ML20247H492

Discusses SEP Topic III-4A Re Tornado Generated Loading on Diesel Generator Bldg.Diesel Generator Bldg at Plant Adequately Protected from Postulated Tornado Missiles & Tornado Wind

ML20247H492
Person / Time
Site:	Oyster Creek
Issue date:	07/24/1989
From:	Croneberger D GENERAL PUBLIC UTILITIES CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
TASK-03-04.A, TASK-3-4.A, TASK-RR 5000-89-1793, NUDOCS 8907310042
Download: ML20247H492 (5)

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a GPU Nuclear Corporation V3 ~

k;- W.d fI Ng gpIggn Hw wMs One Upper Pond Road Parsippany, New Jersey 07054 201-316-7000 TELEX 136-482 Writer's Direct Dial Number: j i '

July 24, 1989 5000-89-2793 l

l U.S. Nuclear Regulatory Commission Attention Document Control Desk j Washington, D.C. 20555 j I

Gentlemen

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i Subjects Oyster Creek Nuclear Generating Station l Docket No. 50-219 Tornado Generated Loadings on Diesel Generator Building (SEP)

(1) PLG-0276, Rev. 1 (transmitted by GPUN letter dated September 16, 1983)

(2) GPUN Letter to NRC " Tornado and Wind Generated Missiles" dated October 15, 1984.

(3) GPUN Calculation 1302 x-322C-A55 (4) NRC Letter to GPUN " Integrated Plant Safety Assessment Section 4.3, Wind  ;

and Tornado Loadings - Cyster Creek" dated March 8, 1986. 1 (5) GPUN letter to NRC " Tornado Missile" dated Aug. 14, 1987 (6) NRC letter to GPUH CRequest for Additional Information - OCNGS - Tornado Generated Loadings on Diesel Cenerator Buildlug" dated Feb. 10, 1989.

I During the integreted assessment of SEP Topic No. III-4A, Tornado Missiles, the l NRC staf f stated that although there are multiple sourcos of water and supply j rfysteme on which Oyster Creek can rely to accomplish safe shutdown, they are not protected from tornado missiles. It was also the staff's position that .

redundancy is not acceptable protection for tornado missiles. j GPUN initially proposed to prov0de a porteble pump in a protected area and a hose connection to a protected water supply to be used in conjunction with the isolation condenser to achieve the hot shutdown (IPSAR Section 4.6.4).

1 l l Subsequently, through a detailed field walkdown and line loss analysis of an i i existing system interconnection between the Core Spray and the Condensate and Demineralized Water Transfer Systems, it was determined that the existing plant l configuration is capable of supplying make-up water to the Isolation Condenser

! from the suppression chamber and is, therefore, sufficient to address the

! staff's concern (Ref. 5).

l. The z.taff, after their detailed review, concluded that the use of the existing l system is acceptablc if the diesel generator, which powers the Core Spray pump upon a loss of offsite power, is protected from tornado wind and missile i loadings.

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GPU Nuclear Corporation is a subsidiary of General P,.3ic Utikties Corporation I

Oyster Creek Nuclear Generating Station-Docket No. 50-219 Page 2 GPUN had previously performed a probablistic analysis to determine the frequency of tornado missiles causing damage to the Diesel Generator Building including the exhaust stack and roof gratings, and to evaluate the consequences in terms of core melt ffequency. The results indicate that the probability of: l c missile hitting the exbnust stack opening or. roof gratings is approximately.

10'7 per year. It was.however,' reported that the missile hit probability of the Diesel Generator Buildings is estimated as 4.6 x 10 -5 (Da-Unit 1) and'5.4 x 10 -6 (DG-Unit 2) per year, respectively. The analysis indicated that neither diesel generater compartment was scabbed on the 18 inch reinforced concrete walls or the 12 inch roof barriers due to tornado missile impact. The description and results of the probablistic analysis were submitted to the NRC on September 16, 1983.

The NRC letter dated February 10, 1989 (Ref. 6) requested GPUN to perform a structural evaluation of Oyster Creek Diesel Generator Building under the j combined tornado generated missile and wind loads having frequency higher than j 10-6 per' year.

Subsequently on March 28, 1989, a telephone conference was held between the NRC staff (Messrs. A. Dromerick and H. Ashar) and GPUN representatives. The purpose of the conference was to clarify both the probabilistic and deterministic evaluation performed by GPUN. The results of our analysis show that the East and West walls of the Diesel Generator Building can withstand a missile (a utility pole hitting at a right angle) loading associated with tornado wind speed of up to 168 mph which corresponds to an exceedence frequency of approximate 1y 7x10-6/ year. The North and South walls can withstand a missile loading associated with tornado wind speed much greater j than the 168 mph. It waa j speedcorrecpondingto10~gointedoutthatGinnaNuclearPlantusedawind

/ year occurrence level to justify their Reactor Building structure in their systematic evaluation program. .GPUN believes that

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the safety afforded by protection to a windspoed associated with a probability of 10 -5 per year is adequate. This probability level is considered cc,ngruent I with the protection levels associated with other severe' natural phenomena, such l as earthquakes and flooding, and with postulated events, such as pipe break.

As you requested during the telephone conference, our technical discussion on this issue is documented below: l I. INTRODUCTION In order to better understand the tornado missile analysis, it helps to briefly review the types of missiles considered, the' characteristics oi' the various portions of the Diesel Generator Building, and the failure modes to be considered.

The missiles can be divided into three categories:

l (1) Penetrator Missiles (SRP Section 3.5.1.4 Misslle Spectrum B; A l through E) l (2) Utility Pole (F)

(3) Automobile (G) 1 DOCKET 50 .

