ML20236M688

Forwards Request for Addl Info Re Braidwood Individual Plant Exam of External Events Submittal

ML20236M688
Person / Time
Site:	Braidwood
Issue date:	07/09/1998
From:	Stewart Bailey NRC (Affiliation Not Assigned)
To:	Kingsley O COMMONWEALTH EDISON CO.
References
TAC-M83593, TAC-M83594, NUDOCS 9807140206
Download: ML20236M688 (15)

Text

I July 9, 1998 Mr. Oliver D. Kingsley, President Nuclear Generation Group Commonwealth Edison Company Executive Towers West 111 1400 Opus Place, Suite 500 Downers Grove, IL 60515

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION REGARDING BRAIDWOOD INDIVIDUAL PLANT EXAMINATION OF EXTERNAL EVENTS (TAC NOS. M83593 AND M83594)

Dear Mr. Kingsley:

s By letter dated June 27,1997, Commonwealth Edison Company (Comed) submitted the Individual Plant Examination of Extemal Events (IPEEE) for Braidwood Station, Units 1 and 2. j During review of the submittal, the NRC staff identified the need for further information as I I

discussed in the enclosed request for additional information (RAI) related to the Fire; Seismic; and High Wind, Flood, and Other Extemal Events (HFO) areas of the Braidwood IPEEE. Please respond to the enclosed RAI within 60 days to support the staff's review schedule.

Sincerely, ORIG. SIGNED BY JOHN B. HICKMAN for Stewart N. Bailey, Project Manager j Project Directorate 111-2 i Division of Reactor Projects - lil/IV l Office of Nuclear Reactor Regulation Docket Nos. STN 50-456, STN 50-457

Enclosure:

As sisted cc w/ encl: See next page hh 'U "

Distribution:

Docket File PUBLIC PDill-2 r/f E. Adensam, EGA1 ACRS,T2E26 S. Richards C. Moore M. Jordan, Rill l S. Bailey OGC, O15B18 A. Rubin, RES '

'1 DOCUMENT NAME: G:CMNTSP\ BRAID \BRIPEEE.RAI Ta receive a copy of this document. Indicstente in x: "C" = Copy without enclosures "E" = Copy with enclosures *N" = No copy OFFICE PM:PDlil-2 E 4:FDI -Z lUD:PDill-2 C, l NAME SBAILEYMM Db4QDFfE SRICHARDS 4 ~

DATE 07/ 'f/98 07/ V /98

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07/ 9 /98 OFFICIAL RECORD COPY 9& _,

9807140206 900709 PDR ADOCK 05000456 P PDR _

L__ _____ _ _ _ _

an zuq p k UNITED STATES g j NUCLEAR REGULATORY COMMISSION WASHINGTON, D.c. 30666 4 001 o

%*****/ July 9, 1998 1

l ,

l Mr. Oliver D. Kingsley, President Nuclear Generation Group Commonwealth Edison Company Executive Towers West 111 1400 Opus Place, Suite 500 l Downers Grove,IL 60515

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION REGARDING BRAIDWOOD l

INDIVIDUAL PLANT EXAMINATION OF EXTERNAL EVENTS (TAC NOS. M83593 AND M83594)

Dear Mr. Kingsley:

By letter dated June 27,1997, Commonwealth Edison Company (Comed) submitted the l

Individual Plant Examination of Extemal Events (IPEEE) for Braidwood Station, Units 1 and 2.

l During review of the submittal, the NRC staffidentified the need for furtherinformation as l discussed in the enclosed request for additional information (RAI) related to the Fire; Selsmic; i

and High Wind, Flood, and Other Extemal Events (HFO) areas of the Braidwood IPEEE. Please l respond to the enclosed RAI within 60 days to support the staff's review schedule.

