**NRC INSPECTION MANUAL**APOB

INSPECTION MANUAL CHAPTER 0609 APPENDIX G, ATTACHMENT 2

PHASE 2 SIGNIFICANCE DETERMINATION PROCESS TEMPLATE

FOR PWR DURING SHUTDOWN

Effective Date:  03/01/2020

0609, App F		Issue Date: 02/28/05

TABLE OF CONTENTS0609G Att 2-01	Purpose	101.01	ENTRY CONDITIONS FOR SDP-RELATED INSPECTION FINDING	101.02	MANAGEMENT DIRECTIVE 8.3 ENTRY	101.03	APPLICABILITY	10609G Att 2-02	LIMITS AND PRECAUTIONS	10609G Att 2-03	ABBREVIATIONS AND DEFINITIONS	30609G Att 2-04	PROCEDURE FOR SIGNIFICANCE DETERMINATION	6Step 4.1 - Transition from SDP Phase 1	6Step 4.2 -  Determine if the finding is a precursor to an initiating event (a loss of the DHR function) or a condition finding	6Step 4.3 – Process for Assessing Precursor Findings	6Step 4.4 – Process for Assessing SDP Condition Findings	9Step 4.5 – Process for Assessing Events Under MD 8.3	11

List of Tables

Table 1 – Initiating Event Likelihood (IELs) for LOLC Precursors	15

Table 2 – Initiating Even Likelihoods (IELs) for LOOP Precursors	16

Table 3 – Initiating Event Likelihood (IELs) for Loss of Inventory (LOI) Precursors	17

Table 4 – Initiating Event Likelhoods (IELs) for LORHR Precursors	18

Table 5 – Initiating Even Likelihoods (IELs) for Condition Findings – PWRs	19

Table 6 - Mitigation Capability Credits for Installed Equipment	20

Table 7 - Credit for Temporary Equipment	21

Table 8 - Definitions and Characterizations of Time Windows from Surry Shutdown PRA	22

Table 9 - Counting Rule Worksheet...........................................................................   24

List of Figures

Figure 1 – Determination of Applicable POSs and Time Windows – PWRs	14

Figure 2 – Event Tree for Loss of Inventory – PWR POS – 1	45

Figure 3 – Event Tree for Loss of Inventory – PWR POS – 2	46

Figure 4 – Event Tree for Loss of Inventory PWR POS - 3	47

Figure 5 -  Event Tree for Loss of Level Control -  PWR POS - 1	48

Figure 6 – Event Tree for Loss of Level Control – POS – 2	49

Figure 7 – Event Tree for Loss of Offsite Power – PWR POS – 1	50

Figure 8 – Event Tree for Loss of Offsite Power – PWR POS-2	51

Figure 9 – Event Tree for Loss of RHR – PWR POS-1	52

Figure 10  - Event Tree for Loss of RHR – PWR POS – 2	53

List of Worksheets

Worksheet 1 – Loss of Level Control in POS 1 (RCS Closed)

Worksheet 2 – Loss of Level Control in POS 2 (RCS Vented)

Worksheet 3 – Loss of Offsite Power in POS 1 (RCS Closed) 

Worksheet 4 – Loss of Offsite Power in POS 2 (RCS Vented)

Worksheet 5 – Loss of Inventory in POS 1 (RCS Closed)

Worksheet 6 – Loss of Inventory in POS 2 (RCS Vented)

Worksheet 7 – Loss of Inventory in POS 3 (Cavity Flooded)

Worksheet 8 – Westinghouse 4-Loop Plant Loss of RHR in POS 1 (RCS Closed)

Worksheet 9 – Westinghouse 4-Loop Plant Loss of RHR in POS 2 (RCS Vented)

Issue Date:  01/08/20	i	0609 App G Att 2 

# 0609G Att 2-01	PURPOSE

The shutdown Significance Determination Process (SDP) consists of three phases:  Phase 1, Initial Screening and Characterization of Findings; Phase 2, Initial Risk Significance Approximation and Basis; and Phase 3, Risk Significance Finalization and Justification. Inspection Manual Chapter (IMC) 0609 Appendix G, Attachment 1, Shutdown Operations Significance Determination Process Phase 1 Initial Screening and Characterization of Findings is used by inspectors to conduct the phase 1 screening analysis. This template is used by SRAs or headquarters risk analysts to perform phase 2 analyses for certain PWR shutdown findings discussed below. 

# 01.01 ENTRY CONDITIONS FOR SDP-RELATED INSPECTION FINDING

This template provides a simplified risk-informed framework to estimate the increase in core damage frequency (CDF) during shutdown operations due to findings that are identified as requiring quantitative assessment from the Phase 1 screening in IMC 0609 Appendix G, Attachment 1.

