ML19101A341

Fpra FAQ 18-0018 NSP Update Draft 0G

ML19101A341
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Issue date:	02/11/2019
From:	Shivani Mehta NRC/NRR/DRA/APLB
To:
Mehta S
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Download: ML19101A341 (19)

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FAQ Number 18-0018 FAQ Revision 0 (Draft G)

FAQ Title Updated Non-Suppression Probability (NSP)

Plant: Various Date: February 11, 2019 (Received by NRC 4/3/2019)

Contact:

Beth Meade Phone: (508) 532-7139 Mark Schairer (508) 532-7137 Rob Cavedo (301) 938-0397 Email: bah@epm-inc.com mvs@epm-inc.com robert.cavedo@exeloncorp.com Distribution: (NEI Internal Use)

FPRA TF BWROG PWROG Purpose of FAQ:

This FAQ provides an update to the non-suppression probabilities (NSPs) based on Bayesian approach separating the data before Jan 1st, 2000 and after.

Relevant NRC document(s):

NUREG/CR-6850 NUREG/CR-6850 Supplement 1 (FAQ 08-0050)

NUREG 2169 Details:

NRC document needing interpretation (include document number and title, section, paragraph, and line numbers as applicable):

See list of relevant NRC documents Circumstances requiring interpretation or new guidance:

The non-suppression probabilities (NSP) provided in NUREG 2169 Table 5-1 are considered overly conservative due to the equal treatment of fire data over a prolonged period. As a result, the risk associated with fires may not reflect the current NSP rates.

Detail contentious points if licensee and NRC have not reached consensus on the facts and circumstances:

FAQ Number 18-0018 FAQ Revision 0 (Draft G)

FAQ Title Updated Non-Suppression Probability (NSP)

Although recent guidance has sought to provide a better estimate of non-suppression probability, in the case of fire events over a prolonged period, the probability of non-suppression is believed to be non-representative of the current NSPs.

Potentially relevant existing FAQ numbers:

FAQ 08-0050, Manual Non-Suppression Probability Response Section:

Proposed resolution of FAQ and the basis for the proposal:

The fire NSPs are adjusted using a Gamma-Poisson Bayesian model using the data before Jan 1st, 2000 as a prior distribution. There have been numerous improvements to plant process controls that affect both the likelihood, control, and severity of fire scenarios. This includes smoking controls, foreign material exclusion, cutting and welding improvements, combustion controls, brigade training, etc. It is for these reasons among others, that the conclusion in NUREG 2169 is that data from 2000 and later is the most applicable in fire analysis.

It seems reasonable to assume that the data before 2000 would have some influence on the data 2000 and beyond but certainly not more influence. The prior distribution must have less influence than the posterior data. This is ensured by making the alpha factor of the prior distribution half that of the posterior data while maintaining the mean. This ensures that the data after 2000 has more influence that the data prior to 2000.

The NSP for HEAF is developed using the data from FAQ 17-0013.

The results for this process are presented for each suppression curve:

FAQ Number 18-0018 FAQ Revision 0 (Draft G)

FAQ Title Updated Non-Suppression Probability (NSP)

T/G Fires:

Before 2000 After 2000 Combined Alpha 23 7 Alpha 30 Beta 1057 110 1167 Mean 0.022 0.064 0.026 5th% 0.0149 0.0299 0.019 25th% 0.0186 0.0462 50th% 0.0214 0.0606 0.025 75th% 0.0246 0.0778 95th% 0.0297 0.1077 0.034 Prior Development Rule:

The prior Alpha factor from the before 2000 data is considered to be half that of the distribution that would be developed without a prior (i.e. the data after 2000 is more signficant than the data prior to 2000)

Gamma/Poisson Weak Prior Bayesian Model Before 2000 After 2000 Combined Alpha 4 7 Alpha 11 Beta 184 110 Beta 294 Mean 0.022 0.064 Mean 0.037 5th% 0.007 0.030 5th% 0.021 25th% 0.014 0.046 25th% 0.029 50th% 0.020 0.061 50th% 0.036 75th% 0.028 0.078 75th% 0.044 95th% 0.042 0.108 95th% 0.058

FAQ Number 18-0018 FAQ Revision 0 (Draft G)

FAQ Title Updated Non-Suppression Probability (NSP)

Control Room:

Before 2000 After 2000 Combined Alpha 7 4 Alpha 11 Beta 28 8 36 Mean 0.250 0.500 0.306 5th% 0.1173 0.1708 0.171 25th% 0.1815 0.3169 50th% 0.2382 0.4590 0.296 75th% 0.3057 0.6387 95th% 0.4229 0.9692 0.471 Prior Development Rule:

The prior Alpha factor from the before 2000 data is considered to be half that of the distribution that would be developed without a prior (i.e. the data after 2000 is more signficant than the data prior to 2000)

Gamma/Poisson Weak Prior Bayesian Model Before 2000 After 2000 Combined Alpha 2 4 Alpha 6 Beta 8 8 Beta 16 Mean 0.250 0.500 Mean 0.375 5th% 0.044 0.171 5th% 0.163 25th% 0.120 0.317 25th% 0.264 50th% 0.210 0.459 50th% 0.354 75th% 0.337 0.639 75th% 0.464 95th% 0.593 0.969 95th% 0.657 Notes: The calculation sheet for NUREG-2169 uses one additional event: 537, 9/4/1986, 1 minute.

This event is excluded as the event occurred during pre-operation testing and will no longer counted in the upcoming suppression rate as estimated for Chapter 8 of Rachelle Fire II.

FAQ Number 18-0018 FAQ Revision 0 (Draft G)

FAQ Title Updated Non-Suppression Probability (NSP)

PWR Containment (AP):

Before 2000 After 2000 Combined Alpha 3 0 Alpha 3 Beta 36 0 36 Mean 0.083 N/A 0.083 5th% 0.0227 N/A 0.023 25th% 0.0480 N/A 50th% 0.0743 N/A 0.074 75th% 0.1089 N/A 95th% 0.1749 N/A 0.175 Prior Development Rule:

The prior Alpha factor from the before 2000 data is considered to be half that of the distribution that would be developed without a prior (i.e. the data after 2000 is more signficant than the data prior to 2000)

Gamma/Poisson Weak Prior Bayesian Model Before 2000 After 2000 Combined Alpha 1 0 Alpha 1 Beta 12 0 Beta 12 Mean 0.083 N/A Mean 0.083 5th% 0.004 N/A 5th% 0.004 25th% 0.024 N/A 25th% 0.024 50th% 0.058 N/A 50th% 0.058 75th% 0.116 N/A 75th% 0.116 95th% 0.250 N/A 95th% 0.250 Note: The calculations utilized to develop the NSP values in NUREG-2169 Table 5-3 included an error. Fire Event 66 was associated with a suppression duration of 14 minutes, but the actual duration is 10 minutes. Therefore, the combined duration is 36 minutes versus the 40 minutes reported in NUREG-2169.

FAQ Number 18-0018 FAQ Revision 0 (Draft G)

FAQ Title Updated Non-Suppression Probability (NSP)

Containment (LPSD):

Before 2000 After 2000 Combined Alpha 10 21 Alpha 31 Beta 141 158 299 Mean 0.071 0.133 0.104 5th% 0.0385 0.0891 0.075 25th% 0.0548 0.1124 50th% 0.0686 0.1308 0.103 75th% 0.0845 0.1512 95th% 0.1114 0.1839 0.136 Prior Development Rule:

The prior Alpha factor from the before 2000 data is considered to be half that of the distribution that would be developed without a prior (i.e. the data after 2000 is more signficant than the data prior to 2000)

Gamma/Poisson Weak Prior Bayesian Model Before 2000 After 2000 Combined Alpha 10 21 Alpha 31 Beta 141 158 Beta 299 Mean 0.071 0.133 Mean 0.104 5th% 0.038 0.089 5th% 0.075 25th% 0.055 0.112 25th% 0.091 50th% 0.069 0.131 50th% 0.103 75th% 0.084 0.151 75th% 0.116 95th% 0.111 0.184 95th% 0.136

FAQ Number 18-0018 FAQ Revision 0 (Draft G)

FAQ Title Updated Non-Suppression Probability (NSP)

Outdoor Transformers:

Before 2000 After 2000 Combined Alpha 18 6 Alpha 24 Beta 635 293 928 Mean 0.028 0.020 0.026 5th% 0.0183 0.0089 0.018 25th% 0.0236 0.0144 50th% 0.0278 0.0194 0.026 75th% 0.0325 0.0253 95th% 0.0402 0.0359 0.035 Prior Development Rule:

The prior Alpha factor from the before 2000 data is considered to be half that of the distribution that would be developed without a prior (i.e. the data after 2000 is more signficant than the data prior to 2000)

Gamma/Poisson Weak Prior Bayesian Model Before 2000 After 2000 Combined Alpha 3 6 Alpha 9 Beta 106 293 Beta 399 Mean 0.028 0.020 Mean 0.023 5th% 0.008 0.009 5th% 0.012 25th% 0.016 0.014 25th% 0.017 50th% 0.025 0.019 50th% 0.022 75th% 0.037 0.025 75th% 0.027 95th% 0.059 0.036 95th% 0.036

FAQ Number 18-0018 FAQ Revision 0 (Draft G)

FAQ Title Updated Non-Suppression Probability (NSP)

Flammable Gas:

Before 2000 After 2000 Combined Alpha 5 3 Alpha 8 Beta 199 35 234 Mean 0.025 0.086 0.034 5th% 0.0099 0.0234 0.017 25th% 0.0169 0.0494 50th% 0.0235 0.0764 0.033 75th% 0.0315 0.1120 95th% 0.0460 0.1799 0.056 Prior Development Rule:

The prior Alpha factor from the before 2000 data is considered to be half that of the distribution that would be developed without a prior (i.e. the data after 2000 is more signficant than the data prior to 2000)

Gamma/Poisson Weak Prior Bayesian Model Before 2000 After 2000 Combined Alpha 2 3 Alpha 5 Beta 80 35 Beta 115 Mean 0.025 0.086 Mean 0.044 5th% 0.004 0.023 5th% 0.017 25th% 0.012 0.049 25th% 0.029 50th% 0.021 0.076 50th% 0.041 75th% 0.034 0.112 75th% 0.055 95th% 0.060 0.180 95th% 0.080

FAQ Number 18-0018 FAQ Revision 0 (Draft G)

FAQ Title Updated Non-Suppression Probability (NSP)

Oil Fires:

Before 2000 After 2000 Combined Alpha 32 18 Alpha 50 Beta 464 98 562 Mean 0.069 0.184 0.089 5th% 0.0502 0.1187 0.069 25th% 0.0604 0.1529 50th% 0.0682 0.1803 0.088 75th% 0.0768 0.2107 95th% 0.0902 0.2602 0.111 Prior Development Rule:

The prior Alpha factor from the before 2000 data is considered to be half that of the distribution that would be developed without a prior (i.e. the data after 2000 is more signficant than the data prior to 2000)

Gamma/Poisson Weak Prior Bayesian Model Before 2000 After 2000 Combined Alpha 9 18 Alpha 27 Beta 131 98 Beta 229 Mean 0.069 0.184 Mean 0.118 5th% 0.036 0.119 5th% 0.083 25th% 0.052 0.153 25th% 0.102 50th% 0.066 0.180 50th% 0.117 75th% 0.083 0.211 75th% 0.133 95th% 0.111 0.260 95th% 0.158

FAQ Number 18-0018 FAQ Revision 0 (Draft G)

FAQ Title Updated Non-Suppression Probability (NSP)

Cable Fires:

Before 2000 After 2000 Combined Alpha 4 0 Alpha 4 Beta 29 0 29 Mean 0.138 N/A 0.138 5th% 0.0471 N/A 0.047 25th% 0.0874 N/A 50th% 0.1266 N/A 0.127 75th% 0.1762 N/A 95th% 0.2674 N/A 0.267 Prior Development Rule:

The prior Alpha factor from the before 2000 data is considered to be half that of the distribution that would be developed without a prior (i.e. the data after 2000 is more signficant than the data prior to 2000)

Gamma/Poisson Weak Prior Bayesian Model Before 2000 After 2000 Combined Alpha 1 0 Alpha 1 Beta 7 0 Beta 7 Mean 0.138 N/A Mean 0.138 5th% 0.007 N/A 5th% 0.007 25th% 0.040 N/A 25th% 0.040 50th% 0.096 N/A 50th% 0.096 75th% 0.191 N/A 75th% 0.191 95th% 0.413 N/A 95th% 0.413 0.0%

FAQ Number 18-0018 FAQ Revision 0 (Draft G)