Sincerely, os ' Stewart N. Dailey, Project Manager Project Directorate 111-2 Division of Reactor Projects - lil/IV Office of Nuclear Reactor Regulation Docket Nos. STN 50-456, STN 50-457

Enclosure:

As stated cc w/ encl: See next page I

I l O. Kingsley Braidwood Station .

l Commonwealth Edison Company Units 1 and 2 cc:

Michael Miller, Esquire Ms. Lorraine Creek

Sidley and Austin RR 1, Box 182 One First National Plaza Manteno, Illinois 60g50 Chicago, Illinois 60603 Mr. Ron Stephens Regional Administrator lilinois Emergency Services & Disaster Agency U.S. NRC, Region lli 110 E. Adams Street 801 Warrenville Road Springfield, Illinois 62706 Lisle, Illinois 60532-4351 4 Chairman '

lilinois Department of Nuclear Safety Will County Board of Supervisors Office of Nuclear Facility Safety Will County Board Courthouse 1035 Outer Park Drive Joliet, Illinois 60434 Springfield, Illinois 62704 Attomey General Document Control Desk-Licensing 500 S. Second Street Commonwealth Edison Company Springfield, Illinois 62701 1400 Opus Place, Suite 400 Downers Grove, Illinois 60515 George L. Edgar Morgan, Lewis and Bochius Ms. C. Sue Hauser, Project Manager 1800 M Street, N.W.

Westinghouse Electric Corporation Washington, DC 20036 t Energy Systems Business Unit  !

Post Office Box 355 Commonwealth Edison Company Pittsburgh, Pennsylvania 15230 Braidwood Station Manager RR 1, Box 84 Joseph Gallo Bracoville, Illinois 60407 Gallo & Ross 1250 Eye St., N.W., Suite 302 Commonwealth Edison Company Washington, DC 20005 Site Vice President - Braidwood

, RR 1, Box 84

l. Ms. Bridget Little Rorem Braceville,IL 60407 Appleseed Coordinator 117 N. Linden Street Mr. David Helwig l Essex, Illinois 60g35 Senior Vice President i

Commonwealth Edison Company Howard A. Leamer Executive Towers West lli Environmental Law and Policy 1400 Opus Place, Suite g00 Center of the Midwest Downers Grove, IL 60515 35 East Wacker Dr., Suite 1300 Chicago, Illinois '0601 Mr. Gene H. Stanley PWR's Vice President U.S. Nuclear Regulatory Commission Commonwealth Edison Company Braidwood Resident inspectors Office Executive Towers West lll RR 1, Box 7g 1400 Opus Place, Suite g00 Braceville, Illinois 60407 Downers Grove,IL 60515

O. Kingsley Braidwood Station .

Commonwealth Edison Company Units 1 and 2 Commonwealth Edison Company Mr. Michael J. Wallace Reg. Assurance Supervisor - Braidwood Senior Vice President RR 1, Box 79 Commonwealth Edison Company l

Braceville, Illinois 60407 Executive Towers West lil i 1400 Opus Place, Suite 900 Mr. Steve Perry Downers Grove,IL 60515 BWR's Vice President i Commonwealth Edison Company

! Executive Towers West lil 1400 Opus Place, Suite 900 Downers Grove,IL 60515 Mr. Dennis Farrar Regulatory Services Manager Commonwealth Edison Company Executive Towers West 111 1400 Opus Place, Suite 500 ,

Downers Grove, IL 60515 l l

Ms. Irene Johnson, Licensing Director Nuclear Regulatory Services Commonwealth Edison Company Executive Towers West lil 1400 Opus Place, Suite 500 Downers Grove, IL 60515 '

i Request for Additional Information (RAI) on Braidwood Individual Plant Examination of Extemal Events (IPEEE) Submittal FIRE

1. The main control room (MCR) abandonment procedure (PRI-5) calls for several actions to be taken within the MCR after a decision to abandon has been made but before the MCR is actually abandoned (see page 4-68 of the submittal). These pre-abandonment actions effectively would place the plant in hot standby so that the remote shutdown i panels are only required to maintain hot standby and eventually achieve cold shutdown. i lt is unclear that the cited pre-abandonment functions will be possible given that (as l assumed in the analysis) an uncontrolled fire has been buming for at least 15 minutes, a thick smoke layer has developed in the MCR, and operators are being forced to abandon. It also appears that the submittal has not given consideration to the actions i required of the operators using remote actions should the cited pre-abandonment actions not be possible.

