NRC Inspection Manual 0609/Appendix F
https://www.nrc.gov/docs/ML1808/ML18087A414.pdf
- Attachment 1: Fire Protection Significance Determination Process - https://www.nrc.gov/docs/ML1808/ML18087A417.pdf
- Attachment 2: Degradation Rating Guidance - https://www.nrc.gov/docs/ML1808/ML18087A404.pdf
- Attachment 3: Guidance for Identifying Credible Fire Scenarios - https://www.nrc.gov/docs/ML1808/ML18087A405.pdf
- Attachment 4: Guidance for Determining Fire Ignition Frequency - https://www.nrc.gov/docs/ML1808/ML18087A406.pdf
- Attachment 5: Characterizing Fire Ignition Sources - https://www.nrc.gov/docs/ML1808/ML18087A409.pdf
- Attachment 6: Guidance for the Identification of Targets and Their Ignition and Damage Criteria - https://www.nrc.gov/docs/ML1808/ML18087A410.pdf
- Attachment 7: Guidance for Fire Non-Suppression Probability Analysis - https://www.nrc.gov/docs/ML1808/ML18087A412.pdf
- Attachment 8: Tables and Plots Supporting the Phase 2 Risk Quantification - https://www.nrc.gov/docs/ML1808/ML18087A413.pdf
NRC INSPECTION MANUAL
INSPECTION MANUAL CHAPTER 0609 APPENDIX F
FIRE PROTECTION
SIGNIFICANCE DETERMINATION PROCESS
APHB
0609F-01 PURPOSE
The Fire Protection Significance Determination Process (SDP) involves a series of qualitative
and quantitative analysis steps for estimating the risk significance of inspection findings related
to licensee performance meeting the objectives of the fire protection defense-in-depth (DID)
elements. The fire protection DID elements are:
Prevention of fires from starting,
Rapid detection and suppression of fires that occur, and
Protection of the reactor’s ability to safely shutdown if a fire is not promptly extinguished.
0609F-02 OBJECTIVES
Phase 1 of the Fire Protection SDP is primarily qualitative. Phase 1 provides initial
characterization of the fire finding and serves to screen out fire findings that may have very low
risk significance (Green). If the Phase 1 screening criteria do not screen out a fire finding as
Green, then the evaluation process continues to Phase 2.
Phase 2 of the Fire Protection SDP is quantitative and based on simplified methods and
approaches used in typical fire probabilistic risk assessments (PRA). The general philosophy of
the Fire Protection SDP is to minimize the potential for false-negative findings, while avoiding
undue conservatism. The duration (or exposure time) of the degraded conditions is considered
at all stages of the analysis. Compensatory measures that might offset (in part or in whole) the
observed degradation are considered in Phase 2.
02.01 Fire Protection SDP Phase 1 Overview
Phase 1 of the Fire Protection SDP is a preliminary screening check intended for use by the
Resident or Regional Office Inspector(s) to identify fire protection findings with very low risk
significance (Green findings). If a fire finding meets a screening criterion, the finding is
determined to be very low risk significant and no Phase 2 analysis is required. If the Phase 1
screening criteria are not met, the analysis proceeds to Phase 2 for further evaluation of risk
significance.
Phase 1 of the Fire Protection SDP contains five steps as illustrated in Figure F.1. A fire finding
is first characterized (Step 1.1) and assigned a category (Step 1.2) based on the fire protection
program element that was found to be degraded. The fire finding is then evaluated to determine
if it has a low degradation rating (Step 1.3). Low degradation rating fire findings are screened to
Green. If the fire finding is not low degradation, the next step (Step 1.4) attempts to screen the
finding using a series of qualitative questions based on the finding category assigned in Step
1.2. The final step in Phase 1 (Step 1.5) is for plants that have fire PRA. The licensee’s fire
PRA-based risk evaluation may be used to determine whether the fire finding is of very low risk
significance.
Issue Date: 05/02/18 2 0609 App F
Figure F.1 – Phase 1 Flow Chart
No
Yes
Yes
Yes
1.4.1 Fire Prevention and
Administrative
Controls
1.4.2 Fixed Fire
Protection Systems
1.4.3 Fire Water Supply
1.4.4 Fire Containment
1.4.5 Manual Fire Fighting
1.4.6 Localized Cable or
Component
Protection
1.4.7 Post-Fire Safe
Shutdown
1.4.8 Main Control Room
Fires
Step 1.2 – Assign a Fire Finding Category
Step 1.1 – Provide Statement of Fire Finding
Step 1.3 – Does the fire
finding have a low
degradation rating?
Step 1.4 – Do any of the
qualitative screening
questions screen the
fire finding to Green?
Step 1.5 – Does the
licensee have a Fire
PRA that indicates the
fire finding is Green?
Proceed to Phase 2 Evaluation
Fire Finding
Screens to
Green
Fire Finding
Screens to
Green
Has the SRA
reviewed and
accepted the
licensee’s results?
Fire Finding
Screens to
Green
No
No
No Yes
Issue Date: 05/02/18 3 0609 App F
02.02 Fire Protection SDP Phase 2 Overview
Phase 2 of the Fire Protection SDP is a quantitative assessment of the change in core damage
frequency (CDF) due to a finding. Phase 2 involves the seven analysis steps as illustrated in
Figure F.2. The first three steps are intended to be performed in sequence. The remaining four
steps can be (partially) completed in any order, and the analyst is encouraged to choose the
step which will reduce the bounding CDF as much as possible first, then second, etc., to
minimize effort. Each step represents the introduction of new detail and/or the refinement of
previous analysis results.
The Phase 2 analysis includes six distinct screening checks. Each time new or refined analysis
results are developed, a screening check is made to determine if a sufficient basis has been
developed to justify assignment of a preliminary significance of Green. If at any time the
quantitative screening criteria are met, the analysis is considered complete, and any remaining
steps need not be performed.
Figure F.2 – Phase 2 Flow Chart
The seven steps in Phase 2 are summarized below:
Step 2.1 introduces the “six-factor” formula that is used to quantify the risk significance
of the finding and calculates a bounding estimate of the ∆CDF based on the Duration
Factor (DF) and conservative values for the five remaining factors. These remaining
factors are the Fire Ignition Frequency (FIF) and applicable Adjustment Factors (AF),
Conditional Core Damage Probability (CCDP), Severity Factor (SF), and NonSuppression Probability (NSP). The six-factor formula quantifies the CDF as the sum
CDF < 1E-6
Screen to CDF < 1E-6
Green
CDF < 1E-6 CDF < 1E-6 CDF < 1E-6 CDF < 1E-6
Step 2.1
Bounding Risk
Quantification
Step 2.2
Identify Scenarios
Step 2.4
Final FIF
Estimates
Step 2.6
Final SF
Estimates
Step 2.5
Final CCDP
Estimates
Screen to Green Screen to Green Screen to Green Screen to Green
Screen to Green
Step 2.7
Final NSP
Estimates
Step 2.3
Refine Scenarios
Data Collection
Ignition Source Screening
Issue Date: 05/02/18 4 0609 App F
of the risk contributions of all fire scenarios that need to be evaluated for a given finding.
However, the bounding CDF estimate obtained in this step is based on the duration
factor, and bounding area-wide values for all other factors.
Step 2.2 defines discrete stages of fire growth and damage, referred to as Fire Damage
States (FDSs), and identifies credible fire scenarios that may need to be considered in
the Phase 2 assessment. This step also collects detailed information about the ignition
sources, secondary combustibles, equipment and/or cable targets, etc. involved in these
scenarios. Each scenario is uniquely defined by the ignition source that starts the fire
and the extent of the damage caused by the fire (FDS).
Step 2.3 screens ignition sources that are not capable of causing target damage or
ignition of secondary combustibles. Fire scenarios identified in Step 2.2 that are initiated
by a screened ignition source do not require further analysis and can be eliminated at
this stage.
Step 2.4 determines the final FIF and applicable AFs for the ignition sources that are not
screened in Step 2.3.
Step 2.5 identifies the damaged target set for each unscreened ignition source and each
applicable FDS, and quantifies the corresponding CCDP for each scenario.
Step 2.6 estimates the SF for each unscreened fixed or transient ignition source based
on the heat release rate (HRR) required to cause damage to the target set for the fire
scenario under evaluation, or to cause ignition of a secondary combustible. Liquid fuel
spill and high energy arcing fault (HEAF) fires are assigned an SF that is independent of
the HRR required to cause damage or ignition.
Step 2.7 quantifies the final NSP for each fire growth and damage scenario based on an
estimate of the time required to damage of the target set and an analysis of the detection
and suppression methods available for the scenario.
The CDF is re-evaluated at the end of Step 2.1 and the end of Steps 2.3 through 2.7. If the
refined CDF is less than 1E-6 at any time in Phase 2, the analysis in complete and the finding
screens to Green. When all steps have been completed and the final CDF is still 1E-6 or
greater, a Phase 3 assessment is required to determine the final risk significance of the finding.
02.03 Assumptions and Limitations
This document describes a simplified tool that provides a slightly conservative, nominally orderof-magnitude assessment of the risk significance of inspection findings related to the fire
protection program. The Fire Protection SDP is a tool that NRC inspectors can easily use to
obtain an assessment of the risk significance of a finding.
The Fire Protection SDP approach has a number of inherent assumptions and limitations. A
more detailed discussion of these assumptions and limitations is contained in the Supplemental
Guidance/Technical Basis for Appendix F (IMC 0308, Attachment 3, Appendix F).
The Fire Protection SDP assesses the change in core damage frequency (∆CDF), rather
than large early release frequency (LERF), as a measure of risk significance. Typically
the change in CDF and LERF are assumed to be proportional, such that assessing one
is sufficient. However, if a finding increases the likelihood of otherwise low probability
events that primarily impact LERF (such as fire-induced spurious opening of a
containment isolation valve), the change in LERF may be the more appropriate risk
metric. In this case, the SDP analysis should proceed directly to Phase 3.
The quantification approach and analysis methods used in this Fire Protection SDP are
largely based on existing fire PRA analysis methods. As such, the methods are also
limited by the current state of the art in fire PRA methodology.
The Fire Protection SDP focuses on risks due to degraded conditions of the fire
protection program during full power operation of a nuclear power plant. This tool does
not address the potential risk significance of fire protection inspection findings in the
context of other modes of plant operation (i.e., low power or shutdown). In this case, the
SDP analysis should proceed directly to Phase 3.
In the process of simplifying existing fire PRA methods for the purposes of the Phase 2
Fire Protection SDP analysis, compromises in analysis complexity have been made.
The process strives to achieve order of magnitude estimates of risk significance.
However, it is recognized that fire PRA methods in general retain considerable
uncertainty. The Fire Protection SDP strives to minimize the occurrence of falsenegative findings.
The Fire Protection SDP does not include findings associated with performance of the
on-site fire brigade or fire department. On-site fire brigade findings are evaluated in
accordance with IMC 0609, Appendix A.
The Fire Protection SDP Phase 2 quantitative screening method is mainly intended to
support the assessment of issues associated with an individual fire area. However, the
Phase 2 process may be appropriate for some issues involving multiple fire areas. It is
recommended that additional guidance be sought from a risk analyst in the conduct of
such an analysis. A systematic plant-wide search and assessment effort is beyond the
intended scope of Phase 2. In such cases, the SDP analysis can proceed directly to
Phase 3.