FAQ Title Updated Non-Suppression Probability (NSP)

Electrical NSP (relocated two events to HEAF per FAQ 17-013):

Before 2000 After 2000 Combined Alpha 110 64 Alpha 174 Beta 1177 628 1805 Mean 0.093 0.102 0.096 5th% 0.0793 0.0819 0.085 25th% 0.0873 0.0931 50th% 0.0932 0.1014 0.096 75th% 0.0993 0.1102 95th% 0.1086 0.1237 0.109 Prior Development Rule:

The prior Alpha factor from the before 2000 data is considered to be half that of the distribution that would be developed without a prior (i.e. the data after 2000 is more signficant than the data prior to 2000)

Gamma/Poisson Weak Prior Bayesian Model Before 2000 After 2000 Combined Alpha 32 64 Alpha 96 Beta 342 628 Beta 970 Mean 0.093 0.102 Mean 0.099 5th% 0.068 0.082 5th% 0.083 25th% 0.082 0.093 25th% 0.092 50th% 0.092 0.101 50th% 0.099 75th% 0.104 0.110 75th% 0.106 95th% 0.122 0.124 95th% 0.116 Note: FAQ 17-0013 revised the event count by removing fire events #792 and #922 with a duration of 5 and 3 minutes respectively. Even without the HEAF FAQ adjustments, the totals obtained from the fire event data differ slightly from those reported in NREG-2169. When the data from NUREG 2169 is totaled there are 177 events with a duration of 1816 minutes, versus the total of 1815 minutes reported in NUREG-2169 Table 5-3. This one-minute increase from the original data results in a minor decrease to the lambda mean (from 0.098 to 0.097) that is not expected to result in statistically significant changes to the overall risk calculations.

FAQ Number 18-0018 FAQ Revision 0 (Draft G)

FAQ Title Updated Non-Suppression Probability (NSP)

Welding Fires:

Before 2000 After 2000 Combined Alpha 26 26 Alpha 52 Beta 248 236 484 Mean 0.105 0.110 0.107 5th% 0.0735 0.0772 0.084 25th% 0.0903 0.0949 50th% 0.1035 0.1088 0.107 75th% 0.1179 0.1239 95th% 0.1408 0.1479 0.133 Prior Development Rule:

The prior Alpha factor from the before 2000 data is considered to be half that of the distribution that would be developed without a prior (i.e. the data after 2000 is more signficant than the data prior to 2000)

Gamma/Poisson Weak Prior Bayesian Model Before 2000 After 2000 Combined Alpha 13 26 Alpha 39 Beta 124 236 Beta 360 Mean 0.105 0.110 Mean 0.108 5th% 0.062 0.077 5th% 0.081 25th% 0.084 0.095 25th% 0.096 50th% 0.102 0.109 50th% 0.107 75th% 0.123 0.124 75th% 0.119 95th% 0.157 0.148 95th% 0.138

FAQ Number 18-0018 FAQ Revision 0 (Draft G)

FAQ Title Updated Non-Suppression Probability (NSP)

Transient fires:

Before 2000 After 2000 Combined Alpha 27 16 Alpha 43 Beta 252 136 388 Mean 0.107 0.118 0.111 5th% 0.0756 0.0738 0.085 25th% 0.0926 0.0967 50th% 0.1058 0.1152 0.110 75th% 0.1202 0.1359 95th% 0.1432 0.1698 0.140 Prior Development Rule:

The prior Alpha factor from the before 2000 data is considered to be half that of the distribution that would be developed without a prior (i.e. the data after 2000 is more signficant than the data prior to 2000)

Gamma/Poisson Weak Prior Bayesian Model Before 2000 After 2000 Combined Alpha 8 16 Alpha 24 Beta 75 136 Beta 211 Mean 0.107 0.118 Mean 0.114 5th% 0.053 0.074 5th% 0.079 25th% 0.080 0.097 25th% 0.097 50th% 0.103 0.115 50th% 0.112 75th% 0.130 0.136 75th% 0.129 95th% 0.176 0.170 95th% 0.155 Note: The transient fire total duration is slightly larger than the NUREG-2169 total of 386. This two-minute difference over 388 minutes is conservative, but not significantly conservative.

