05000454/LER-2016-002, Regarding Inadequate Protection from Tornado Missiles Identified Due to Non-Conforming Design Conditions
| ML16203A007 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 07/21/2016 |
| From: | Kanavos M Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| BYRON 2016-0071 LER 16-002-00 | |
| Download: ML16203A007 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 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)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4542016002R00 - NRC Website | |
text
__r Byron Generating Station Exeton Generat i Qfl Rd www.exeloncorp.com July21, 2016 LTR:
BYRON 2016-0071 File:
1.10.0101 (1D.101) 2.07.0100 (5A.108)
United States Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Byron Station, Units 1 and 2 Renewed Facility Operating License Nos. NPF-37 and NPF-66 NRC Docket Nos. STN 50-454 and STN 50-455
Subject:
Licensee Event Report (LER) No. 454-20 1 6-002-00, Inadequate Protection from Tornado Missiles Identified Due to Non-Conforming Design Conditions Enclosed is Byron Station Licensee Event Report (LER) No. 454-20 1 6-002-00 regarding non-conforming conditions in the plant design such that specific TS equipment on both units was considered to not be adequately protected from tornado missiles. This condition is being submitted in accordance with 10 CFR 50.73, Licensee Event Report System.
There are no regulatory commitments in this report.
Should you have any questions concerning this submittal, please contact Mr. Douglas Spitzer, Regulatory Assurance Manager, at (815) 406-2800.
Respectfully, Mark E. Kanavos Site Vice President Byron Generating Station MEK/GC/sg
Enclosure:
LER 454-2016-002-00 cc:
Regional Administrator NRC Region III NRC Senior Resident Inspector Byron Generating Station
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 10/31/2018 (11-201 5)
Eshmated, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Byron Station Unit 1 05000454 1
OF 4
- 4. TITLE Inadequate Protection from Tornado Missiles Identified Due to Non-Conforming Design Conditions
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEUAL MONTH DAY YEAR Byron Station Unit 2 05000455 FACILITY NAME DOCKET NUMBER 05 25 16 2016
- - 002 00 07 21 16 N/A N/A
- 9. OPERATING MODE
- 11. ThIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
LI 20.2201(b)
LI 20.2203(a)(3)(i)
[7 50.73(a)(2)(U)(A)
LI 50.73(a)(2)(viii)(A)
LI 20.2201(d)
[7 20.2203(a)(3)(ii) 50.73(a)(2)fii)(B)
LI 50.73(a)(2)fviii)(B)
[7 20.2203(a)(1)
LI 20.2203(a)(4)
LI 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A)
LI 20.2203(a)(2)(i)
LI 50.36(c)(1)Q)(A)
LI 50.73(a)f2)(iv)(A)
LI 50.73(a)f2)(x)
LI 20.2203(a)(2)Øi)
LI 50.36fc)(1)(ii)(A)
LI 50.73(a)(2)(v)(A)
LI 73.71(a)(4)
LI 20.2203(a)(2)(iii)
LI 50.36fc)(2) 50.73(a)(2)(v)(B)
LI 73.71(a)f5)
LI 20.2203(a)(2)(iv)
LI 50.46(a)(3)Oi)
LI 50.73(a)(2)fv)(C)
[7 73.77(a)(1)
LI 20.2203(a)(2)(v)
LI 50.73(a)(2)(i)(A)
LI 50.73(a)(2)(v)(D)
LI 73.77(a)(2)(i)
LI 20.2203(a)(2)(vi) 50.73(a)(2)fi)(B)
LI 50.73(a)(2)(vii)
LI 73.77(a)(2)(U)
LI 50.73(a)(2)C)(C)
LI OTHER Specify in Abstract below or in by the EGM and DSS. The TS LCOs and Technical Requirements Manual (TRM) limiting conditions for operation (TLCOs) 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 [EJJ, the Unit 1 and Unit 2 112/114/212/214 ESF Inverters [EF], the Main Control Room radiation monitors (OPR31J, OPR32J, OPR33J, 0PR34]) [IL], the Unit 1 and Unit 2 RWSTs, the Unit 1 and Unit 2 emergency core cooling system both trains, the Unit 1 and Unit 2 containment spray [BE]for both trains, and the Byron Essential Service Water Cooling Towers (Ultimate Heat Sink).
NRC Event Notification51958 was made on May 25, 2016 at 1650 EDT.
This condition is reportable in accordance with 10 CFR 50.73(a)(2)(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(a)(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 also being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) for any operation or condition which was prohibited by TS. Additionally, this event is being reported in accordance with 10 CFR 50.73a)(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 that 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 Byron 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 states 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 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 tail 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 NRC 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 stated 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 tornados 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 Ops Standing Order and an associated read and sign was 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, or revise the design/licensing bases.
3.
Modify the Miscellaneous Electrical Equipment Room ventilation openings to eliminate tornado missile vulnerability, or revise the design/licensing bases.
4.
Obtain a license amendment for the use of the TORMIS computer code for assessment of tornado missile protection
F. Previous Occurrences
There have been no previous Licensee Event Reports at Byron on this issue.
G. Component Failure Data
Manufacturer Nomenclature Model Mfg. Part Number N/A N/A N/A N/A