The Fire Protection SDP Phase 1 qualitative screening process includes a limited set of
questions regarding main control room (MCR) fires. However, the Phase 2 quantitative
screening method does not currently include explicit treatment of MCR fires or fires
leading to MCR abandonment (either due to fire in the MCR or due to fires in other fire
areas that would impair the ability to control the reactor from the MCR). The Phase 2
process may be able to address such scenarios, but it is recommended that additional
guidance be sought from a risk analyst in the conduct of such an analysis.
0609F-03 STEP 1 – FIRE PROTECTION SDP PHASE 1 SCREENING
Phase 1 of the Fire Protection SDP serves to screen out very low risk significant findings. This
qualitative screening approach is entered when the following items are met:
The inspection finding clearly states the licensee performance deficiency and the morethan-minor criteria met in accordance with IMC 0612, Appendix B, “Issue Screening”.
The finding should discuss, as applicable, the noncompliance with any applicable
licensing basis requirements. The SDP analysis should not proceed if the condition of
the fire protection feature was specifically approved in a Safety Evaluation Report (SER)
during the fire protection licensing process (i.e., there is no performance deficiency),
provided cited compensatory measures or other caveats imposed through the SER
remain uncompromised.
The worksheet for recording the Fire Protection SDP Phase 1 screening results is provided in
Attachment 1.
Step 1.1 – Provide Statement of Fire Inspection Finding
Provide a clear statement of the fire inspection finding and the non-compliance in Attachment 1.
Step 1.2 – Assign a Fire Finding Category
Assign the fire finding to the finding category that best fits using the guidance in the table below.
A fire finding can only be assigned to one category. Record the assigned fire finding category in
Attachment 1.
Table 1.2.1 – Finding Categories
Finding Category Elements Covered by Finding Category
O Fire Prevention
and Administrative
Controls
The plant combustible material controls program
Other administrative controls, such as work permit programs
Hot work fire watches
Roving or periodic fire watches (other than those described in
the Fixed Fire Protection Finding Category below)
Training programs
O Fixed Fire
Protection
Systems
Fixed fire detection systems
Fixed fire suppression systems (automatic or manual)
Fire watches posted as a compensatory measure for a fixed
fire protection system outage or degradation
O Fire Water Supply Fire pumps
Yard loop piping
Water sources
O Fire Confinement Fire barrier elements that separate one fire area from another
Penetration seals
Water curtains
Fire and/or smoke dampers
Fire doors
Spatial separation (e.g., per App. R Section III.G.2)
O Manual Firefighting Hose stations
Fire extinguishers
Fire pre-plans
O Localized Cable or
Component
Protection
Passive physical features installed for the thermal/fire
protection of cables, cable raceways, or individual
components
Raceways or component fire barriers (e.g., cable wraps)
Radiant heat shields protecting a component or cable
O Post-fire Safe
Shutdown (SSD)
Systems or functions identified in the post-fire SSD analysis
Systems or functions relied upon for post-fire SSD
Post-fire SSD component list (e.g., completeness)
Post-fire SSD analysis (e.g., completeness)
Post-fire plant response procedures
Alternate shutdown (e.g., control room abandonment)
Circuit failure modes and effects (e.g., spurious operation
issues)
Issue Date: 05/02/18 7 0609 App F
Table 1.2.1 – Finding Categories
Finding Category Elements Covered by Finding Category
O Main Control
Room Fires
Postulated fires occurring in the MCR that affect the
habitability, equipment, or controls in the MCR
Step 1.3 – Low Degradation Deficiencies
Determine if the fire finding can be assigned a low degradation rating using the guidance in
Attachment 2. Provide an explanation of the degradation rating reasoning in Attachment 1.
1.3.1-A Question: Based on the criteria in Attachment 2, is the finding assigned a “Low”
degradation rating?
O Yes – Screen to Green, no further analysis required.
O No – Continue to Step 1.4.
Step 1.4 – Qualitative Screening Questions for Individual Fire Finding Categories
Proceed to the step that corresponds to the fire finding category assigned in Step 1.2 and
answer the screening questions to determine if the finding is of very low risk significance
(Green). There are screening questions for each of the eight finding categories:
Prevention of fires from starting
1.4.1 Fire Prevention and Administrative Controls
Rapid detection and suppression of fires that occur
1.4.2 Fixed Fire Protection Systems
1.4.3 Fire Water Supply
1.4.4 Fire Confinement
1.4.5 Manual Fire Fighting
Protection of the reactor’s ability to safely shutdown if a fire is not promptly extinguished
1.4.6 Localized Cable or Component Protection
1.4.7 Post-Fire Safe Shutdown
1.4.8 Main Control Room Fires
Only evaluate the finding using the screening questions from the assigned fire finding category.
If a question does not apply, skip the question and proceed to the next question for that finding
category. If it is the last question in the category, proceed to Step 1.5. For each question,
indicate your response by checking the circle in Attachment 1. Describe the rationale for the
chosen response in Attachment 1.
Step 1.4.1: Fire Prevention and Administrative Controls
1.4.1-A Question: Could the fire finding increase the likelihood of a fire, delay detection of a fire,
or result in a more significant fire than previously analized such that the
credited safe shutdown strategy could be adversely impacted?
O Yes – Continue to next question.
O No – Screen to Green, no further analysis required.
Issue Date: 05/02/18 8 0609 App F
1.4.1-B Question: Does the fire finding adversely affect an area with adequate automatic
detection and suppression?
O Yes – Screen to Green, no further analysis required.
O No – Continue to Step 1.5.
Step 1.4.2: Fixed Fire Protection Systems
1.4.2-A Question: Does the degraded or non-functional detection or fixed suppression system
adversely affect the ability of the system to protect any equipment important
to safe shutdown?
O Yes – Continue to Step 1.5.
O No – Screen to Green, no further analysis required.
Step 1.4.3: Fire Water Supply
1.4.3-A Question: Would adequate fire water capacity (flow at required pressure) still be
available for protection of equipment important to safe shutdown in the most
limiting location onsite?
O Yes – Screen to Green, no further analysis required.
O No – Continue to Step 1.5 (Phase 2) or Phase 3, as appropriate.
Step 1.4.4: Fire Confinement
1.4.4-A Question: Will the degraded fire confinement element continue to provide adequate fire
endurance (including protection from the transmission of flames, smoke, and
hot gases) to prevent fire propagation through the fire confinement element,
given the combustible loading and location of equipment important to safe
shutdown in the fire area of concern?
O Yes – Screen to Green, no further analysis required.
O No – Continue to next question.
1.4.4-B Question: Is there an adequate automatic suppression system on either side of the fire
confinement element?
O Yes – Screen to Green, no further analysis required.
O No – Continue to next question.
1.4.4-C Question: If the fire finding involves an open or degraded fire door, is there any
equipment important to safe shutdown in the affected fire areas?
O Yes – Continue to the next question.
O No – Screen to Green, no further analysis required.
1.4.4-D Question: If the fire finding involves failure of a fire door to properly latch, but did not
affect the ability of the fire door to close, does the fire door protect an area
with a gaseous fire suppression system:
O Yes – Continue to Step 1.5.
O No – Screen to Green, no further analysis required.
Issue Date: 05/02/18 9 0609 App F
1.4.4-E Question: If a fire were to spread from one fire area (the exposing fire area) to another
(the exposed fire area) due to the degraded fire confinement element, would
any additional targets be damaged in the exposed fire area that could impact
the credited safe shutdown strategy for the exposing fire area (targets include
post-fire safe shutdown components or other plant components whose loss
might lead to a demand for safe shutdown (e.g., a plant trip))?
O Yes – Continue to next question.
O No – Screen to Green, no further analysis required.
1.4.4-F Question:If the answer to Question 1.4.4-E is yes, are the additional damage targets
sufficiently nearby in the adjoining compartment such that they could be
affected by a fire spreading due to the deficiency in the fire confinement
element(e.g., a cable that passes through multiple fire areas)?
O No – Screen to Green, no further analysis required.
O Yes – Continue to Step 1.5.
Step 1.4.5: Manual Fire Fighting
1.4.5-A Question: Is the fire finding associated with portable fire extinguishers not used for hot
work fire watches?
O Yes – Screen to Green, no further analysis required.
O No – Continue to next question.
1.4.5-B Question: Is the fire finding associated with pre-fire plans?
O Yes – Screen to Green, no further analysis required.
O No – Continue to next question.
1.4.5-C Question: Is the fire area associated with the fire finding protected by an adequate
automatic or manual fire suppression system?
O Yes – Screen to Green, no further analysis required.
O No – Continue to the next question.
1.4.5-D Question: For a finding associated with a degraded hose station(s), was an alternative
manual suppression method available to suppress the fire such that
equipment important to safe shutdown would not be adversely affected?
O Yes – Screen to Green, no further analysis required.
O No – Continue to Step 1.5.
Step 1.4.6: Localized Cable or Component Protection
1.4.6-A Question: Is the area with the degraded fire wrap (cable, cable tray, or component)
protected by an adequate automatic detection and suppression system?
O Yes – Screen to Green, no further analysis required.
O No – Continue to next question.
1.4.6-B Question: Is the area with the degraded fire wrap (cable, cable tray, or component)
protected by an adequate automatic detection system and a fire wrap that
would provide sufficient fire endurance to enable suppression of a fire prior to
damage to the target?
O Yes – Screen to Green, no further analysis required.
O No – Continue to Step 1.5.
Issue Date: 05/02/18 10 0609 App F
Step 1.4.7: Post-fire Safe Shutdown
1.4.7-A Question: For a finding associated with emergency lighting, do operators have
adequate alternate lighting (such as flashlights) to perform any necessary
time critical/recovery actions?
O Yes – Screen to Green, no further analysis required.
O No – Continue to Step 1.5.
1.4.7-B Question: Would the impact of the fire finding be limited to equipment which is not
required for the credited safe shutdown success path?
O Yes – Screen to Green, no further analysis required.
O No – Continue to next question.
1.4.7-C Question: Does the fire finding adversely affect the ability to reach and maintain hot
shutdown/hot standby or safe and stable conditions using the credited safe
shutdown success path?
O Yes – Continue to Step 1.5.
O No – Screen to Green, no further analysis required.
Step 1.4.8: Main Control Room Fires
NOTE: This section only applies if there is no equipment greater than or equal to 440V in the
MCR.
1.4.8-A Question: If the finding involves the malfunction (either a spurious operation due to a
hot short or the failure to operate due to fire damage) of two or more
components located in the main control board (MCB) (MCB includes any
panels in the horseshoe area or within the line of sight of the operators), is all
of the internal cabinet wiring in the MCB qualified (such as per IEEE-383) and
are the components located at least 8.2 feet (2.5 meters) apart?
O Yes – Screen to Green, no further analysis required.
O No – Continue to the next question.
1.4.8-B Question: If the finding involves the malfunction (either a spurious operation due to a
hot short or the failure to operate due to fire damage) of two or more
components that are not located in the main control board (MCB), are the
components located in nonadjacent cabinets?
O Yes – Screen to Green, no further analysis required.
O No – Continue to the next question.
1.4.8-C Question: If the finding involves a single fire scenario in the MCR, did the deficiency
exist for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> or less?
