ML17340B098

Meeting Presentation, Conservatism in Non-Suppression Probability (NSP) Data

ML17340B098
Person / Time
Site:	Nuclear Energy Institute
Issue date:	12/13/2017
From:	Schairer M Engineering Planning & Management, Nuclear Energy Institute
To:	Document Control Desk, Office of Nuclear Reactor Regulation
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ML17340B096	List: ML17340B097 ML17340B098 ML17340B100 ML17340B101 ML17340B102 ML17340B103 ML17340B104 ML17340B105 ML17340B106
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Download: ML17340B098 (6)

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Conservatism in Non-Suppression Probability (NSP) Data FPRA FAQ Public Meeting December 13, 2017 Presented by:

Mark Schairer Engineering Planning and Management, Inc.

Description of Potential Realism Improvement: NSP Data Conservatism There is a disconnect between the average durations of fire scenarios in Fire PRAs vs. fire event experience The fire durations include time lags or delays associated with reporting time to control the fire versus time to extinguish the fire and time associated with de-energizing equipment, offsite fire brigade response, and water application In Fire PRAs, the source scenarios reach peak HRR in 12 minutes.

Using FLASH-CAT, multiple trays are involved well before 20 minutes. Peak ZOI and HGL occur before 20 minutes.

Typically, on-site fire brigade arrival is expected to be 10-15 minutes, and upon arrival, fire is under control within 5-10 minutes.

From the NSP data, more than 25% of fire events have durations longer than 20 minutes 2

Identification of Relevant Guidance NUREG-2169, Section 5.2. NSP Estimation Update, provides the following probability distributions for rates of fires suppressed per unit time, (data is based on fire events from 1981-2009) 3

Proposed Approach to Enhance Realism: Initial Assessment Review fire event information obtained from NRC Event Reports, Licensee Event Reports, or through Plant contacts.

Re-examine when the fires were under control, rather than totally extinguished. At the control point, the fire is no longer a threat to fire spread, hot gas layer formation, additional target damage.

Consider limiting data to only the more recent fire events to be consistent with fire ignition frequency data 4

Proposed Approach to Enhance Realism: Initial Assessment Initial scoping of high-duration electrical cabinet fires from NRC Event Reports:

NSP Suppression Time EPRI Fire ID Event Date Power Mode Fire Severity Bin Designation Category (min) 1097 11/15/1986 Low-power operation Undetermined 26 Electrical 95 418 4/28/1984 Low-power operation Challenging 10 Electrical 60 642 11/4/1987 Power operation Challenging 15.1 Electrical 50 98 10/8/1998 RF PC 15 Electrical 46 30362 12/16/2001 RF PC 21 Electrical 45 50829 9/11/2004 PO PC 23 Electrical 45 175 11/22/2009 CD CH 15 Electrical 45 121 4/26/2003 PO U 21 Electrical 37 505 1/8/1986 Low-power operation Undetermined 21 Electrical 36 20302 7/25/1993 PO U 15 Electrical 35 238 1/24/1981 Power operation Challenging 21 Electrical 30 557 1/31/1987 Low-power operation Challenging 22 Electrical 30 656 12/17/1987 Power operation Challenging 22 Electrical 30 97 6/10/1998 PO PC 22 Electrical 29 10626 12/11/2002 PO PC 21 Electrical 27 235 12/30/1992 PO PC 26 Electrical 25 5

Summary of Anticipated Realism Improvements Preliminary estimates based on expert judgement For events over 20 minutes in duration, reduce the duration by half, but not less than 20 minutes; Events under 20 minutes were unaltered i.e., 50 min event was reduced to 25 min, while 30 min event to 20 min Average Total Number Sum of NSP at time =

NSP Curve Duration Events Durations 20

[min]

NUREG-2169 177 1815 10.3 0.142 Estimate of Improvement 177 1492 8.4 0.093 The average duration was reduced by ~20%

NSP at 20 minutes reduced by 35%

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