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Oyster Creek Huclear Gansrating Station pocket No. 50-219 Page 3 The Diesel Generator (DG) building can be considered in the following units:

(1) The 18-inch thick reinforced concrete North and South walls (the short walls)

(2) The 18-inch thick reinforced concrete East and West walls (the long walls)

(3) The 18-inch thick reinforced concrete Diesel Oil Tank Compartment walls (similar to (1) above)

(4) The 12-inch thick precast concrete roof panels (5) The gratinQ covered intaka and exhaust roof openings (6) The exhaust stack opening Failure can come from one of four general modes:

(1) Entry of a missile through an opening (2) Penetration through a wall, roof slab, or grating (3) Scabbing of a concrete wall or roof slab (4) Structural failure of a wall, roof slab or grating II. FJNETRATOR MISSILES For the first category of missiles listed above (penet rator missiles Table III-1 of Ref. I shows impact frequencies as high as 4.6 x 10-5,)

but also reports that no scabbing or perforation damage occurred in the tornado missile simulations. The exhaust stack openings were entered by missiles at a frequency of 1.1 x 10~7, which is acceptably low. 'The penetrator type missiles are not considered to be capable of causing a structural type failure.

III. 21IkITY POLE MISSILES The second category of missiles (utility pole) is in Table III-1 of Reference 2 and in a GPUN calculation (Ref. 3). The table shows impact frequencies es high as 4.5 x 10-6, but no scabbing or perforation damage occurred in the tornado missile simulation. This probabilistic analysis did not consider structural typ3 failures, which are analyzed separately in the GPUN structural calculation.

'The structural calculation showed that the North and South walla of the DG building could withstand a utility pole missile carried by tornado winds of up to 240 mph, including the effect of the wind itself.

Depressurization (pressure drop) was not considered due to the large open areas of the bzilding. The 240 mph windspeed has a frequency of exceedence of approximately 1 x 10-6 per year as reported in Ref. 1 and approximately 5 x 10-7 per year in Ref. 4, which is a more realistic {

assessment. Based on this low frequency for the wind alone, the ut.lli.ty I pole impact on these wallo in conjunction with the wind han a very low, and clearly acceptable, frequency.

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1 Oyster Crssk Nuclear Gansrating Station Docket No. 50-219 Page 4 i

l This structural calculation applies equally well to the Diesel Oil Tank f compartment walls, which exe very similar to the North and South walls of j the DG building. l l

The diesel fuel supply lins (3 inch diameter) for the Diesel Oil Tank and )

a valve are installed outside the North wall of the Diesel Oil Tank I compartmer't. Most portions of the supply line is installed underground before re-sarfacing by the North wall. The line penetrates the wall at approximately a foot above the grade level. The target area (i.e., the line and the valve) is only a small fractior of the Diesel Generator <

Compartment and therefore, the probr5111ty of the target crea being hit by I a missile is expected to be well be aw lx10-6 per year. The fuel supply line passes through a six inch diameter penetration sleeve embedded in the North wall of the tank compartment. The penetration is sealed with fire proof foam. Consequently, if a missile impacts the North wall, the vib:atory effects of the wall will not impair the structural integrity of the fuel line, i I

The structural calculation showed that the East and West walls of the DG l building could withstand a utility pole missile carried by tornado winds )

oi up to 168 mph, including the effect of the wind itself. Pressure drop, ]

as discussed above, was not considered. The 168 mph wind has a frequency j of exceedence of approximately 2 x 10-5 per year as reported in Ref. 1 )

and approximately 7 x 10-6 per year in Ref. 4, which is a more realistic '

j assessment. The frequency of utility pole impacts on these walls in conjunction with the 168 mph or greater windepeed has a lower frequency than does the wind alone. Additionally, the frequency of missile impacts includes oblique impacts, which statistically are more common thcn impacts at 90' to the target, and which impart less energy to the target. Another SEP plant, Ginna, used 10-5 per year as the acceptance criteria for tornado wind protection, and on that basis this result would be acceptable i without further analysis. j l

9tility pole niissile impactn on the roof of the building have a very low frequency. The som of 'the impact frequencies on the gratings and exhaust openings (from Ref. 2) is approximately 3 x 10-7 Since these targets total about 1/4 of the total roof area, the total impact frequency would be approximately 1.2 x 10-6 For the roof, especially, impacts tend to i be at low angles (as described in Ref. 1, pages III-9 to 13). These obligae impacts impart less energy to the roof structure.

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. e Oyster Crock Nuclear Gansrating Station D,ocket No. 50-219 Page 5 IV. AUTOMOBILE MISSILES The third category of missiles listed above (the automobile missile) can be discussed most readily by reference to Table III-l of Ref. 1. Only targets numbered 1 and 2 (which include buildin were impacted at a frequency greater than 10~7.g Im units 1, 2 and 4 above) velocities (>57 mph) were rare, less than 2 X 10-8. pacts at higher Impacts at lower velocities are not expected to cause failure, especially when tha energy absorbing (deformation) characteristics of the automobile missile are considered. In addition, the impact frequency includes oblique impacts, which statistically are more common than impacts at 90" to the target, and which impart less energy'to the target.

Based on the above discussion we believe that the Diesel Generator Building at Oyster Creek Nuclear Generating Station is adequately protected from the postulated tornado generated missiles and tornado wind.

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b. K. Croneberge Acting Director, Technical Functions cc Regional Administrator Region I U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406 Resident Inspector Oyster Creek Nuclear Generating Station Mr. Alex Dromerick U.S. Nuclear Regulatory Commission Mail Station Pl-137 Washington, DC 20555 l

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