O Yes – Screen to Green, no further analysis required.
O No – Continue to Step 1.5.
Issue Date: 05/02/18 11 0609 App F
Step 1.5 – Screen Based on Licensee Fire PRA Results
For plants with a fire PRA, the results of the licensee’s PRA-based risk evaluation can serve as
the basis for screening a finding to Green, provided a Senior Reactor Analyst (SRA) reviews
and approves. For this process the licensee has to provide a risk evaluation based on its fire
PRA, including the dominant cut sets and information on how the deficiency is modeled. With
this information, an SRA may be able to determine whether the licensee’s evaluation is
acceptable. If the plant does not have a fire PRA or the fire finding cannot be adequately
modeled using the plant’s existing fire PRA, proceed to a Phase 2 evaluation. If the licensee’s
risk evaluation indicates that the fire finding has more than a very low risk significance (greater
than green), the SDP risk evaluation should continue to Phase 2 or Phase 3, at the discretion of
the SRA.
Step 1.5.1: Screen by Licensee Fire PRA-based Risk Evaluation
Based on results from the licensee’s fire PRA-based risk evaluation, evaluate whether a
determination can be made that the finding is of very low risk significance. Provide an
explanation of the evaluation of the licensee’s fire PRA results in Attachment 1.
1.5.1-A Question: Does the plant have a fire PRA capable of adequately evaluating the risk
associated with the finding, as determined by an SRA?
O Yes – Continue to the next question.
O No – Continue to Phase 2 evaluation.
1.5.1-B Question: Does the licensee’s risk-based evaluation for this fire finding indicate a ∆CDF
of less than 1E-6, and is the evaluation result accepted by an SRA?
O Yes – Screen to Green, no further analysis required.
O No – Continue to Phase 2 or 3 evaluation, as determined by the SRA.
0609F-04 STEP 2 – FIRE PROTECTION SDP PHASE 2 SCREENING
The worksheet for recording the Fire Protection SDP Phase 2 screening results is provided in
Attachment 1.
In preparation for the analysis, request and review the following licensee documents, as
needed:
The licensee’s fire hazards analysis for the fire area(s) to be evaluated
The post-fire safe shutdown analysis for the fire area(s) to be evaluated
The licensee’s lists of required and associated circuits
Post-fire operating procedures applicable to the fire area(s) to be assessed
Documentation for any USNRC approved deviations or exemptions relevant to the fire
area(s) to be assessed.
Any PRA documentation that can support the analyses for the fire area(s) to be
evaluated.
Issue Date: 05/02/18 12 0609 App F
Step 2.1 – Bounding Risk Quantification
This step introduces the equation that is used in the Phase 2 risk quantification, and helps the
analyst to determine which contributing factor(s) in the equation to focus on. It is very unlikely
that a finding in the “Post-Fire SSD” category will be screened to Green in this step, and the
analyst may choose continuing directly to Step 2.2.
Phase 2 of the Fire Protection SDP is a quantitative assessment of the increase in annualized
core damage probability (i.e., CDF integrated over an appropriate fraction of a year,
subsequently referred to as the “CDF “) due to a finding. The following six-factor formula is
used to estimate the screening CDF:
ΔCDF ≈ DF × ∑[FIFi × (∏AF)
i
× SFi × NSPi × CCDPi
]
N
i=1
[1]
Where:
N = Number of fire scenarios evaluated for a given finding;
DF = Duration factor;
FIFi = Fire frequency for the fire ignition source that started scenario i;
AF = Ignition source specific frequency adjustment factors;
SFi = Severity factor for scenario i;
NSPi = Non-suppression probability for scenario i;
CCDPi = Conditional core damage probability for scenario i.
Equation 1 estimates the screening CDF as the sum of the risk contributions of all fire
scenarios that need to be evaluated for a given finding. Only scenarios that are made possible
as a result of the finding need to be considered. These scenarios are identified as a function of
the finding category assigned in Step 2.2. Equation 1 is based on the assumption that the
baseline risk for these scenarios is negligible such that the “adjusted” risk is a reasonable but
conservative approximation of the risk increase.
A bounding estimate of the change in CDF value for an entire area due to fires in the area is
calculated from the following equation:
ΔCDF ≈ DF × FIF × SF × NSP × CCDP [2]
Where:
FIF = Fire ignition frequency for the entire area;
SF = Bounding severity factor for the area;
NSP = Bounding non-suppression probability for the area;
CCDP = Bounding conditional core damage probability for the area.
The sixth factor in Equation 1, AF, is not retained in Equation 2 because the area-wide FIF
accounts for any adjustments. If the finding affects multiple areas (e.g., if the finding pertains to
a degraded barrier between two areas that contain different risk-significant target sets), a
bounding estimate of the change in CDF value can be obtained by summing the CDF
estimated according to Equation 2 over all affected areas. A brief discussion and bounding
Issue Date: 05/02/18 13 0609 App F
estimates for each of the six factors in the formula are provided in Steps 2.1.1 through 2.1.6. A
bounding estimate of the ΔCDF is obtained in Step 2.1.8.
Methods for refining the bounding estimates are described in Steps 2.3 through 2.7. A brief
description of these steps can be found after Figure F.2. A refined estimate of the ΔCDF is
obtained in Step 2.3 based on the information collected in Step 2.2. Steps 2.4 through 2.7
further refine the factor and ΔCDF estimates. The ΔCDF can be re-calculated at any time
during the Phase 2 evaluation since the various steps need not be performed sequentially, but
can be performed iteratively, i.e., the CDF can be updated each time a step is (partially)
completed. Since the SF and NSP rarely reduce the CDF by more than an order of
magnitude, the analyst usually should focus on estimating the FIF and CCDP first. If at any time
in the process the updated value of the ΔCDF is below 1E-6, the finding screens to Green, and
the analysis is complete. If, the ΔCDF is still at least 1E-6 after Steps 2.3 through 2.7 have
been completed, the finding is potentially risk significant and a Phase 3 assessment is required
to determine the final risk significance of the finding, which is a function of the final ΔCDF value
as shown in Table 2.1.1.
Table 2.1.1 – Risk Significance Based on ΔCDF
Frequency Range ( per yr) SDP Based on ΔCDF
ΔCDF ≥ 1E-4 Red
< 1E-6 Green
Step 2.1.1: Estimate the Duration Factor (DF)
DF is the length of time in years (days divided by 365 days/year) that the noted performance
deficiency was, or will be, in existence (i.e., the duration of the degradation). In practice, DF
may vary between approximately 1E-4 (duration of ~1 hour [1/8760 year]) and 1 (duration of 1
year). The value of DF calculated in this step is used in all risk calculations throughout Phase 2
of the Fire Protection SDP, i.e., there is no further refinement in subsequent steps.
Step 2.1.2: Estimate Bounding Value of the Fire Ignition Frequency (FIF)
Any ignition source is assumed to start a fire with a given probability, which is based on plant
fire event frequency statistics. This probability is referred to as the Fire Ignition Frequency, or
FIF. FIFi applies to the ignition source that initiates fire scenario i. FIFs for a range of ignition
sources are tabulated in NUREG-2169 and vary between 3.0E-6 and 1.6E-2. A subset of the
NUREG-2169 FIFs are reproduced in Attachment 4, Table A4.1. The fire ignition sources are
divided into groups called bins that represent location, causal, and mechanistic factors deemed
important to depict frequencies of initiating fire scenarios at different plants. The generic bin
definitions, plant operating mode applicability, and associated frequencies were originally
developed and provided in NUREG/CR-6850, Vol. 2, and subsequently re-evaluated in NUREG2169.
A bounding FIF value can be obtained by summing the FIFs for all ignition sources in the area
under investigation. Generic area-wide FIFs that can be used at this point in the screening
Issue Date: 05/02/18 14 0609 App F
process are given in Tables 2.1.2 and 2.1.3 below. Should a finding qualify in two or more
generic areas, the FIF that is highest for those areas should be used. Guidance for refining the
FIF is provided in Step 2.4.
Table 2.1.2 – Generic Area-Wide Fire Ignition Frequencies
Area FIF/reactor-year
Battery Room 4E-3
Cable Spreading Room
(Containing Cables Only) 2E-3
Cable Spreading Room
(Also Containing Electrical Enclosures*)
Cable Vault (Cables Only) 2E-3
Diesel Generator Room 3E-2
Intake Structure 2E-2
Main Control Room 1E-2
Radioactive Waste Area 1E-2
Switchgear Room 2E-2
Transformer Yard 2E-2
Turbine Building 8E-2
- Limited to low voltage electrical components (< 440 V)
Table 2.1.3 – Bounding FIFs for Hot Work and Transient Fires
Ignition Source FIF/reactor-year
Welding and Cutting (Hot Work Issues Only) 4E-2
Transients (Combustible Controls Program Issues Only) 5E-3
Step 2.1.3: Estimate Bounding Values of Ignition Frequency Adjustment Factors (AF)
At this point in the process, a bounding AF of 1.0 is assumed. If the finding category assigned
in Step 1.2 is “Fire Prevention and Administrative Controls”, an increase of the FIF by up to a
factor of 10 may be applicable to hot work and transient combustible fires. These increases are
accounted for in the generic FIFs for hot work and transient combustible fires provided in Table
2.1.3. Guidance for determining the applicable adjustments to the FIF for hot work and transient
combustible fires when not using the bounding FIF estimates in Table 2.1.3 is provided in Steps
2.4.2 and 2.4.3.
Step 2.1.4: Estimate Bounding Value of the Severity Factor (SF)
SFi is the probability that the HRR of the ignition source for scenario i is sufficient to cause
damage to or ignition of the nearest and most vulnerable target. At this point in the process, a
Issue Date: 05/02/18 15 0609 App F
bounding SFi of 1.0 is assumed. Since ignition sources are screened based on the 98th
percentile of the HRR probability distributions, the assigned SF can range from 2E-2 to 1. SFi,
is a function of the type of ignition source and the distance to and characteristics of the nearest
and most vulnerable combustible or damage target. Guidance for determining the SF for
specific ignition sources is provided in Step 2.6. In the absence of detailed information on the
type and location of ignition sources and targets in the area(s) under evaluation, a bounding SF
of 1.0 is assumed for the area.
Step 2.1.5: Estimate Bounding Value of the Non-Suppression Probability (NSP)
NSPi is the probability that fire suppression efforts fail to suppress the fire before the scenariospecific fire damage state is reached. At this point in the process, a bounding NSPi of 1.0 is
assumed. NSPi can be between 0 (suppression always succeeds before the damage state is
reached) and 1.0 (all suppression fails). For cases where fixed fire suppression is not being
credited, NSP is based entirely on the response of the manual fire brigade compared to the
predicted damage time. For fire areas protected by fixed suppression (either automatic or
manually activated), two suppression paths are considered: success of the fixed suppression
system; and failure of the fixed suppression system to activate on demand combined with the
response of the manual fire brigade. Guidance for calculating scenario-specific NSPs is
provided in Step 2.7. In the absence of detailed information concerning the type and location of
ignition sources and targets in the area(s) under evaluation, a bounding area-wide NSP of 1.0 is
assumed.
