ML103640204

MHIs Responses to US-APWR DCD RAI No. 669-5219 Revision 2 (SRP 19.0)

ML103640204
Person / Time
Site:	05200021
Issue date:	12/27/2010
From:	Ogata Y Mitsubishi Heavy Industries, Ltd
To:	Ciocco J Document Control Desk, Office of New Reactors
References
UAP-HF-10345
Download: ML103640204 (61)

Text

At MITSUBISHI HEAVY INDUSTRIES, LTD.

16-5, KONAN 2-CHOME, MINATO-KU TOKYO, JAPAN December 27, 2010 Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Attention:

Mr. JeffreyA. Ciocco, Docket No.52-021 MHI Ref: UAP-HF-10345

Subject:

MHI's Responses to US-APWR DCD RAI No.669-5219 Revision 2 (SRP 19.0)

References:

1)

"Request for Additional Information No. 669-5219 Revision 2, SRP Section:

19 -

Probabilistic Risk Assessment and Severe Accident Evaluation,"

dated November 29, 2010.

With this letter, Mitsubishi Heavy Industries, Ltd. ("MHI") transmits to the U.S. Nuclear Regulatory Commission ("NRC") a document entitled "Responses to Request for Additional Information No. 669-5219 Revision 2".

Enclosed are the responses to all of the RAIs that are contained within Reference 1.

Please contact Dr. C. Keith Paulson, Senior Technical Manager, Mitsubishi Nuclear Energy Systems, Inc. if the NRC has questions concerning any aspect of the submittals.

His contact information is below.

Sincerely, Yoshiki Ogata, General Manager-APWR Promoting Department Mitsubishi Heavy Industries, LTD.

Enclosure:

1. Responses to Request for Additional Information No. 669-5219 Revision 2

CC: J. A. Ciocco C. K. Paulson Contact Information C. Keith Paulson, Senior Technical Manager Mitsubishi Nuclear Energy Systems, Inc.

300 Oxford Drive, Suite 301 Monroeville, PA 15146 E-mail: ck-paulson@mnes-us.com Telephone: (412) 373-6466 UAP-HF-10345 Docket Number 52-021 Responses to Request for Additional Information No.669-5219 Revision 2 December, 2010

RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION 12/24/2010 US-APWR Design Certification Mitsubishi Heavy Industries Docket No.52-021 RAI NO.:

NO. 669-5219 REVISION 2 SRP SECTION:

19 -Probabilistic Risk Assessment and Severe Accident Evaluation APPLICATION SECTION:

19 DATE OF RAI ISSUE:

11/16/2010 QUESTION NO. : 19-492 USAPWR shutdown risk results. In Table 19-119, page 19.1-963, of the DCD, the applicant states that, "for manual operation, one hour is conservatively assumed to be the allowable time until exposure of reactor core."

Based on the information in the DCD and the PRA, the staff is concerned that midloop operations are not being conducted in a manner that is consistent with staff guidance from GL 88-17 and industry guidance in NUMARC 91-06 which could lead to reduced times to core uncovery and core damage. As stated in GL 88-17 Section 2.1.1, Pressurization, "Inappropriate use of SG nozzle dams can lead to complete core voiding within 15 or 20 minutes of a loss of RHR." It also states, "Cold leg openings can allow water to be ejected from the vessel following loss of DHR until sufficient water is lost that steam is relieved by clearing of the crossover pipes." In page 2.7.1, Recommendation, GL 88-17 states, "We recommend that licensees consider removing a pressurizer manway (if analysis shows this to provide a sufficient vent path) or otherwise create a suitable opening if a pressurization potential exists so as to limit the pressurization which could follow loss of DHR while nozzle dams and the reactor vessel head are in place. "The staff requests the following information:

(a)

The staff requests MHI to document in the DCD in Chapter 19 Table 19-119 and Section 5.4.7.2.3.6, what large path will opened in POS 4-2 to prevent pressurization of the upper plenum of the reactor vessel before the steam generators channel head manway covers are opened to install and remove nozzle dams. If a pressurizer manway is not used, please provide the staff with an analysis to show that this vent path is sufficient.

(b)

The staff requests MHI to document in Table 19-119 and Section 5.4.7.2.3.6. of the DCD that the COL applicant will implement procedures and administrative controls to assure that all hot legs are not blocked simultaneously by nozzle dams unless a vent path is provided that is large enough to prevent pressurization of the upper plenum of the reactor vessel.

(c)

The staff learned during recent conference calls that the installation and removal of the In-core Instrumentation System (ICIS) will not be done at mid-loop but will be done when the RCS level is approximately one foot below the flange. Please document this assumption in 5.4.7.2.3.6 and Chapter 19 Table 19-119 of the DCD.

(d)

The staff is requesting MHI to document in Section 5.4.7.2.3.6 and Table 19-119 of the 19.492-1

DCD to provide an analysis to support whether Gravity Injection is feasible in POS 4-2 and POS 8-2 given the large RCS vent assigned to prevent RCS pressurization given a postulated loss of RHR.

(e)

The staff is requesting MHI to revise the PRA and Chapter 19 of the DCD based on the answers to questions (a)- (e).

ANSWER:

(a)

GL 88-17 requires to "... create a suitable opening if a pressurization potential exists so as to limit the pressurization which could follow loss of DHR while nozzle dams and the RV head are in place.".

MAAP analysis was performed to demonstrate that the SG nozzle dams can withstand RCS pressure rising caused by a loss of RHR event in POS 4-3. Before the analysis, MHI confirmed that the MAAP code can be used to model of the loss of RHR event, by comparison of MAAP and RELAP5 codes. Table 19.492-1 lists the analysis condition in which the pressurizer safety valves are considered as a RCS vent path and RCS water level is assumed to be at the top of the main coolant piping (MCP). Figure 19.492-1 shows the variation of RCS pressure after a loss of RHR event. The maximum pressure is approximately 2.0 kg/cm 2 (28.8 psig). The SG nozzle dams are designed as follows:

Normal operating pressure: 1.5kg/cm 2 Design pressure: 1.5 times of normal operating pressure (2.25 kg/cm 2)

The above shows that the SG nozzle dam can withstand the 2.25 kg/cm 2 maximum pressure.

The maximum pressure that the SG nozzle dams can withstand is higher than the pressure estimated by MAAP analysis (2.0 kg/cm2). Therefore, the current design meets the requirement of GL 88-17 without design change of SG nozzle dams or additional procedures.

Also, the maximum pressure caused by a loss of RHR in POS 8-1 is less than that in POS 4-3, because the plant configuration in these POSs is same and the decay heat in POS 8-1 is lower than that in POS 4-3, resulting in a lower pressure in POS 8-1. Therefore, the SG nozzle dams will also withstand the maximum pressure in POS 8-1.

(b)

The following discussion will be documented in DCD Section 5.4.7.2.3.6 and Table 19.1-119.

Operators perform actions to install and remove the SG manways and SG nozzle dams before and after refueling. The pressurizer safety valves (removed) are used in the US-APWR design as a RCS vent path to prevent significant RCS pressurization as required by GL 88-17. The sequence of the actions described below will be controlled by US-APWR operating procedures.

Before Refueling

1. RCS draining

2. Removal of the SG manway on the hot leg side

3. Removal of the SG manway on the cold leg side (End of POS 4-1) 19.492-2

4. Removal of the pressurizer safety valves

5. Installation of the SG nozzle dam on the cold leg side

6. Installation of the SG nozzle dam on the hot leg side (End of POS 4-2)

7. Removal of the reactor vessel head for fuel offload (During POS 4-3)

After Refuelinq

1. RCS draining

2. Installation of the reactor vessel head (During POS 8-1)

3. Removal of the SG nozzle dam on the hot leg side

4. Removal of the SG nozzle dam on the cold leg side (End of POS 8-1)

5. Installation of the pressurizer safety valves

6. Installation of the SG manway on the cold leg side

7. Installation of the SG manway on the hot leg side (End of POS 8-2)

(c)

The following discussion will be documented in DCD Section 5.4.7.2.3.6 and Table 19.1-119.

One of the characteristic design of the US-APWR is that it allows installation and removal of the ICIS from the top of the RV head. Operators can start to remove (before refueling) and install (after refueling) the ICIS after the end of RCS draining as shown in Fig.19.492-2. This action cannot be done during RCS draining, which results in an extended duration of mid-loop operation.

During actual plant operation, the action to install and remove the ICIS will be performed when the RCS water level is above the top of MCP. The LPSD PRA conservatively assumes that the action will be done with water level at the center of the MCP. This assumption is used in the estimation of allowable time to core uncovery after a loss of RHR.

(d)

As mentioned by the NRC staff, gravity injection is available in POSs 4-2 and 8-2 where there is a large RCS vent (i.e., SG manways) to prevent RCS pressurization. The discussion below will be documented in DCD Section 5.4.7.2.3.6 and Table 19.1-119.

MAAP analysis was performed in order to study the feasibility of gravity injection during POS 4-2. The analysis condition listed in Table 19.492-2 conservatively assumes that the initial RCS water level is at the top of the MCP and all pressurizer safety valves are installed. (In actual plant operation, pressurizer safety valves are removed during this POS.)

Gravity injection is available if the RCS pressure is maintained near atmospheric pressure so that water in the spent fuel pit is able to drain into the RCS.

Figure 19.492-3 shows the variation of RCS pressure. After boiling around the core occurs, coolant in the liquid phase flows out from the SG manways and a bypass path for pressure relief is generated around the top of the MCP due to the decrease of RCS inventory. Thus, the SG manways function as the RCS vent path and the RCS is maintained at atmospheric pressure. The analysis result indicates gravity injection is available in POS 4-2 after a loss of RHR event. Also, by inspection, gravity injection is available in POS 8-2. This is because (1) the plant configuration in POS 8-2 is the same as that in POS 4-2 and (2) the decay heat in POS 19.492-3

8-2 is less than that for POS 4-2 due to the longer time after shutdown.

The following discusses the feasibility of gravity injection in POSs other than POSs 4-2 and 8-2.

POSs 4-1 and 8-3:

There is no large RCS vent to prevent RCS pressurization caused by a loss of RHR, and gravity injection is unavailable. In these POSs, SG reflux cooling is the heat removal mechanism that is credited.

POSs 4-3 and 8-1:

As shown in Fig.19.492-1, the RCS pressure substantially exceeds atmospheric pressure after a loss of RHR in POS 4-3. When the RV head is removed for refueling, a large RCS vent is provided. However, there is little water in the RWSP (the water source for gravity injection) because the water is transferred to the reactor cavity. Therefore, gravity injection is unavailable in POS 4-3. The plant configuration in POS 8-1 is the same as that in POS 4-3, with exception of the lower decay heat level. Thus, gravity injection in neither POS 4-3 nor 8-1 is possible.

Based on the above, gravity injection is feasible during POSs 4-2 and 8-2.

(e)

The DCD will be revised to reflect the above discussion in DCD Rev.3.

Impact on DCD DCD Section 5.4.7.2.3.6 and Table 19.1-119 will be revised as follows:

Section 5.4.7.2.3.6 Item E will be revised as follows:

E. Water supply from spent fuel pit When the water level of RCS abnormally drops and all RHR pumps cannot be operated because of air intake, operators can supply water from the spent fuel pit (SFP) to the reactor vessel when the RCS is at atmospheric pressure. Since the RHRS is connected to the SFP, SFP water can be injected by gravity.

The following will be documented after the last paragraph of Section 5.4.7.2.3.6.

In addition to the above features, to reduce the risk of loss of Decay Heat Removal, the following operational considerations are incorporated into the US-APWR operating procedures:

Removal of the pressurizer safety valves is performed before the SG channel head manway covers are opened to prevent pressurization of the RV upper plenum.

Hot legs are not all blocked simultaneously by nozzle dams unless a vent path is provided that is large enough to prevent pressurization of the RV upper 19.492-4

plenum.

The installation and removal of the in-core instrumentation system (ICIS) is not done at mid-looD ooeration but is done when the RCS water level is above the too of the MCP.

The installation and removal of SG nozzle dams is done when the RCS water level is above the toD of the MCP.

Removal of the pressurizer safety valves is performed during the period between removal of the SG manwavs and installation of the SG nozzle dams.

betw en.r.ov..of.he.........ad..

lltionof....S no zl dams....

In~taIIatinn nf th~ nra~IIri7ar c~afptv vaIvac~ k~ n~rformad diirino a n~riod between removal of the SG nozzle dams and installation of the SG manways.

Table 19.1-119 will be revised to reflect the discussion in the response.

Table 19.1-119 Key Insights and Assumptions (Sheet 13 of 23)

Key Insights and Assumptions Dispositions Operator actions (LPSD)

1. When the RCS is uinder at atmospheric pressure, gravity 19.1.6 injection from SFP is effective. Operators will perform the 19.2.5 gravity injection by opening the injection flow path from SFP COL 19.3(6) to RCS cold legs, and supplying water from RWSP to SFP COL 13.5(7) 5.4.7.2.3.6 19.492-5

Table 19.1-119 Key Insights and Assumptions (Sheet 17 of 23)

Key Insights and Assumptions Dispositions Key Activities durinq LPSD

1.

Removal of the pressurizer safety valves is performed before SG channel head manway covers are opened to prevent pressurization of the RV upper plenum.

2.

Hot legs are not blocked simultaneously by nozzle dams unless a vent path is provided that is large enough to prevent pressurization of the RV upper plenum.

3.

The installation and removal of SG nozzle dams are done when the RCS water level is above the toD of the MCP.

5.4.7.2.3.6 5.4.7.2.3.6 5.4.7.2.3.6 5.4.7.2.3.6

4.

Removal of the pressurizer safety valves is performed during the period between removal of the SG manway and installation of the SG nozzle dam. Installation of the pressurizer safety valves is performed during a period between removal of the SG nozzle dam and installation of SG manway.

Impact on R-COLA and S-COLA.

There is no impact on R-COLA and S-COLA.

Impact on PRA There is no impact on PRA.

