NRC-13-0053, Response to Request for Additional Information (RAI) Regarding the License Amendment Request to Revise the Fermi 2 Licensing Bases for Protection from Tornado-Generated Missiles

Response to Request for Additional Information (RAI) Regarding the License Amendment Request to Revise the Fermi 2 Licensing Bases for Protection from Tornado-Generated Missiles

ML13273A467
Person / Time
Site:	Fermi
Issue date:	09/27/2013
From:	Conner J T DTE Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NRC-13-0053
Download: ML13273A467 (11)

Text

Enclosure to NRC-13-0053

Fermi 2 NRC Docket No. 50-341 Operating License No. NPF-43

Response to Request for Additional Information (RAI) Regarding the License Amendment Request to Revise the Fermi 2 Licensing Bases for Protection from Tornado-Generated Missiles

Enclosure to NRC-13-0053

Page 1

Response to Request for Additional Information (RAI) Regarding the License Amendment Request to Revise the Fermi 2 Licensing Bases for Protection from Tornado-Generated Missiles

RAI 1 Section 2.0, 2nd paragraph states: "-methodology, the probability of multiple missile strikes causing unacceptable damage to unprotected, safety-related plant features-"

Describe what Fermi has done to address the potential damage of safety-related equipment caused by the failure of non-safety related equipment due to a tornado missile strike. An example would be a tornado mi ssile that damages a non-safety related tank and causes water leakage which subseque ntly damages safety-related cables.

Response Prior to performing the tornado missile hazard analysis, the site conducted a tornado missile hazard assessment. The purpose of the assessment was to identify and evaluate any vulnerable situations that may affect th e protection of safety-related equipment from potential hazards resulting from damage caused by a tornado strike. This assessment identified several instances of potential weaknesses of non-safety related structures having the potential to impact safety-related equipment. The potential weaknesses were addressed by installing engineered protection to eliminate the threat or protect the impacted equipment. Where the threats were eliminated, the features were generally not represented in the TORMIS modeling. The following are examples of actions taken to protect several features:

a. Large lightning rods on the roof of the Residual Heat Removal (RHR) complex were determined to be potential missile threats to the RHR cooling towers. Accordingly, a modification was made to restrain the rods to preclude them from creating missile threats.

b. Safety-related piping located at the interior interface between the non-safety-related

turbine building and safety-related auxiliary building was determined to be at risk due to tornado missiles originating from the turbine building. In this instance a missile shield was erected to protect against the potential threat.

c. The steel access doors on the east set of north and south mech anical draft cooling tower fan motor enclosures were identified as ha ving insufficient capability to protect the motors from all missiles. Additional reinforcement was designed and added to augment the missile protection capability of these doors.

d. One 18-inch diameter pipe penetration and a 10 ft x 10 ft removable access panel in the south wall of the reactor and auxiliary buildings were reinforced against damage from design basis tornado missiles.

e. Penetrations in the RHR complex west wall associated with the non-safety-related EDG fuel supply equipment were included as TORMIS targets and reflected in the submitted plant risk value.

Enclosure to NRC-13-0053

Page 2

The Fermi 2 Condensate Storage Tank (CST) and Condensate Return Tank (CRT) are located away from the plant near ground elevation. The Emergency Diesel Generators (EDGs) at Fermi 2 are elevated above ground such that they would not be impacted by the site maximum probable flood level. The only safety-related equipment located near the non-safety related CST is the level instrumentation that is used to transfer the High Pressure Coolant Injection (HPCI) system and Reactor Core Isolation Cooling (RCIC) system suction lines from their normal alignment to the CST to the suppression pool suction paths. The failure modes of these instrumentation circuits have been evaluated such that their inundation with water, de-energization due to a missile strike, or the occurrence of a tank low level will result in a suction

swap to the qualified suppression pool suction source. This was also discussed in Item 2e on page 14 of Enclosure 1 of Reference 2.

RAI 2 Section 3.0, page 6, states "Mis sile sources (building-) were catalogued and modeled to a distance of approximately 2,500 feet."

What is the basis of 2,500 feet?

Response The 2,500 feet maximum missile source distance is derived from EPRI NP-769, Section 2.3.3, Off-Site Missile Assessment, on pages 2-22 and 2-23.

The section of the or iginal research that produced TORMIS describes a trajectory simulation study which determined the appropriate distance to survey missile sources to analyze a plant. The conclusion was that 2,000 feet would cover the statistically significant missile sources in terms of missile impact risk. The Fermi 2 analysis used 2,500 feet. This distance is computed from the perimeter of a safety polygon that is drawn around the safety-related targets at the plant. Therefore, the distances from various safety targets to the edge of the missile origin zones are a minimum of 2,500 feet. Missiles were not considered to originate in Lake Erie since there are no structures in the lake to form any missiles. Figure 1 below shows the missile origin zones that were considered in the TORMIS analysis.

Enclosure to NRC-13-0053

Page 4

RAI 3 Section 3.0, page 13 states:

-the EDG fuel oil tank vents and the EDG e xhaust stacks, which ar e located on the roof of the RHR complex. Both of these rooftop features are provided with tornado missile shield protection specifically designed to prevent vertically traveling missiles from entering the RHR complex and damaging the ED G fuel oil tanks and diesel engines.

Are the vent stacks protected from horizontally traveling missiles? A missile traveling horizontally could crimp the vent to significantly reduce air flow and prevent the EDG fuel oil tanks and diesel engines fr om functioning properly.

Response Substantial tornado missile protection of the EDG fuel oil tank vents and the EDG exhaust stacks exists by virtue of the immediate adjacent rein forced concrete enclos ures and the elevated location on the roof of the RHR complex (Figures 2 through 4). The safety-related EDG exhaust silencers are enclosed on the top and three sides (North, South, and West) by thick reinforced concrete enclosures which protect the exhaust penetrations from tornado missile strike. The attached non-safety related exha ust extensions (stacks) that extend beyond the silencers have been analyzed to ensure that they can withstand tornado winds and to verify compliance to seismic II/I criteria such that they will not crumple and crimp to block diesel exhaust flow. As provided in the list of excluded targets in Enclosure 4 of Reference 2, for targets 41 through 44

and 75 through 78, the configuration of the EDG e xhaust stacks, fuel oil tank vent stacks and associated missile protection barriers are part of the original plan t licensing bases.