# 01.02	MANAGEMENT DIRECTIVE 8.3 ENTRY

Procedures are given in Section 4 for using this template to perform quantitative assessment of shutdown events to satisfy Management Directive (MD) 8.3.   

# 01.03	APPLICABILITY

The process in this template is designed to provide SRAs with a simple, scrutable probabilistic risk framework for use in identifying potentially risk-significant shutdown issues within the Initiating Events, Mitigation Systems, and Barrier Integrity cornerstones. The results from this SDP tool are intended to facilitate communication on the basis of risk significance between the NRC and licensees. 

# 0609G Att 2-02	LIMITS AND PRECAUTIONS

02.01	LIMITS

This template is a simplified tool that generates an order-of-magnitude assessment of the risk significance of inspection findings during shutdown. If appropriate, a more detailed risk assessment may be performed in an SDP Phase 3 evaluation, especially if the analyst feels that the risk is not being properly assessed in the Phase 2 evaluation. Program guidance in IMC 0609, Attachment 5, “Inspection Finding Review Board” and IMC 0609, Attachment 1, “Significance and Enforcement Review Panel Process,” should be followed to determine if a planning SERP is required before committing significant resources to a detailed risk evaluation in a Phase 3 analysis.    

02.02	PRECAUTIONS

· The SRA or analyst should consider each evaluated Core Damage sequence using the event trees included at the end of this procedure to ensure that the scenario makes sense for the deficiency.  The variability of plant configurations at shutdown and timing issues may result in performance deficiencies which do not directly map on the event trees.  Contact a risk analyst in NRR/APOB for assistance if needed. 

· The SRA or analyst must understand: (1) the differences between precursor and condition findings, (2) the definitions of the plant operational states (POSs), and (3) the definitions of the shutdown initiating events. These terms are defined in IMC 0609, Appendix G.  

· The availability of standby reactor coolant system (RCS) injection along with operator error drives shutdown risk.  As long as standby injection is available, in most cases, standby injection buys time for other operator recovery actions such as: leak path termination and residual heat removal (RHR) recovery.  If there are factors that could render the standby RCS injection unavailable such as: gas intrusion or support system unavailability, then these factors (assumptions) become risk significant and should be assessed carefully.   

· Upon RWST depletion and long term failure of RHR, recirculation of RCS inventory from the sump is not credited in this phase 2 model except when the refueling cavity is flooded, since: (1) for many licensees, the low pressure injection pumps that are necessary for recirculation are the same pumps used for RHR, and (2) there is a high likelihood that trash accumulated during the outage could block the sump screens.  

· Some findings are not covered by these templates and go directly to Headquarters for Phase 3 analysis.  Examples of such findings are as follows:		

· Potential over-pressurization of low-pressure piping and deficiencies associated with maintaining low temperature over pressure protection.

· Use of Nozzle Dams without an adequate RCS vent path that would prevent the RCS from re-pressurizing above 25 psig following an extended loss of RHR (25 psi represents an approximate differential pressure capability for the nozzle dams).

· Findings that increase the likelihood of having a boron dilution event such as the source range monitors being inoperable or the RWST having boron concentrations lower than Technical Specifications prescribed values.

· Findings involving open cold leg penetrations without an adequate, large hot leg vent path (such as a steam generator plenum manway) are a concern due to the potential of creating a hot leg to cold leg differential pressure that could force water out of the core. Vent paths in the pressurizer or reactor vessel head are often not adequate to prevent pressurization of the reactor coolant system after the boiling point is reached. Information Notice 88-36 provides more information.

· Findings that involve containment closure are assessed using IMC 0609 Appendix H.

· AP1000 plants are not modeled in this procedure, and instead of performing a Phase 2 SDP for those situations, the SRA or risk analyst are to perform a risk analysis using the generic AP1000 standardized plant analysis risk (SPAR) model. The AP1000 SPAR model is modeled for shutdown events.

· Findings that involve freeze seals that are installed in systems connected to the RCS where failure could lead to a loss of inventory are not covered by these worksheets and should go directly to Headquarters for a Phase 3 analysis.

· It has been identified that it’s possible for operator dominated sequences to have human error probability (HEP) values that are below levels recommended in the Risk Assessment of Operational Events (RASP) manuals Volumes 1 and 4 when following this procedure. Analysts should be cognizant of this potential and pay closer attention to operator action dominated sequences. If an analyst feels that this procedure is not adequately capturing the risk, they may depart from this procedure and perform a Phase 3 detailed risk assessment. Refer to IMC 0609, Attachment 5, and IMC 0609, Attachment 1 for guidance.

