05000456/LER-2016-002, Regarding Inadequate Protection from Tornado Missiles Identified Due to Non-Conforming Design Conditions

Regarding Inadequate Protection from Tornado Missiles Identified Due to Non-Conforming Design Conditions

ML16201A336
Person / Time
Site:	Braidwood
Issue date:	07/19/2016
From:	Marchionda-Palmer M Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
BW160058 LER 16-002-00
Download: ML16201A336 (6)

LER-2016-002, Regarding Inadequate Protection from Tornado Missiles Identified Due to Non-Conforming Design Conditions

Event date:
Report date:
Reporting criterion:	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)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(b)(3)(ii)(B) 10 CFR 50.73(b)(2)(v)
4562016002R00 - NRC Website

text

Exelon Generation Company, LLC Braidwood Station 35100 South Route 53, Suite 84 Braceville, IL 60407-9619 July 19, 2016 BW160058 ti n www.exeloncorp.com U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Braidwood Station, Units 1 and 2 Renewed Facility Operating License Nos. NPF-72 and NPF-77 N RC Docket Nos. STN 50-456 and STN 50-457 10 CFR 50.73

Subject:

Licensee Event Report 2016-002 Inadequate Protection from Tornado Missiles Identified Due to Non-Conforming Design Conditions The enclosed Licensee Event Report (LEA) is being submitted in accordance with 10 CFR 50.73, "Licensee Event Report System."

There are no regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact Mr. Steven Reynolds, Regulatory Assurance Manager, at (815) 417-2800.

Marri chionda-Palmer Site Vic President Braidwood Station

Enclosure:

LER 2016-002-00 cc: NRA Project Manager-Braidwood Station Illinois Emergency Management Agency - Division of Nuclear Safety US NRC Regional Administrator, Region Ill US NRC Senior Resident Inspector (Braidwood Station)

Illinois Emergency Management Agency-Braidwood Representative

bee: Site Vice President - Braidwood Station Director - Licensing Manager, Licensing - Braidwood, Byron and LaSalle County Stations Regulatory Assurance Manager - Braidwood Station Braidwood Nuclear Licensing Administrator Exelon Document Control Desk Licensing Corporate Commitment Management Coordinator Braidwood Commitment Management Coordinator

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150*0104 EXPIRES: 10/31/2018 (11-2015)

1. "lllllu~

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information coHection.

3. PAGE Braidwood Station, Unit 1 05000456 1 OF 4

4. TITLE Inadequate Protection from Tornado Missiles Identified Due to Non-Conforming Design Conditions

5. EVENT DATE

6. LEA NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED I

SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO.

MONTH DAY YEAR Braidwood Station, Unit 2 05000457 FACILITY NAME DOCKET NUMBER 05 25 2016 2016 - 002 00 07 19 2016 N/A N/A

9. OPERATING MODE

11. THIS REPORT IS SUBMITIED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: {Check all that apply)

D 20.2201(b)

D 20.22os(a)(s)(i)

D 50.73(a)(2)(ii)(A)

D 50.73(a)(2)(viii)(A) 1 D 20.2201(d)

D 20.22os(a)(s)(iil IZ! 50.73(a)(2)(ii)(B)

D 50.73(a)(2)(viii)(B)

D 20.22os(a)(1)

D 20.22os(a)(4)

D so.1s(a)(2)(iii)

IZ! 50.73(a)(2)(ix)(A)

D 20.22os(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 20.22os(a)(2)(ii)

D 50.36(c)(1)(ii)(A)

D 50.73(a)(2)(v)(A)

D 1s.11(a)(4)

D 20.22os(a)(2)(iii)

D so.s6(c)(2)

D 50.73(a)(2)(v)(B)

D 1s.11(a)(5l D 20.2203(a)(2)(iv)

D so.46(a)(s)(iil D 50.73(a)(2)(v)(C)

D 1s.11(a)(1) 100 D 20.2203(a)(2)(v)

D 50.73(a)(2)(i)(A)

IZ! 50. 73(a)(2)(v)(D)

D 1s.11(a)(2)(il D 20.2203(a)(2)(vi)

IZ! 50.73(a)(2)(i)(B)

D 50.73(a)(2)(vii)

D 1s.11(a)(2)(ii)

D 50.73(a)(2)(i)(C)

D OTHER Specify in Abstract below or in inside the RWST, could be impacted by tornado missiles entering the RWST roof access: the six inch RWST recirculation pipe; the three inch overflow pipe; and the twenty-four inch suction pipe.

