ML19011A450

Workshop 5 External Hazards 2019-01-18

ML19011A450
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Issue date:	01/16/2019
From:	Office of Nuclear Regulatory Research
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Nathan Siu 415-0744
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Text

External Hazards Analysis Workshop 5 1

Learning Objectives

• Practice identifying potentially important external hazards

• Practice modifying PRA models to address external hazards Important:

a) The workshop problems can be performed as group exercises.

b) The purpose is to exercise the modeling thought process, not to get the right answer.

2

=

Background===

In Workshop 3, you identified some potentially important hazards to the Fenwick 1 NPP. This workshop builds on your work, using information from Lecture 6-2.

Assume the following

• Elevations:

- Fenwick River (nominal): 6860 ft

- Fenwick distillery: 6880 ft

- Turbine Building equipment door: 6885 ft

- Switchyard: 6890 ft

- Safeguards building entrance: 6895 ft

• Locations:

- Turbine Building: NS (most), FW, SW systems, non-vital electrical distribution

- Safeguards Building: SI system, EDG, vital electrical distribution 3

Problem #1 - Hazard Identification Considering the list of external hazards from Lecture 6-2 (reproduced below), which (if any) of these should be added to your list? Justify your selections.

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External Hazards - Example List Hazard Include? Hazard Include?

Aircraft impact Local intense precipitation Avalanche Low lake or river water level Biological events Low winter temperature Coastal erosion Meteor or satellite strike Drought Onsite chemical release External fire Pipeline accident External flooding River diversion Extreme winds and tornadoes Sandstorm Fog Seiche Forest fire Seismic activity Frost Severe temperatures Hail Snow High summer temperature Soil shrink-swell High tide Space weather Hurricane Storm surge Ice cover Transportation accident Industrial/military facility accident Tsunami Internal flooding Turbine-generated missiles Landslide Volcanic activity Lightning 5

Problem #2 - Qualitative Analysis Consider the possibility of flooding of the Fenwick River.

A. Identify some of the potential plant vulnerabilities to such an event.

B. Identify some of the flooding-caused initiating events that would need to be analyzed in the plant PRA.

C. For the event tree/fault tree model you developed in Workshop 2, identify some of the flooding-induced spatially-dependent failures that would need to be analyzed.

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Problem #3 - Probabilistic Hazards Analysis Assume:

• Major flooding of the Fenwick River can be reasonably modeled as a Poisson process with frequency of 0.01/yr.

• Given the occurrence of a major flood, assume the probability distribution for flooding heights is given by a Gumbel Type I distribution (see next page).

A. What is the frequency of floods that might affect:

i. The Turbine Building ii. The Switchyard iii. The Safeguards Building B. How would you modify your event tree/fault tree model to address floods severe enough to affect the switchyard?

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Fenwick 1 - Flooding Hazard Type 1 Gumbel distribution (an extreme value distribution):

1.00

• Range - < X <

0.90 µ = 30.07 1 0.80 = 2.18

• pdf + exp 0.70 0.60 P{X > x}

• CDF 0.50 0.40

• Mean + 0.5772 0.30 0.20 2 2

• Variance 0.10 6 0.00 25 30 35 40 Flood Height (ft) 8

Fenwick River - Major Flood Heights*

Date Flood Height (ft) 11/25/1877 29.2 6/1/1889 34.8 10/1/1896 33.0 3/19/1936 36.5 4/27/1937 29.0 10/16/1942 33.8 6/23/1972 27.7 11/6/1985 30.1 1/21/1996 29.4 9/8/1996 29.8 Mean 31.3 Std Dev 2.8

• akaKaro Engineering: Any correspondence with flooding data from Harpers Ferry is purely coincidental! 9

Fenwick 1 Location and Plan 10

Fenwick 1 - NSSS and Safety System (Schematic)

Designator Description Pre-hyphen FW Feedwater NS NSSS SI Safety Injection SW Service Water Post-hyphen C Condenser F Filter P Pump R Reactor V Valve T Turbine Other NSSS Nuclear Steam Supply

©akaKaro Engineering, 2018 11

Designator Description Fenwick 1 - Electrical Distribution Pre-hyphen A 6900 VAC non-vital bus A B 4160 VAC non-vital bus B C 250 VDC non-vital bus C FW Feedwater NI 125 VDC non-vital I&C bus NV Notes: NS NSSS

1) Small box indicates SI Safety Injection a breaker SW Service Water VI 125 VDC vital I&C bus VI

2) Large box indicates X 6900 VAC vital bus X a load Y 4160 VAC vital bus Y Z 250 VDC vital bus Z Post-hyphen B Battery C Condenser F Filter G Emergency Diesel Generator M MGS P Pump R Reactor S Switchgear/M-CC/Distribution Panel V Valve T Turbine X Transformer Other Bat. Battery M-CC Motor Control Center MCR Main Control Room MGS Motor Generator Set NSSS Nuclear Steam Supply System VAC Volts (Alternating Current)

VDC Volts (Direct Current)

©akaKaro Engineering, 2018 12