# 0609G Att 2-03	ABBREVIATIONS AND DEFINITIONS

03.01	ABBREVIATIONS

CETs			Core Exit Thermocouples

CD			Core Damage

High Decay Heat	Decay heat of early time window

Low Decay Heat	Decay heat of late time window

CCW			Component Cooling Water

DHR			Decay Heat Removal

ECCS			Emergency Core Cooling System

IEL			Initiating Event Likelihood

INDIC			Indication

IMC			Inspection Manual Chapter

LOI			Loss of Reactor Inventory Initiating Event

LER			Licensee Event Report

LOOP			Loss of Offsite Power

LORHR		Loss of RHR Initiating Event

OP			Operator

POS			Plant Operational State

PRA			Probabilistic Risk Assessment

RCS			Reactor Coolant System

RHR			Residual Heat Removal

ROP			Reactor Oversight Process

SDP			Significance Determination Process

SG			Steam Generator

SG PORV		Steam Generator Power Operated Relief Valve

SRW			Service Water

TBB			Time to Boiling

TW			Time Window

TW-E			Early Time Window, before refueling operation

TW-L			Late Time Window, after refueling operation

03.02	DEFINITIONS

For a complete list of definitions refer to IMC 0609, Appendix G.

Available - A piece of equipment is considered available if:  (1) it can be put into service within half the time that is needed before the equipment will be used to perform its function, (2) procedures or standing orders exist for using the equipment to meets its intended function, (3) all necessary supporting systems (such as AC power, cooling water, and DC control power) can be put into service within half the time that is needed before the equipment will be used to perform its function, and (4) operators have been trained for using the equipment for the given situation.  

Cavity Flooded - An RCS condition with the reactor head removed and the water level raised to the refuel floor.

Gravity Feed -– Gravity feeding is the process of adding water to the RCS from a storage source (e.g., condensate storage tank or refuel storage tank) without an active component (e.g., pump). It requires the water source to be higher than the reactor and the reactor to be at or capable of reaching atmospheric pressure. Gravity feeding may be credited if gravity feed is expected to be available AFTER RCS boiling initiates.  To credit Gravity Feed, the analyst needs to consider the following factors that can negate the elevation head provided by the RWST or other sources of RCS inventory: (1) pressure drops in the surge line, (2) entrained water accumulating in the pressurizer, (3) RCS vent paths that are restricted (to control loose parts or control off gassing).

Mid-loop Operation - Mid-loop conditions exist whenever the RCS water level is below the top of the flow area of the hot legs at the junction with the reactor vessel. 

Operation with Potential to Drain Reactor Vessel - A planned maintenance evolution that if it is not conducted properly can lead to a loss of inventory event.  Therefore, any issues with operations with potential to drain the reactor vessel should be evaluated using the appropriate LOI criteria.

Reduced Inventory Operations - As defined in Generic Letter 88-17, reduced inventory operation exists whenever the reactor vessel water level is lower than 3 feet below the reactor vessel flange.

RCS Vented - The RCS is considered vented with such that (1) SG heat removal cannot be sustained, and (2) the vent path is large enough to support feed and bleed.  Examples of vent paths include: open pressurizer manways, safety relief valve removal, or vessel head removal.

RWST Depletion - RWST level reaches the level that requires makeup or recirculation to continue injection to RCS.

Self-Limiting LOI - These are loss of inventory events where the leakage point is above the location where the RHR system attaches to the RCS.  Therefore, the leakage will stop without human intervention before the RHR/SDC system is lost.  For these types of LOIs there shall be no reliance on manual or automatic actions.  

Shutdown Operations - Shutdown Operation exists during refueling outages, forced outages, and maintenance outages starting when the plant has met the entry conditions for RHR/DHR and cooling has been initiated, and ending when the plant is heating up and RHR/DHR has been secured. 

Types of Shutdown Findings

Precursor Finding - Inspection Findings that: Inspection findings that: (1) cause an event (e.g., a loss / interruption of the operating train of RHR/DHR) or, (2) increase the likelihood of an event.  

Condition findings - Inspection findings that only involve a degradation of the licensee’s capability to mitigate an event if an event were to occur. Findings only affecting the standby train of RHR are condition findings.  

Shutdown Initiating Events

Loss of RHR (LORHR) - Includes losses of RHR/DHR resulting from failures of the RHR/DHR system (such as RHR pump failure) or failures of the RHR/DHR support systems other than offsite power.

Loss of Offsite Power (LOOP) - Includes losses of offsite power which cause a loss of RHR.  

Loss of Reactor Inventory (LOI) - Includes losses of RCS inventory that cause or could cause a loss of RHR due to loss of RHR pump suction. 

Loss of Level Control (LOLC) - This initiating event category includes: (1) the operator overdrains the RCS to reach midloop conditions such that RHR is lost, and (2) the operator fails to maintain level or flow control while in midloop such that the RHR function is lost.

Overdrain (OD) - Overdrain is intended to capture those events where while the RCS is being drained, from one target level range to a second lower range, the evolution is not stopped within the desired final range.  For example, starting level is one foot below the reactor flange and the target range is six to twelve inches above the top of the hotleg.  If the drain down evolution was not stopped until level reached the top of the hotleg, then an overdrain event has occurred.