Please provide an analysis to demonstrate that the MCR pre-abandonment actions cited  !

in PRI-5 would be possible given the conditions that are assumed to exist at the time a decision to abandon the MCR would be made (i.e., the room has been filled with a dense  ;

smoke layer and the fire remains un-suppressed). This should include an assessment of  !

how long it will take the operators to complete the pre-abandonment actions once the  !

procedure is invoked including considerations of performance shaping factors to assess the operator actions that are needed to complete these procedures. Finally, provide an assessment of the impact on core damage frequency (CDF) if it is assumed that these pre-abandonment actions cannot be completed and the necessary actions must be completed from outside the MCR.

2. The analysis of MCR scenarios is considered optimistic and incomplete. Among the concerns identified in a review of the submittal are the following items; i

In determining the MCR panel fire frequency, the licensee partitioned the generic fire frequency into three separate areas for each unit: the MCR and two auxiliary electric equipment rooms (AEERs). As a result, the fire frequency was reduced by a factor of 26.8 in comparison to the Fire-induced Vulnerability Evaluation (FIVE) methodology (2/11 for the partitioning based on fire source and 31/151 based on the panel count).

The assumption that the Braidwood MCR is sufficiently unique in comparison lo general industry so as to warrant such partitioning has not been substantiated.

The submittal states that "no barrier exists between cabinets in the main control board,"

and yet, the horseshoe is treated as if it were made up of, apparently,14 individual panels (the submittal cites a total of 31 panels in the MCR, and 17 *back panels" not included in the main control board apparently leaving 14 in the " horseshoe"). The analysis assumed that the ventilation configuration will prevent the spread of fire from

" cubicle to cubicle" by preventing the accumulation of any localized hot layers within the panel (page 4-61, bullet item 10). This assumption has not been substantiated but has ENCLOSURE I

4 L_ _ . . _ _

l had a significant impact on the analysis. The analysis does include consideration of damage to either one or two adjacent panels in the

• horseshoe," but does not consider the potential for more extensive damage, possibly including loss of the entire main control boari due to an uncontrolbd fire. Presumably, while the likelihood of more severe fires might be low in comparison to the scenarios that were considered, the conditional core damage probabilities (CCDPs) may also be subriantially higher. Herice, the submittal rnay have heglected a significant potential risk contributor.

The analysis assumes a conditional probability of abandonment given a panel fire of 3.4E-3 based on the EPRI Fire PRA Ireptementation Guide. Among the factors inherently credited in this value is the presence of optimally placed, in-cabinet fire aetection. At Braidwood, area detection above the ceiling (pege 4-27) and ventilation duct detectors (page 4-61) are cited. There is no technical basis to support the assumption that human detection will be at least as effective as in-cabinet detectors (page 4-60). Given the location of smoke detectors at Braidwood, the value of 3.4E-3 may be optimistic.

The main control board (the " horseshoe") is cited as being connected directly to the ventilation exhaust system. Hence, it is assumed that even in the event of an uncontrolled fire in these panels, MCR abandonment would not be needed. This assumption has not been substantiated. It is not clear that the ventilation system can, in fact, p.~ event significant build-up of smoke in the MCR in the event of a severe fire in the

" horseshoe." Further, it is possiole that in uw event of a severe fire in the " horseshoe,"

sufficient damage to the available instrumentation and controls may be realized such that abandonment of the MCR may be necessary even if smoke build-up can be avoided.

This approach may have resulted in an optimistic treatment of the MCR abandonment scenarios because (1) the frequency of MCR abandonment events was reduced by a factor of approximately two by virtue of the elimination of the main control board panels from the fire frequencies for these events, and (2) the abandonment scenarios that were analyzed may not have considered the ability to achieve safe shutdown from the remote shutdown panels given damage to the critical instrumentation and control circuits housed in the

• horseshoe."

Please reassess the CDF contribution of fires in the MCR. The control room reassessment should include (1) a redetermination of fire frequencies without partitioning generic database fire events from the MCR to the AEERs, (2) an assessment of the potential for more extensive fire spread within the main control board, and (3) the potentiat for MCR fires leading to either MCR abandonment or non-abandonment and subsequent plant shutdown, their probabilities, and CDF contributions.

3.

The assessment of MCR abandonment scenarios has not included the consideration of potential fires outside the MCR that might force MCR abandonment. In particular, certain fires outside the MCR (as noted on page 4-67 of the submittal) might compromise a sufficient set of instrumentation and control circuits so as to force MCR abandonment.