Step 2.1.6: Estimate Bounding Conditional Core Damage Probability (CCDP)
CCDPi is the probability that fire-induced damage to plant components and cables in scenario i
will lead to core damage. A bounding value for CCDP can be obtained based on an
assessment of the unavailability and independence of the designated safe shutdown (SSD) path
for the area(s) under evaluation, as described below. These bounding CCDP values vary from
0.01 to 1.0. Alternatively, a conservative estimate can be determined by the SRA using the
plant-specific SPAR models and assuming that all targets that are potentially vulnerable due to
the deficiency will be damaged (full room burnout). Additional guidance for refining the CCDP
estimate is provided in Step 2.5.
Identify the Designated Post-fire SSD Path
Identify the designated post-fire SSD path for the fire area(s) under analysis. All plant fire areas
should have such a SSD path identified as a part of the plant’s fire protection program. The
identified SSD must meet the following criteria in order to be considered at this stage of the
Phase 2 analysis:
The SSD path must be identified as the designated post-fire SSD path in the plant’s fire
protection program.
The SSD path must be supported by a documented post-fire SSD analysis consistent
with regulatory requirements.
Use of the SSD path must be documented and included in the plant operating
procedures.
Issue Date: 05/02/18 16 0609 App F
Assess the Unavailability Factor for the Identified SSD Path
Assign an SSD unavailability factor to the identified SSD path in its as found condition. The
total unavailability factors to be applied in the screening CCDP evaluation are shown in Table
2.1.4. If remaining mitigation capability meeting the criteria in Table 2.1.4 is not available, the
screening CCDP is either assessed as 1.0, or obtained from the SRA. If the CCDP is assessed
as 1.0, the evaluation proceeds with Step 2.1.7 (i.e., there is no need to assess the
independence of the SSD path). The CCDP can be refined later in accordance with Step 2.5.
Table 2.1.4 – Total Unavailability Values for SSD Path Based Screening CCDP
Type of Remaining Mitigation Capability
Screening
Unavailability
Factor
1 Automatic Steam-Driven Train: A collection of associated equipment
that includes a single turbine-driven component to provide 100% of a
specified safety function. The probability of such a train being
unavailable due to failure, test, or maintenance is assumed to be
approximately 0.01 when credited as “Remaining Mitigation Capability.”
0.01
1 Train: A collection of associated equipment (e.g., pumps, valves,
breakers, etc.) that together can provide 100% of a specified safety
function. The probability of this equipment being unavailable due to
failure, test, or maintenance is approximately 0.01 when credited as
“Remaining Mitigation Capability.”
0.01
Use of an Alternate Shutdown Strategy: The capability to safely shut
down the reactor in the event of a fire using existing systems that have
been rerouted, relocated, or modified (alternate or remote shutdown
equipment). The probability of alternate or remote shutdown equipment
being unavailable due to failure, test, or maintenance is assumed to be
0.1 when credited as “Remaining Mitigation Capability.”
0.1
Assess Independence of the Identified SSD Path
Crediting of any SSD path prior to the development of specific fire damage scenarios requires
that a high level of independence be verified. Once the designated post-fire SSD path has been
identified, verify the following characteristics of this SSD path:
The licensee has identified and analyzed the SSD SSCs required to support successful
operation of the SSD path.
The licensee has identified and analyzed SSCs that may cause mal-operation of the
SSD path (e.g., the required and associated circuits).
The licensee has evaluated any manual actions required to support successful operation
of the SSD path and has determined that the actions are feasible.
All manual actions take place outside the fire area under analysis and are specifically
identified in the appropriate plant specific procedures. No credit is given for manual
actions impacted by fire effects such as smoke or high temperatures, or by discharge of
carbon-dioxide fixed suppression systems.
The licensee has conducted an acceptable circuit analysis. Any known unresolved
circuit analysis issues that could adversely impact the functionality of the designated
SSD path are identified.
Issue Date: 05/02/18 17 0609 App F
No known circuit analysis issues (e.g., a known spurious operation issue) for exposed
cables should hold the potential to compromise functionality of the identified SSD path.
o Cables within the fire area under analysis are not considered exposed if they are
protected by a non-degraded raceway fire barrier with a minimum 3-hour fire
resistance rating.
o Cables within the fire area under analysis are not considered exposed if they are
protected by a raceway fire barrier with a minimum 1-hour fire resistance rating,
the area is provided with automatic detection and suppression capability, and
none of these elements is found to be degraded.
o Cables in an adjoining fire area are not considered exposed if the fire barrier
(rated for at least one hour) separating adjoining fire area from the fire area
under analysis is not degraded.
o If the finding category assigned in Step 1.2 was “Fire Confinement,” cables
located in the adjacent fire area are considered exposed unless they are
protected by a non-degraded localized fire barrier with a minimum 1-hour fire
resistance rating.
The licensee’s compliance strategy for the separation of redundant SSD circuits (i.e., in
the context of Appendix R Section III.G.2) are identified. If the finding category assigned
in Step 1.2 is “Fire Confinement,” any required or associated circuit components or
cables that are located in the adjacent fire area(s) separated by the degraded fire barrier
element are identified. Also, any supplemental fire protection (i.e., beyond separation by
the degraded barrier element) provided for any such cable or components are identified.
If the licensee has a fire PRA, the SSD strategy should be credited in the PRA. Any
aspects of the above that are not credited for the SSD strategy in the PRA should not be
credited in this SDP analysis.
A second aspect of the independence check depends on the nature of the fire protection
that has been provided for the designated SSD path (i.e., in the context of 10CFR50
Appendix R Section III.G.2). Table 2.1.5 provides a matrix of independence criteria for
the major options under III.G.2.
Issue Date: 05/02/18 18 0609 App F
Table 2.1.5 – SSD Path Independence Check Criteria
Section III.G.1 or III.G.2 compliance
strategy for SSD path
SSD path independence criteria (all criteria for a
given strategy must be met)
Physical separation into a separate fire
area (II.G.1)
The fire area boundary separating the SSD
path is rated for at least one hour or is
otherwise creditable, and is not impacted by
the finding under analysis.
Separation by a 3-hour rated localized
fire barrier (e.g., a raceway barrier)
(III.G.2.a)
The fire barrier qualification rating is not in
question, and
The fire barrier protecting the redundant
train is not impacted by the finding.
Separation of more than 20 ft. plus
automatic fire detection and suppression
coverage for the fire area (III.G.2.b)
No intervening combustibles or fire hazards,
The fire detection system is not impacted by
the finding, and
The fire suppression system is not impacted
by the finding.
Separation by a 1-hour rated localized
fire barrier (e.g., a raceway barrier) plus
automatic fire detection and suppression
coverage for the fire area (III.G.2.c)
The fire barrier qualification rating is not in
question,
The fire barrier protecting the redundant
train is not impacted by the finding,
The fire detection system is not impacted by
the finding, and
The fire suppression system is not impacted
by the finding.
Other means of protection (e.g.,
exemptions, deviations, reliance on
SSD path will not be credited pending
further refinement of the SDP fire scenarios
Estimate the CCDP
If the designated post-fire SSD path meets the established physical independence criteria, its
unavailability is credited for all fire scenarios (i.e., CCDP = SSD Unavailability Factor. If any of
the independence criteria are not met, the SSD path is not credited (i.e., CCDP =1.0).
NOTE: Later steps include the possibility of crediting the identified SSD path in the context of
specific fire scenarios and specific Fire Damage States (FDSs). Hence, the unavailability
estimates for the identified SSD path should not be discarded, even if they will not be applied at
this stage of the analysis. Rather, the results should be retained for potential use in later steps.
Issue Date: 05/02/18 19 0609 App F
Step 2.1.7: Effect of the Finding Category
In Step 1.2 the fire finding was assigned to one of the following eight categories:
Fire Prevention and Administrative Controls
Fixed Fire Protection Systems
Fire Water Supply
Fire Confinement
Manual Fire Fighting
Localized Cable or Component Protection
Post-Fire SSD
Main Control Room Fires
Since the objective of a Phase 2 assessment is to quantify the CDF due to the deficiencies
that resulted in the finding, only scenarios that contribute to this risk increase need to be
considered. Consequently, the bounding CDF obtained in Step 2.1.8 may be affected by the
finding category. For example, for a finding in the Fire Confinement category, fire scenarios in
the areas on both sides of the degraded barrier may need to be accounted for. A discussion of
the effect of the finding category on the fire scenarios that need to be included in a Phase 2
analysis can be found in Attachment 3.
Step 2.1.8: Estimate Bounding Value of CDF
A bounding estimate of the change in CDF value for the entire area(s) affected by the fire is
calculated from
ΔCDF ≈ DF × ∑[FIFj × SFj × NSPj × CCDPj
]
M
j=1
[3]
Where:
M = Number of areas affected by the finding
DF = Duration factor (from Step 2.1.1);
FIFj = Generic fire ignition frequency for area j (from Table 2.1.2 or 2.1.3);
SFj = Bounding severity factor for area j (from Step 2.1.4);
NSPj = Bounding non-suppression probability for area j (from Step 2.1.5);
CCDPj = Bounding conditional core damage probability for area j (from Step 2.1.6).
Use Table 2.1.8 in Attachment 1 to calculate the CDF according to Equation 3. For findings in
the “Fire Confinement” category, complete a separate table for each area affected, and
calculate the total CDF as the sum of the CDF values for each table.
It is very unlikely that CDF for an area, let alone multiple areas, will be below 1E-6. However,
the bounding CDF estimate provides an initial indication of the likelihood that the finding can
ultimately be screened to Green, and helps identifying the factor(s) the analysis should focus on
to reduce the CDF below the 1E-6 threshold.
Issue Date: 05/02/18 20 0609 App F
Step 2.2 - Identifying Credible Fire Scenarios and Information Gathering
This step defines discrete stages of fire growth and damage, referred to as Fire Damage States
(FDS), and identifies credible fire scenarios that may need to be considered in the Phase 2
assessment. The step also collects detailed information about the ignition sources, secondary
combustibles, targets sets, etc. involved in these scenarios.
Step 2.2.1: Initial FDS Assignment
The FDS is a discrete stage of fire growth and damage postulated in the development of Fire
Protection SDP fire scenarios. Four fire damage states are defined as follows:
FDS0: Only the fire ignition source and initiating fuels are damaged by the fire. FDS0 is
not analyzed in the FP SDP as a risk contributor even if the ignition source is also a
target, such as an electrical enclosure that will yield a non-zero CCDP by itself (in this
case the FDS0 scenario will contribute to the baseline risk regardless of the finding).
FDS1: Fire damage occurs to components or cables protected by a degraded local fire
barrier system (e.g., a degraded cable tray fire barrier wrap), or to unprotected
components or cables located near the fire ignition source. This damage state also
includes ignition of secondary combustibles (cable trays) near the fire ignition source.
FDS2: Widespread fire damage occurs to unprotected components or cables within the
fire area of fire origin, to components or cables protected by a degraded local fire barrier
system, or to unprotected components or cables due the development of a damaging
HGL.
FDS3: Fire damage extends to a fire area adjacent to the fire area of fire origin, in
general, due to postulated fire spread through a degraded inter-area fire barrier element
(e.g., wall, ceiling, floor, damper, door, penetration seal, etc.).
The FDS/Finding Category Matrix in Table 2.2.1 below identifies, given the finding category
assigned in Step 1.2, which FDSs have the potential of contributing to the CDF and need to be
considered in the analysis. The table indicates, for example, that for a finding in the Fire
Confinement Category only fires that spread through the degraded barrier to an adjacent
compartment have the potential of increasing the CDF over the baseline since FDS1 and FDS2
scenarios are not affected by the finding.