Plant Operational States (POSs)

POS 1 - This POS starts when the RHR system is put into service.  The RCS is closed such that a steam generator(s) could be used for decay heat removal, if the secondary side of each steam generator(s) has sufficient inventory to be considered available as a heat sink.  The RCS may have a bubble in the pressurizer.  This POS ends when the RCS is vented such that the steam generators cannot sustain core heat removal.  This POS typically includes Mode 4 (hot shutdown) and portions of Mode 5 (cold shutdown). 

POS 2 - This POS starts when the RCS is vented such that: (1) the steam generators cannot sustain core heat removal and (2) a sufficient vent path exists for feed and bleed.  This POS includes portions of Mode 5 (cold shutdown) and Mode 6 (refueling).  Reduced inventory operations and midloop operations with a vented RCS are subsets of this POS.

NOTE:  Findings occurring during vacuum refill of the RCS require use of the POS 1 event trees. 

POS 3 - This POS represents the shutdown condition when the refueling cavity water level is at or above the minimum level required for movement of irradiated fuel assemblies within containment as defined by Technical Specifications.  This POS occurs during Mode 6. 

Time Windows

Early Time Window (TW-E) - This time widow represents the time before POS 3 is entered.  The decay heat is relatively high.  The reactor is either in POS 1 or 2.  

Late Time Window (TW-L) - This time window represents the time after POS group 3.  The decay heat is relatively low.  

# 0609G Att 2-04	PROCEDURE FOR SIGNIFICANCE DETERMINATION

Step 4.1 – Transition from SDP Phase 1

Use the Information Gathered in the Phase 1 process to identify the set of equipment that the licensee planned to meet the following safety functions:  Standby RCS injection, RCS pressure control, and steam generator cooling if applicable.  

Caution: If the finding required a licensee to enter into a high-risk POS (such as reduced inventory conditions) or increased the time the licensee remained in a high-risk POS, call the PRA Branch (APOB) in NRR for assistance in estimating the average CDF of the POS as a basis for evaluating the delta CDF for the finding. An example of such a finding is the following. A licensee exited midloop conditions prematurely due to leaking SG nozzle dams because the incorrect nozzle dam pins were used. As a result, the licensee re-entered midloop conditions. The delta CDF of this finding is represented by the risk of draining the vessel for the second time to reach midloop conditions added to the risk of the additional time spent at midloop beyond what was originally anticipated.

Step 4.2 – Determine if the finding is a precursor to an initiating event (a loss of the DHR function) or a condition finding.

NOTE:  Precursor findings:  (1) cause an event (e.g., a loss / interruption of the operating train of RHR/DHR) or (2) increase the likelihood of an event. Condition findings only involve a degradation of the licensee’s capability to mitigate an event if an event were to occur.  Findings only affecting the standby train of RHR are condition findings.  The template treats precursor and condition findings differently. 

Go To Step 4.3 for Precursor Findings 

OR

Go To Step 4.4 for Condition Findings

NOTE:  If this tool is being used to assess a shutdown event under Management Directive 8.3, Go to Step 4.5.

# Step 4.3 – Process for Assessing Precursor Findings

Step 4.3.1 – Identify each time window (TW) and plant operation state (POS) where the finding could have occurred.

Figure 1 defines the POS and TWs for a PWR plant. It also shows the relationship between the POS and the modes defined in the Technical Specifications.

Step 4.3.2 – Determine the IEL.

The initiating event likelihood (IEL) is the conditional likelihood of having a loss of the RHR function given the occurrence of the findings.

· IF a finding increases the likelihood of a loss of level control (LOLC) or actually caused a LOLC, THEN LOLC is the applicable initiating event.  Use Table 1 to determine the IEL.  Go to Step 4.3.3.

· IF a finding increases the likelihood of a loss of offsite power (LOOP) or actually caused a LOOP, THEN LOOP is the applicable initiating event.  Use Table 2 to determine the IEL.  Go to Step 4.3.3.

· IF a finding increases the likelihood of a loss of reactor inventory (LOI) or actually caused a LOI, THEN LOI is the applicable initiating event.  Use Table 3 to determine the IEL. Go to Step 4.3.3.

· IF a finding increases the likelihood of a loss of the operating train of RHR (LORHR) or actually caused a LORHR (except for LOOP and LOI), THEN LORHR is the applicable initiating event.  Use Table 4 to determine the IEL.  Go to Step 4.3.3.

· IF a finding involves the RHR support systems (except for LOOP and LOI), THEN LORHR is the applicable initiating event.  Use Table 4 to determine the IEL.  Go to Step 4.3.3.

Step 4.3.3 – Use the SDP worksheet.

