05000282/FIN-2018011-02
Finding | |
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| Title | Potential Failure to Protect Class I Structures, Systems,and Components from Tornado Generated Missiles |
| Description | Inspectors identified a number of structure, systems,and components (SSCs) that lacked protection from tornado generated missiles. The following SSCs were identified: Division 1 and Division 2 Emergency Diesel Generators (D1/D2 EDGs)engine exhaust, fuel oil day tank vents, and main fuel oil storage tanks vents; and Diesel Driven Cooling Water Pumps (DDCWPs) main fuel storage tank vents, day tank vents, engine exhausts, and rooms ventilation intake and exhaust equipment. In various cases susceptible SSCs for redundant equipment (e.g. fuel tank vents) were right next to or within a few feet of each other such that a single missle could affect both trains of the system
A review of the sites licensing bases, including the original FSAR, identified the D1/D2 EDGs and the DDCWPs as Class I, safety-related SSCs, which are required to be designed to withstand, without loss of capability, environmental phenomena including tornadoes and tornado generated missiles. Specifically, the current USAR Table 12.2-1, Classification Of Structures, Systems and Components, list both systems as Class I and has two notes of interest. Note 1 applies to the Diesel Generators and their associated [Main] Fuel Oil Storage Tank, which states, in part, The indicated Design Class I is applicable to D1/D2 Diesel Generators and associated[emphasis added] safety related components and systems. The second note is listed at the beginning of the Table, which states,in part,To determine detail design classifications and boundaries separating different design classes within the overall classification scheme listed here, refer to controlled drawings. A review of controlled drawings, including NF-39255-1, Flow Diagram Diesel Generators D1 & D2 Unit 1 & 2,Revision 85, and NF-39232, Flow Diagram Fuel & Diesel System Unit 1 & 2, Revision 86,showed the fuel oil vents for the main storage tanks, fuel oil vents for the day tanks,engine exhaust piping,mufflers, and silencers for the D1/D2 EDGs and DDCWPs were classified as safety-related Class I SSCs. A review of the current UFSAR identified the following sections of interest:The USAR Section 1.5.I, Overall Plant Requirements, Criterion 2 -Performance Standards, Answer, established in part The system and components designated Class I in Section 12, in conjunction with administrative controls and analysis, as applicable, are designed to withstand, without loss of capability to protect the public, the most severe environmental phenomena ever experienced at the site with appropriate margins included in the design for uncertainties in historical dataThe USAR Section 12.2.1.1.a, Classification of Structures and Components, defines Design Class I as Those structures and components including instruments and controls whose failure might cause or increase the severity of a loss-of-coolant accident or result in an uncontrolled release of substantial amounts of radioactivity, and those structures and components vital to safe shutdown and isolation of the reactor.The USAR Section 12.2.5.1.g.1, Protection for Class I Items, establishes, in part, that Class I items are protected against damage from: Missiles from different sources.These sources comprise: Tornado created missiles.The USAR Section 12.2.1.3.2.c., Tornado Loads, defines the design tornado driven missile as assumed equivalent to an airborne 4 x 12 x 120 plank travelling end-on at 300 mph, or a 4000 lbs automobile flying through the air at 50 mph and at not more than 25 feet above ground level.Based on the above, the inspectors were concerned the susceptible SSCs could lose the capability to perform their safety-related function if they were impacted by tornado generated missiles. For example, an impact to the fuel oil vents could crimp the vent path resulting in a vacuum inside the tanks that could collapse the tank and/or cause the associated fuel transfer pump to lose net positive suction head The licensee provided a position paper proposing the susceptible SSCs identified by the inspectors were meeting their current licensing bases and no further actions were required. The inspectors disagreed, but decided to request support from the Office of Nuclear Reactor Regulation (NRR) to obtain clarification on the sites licensing bases related to tornado generated missiles. Planned Closure Action: The inspectors have requested NRR to provide clarification on the sites current licensing bases regarding tornado generated missiles required protection.Licensee Action: Licensee is considering doing a self-review of design and licensing basis of the fuel oil storage tank vent lines to understand and clarify design class of the lines Corrective Action Reference:501000012997 |
| Site: | Prairie Island  |
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| Report | IR 05000282/2018011 Section 1R21 |
| Date counted | Jun 30, 2018 (2018Q2) |
| Type: | URI: |
| cornerstone | No Cornerstone |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.21M |
| Inspectors (proximate) | A Dunlop J Benjamin V Meghani V Petrella S Kobylarz W Hopf J Corujo-Sandin M Jeffers K Takiyoshi K Yonebayashi |
| Violation of: | Pending |
| INPO aspect | |
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Finding - Prairie Island - IR 05000282/2018011 | |||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Prairie Island) @ 2018Q2
Self-Identified List (Prairie Island)
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