19.492-6

Table 19.492-1 MAAP Analysis Condition (POS 4-3)

Accident Sequence Loss of RHR subsequent to SBO Initial Temperature 140 OF RCS Initial Pressure 0 psig Initial Water Level Top of MCP Time After Shutdown 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Initial Decay Heat 18.1 MW Pressurizer Safety Valve Removed SG Manway Open SG Nozzle Dam Installed RV Upper Plenum Installed 19.492-7

Table 19.492-2 MAAP Analysis Condition (POS 4-2)

Accident Sequence Loss of RHR subsequent to SBO Initial Temperature 140 OF RCS Initial Pressure 0 psig Initial Water Level Top of MCP NOTE Time After Shutdown 60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br /> Initial Decay Heat 19.3 MW Pressurizer Safety Valve Installed SG Manway Open SG Nozzle Dam Removed RV Upper Plenum Installed NOTE:

RCS water level is conservatively assumed to be at the top of MCP for RCS pressurization 19.492-8

35 Sý 30 E

• 25

-a 20 0

t 15

.E 10 0~

0 0.5 1

1.5 2

2.5 3

3.5 Time [hours]

Figure 19.492-1 Variation of the RCS Pressure (POS 4-3) 19.492-9

Performed KeyActivities VionR o

IicuumVenting (0

1 1

1

,14 RernoveICPSV, !

I "

"I

__ _ _ __ _ __1

_. L.

.L. J. J.. 1... L

. +/- L LL---

C>~

Ietninn VHa tdB Remove RV Head]

Intl RV He dn Tensioning RV Head Stud Bolts i~~~~~

i

'I!

,~l Note 1: Automaitic isolation for low-pressure letdown line when Low signal actuates CVCS: Chemical and Volume Control System RV: Reactor Vessel Note 2: Initiation of gravity injection when Low-Low signal actuates PSV: Pressurizer Safety Vavle H/L: Hot Leg Note 3: Assumptiion that RCS level is at a center of MCP is used for estimation of allowable time for core uncovery lCIS: In-Core Instrumentation System C/L: Cold Leg MCP: Main Coolant Piping Figure 19.492-2 Schematic Images for Inspection considered in LPSD PRA

0.1 0.05 E

0 S 0 ci Q.

-0.05 0

a-0

-0.15

-0.2 Tme[hours]

Figure 19.492-3 Variation of the RCS Pressure (POS 4-2) 19.492-11

RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION 12/24/2010 US-APWR Design Certification Mitsubishi Heavy Industries Docket No.52-021 RAI NO.:

NO. 669-5219 REVISION 2 SRP SECTION:

19 - Probabilistic Risk Assessment and Severe Accident Evaluation APPLICATION SECTION:

19 DATE OF RAI ISSUE:

11/29/2010 QUESTION NO.: 19-493 The staff has reviewed Chapter 19 of the DCD and the US-APWR shutdown PRA and finds insufficient justification to support that POS 8-1, midloop after refueling, is the limiting operational state. Based on information that MHI has provided, it appears that POS 4-2 and POS 4-3, midloop before refueling, are the limiting operational states due to high decay heat load. The staff also found POS durations that are not consistent with US refueling outage data.

Therefore, the staff has the following questions.

(a)

MHI is requested to document in Section 5.4.7.2.3.6 and Chapter 19 of the DCD operational activities to be conducted during midloop that are not related to steam generator nozzle dam installation or removal.

(b)

MHI is requested to document in Section 5.4.7.2.3.6 and Chapter 19 of the DCD at what RCS vessel level will de-tensioning of the reactor head studs in preparation for reactor vessel head removal will be performed. The staff understands that this evolution will be performed at flange level but was analyzed to occur at midloop.

(c)

MHI is requested to document in Section 5.4.7.2.3.6 and Chapter 19 of the DCD at what RCS vessel level will tensioning of the reactor head studs in preparation for reactor vessel head installation will be performed. The staff understands that this evolution will be performed at flange level but was analyzed to occur at midloop.

(d)

MHI is requested to document in Chapter 19 of the DCD and the shutdown PRA a summary of the POSs considered in LPSD, including the state of the RCS, effectiveness of SG and gravity injection, key activities performed, etc. for each POS.

(e)

MHI is requested to use US refueling outage data to develop POS durations for POSs 4-1, 4-2, 4-3, 8-1, 8-2, and 8-3 or justify why US refueling outage data does not apply. Please revise the DCD and PRA as appropriate.

(f)

The staff learned that the duration of POS 4-3 has been extended from 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> to 39 hours4.513889e-4 days <br />0.0108 hours <br />6.448413e-5 weeks <br />1.48395e-5 months <br /> to account for ICIS removal from the top of the RV head. Please revise the results, dominant sequences and sensitivity studies in the DCD and LPSD PRA, as appropriate.

19.493-1

ANSWER:

Table 19.493-1 summarizes conditions considered in the LPSD PRA, and includes the configuration of the RCS, effectiveness of SG reflux cooling and gravity injection, time to RCS boiling and core uncovery, decay heat, key activities, etc., for each POS during mid-loop operation. Figure 19.493-1 shows the timeframe assumed in the LPSD PRA including RCS water level and key activities during mid-loop operation. Questions to Item (a) through (c) are discussed using the table and figure as a basis.

(a)

The following are the key activities considered in LPSD PRA and each of the descriptions will be documented in DCD Section 5.4.7.2.3.6 and Table 19.1-119:

(1) Installation and removal of the SG nozzle dams (2) Installation and removal of the SG manways (3) Installation and removal of the In-core instrumentation system (ICIS)

(4) Hydrogen peroxide addition (5) De-tensioning and tensioning of the reactor vessel (RV) head stud bolts (6) Installation and removal of the pressurizer safety valves Items (1) to (3) and Item (4) are described in the response to No 19-492 of RAI #669-5219 and No 19.01-10 of RAI #668-5180, respectively. Also, Item (5) is discussed in the response to Questions (b) and (c) of this RAI. Here, Items (6) is addressed.

(6) Installation and removal of Pressurizer safety valve A summary of the discussion below will be documented in DCD Subsection 5.4.7.2.3.6 and Table 19.1-119.

GL 88-17 requires that a large RCS vent path be provided before all SG nozzle dams on the hot leg side are installed. MHI plans to use (removal of) the pressurizer safety valves as a RCS vent path to prevent RCS pressurization. Timing to remove the valves before refueling and to install after refueling is discussed below:

Before Refuelinq Providing a large RCS vent path is not required in POS 4-1 since LPSD PRA considers that SG reflux cooling is an effective means to prevent core damage. According to GL 88-17, it is necessary to provide a large vent path before installing all SG nozzle dams on the hot leg side. In other words, pressurizer safety valves are removed at the beginning of POS 4-3.

Therefore, the pressurize safety valves will be removed during POS 4-2.

After Refuelinq Pressurizer safety valves remain off during POS 8-1 in accordance with GL 88-17 because there is no RCS vent path due to installation of SG nozzle dams. Also, the PRA considers that SG reflux cooling is an effective means for prevention of core damage in POS 8-3, when there is no vent path at the beginning of POS 8-3. Therefore, the pressurizer safety valves will be installed during POS 8-2.

19.493-2

(b) and (c)

De-tensioning and tensioning the reactor head studs for removal and installation of reactor vessel head when RCS water level is between the flange and the top of the MCP will be documented in DCD Section 5.4.7.2.3.6 and Table 19.1-119.

(d)

Table 19.493-1 and Figure 19.493-1 will be inserted in DCD Rev.3.

(e) and (f)

The durations of POSs applied in the LPSD PRA of DCD Rev.3, will take into account the US operational PWR plant data extracted from EPRI TR 1003465. The durations developed with consideration of US-APWR design and operational features will be applied to a sensitivity analysis in the LPSD PRA of DCD Rev.3.

The duration used in DCD Rev.3 is summarized in Table 19.493-2. Initiating event frequencies have been re-estimated to account for modified durations and the LOCA frequency extracted from EPRI 1003113. The re-estimated initiating event frequencies are listed in Table 19.493-3.

Detailed accident sequence quantification was performed for POS 8-1 andPOS 4-3 because both POSs are anticipated to be dominant contributors to the total CDF when considering longer durations, more types of initiating events and fewer available mitigation systems compared to other POSs. The risk from other POSs were quantified by the same method used in LPSD PRA of DCD Rev.2 (i.e., simplified accident sequence quantification).

As a result of detailed accident sequence quantification, CDFs for POSs 4-3 and 8-1 are the following; CDF for POS 4-3 3.OE-08/ry (DCD Rev.2: 3.OE-08/ry)

CDF for POS 8-1 8.OE-08/ry (DCD Rev.2: 6.OE-08/ry)

Initiating event contribution to CDF in POSs 4-3 and 8-1 is shown in Figure 19.493-2 and Figure 19.493-3, respectively. Moreover, total CDF including the result of the simplified accident sequence quantification for other POSs is shown in Table 19.493-4. According to this result, total CDF of US-APWR LPSD PRA is the following; Entire CDF for LPSD

1.8E-07/ry (DCD Rev.2: 2.2E-07/ry)

The results of this analysis indicate that the dominant contributors to shutdown core damage are loss of offsite power (LOOP) and LOCA events shown in Figure 19.493-4.

The dominant sequences for POS 4-3 and POS 8-1 are respectively given in Table 19.493-5 and Table 19.493-6. Table 19.493-7 shows the top 10 dominant cutsets corresponding to POS 4-3 and POS 8-1 as a combination. The top 10 dominant cutsets associated with the three most dominantsequences are respectively shown in Tables 19.493-8, 19.493-9 and 19.493-10.

19.493-3

Dominant Sequences for POS 4-3 The top 10 accident sequences individually contribute more than 1 percent of the CDF in POS 4-3. These dominant sequences are as follows:

1. LOOP event with the success of Class 1E gas turbine generators and the failure of all mitigation systems, which contributes 35 percent to the CDF in POS 4-3.

2. LOOP event with the SBO sequence, including the failure of offsite power recovery, which contributes 16 percent to the CDF in POS 4-3.

3.

LOCA event with flow path isolation success, RCS makeup and failures of all mitigation systems, which contributes 11 percent to the CDF in POS 4-3.

4. FLML event with the success of letdown line isolation and failure of RCS makeup and safety injection, which contributes 10 percent to the CDF in POS 4-3.

5. LOCA event with the failure of flow path isolation, safety injection and charging injection, which contributes 8 percent to the CDF in POS 4-3.

6. LORH event with the failure of safety injection and charging injection, which contributes 6 percent to the CDF in POS 4-3.

7. LOOP event with the success of Class 1 E gas turbine generators and the failure of CCW re-start and alternate component cooling, which contributes 5 percent to the CDF in POS 4-3.

8. LOOP event with SBO sequence and the success of AAC, and failure of all mitigation systems, which contributes 5 percent to the CDF in POS 4-3.

9. LOCS event with the failure of alternate component cooling, which contributes 3 percent to the CDF in POS 4-3.

10. LOCA event with the success of flow path isolation and the failure of RCS makeup and safety injection, which contributes 2 percent to the CDF in POS 4-3.

The descriptions of the top five sequences are provided in the following:

LOOP event with the success of Class IE gas turbine generators and the failure of mitigation systems (1.OE-08/ry)

This is sequence No.6 of the LOOP event tree in POS 4-3. In this sequence, the Class 1 E gas turbine generators succeeds to start and run automatically following the initiating event. Multiple random failures such as RHR operation, charging injection and safety injection lead to core damage (the decay heat removal via SGs and gravity injection are not available due to the plant configuration in this POS). The major contributor to CDF is a combination of:

Human error for the re-start of RHRS (ID: RSSOO02P)

Human error for the initiation of safety injection pump (ID: HPIOO02S-DP2)

Human error for the initiation of charging pump and refill of RWSP water (ID:

CHIOO02P+RWS-DP3)

LOOP event with the SBO sequence including failure of offsite power recovery (4.7E-09/ry)

This is sequence No.37 of the LOOP event tree in POS 4-3. This is station blackout sequence, Class 1 E gas turbine generators and AAC fail following the initiating event.

The recovery of offsite power is not successful either. All mitigation systems that are supported by ac power are unavailable. The major contributor to CDF is a combination of:

CCF of class 1 E (A, B, C and D) gas turbine generators 19.493-4

(ID: EPSCF4DLLRGTG-ALL)

Human error for the connection of AAC generator (ID: EPSOO02RDG)

Failure of offsite power recovery (ID: ACRPOS8-1-F)

LOCA event with the success of isolation and RCS makeup and the failure of other mitigation systems (3.3E-09/ry)

This is sequence No.6 of the LOCA event tree in POS 4-3. In this sequence, the isolation of the LOCA and the RCS makeup are successful. Multiple random failures such as RHR operation, safety injection and charging injection lead to core damage.

The major contributor to CDF is a combination of:

Human error for the initiation of RHRS (ID: RSSOO02LINE+P)

Human error for the initiation of safety injection pump (ID: HPIOO02S-DP2)

Human error for the initiation of charging pump and refill RWSP water (ID: CHIOO02RWS-DP3)

FLML event with the success of isolation and failure of RCS makeup and safety injection (2.9E-09/ry)

This is sequence No.10 of the FLML event tree in POS 4-3. In this sequence, the isolation of the source of initiating event is successful. Multiple random failures such as RCS makeup and safety injection lead to core damage. The major contributor to CDF is a combination of:

Failure of low-pressure letdown line isolation valve (ID: CVCAVCD024C or CVCAVCD024B) (initiating event frequency contributors)

Human error for initiation of safety injection pump (ID: HPIOO02S)

LOCA event with the failure of isolation, safety injection and charging injection (2.3E-09/ry)

This is sequence No.14 of the LOCA event tree in POS 4-3. Multiple random failures such as the isolation of LOCA, the safety injection and the charging injection lead to core damage. The major contributor to CDF is a combination of:

Human error for the isolation of LOCA (ID: LOAOO02LC)

Human error for the initiation of safety injection pump (ID: HPIOO02S-DP2)

Human error for the refill of RWSP water (ID: CHIOO02RWS-DP3)

Dominant Sequences for POS 8-1 The top 9 accident sequences individually contribute more than 1 percent of the CDF in POS 8-1. These dominant sequences are as follows:

1. LOCA event with the success of flow path isolation and the failure of RCS makeup and all mitigation systems, which contributes 31 percent to the CDF in POS 8-1.

2. LOOP event with the success of Class 1E gas turbine generators and the failure of all mitigation systems, which contributes 22 percent to the CDF in POS 8-1.

3. LOOP event with the SBO sequence and failure of offsite power recover, which contributes 12 percent to the CDF in POS 8-1.

4. LOCS event with the failure of alternate component cooling, which contributes 10 percent to the CDF in POS 8-1.

5. LOCA event with the success of flow path isolation and makeup and the failure of all mitigation systems, which contributes 7 percent to the CDF in POS 8-1.