Table 2.2.1 – FDS/Finding Category Matrix
Finding Type or Category: FDS1 FDS2 FDS3
Fire Prevention and Administrative Controls Retain Retain N/A
Fixed Fire Protection Systems Retain Retain N/A
Fire Confinement N/A N/A Retain
Localized Cable or Component Protection Retain Retain N/A
Post-fire SSD Retain Retain N/A
Step 2.2.2: Information Gathering
The objective of this step is to collect the information needed to perform a fire growth and
damage analysis for each credible fire scenario. A scenario is uniquely defined by the ignition
source that starts the fire and the extent of the damage caused by the fire (FDS). Guidance for
identifying fire scenarios and for obtaining the necessary information from walkdowns, plan and
document reviews, etc., is provided in Attachment 3. Note that for a licensee with a fire PRA,
this information should be readily available via the fire PRA documentation. Several tables are
provided in Attachment 1 to facilitate the data collection process:
Table 2.2.2a in Attachment 1: This table is used to record general information about the
fire area under evaluation. The information in this table includes the dimensions of the
compartment and FDS2 target type (for HGL calculations), and a list of relevant ignition
sources in the area under evaluation. The latter does not necessarily include all ignition
sources in the area, since only those sources that have the potential of starting a fire that
causes damage and contributes to the CDF need to be considered. Since no analysis
has been performed at this point, it is usually not trivial to determine which sources can
be omitted. If the finding is in the “Fire Confinement” category, Table 2.2.2a must be
completed for each compartment affected by the finding, typically the two compartments
on either side of the degraded barrier.
Table 2.2.2b in Attachment 1: This table is used to record detailed information about a
fixed ignition source or an oil fire, and all targets that are expected to be within its zone
of influence (ZOI). A separate form is used for each ignition source.
Table 2.2.2c in Attachment 1: This table is similar to Table 2.2.2b in Attachment 1, but is
used for transient combustibles.
Table 2.2.2d in Attachment 1: This table contains information about secondary
combustibles and details needed for the detection and suppression analysis.
Since most fire scenarios involve a fixed or a transient ignition source, the analyst may find it
useful to consult the ZOI tables for these ignition sources during walkdowns. The vertical and
radial ZOI for fixed and transient ignition sources are tabulated as a function of the 98th
percentile HRR of the ignition source in Attachment 8 (Figures A.01 and A.02, respectively). In
these tables, the vertical ZOI is provided for ignition sources that are at least 2 ft. from the
nearest wall or corner (referred to as “free-burn” fires) and ignition sources that are within 2 ft. of
a corner (referred to as “corner” fires). At the discretion of the analyst, a fire within 2 ft. of a
single wall can be treated either as a corner or as a free-burn fire.
The 98th percentile HRR of fixed and transient ignition sources can be found in Table A5.1 in
Attachment 5. Whether an electrical cabinet is considered “open” or “closed” for determining its
HRR is based on the criteria developed in NUREG-2178, Vol. 1. A discussion of these criteria
can be found on page 3 of Attachment 3.
The HRR and ZOI tables for fixed and transient ignition sources are duplicated in Tables 2.2.2,
2.2.3, and 2.2.4 below for the analyst’s convenience.
Issue Date: 05/02/18 22 0609 App F
Table 2.2.2 – HRR for ZOI of Fixed and Transient Ignition Sources
Ignition Source Configuration*
HRR
(kW)
Motors NA 69
Pumps NA 211
Loose Transients NA 317
Contained Transients NA 317 Enclosure Set 1
Small Electrical Enclosures (V ≤ 12 ft3
) Open or Closed 45
MCCs & Battery Chargers Closed 130
Switchgear & Load Centers Closed 170
Power Inverters Closed 200
Enclosure
Set 2
Medium Enclosures (12 ft3 < V ≤ 50 ft3
) Closed 200
Medium Enclosures (12 ft3 < V ≤ 50 ft3
) Open 325
Large Enclosures (V > 50 ft3
) Closed 400
Large TP Enclosures (V > 50 ft3
) Open 1000
- See Attachment 3 for definition of “open” and “closed” cabinets
Table 2.2.3 – Vertical ZOI for Fixed and Transient Ignition Sources (ft.)
Electrical Enclosure Fires
HRR Free-Burn Fires Corner Fires
(kW) TS Targets TP Targets TS Targets TP Targets
45 2.6 3.8 5.0 7.1
130 4.5 6.3 8.1 11.4
170 5.1 7.1 9.2 12.8
200 5.5 7.7 9.9 13.7
325 6.9 9.6 12.2 16.9
400 7.6 10.5 13.3 18.4
700 9.7 13.4 16.9 23.3
1000 11.4 15.6 19.7 27.0
Motor Pump, and Transient Fires
HRR Free-Burn Fires Corner Fires
(kW) TS Targets TP Targets TS Targets TS Targets
69 4.2 5.7 7.1 9.6
211 6.6 8.9 11.1 15.0
317 7.8 10.5 13.1 17.7
Issue Date: 05/02/18 23 0609 App F
Table 2.2.4 – Radial ZOI for Fixed and Transient Ignition Sources (ft.)
Electrical Enclosure Fires
HRR TS Targets TP Targets Sensitive Electronic
(kW) Targets
45 1.0 1.4 2.0
130 1.7 2.4 3.5
170 2.0 2.8 3.9
200 2.1 3.0 4.3
325 2.7 3.8 5.5
400 3.0 4.2 6.1
700 4.0 5.6 8.0
1000 4.7 6.7 9.6
Motor, Pump, and Transient Fires
HRR TS Targets TP Targets Sensitive Electronic
(kW) Targets
69 1.2 1.8 2.5
211 2.2 3.1 4.4
317 2.7 3.8 5.4
Switchgear and load centers 440V and above are subject to high energy arcing faults (HEAFs)
in addition to the possibility of a general or thermal fire. As a result, two ignition scenarios need
to be considered for electrical cabinets 440 V; HEAF and non-HEAF. For the HEAF scenario,
the vertical ZOI is within 5 ft. above the top of the cabinet, and the horizontal ZOI is within 3ft. of
all sides of the cabinet. All unprotected targets within this region are assumed to be damaged
instantaneously when the HEAF occurs and all unprotected secondary combustibles within the
region are assumed to ignite instantaneously. The HRR profile for a HEAF fire has no t-squared
growth stage. The HEAF fire reaches HRRpeak instantaneously at ignition (t = 0 seconds),
remains at HRRpeak for 1200 seconds, and subsequently decays linearly to 0 kW in 1200
seconds. The ZOI and HRR profile for non-HEAF scenarios is determined in the same manner
as for electrical cabinets < 440 V.
To optimize the efficiency of the data gathering process, different approaches can be used
depending on whether the targets of concern are known a priori, or not. The two approaches
are described in some detail below.
Approach for Information Gathering when Targets of Concern Are Not a Priori Known
For some findings (e.g., findings in the “Fixed Fire Suppression Systems” category), the targets
of concern are not a priori known. In this case, it usually is more efficient to do the data
gathering iteratively. For example, if a large number of ignition sources are present in the fire
area under evaluation, often many will be screened out in Step 2.3. In this case, it would be
more efficient to first collect the information that is needed to screen ignition sources, and to
gather the remaining information after Step 2.3 has been completed. Specific guidance is
provided below:
Issue Date: 05/02/18 24 0609 App F
Identify Ignition Sources
In Table 2.2.2a in Attachment 1, develop a list of the ignition sources that are present in the
area(s) being evaluated. Only ignition sources that have the potential of starting a fire that
contributes to the CDF need to be included.
In the specific case of findings categorized as “Fire Confinement” in Step 1.2, the fire ignition
sources and associated nearest most vulnerable ignition targets must be identified on both
sides of the degraded fire barrier. That is, the scope of Step 2.3 and subsequent steps expands
to encompass two or more fire areas; and in particular, those fire areas that are separated by
the degraded fire barrier element(s).
To screen ignition sources that are not capable of releasing heat at a sufficient rate to create a
damaging HGL it is necessary to record the floor area and the height of the compartment(s)
being evaluated (i.e., compartment volume) on Table 2.2.2a in Attachment 1.
Detailed guidance for the treatment and counting of fire ignition sources is provided in
Attachment 4. Fire ignition sources are binned by type or general classifications that are predefined in Attachment 3 (HRR bins) and Attachment 4 (FIF bins). All fire ignition sources are
assigned to one, and only one, of the identified fire ignition source type bins. Each fire ignition
source bin has a corresponding fire scenario characterization bin or bins as identified in
Attachment 4, Table A4.1. Cataloging of the fire ignition sources includes a count of the number
of fire ignition sources of each type present.
The risk-significance of a finding is determined by summing the CDF for all credible fire
scenarios in the area(s) being evaluated. However, some fire scenarios are not affected by the
degraded conditions, and the corresponding CDF values are equal to zero. Consequently, the
ignition sources involved in these scenarios can be omitted from the list. For example, if a
finding is related to the degradation of specific portions of a water-based fire suppression
system, it may be appropriate to limit the fire ignition source search to those sources whose
coverage is impacted by the specific degradation.
One fire ignition source scenario that is applicable to all areas of the plant is transient fuel fires
(e.g., trash, refuse, temporary storage materials, etc.)
An ignition source is either considered to be in a corner, against a wall, or free-burning. The
corner and wall locations are assumed for ignition sources that are within 2 ft. of two intersecting
walls or within 2 ft. of a single wall, respectively. Ignition sources that are more than 2 ft. away
from a wall are considered to be free-burning. At the discretion of the analyst, a wall fire can
be treated either as a corner or as a free-burn fire.
For most fire ignition sources, the fire frequency is provided on a per component basis.
However, for thermoplastic cables, transients, and hot work a likelihood rating assignment as
low, medium, or high is required. The guidance for assigning these ratings is provided in
Attachment 4.
Should a fire protection program degradation finding be encountered that is very specific to fires
involving one or more specific fire ignition sources, then the SDP Phase 2 analysis should be
focused on only those specific sources. It is recommended that additional guidance and
support in making such a decision should be sought in such cases. Careful and complete
documentation of the decision will also be required.
Issue Date: 05/02/18 25 0609 App F
Identify Nearest and Most Vulnerable Targets
For each unique fire ignition source, identify the ignition and/or damage targets that will be:
Thermal damage targets (components or cables) directly above the fire ignition source
that might be damaged by the flame zone or plume effects,
Thermal damage targets (components or cables) within a direct line of sight of the fire
ignition source that may be damaged direct radiant heating, and
The most fragile thermal damage target in the general fire area (for damaging HGL
exposure considerations).
Secondary combustible materials (vertical stacks of horizontal cable trays) directly above
the fire ignition source that might be ignited by the flame zone and/or plume,
Record each ignition and/or damage target and its distance from the appropriate fire ignition
source on the Table 2.2.2b or 2.2.2c in Attachment 1. If a vertical stack of horizontal cable trays
is located above an ignition source, record the number of trays, the width of the trays, and the
dominant type of cables in the tray (thermoset, thermoplastic, or Kerite) on Table 2.2.2d in
Attachment 1.