Please discuss the potential for fires outside the MCR to lead to MCR abandonment and shutdown from the remote panels. An assessment of the CDF contribution from any

1

. . i such scenarios is also requested. In particular, the assessment should include the consideration of such scenarios arising from fires either in the cable spreading rooms (CSRs) or in the AEERs.

4. NUREG-1407, Section 4.2 and Appendix C, and Generic Letter 88-20, Supplement 4, request that documentation be submitted with the IPEEE submittal with regard to the fire risk scoping study (FRSS) issues, including the basis and assumptions used to address these issues, and a discussion of the findings and conclusions. NUREG-1407 also requests that evaluation results and potential improvements be specifically highlighted.

Control system interactions involving a combination of fire-induced failures and high

, probability random equipment failures were identified in the FRSS as potential contributors to fire risk.

The issue of control systems interactions is associated primarily with the potential that a fire in the plant (e.g., the MCR) might lead to potential control systems vulnerabilities.

Given a fire in the plant, the likely sources of control systems interactions are between the control room, the remote shutdown panel, and shutdown systems. Spedfic areas that have been identified as requiring attention in the resolution of this issue include:

(a) Electricalindependence of the remote shutdown control systems: The primary concern of control systems interactions occurs at plants that do not provide independent remote shutdown control systems. The electricalindependence of the remote shutdown panel and the evaluation of the level of indication and control of remote shutdown control and monitoring circuits need to be assessed.

(b). Loss of control equipment or power before transfer: The potential for loss of control power for certain control circuits as a result of hot shorts and/or blown fuses before transferring control from the MCR to remote shutdown locations needs to be assessed.

(c) Spurious actuation of components leading to component damage, loss-of-coolant accident (LOCA), or interfacing systems LOCA: The spurious actuation of one or more safety-related to safe-shutdown-related components as a result of fire-induced cable faults, hot shorts, or component failures leading to component damage, LOCA, or interfacing systems LOCA, prior to taking control from the remote shutdown panel, needs to be assessed. This assessment also needs to include the spurious starting and running of pumps as well as the spurious repositioning of valves.

(d) Total loss of system function: The potential for totalloss of system function as a result of fire-induced redundant component failures or electrical distribution l system (power source) failure needs to be addressed. j Please describe your remote shutdown capability, including the nature and location of the l shutdown station (s), as well as the types of control actions which can be taken from the  ;

remote panel (s). Describe how your procedures provide for transfer of control to the i remote station (s). Provide an evaluation of whether loss of control power due to hot j l

shorts and/or blown fuses could occur prior to transferring control to the remote shutdown location and identify the risk contribution of these types of failures (if these failures are screened, please provide the basis for the screening). Finally, provide an evaluation of whether spurious actuation of components as a result of fire-induced cable faults, hot shorts, or component failures could lead to component damage, a LOCA, or an interfacing systems LOCA prior to taking control from the remote shutdown panel (considering both spurious starting and running of pumps as well as the spurious repositioning of valves).

5. From the submittal it can not be determined whether hot shorts and spurious actuations have been considered as a failure mode for control or instrumentation cables. In particular, consideration should include the treatment of conductor-to-conductor shorts within a given cable. Hot shorts in control cables can simulate the closing of control switches leading, for example, to the repositioning of valves, spurious operation of motors and pumps, the shutdown of operating equipment, and permenent, unrecoverable damage to motor-operated valves (see information Notice 92-18). These types of faults might, for example, lead to a LOCA, diversion of flow within various plant systems, deadheading and failure of important pumps, premature or undesirable switching of pump suction sources, or undesirable equipment operations. For MCR abandonment scenarios, such spurious operations and actions may not be indicated at the remote shutdown panel (s), may not be directly recoverable from remote shutdown locations, or may lead to the loss of remote shutdown capability (e.g. through loss of shutdown panel power sources). In instrumentation circuits hot shorts may cause misleading plant readings potentially leading to inappropriate control actions or generation of actuation signals for emergency safeguard features.

Discuss to what extent these issues have been considered in the IPEEE (Information Notice 92-18 provided an example of the manner in which the motor of an MOV is damaged by a hot short). If they have not been considered, please provide an assessment of how inclusion of potential hot shorts and spurious actuations would impact the quantification of fire CDF in the IPEEE.