19.493-5

6. LOOP event with the success of Class 1 E gas turbine generators and the failure of CCW re-start and alternate component cooling, which contributes 5 percent to the CDF in POS 8-1.

7. LOCA event with the failure of flow path isolation, safety injection and charging injection, which contributes 5 percent to the CDF in POS 8-1.

8. LORH event with the failure of safety injection and charging injection, which contributes 5 percent to the CDF in POS 8-1.

9.

OVDR event with the success of flow path isolation, the failure of RCS makeup and safety injection, which contributes 2 percent to the CDF in POS 8-1.

The descriptions of the top five sequences are provided in the following:

LOCA event with the success of flow path isolation and the failure of other mitigation systems (2.5E-08/ry)

This is sequence No.10 of the LOCA event tree in POS 8-1. In this sequence, the isolation of the source of the LOCA is successful. Multiple random failures such as RCS makeup by CVCS and safety injection lead to core damage (The decay heat removal via SGs and gravity injection are not available due to the plant configuration in this POS). The major contributor to CDF is a combination of:

Human error for the initiation of charging pump (ID: CHIOO02P)

Human error for the initiation of safety injection pump (ID: HPIOO02S-DP2)

LOOP event with the success of class 1 E gas turbine generators and the failure of mitigation systems (I.7E-08/ry)

This is sequence No.6 of the LOOP event tree in POS 8-1. In this sequence, the Class 1 E gas turbine generators succeeds to start and run automatically following the initiating event. Multiple random failures such as RHR operation, charging injection and safety injection lead to the core damage (the decay heat removal via SG and gravity injection are not available due to the plant configuration in this POS). The major contributor to CDF is a combination of:

Human error for the re-start of RHRS (ID: RSSOO02P)

Human error for the initiation of safety injection pump (ID: HPIOO02S-DP2)

Human error for the initiation of charging pump and refill of RWSP water (ID: CHIOO02P+RWS-DP3)

LOOP event with the SBO sequence and failure of offsite power recover (9.3E-09/ry)

This is sequence No.37 of the LOOP event tree in POS 8-1. This is station blackout sequence, Class 1 E gas turbine generators and AAC fail following the initiating event.

The recovery of offsite power is not successful either. All mitigation systems that are supported by ac power are unavailable. The major contributor to core damage frequency is a combination of:

CCF of class 1E gas turbine generators (ID: EPSCF3DLLRGTG-ALL)

Human error for the connection of AAC generator (ID: EPSOO02RDG)

Failure of offsite power recovery (ID: ACRPOS8-1-F)

LOCS event with the failure of alternate component cooling (8.1E-09/ry)

This is sequence No.3 of the LOCS event tree in POS 8-1. This sequence has a loss of 19.493-6

CCW/ESW initiator. The mitigation systems such as RHR operation, charging injection, and high head injection system that are supported by CCWS/ESWS are unavailable for this initiating event. Moreover, the decay heat removal via SGs and gravity injection are unavailable for the same reason described above. Failure of injection by charging pump using the alternate component cooling water system leads to core damage. The major contributors to CDF due to loss of CCW/ESW are:

CCF of CCW/ESW pumps (A, B and C) or CCF of CCW heat exchangers (A, B and C) (initiating event frequency contributors)

Human error for initiation of alternate component cooling (ID: ACWOO02SC)

Failure of offsite power recovery (ID: ACRPOS8-1-F)

LOCA event with the success of flow path isolation and makeup and the failure of other mitigation systems (5.9E-09/ry)

This is sequence No.6 of the LOCA event tree in POS 8-1. In this sequence, the isolation of the source of the LOCA and the RCS makeup are successful. Multiple random failures such as RHR operation, safety injection and charging injection lead to core damage. The major contributor to CDF is a combination of:

Human error for the initiation of RHRS (ID: RSSOO02LINE+P)

Human error for the initiation of safety injection pump (ID: HPIOO02S-DP2)

Human error for the initiation of charging pump and refill RWSP water (ID: CHIOO02RWS-DP3)

Importance Analysis Importance assessment has been individually performed for POS 4-3 and POS 8-1. The results of basic event importance are organized by the FV importance and RAW. The FV importance which value is greater than 0.5% is shown in Table 19.493-11 for POS 4-3 and Table 19.493-13 for POS 8-1. The RAW which value is greater than 2 is normally clarified in PRA report, but Table 19.493-12 for POS 4-3 and Table 19.493-14 for POS 8-1 show the RAW top 20 for the simplification point of view.

The top five most significant basic events, based on the FV importance, are as follows:

FV Importance for POS 4-3 (Table 19.493-11)

HPIOO02S-DP2 (Operator fails to start standby safety injection pump under the condition of failing their previous task (HE)) -

This basic event applies to conditions where operators have failed to establish decay heat removal by the RHRS.

If the operator fails to start the standby safety injection pumps, RCS injection function by the safety injection system is lost. The CDF of POS 4-3 is decreased by a factor of 50% if the probability of this failure is set to 0.0.

RSSOO02P (Operator fails to start standby CS/RHR pump (HE)) - This basic event applies to conditions where the power supply has recovered after LOOP initiating event. If the operator fails to restart the CS/RHR pumps, decay heat removal function by the RHRS is lost. The CDF of POS 4-3 is decreased by a factor of 33% if the probability of this failure is set to 0.0.

CHIOO02P+RWS-DP3 (Operator fails to establish charging injection (start standby charging pump and connect the RWSAT makeup line) under the 19.493-7

condition of failing their previous two tasks (HE)) - This basic event applies to conditions where the operators have failed to establish decay heat removal by RHRS and also fails to establish RCS injection by safety injection pumps. If the operator fails to establish charging injection, RCS injection function by the charging pumps is lost.

The CDF of POS 4-3 is decreased by a factor of 30% if the probability of this failure is set to 0.0.

ACRPOS4-3-F (Failure of offsite power recovery POS4-3) - This basic event applies to conditions where the offsite power recovery fails within the allowable time (1.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />) for core uncovery. If the offsite power fails to recovery, AC power is lost.

The CDF of POS 4-3 is decreased by a factor of 20% if the probability of this failure is set to 0.0.

CHIOO02RWS-DP3 (Operator fails to refill RWSAT water from RWSP (HE)) - This basic event applies to conditions where the operators have failed to establish decay heat removal by RHRS and also fails to establish RCS injection by safety injection pumps. Refueling water storage auxiliary tank (RWSAT) is water source for charging injection pump. If the operator fails to refill RWSAT water from refueling water storage pit (RWSP), RCS injection function by the charging pumps is lost. The CDF of POS 4-3 is decreased by a factor 18% if the probability of this failure is set to 0.0.

FV Importance for POS 8-1 (Table 19.493-13)

HPIOO02S-DP2 (Operator fails to start standby safety injection pump under the condition of failing their previous task (HE)) -

This basic event applies to conditions where operators have failed to establish decay heat removal by the RHRS.

If the operator fails to start the standby safety injection pumps, RCS injection function by the safety injection system is lost. The CDF of POS 8-1 is decreased by a factor of 60% if the probability of this failure is set to 0.0.

CHIOO02P (Operator fails to start standby charging pump) - This basic event applies to conditions where the RCS inventory decreases due to LOCA and OVDR events. If the operator fails to start standby charging pump, RCS injection function by the charging pump is lost. The CDF of POS 8-1 is decreased by a factor 29% if the probability of this failure is set to 0.0.

CHIOO02P+RWS-DP3 (Operator fails to establish charging injection (start standby charging pump and connect the RWSAT makeup line) under the condition of failing their previous two tasks (HE)) - This basic event applies to conditions where the operators have failed to establish decay heat removal by RHRS and also fails to establish RCS injection by safety injection pumps. If the operator fails to establish charging injection, RCS injection function by the charging pump is lost.

The CDF of POS 8-1 is decreased by a factor of 23% if the probability of this failure is set to 0.0.

RSSOO02P (Operator fails to start standby RHR pump (HE)) - This basic event applies to conditions where the power supply has recovered after LOOP initiating event. If the operator fails to restart the RHR pumps, decay heat removal function by the RHRS is lost. The CDF of POS 8-1 is decreased by a factor of 20% if the probability of this failure is set to 0.0.

ACRPOS8-1-F (Failure of offsite power recovery POS8-1) - This basic event 19.493-8

applies to conditions where the offsite power recovery fails within the allowable time (4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />) before core uncovery. If the offsite power fails to recovery, AC power is lost. The CDF of POS 8-1 is decreased by a factor of 12% if the probability of this failure is set to 0.0.

The top five most significant basic events, based on the RAW, are as follows:

RAW for POS 4-3 (Table 19.493-12)

RTPBTSWCCF (CCF of Basic Software) - The CDF of POS 4-3 would increase approximately 2.5E+04 times if the probability of this failure were set to 1.0. If this failure occurs, all of digital I&C software will be inoperable and result in failure of automatic signals and manual actions which need the digital I&C software.

SWSCF4PMYRO01 -ALL (CCF of Essential Service Water Pumps A, B, C and D to run) - The CDF of POS 4-3 would increase approximately 1.4E+04 times if the probability of this failure were set to 1.0. If this failure occurs, all trains of essential service water will be lost. This basic event leads to the total loss of component cooling water.

CWSCF4PCYRO01 -ALL (CCF of CCW Pump A, B, C and D to Run) - The CDF of POS 4-3 would increase approximately 1.4E+04 times if the probability of this failure were set to 1.0. If this failure occurs, all trains of CCW will be lost. This basic event leads to the total loss of CCW.

CWSCF4RHPF001 -ALL (CCF of CCW Heat Exchanger A, B, C, and D Plug) - The CDF of POS 4-3 would increase approximately 1.4E+04 times if the probability of this failure were set to 1.0. If this failure occurs, all trains of CCW will be lost. This basic event leads to the total loss of CCW.

EPSCF4CBSO52STH-ALL (CCF of Breaker between Class I E 6.9 kV switchgear and 6.9kV-480V transformer A, B, C and D Spurious Open) - The CDF of POS 4-3 would increase approximately 1.4E+04 times if the probability of this failure were set to 1.0. If this failure occurs, the power supply from all Class 1 E 480V load centers will be lost. This basic event leads to the total loss of power supply to the Motor-operated valve which is necessary for the mitigation of shutdown accident.

RAW for POS 8-1 (Table 19.493-14)

RTPBTSWCCF (CCF of Basic Software) - The CDF of POS 8-1 would increase approximately 2.9E+04 times if the probability of this failure were set to 1.0. If this failure occurs, all of digital I&C software will be inoperable and result in failure of automatic signals and manual actions which need the digital I&C software.

SWSCF3PMYRO01 -ALL (CCF of Essential Service Water Pumps A, B and C to run) - The CDF of POS 8-1 would increase approximately 1.1E+04 times if the probability of this failure were set to 1.0. If this failure occurs, all effective trains of essential service water will be lost. This basic event leads to the total loss of component cooling water.

CWSCF3PCYR001-ALL (CCF of CCW Pump A, B and C to Run) - The CDF of POS 8-1 would increase approximately 1.1 E+04 times if the probability of this failure were 19.493-9

set to 1.0. If this failure occurs, all effective trains of CCW will be lost. This basic event leads to the total loss of CCW.

CWSCF3RHPF001-ALL (CCF of CCW Heat Exchanger A, B and C Plug) - The CDF of POS 8-1 would increase approximately 1.1 E+04 times if the probability of this failure were set to 1.0. If this failure occurs, all effective trains of CCW will be lost. This basic event leads to the total loss of CCW.

EPSCF4CBSO52STH-ALL (CCF of Breaker between Class 1 E 6.9 kV switchgear and 6.9kV-480V transformer A, B, C and D Spurious Open) - The CDF of POS 8-1 would increase approximately 8.4E+03 times if the probability of this failure were set to 1.0. If this failure occurs, the power supply from all Class 1 E 480V load centers will be lost. This basic event leads to the total loss of power supply to the Motor-operated valve which is necessary for the mitigation of shutdown accident.

Uncertainty Analysis The results of uncertainty quantification for CDF in POSs 4-3 and 8-1 are shown in Figure 19.493-5 and Figure 19.493-6. Mean value, median value, lower (5 percentile) and upper (95 percentile) values of the distribution, and error factor (EF) are shown below, where EF is estimated by square root of ratio of upper and lower values.

POS 4-3 POS 8-1 Upper 8.3E-08/ry 2.3E-07/ry Mean 2.9E-08/ry 8.1 E-08/ry Median 1.8E-08/ry 4.8E-08/ry Lower 4.4E-09/ry 1.3E-08/ry EF 4.3 4.2 (Point estimation) 3.OE-08/ry 8.OE-08/ry The risk profile characteristics from the updated LPSD PRA remain unchanged from previous risk assessment in DCD Rev.2. The above results will be documented in DCD Rev.3.

Impact on DCD The following will be documented after the last paragraph of Section 5.4.7.2.3.6.

In addition to above features, to reduce the risk of loss of Decay Heat Removal, the following operational considerations are incorporated into the US-APWR operating procedures.

The de-tensioning and tensioning of RV head stud bolts are performed at an RCS water level between the flange and the top of the MCP.

Pressurize safety valves are used as a vent path to prevent RCS pressurization. Removal of the pressurizer safety valves is performed during the period between removal of the SG manways and installation of the SG nozzle dams. Installation of the pressurizer safety valves is performed during a period between removal of the SG nozzle dams and installation of the SG manways.

Table 19.1-119 will be revised as follows:

19.493-10

Table 19.1-119 Key Insights and Assumptions (Sheet 17 of 23)

Key Insights and Assumptions Dispositions Key Activities during LPSD

1.

The de-tensioning and tensioning of RV head stud bolts are 5.4.7.2.3.6 performed at an RCS water level between the flange and the top of the MCP.

2.

Pressurize safety valves are used as a vent path to prevent 5.4.7.2.3.6 RCS pressurization caused by loss of decay heat removal.

Removal of the pressurizer safety valves is performed during a period between removal of the SG manway and installation of the SG nozzle dam. Installation of the pressurizer safety valves is performed during a period between removal of the SG nozzle dam and installation of the SG manway.

LPSD PRA results in the RAI response will be documented in DCD Section 19.1.6.

Impact on R-COLA and S-COLA.

There is no impact on R-COLA and S-COLA.

Impact on PRA LPSD PRA model will be updated to reflect the response to this RAI.