FAQ Number 18-0018 FAQ Revision 0 (Draft G)

FAQ Title Updated Non-Suppression Probability (NSP)

HEAFs (updated per FAQ 17-0013):

Before 2000 After 2000 Combined Alpha 6 5 Alpha 11 Beta 146 239 385 Mean 0.041 0.021 0.029 5th% 0.0179 0.0082 0.016 25th% 0.0289 0.0141 50th% 0.0388 0.0195 0.028 75th% 0.0508 0.0263 95th% 0.0720 0.0383 0.044 Prior Development Rule:

The prior Alpha factor from the before 2000 data is considered to be half that of the distribution that would be developed without a prior (i.e. the data after 2000 is more signficant than the data prior to 2000)

Gamma/Poisson Weak Prior Bayesian Model Before 2000 After 2000 Combined Alpha 3 5 Alpha 8 Beta 73 239 Beta 312 Mean 0.041 0.021 Mean 0.026 5th% 0.011 0.008 5th% 0.013 25th% 0.024 0.014 25th% 0.019 50th% 0.037 0.020 50th% 0.025 75th% 0.054 0.026 75th% 0.031 95th% 0.086 0.038 95th% 0.042

FAQ Number 18-0018 FAQ Revision 0 (Draft G)

FAQ Title Updated Non-Suppression Probability (NSP)

All Fires (adjusted per FAQ 17-013):

Before 2000 After 2000 Combined Alpha 271 170 Alpha 441 Beta 4412 1941 6353 Mean 0.061 0.088 0.069 5th% 0.0554 0.0768 0.064 25th% 0.0589 0.0830 50th% 0.0613 0.0874 0.069 75th% 0.0639 0.0920 95th% 0.0677 0.0989 0.075 Prior Development Rule:

The prior Alpha factor from the before 2000 data is considered to be half that of the distribution that would be developed without a prior (i.e. the data after 2000 is more signficant than the data prior to 2000)

Gamma/Poisson Weak Prior Bayesian Model Before 2000 After 2000 Combined Alpha 85 170 Alpha 255 Beta 1384 1941 Beta 3325 Mean 0.061 0.088 Mean 0.077 5th% 0.051 0.077 5th% 0.069 25th% 0.057 0.083 25th% 0.073 50th% 0.061 0.087 50th% 0.077 75th% 0.066 0.092 75th% 0.080 95th% 0.073 0.099 95th% 0.085 Notes: The calculation sheet for NUREG-2169 uses one additional event: 537, 9/4/1986, 1 minute.

This event is excluded as the event occurred during pre-operation testing and will no longer counted in the upcoming suppression rate as estimated for Chapter 8 of Rachelle Fire II. As Part of FAQ 17-0013, Event 162 was added to HEAF. As discussed under the EC NSP, there is one event missing. Therefore, the total for this FAQ is one event lower than NUREG-2169.

FAQ Number 18-0018 FAQ Revision 0 (Draft G)

FAQ Title Updated Non-Suppression Probability (NSP)

Summary Results:

If appropriate, provide proposed rewording of guidance for inclusion in the next Revision:

The following are proposed revisions to NUREG 2169:

FAQ Number 18-0018 FAQ Revision 0 (Draft G)

FAQ Title Updated Non-Suppression Probability (NSP)

Table 5-1 Probability distribution for rate of fires suppressed per unit time, (Originally, Table P-2 from NUREG/CR-6850)

Number Total Rate of Fire Suppressed ()

of Events Duration Suppression Curve 5th 50th 95th in Curve (minutes) Mean Percent Percent Percent T/G Fires. 30 1167 0.037 0.021 0.036 0.058 Control Room 11 36 0.375 0.163 0.354 0.657 PWR Containment (AP) 3 36 0.083 0.004 0.058 0.250 Containment (LPSD) 31 299 0.104 0.075 0.103 0.136 Outdoor transformers 24 928 0.023 0.012 0.022 0.036 Flammable gas 8 234 0.044 0.017 0.041 0.080 Oil fires 50 562 0.118 0.083 0.117 0.158 Cable fire 4 29 0.138 0.007 0.096 0.413 Electrical fires 174 1805 0.099 0.083 0.099 0.116 Weld fires 52 484 0.108 0.081 0.107 0.138 Transient fire 43 388 0.114 0.079 0.112 0.155 HEAFs 11 385 0.026 0.013 0.025 0.031 All fires 441 6353 0.077 0.069 0.077 0.085

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