Choose the SDP worksheet that contains the POS and initiating event that were determined to be applicable in steps 4.3.1 and 4.3.2. The SDP worksheets are included at the end of this procedure.

EXCEPTIONS:

(1) For LOI POS 1 if RCS < 200F, use the POS 1 LOLC worksheets and event trees.  

(2) If failure of the cavity seal could occur following LOOP or SBO, use the LOOP POS 2 worksheet.

Step 4.3.4 – Enter the time to RCS boiling.

Enter the time to RCS boiling and an approximate time to core uncover/core damage in the first line of the Worksheet.

Table 8 can be used to approximate a time to core damage from hot leg midplane conditions. Other tools exist as well, including an electronic Core Uncovery Calculator located on the RASP Tool Box web page, or by using licensee values if available.

Step 4.3.5 – Fill-in the IEL determined in step 4.3.2 in each row of the lower section of the applicable worksheet. 

Step 4.3.6 – Determine the credit for each top event function.

Determine the credit for each top event function.

A.	Verify that the licensee has the important instrumentation referenced for the top event function.  

NOTE:	If the licensee does not have the referenced instrumentation available or the referenced instrumentation is not reflective of RCS conditions, then the default operator credit MUST by decreased by two. 

B.  	To obtain the Equipment Credit, credit each available system that is (1) capable of maintaining the top event function and (2) is not impacted by the finding. Use the event tree associated with the worksheet to help understand the successes and failures associated with each accident sequence.  Use guidance in Tables 6 and 7 to determine equipment credits.  Document key assumptions.  

C.	To obtain the Operator Credit, use the default operator credit unless any of the following four conditions are applicable:

1. If the referenced instrumentation is missing or misleading, then decrease the operator credit by two.

2. The default time is incorrect and significantly reduced.  If the diagnosis time is less than 20 minutes OR the time to perform the action is approximately the time required, then decrease the operator credit by one.

3. If the action is complicated by missing or inaccessible equipment, steam or high radiation, or loop seals for venting pumps, then decrease the operator credit by two.

4. If the procedures are incomplete for the shutdown plant configuration, then decrease the operator credit by one.

NOTE:  If the default operator credit is changed and results in a negative operator credit, then the operator credit is zero.

D.	Determine the Credit for Function for each Top Event Function needed.  Select the lower of Equipment Credit and Operator Credit and enter the value in this column.

Step 4.3.7 – Quantification of Core Damage Scenarios

Quantify each accident scenario by adding the credits for IEL + Mitigation Credit.   Enter the sum in the Result column.

NOTE:  For phase 2 analyses, the recovery credit is not used.****

Step 4.3.8 – Identifying the frequency of finding occurrence

Select between Condition A or B.

A. If the finding occurred during an outage (forced outage, refueling outage, etc.), the preliminary color of the finding is determined by using Table 9 – Counting Rule Worksheet. The resulting ICCDP associated with the finding is interpreted as the addition to the licensee’s total CDF contribution over the previous year (previous 12 months).  Therefore, the resulting ICCDP becomes the increase in delta CDF.

B.	If the deficiency needs a random event to reveal the deficiency (e.g. at Palisades, the digging of a sign revealed underground protective cabling common to both offsite power sources outside the protected area), then the frequency of the random event (1/32 calendar years of operation) is multiplied by: 

The Frequency that the licensee enters an outage (1 outage per 18 months) * (12 months/ calendar year) *(Number of Days of POS 1 operation/ outage) * (1 calendar year/365 days) *(CCDP of POS 1 operation)

Added to:

The Frequency that the licensee enters an outage (1 outage per 18 months) * (12 months/ calendar year) *(Number of Days of POS 2 operation/ outage) * (1 calendar year/365 days) *(CCDP of POS 2 operation).

# Step 4.4 – Process for Assessing SDP Condition Findings

NOTE:  Only the core damage scenarios impacted by the finding are quantified.

Step 4.4.1 – Select the applicable initiating events.

Select the applicable initiating events (the lost function causes the failure of a top event used to mitigate the initiating event scenario) by identifying the equipment or safety functions affected and determine the initiating event scenarios that must be evaluated (i.e., the affected function plays some role in mitigating the initiating event scenario). 

Step 4.4.2 – Determine the exposure times.

Determine the exposure times for the degraded condition in the mitigating system.  A separate exposure time must be determined for each POS for findings that span one or more POS.  Using Table 5, determine an IEL for each applicable initiating event in each applicable POS.

Step 4.4.3 – Choose the SDP Worksheet(s)

Choose the SDP worksheet(s) that contain the POSs and initiating events that were determined to be applicable in Steps 4.4.1 and 4.4.2.   Perform the following steps on the Worksheet for each applicable POS and initiating event.  The SDP worksheets are included at the end of this procedure.