19.493-11

Co CD Ce)

N)

Table 19.493-1 Plant Configuration and Assumptions Considered in LPSD PRA (Sheet I of 2)

.e....ptio D rat. ed [hr]i RC

-CS edraguOaon INe vane of Plan Ste Fre o-Epta M

$ph~el Posaildifity of RV Head Stud Boft RCS Vant edi.

Plant Staite Fron.0bAP RFre

.n To sue bspe e

PssbltRfHoH aCtdBot H NRoS boo ndaty) ooling lnjentlwr To

-Pa100045 T

dtaled by OROR or FLML Snghity below MOP lop Slightly below MCP A14 RCS Fult ot 14 by FVOS Yes On Fully P--sanyeOpen

Yet, No Mid-loop operation with RHR RCS dtanoing MCP oenter MCP center (OVDR) tesynayei vent Ne

-li*tng POS 4-1 (forond ation of dreinig the 24 Slightly below MCP Slightly below MCP RCS t tenmot of ithne SG Slightly below MCP top Reloop of the l1p top Not droined but Yen Les Pressurizer spray open Ye NO H

onanway)

S.

m.nw.y 36 n...

rolld by CVCS (FLML)

"OTr On tensione d vent va eO e

contetd Yesd Noc N

MO P 't3 MCP ednter MCP oontor Mid-oop opetation W4th RHR Slightly below MOP Abov MCP top ooling Removal of the MOP.

l PO4 1mttnalowe eooofte Ins~alataton of thre 12 opNot droined bud Yes On Less Smnss pn N

e manwy to Instaaltion ot SO etanwey SO nozzl dam MOP MOP venter Mnt rolled by CVCS (FIML) tensioned Safety Vabes)

SG noodzo dam)

Instalathion of the Initation of Above MCP top Above MCP top Not drained but Yes Len Prenssizrer A

On

.=ta vle PO lSO nozzle dew RCh supplying oC ne CPcne ontrolled by 0V01 (FIML)

O tensioned s~afety vane Open I

NO NO"'

Indtatin of RCP 36 Flane Le top Supplied by RWR Les Prensurizet open No RCS nsupplying flange level M P enterLve pomp Negligihe On tensioned sfely va ne No' Midloop operotion slth RHR orn tnliong of th 36eFSnRoR Not drained and Les Pressurizer nozzle dam to oavity fut) flange leve fge lveel Fsuppted tensioned safety vale RCS RCS Notd ned and D

lange lovet flangel Flange Level Flange Leovel uppled Negligible Off No Rhhed RV had oh Open No co Coity hug 72 Flange Level y F upplied CS/RHR Negligible Off No RV head RV head off Open No NO' t gange levat pump Fnulation ot Fuel movement 72 CFo ity Ful Not drained and P015S Fuel offived fuel otflod ends 7upplied Negligible Off No RV head RV head off Open NIA N/A POFu No fuel oritiation of ofo CaviyFul aoy Not drained and Negligible Oh No RV hed RV head off Open NIA N/A ends fuel load soppled 168 P0t7 Fuelload Indian of Fuel movement 72 taviy Full Cary Ful Not dained and Negligibe Off No RV head RV head oft Open NIA N/A fuel load endt ppled A

Cavity fuol R00 72 Cavity Fuo Flange Level DSained by CS/RHR Negligible Off No RV head RV head off Open No NO" 0

tangelevel pump BRob RCS Not drained and lRange Lvel Flange Level Negligible Off No RV head RV head off Open No No" Bflange leoel flange leoe ag eel suJppled Mid....opoedn.n.h.R.

RCS RS Not d.rin.esd Lesd OpenP N"t C

ving flange level n

ln vel l

Range Level Flange Level Sup Negligible On teoed sely v.ev POS 8-1 (fhor cavey ful to removl of Ro the SO nozzle dm)

Above MCP top Above MCP top Yes Les Pressourizet O

Relflange Rvlevel MP-n---------...

M rDined by 0V00 7OVDR)