Three different types of electrical damage targets are considered; thermoset cables,
thermoplastic cables, and sensitive electronics. Only the first two are considered as ignition
targets. Kerite cables are assumed to have the same damage thresholds as thermoplastic
cables, but behave as thermoset cables in terms of ignition and flame spread propensity.
Detailed guidance for the identification of targets and their ignition and damage criteria is
provided in Attachment 6.
With this approach, Tables 2.2.2b and/or 2.2.2c are only partially completed at this stage, i.e.,
only the nearest and most vulnerable targets are listed. After finishing Step 2.3, the analyst will
need to complete Tables 2.2.2b, 2.2.2c, and 2.2.2d for the unscreened ignition sources, and
add the required information for the other targets that are located within the ZOI of the ignition
source.
Approach for Information Gathering when Targets of Concern Are Known
For other findings (e.g., findings in the “Localized Cable and Component Protection”), the
targets of concern are known. In this case, the analyst first identifies the ignition sources that
may cause damage to one of the known targets or may have the capability of igniting a
secondary combustibles. These are the ignition sources that are either directly below one of the
known targets of concern, directly below a secondary combustibles, or within a direct line of
sight of a target or secondary combustible. Tables 2.2.2a, 2.2.2b, and 2.2.2c can be completed
at this stage. For each ignition source that was identified, only one damage or ignition target will
be listed on Table 2.2.2a or Table 2.2.2b. Table 2.2.2d can also be completed at this stage, or
its completion can be deferred until after the ignition sources that do not screen in Step 2.3 are
known.
Issue Date: 05/02/18 26 0609 App F
Step 2.3 – Ignition Source Screening and Fire Scenario Refinement
Step 2.3.1: Characterize Fire Ignition Sources
For each unique fire ignition source identified in Step 2.2.2, a HRR profile and nominal location
are assigned. The HRR profiles for various fixed and transient ignition sources can be found in
Attachment 5. The 98th percentile peak HRR of fixed and transient ignition sources is provided
in Attachment 5, Table A5.1. The 98th percentile HRR is used to screen ignition sources in
Steps 2.3.2. The electrical enclosures in Attachment 5, Table A5.1 are grouped in the same
manner as in NUREG-2178, Vol.1. The 98th percentile HRRs for motors, pumps, and transients
are based on the values in NUREG/CR-6850, Vol.2, Table G-1. Two types of HRR profiles are
considered for electrical cabinets 440 V; one for HEAF scenarios and another one for nonHEAF scenarios. A distinction is made between two types of transients; the first has a t2 growth
time to peak HRR of 2 minutes (typical of loose trash), and the second has a time to peak HRR
of 8 minutes (typical of trash in a container). Both types of transients have the same 98th
percentile HRR (317 kW).
Liquid fuel spills can be confined or unconfined. For confined liquid fuel pool fires the area is
known. The HRRs for confined pool fires of common fuels as a function of pool diameter are
tabulated in Attachment 5, Table A5.2. The HRRs of unconfined liquid fuel spill fires are
tabulated for the same fuels as a function of spill volume in Attachment 5, Table A5.3. Confined
liquid pool fires and unconfined liquid spill fires are assumed to grow at an infinitely fast rate,
i.e., the tabulated HRR is reached without delay at ignition.
Two distinct oil spill fires may need to be considered. The first scenario assumes a spill of
100% of the amount of fuel or oil that can be spilled. The second scenario considers a 10%
spill. A severity factor of 0.02 is assigned to the first scenario, and 0.98 is used for the second
scenario. For confined liquid pool fires it is not necessary to evaluate the two scenarios
separately if the containment is large enough to hold 100% of the amount of fuel or oil that can
be spilled.
Guidance for treating other fire ignition sources is provided in Attachment 5.
Step 2.3.2: FDS1 Ignition Source Screening
Assess the damage/fire spread potential of each fire ignition source using the ZOI tables and
plots (table/plot set A in Attachment 8). Fire ignition sources will be screened out if they meet
the following criteria:
1. The fire ignition source cannot cause damage to targets located near the ignition source,
and
2. The fire ignition source cannot cause ignition of secondary combustible fuels.
The 98th percentile HRRs of fixed and transient ignition sources are given in Attachment 5,
Table A5.1. The vertical ZOI can be determined as a function of the HRR of the ignition source
and its location from the table or plots in Figure A.01 in Attachment 8. If the ignition source is
within 2 ft. of a wall, the analyst may use the ZOI for corner fires. If the nearest and most
vulnerable damage or ignition target is within the vertical ZOI, the ignition source is capable of
damaging and/or igniting the target and it does not screen. The radial ZOI can be determined
as a function of the HRR of the ignition source from the table or plots in Figure A.02 in
Attachment 8 If the nearest and most vulnerable damage target is within the radial ZOI, the
Issue Date: 05/02/18 27 0609 App F
ignition source is capable of damaging and/or igniting the target and it does not screen. The
approach is similar for confined liquid fuel pool fires and unconfined liquid fuel spill fires, except
that the tables and plots in Figures A.04-A.15 are used to determine the vertical and radial ZOI.
Use the FDS1 ignition source screening worksheet (Table 2.3.2 in Attachment 1) to perform the
FDS1 screening for each ignition source.
Step 2.3.3: FDS2 Ignition Source Screening
Assess the capability of each fire ignition source to release heat at a sufficient rate to create a
damaging HGL. The minimum HRR required for the development of a damaging HGL can be
determined as a function of compartment floor area, ceiling height, and type of most vulnerable
target using the HGL tables and plots (table/plot set B) in Attachment 8.
Use the FDS2 ignition source screening worksheet (Table 2.3.3 in Attachment 1) to perform the
FDS2 screening for each ignition source.
Step 2.3.4: FDS3 Ignition Source Screening
For findings in the “Fire Confinement” category Table 2.3.3 in Attachment 1 is also used to
screen ignition sources that, possibly in combination with secondary combustibles, are not
capable of causing the development of a damaging HGL in the exposed compartment. In this
case the two compartments separated by the degraded barrier are combined into one. The
floor area of the combined compartment is the sum of the floor areas of the two compartments.
The ceiling height is the lower of the ceiling heights in the two compartments. The target type is
that in the exposed compartment, i.e., not the compartment where the fire is postulated.
Step 2.3.5: Screening Check
This screening check considers whether or not one or more potentially challenging fire
scenarios have been identified. If no such fire ignition source scenarios have been identified,
then the finding screens to Green and the analysis is complete. The screening criteria for this
step are as follows:
For findings in the “Fire Confinement” category, if all identified ignition sources on
both sides of the degraded barrier screen out in Step 2.3.3, then no potentially
challenging fire scenarios were developed. In this case, the Phase 2 analysis is
complete and the finding should be assigned a Green significance determination
rating. Subsequent analysis steps need not be completed.
For findings in other categories, if all identified fire ignition sources screen out in
steps 2.3.2 and 2.3.3, then no potentially challenging fire scenarios were developed.
In this case, the Phase 2 analysis is complete and the finding should be assigned a
Green significance determination rating. Subsequent analysis steps need not be
completed.
If one or more fire damage states is retained for any of the ignition sources, then the
analysis continues to Steps 2.4 through 2.7, not necessarily sequentially (although
they are discussed in sequence for convenience). For findings that are not
categorized as “Fire Confinement”, include the unscreened ignition source-FDS
combinations from Steps 2.3.2 and 2.3.3 in Table 2.1.8 in Attachment 1, starting at
row 2. For findings that are categorized as “Fire Confinement”, only include the
unscreened ignition source-FDS3 combinations from Step 2.3.4.
Issue Date: 05/02/18 28 0609 App F
Step 2.4 – Final Fire Ignition Frequency Estimates
In Step 2.1, a bounding area-wide FIF was used in the risk calculation. In this step, the fire
frequency for each unscreened fire ignition source scenario is refined by multiplying the
individual fire frequencies for each type of ignition source by the number of ignition sources in
the scenario. The fire frequency for each unscreened fire ignition source is then further refined
to reflect adjustments to findings within certain fire prevention and other administrative controls
programs, and to take credit for compensatory measures, if appropriate.
Step 2.4.1: Nominal Fire Frequency Estimation
A frequency for each fire ignition source bin on a per component basis has been developed and
is provided in Attachment 4. Using the screening results obtained in Step 2.3, record for each
fire source, the number of sources retained and the fire frequency per counting unit for each
unscreened fire ignition source bin in the risk quantification worksheet (Table 2.1.8 in
Attachment 1).
Step 2.4.2: Findings Based on Increase in Fire Frequency
The fire frequency increase is only applicable to certain types of fire ignition sources; namely,
hot work fires and transients:
If the finding category assigned is anything other than “Fire Prevention and
Administrative Controls,” no adjustment of the nominal fire frequencies is applied. The
analysis continues with Step 2.4.4.
Within the general category of “Fire Prevention and Administrative Controls” findings,
only the inspection findings associated with any of the following fire protection DID
elements will result in an increase in fire frequency:
o Combustible controls programs,
For a fire area nominally ranked as a low or medium likelihood for
transient fires, the likelihood rating will be raised by one level of likelihood
(i.e., a low likelihood area becomes a moderate area, and a moderate
likelihood area becomes a high area) and the fire frequency is adjusted
according to the revised likelihood fire frequency value.
For a fire area already ranked as a high likelihood area for transient fires,
the high likelihood transient fire frequency is multiplied by a factor of 3.
o Hot work permitting and/or hot work fire watch provisions of the fire protection
program,
The fire area hot work fire likelihood is set to high, and the hot work fire
frequency for high likelihood is multiplied by a factor of 3.
If a finding within the general category of “Fire Prevention and Administrative Controls” is
not against any of the fire protection DID elements listed above, then no adjustment of
the fire frequency is applied. The analysis continues with Step 2.4.3.
Record the appropriate changes to likelihood frequencies and adjustment factors in Table 2.1.8
the Attachment 1 Worksheet. Criteria for assigning transient or hot work likelihood ratings are
discussed in Attachment 4. The fire ignition frequencies for transient and hot work fires with a
low, medium, or high likelihood rating are provided in Attachment 4, Table A4.1.
Issue Date: 05/02/18 29 0609 App F
Step 2.4.3: Credit for Compensatory Measures
If any of the following compensatory measures are in place and credited with reducing the
frequency of transient fuel or hot work fires for the fire area under analysis, assign a
compensatory measures adjustment factor of 0.0 to the appropriate fire ignition source
scenarios:
For transient combustible fire frequency: A combustible control system exists with
frequent surveillance patrols (at least once per shift) and a review of surveillance reports
show no discovery of improperly stored combustibles. There must be no documented
surveillance reports indicating improperly stored materials during the finding exposure
period.
For hot work fire frequency: The area has not been used for hot work as verified through
a review of hot work permits issued. Review the hot work permits associated with these
activities and confirm that no hot work occurred in the fire area under review during the
finding exposure period.
Record the appropriate adjustment factor(s) in the Table 2.1.8 in Attachment 1. If none of the
above listed compensatory measures are active for the fire area under analysis, no adjustment
to the fire frequency is needed. If either hot work or transient fuels can be shown to never exist
in the fire area, no further development of the corresponding fire scenarios is required to
complete the Phase 2 analysis.