6. In the Braidwood submittalit is assumed that the heat release rate (HRR) from any electrical panel will be limited to 65 BTU /s. This value is cited as deriving from the EPRI Fire PRA Implementation Guide; however, in that document test results for the control cabinet HRR have been misinterpreted and have been inappropriately extrapolated.

Experiments on control panels have measured HRRs ranging from 23 to 1171 Btu /sec.

Considering the range of HRRs that could be applicable to different control cabinet fires, and to ensure that cabinet fire areas are not prematurely screened out of the analysis, a HRR in the mid-range of the currently available experimental data (e.g.,550 Btu /sec) should be used for the analysis. Also, since the cabinet HRR of 65 Btu /sec was used in the screening portion of the analysis, important contributors to risk could have been screened out.

Discuss the HRRs used in the assessment of electrical cabinet fires. Please provide a discussion of changes in the IPEEE fire assessment results if it is assumed that the heat release from a cabinet fire is increased to 550 Btu /sec.

l

)

1 Include a discussion of both the impact on screening results and on the detailed quantification of unscreened areas.

7. The heat loss factor (HLF) is defined as the fraction of energy released by a fire that is transferred to the enclosure boundaries. This is a key parameter in the prediction of component damage, as it determines the amount of heat available to the hot gas layer.

In FIVE, the HLF is modeled as being inversely related to the amount of heat required to cause a given temperature rise. Thus, for example, a larger HLF means that a larger amount of heat (due to a more severe fire, a longer burning time, or both) is needed to l cause a given temperature rise. It can be seen that if the value assumed for the HLF is l unrealistically high, fire scenarios can be improperly screened out. Figure A provides a i

representative example of how hot gas layer temperature predictions can change assuming different HLFs. Note that: 1) the curves are computed for a 1000 kW fire in a 10m x Sm x 4m compartment with a forced ventilation rate of 1130 cfm; 2) the FIVE-recommended damage temperature for qualified cable is 700*F for qualified cable and l 450*F for unqualified cable; and,3) the Society for Fire Protection Engineers (SFPE) curve in the figure is generated from a correlation provided in the SFPE Handbook (A.1).

Based on evidence provided by a 1982 paper by Cooper et al. [A.2], the EPRI Fire PRA i Implementation Guide recommends a HLF of 0.94 for fires with durations greater than five minutes and 0.85 for " exposure fires away from a wall and quickly developing hot l gas layers." However, as a general statement, this appears to be a misinterpretation of the results. Reference [A.2), which documents the results of multi-compartment fire experiments, states that the higher HLFs are associated with the movement of the hot gas layer from the buming compartment to adjacent, cooler compartments. Earlier in the experiments, where the hot gas layer is limited to the burning compartment, Reference

[A.2] reports much lower HLFs (on the order of 0.51 to 0.74). These lower HLFs are more appropriate when analyzing a single compartment fire, in summary, (a) hot gas layer predictions are very sensitive to the assumed value of the HLF; and (b)large HLFs cannot be justified for single-room scenarios based on the information referenced in the EPRI Fire PRA implementation Guide.

The submittal used a HLF of 0.94 in at least some of the analyses. In particular, this value is cited in conjunction with the multi-zone interaction analyses (page 4-56), but it is unclear what value was used in other (single rcom) scenario analyses.

For each scenario where the hot gas layer temperature was calculated, please specify the HLF value used in the analysis. In light of the preceding discussion, please either: j a) Justify the value used and discuss its effect on the identification of fire vulnerabilities, or b) repeat the analysis using a more justifiable value and provide the resulting change in scenario contribution to CDF.

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Time-Temperature Curves 900 1 < e 800. SFE e_. M = 0.70

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+ M = 0.85 E 600 + M = 0.94 x M = 0.99 300 200  ;

100 ~ .s:*wx x xm xm:x:x:xm x wxx x**#N

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b$k$$k$$$k0$$$$

l Time (s) i 1 _

Figure A.1 Sensitivity of the hot gas layer temperature predictions to the assumed heat loss factor.

References A.1 P.J. DiNenno, et al, eds., "SFPE Handbook of Fire Protection Engineering," 2nd Edition, National Fire Protection Association, p. 3-140,1995.