On tensioned bsety vaove Open No No" E aAbove MCP lop Remove of the Above MCP top Abooe MCP top Not drained but Yen Less Presurer

~~~~ --

On;*

b..

p.*..

open N o No" MCP venter MO nester MOP venter ontroled by 0400 (FLMLr tioned sately valve O

Mbd4oop operation W.th RHR Above MOP rp Slightly below MOP cooling the M

tlp top Not drained but Yen Less0Lt manways P0n I-2 hn e o tre S Renoif the noltio of 2

On (Pressurizer Open No Yes no-oe darnetomnotatl of the SO nozzle dem the SG monsay controlled by CVC0 (FLML) tensioned Safely VaNes) nozzle den to Ins.Utallan MCofha MCP oenter the SO monvoy)I Slightly below MCP Slightly below MCP Pip~

Not drotnd but Yeas O

Fully ovn be Yn N

Mid4oop opetanon with RHR MCP venter MOP carro t

lled by 0400 (FLML) tensioned cooling Installatfon of RCS ful 24 24 POS B (hor instelatlon of the SG the SG manosy Slightly below MCP

-marwy to RCb full(

topP-RIDb Fill Supplied by 0

Negligible On he Fully P...re.sutt spry Open yes, no-"

N onMcp i

.oned v entoa.

N-T

Upper and lower show realiasti operatton and PRA assumption, respectively.

2: Analyss vendnion (Deooy hent) and resutls (lime) in MAAP 3:1 Its considered that Inheating event "OhR" indOudes incioting event "FLML".

4: Analysis tesults asuming the pressurizer vent vale are kept open dernonstate the efrect-eness with 20 bouts.

MCP: Main eolant piping CVCS: Chenal and voolme vntrol system RWR pomp Reluelng wter

.eo.rvu.aion pimp CS/RHR pimp: Containment sprayresddual heat removal pump OVDR: Over-drin FLML: Loss of RHR e.used by failng to maintain water level ICIS: tn-cona instruentation system

Table 19.493-1 Plant Confilauration and Assumotions Considered in LPSD PRA (Sheet 2 of 21 Co0 I

Performed key actTo cor tncoe Dcy Heat Perfoenedshutdoy acautte MAAp Resuis Cosidere in1.

re shutdown

=PRA Open pressorie spray oet.a1. for RCE draining.

Drain RCS below a top of MCP by the CVCS.

Control RCSi ry by CVC0.

35 0.3 13.0 12.0 M.7 SO reflu cooling is aailabls bid grawry loaecton lo unavaiable beause the RCS i higher them atmosphedepressure Stan o dRainintg.

and there is a ptessre boundary in the RC&.

Stan to loosen the RV head stud botts for remoal of the RV head and to renroue the ICIS fron the top of RV head.

Open SG manwmys on hot leg side and then on old leg aide (End of POS 4-f1).

Control P0S inoentory by the CVCS to keep aboe a top of MOP.

00 refun cooling is unavilabte bud grauity injection is ava jabe because ha R00 pressure is squat to atmospherc Remove pressurizer safety valves pressura due o opening the SO manosys.

Continue Iosening the RV head stud bobs and removing the ICIS.

60 1.3 1.7 1.5 19.3 Instal SO nozzte dams on cotd leg side and then on hot leg side (End of POS 8-2).

!,CIS remoual is actually performed at one foot below the RCS fange tevel, but is conservaively assumed by the PRA tobe at the center of MCP.

Control RCS inuentory by the CVCS.

Finish to Ioosn the RV stud bobts.

POS 43 consenvatively assumes POS 4-3* configuration that is the most svere plan configuration in POS 43 becaus neither graWty injection nor SO refluo coling is ayilalae and there is a p.ssibi ey of FLML in POS 4-3A-Supply RCS inventory to me foot below flange levd for removal RV head by the RWR pump.

"1: Although there is RCS vent path lie., pressurizer safety valt)s, gravity injection is unavailable. This is beause (1)

RCS is pressurized above acmospheric pressaure by a loss of RHO, (2) there isa possibility that the primary aide s, Fisi to removl the IC0S.

72 1.3 1.8 t1.5 8.1 pressuozed by the uster level of the pressuvzer and (3) btat there is a pressure loss due to the piping of pressurizer Stan to remove the RV head.

safety valoes before and after Oe eevufion of the gravty injection.

-2: Graoy injection may be available due to remt of the RV head. Hiowever, sie (1) POS 4-3A is represented as Stan to hoist the RV head for removal.

POS 4-3 and 12) water in RWSP, whict is he w

th r sour, e f gravity itietbion, is swat (bwing tansfered to carty),

gravity injection is assun to b "o'.

Transfer the RV head fur fuel offload wiah supplying R00 ivntory to cavty full by the CSRHR pump.

Puel offtoad.

NIA NIA N/A M5A NIA This PO is not modeled in the LPSD PRO, beca.e-the elowabhe time is mush longer due to the large RCS inerotoy.

Tfus P00 is nut modeied in the LPSO PORA, becaue there is either no fuel in the reactor mithe fuel is pertially Either no fuel l ther sctor care or partially ffoaded.

N/A NIA A

N/A SNlA Tobtoded.

Fuel load.

N/A N/A N/A P

NIA SlN/A

]Tima POS is not modeled in the LPSD PRO because the allowable time is much longer due to the large RCS inentory.

Transfer the RV head above the RV allt draining RCS inventory to nes foot below flange level by the 0S/RHR pump.

POS 5-1 consrvatwvely assumes "POSs 8-1 D and E' configuraton that is the most scorer plant conbiguration in POS B-1 because neither gravity injection nor SG reflu, caling is aHavla and there is a yossahilty of OVDR and FLML in Place the RV head.

POSs Z1 0 and E..

The uster around the cavity is drained by the P10 pump.

-3. Gravity injection may be available due to removal of the RV head. However, since (1) POSs 8-1D and E are 420 0.6 4.2 4.0 0.0 represented as POS 8-1 and (2) the duration is short and (3) water in OWOP, which is the onter source for gravity injection, is smell (being transfered to cauy), gravity injection is aesumed tobe "No".

-4 Although there is RCS vent path (ie.,, pressurizer sfeyt vales), gravity injection is unaatirable. This is because (1)

Drain 000 inventory by the CVCS to keep above a top of MOP.

RCS is pressuried above atmospheric pressure by a loss of RHO, 12) there is a possibilny that thie pdmrimy side is pressurized by the water level of the pressurizer and (3) that there isa pressure toss due to the piping of pressurizer Control RCS inventory by the CVCS.

safety valbes before and afber the execdion of the graty injaction.

Star to instell the ICIS from the top of RV, clench the RV head stud bolts.

Remove SG n lie dams on the hot leg side and then the old leg side lEd of POS 0-fl.

Coatrom0l 0 inventory by the CVCS.

SG reu cooling is unave ilable but gravity injection is a-tlable because the RCS pressure is equal to amomapheric wetal pressutier safety vtah4es, p06 4.4 4.1) 8.3 pressure.

Continue instatiing the IChtS and 0lenc.ng the RV head stud bolts.inwealion isacually perfonned atone toot betow the 000 tongs isvet, t is ae tiveiy assumed by Ore nswl SO manwoys on odk leg side and then on hot leg side (End of POS 8-2).

PRA lotbe at tn p

center of MOP.

Control 000 inventory by the CVCS.

Perform soccumo vemng to remov air in RCS.

4S ISG rettcu 1rng is available but gravy ieooio is unauslzble because the RCS pressure is higher then atmospheric 492 0OP 22.3 2230 0.2 pressure snd there is a presure beundary in the RCS.

ISupply RCS inventory to RCS above the top of MCP for startup.

I Upper and lower shtooeaeliaic operation and PRA assumption, asipeotivsy.

MCP: Main colant piping OVDR: Ovet-tdrtin 2: Analysis conddion (Decy hear) and resiuts (Time) in MAAp CVCS: Chemical and volume control sysem FLML: Los of RHR ceued by failing to maintain water sodel 3: it is consdered that hntiating ever "OVDR" includes inmeaing event "FLML".

RWR pump: Refueling water reciroulation pump ICI0- In-cure in-rwmentation system 4: Analysis reuitds asuming the pressurizaruent calve are kept opan demonstrate the eftetyemenes with 20 hour2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />. CSORHR pump: Containment spraylrsidcal heat removl pump

co CD Table 19.493-2 Duration of each POS for LPSD PRA Case Base Sensitivity Plant Configuration Source EPRI data (Hr)

Japanese Data (Hr)

____DurationTime after Duration Time after from to P0S Duration shutdown shutdown 1

3 0

2 0.0 Power operation Insertion of control rods 2

9 3

7.7 2.0 Insertion of control rods RHR connection 3

24 12 2.3 9.7 RHR connection Initiation of RCS draining 4-1 24 36 39.2 12.0 Initiation of RCS draining Opening the SG manhole 4-2 12 60 12 51.2 Opening the SG manhole Installation of SG nozzle lid 4-3 36 72 39 63.2 Installation of SG nozzle lid Cavity full 5

72 108 82.7 102.2 Initiation of fuel offload Fuel movement ends 6

168 180 108 184.9 Fuel movement ends Initiation of fuel load 7

72 348 75.8 292.9 Initiation of fuel load Fuel movement ends 8-1 60 420 55.5 368.7 Cavity full Removal of the SG nozzle lid 8-2 12 480 12 424.2 Removal of the SG nozzle lid Installation of the SG manhole 8-3 24 492 11 436.2 Installation of the SG manhole RCS full 9

8 516 10 447.2 RCS full Initiation of the RCS leakage test 10 16 524 20.5 457.2 Initiation of the RCS leakage test End of the RCS leakage test 11 33 540 43.5 477.7 End of the RCS leakage test Isolation of RHR 12 38 573 51 521.2 Isolation of RHR Critical state of the reactor 13 3

611 4

572.2 Critical state of the reactor Power operation (for start-up)

Highlighted POSs: Scope of LPSD PRA

C.0 01 Table 19.493-3 Frequency of Initiating Events for LPSD PRA IE Event IEPOS3 IEEos 4.1 IEpos4-2 IEpos4-3 IEpos 8-1 IEpos[-2 IEpos8-3 IEpos9 IEp~os1 Reference Description Loss of EPRI LOCA coolant 6.5E-05 6.5E-05 3.2E-05 9.7E-05 1.6E-04 3.2E-05 6.5E-05 2.2E-05 8.9E-05 ERI accident Loss of Fault tree OVDR RHRS due to N/A 3.7E-06 N/A N/A 3.7E-06 N/A N/A N/A N/A analysis and over-drain human reliability analysis Loss of RHRS FLML caused by N/A N/A 5.7E-07 5.7E-07 N/A 5.7E-07 5.7E-07 N/A N/A Fault tree failing to analysis maintain water level Loss of L RH RSFault tree LORH caus 3.1E-06 5.5E-06 1.6E-06 4.7E-06 1.OE-05 1.6E-06 3.2E-06 1.1E-06 4.3E-06 anlysis caused by analysis other failures Loss of Fault tree LOCS C

/

1.OE-07 1.6E-07 9.6E-09 2.9E-08 2.8E-07 2.OE-08 3.9E-08 1.3E-08 1.4E-07 anlysis CCW/ESW analysis Loss of offsite NUREG/CR-LOOP 2.7E-04 2.7E-04 1.3E-04 4.OE-04 6.7E-04 1.3E-04 2.7E-04 8.9E-05 3.7E-04 6890 power 6890 N/A: Not Applicable Unit: /ry

(0 (0D Table 19.493-4 Core Damage Frequencies for LPSD PRA IE Event POS 3 POS 4-1 POS 4-2 POS 4-3 POS 8-1 POS 8-2 POS 8-3 POS 9 POS 11 Total Description LOCA Loss of coolant 3.7E-09 2.6E-09 9.4E-10 6.OE-09 3.5E-08 1.OE-09 2.6E-09 8.8E-10 5.1E-09 5.8E-08 accident OVDR Loss of RHRS N/A 6.5E-10 N/A N/A 1.8E-09 N/A N/A N/A N/A 2.4E-09 due to over-drain Loss of RHRS FLML caused by failing N/A N/A 3.2E-10 3.OE-09 N/A 3.2E-10 4.4E-10 N/A N/A 4.1E-09 to maintain water level Loss of RHRS LORH caused by other 2.3E-10 4.OE-10 2.9E-10 1.6E-09 3.8E-09 2.9E-10 2.3E-10 7.7E-11 3.2E-10 7.2E-09 failures Loss of LOCS CCW/essential 3.OE-09 4.5E-09 5.5E-11 8.3E-10 8.1E-09 1.1E-10 1.1E-09 3.8E-10 4.1E-09 2.2E-08 service water LOOP Loss of offsite 6.6E-09 5.1 E-09 3.7E-09 1.8E-08 3.2E-08 3.9E-09 6.2E-09 2.OE-09 8.4E-09 8.6E-08 power Total 1.3E-08 1.3E-08 5.3E-09 3.OE-08 8.0E-08 5.6E-09 1.1E-08 3.4E-09 1.8E-08 1.8E-07 N/A: Not Applicable Unit: /ry

Table 19.493-5 Dominant Sequences of POS 4-3 for LPSD PRA D

Sene Name 1

Sequence Percent Percent equec Frequency (ry)

Contrib.

Contrib.Total 1

LOOP 4-3 0006 05 LOOP: POS4-3-RHB-SG-SIB-CVB-GI 1.OE-08 34.7%

34.7%

2 LOOP 4-3 0037 05 LOOP: POS4-3-GT-SP-AC 4.7E-09 15.7%

50.3%

3 LOCA 4-3 0006 01 LOCA: POS4-3-RHA-SG-SIA1-CVAI-GI 3.3E-09 11.0%

61.3%

4 FLML 4-3 0010 06 FLML: POS4-3-MC2-SG-SIA4-GI 2.9E-09 9.8%

71.1%

5 LOCA 4-3 0014 01 LOCA: POS4-3-LOA-SIA1-CVAI-GI 2.3E-09 7.6%

78.7%

6 LORH 4-3 0005 03 LORH: POS4-3-SG-SIA3-CVA3-GI 1.6E-09 5.5%

84.2%

7 LOOP 4-3 0009 05 LOOP: POS4-3-PR-GI-SC2 1.5E-09 5.1%

89.3%

8 LOOP 4-3 0024 05 LOOP: POS4-3-GT-AC-RHB-SG-SIB-CVB-Gi 1.4E-09 4.6%

93.9%

9 LOCS 4-3 0003 04 LOCS: POS4-3-GI-SC1 8.3E-10 2.8%

96.7%

10 LOCA 4-3 0010 01 LOCA: POS4-3-MC1-SG-SIA1-GI 4.9E-10 1.7%

98.3%

11 LOOP 4-3 0015 05 LOOP: POS4-3-GT-RHB-SG-SIB-CVB-GI 2.2E-10 0.7%

99.1%

12 FLML 4-3 0014 06 FLML: POS4-3-LOB-SIA4-CVA4-GI 1.5E-10 0.5%

99.6%

13 LOOP 4-3 0036 05 LOOP: POS4-3-GT-SP-PR-GI-SC2 6.9E-1 1 0.2%

99.8%

14 LOOP 4-3 0033 05 LOOP: POS4-3-GT-SP-RHB-SG-SIB-CVB-GI 3.4E-11 0.1%

99.9%

15 LOOP 4-3 0027 05 LOOP: POS4-3-GT-AC-PR-GI-SC2 2.7E-11 0.1%

100.0%

16 LOOP 4-3 0018 05 LOOP: POS4-3-GT-PR-GI-SC2 1.8E-12 0.0%

100.0%

17 FLML 4-3 0006 06 FLML: POS4-3-RHA-SG-SIA4-CVA4-GI E

E 100.0%

to (0.

Table 19.493-6 Dominant Sequences of POS 8-1 for LPSD PRA No SequenceD Seqence Name Sequence Percent Percent No equnc IDSeqene NmeFrequency (ry)

Contrib.

Contrib.Total 1

LOCA 8-1 0010 01 LOCA: POS8-1-MC1-SG-SIA1-GI 2.5E-08 31.2%

31.2%

2 LOOP 8-1 0006 05 LOOP: POS8-1-RHB-SG-SIB-CVB-GI 1.7E-08 21.6%

52.8%

3 LOOP 8-1 0037 05 LOOP: POS8-1-GT-SP-AC 9.3E-09 11.6%

64.5%

4 LOCS 8-1 0003 04 LOCS: POS8-1-GI-SC1 8.1E-09 10.0%

74.5%

5 LOCA 8-1 0006 01 LOCA: POS8-1-RHA-SG-SIA1-CVAI-GI 5.9E-09 7.3%

81.8%

