05000263/FIN-2009007-06
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Finding | |
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Title | Inadequate Tornado Missile Protection for the EDG System Components |
Description | The inspectors identified an unresolved item (URI) regarding the design and licensing basis for the standby diesel generator (EDG) building ventilation system and whether the ventilating system had to be protected from the effects of a design basis tornado. During a walkdown of the EDG building, the inspectors noted that temperature control dampers in the ventilation system were mounted flush with the outside walls of the building with only a metal grating serving as a barrier for tornado missiles. The inspectors questioned the adequacy of the design and received the licensee position that the EDG building was a Class 1 building designed to protect the EDG and the fuel oil day tank from tornado missiles. However, the licensee stated that the temperature control dampers and ventilation fans (V-SF-9 and - 10) were not designed to be protected from a tornado missile. The licensee stated that the designer and the licensee intended on protecting Class 1 equipment required to assure safe-shutdown of the reactor from a missile event based on the credibility of the missile. The licensee agreed that the ventilation fans were necessary for the EDGs to be operable and that the EDGs could only run for a short period of time without the fans running. However, the licensee maintained that the EDGs could perform their safe-shutdown function without the ventilation fans. The inspectors disagreed as the EDGs could not run long enough to shut the reactor down, remove latent and decay heat, and maintain the reactor in a cold shutdown condition following the loss of the EDG ventilation systems. The licensee maintained that a single missile could not take out both fans as a full height reinforced concrete wall separated the two ventilation systems. The inspectors reviewed the original design submittal (NSP-1 dated October 17, 1969), and found that the Class 1 equipment included the Standby Diesel Generator System, and the Emergency Buses and other electrical gear to and including power equipment required for safe-shutdown. The ventilation systems were not included in the list of Class 1 equipment or in the list of Class 2 equipment. However, the licensee believed the ventilation systems were considered Class 2 based on the last entry in the Class 2 list: All Other Piping and Equipment not listed under Class 1. After further research, the licensee stated that there was no specific statement regarding the EDG building ventilation in any licensing document. The inspectors identified the following statements in various licensing documents. Section 2.2.4, Standby Diesel Generating Building, of the USAR stated, the principal function of this building is to provide a safe enclosure and protection for the Enclosure 22 standby diesel generators and portions of the power distribution systems enclosed therein. Section 2.2.4.1, Structure Description, stated, in part, A north-south [sic] interior wall of reinforced concrete extends the full height of the structure providing physical separation of the diesel generator systems. The original Monticello SER, Section 3.1.2, Meteorology, stated, in part, that the facility structures and systems, which are necessary for a safe-shutdown of the reactor are designed to withstand the effects of wind loadings and potential missiles resulting from a tornado. In the current Revision 25 of the USAR the inspectors noted the following: Section 8.4.1.1, Design Basis, stated that two independent EDGs provide redundant standby power sources. Section 8.4.1.1.b stated, The EDG sets shall be complete package units with all auxiliaries necessary to make them self-sufficient power sources capable of automatic start at any time and capable of continued operation at rated full load voltage and frequency until either manually or automatically stopped. Section 8.4.1.1.d stated, The EDGs shall be located in Class 1 structures.Section I.4.3.14, HVAC Systems, stated: The only HVAC Equipment required for safe-shutdown are the ECCS Room Coolers, V-AC-5 (Division I) and V-AC-4 (Division II), located in respective Reactor Building corner rooms on the 920-foot elevation, and the EDG supply fan, V-SF-9 for EDG No. 12, and V-SF-10 for EDG No.11. USAR Table J.4.5-1, Appendix R Safe-shutdown Equipment List, identified fans V-SF-9 and -10 as safe-shutdown equipment. The inspectors concluded that the EDG ventilation fans were an auxiliary necessary for the EDG system and that the term EDGs in the USAR included all of the auxiliaries for the EDGs; therefore, the ventilation fans were necessary for safe-shutdown of the reactor (to achieve and maintain cold shutdown). Based on no actual licensing document specifically mentioning the EDG ventilation, the necessity of the fans for EDG operability, the USAR references to the fans being safe-shutdown equipment, and the NSP-1 statement that the full-height wall separated the EDG systems, the inspectors concluded that the fans and temperature control dampers should be considered Class 1 equipment and should have been protected from tornado missiles, as well as the effects of tornadoes on the ventilation ducts as described in RIS 2006-023, Post Tornado Operability of Ventilating and Air Conditioning Systems Housed in Emergency Diesel Generator Rooms. However, because this issue was not clearly defined in the original licensing documents, this will be an unresolved item pending consultation with NRC headquarters for clarification of whether the EDG building ventilation was or was not required to be a Class 1 system. (URI 05000263/2009007-006 |
Site: | Monticello |
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Report | IR 05000263/2009007 Section 1R21 |
Date counted | Dec 31, 2009 (2009Q4) |
Type: | URI: |
cornerstone | Barrier Integrity |
Identified by: | NRC identified |
Inspection Procedure: | IP 71111.21 |
Inspectors (proximate) | A Dunlop A Stone C Brown H Campbell J Bozga L Jones M Munir N Feliz Adomo S Kobylarzm Munirr Daley R Langstaff D Szwarc J Corujo-Sandin |
INPO aspect | |
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Finding - Monticello - IR 05000263/2009007 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Monticello) @ 2009Q4
Self-Identified List (Monticello)
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