A.2 L. Y. Cooper, M. Harkleroad, J. Quintiere, W. Rinkinen, "An Experimental Study of Upper Hot Layer Stratification in Full-Scale Multiroom Fire Scenarios," ASME Journal of Heat Transfer,1Q4,741-749, November 1982.

8. Fire severity factors were used in the analysis of many fire compartments in the fire assessment. No source is cited, and values were not typically specified for a given scenario. The severity factors were used in scenarios where fire suppression was credited. Since the potential for a large fire is dependent upon fire suppression, there appears to be a significant possibility that the use of a fire severity factor, when fire suppression is explicitly modeled, takes double credit for suppression efforts.

For the scenarios where manual and/or automatic fire suppression and severity factors were credited, please explain why crediting both does not constitute redundant credit for suppression. Also, provide the bases for all of the fire severity factors used in the study.

9. Section 4.7.3.3.3.3 notes that unrated fire barriers have been credited in the fire study's multi-compartment analysis. Such assumptions can have a major impact on the screening of multi-compartment fires. Also from the discussions provided for multi-compartment fire scenarios (Section 4.7.3), it can not be determined that the potential for fire barrier failure due to fires in high-hazard areas (e.g., large spills of oil or other liquid fuel, oil filled transformers, large turbine fires) has been considered.

a) Please provide a discussion of the screening of multi-compartment fires. The discussion should include a description of the compartment, its boundaries, any penetrations, any fire protection system elements present, the ignition sources and combustibles, and the safe shutdown equipment targets and initiators.

b) Please provide an assessment of the potential that high hazard fire sources '

might lead to failure of fire barriers at Braidwood and the resulting CDF contribution from such scenarios.

10. The EPRI Fire PRA implementation Guide assumes that all enclosed ignition sources cannot lead to fire propagation or other damage. This can be an optimistic assumption for oil-filled transformers and high-voltage cabinets. The Guide also assumes that fire spread to adjacent cabinets cannot occur if the cabinets are separated by a double wall with an air gap or if the cabinet in which the fire originates has an open top. This can also be an optimistic assumption for high-voltage cabinets since an explosive breakdown of the electrical conductors may breach the integrity of the cabinet and allow fire to spread to combustibles located above the cabinet. For example, switchgear fires at Yankee-Rowe in 1984 and Oconee Unit 1 in 1989 both resulted in fire damage outside the cubicles.

Please provide the basis for the assumption and a discussion on how the specific enclosures were analyzed to ascertain that the assumption is applicable to them. For those cabinets determined not to be capable of fire confinement, and in light of the discussion above, please assess the impact of the propagation of cabinet fires on the fire CDF.

11. The submittalimplies that some plant areas had a CCDP of 1.0 (see page 4-57, Section 4.7.3.3.2.3, bullet item 2). There is no discussion of which areas are characterized by this value, or the corresponding screening / analysis results. Nominally, a fire area with a CCDP of 1.0 would be very important to fire risk.

Please identify any plant fire areas (excluding the MCR) where a CCDP of 1.0 has been calculated assuming the loss of all equipment in the area due to fire. For each such area, please describe in detail how the area CDF contribution of was calculated and the results.

12. In computing the extent of fire propagation and equipment damage for a given scenario, it is important that experimental results not be used out of context. Inappropriate use of experimental results (e.g., employing propagation times specific to a particular cable tray separation and exposure condition to fires involving cable trays with lesser 7

separation or more severe exposures) can lead to improper assessments of scenario importance. in the EPRI Fire PRA Implementation Guide the fire growth behavior recorded for a single SNL test is described. Braidwood appears to have utilized this test

, description as the basis for assessing fire growth and spread behavior of cable trays (see Section 4.4.3, second bullet item). However, the SNL test described in this reference involved fire propagation initiated by a fire in a single tray and in tne absence of any other exposure fire source. The scenarios being modeled at Braidwood involve l' exposure fires; hence, the SNL test is not relevant to these cases.

For each fire scenario in which experimental data were used to estimate the rate and extent of fire propagation, please: (a) indicate if FIVE (or similar) calculations were  !

l performed for the scenario and provide the results (fire growth and equipment damage) ,

l of these calculations; (b) indicate which experimental results were used and how they l l were utilized in the analysis; and, (c) justify the applicability of these experimental results

! to each of the scenarios being analyzed. The discussion of results applicability should I

compare the geometries, ignition sources, fuel type and loadings, ventilation  !

characteristics, and compartment characteristics of the experimental setup (s) with those of the scenario ofinterest.