6 LOOP 8-1 0009 05 LOOP: POS8-1-PR-GI-SC2 4.2E-09 5.2%

87.0%

7 LOCA 8-1 0014 01 LOCA: POS8-1-LOA-SIA1-CVA1-GI 3.8E-09 4.8%

91.8%

8 LORH 8-1 0005 03 LORH: POS8-1-SG-SIA3-CVA3-GI 3.8E-09 4.7%

96.5%

9 OVDR 8-1 0010 02 OVDR: POS8-1-MC1-SG-SIA2-GI 1.3E-09 1.6%

98.1%

10 LOOP 8-1 0015 05 LOOP: POS8-1-GT-RHB-SG-SIB-CVB-GI 4.5E-10 0.6%

98.7%

11 OVDR 8-1 0014 02 OVDR: POS8-1-LOB-SIA2-CVA2-GI 3.2E-10 0.4%

99.1%

12 LOOP 8-1 0036 05 LOOP: POS8-1-GT-SP-PR-GI-SC2 3.2E-10 0.4%

99.5%

13 LOOP 8-1 0024 05 LOOP: POS8-1-GT-AC-RHB-SG-SIB-CVB-GI 1.5E-10 0.2%

99.7%

14 OVDR 8-1 0006 02 OVDR: POS8-1-RHA-SG-SIA2-CVA2-GI 1.3E-10 0.2%

99.8%

15 LOOP 8-1 0033 05 LOOP: POS8-1-GT-SP-RHB-SG-SIB-CVB-GI 8.6E-11 0.1%

99.9%

16 LOOP 8-1 0018 05 LOOP: POS8-1-GT-PR-GI-SC2 2.8E-11 0.0%

100.0%

17 LOOP 8-1 0027 05 LOOP: POS8-1-GT-AC-PR-GI-SC2 2.8E-11 0.0%

100.0%

(0 CD

(0 (0

C~3 Co Table 19.493-7 Dominant Cutsets of POS 4-3 and POS 8-1 for LPSD PRA (Sheet 1 of 3)

No Cutsets Percent Cutsets Frequency Basic Event Description No Freq. (/ry) J re Cutsets probability 1

2.3E-08 20.5

!LOCA8-1 1.6E-04 LOSS OF COOLANT ACCIDENT - POS8-1 (in POS8-1)

CHIOO02P 2.6E-03 (HE) FAIL TO START STANDBY CHARGING PUMP SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 2

1.5E-08 13.5

!LOOP8-1 6.7E-04 LOSS OF OFFSITE POWER - POS8-1 (in POS8-1)

RSSOO02P 2.6E-03 (HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN THE LOOP EVENT OCCURS SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP CHIOO02P+RWS-DP3 1.6E-01 (HE) FAIL TO START STANDBY CHARGING PUMP AND REFILL RWSAT WATER FROM RWSP GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 3

8.9E-09 8.1

!LOOP4-3 4.OE-04 LOSS OF OFFSITE POWER - POS4-3 (in POS4-3)

RSS0002P 2.6E-03 (HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN THE LOOP EVENT OCCURS SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP CHIOO02P+RWS-DP3 1.6E-01 (HE) FAIL TO START STANDBY CHARGING PUMP AND REFILL RWSAT WATER FROM RWSP GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 4

6.2E-09 5.6

!LOCS8-1 2.8E-07 LOSS OF CCW/ESW-POS8-1 (in POS8-I) ACW0002SC 2.2E-02 (HE) FAIL TO ESTABLISH THE ALTERNATE CCWS BY FIRE PROTECTION WATER SUPPLY SYSTEM GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION

CD C~)

N)*

0*

Table 19.493-7 Dominant Cutsets of POS 4-3 and POS 8-1 for LPSD PRA (Sheet 2 of 3)

No Cutsets Percent Cutsets Frequency Basic Event Description Freq. (/ry) probability 5

5.3E-09 4.8

!LOCA8-1 1.6E-04 LOSS OF COOLANT ACCIDENT - POS8-1 (in POS8-I)

RSSOOO2LINE+P 3.8E-03 (HE) FAIL TO ESTABLISH RHR INJECTION LINE AND START STANBY PUMP SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP CHIOO02RWS-DP3 1.6E-01 (HE) FAIL TO REFILL RWSAT WATER FROM RWSP GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 6

3.6E-09 3.3

!LOCA8-1 1.6E-04 LOSS OF COOLANT ACCIDENT - POS8-1 (in P058-I)

LOA0002LC 2.6E-03 (HE) FAIL TO ISOLATE THE LEAKAGE TRAIN OF RHR SYSTEM HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP CHIOOO2P+RWS-DP3 1.6E-01 (HE) FAIL TO START STANDBY CHARGING PUMP AND REFILL RWSAT WATER FROM RWSP GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 7

3.4E-09 3.1

!LORH8-1 1.OE-05 LOSS OF RHR CAUSED BY OTHER FAILURES - POS8-1 (in POS8-1)

HPIOO02S 4.9E-03 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG CHIOOO2P+RWS-DP2 6.8E-02 (HE) FAIL TO START STANDBY CHARGING PUMP AND REFILL RWSAT WATER FROM RWSP GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 8

3.2E-09 2.9

!LOCA4-3 9.7E-05 LOSS OF COOLANT ACCIDENT - POS4-3 (in POS4-3)

RSSOOO2LINE+P 3.8E-03 (HE) FAIL TO ESTABLISH RHR INJECTION LINE AND START STANBY PUMP SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP CHIOO02RWS-DP3 1.6E-01 (HE) FAIL TO REFILL RWSAT WATER FROM RWSP GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION

Table 19.493-7 Dominant Cutsets of POS 4-3 and POS 8-1 for LPSD PRA (Sheet 3 of 3)

NoF Cutsets Percent Cutsets FrequencyBasic Event Description Freg. (/ry) probability 9

2.6E-09 2.3

!LOOP4-3 4.OE-04 LOSS OF OFFSITE POWER - POS4-3 CLASS-1E GTG A,B,C, D FAIL TO LOAD AND RUN AFTER (in P0S4-3)

EPSCF4DLLRGTG-ALL 9.9E-04 FISHORFOPATN(C)

FIRST HOUR OF OPERATION (CCF)

EPSOO02RDG 2.1E-02 (HE) FAIL TO CONNECT THE ALTERNATE AC POWER SOURCE TO CLASS 1 E BUS ACRPOS4-3-F 3.1E-01 FAILURE OF OFFSITE POWER RECOVERY (POS4-3) 10 2.1E-09 1.9

!LOCA4-3 2.6E-07 LOSS OF COOLANT ACCIDENT-POS4-3 LOAOO02LC 2.6E-03 (HE) FAIL TO ISOLATE THE LEAKAGE TRAIN OF RHR SYSTEM HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP CHIOO02RWS-DP3 1.6E-01 (HE) FAIL TO REFILL RWSAT WATER FROM RWSP GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION Co

Co r..3 Table 19.493-8 Dominant Cutsets of LOCA Sequence No.10 of POS 8-1 (Sheet 1 of 2)

[1CutsetsFrqec/

No Freq/

Percent Cutsets pFrequency Basic Event Description LiFreq. (Iry)

___________jprobability 1

2.3E-08 89.8

!LOCA8-1 1.6E-04 LOSS OF COOLANT ACCIDENT - POS8-1 CHIOO02P 2.6E-03 (HE) FAIL TO START STANDBY CHARGING PUMP GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG 2

1.6E-09 6.3

!LOCA8-1 1.6E-04 LOSS OF COOLANT ACCIDENT - POS8-1 CHIPMBD001A 2.OE-03 CVS-MPP-001A (A-CHI PUMP) FAIL TO START GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION HP10002S 4.9E-03 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG 3

1.1E-10 0.43

!LOCA8-1 1.6E-04 LOSS OF COOLANT ACCIDENT - POS8-1 CHICF2MVCDO31 BC-ALL I.4E-04 CVS-LCV-031B,C FAIL TO CLOSE (CCF)

GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION HPIOO02S 4.9E-03 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG 4

9.5E-1 1 0.38

!LOCA8-1 1.6E-04 LOSS OF COOLANT ACCIDENT - POS8-1 CHIPMYR001A 1.2E-04 CVS-MPP-001A (A-CHI PUMP) FAIL TO RUN GI 1.0E+00 GUARANTEED FAILURE OF GRAVITY INJECTION HPIOO02S 4.9E-03 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG 5

9.OE-1 1 0.36

!LOCA8-1 1.6E-04 LOSS OF COOLANT ACCIDENT - POS8-1 CHICF4MVOD031-ALL 1.1 E-04 CVS-LCV-031D,E,F,G FAIL TO OPEN (CCF)

GI 1.0E+00 GUARANTEED FAILURE OF GRAVITY INJECTION HP10002S 4.9E-03 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG

(0 (0

Table 19.493-8 Dominant Cutsets of LOCA Sequence No.10 of POS 8-1 (Sheet 2 of 2) uesCutsets Frequency Basic Event Description No Freq. (/ry)

P uses probability 6

7.9E-1 1 0.31

!LOCA8-1 1.6E-04 LOSS OF COOLANT ACCIDENT - POS8-1 SGNBTSWCCF1 1.OE-04 GROUP-1 APPLICATION SOFTWARE CCF GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION HPIOO02S 4.9E-03 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG 1.0E+00 SG 7

6.3E-1 1 0.25

!LOCA8-1 1.6E-04 LOSS OF COOLANT ACCIDENT - POS8-1 CHIOO02P 2.6E-03 (HE) FAIL TO START STANDBY CHARGING PUMP GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION HPICF2PMAD001AC-ALL 1.5E-04 SIS-MPP-001A,C (SI PUMP) FAIL TO START (CCF)

GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG 1.0E+00 S

SG 8

5.7E-1 1 0.23

!LOCA8-1 1.6E-04 LOSS OF COOLANT ACCIDENT - POS8-1 CHIAVFC048 7.2E-05 CVS-FCV-048 FAIL TO CONTROL GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION HPIOO02S 4.9E-03 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG 1.OE+00 SG 9

5.OE-1 1 0.2

!LOCA8-1 1.6E-04 LOSS OF COOLANT ACCIDENT - POS8-1 SDLOCA 1.OE-04 LOSS OF COOLANT ACCIDENT CHIPMBDO01A 2.OE-03 CVS-MPP-001A (A-CHI PUMP) FAIL TO START GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION HPICF2PMAD001AC-ALL 1.5E-04 SIS-MPP-001A,C (SI PUMP) FAIL TO START (CCF) 10 1.9E-1 1 0.08

!LOCA8-1 1.6E-04 LOSS OF COOLANT ACCIDENT - POS8-1 SWSCF3PMYRO01ABC-ALL 1.2E-07 EWS-MPP-001A,B,C (ESW PUMP) FAIL TO RUN (CCF)

GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG

CO CO C~)

Table 19.493-9 Dominant Cutsets of LOOP Sequence No.6 of POS 8-1 (Sheet 1 of 3)

No Cutsets Percent Cutsets Frequency Basic Event Description Freq. (/ry) probability 1

1.5E-08 85.2

!LOOP8-1 6.7E-04 LOSS OF OFFISTE POWER - POS8-1 RSSOO02P 2.6E-03 (HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN THE LOOP EVENT OCCURS SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP CHIOO02P+RWS-DP3 1.6E-01 (HE) FAIL TO START STANDBY CHARGING PUMP AND REFILL RWSAT WATER FROM RWSP GI 1.0E+00 GUARANTEED FAILURE OF GRAVITY INJECTION 2

1.9E-10 1.1

!LOOP8-1 6.7E-04 LOSS OF OFFISTE POWER - POS8-1 RSSOO02P 2.6E-03 (HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN THE LOOP EVENT OCCURS SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP CHIPMBDO01A 2.OE-03 CVS-MPP-001A (A-CHI PUMP) FAIL TO START GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 3

8.1E-11 0.46

!LOOP8-1 6.7E-04 LOSS OF OFFISTE POWER - POS8-1 SWSCF3PMYR001ABC-ALL 1.2E-07 EWS-OPP-001A,B,C (ESW PUMP) FAIL TO RUN (CCF)

SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 4

7.5E-1 1 0.43

!LOOP8-1 6.7E-04 LOSS OF OFFISTE POWER - POS8-1 RSSOO02P 2.6E-03 (HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN THE LOOP EVENT OCCURS SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP RWSOO04XV051 8.OE-04 (HE) MISALIGNMENT OF RWS-VLV-051 AFTER TEST OR MAINTENANCE GI 1.0E+00 GUARANTEED FAILURE OF GRAVITY INJECTION

(0 0'1 Table 19.493-9 Dominant Cutsets of LOOP Sequence No.6 of POS 8-1 (Sheet 2 of 3)

Freq.

(ry) rFrobabiliy No Cutsets Percent Cutsets Frequency Basic Event Description NoFreq. (/ry) probability 5

6.5E-1 1 0.38

!LOOP8-1 6.7E-04 LOSS OF OFFISTE POWER - POS8-1 RSSOO02P 2.6E-03 (HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN THE LOOP EVENT OCCURS SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP RWSXVOD021 7.OE-04 RWS-VLV-021 FAIL TO OPEN GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 6

6.5E-1 1 0.38

!LOOP8-1 6.7E-04 LOSS OF OFFISTE POWER - POS8-1 RSSOO02P 2.6E-03 (HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN THE LOOP EVENT OCCURS SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP RWSXVOD052 7.OE-04 RWS-VLV-052 FAIL TO OPEN GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 7

5.7E-1 1 0.33

!LOOP8-1 6.7E-04 LOSS OF OFFISTE POWER - POS8-1 EPSCF3DLLRGTG-23 5.1 E-04 CLASS-1E GTG A,B,C FAIL TO LOAD AND RUN AFTER FIRST HOUR OF OPERATION (CCF)

SWSSTPRST003A 1.7E-04 EWS-SST-003A (STRAINER) PLUG SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 8

4.5E-1 1 0.26

!LOOP8-1 6.7E-04 LOSS OF OFFISTE POWER - POS8-1 CWSCF3PCYR001ABC-ALL 6.7E-08 NCS-MPP-001A,B,C (CCW PUMP) FAIL TO RUN (CCF)

SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION

Table 19.493-9 Dominant Cutsets of LOOP Sequence No.6 of POS 8-1 (Sheet 3 of 3)

Cutsets Percent T Cutsets Frequency Basic Event Description No Freq. (/ry) probability 9

4.1 E-1 1 0.23

!LOOP8-1 6.7E-04 LOSS OF OFFISTE POWER - POS8-1 CLASS-1E GTG A,B,C FAIL TO LOAD AND RUN AFTER FIRST HOUR OF OPERATION (CCF)

SWSPMYR001A-ABC 1.2E-04 EWS-MPP-001A (A-EWS PUMP) FAIL TO RUN SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 10 3.3E-11 0.19

!LOOP8-1 6.7E-04 LOSS OF OFFISTE POWER - POS8-1 A-CLASS 1E GTG FAIL TO LOAD AND RUN AFTER FIRST EPSDLLREGTGA-ABC 1.9E-02 HORFOPATN HOUR OF OPERATION EPSOO02RDG 2.1E-02 (HE) FAIL TO CONNECT THE ALTERNATE AC POWER SOURCE TO CLASS 1 E BUS RSS0002P 2.6E-03 (HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN THE LOOP EVENT OCCURS SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION CD 0'0

Co Co

-1 Table 19.493-10 Dominant Cutsets of LOOP Sequence No.6 of POS 4-3 (Sheet 1 of 3)

NoCutsets Percent Cutsets Frequency Basic Event Description Freq. (/ry) probability 1

8.9E-09 86.8

!LOOP4-3 4.OE-04 LOSS OF OFFISTE POWER - POS4-3 RSSOO02P 2.6E-03 (HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN THE LOOP EVENT OCCURS SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP CHIOO02P+RWS-DP3 1.6E-01 (HE) FAIL TO START STANDBY CHARGING PUMP AND REFILL RWSAT WATER FROM RWSP GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 2

4.8E-1 1 0.5

!LOOP4-3 4.OE-04 LOSS OF OFFISTE POWER - POS4-3 SWSCF4PMYR001-ALL 1.2E-07 EWS-MPP-001A,B,C,D (EWS PUMP) FAIL TO RUN (CCF)

SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 3

4.5E-1 1 0.44

!LOOP4-3 4.OE-04 LOSS OF OFFISTE POWER - POS4-3 RSSOO02P 2.6E-03 (HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN THE LOOP EVENT OCCURS SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP RWSOO04XV051 8.OE-04 (HE) MISALIGNMENT OF RWS-VLV-051 AFTER TEST OR MAINTENANCE GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 4

3.9E-1 1 0.38

!LOOP4-3 4.OE-04 LOSS OF OFFISTE POWER - POS4-3 RSSOO02P 2.6E-03 (HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN THE LOOP EVENT OCCURS SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP RWSXVOD021 7.OE-04 RWS-VLV-021 FAIL TO OPEN GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION

Table 19.493-10 Dominant Cutsets of LOOP Sequence No.6 of POS 4-3 CSheet 2 of 3D Co No No Cutsets Percent Cutsets Frequency /Basic Event Description Freq. (try) probability 5

3.9E-1 1 0.38