Step 4.4.4 – Enter the time to RCS boiling

Enter the time to RCS boiling and an approximate time to core uncovery/core damage in the first line of the worksheet.

Table 8 can be used to estimate time to core damage from hot leg midplane conditions.  Other tools exist as well, including an electronic Core Uncovery Calculator located on the RASP Tool Box web page, or by using the licensee values if available.

Step 4.4.5 –Fill-in the IEL determined in step 4.4.2 in each row of the lower section of the worksheet.

Step 4.4.6 – Determine the revised credit for each top event function impaired by the Finding.

A.	Verify that the licensee has the important instrumentation referenced for the top event function.  

NOTE:  If the licensee does not have the referenced instrumentation available or the referenced instrumentation is not reflective of RCS conditions, then the default operator credit must be decreased by two.  

B.  	To obtain the Equipment Credit, credit each available system that is (1) capable of maintaining the top event function and (2) is not impacted by the finding. Use the Event Tree associated with the Worksheet to help understand the successes and failures associated with each accident sequence.  Use guidance in Tables 6 and 7 to determine equipment credits.  Document key assumptions.  

NOTE:  Each top event has an equipment credit and an operator credit, only the equipment credit change or the operator credit change is propagated through the worksheets.  See the following example:

Example:  If the licensee has a finding that changes the FEED equipment credit from 5 to 3, then the revised credit for the FEED & BLEED FUNCTION becomes 3, regardless of the BLEED credit or the operator credit.

C.	Determine the revised Operator Credit. Use the default operator credit listed in the worksheet unless any of the following four conditions are applicable.

1. If the referenced instrumentation is missing or misleading, then decrease the operator credit by two.

2. The default time is incorrect and significantly reduced.  If the diagnoses time is less than 20 minutes OR the time to perform the action is approximately the time required, then decrease the operator credit by one.

3. If the action is complicated by missing or inaccessible equipment, steam or high radiation, or loop seals for venting pumps, then decrease the operator credit by two.

4. If the procedures are not complete for the shutdown plant configuration, then the operator credit is decreased by one.

Caution: It has been identified that it’s possible for operator dominated sequences to have HEP values that are below levels recommended in the Risk Assessment of Operational Events (RASP) manuals Volumes 1 and 4 when following this procedure. Analysts should be cognizant of this potential and pay closer attention to operator action dominated sequences. If an analyst feels that this procedure is not adequately capturing the risk, they may depart from this procedure and perform a Phase 3 detailed risk assessment.

NOTE:  If the default operator credit is changed and results in a negative operator credit, then the operator credit is zero.

Example: If the licensee has a finding that changes the operator credit from a 5 to a 3 due to a loss of instrumentation, then the revised credit for the FEED & BLEED FUNCTION becomes 3, regardless of the equipment FEED & BLEED equipment credit.  

D. 	Determine the Credit for Function for each Top Event Function needed.****Select the lower of Equipment Credit and Operator Credit and enter the value in the Credit for Function column.

Step 4.4.7 – Quantification of Core Damage Scenarios.

Quantify each accident scenario that is impacted by the finding adding the credits for IEL + Mitigation Credit.   Enter the sum in the Result column.

NOTE:  For phase 2 analyses, the recovery credit is not used.****

Step 4.4.8 – Go to the next applicable worksheet and begin at step 1.4.1, or if all worksheets are completed, continue to step 1.4.9.

Step 4.4.9 – Estimating the Risk Significance of the Inspection Finding

 The preliminary color of the finding is determined by using Table 9 – Counting Rule Worksheet.

# Step 4.5 – Process for Assessing Events Under MD 8.3

Step 4.5.1 – Identify the TW and POS where the shutdown event occurred.

Step 4.5.2 – Identify the appropriate shutdown initiating event.

Use an IEL = 0 if the event caused a loss or interruption of the RHR

function. 

OR

Determine the IEL.  Evaluate each question in order. Only one of the following will apply:

· IF a finding increases the likelihood of a loss of level control (LOLC) or actually caused a LOLC, THEN LOLC is the applicable initiating event.  Use Table 1 to determine the IEL.  Go to Step 4.5.3.

· IF a finding increases the likelihood of a loss of offsite power (LOOP) or actually caused a LOOP, THEN LOOP is the applicable initiating event.  Use Table 2 to determine the IEL.  Go to Step 4.5.3.

· IF a finding increases the likelihood of a loss of reactor inventory (LOI) or actually caused a LOI, THEN LOI is the applicable initiating event.  Use Table 3 to determine the IEL. Go to Step 4.5.3.

· IF a finding increases the likelihood of a loss of the operating train of RHR (LORHR) or actually caused a LORHR (except for LOOP and LOI), THEN LORHR is the applicable initiating event.  Use Table 4 to determine the IEL.  Go to Step 4.5.3.