On May 25, 2016 at 1415, Operations declared the affected equipment inoperable, implemented EGM 15-002 and the required compensatory measures, and then declared the affected equipment operable but non-conforming, as allowed by the EGM and DSS. The TS LCOs and Technical Requirements Manual (TRM) Limiting Conditions for Operation (TLCO) that were entered and exited were for the following equipment: The two Unit 0 A and B trains of control room ventilation [VI], the Unit 1 (Division 11) and Unit 2 (Division 21) train A battery chargers and DC buses [EJ], the Unit 1 and Unit 2 112/114/212/214 ESF inverters [EF], the main control room radiation monitors (OPR31 J, OPR32J, OPR33J, OPR34J) [IL], the Unit 1 and Unit 2 RWSTs, the Unit 1 and Unit 2 emergency core cooling system trains, the Unit 1 and Unit 2 containment spray [BE] for both trains, and the Unit 1 and Unit 2 B train (diesel driven) auxiliary feedwater [SJ] pumps. NRG Event Notification51959 was made on May 25, 2016 at 1710 EDT.

This condition is reportable in accordance with 10 CFR 50.73(b)(3)(ii)(B) for any event or condition that results in the nuclear power plant being in an unanalyzed condition that significantly degrades plant safety, and in accordance with 10 CFR 50.73(b)(2)(v)(D) for any event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident. As the issues have been in place per original plant design, this condition existed for a longer period of time than is allowed by TS; therefore, this event is reportable in accordance with 1 O CFR 50.73(a)(2)(i)(B) for any operation or condition which was prohibited by TS. Additionally, this event is reportable in accordance with 10 CFR 50.73(a)(2)(ix)(A) for any event or condition that as a result of a single cause could have prevented the fulfillment of a safety function for two or more trains or channels in different systems that are needed to mitigate the consequences of an accident.

C. Cause of Event

The cause of this issue was a lack of clarity and changing requirements during the original licensing of the plants which led to inadequate understanding of the original NRC regulatory guidance.

D. Safety Consequences

This condition had no actual safety consequences impacting plant or public safety since Braidwood Station did not experience a tornado missile event.

During a postulated design basis tornado, this could have resulted in the loss of one or more of the equipment listed above under Description of Event, and result in the loss of safety function of one or more systems.

EGM 15-002, in providing the basis for granting the enforcement discretion stated that, in general, tornado missile scenarios that may lead to core damage are very low probability events, because safety-related systems, structures and components (SSCs) are typically designed to withstand the effects of tornadoes. 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 safety related equipment and/or unprotected safety related 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.

EMG 15-002 states that the NRG completed a generic risk analysis of potential tornado missile protection non-compliances to examine the risk significance of these scenarios. The generic nature of this analysis did not afford the staff the capability to assess plant-specific tornado missile protections which likely exist at many reactors that would result in lower risk determinations, and it did not consider the plant-specific nature of the non-compliances or the redundancies of SSCs. 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.

Further, the study did not account for a number of conservatisms. For example, whereas the study assumed the failure of redundant systems due to tornado generated missiles, actual spatial configurations of redundant systems at a plant could lower the probability of complete system failures as a result of tornado generated missiles.

Additionally, some tornado generated missiles may not cause system failures at all or may cause failures that are repairable or recoverable within a reasonable time frame.

In summary, EGM 15-002 states that the generic bounding risk analysis performed by the NRC concluded that this issue is of low risk significance. Therefore, enforcement discretion until June 10, 2018, will not impose significant additional risk to public health and safety.

E. Corrective Actions

Immediate Actions Completed

1. Abnormal Operating Procedure addressing tornadoes and high winds was revised to add additional guidance for performing actions in the event of a tornado watch or warning.

2. A description of the nonconforming SSCs and associated compensatory measures has been added to the Operations turnovers, and a briefing discussing these actions was performed during each shift turnover briefing.

3. An Operations Standing Order and an associated read and sign were created to document all Operations personnel understanding of the additional requirements.

4.

Log entries were made documenting the inoperability and subsequent transition to operable but nonconforming.

The initial briefing actions were also completed and logged.

Corrective Actions Planned

1. Complete the EGM 60-day comprehensive compensatory measures to demonstrate a discernable change from its pre-discovery actions.

2.

Modify the RWST hatches to eliminate the tornado missile vulnerability.

3.

Obtain and implement a license amendment for an analytical solution dispositioning tornado generated missile nonconforming conditions.

F. Previous Occurrences

There have been no previous Licensee Event Reports at Braidwood on this issue.

G. Component Failure Data

Manufacturer Nomenclature Mfg. Part Number NIA NIA NIA NIA