!LOOP4-3 4.OE-04 LOSS OF OFFISTE POWER - POS4-3 RSS0002P 2.6E-03 (HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN THE LOOP EVENT OCCURS SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HP10002S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP RWSXVOD052 7.OE-04 RWS-VLV-052 FAIL TO OPEN GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 6

2.7E-1 1 0.26

!LOOP4-3 4.OE-04 LOSS OF OFFISTE POWER - POS4-3 CWSCF4PCYR001-ALL 6.7E-08 NCS-MPP-001A,B,C,D (CCW PUMP) FAIL TO RUN (CCF)

SG 1.0E+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 7

2.0E-1 1 0.19

!LOOP4-3 4.OE-04 LOSS OF OFFISTE POWER - POS4-3 EPSCBFO52UAT-D 3.5E-04 EPS 52/UATD (BREAKER) FAIL TO OPEN RSS0002P 2.6E-03 (HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN THE LOOP EVENT OCCURS SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 8

2.OE-1 1 0.19

!LOOP4-3 4.0E-04 LOSS OF OFFISTE POWER - POS4-3 EPSCBFO52RAT-D 3.5E-04 EPS 52/RATD (BREAKER) FAIL TO OPEN RSS0002P 2.6E-03 (HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN THE LOOP EVENT OCCURS SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION

(0D (0.

(A, r%)O Table 19.493-10 Dominant Cutsets of LOOP Sequence No.6 of POS 4-3 (Sheet 3 of 3)

No Cutsets P

r Frequency Basic Event Description

[o Freq. (/ry)

Percent Cutsets probability B

9 1.9E-1 1 0.19

!LOOP4-3 4.OE-04 LOSS OF OFFISTE POWER - POS4-3 EPSDLLREGTGD-ABCD 1.9E-02 D-CLASS 1E GTG FAIL TO LOAD AND RUN AFTER FIRST HOUR OF OPERATION EPSOO02RDG 2.1E-02 (HE) FAIL TO CONNECT THE ALTERNATE AC POWER SOURCE TO CLASS 1E BUS RSSOO02P 2.6E-03 (HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN THE LOOP EVENT OCCURS SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG HPIOO02S-DP2 5.5E-02 (HE) FAIL TO START STANDBY SAFETY INJECTION PUMP GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION 10 1.9E-11 0.19

!LOOP4-3 4.OE-04 LOSS OF OFFISTE POWER-POS4-3 EPSDLLREGTGB-ABCD 1.9E-02 B-CLASS 1E GTG FAIL TO LOAD AND RUN AFTER FIRST HOUR OF OPERATION EPSDLLREGTGC-ABCD 1.9E-02 C-CLASS 1E GTG FAIL TO LOAD AND RUN AFTER FIRST HOUR OF OPERATION RSSOO02P 2.6E-03 (HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN THE LOOP EVENT OCCURS SG 1.OE+00 GUARANTEED FAILURE OF DECAY HEAT REMOVAL BY SG CHIOO02P+RWS-DP2 6.8E-02 (HE) FAIL TO START STANDBY CHARGING PUMP AND REFILL RWSAT WATER FROM RWSP GI 1.OE+00 GUARANTEED FAILURE OF GRAVITY INJECTION

C,o (0

C>o Table 19.493-11 Basic Event FV Importance of POS 4-3 (Sheet 1 of 2)

Basic Event F

A No Basic Event ID Basic Event Description baii Ety FVW 1

HPIOO02S-DP2 (HE) FAIL TO START STANDBY SAFETY INJECTION 5.5E-02 5.OE-01 9.6E+00 PUMP 2

RSS0002P (HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN 2.6E-03 3.3E-01 1.3E+02 THE LOOP EVENT OCCURS 3

CHIOOO2P+RWS-DP3 (HE) FAIL TO START STANDBY CHARGING PUMP AND 1.6E-01 3.OE-01 2.6E+00 3__ C+REFILL RWSAT WATER FROM RWSP 4

ACRPOS4-3-F FAILURE OF OFFSITE POWER RECOVERY (POS4-3) 3.1E-01 2.OE-01 1.5E+00 5

CHIOO02RWS-DP3 (HE) FAIL TO REFILL RWSAT WATER FROM RWSP 1.6E-01 1.8E-01 2.OE+00 6

HP10002S (HE) FAIL TO START STANDBY SAFETY INJECTION 4.9E-03 1.6E-01 3.5E+01 PUMP 7

(HE) FAIL TO CONNECT THE ALTERNATE AC POWER 2.1E-02 1.4E-01 7.6E+00 EPSOO02RDG SOURCE TO CLASS 1E BUS 8

RSSOO02LINE+P (HE) FAIL TO ESTABLISH RHR INJECTION LINE AND 3.8E-03 1.1E-01 3.OE+01 START STANBY PUMP 9

EPSCF4DLLRGTG-ALL CLASS-1E GTG A,B,C, D FAIL TO LOAD AND RUN 9.9E-04 1.1E-01 1.1E+02 EPSCF4DLLRGTG-ALL AFTER FIRST HOUR OF OPERATION (CCF) 10 LOA0002LC (HE) FAIL TO ISOLATE THE LEAKAGE TRAIN OF RHR 2.6E-03 7.4E-02 3.OE+01 10 LASYSTEM 11 SGNBTSWCCF3 NON-SAFETY (PSMS) APPLICATION SOFTWARE CCF 1.OE-05 5.3E-02 5.3E+03 12 CHIOO02RWS-DP2 (HE) FAIL TO REFILL RWSAT WATER FROM RWSP 6.7E-02 5.3E-02 1.7E+00 13 CVCAVCD024C RHS-AOV-024C FAIL TO CLOSE 1.2E-03 4.9E-02 4.2E+01 14 CVCAVCDO24B RHS-AOV-024B FAIL TO CLOSE 1.2E-03 4.9E-02 4.2E+01

Co Co CA, Table 19.493-11 Basic Event FV Importance of POS 4-3 (Sheet 2 of 2)

No Basic Event ID Basic Event Description Basic Event FV RAW 15 ACW0002SC (HE) FAIL TO ESTABLISH THE ALTERNATE CCWS BY 2.2E-02 4.9E-02 3.2E+00 FIRE PROTECTION WATER SUPPLY SYSTEM 16 EPSCF4DLADGTG-ALL CLASS-1E GTG A,B,C,D FAIL TO START (CCF) 2.1E-04 2.2E-02 1.1E+02 17 SWSCF4PMBD001-ALL EWS-MPP-001A,B,C,D (EWS PUMP) FAIL TO RE-START 4.8E-05 2.1E-02 4.3E+02 (CCF) 18 EPSCF4DLSRGTG-ALL CLASS-1E GTG A,B,C, D FAIL TO LOAD AND RUN 1.6E-04 1.7E-02 1.1E+02 DURING FIRST HOUR OF OPERATION (CCF) 19 CWSCF4PCBD001-ALL NCS-MPP-001A,B,C,D (CCW PUMP) FAIL TO RE-START 2.6E-05 1.1E-02 4.3E+02 (CCF) 20 ACRPOS4-3-S SUCCESS OF OFFSITE POWER RECOVERY (POS4-3) 6.9E-01 1.OE-02 1.OE+00 21 EPSDLLRAACB B-AAC FAIL TO LOAD AND RUN AFTER FIRST HOUR OF 1.8E-02 9.9E-03 1.6E+00 OPERATION 22 EPSCF2DLLRAAC-ALL AAC A,B FAIL TO RUN AFTER FIRST HOUR OF 1.5E-03 9.8E-03 7.7E+00 OPERATION (CCF) 23 CHIOOO2P+RWS-DP2 (HE) FAIL TO START STANDBY CHARGING PUMP AND 6.8E-02 8.1E-03 1.1E+00 I

REFILL RWSAT WATER FROM RWSP 24 CH10001 RECOV (HE) FAIL TO START CHARGING PUMP AND SAFETY 5.8E-02 7.5E-03 1.1E+00 INJECTION PUMP - LOCAL ACTION 25 SGNBTSWCCF1 GROUP-1 APPLICATION SOFTWARE CCF 1.OE-04 6.4E-03 6.5E+01 26 EPSDLLREGTGD-ABCD D-CLASS 1E GTG FAIL TO LOAD AND RUN AFTER 1.7E-02 6.OE-03 1.4E+00 FIRST HOUR OF OPERATION 27 EPSDLLREGTGB-ABCD B-CLASS 1E GTG FAIL TO LOAD AND RUN AFTER 1.7E-02 5.8E-03 1.3E+00 FIRST HOUR OF OPERATION 28 SWSCF4MVOD503-ALL EWS-MOV-503A,B,C,D FAIL TO OPEN (CCF) 1.3E-05 5.4E-03 4.3E+02

Table 19.493-12 Basic Event RAW of POS 4-3

_(Sheet 1 of 2)

No Basic Event ID Basic Event Description Basic Event FV RAW 1

RTPBTSWCCF BASIC SOFTWARE CCF 1.OE-07 2.5E-03 2.5E+04 2

SWSCF4PMYRO01-ALL EWS-MPP-001A,B,C,D (EWS PUMP) FAIL TO RUN 1.2E-07 1.6E-03 1.4E+04 (CCF) 3 CWSCF4PCYRO01-ALL NCS-MPP-001A,B,C,D (CCW PUMP) FAIL TO RUN 6.7E-08 9.1E-04 1.4E+04 (CCF) 4 CWSCF4RHPF001-ALL NCS-MHX-001A,B,C.D (CCW HX) PLUG / FOUL(CCF) 1.8E-08 2.5E-04 1.4E+04 5

EPSCF4CBSO52STH-ALL EPS 52/STHA,B,C,D (BREAKER) SPURIOUS OPEN 1.6E-07 2.2E-03 1.4E+04 (CCF) 6 EPSCF4CBSO52STL-ALL EPS 52/STLA,B,C,D (BREAKER) SPURIOUS OPEN 1.6E-07 2.2E-03 1.4E+04 (CCF) 7 EPSCF4CBSO52LC-ALL EPS 52/LCA,B,C,D (BREAKER) SPURIOUS OPEN 1.6E-07 2.1E-03 1.4E+04 E(CCF) 1602E-1.+

8 SGNBTSWCCF3 NON-SAFETY (PSMS) APPLICATION SOFTWARE CCF 1.OE-05 5.3E-02 5.3E+03 9

EPSCF4CBSC52RAT-ALL EPS 52/RATA,B,C,D (BREAKER) SPURIOUS CLOSE 1.6E-07 6.6E-04 4.2E+03 (CCF) 1606E-4.+

10 EPSCF4CBSC52UAT-ALL EPS 52/UATA,B,C,D (BREAKER) SPURIOUS CLOSE 1.6E-07 6.6E-04 4.2E+03 10 (CCF)

I6-7.E0 co Co N)

Table 19.493-12 Basic Event RAW of POS 4-3 (Sheet 2 of 2)

,Basic Event FV No1 Basic Event ID Basic Event Description Probability Importance RAW 11 CWSCF4RHPF-FF NCS-MHX-001A,B,C,D (A,B,C,D-CCW HX) PLUG /

3.6E-08 1.3E-04 3.5E+03 FOUL (CCF) 12 SWSCF4PMYR-FF EWS-MPP-001A,B,C,D (A,B,C,D-EWS PUMP) FAIL 1.2E-08 4.2E-05 3.5E+03 TO RUN (CCF) 13 CWSCF4PCYR-FF NCS-MPP-001A,B,C,D (A,B,C,D-CCW PUMP) FAIL 6.7E-09 2.3E-05 3.5E+03 TO RUN (CCF) 14 EPSCF4CBSO52STL-234 EPS 52/STLA,B,C,D (BREAKER) SPURIOUS OPEN 2.9E-08 1.9E-05 6.5E+02 (CCF) 15 EPSCF4CBSO52STH-1 34 EPS 52/STHA,B,C,D (BREAKER) SPURIOUS OPEN 2.9E-08 1.9E-05 6.5E+02 (CCF) 16 EPSCF4CBSO52LC-134 EPS 52/LCA,B,C,D (BREAKER) SPURIOUS OPEN 2.9E-08 1.8E-05 6.2E+02 (CCF) 17 CWSCF4RHPF001-134 NCS-MHX-001A,B,C.D (CCW HX) PLUG / FOUL(CCF) 6.OE-09 3.4E-06 5.7E+02 18 EPSCF4CBSO52STH-1 24 EPS 52/STHA,B,C,D (BREAKER) SPURIOUS OPEN 2.9E-08 1.5E-05 5.OE+02 18__

EPSCF4CBSO52STH-124_

(CCF) 19 EPSCF4CBSO52STL-134 EPS 52/STLA,B,C,D (BREAKER) SPURIOUS OPEN 2.9E-08 1.5E-05 5.0E+02 (CCF) 20 EPSCF4CBSO52LC-124 EPS 52/LCA,B,C,D (BREAKER) SPURIOUS OPEN 2.9E-08 1.4E-05 4.8E+02

,(CCF) 1__1 C,.,o C.)

CD CD Table 19.493-13 Basic Event FV Importance of POS 8-1 (Sheet 1 of 2)

No 7

Basic Event ID Basic Event Description Basic Event Imprance AW 1

HPIOO02S-DP2 (HE) FAIL TO START STANDBY SAFETY INJECTION 5.46E-02 6.0E-01 1.1E+01 PUMP 2

CHIOO02P (HE) FAIL TO START STANDBY CHARGING PUMP 2.55E-03 2.9E-01 1.1 E+02 3

CHIOOO2P+RWS-DP3 (HE) FAIL TO START STANDBY CHARGING PUMP AND 1.59E-01 2.3E-01 2.2E+00 REFILL RWSAT WATER FROM RWSP 4

(HE) FAIL TO RE-START THE CS/RHR PUMPS WHEN 2.55E-03 2.OE-01 7.8E+01 4 RSSOO02P THE LOOP EVENT OCCURS 5

ACRPOS8-1-F FAILURE OF OFFSITE POWER RECOVERY (POS8-1) 1.29E-01 1.2E-01 1.8E+00 6

ACW0002SC (HE) FAIL TO ESTABLISH THE ALTERNATE CCWS BY 2.21E-02 1.OE-01 5.5E+00 FIRE PROTECTION WATER SUPPLY SYSTEM 7

(HE) FAIL TO START STANDBY SAFETY INJECTION 4.88E-03 9.1E-02 2.OE+01 7 HPIOO02S PUMP 8

(HE) FAIL TO ESTABLISH RHR INJECTION LINE AND 3.79E-03 6.8E-02 1.9E+01 8

RSSOO02LINE+P START STANBY PUMP 9

CHIOO02RWS-DP3 (HE) FAIL TO REFILL RWSAT WATER FROM RWSP 1.58E-01 6.7E-02 1.4E+00 10 EPSCF3DLLRGTG-ALL CLASS-1E GTG A,B,C FAIL TO LOAD AND RUN AFTER 1.12E-03 6.7E-02 6.1E+01 FIRST HOUR OF OPERATION (CCF) 11 EPS0002RDG (HE) FAIL TO CONNECT THE ALTERNATE AC POWER 2.1OE-02 4.8E-02 3.2E+00 SOURCE TO CLASS 1 E BUS 12 LOAOO02LC (HE) FAIL TO ISOLATE THE LEAKAGE TRAIN OF RHR 2.55E-03 4.6E-02 1.9E+01 SYSTEM 13 CHIOOO2P+RWS-DP2 (HE) FAIL TO START STANDBY CHARGING PUMP AND 6.81E-02 4.4E-02 1.6E+00 REFILL RWSAT WATER FROM RWSP 14 EPSDLLRAACA A-AAC FAIL TO LOAD AND RUN AFTER FIRST HOUR 1.75E-02 3.9E-02 3.2E+00 OF OPERATION 15 CHIPMBDO01A CVS-MPP-001A (A-CHI PUMP) FAIL TO START 2.OOE-03 2.5E-02 1.4E+01 16 SWSCF3PMBD001ABC-ALL EWS-MPP-001A,B,C (ESW PUMP) FAIL TO RE-START 5.98E-05 1.6E-02 2.7E+02 (CCF)

I-I I

Co 0'1 Table 19.493-13 Basic Event FV Importance of POS 8-1

. (Sheet 2 of 2)

No Basic Event ID Basic Event Description Basic Event Imporance RAW I________________________

Probability Imprtnc 17 EPSCF3DLADGTG-ALL CLASS-1E GTG A,B,C FAIL TO START (CCF) 2.37E-04 1.4E-02 6.1E+01 18 SGNBTSWCCF1 GROUP-1 APPLICATION SOFTWARE CCF 1.OOE-04 1.2E-02 1.2E+02 19 SGNBTSWCCF3 NON-SAFETY (PSMS) APPLICATION SOFTWARE CCF 1.OOE-05 1.2E-02 1.2E+03 20 ACRPOS8-1-S SUCCESS OF OFFSITE POWER RECOVERY (POS8-1) 8.71 E-01 1.1E-02 1.OE+00 21 EPSDLLREGTGC-ABC C-CLASS 1E GTG FAIL TO LOAD AND RUN AFTER 1.69E-02 1.1E-02 1.6E+00 FIRST HOUR OF OPERATION 22 EPSCF3DLSRGTG-ALL CLASS-1E GTG A,B,C FAIL TO LOAD AND RUN 1.77E-04 1.1E-02 6.1E+01 DURING FIRST HOUR OF OPERATION (CCF) 23 EPSDLADAACA A-AAC FAIL TO START 4.70E-03 1.1 E-02 3.2E+00 24 CWSCF3PCBDO01ABC-ALL NCS-MPP-001A,B,C (CCW PUMP) FAIL TO RE-START 3.29E-05 8.7E-03 2.7E+02 (CCF) 25 EPSDLLREGTGA-ABC A-CLASS 1E GTG FAIL TO LOAD AND RUN AFTER 1.69E-02 8.OE-03 1.5E+00 FIRST HOUR OF OPERATION 26 EPSDLLREGTGB-ABC B-CLASS 1E GTG FAIL TO LOAD AND RUN AFTER 1.69E-02 7.7E-03 1.5E+00 FIRST HOUR OF OPERATION 27 CHIPMAD001A CVS-MPP-001A (A-CHI PUMP) FAIL TO START 1.50E-03 6.9E-03 5.6E+00 28 SWSCF3MVOD503ABC-ALL EWS-MOV-503A,B,C FAIL TO OPEN (CCF) 2.50E-05 6.6E-03 2.7E+02 29 EPSSEFFAACA A-AAC SEQUENCER FAIL TO OPERATE 2.86E-03 6.4E-03 3.2E+00 30 EPSDLSRAACA A-AAC FAIL TO LOAD AND RUN DURING FIRST HOUR 2.77E-03 6.2E-03 3.2E+00 OF OPERATION 31 CHIOO01RECOV (HE) FAIL TO START CHARGING PUMP AND SAFETY 5.83E-02 6.1E-03 1.1E+00 INJECTION PUMP - LOCAL ACTION 32 CHIOO02RWS-DP2 (HE) FAIL TO REFILL RWSAT WATER FROM RWSP 6.65E-02 6.1E-03 1.1E+00 33 EPSCBFO52RAT-ABC EPS 52/RATA,B,C (BREAKER) FAIL TO OPEN (CCF) 5.18E-06 5.6E-03 1.1E+03 341 EPSCBFO52UAT-ABC EPS 52/UATA,B,C (BREAKER) FAIL TO OPEN (CCF) 5.18E-06 5.6E-03 1.1E+03

Table 19.493-14 Basic Event RAW of POS 8-1 (Sheet I of 2)

Basic Event FV No Basic Event ID Basic Event Description Probability Importance RAW 1

RTPBTSWCCF BASIC SOFTWARE CCF 1.OOE-07 2.9E-03 2.9E+04 2

SWSCF3PMYRO01ABC-ALL EWS-OPP-001A,B,C (ESW PUMP) FAIL TO RUN (CCF) 1.20E-07 1.3E-03 1.1E+04 3

CWSCF3PCYRO01ABC-ALL NCS-MPP-001A,B,C (CCW PUMP) FAIL TO RUN (CCF) 6.72E-08 7.1 E-04 1.1 E+04 4

CWSCF3RHPF001ABC-ALL NCS-MHX-001A,B,C (CCW HX) PLUG / FOUL(CCF) 3.60E-08 3.8E-04 1.1E+04 5

EPSCF4CBSO52STH-ALL EPS 52/STHA,B,C,D (BREAKER) SPURIOUS OPEN (CCF) 1.58E-07 1.3E-03 8.4E+03 6

EPSCF4CBSO52STL-ALL EPS 52/STLA,B,C,D (BREAKER) SPURIOUS OPEN (CCF) 1.58E-07 1.3E-03 8.4E+03 7

EPSCF4CBSO52LC-ALL EPS 52/LCA,B,C,D (BREAKER) SPURIOUS OPEN (CCF) 1.58E-07 1.3E-03 8.3E+03 8

EPSCF4CBSO52STL-124 EPS 52/STLA,B,C,D (BREAKER) SPURIOUS OPEN (CCF) 2.92E-08 2.4E-04 8.3E+03 9

EPSCF4CBSO52STH-123 EPS 52/STHA,B,C,D (BREAKER) SPURIOUS OPEN (CCF) 2.92E-08 2.4E-04 8.3E+03 10 EPSCF4CBSO52LC-123 EPS 52/LCA,B,C,D (BREAKER) SPURIOUS OPEN (CCF) 2.92E-08 2.4E-04 8.3E+03 Co oD

Table 19.493-14 Basic Event RAW of POS 8-1 (Sheet 2 of 2)

No Basic Event ID Basic Event Description PBasic Event I

rFVc RAW 11 SGNBTSWCCF3 NON-SAFETY (PSMS) APPLICATION SOFTWARE CCF 1.OOE-05 1.2E-02 1.2E+03 12 EPSCBFO52RAT-ABC EPS 52/RATA,B,C (BREAKER) FAIL TO OPEN (CCF) 5.18E-06 5.6E-03 1.1E+03 13 EPSCBFO52UAT-ABC EPS 52/UATA,B,C (BREAKER) FAIL TO OPEN (CCF) 5.18E-06 5.6E-03 1.1E+03 14 EPSCF4CBSC52UAT-ALL EPS 52/UATA,B,C,D (BREAKER) SPURIOUS CLOSE 1.58E-07 1.7E-04 1.1E+03 (CCF) 15 EPSCF4CBSC52RAT-ALL EPS 52/RATA,B,C,D (BREAKER) SPURIOUS CLOSE 1.58E-07 1.7E-04 1.1E+03 (CCF) 16 EPSCF4CBSC52RAT-124 EPS 52/RATA,B,C,D (BREAKER) SPURIOUS CLOSE 2.92E-08 3.1E-05 1.1E+03 (CCF) 17 EPSCF4CBSC52UAT-123 EPS 52/UATA,B,C,D (BREAKER)