Sum the revised fire frequencies over all identified fire ignition source scenarios to generate an
updated estimate of the fire frequency for the fire area(s) under review. If the sum is less than
3E-6, use this value as an estimate of the fire frequency for the area(s) under evaluation.
Step 2.4.4: Screening Check
Recalculate ΔCDF from Equation 1 using the updated estimate(s) of the fire frequency for the
fire area(s) under review, and the most recent values for the remaining factors. Record the
adjusted ΔCDF value in the Table 2.1.8 in Attachment 1.
If the recalculated value of ΔCDF is lower than 1E-6, then the finding Screens to Green, and the
analysis is complete.
If the recalculated value of ΔCDF exceeds 1E-6, then the analysis continues to another step in
the Phase 2 analysis or to Phase 3 if all Phase 2 steps have been completed.
Step 2.5 – Final Conditional Core Damage Probability Estimates
This step refines the bounding CCDP value that was calculated in Step 2.1.6. Once all the
credible fire scenarios have been developed, an SRA can calculate a scenario-specific CCDP
based on the equipment affected by the fire. Step 2.5 starts with refining the damaged target
sets for the retained FDS1, FDS2, and FDS3 scenarios. Once the damaged target set is known
for each scenario, the corresponding CCDPs can be determined by an SRA from the SPAR
models. The step concludes with a screening check, which involves recalculating ΔCDF based
on the updated CCDPs.
Issue Date: 05/02/18 30 0609 App F
Step 2.5.1: Determine Damaged Target Set and CCDP for FDS1 Scenarios
Skip to Step 2.5.2 if the finding is in the “Fire Confinement” category.
Determine the damaged target set for each FDS1 scenario that is retained in the final
FDS/ignition source matrix developed in Step 2.3. The set consists of all targets that are within
the vertical and radial ZOI. The ZOI tables and plots in Attachment 8 (table/plot set A) are used
in conjunction with information about the location of damage targets near the ignition source to
identify the damaged targets. Target locations may have been obtained as part of Step 2.2.2,
but quite often require an additional walkdown and/or plan review. The FDS1 damaged target
set is recorded for each ignition source on Table 2.2.2.b or Table 2.2.2c in Attachment 1.
Step 2.5.2: Determine Damaged Target Set and CCDP for FDS2 Scenarios
First determine for each FDS2 scenario whether the HRR is sufficient for the generation of a
damaging HGL. Two possibilities may need to be considered:
1. The ignition source releases heat at a sufficient rate to generate a damaging HGL.
2. The ignition source is capable of igniting secondary combustibles, and the combined
HRR of the ignition source and the secondary combustible exceeds the threshold.
The first case is likely to have been examined in Step 2.3.3. It is unlikely that the HRR of a fixed
or transient ignition source alone would exceed the threshold for HGL development. However
the HRR of oil fires can easily lead to the development of a damaging HGL.
The second case is more common and requires additional analysis. The screening first involves
estimating the minimum HRR required for the development of a damaging HGL from the tables
and plots (table/plot set B) in Attachment 8 based on the floor area and ceiling height of the
compartment, and the type of damage targets in the compartment. The HRR profile for the
ignition source in combination with the applicable cable tray configuration from table/plot set C is
then used to determine if and when the minimum HRR is exceeded. Table 2.3.3 in Attachment
1 can be used to facilitate the FDS2 screening process.
If the analysis shows that a damaging HGL can develop, the FDS2 scenario is retained and all
targets in the compartment are included in the damage set, except those that are damaged in
the FDS1 scenario for the same ignition source. Unless the finding category is Fire
Confinement, the HGL scenario is added to Table 2.1.8 in Attachment 1.
Step 2.5.3: Determine Damaged Target Set and CCDP for FDS3 Scenarios
FDS3 is only possible if FDS2 is reached in the exposing compartment. FDS3 is only
considered if the barrier is degraded. In this case fires usually need to be postulated on either
side of the barrier. The approach to determine whether a HGL can develop in a compartment
due to a severe fire in an adjacent compartment is similar to that in Step 2.5.2. The two
compartments are combined into one and the minimum HRR for the creation of a damaging
HGL is determined from the tables and plots in set B based on the total floor area of the two
compartments and a representative ceiling height (typically the lower of the two compartments).
Table 2.3.3 in Attachment 1 can be used to facilitate the FDS3 screening process.
If a fire involving secondary combustibles in the exposing room is found to cause damaging
HGL conditions in the adjacent room, the FDS3 scenario is retained and the targets in the
Issue Date: 05/02/18 31 0609 App F
exposed room are included in the damaged target set. The multi-compartment is added to
Table 2.1.8 in Attachment 1.
Step 2.5.4: Screening Check
Recalculate ΔCDF from Equation 1 using the updated estimates of the CCDPs obtained from an
SRA for the retained fire scenarios in the fire area(s) under review, and the most recent values
for the remaining factors. Record the adjusted ΔCDF value in the Table 2.1.8 in Attachment 1.
If the recalculated value of ΔCDF is lower than 1E-6, then the finding Screens to Green, and the
analysis is complete.
If the recalculated value of ΔCDF exceeds 1E-6, then the analysis continues to another step in
the Phase 2 analysis or to Phase 3 if all Phase 2 steps have been completed.
Step 2.6 – Final Fire Severity Factor Estimates
This step estimates the fire severity factor (SF) for all unscreened ignition sources identified in
Step 2.3.2.
Step 2.6.1: Determine Severity Factors
Estimate the SF for each unscreened fixed or transient ignition source from table/plot sets D
and E in Attachment 8. If the nearest and most vulnerable target has a low CCDP, the analyst
may choose to determine the SF based on a more risk-significant target in the target set. Table
2.6.1 in Attachment 1 can be used to facilitate the SF determination process. Enter the results
on the Table 2.1.8 in Attachment 1. If the finding category is Fire Confinement, the SF only
applies to FDS3 scenarios initiated by the ignition source. For findings in another category, the
SF applies to FDS1 and FDS2 scenarios.
Each table and plot in set D provides the elevations corresponding to SFs ranging from 0.02 to
0.95 for one of the fixed or transient ignition sources listed in Attachment 5, Table A5.1, located
either in the open, or in a corner. Table/plot set D is used to conservatively estimate the SF for
each target or secondary combustible located within the vertical ZOI based on its elevation
above the ignition source.
Each table and plot in set E provides the radial distances corresponding to SFs ranging from
0.02 to 0.95 for one of the ignition sources listed in Attachment 5, Table A5.1. Table/plot set E
is used to conservatively estimate the SF for each target or secondary combustible located
within the radial ZOI based on its distance from the ignition source.
The SF for HEAFs is equal to 1.0. Two scenarios are considered for liquid fuel spill fires. The
first scenario assumes a spill of 100% of the amount of fuel or oil that can be spilled, and the
second scenario assumes a 10% spill. A severity factor of 0.02 is assigned to the first scenario,
and 0.98 is used for the second scenario.
Step 2.6.2: Screening Check
Recalculate ΔCDF from Equation 1 using the updated estimates of the SFs for the retained fire
scenarios in the fire area(s) under review, and the most recent values for the remaining factors.
Record the adjusted ΔCDF value in the Table 2.2.2d in Attachment 1.
Issue Date: 05/02/18 32 0609 App F
If the recalculated value of ΔCDF is lower than 1E-6, then the finding screens to Green, and the
analysis is complete.
If the recalculated value of ΔCDF is equal to or exceeds 1E-6, then the analysis continues to
another step in the Phase 2 analysis or to Phase 3 if all Phase 2 steps have been completed.
Step 2.7 – Final Non-Suppression Probability Estimates
In Step 2.7, the Non-Suppression Probability for each fire growth and damage scenario of
interest (NSPi) is quantified. Detailed guidance on this step is provided in Attachment 7. All
detection/suppression times will be recorded to the nearest whole minute rounded up. The
results of the detection suppression analysis and the final NSP determination are recorded in
the non-suppression probability worksheet (Table 2.7 in Attachment 1).
Step 2.7.1: Determine Damage and Ignition Times
For FDS1 scenarios, use table/plot set F in Attachment 8 to conservatively estimate the damage
time of the nearest and most vulnerable damage and/or ignition target located within the vertical
ZOI based on its elevation above the fixed or transient ignition source. In addition, use
table/plot set G in Attachment 8 to conservatively estimate the damage or ignition time of the
nearest and most vulnerable target within the radial ZOI based on its radial distance from the
fixed or transient ignition source.
For FDS2 and FDS3 scenarios determine the damage time as the time when the combined
HRR of the fixed or transient ignition source and secondary combustibles (from table/plot set C)
reaches the minimum HRR required for the creation of a damaging HGL in the compartment(s)
under evaluation. The minimum HRR to create a damaging HGL is determined as a function of
compartment floor area, ceiling height, and type of the most fragile thermal damage target in the
area(s) under evaluation. The damage time is then determined from the tables and plots in set
C in Attachment 8 for the applicable combination of fixed or transient ignition source and cable
tray configuration.
The damage time for HEAFs and oil fires is assumed to be 0 and 1 minute, respectively.
Step 2.7.2: Fire Detection
The fire detection analysis considers the possibility of detection by any one of the following
mechanisms:
Prompt detection by a posted and continuous fire watch (tdetection = tignition = 0, if general
rules in Attachment 7 are met)
Detection by a roving fire watch (½ the duration of the roving patrol),
Detection by fixed fire detection systems, and
Detection by general plant personnel (tdetection = 5 minutes if fire area is continuously
manned; otherwise tdetection is estimated by the analyst absent detection by other means)
Estimate the time to fire detection by using the guidance in Attachment 7. Only one of the
above means of detection needs to succeed in order for the fire to be detected. The first and/or
most likely mechanism of detection is generally credited.
Issue Date: 05/02/18 33 0609 App F
If a fire area is covered by a fixed fire detection system, but is not covered by a continuous fire
watch, then the response time of the fixed system will be assumed to dominate the overall fire
detection time. As explained in Attachment 7, fire detection response time is estimated for the
fixed and transient ignition sources listed in Attachment 5, Table A5.1, as a function of ceiling
height and radial distance between the source and the detector from Figures H.01-H.05 in
Attachment 8. Convert this value to minutes, rounding up to the nearest minute. The tables
may indicate that time to detection is infinite (i.e., the system will not actuate). In this case, the
time to detection is determined by the other means of fire detection available including detection
by plant personnel.
Step 2.7.3: Fixed Fire Suppression Analysis
Assess the performance and actuation timing of fixed fire suppression systems and any findings
against a fixed fire suppression system.
NOTE: If the fire area under analysis is not equipped with a fixed fire suppression system or the
fixed fire suppression system has been found to be highly degraded, skip Step 2.7.3 and
continue the analysis with Step 2.7.4.
Both automatically-actuated and manually-actuated fixed fire suppression systems will be
considered in this step. Two key factors to the fixed suppression assessment are:
Effectiveness: If the fixed suppression system actuates, will it control a fire involving the
postulated fire ignition source?
Timing: When will the system discharge the fire suppressant?
If the suppression system is deemed effective, then its actuation will be assumed to disrupt the
fire scenario and prevent further fire damage thereby ending the fire scenario.