13. In Sections 4.4.3 and 4.5.1 of the submittal, a delay of 20 minutes is assumed before cables in solid-bottom cable trays or enclosed risers can be damaged given any fire.

This was cited as being based on Appendix J of the EPRI Fire PRA Implementation Guide. A review of that reference reveals that the SNL tests cited as supporting this assumption are not representative of the scenarios being modeled at Braidwood. In particular, the Braidwood scenarios involve substantial and sustained external exposure i fires whereas the cited SNL tests do not (the SNL tests used intermittent burners and in the two-tray tests, a solid non-combustible barrier was placed between the two trays

, during the burner operation). Those few tests performed by SNL with continuous exposure fires and no supplemental tray-to-tray barriers did not include testing of solid-bottom trays. For those barriers and coatings that were tested under such conditions, a significantly poorer performance was noted in all cases as compared to the performance noted in exposures similar to the conditions used in the solid-bottom tray tests. Hence, l the cited 20 minute delay times are not applicable to the Braidwood fire scenarios.

Similarly, in Section 4.7.2.1 solid-bottoms were credited with preventing ignition of cable tunnel cable trays by transient fires. Again, no applicable basis for such an assumption was presented.

Please provide a re-analysis of the CDF for those areas where credit was taken for the thermal protection provided by virtue of solid-bottom cable trays and/or enclosed risers.

This analysis should assume that thermal damage to the trays will not be substantially delayed by virtue of the solid-bottom cable trays which are treated as barriers credited with a 20 minutes propagation delay. The re-assessments should include both the i

screening results and the detailed analyses. For the cable tunnel, determine the importance of the ignition-preventing properties by dropping the credit given to the barriers and re-determining the CDF contribution of the compartment. The re-assessment should include information provided in Information Notices 93-41 and 1

L -

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95-52, regarding qualification of 3M fire barriers, and Information Notice 95-27 regarding Thermo-Lag ignition properties.

14. The Braidwood fire analysis has assumed a cable ignition temperature of 932*F (see page 4-17 of the submittal) and cites the EPRI Fire PRA implementation Guide as the basis for this value. The PRA Guide recommends that this value be used for both spontaneous and piloted ignition. This value is significantly optimistic in comparison to piloted ignition temperatures observed in tests by Sandia National Laboratories (SNL)

(see NUREG/CR-5546). The SNL tests show that the piloted ignition temperature for cables will be as low or lower than the thermal damage threshold; hence, use of a piloted ignition temperature of no greater than 700*F would be appropriate. This assumption may have resulted in the optimistic treatment of cable fire growth behvior.

Please provide an assessment of the change in fire CDF if it is assumed that the piloted q

ignition temperature of the cables is 700*F. Include in the response an assessment of how a reduced piloted ignition temperature would impact the screening results of the analysis as well.

15. Some scenarios (e.g., p.4-53) credited manual fire suppression which was characterized by a 20 minute response time, based on drills at the plant. The 20 minute interval was then used with a generic suppression curve to infer a 94% probability of suppression success. As used, the " response time" appears to include time for brigade assembly, donning gear, transit to the fire, fire assessment, and successful fire fighting for all locations in the plant. Fire brigade response times are more typically 30 minutes for this high level of success. Also important in assessing the success of manual fire fighting was the 20 minute delay of damage attributed to solid-bottom cable trays (see question above). Taken together, the assumption of 94% success in preventing damage to sensitive targets is regarded as optimistic.

Please reassess the contribution to the fire CDF from scenarios where credit was given for manual fire suppression by dropping the damage-delaying credit given to solid-bottom trays and crediting suppression with 50% success in 20 minutes, and 95%

success in 30 minutes.

16. Section 4.5.3.2.3 addresses the treatment of operator errors in the fire study. The submittal states that human errors probabilities (HEPs) were added to component random failure probabilities to obtain total failure probabilities. This treatment ignores interdependencies between component failures and operator errors.

Please provide a discussion and/or listing of the fire scenarios treated in this manner, the operator actions that were considered, the random and operator error probabilities assumed, and any reasoning supporting the assumption that dependencies may be ignored.