· IF a finding involves the RHR support systems (except for LOOP and LOI), THEN LORHR is the applicable initiating event.  Use Table 4 to determine the IEL.  Go to Step 4.5.3.

Step 4.5.3 – Use the SDP worksheet that contains the POS and initiating event that were determined to be applicable in Step 4.5.1.

EXCEPTIONS:

(1) For LOI POS 1 if RCS < 200F, use the POS 1 LOLC worksheets and event trees.  

(2) If failure of the cavity seal could occur following LOOP or SBO, use the LOOP POS 2 worksheet.

Step 4.5.4 – Enter the time to RCS boiling.

Enter the time to RCS boiling and an approximate time to core uncover/core damage in the first line of the worksheet.

Table 8 can be used to approximate a time to core damage from hot leg midplane conditions. Other tools exist as well, including an electronic Core Uncovery Calculator located on the RASP Tool Box web page, or by using licensee values if available.

Step 4.5.5 – Fill-in the IEL determined in step 4.5.2 in each row of the lower section of the worksheet.

Step 4.5.6 – Determine the revised Credit for Function for each top event function impacted by the finding for the as found condition during the event.

LISTNUM AutoList4 \l 1 \s 1A.	Verify the licensee has the important instrumentation referenced for the top event function.  

NOTE:  If the licensee does not have the referenced instrumentation available or the referenced instrumentation is not reflective of RCS conditions, then the default operator credit MUST be reduced by two. 

B.  	To obtain the Equipment Credit, credit each available system that is (1) capable of maintaining the top event function and (2) is not impacted by the finding. Use the event tree associated with the Worksheet to help understand the successes and failures associated with each accident sequence.  Use guidance in Tables 6 and 7 to determine equipment credits.  Document key assumptions.  

C.	To obtain the Operator Credit, use the default operator credit unless any of the following four conditions are applicable:

1. If the referenced instrumentation is missing or misleading, then decrease the operator credit by two.

2. The default time is incorrect and significantly reduced.  If the diagnoses time is less than 20 minutes OR the time to perform the action is approximately the time required, then decrease the operator credit by one.

3. If the action is complicated by missing or inaccessible equipment, steam or high radiation, or loop seals for venting pumps, then decrease the operator credit by two.

4. If the procedures are not directed for the shutdown configuration that the plant is in, then the operator credit is decreased by one.

NOTE:  If the default operator credit is changed and results in a negative operator credit, then the operator credit is zero.

D.	Determine the Credit for Function for each Top Event Function needed.****Select the lower of Equipment Credit and Operator Credit and enter the value in the Credit for Function column.

Step 4.5.7 – Quantification of Core Damage Scenarios

Quantify each accident scenario by adding the credits for IEL + Mitigation Credit.   Enter the sum in the Result column.

NOTE:  For phase 2 analyses, the recovery credit is not used. 

Step 4.5.8 – Go to the next applicable worksheet and begin at step 4.5.1, or if all worksheets are completed, continue to step 4.5.9.

Step 4.5.9 – Estimating the Risk Significance of the Inspection Finding

The preliminary color of the finding is determined by using Table 9 – Counting Rule Worksheet.

Issue Date:  01/08/20	14	0609 App G Att 2 

Figure 1 – Determination of Applicable POSs and Time Windows – PWRs

Issue Date:  01/08/20	14		0609 App G Att 2 

Table 1 – Initiating Event Likelihood (IELs) for LOLC Precursors

Table 2 – Initiating Even Likelihoods (IELs) for LOOP Precursors

Table 3 – Initiating Event Likelihood (IELs) for Loss of Inventory (LOI) Precursors

Table 4 – Initiating Event Likelihoods (IELs) for LORHR Precursors

Table 5 – Initiating Even Likelihoods (IELs) for Condition Findings – PWRs

LOLC is only applicable to POS group II.  

LORHR and LOI are not applicable to POS group III. 

Table 6 - Mitigation Capability Credits for Installed Equipment

Table 7 - Credit for Temporary Equipment

****

Issue Date:  01/08/20	14	0609 App G Att 2 

Table 8 - Definitions and Characterizations of Time Windows from Surry Shutdown PRA (NUREG/CR-6144 Table 5.4-20) assuming a vented RCS (RCS temperature initially 140F)

****

0609, App G, Att 2	G2-28	Issue Date: 02/28/05

Issue Date:  01/08/20	25	0609, App G, Att 2

Worksheet 1. SDP for a PWR Plant - Loss Level Control in POS 1 (RCS Closed)

Worksheet 1. SDP for a PWR Plant - Loss Level Control in POS 1 (RCS Closed) - Continued

****

Worksheet 2. SDP for a PWR Plant - Loss Level Control in POS 2 (RCS Vented)

****

Worksheet 2. SDP for a PWR Plant - Loss Level Control in POS 2 (RCS Vented) – Continued

Notes:  Failure to recover RHR before RWST depletion is assumed to fail recirculation from the sump since the RHR pumps are also used to perform the recirculation function.  Recovery of RHR does not guarantee available recirculation since the sump may be unavailable due to trash.