There are a number of time delays that may apply to gaseous systems, deluge, pre-action
sprinklers, or dry-pipe water systems. The time to actual discharge is the sum of the time to
actuate the demand signal plus any applicable discharge timing delays. There may also be a
delay for cross zoned detection system, i.e., the automatic suppression system will not begin
actuation sequence until after the second detector is actuated. If cross-zoning is used, the
detection time analysis should be reviewed to ensure that the cross-zone detection criteria are
met. The time to generation of the actuation signal will be dominated by the slower detector
(typically the detector farther from the fire ignition source). Additional guidance is provided in
Attachment 7.
Activation Time for Sprinkler Systems
As explained in Attachment 7, sprinkler activation time is estimated for the fixed and transient
ignition sources listed in Attachment 5, Table A5.1 as a function of ceiling height and radial
distance between the source and the sprinkler from Figures H.06-H.17 in Attachment 8.
Convert this value to minutes, rounding up to the nearest minute. The table may indicate that
time to detection is infinite (i.e., the system will not activate). In this case, no credit is given to
the fixed fire suppression system.
If the finding being evaluated involves a moderate degradation to the sprinkler system, credit is
given to the system consistent with the as-found condition. The finding may be reflected either
Issue Date: 05/02/18 34 0609 App F
as a reduction in general reliability, or through a delayed actuation time. The treatment depends
on the nature of the finding as follows:
If the finding is associated with improper spacing of discharge heads, the actuation
timing analysis should reflect the as-found spacing conditions.
A moderate degradation may involve less than 25% of the heads in a water-based fire
suppression system being non-functional. In this case, analyze discharge timing
assuming that the head nearest the fire source will not function. Assume that the
second closest fire discharge nozzle will function. Use the location of this second
closest discharge nozzle in estimating response time.
A moderate degradation finding may imply that the fire suppression system does not
provide adequate coverage for some specific subset of the fire ignition sources present.
In this case the fire suppression system is not credited in the analysis of FDS1 fire
scenarios involving those specific fire ignition sources. The system is credited in the
analysis of corresponding FDS2 and FDS3 scenarios and performance is analyzed
consistent with the as-found conditions.
If the fixed fire suppression system is manually actuated, the time to actuation will be based on
the estimated fire brigade response time, plus a nominal period of two minutes to assess the fire
situation and actuate the system.
Step 2.7.4: Plant Personnel and Manual Fire Brigade
Evaluate the timing associated with manual fire suppression. The manual firefighting response
time is based on the application of historical evidence from past fire events. Based on this
historical evidence, non-suppression probability curve values have been pre-calculated for a
number of cases. Select the most representative case from the pre-analyzed set based on the
fire type or location. If none of these specific condition curves provide a reasonable match to
the conditions of the fire scenario, the "all events" curve should be applied. The mean nonsuppression probability curves for each of these fire types/locations are provided in Attachment
7.
1. Turbine Generator Fires
2. High Energy Arcing Faults
3. Outdoor Transformer Fires
4. Flammable Gas Fires
5. Oil Fires
6. Electrical Fires
7. Transient Fires
8. PWR Containment (At-Power) Fires
9. Containment (Low Power/Shutdown) Fires
10. Welding Fires
11. Control Room Fires
12. Cable Fires
13. All Events
Issue Date: 05/02/18 35 0609 App F
For each unscreened fire scenario, subtract the fire detection time determined in Step 2.7.2
from the fire damage time determined in Step 2.7.1.
If the fire detection time subtracted from the fire damage time is zero or negative, then
NSPmanual = 1.0.
If the fire detection time subtracted from the fire damage time is positive, obtain
NSPmanual from the tabulated or graphical non-suppression curves as explained in
Attachment 7.
Step 2.7.5: Determine Non-Suppression Probabilities
Using the results of the completed Steps 2.7.1 through 2.7.4, estimate the likelihood that fire
suppression efforts fail to suppress the fire before the FDS is reached - the probability of nonsuppression (NSP). NSP is assessed on a scenario-specific basis.
The method applied to quantify NSP depends on whether or not a fixed fire suppression is being
credited:
For cases where fixed fire suppression systems are not being credited, NSP is based
entirely on the response of the manual fire brigade compared to the predicted damage
time.
For fire areas protected by fixed suppression (either automatic or manually actuated),
two suppression paths are considered: success of the fixed suppression system; and
failure of the fixed suppression system to actuate on demand combined with the
response of the manual fire brigade.
Fixed Suppression System: NSPfixed-scenario
If the fire area is protected by fixed fire suppression, estimate NSPfixed for each surviving
scenario (NSPfixed-scenario) for which the fire suppression system is deemed effective. A look-up
table is provided in Attachment 7, and an NSPfixed-scenario is assigned based on the difference
between the predicted time to fire damage (from Step 2.7.1) and the predicted time to
suppression system actuation (from Step 2.7.3).
Calculate an estimate of NSPfixed-scenario for each unscreened fire scenario based on the
scenario-specific fire damage and fire suppression times. Record NSPfixed on Table 2.7 in
Attachment 1.
Manual Fire Suppression: NSPmanual-scenario
The value of NSP manual for a given scenario (NSPmanual-scenario) is dependent on three factors:
the predicted time to fire damage (Step 2.7.1), the predicted time to fire detection (Step 2.7.2),
and the selected fire duration curve (Step 2.7.4). Record NSPmanual on Table 2.7 in
Attachment 1.
Composite Suppression Factor: NSPscenario
If the fire area is not covered by fixed fire suppression, or is highly degraded, or is determined to
be ineffective for the fire ignition source, then:
Issue Date: 05/02/18 36 0609 App F
NSPscenario = NSPmanual−scenario [4]
If the fire area is covered by non-degraded wet-pipe sprinklers, a general reliability of 0.98 is
assumed for the fixed suppression system. In this case, the NSP is quantified as follows:
NSPscenario = (0.02 + 0.98 × NSPfixed−scenario) × NSPmanual−scenario [5]
If the fire area is covered by a non-degraded CO2 suppression system, a general reliability of
0.96 is assumed for the fixed suppression system. In this case, the NSP is quantified as
follows:
NSPscenario = (0.04 + 0.96 × NSPfixed−scenario) × NSPmanual−scenario [6]
If the fire area is covered by a non-degraded dry-pipe sprinklers or deluge system, or by a nondegraded Halon suppression system, a general reliability of 0.95 is assumed for the fixed
suppression system. In this case, the NSP is quantified as follows:
NSPscenario = (0.05 + 0.95 × NSPfixed−scenario) × NSPmanual−scenario [7]
One specific type of degradation that may be identified for gaseous fire extinguishment systems
involves the inability of the system to maintain the design concentration of fire suppressant for a
sufficient time to assure the complete extinguishment of a deep-seated fire. The required
suppressant concentration and maintenance time are established by the system design criteria.
This degradation is commonly referred to as an “inadequate soak time.” This can be an issue
for Halon and Carbon Dioxide fire extinguishment systems, as well as for other gaseous
suppression systems (e.g., Halon replacements).
For the inadequate soak time degradation case, special consideration is required to estimate
NSPscenario. See Attachment 7 for guidance on calculating NSPscenario involving gaseous fire
extinguishment systems that are unable to maintain the design concentration of fire suppressant
for a sufficient time to assure the complete extinguishment of a deep-seated fire.
Step 2.7.6: Screening Check
Recalculate ΔCDF from Equation 1 using the updated estimates of the NSPs for the retained
fire scenarios in the fire area(s) under review, and the most recent values for the remaining
factors. Record the adjusted ΔCDF value in the Table 2.1.8 in Attachment 1.
If the recalculated value of ΔCDF is lower than 1E-6, then the finding Screens to Green, and the
analysis is complete.
If the recalculated value of ΔCDF exceeds 1E-6, then the analysis continues to another step in
the Phase 2 analysis or to Phase 3 if all Phase 2 steps have been completed.
Issue Date: 05/02/18 Att1-1 0609 App F
ATTACHMENT 1
Revision History for IMC 0609, Appendix F
Commitment
Tracking
Number
Accession
Number
Issue Date
Change Notice
Description of Change
Description
of Training
Required
and
Completion
Date
Comment Resolution
and Closed
Feedback Form
Accession Number
(Pre-Decisional, NonPublic)
N/A 04/21/2000 Initial Issue None N/A
02/27/2001 Revised to add additional guidance in defining fire scenarios, and to
evaluate the impact on CDF.
05/28/2004 Revised to introduce a new series of qualitative and quantitative analysis
steps for risk informing and thereby estimating the risk significance of fire
protection inspection issues. The Phase 1 screening process is
enhanced to quickly determine the need for Phase 2 evaluation. The
SDP is supported by 8 attachments and a comprehensive basis
document.
02/28/2005
CN 05-007
Revised to correct typographical errors; change all references from 50th
and 95th percentile to 75th and 98th percentile, respectively, for
expected and high confidence fire intensity values; add additional
applicable correlations from NUREG-1805.
09/20/2013
CN 13-022
This update incorporates an expanded Phase 1. This was created in
response to a large number of comments we received from the regional
senior reactor analysts (SRAs) via the ROP feedback and the Risk
Network initiative. Specific key improvements include: (a) inclusion of
additional screening questions for each of the fire finding categories
based on review of archived fire SDP items, fire data, and expertise that
were not available at the previous release of Appendix F, (b) expansion
of initial quantitative screening to include a non-suppression probability
term, and (c) addition of an option to rely on licensees’ fire PRA
assessment of fire findings under appropriate oversight.
None ML12249A185
ML13039A091
Issue Date: 05/02/18 Att1-2 0609 App F
Commitment
Tracking
Number
Accession
Number
Issue Date
Change Notice
Description of Change
Description
of Training
Required
and
Completion
Date
Comment Resolution
and Closed
Feedback Form
Accession Number
(Pre-Decisional, NonPublic)
DRAFT
CN 17-XXX
Major revision of the entire procedure, including all of the attachments, to
update the analysis methods for consistency with the guidance in
NUREG/CR-6850 and superseding guidance in NFPA 805 FAQs,
NUREG-2169, NUREG-2178, and NUREG/CR-7010. Revisions to
Phase 1 include: (a) revision of the screening questions based on
inspector feedback, (b) re-ordering of the steps, (c) removal of the initial
quantitative screening, (d) addition of main control room fire questions,
and (e) removal of fire brigade screening questions. Revisions to Phase
2 include: (a) removal of need to use the Fire Dynamics Tools (FDTs)
Spreadsheets, (b) addition of tables and plots for determining zone of
influence, hot gas layer, heat release rates for fires involving cable trays,
severity factor, damage times, and detector and sprinkler activation times
in lieu of using the FDTs, (c) re-organization of the process, (d) removal
of moderate degradation rating screening criteria, (e) removal of 75th
percentile fire analysis, and (f) update of the ignition source heat release
rates, fire ignition frequencies, and manual fire suppression curves.
This update includes closure of ROP feedback forms 0609F-1714, 2114,
and 0609F1-2168.
CA Note sent 7/18/17 for information only, ML17191A681.
Issued 10/11/17 as a draft publically available document to allow for
public comments.
November
2017
0609F-965
0609F-1343
0609F-1714
0609F-2114
0609F1-2168
ML18087A414
05/02/18
CN 18-010
Re-issued with new accession number in order to issue as an official
revision after receipt of public comments.
Gap training
covering
changes to
the
procedure
completed
November
2017
0609F-965
0609F-1343
0609F-1714
0609F-2114
0609F1-2168