ML20024H839

Provides Addl Info Re Importance of Various Initiating Events Used in Development of Individual Plant Exam Per GL 88-20

ML20024H839
Person / Time
Site:	Monticello
Issue date:	08/17/1993
From:	Richard Anderson NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-88-20, TAC-M74435, NUDOCS 9308250294
Download: ML20024H839 (2)

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I Northem States Power Company l

l 414 Nicol!et Mall Minneapolis, Minnesota 55401 1927 Telephone (612) 330-5500 August 17, 1993 US Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C.

20555 MONTICELLO NUCLEAR CENERATING PIANT Docket No. 50-263 License No. DPR-22 Additional Information Concerning Initiating Events used in the Monticello Individual Plant Examination (IPE) Submittal - Generic Letter 88-20 (TAC No. M74435)

As requested by Mr. E Rodrick (NRC-RES/SAIB) during a telephone conversation with Mr. T Coss (NSP) and Mr R Rohrer (NSP) on August 4,1993, we are hereby providing l

additional information concerning the relative importance of the various initiating events used in the development of our Individual Plant Examination (IPE). The probability of the most important initiating events, and the overall contribution to core damage frequency is provided as Attachment A.

This letter contains no new NRC commitments, nor does it modify any previous commitments.

Please contact Terry Coss, Sr Licensing Engineer, at (612) 295-1449 if you I

require additional information.

tynJ f' T-6 h a)

(oc Roger O Anderson Director Licensing and Management Issues cc: Regional Administrator-lII, NRC NRR Project Manager, NRC Resident Inspector, NRC State of Minnesota, Attn: Kris Sanda 1

J Silberg l

Attachment A: Monticello Initiating Event Importance I

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44 a 9308250294 930817 DR ADOCK 05000263 [

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o Attachment A

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Monticello Initiating Event Importance Initiating Event CDF/yr

% Core Damage Loss of Offsite Power 1.33E-05 50.8%

Turbine Building 931' Service Water Flood 2.47E-06 9.4%

Rx Bldg 896' and higher Service Water Flood 2.44E-06 9.3%

Turbine Trip 1.82E-06 7.0%

{

Turbine Building 911' Service Water Flood 1.74E-06 6.6%

{

Loss of Feedwater 9.96E-07 3.8%

Manual Shutdown 6.92E-07 2.6%

(

MSIV Closure 6.86E-07 2.6%

}

Medium LOCA 4.98E-07 1.9%

j Large LOCA 3.20E-07 1.2%

Small LOCA 2.24E-07 0.9%

Loss of Condenser Vacuum 2.05E-07 0.8%

Torus Ring Header Break 1.93E-07 0.7%

l ATWS without Turbine Trip 1.16E-07 0.4%

West Diesel Gen Room Flood 9.54E-08 0.4%

Reference Leg Leak 8.67E-08 0.3%

Condensate Service Water Flood 8.25E-08 0.3%

l Loss of Service Water 7.31E-08 0.3%

I Loss of Instrument Air 4.72E-08 0.2%

Southeast RER Room Flood 3.07E-08 0.1%

Turbine Building 931' West Flood 2.41E-08 0.1%

l Southwest RHR Room Flood 2.24E-08 0.1%

4 Loss of a DC 125 Volt Bus 1.33E-08 0.1%

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Loss of Drywell Cooling 5.50E-09 0.0%

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j Total 2.62E-05 100.0%

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