SPURIOUS CLOSE 2.92E-08 3.1E-05 1.1E+03 (CCF) 18 EPSCF4CBSO52STL-234 EPS 52/STLA,B,C,D (BREAKER) SPURIOUS OPEN (CCF) 2.92E-08 1.OE-05 3.5E+02 19 EPSCF4CBSO52STH-134 EPS 52/STHA,B,C,D (BREAKER) SPURIOUS OPEN (CCF) 2.92E-08 1.0E-05 3.5E+02 20 CWSCF3RHPF001ABC-13 NCS-MHX-001A,B,C (CCW HX) PLUG / FOUL(CCF) 1.80E-08 6.2E-06 3.5E+02 co

-4I

1 A.I A4-if_

I

_ II I __,

I,__

"II (0)

Center of MCP I

a',;

',4 i-I

• .----',/

CD0

______I\\

It _

Ii I

__.$-.--*t

1. Open SG Manhole on H/I side I11 Install SG Nozzle Dam on C/IL side.

1. Remove SG Nozzle Dam on H/L side

1. Close SG Manhole on C/L side F2. Open SG Manhole on C/L side

12. Install SG Nozzle Dam on H/L side

12. Remove SG Nozzle Dam on C/IL side

2. Close SG Manhole on H/L side l

I l

r I l l

I I

vi I

!___n__b vc Controlled by CVCS I

I Conrl b YI I

II i " i i!"

• I, I

I I,

l I

Performed Key Activities vG Drain I

I Vacuum Ventin Remove PSII I

InstallPSVs De-tensioning RV Head Stud Bots i IRemove RV He I

I I RvH Tensioning RV Head Stud I

Noe1uow l wi lo sig c

C mica an Vu C

as RemovelýS I

I I

l lnt!,CS Note 1: Automaitic isolation for low-pressure letdown line when Low signal actuates CVCS: Chemical and Volume Control System RV: Reactor Vessel Note 2: Initiation of gravity injection when Low-Low signal actuates PSV: Pressurizer Safety Vavle H/I: Hot Leg Note 3: Assumptiion that RCS level is at a center of MCP is used for estimation of allowable time for core uncovery ICIS: In-Core Instrumentation System C/L: Cold Leg MCP: Main Coolant Piping Figure 19.493-1 Schematic Images for Inspection considered in LPSD PRA

LORH 5.5%

FLML F5

'10.3%

LOOP

,*4

.4n1 LOCS 0o.170 2.8%

LOCA 20.3%

Figure 19.493-2 Core Damage Frequency Contribution in POS 4-3 19.493-39

OVDR LF 2.2%

LOOP LOCS JX/

10.0%

LOCA 43.3%

Figure 19.493-3 Core Damage Frequency Contribution in POS 8-1 19.493-40

FLML 2.3%

OVDR 1.4%

LOOP lk 47.8%

LOCS 12.4%

LOCA 32.1%

Figure 19.493-4 Core Damage Frequency Contribution in all POSs 19.493-41

1E-06 1 E-07 C

95%

8.3E-08 D

F 7

Mean 2.9E-08 r

Median 1.8E-08 Y

1E-08 5%

4.4E-09 1E-09 Figure 19.493-5 Uncertainty Analysis Results in POS 4-3 (CDF by point estimation is 3.OE-08/ry) 19.493-42

1 E-06 95%

2.3E-07 1 E-07 C

Mean 8.1 E-08 D

F Median 4.8E-08 r

Y 5%

1.3E-08 1 E-08 1 E-09 Figure 19.493-5 Uncertainty Analysis Results in POS 8-1 (CDF by point estimation is 8.OE-08/ry) 19.493-43

RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION 12/24/2010 US-APWR Design Certification Mitsubishi Heavy Industries Docket No.52-021 RAI NO.:

NO. 669-5219 REVISION 2 SRP SECTION:

19 - Probabilistic Risk Assessment and Severe Accident Evaluation APPLICATION SECTION:

19 DATE OF RAI ISSUE:

11/29/2010 QUESTION NO. : 19-494 The staff has reviewed MHI's response to RAI 19-442. Based on the US-APWR shutdown risk results on page 19.1-146 of the DCD, the shutdown CDF equals the shutdown LRF frequency.

No credit was given for containment closure in the risk assessment. In their response to RAI 19-442, MHI reported that the USAPWR shutdown CDF removing all equipment not required by TS to be 2.1 E-5 per reactor year. This result means that the LRF removing all equipment not required by Technical Specifications (TS) to be 2.1 E-5 per reactor year which exceeds the Commission's safety goals for new reactors. The staff concludes that voluntary initiatives must be implemented by the COL applicant for the USAPWR design to meet the Commission's safety goals. The staff is requesting MHI to consider adding shutdown TS in accordance with Criterion 4 of 1 OCFR50.36 (c)(2)(ii) so that this design meets the Commission's safety goals for new reactors without voluntary initiatives or justify in the DCD why these actions are not necessary.

ANSWER:

The RAI indicates that the sensitivity case described "means that the LRF removing all equipment not required by Technical Specifications (TS) to be 2.1E-5 per reactor year which exceeds the Commission's safety goals for new reactors."

This sensitivity case does not numerically take into account the low probability that all such equipment would actually be removed from service.

The likelihood that this would occur is low. This is a conditional CDF and not an actual CDF calculation.

As a result the LRF inference is a conditional LRF and not an LRF calculation??.

Further, the inference for LRF assumes no containment isolation, which is not evaluated in the sensitivity case.

Removing all equipment from service without evaluating plant safety would violate the maintenance rule.

While it is difficult to quantify such an action, it is at least two to three orders of magnitude or more below the sensitivity case.

It should not be compared to the safety goal without including this probability.

Taking into account the low probability of this condition existing results in high 19.494-1

confidence that the safety goal is met.

The maintenance rule implementation will assure that the safety in the design is preserved and that the safety goal is met.

Separate Technical Specifications for shutdown are not warranted.

Administrative controls will be adequate to assure that the safety goal remains met through all maintenance evolutions.

The question raised in RAI-442 quotes from SECY97-168 that the staff identified that, "a significant level of safety is dependent upon measures that are not traceable to specific undeHying regulations, and that could, therefore be withdrawn by the licensee without prior staff approval." This SECY was understood to have been written during consideration of a shutdown rule that the Commission elected not to issue.

It is further understood that this decision was in part based upon the effectiveness of the maintenance rule.

The SECY also states, "The shutdown operations section of the rule has been structured with the specific objectives of:

(1) reducing the frequency of events that can lead to loss of the decay heat removal

function, (2) assuring that mitigative equipment is available for those events that do occur (3) providing a measure of performance through monitoring of parameters that represent necessary safety functions, and (4) facilitating inspection and enforcement activities.

These goals are to be achieved through a combination of procedural, monitoring, and mitigation capability requirements. The proposed rule would require licensees to establish and implement procedures for training, quality assurance, and corrective actions to ensure that the safety functions of decay heat removal, inventory control, and pressure control are maintained and monitored, and that mitigation capability is provided.

The procedures would be described in the administrative controls section of the technical specifications. This would establish a clear regulatory requirement while allowing licensees flexibility in terms of implementing these programs. The proposed rule would also require licensees to monitor safety function performance and prescribes limits for each safety function. Licensees would choose the specific parameters, parameter limits and instrumentation to be used to demonstrate compliance with the safety function limits. These details would have to be maintained available for inspection in a licensee-controlled document. The criteria and methods used for selecting the parameters and parameter limits, however, would have to be described in the administrative controls section of the technical specifications.

The administrative controls section of the technical specifications will include a description of the implementation of the maintenance rule 10CFR50.65.

As paraphrased from the statement above, these details would be maintained available for inspection in a licensee-controlled document. This is further addressed in and is consistent with the SECY which states as follows:

(3) Mitigation Capability. Licensees shall maintain available a mitigation capability to provide adequate core cooling, decay heat removal, and sufficient protection against the uncontrolled release of fission products following the loss or interruption of decay heat removal during shutdown operation. The structures, systems, and components for complying with this section must be identified in a licensee-controlled document that is identified in the administrative controls section of the technical specifications. The criteria and method for licensee selection of the structures, systems, and components necessary for complying with this section must be described in the administrative controls section of technical specifications.

A COL applicant will describe the scoping of the maintenance rule which will include those SSCs that per the Rule, in part:

(b) The scope of the monitoring program specified in paragraph (a)(1) of this section shall include safety related and nonsafety related structures, systems, and components, as follows:

19.494-2

(1) Safety-related structures, systems and components that are relied upon to remain functional during and following design basis events to ensure the integrity of the reactor coolant pressure boundary, the capability to shut down the reactor and maintain it in a safe shutdown condition, or the capability to prevent or mitigate the consequences of accidents that could result in potential offsite exposure comparable to the guidelines in Sec. 50.34(a)(1), Sec. 50.67(b)(2), or Sec. 100. 11 of this chapter, as applicable.

(2) Nonsafety related structures, systems, or components:

(i) That are relied upon to mitigate accidents or transients or are used in plant emergency operating procedures (EOPs);

Containment closure is included under the scope of the Maintenance Rule.

SSCs supporting heat removal and inventory control are also included in the scope of the Maintenance Rule.

The Maintenance Rule further states, "(4) Before performing maintenance activities (including but not limited to surveillance, post-maintenance testing, and corrective and preventive maintenance), the licensee shall assess and manage the increase in risk that may result from the proposed maintenance activities. The scope of the assessment may be limited to structures, systems, and components that a risk-informed evaluation process has shown to be significant to public health and safety. "

The administrative controls section of the Technical Specifications will reference the procedures whereby these requirements are met.

Maintenance rule function will be addressed by administrative procedure prior to performing maintenance activities as required by 10CFR50.65.

The risk assessment will be either quantitative or qualitative, where a qualitative assessment if used is based upon a separate evaluation that considers quantitative insights and inputs.

The level. of risk will be determined and treated generally in risk categories, and controls related to the risk level will be implemented.

High risk evolutions will be limited and only performed with compensatory measures in place. Moderate risk evolutions will be controlled and limited as to duration.

Low risk evolutions will not be restricted.

The program description will include a description of the preservation of key safety functions and the management of the risk increment incurred by the evolution.

The determination of evolution risk level will be defined by the COL applicant and will include definitions for relative increases in CDF or LRF for the period of the maintenance activity.

That is, the implementation will select levels of short duration increased CDF or LRF and take appropriate actions to manage any risk increment incurred including steps to shorten the duration, provide compensatory measures, and assure critical or key system function for the evolution with due consideration of the regulations, the defense in depth, the safety margin, and the risk to be incurred.

Some compensatory measures are not quantifiable but are effective.

These are considered as well.

Relative increase levels such as factors of 2, 10, 20 or more above the baseline risk level are normally used to define thresholds for risk bands that are then used to define the appropriate risk management strategy. These are to be specified in the licensee controlled document to implement the maintenance rule.

Maintenance Rule implementation will include an expert panel and procedures to control its function.

19.494-3

Impact on DCD There is no impact on DCD.

Impact on R-COLA and S-COLA.

There is no impact on R-COLA and S-COLA.

Impact on PRA There is no impact on PRA.

19.494-4