17. The fire submittal has not provided sufficient information to assess the reasonableness of the cited final screening and final numerical results (CDF).

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Please provide a summary table that identifies each of the primary numerical factors that has contributed to the cited final screening results and CDF values. In particular, for each of the 26 areas / compartments (excluding the MCR) that survive qualitative screening and initial quantitative screening (i.e. before introduction of fire severity factors, manual suppression credit, and the elimination of non-damaging fire sources) please identify the PRA targets by system / function, the area / compartment CCDP assuming loss of all PRA targets, and the original / nominal un-modified fire frequency.

For each of the seven areas screened in the final quantitative screening step (in which severity factors, manual suppression prior to damage, and elimination of non-damaging

, fire sources were credited) provide a specific discussion of the basis upon which each area / compartment was quantitatively screened. For each of the 19 unscreened areas (excluding the MCR) identify the systems impacted or plant damage states assumed for each quantified scenario. Include the numerical values used in quantifying the final CDF contribution, that is, the severity factors, fire frequencies, manual and automatic non-suppression factors, scenario CCDP, HEPs and any other numerical parameters.

SEISMIC

, 1. A non-safety related mercury relay was identified as a poor performer during seismic l events. The identified relay is associated with the CO2 fire protection system. Although identified as a potentialissue in seismic / fire interaction, the submittal states that inadvertent actuation of the CO2 fire protection system does not impact the operation of the emergency diesel generators (EDGs) and there is no direct effect of these circuits on the operation of the EDGs. However, the submittal also states in Section 3.4.5.4.2 (under Non-Safety Related Relays) that contact chatter in relays provided in the CO2 fire protection system circuits could cause the diesel room ventilation fire dampers to close, l and therefore, result in loss of ventilation required for continued operation of the EDGs.

l . This does not seem to agree with the previous statement. Please clarify this issue.

j

2. The s'ubmittal has identified several plant improvements resulting from the IPEEE assessment. Please provide the implementation status for these improvements.

! 3. Nonseismic failures and human actions are not specifically addressed in the submittal.

l For nonseismic failures and human actions, NUREG-1407 states that " success paths are chosen based on a screening criterion applied to nonseismic failures and needed human actions. It is important that the failure modes and human actions are clearly identified and have low enough probabilities to not affect the seismic margins evaluation." Please provide a discussion of these issues in accordance with the above l statement from NUREG-1407. For the operator actions, discuss timing, access, stress, l and any other pertinent information to ascertain that operator recovery actions will be reliably performed following the seismic event. For nonseismic failures, verify that such failures (over the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> mission time) will not substantially degrade the reliability of the

' success paths chosen.

4. The condensate storage tanks (CSTs) do not appear on the list of tanks which were evaluated for seismically induced flooding (Table 3.4). Since CSTs are not included in the success path equipment list (SPEL), their seismic capacities under a review level earthquake cannot be established (the essential service water cooling pond, which is seismically qualified, is used instead of the CSTs, to supply auxiliary feedwater).

Additionally, each of the two CSTs holds over 300,000 gallons of water, far exceeding the 1000-gallon volume used for Table 3.4. Please discuss any concems of seismically induced flooding from the CSTs that could affect Braidwood's safe shutdown equipment.

HIGH WIND, FLOOD, AND OTHER EXTERNAL EVENTS

1. NUREG-1407 requests that licensees " perform a confirmatory walkdown of the plant.

The walkdown would concentrate on outdoor facilities that could be affected by high winds, onsite storage of hazardous materials, and offsite developments." Please provide a summary of the findings of this walkdown and resolution of any identified potential vulnerabilities.

l 2. As discussed in Section 5 of NUREG-1407, licensees should review information obtained from the plant walkdown for conformance to 1975 Standard Review Plant (SRP) criteria . One of these criteria is to address the potential for failure of any structure or component not designed for tomado loads, including missiles, to affect the j capability of other safety structures or components. .

J If a tomado analysis and/or a walkdown was performed to identify potential HFO vulnerabilities, were the effects of failure of seismic category ll structures on the integrity of the seismic category I structures during a tornado event considered? Please provide j your findings. If the ll over i effects were not investigated in the walkdown, please l explain why such an investigation was not needed.  !

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