAR NUMBER NO.
05000 FACILITY NAME DOCKET NUMBER 09 07 2017 2017 -
003 - 00 11 02 2017 05000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
D 20.2201(b)
D 20.2203<a><3>
D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A) 1 D
20.2201 (d)
D 20.2203(a)(3)(ii)
[ZJ 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
D 20.2203(a)c1>
D 20.2203ca><4>
D so.13(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
D 202203(a)c2>
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)(ii)
D 50.36(c)(1)(ii)(A)
[Z] 50.73(a)(2)(v)(A)
D 13.11ca)(4)
D 20.2203ca>c2>cm>
D so.36(c)(2)
[Z] 50.73(a)(2)(v)(B)
D 13.11ca>
D 20.2203(a)(2)(iv)
D so.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 13.77(a)(1) 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)(i)
D 20.2203(a)(2)(vi)
[ZJ 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 13_11ca)c2>cn)
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D 50.73(a)(2)(i)(C)
D OTHER Specify in Abstract below or in Therefore, based on the lack of an adequate analysis to demonstrate that one design basis tornado missile couldn't affect the safe shutdown of the plant, at 1325 Central Daylight Time (CDT), on September 7, 2017, the ARVs and MSSVs were declared inoperable. TS LCO 3.7.1 Condition C (one or more SGs with 4 or more MSSVs inoperable) and TS LCO 3.7.4 Condition C (3 or more ARV lines inoperable for reasons other than excessive leakage) were entered at this time. Initial compensatory measures were put in place consistent with EGM 15-002. Based on the guidance provided in EGM 15-002, upon completion of these initial compensatory measures the ARVs and MSSVs were subsequently declared operable but non-conforming. The compensatory measures were completed within the allowed TS LCO Completion times.
This condition is reportable under 10 CFR 50.72. However, consistent with EGM 15-002, after the initial 10 CFR 50.72 notification has been made for tornado missile vulnerabilities the NRG will exercise enforcement discretion for subsequent tornado missile 10 CFR 50. 72 notifications. Therefore, no 10 CFR 50. 72 notification was made for this condition. The initial tornado missile vulnerability notification to the NRG was completed on April 5, 2017 in Event Notification#52666.
BASIS FOR REPORTABILITY This condition is reportable as required by:
10 CFR 50.73(a)(2)(i)(B) for a condition that is prohibited by Technical Specifications.
10 CFR 50.73(a)(2)(ii)(B) for an event or condition that results in the plant being in an unanalyzed condition that significantly degrades plant safety.
10 CFR 50. 73(a)(2)(v)(A) for a condition that at the time of discovery could have prevented the fulfillment of a safety function of structures or systems needed to shut down the reactor and maintain it in a safe shutdown condition.
10 CFR 50.73(a)(2)(v)(B) for a condition that at the time of discovery could have prevented the fulfillment of a safety function of structures or systems needed to remove residual heat.
CAUSE OF EVENT
This condition is an original plant design legacy issue. Due to the historical nature of this vulnerability, a specific cause has not been identified.
CORRECTIVE ACTIONS
All of the following corrective actions are being tracked by Condition Report 115590.
Initial compensatory measures taken in accordance with EGM 15-002 include verification that severe weather procedures were up-to-date, verification that procedures and equipment were up-to-date supporting Diverse and Flexible Coping Strategies (FLEX), ensuring Operations personnel were current on their training to these procedures, and implementing measures to heighten station awareness until the vulnerabilities have been corrected.
More comprehensive compensatory measures have been implemented and consist of revising Wolf Creek procedure OFN SG-003, "Natural Events" to include:
- 1) a requirement to walk down susceptible components post-severe weather, and
- 2) adding staged equipment to address any crimped exhaust pipe.
Ultimately, the nonconformance of the ARVs and MSSVs may be addressed through physical plant modifications, industry approved risk evaluation, or another method consistent with WCGS' licensing basis.
SAFETY SIGNIFICANCE
As documented in EGM 15-002, tornado missile scenarios that may lead to core damage are very low probability events because SR SSCs are typically designed to withstand effects of tornados. For a tornado missile-induced scenario to occur, a tornado would have to hit the site and result in the generation of missiles that would hit and fail vulnerable, unprotected SR equipment, and/or unprotected SR subcomponents in a manner that is non-repairable and non-recoverable. In addition, because plants are designed with redundancy and diversity, the tornado missiles would have to affect multiple trains of safety systems and/or means of achieving safe shutdown.
The NRG has completed a generic risk analysis of potential tornado missile protection noncompliances to examine the risk significance of these scenarios. This assessment documents a conservative, bounding-type analysis of the risk significance for plant facilities. The generic analysis assumed that core damage would occur if a tornado hit a plant located in the most active tornado region in the country and that it caused a tornado-generated missile to fail all emergency core cooling equipment at the plant with no ability to recover. Given this conservative assumption, the staff's study established that the core damage frequency (GDF) associated with tornado missile-related noncompliances are well below CDFs requiring immediate regulatory action. In summary, the generic bounding risk analysis performed by the NRG concluded that this issue is of low risk significance.
During a postulated design basis tornado, the conditions documented could have resulted in a loss of safety function for the ARVs and MSSVs, though with a very low likelihood. The main steam lines from each SG have 1 ARV and 5 MSSVs.
Each of the MSSVs have 2 exhaust pipes. Therefore the total number of exhaust pipes which are exposed to potential tornado missiles is 44, (4 ARV exhausts, 40 MSSV exhausts). The exhaust piping for each of the ARVs is 8" steel pipe, surrounded by a 78" diameter silencer. The exhaust piping for each of the MSSVs is 16" steel pipe. The exposed portions of the ARV and MSSV exhaust piping are 102 feet and 90 feet above ground level respectively. Missile protection is provided from the north by the Turbine building, and the south by the Reactor building. The exhaust pipes are arranged with the ARVs, as well as each set of 5 MSSVs, in a line running east to west. The ARVs and MSSVs would be capable of performing their safety functions in the event that a missile was to shear off any of the exhaust piping.
Thus, the only failure mechanism of concern would be crimping of these exhaust lines. In the unlikely event that tornado conditions would cause design basis tornado missiles to impact the ARV or MSSV exhaust piping, due to their robust design, their elevation, and their physical arrangement, it would be almost impossible to completely crimp enough exhaust lines to cause more than 2 SGs to become nonfunctional. Since WCGS is designed to be able to safely shut down with 2 functioning SGs, the likelihood that the safe shutdown of WCGS would be challenged by this type of event, is very low.
As WCGS has not experienced an actual tornado missile event, this condition had no actual safety consequences impacting plant or public safety. Therefore, this condition had a very low safety significance.
OPERATING EXPERIENCE/PREVIOUS EVENTS The only previous tornado vulnerability identified at WCGS was that reported in LER 2017-002-00. Page 4
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