Worksheet 3. SDP for a PWR Plant - Loss of Offsite Power in POS 1 (RCS Closed)

Worksheet 3. SDP for a PWR Plant - Loss of Offsite Power in POS 1 (RCS Closed) - Continued

Worksheet 4. SDP for a PWR Plant - Loss of Offsite Power in POS 2 (RCS Vented)

Worksheet 4. SDP for a PWR Plant - Loss of Offsite Power in POS 2 (RCS Vented) – Continued

Worksheet 5. SDP for a PWR Plant - Loss of Inventory in POS I (RCS Closed)

Worksheet 5. SDP for a PWR Plant - Loss of Inventory in POS I (RCS Closed) - Continued

****Worksheet 5. SDP for a PWR Plant - Loss of Inventory in POS I (RCS Closed) - Continued

Notes:  Failure to recover RHR before RWST depletion is assumed to fail recirculation from the sump since the RHR pumps are also used to perform the recirculation function. Recovery of RHR does not guarantee available recirculation since the sump may be unavailable due to trash.

Worksheet 6. SDP for a PWR Plant - Loss of Inventory in POS 2 (RCS Vented)

Worksheet 6. SDP for a PWR Plant - Loss of Inventory in POS 2 (RCS Vented) - Continued

## 

Notes:  Failure to recover RHR before RWST depletion is assumed to fail recirculation from the sump since the RHR pumps are also used to perform the recirculation function.  Recovery of RHR does not guarantee available recirculation since the sump may be unavailable due to trash.

Worksheet 7. SDP for a PWR Plant - Loss of Inventory in POS 3 (Cavity Flooded)

## 

Worksheet 7. SDP for a PWR Plant - Loss of Inventory in POS 3 (Cavity Flooded)

## 

## ****

## 

Worksheet 8. SDP for a Westinghouse 4-Loop Plant - Loss of RHR in POS I (RCS Closed)

## 

## 

	Worksheet 8. SDP for a Westinghouse 4-Loop Plant - Loss of RHR in POS I (RCS Closed) – Continued

Notes:  Failure to recover RHR before RWST depletion is assumed to fail recirculation from the sump since the RHR pumps are also used to perform the recirculation function. Recovery of RHR does not guarantee available recirculation since the sump may be unavailable due to trash.

****Worksheet 9. SDP for a Westinghouse 4-Loop Plant - Loss of RHR in POS 2 (RCS Vented)

Worksheet 9. SDP for a Westinghouse 4-Loop Plant - Loss of RHR in POS 2 (RCS Vented) – Continued

Worksheet 9. SDP for a Westinghouse 4-Loop Plant - Loss of RHR in POS 2 (RCS Vented) – Continued

Notes: Failure to recover RHR before RWST depletion is assumed to fail recirculation from the sump since the RHR pumps are also used to perform the recirculation function. Recovery of RHR does not guarantee available recirculation since the sump may be unavailable due to trash.

Figure 2 – Event Tree for Loss of Inventory – PWR POS – 1

Figure 3 – Event Tree for Loss of Inventory – PWR POS – 2

Figure 4 – Event Tree for Loss of Inventory PWR POS - 3

## 

## 

Figure 5 - Event Tree for Loss of Level Control - PWR POS - 1

Figure 6 – Event Tree for Loss of Level Control – POS – 2

Figure 7 – Event Tree for Loss of Offsite Power – PWR POS – 1

Figure 8 – Event Tree for Loss of Offsite Power – PWR POS-2

Figure 9 – Event Tree for Loss of RHR – PWR POS-1

Figure 10 - Event Tree for Loss of RHR – PWR POS – 2

	DRAFT

Issue Date:  XX/XX/2012	Att 1-1	0609, App F

Issue Date:  01/08/20	55 	0609 App G Att 2

ATTACHMENT 1

Revision History for IMC 0609, Appendix G, Attachment 2

Issue Date:  01/08/20	Att1-1 	0609 App G Att 2

Issue Date:  01/08/20	Att1-2 	0609 App G Att 2

Issue Date:  01/08/20	Att1-3 	0609 App G Att 2

# image1.jpeg

# image2.wmf

# oleObject1.bin

# image3.wmf

# oleObject2.bin

# image4.wmf

# oleObject3.bin

# image5.wmf

# oleObject4.bin

# image6.wmf

# oleObject5.bin

# image7.wmf

# oleObject6.bin

# image8.wmf

# oleObject7.bin

# image9.wmf

# oleObject8.bin

# image10.wmf

# oleObject9.bin