NG-12-0419, Response to Second Request for Additional Information, License Amendment Request to Adopt National Fire Protection Association Standard 805 Performance-Based Standard for Fire Protection for Light Water Reactor Generating Plants

Response to Second Request for Additional Information, License Amendment Request to Adopt National Fire Protection Association Standard 805 Performance-Based Standard for Fire Protection for Light Water Reactor Generating Plants

ML122910950
Person / Time
Site:	Duane Arnold
Issue date:	10/15/2012
From:	Richard Anderson NextEra Energy Duane Arnold
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NG-12-0419
Download: ML122910950 (10)

Text

NEXTeraM ENE RGY Y4 October 15, 2012 NG-12-0419 10 CFR 50.90 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Duane Arnold Energy Center Docket No. 50-331 Renewed Op. License No. DPR-49 Response to Second Request for Additional Information, License Amendment Request to Adopt National Fire Protection Association Standard 805, Performance-Based Standard For Fire Protection For Light Water Reactor Generating Plants

References:

1) License Amendment Request (TSCR-128): Transition to 10 CFR 50.48(c) - NFPA 805, Performance-Based Standard For Fire Protection For Light Water Reactor Generating Plants (2001 Edition), NG-11-0267, dated August 5, 2011

2) Clarification of Information Contained in License Amendment Request (TSCR-128): Transition to 10 CFR 50.48(c) - NFPA 805, Performance-Based Standard For Fire Protection For Light Water Reactor Generating Plants (2001 Edition), NG-1 1-0384, dated October 14, 2011

3) Electronic Communication, ME6818 Duane Arnold NFPA-805

- Second Audit Visit Questions, dated June 25, 2012 (ML12284A021)

In the Reference 1 letter, as clarified by Reference 2, NextEra Energy Duane Arnold, LLC (hereafter NextEra Energy Duane Arnold) submitted a License Amendment Request for the Duane Arnold Energy Center (DAEC) pursuant to 10 CFR 50.90. Subsequently, the NRC Staff requested, via Reference 3, additional information regarding that application.

As a result of discussions with the Staff, NextEra Energy Duane Arnold committed to providing responses to the requested information by October 18, 2012. Attachment 1 to this letter contains the responses for information requests numbers 1 through 5. Information request number 6 of Reference 3 requested electronic files be provided to the NRC; those files were provided on NextEra Energy Duane Arnold, LLC, 3277 DAEC Road, Palo, IA52324

Document Control Desk NG-12-0419 Page 2 of 2 July 9, 2012. Information requests numbers 7 and 8 of Reference 3 requested drawings to be uploaded to the electronic portal being used by the Staff. Those drawings were uploaded and available to the Staff in June of 2012.

This additional information does not impact the 10 CFR 50.92 evaluation of "No Significant Hazards Consideration" previously provided in the referenced application.

This additional information does not make changes to any existing commitments and makes the following new commitment.

RAI Response Number 1 The DAEC Fire PRA - NFPA 805 RAI Model Update Quantification Report has been updated to include the new self-ignited fire scenarios and the change in input for fire scenarios with thermoplastic cable targets.

This change will be incorporated in the updated FPRA model in response to RAI-01.

If you have any questions or require additional information, please contact Tom Byrne at 319-851-7929.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on October 15, 2012 Vice President, Duane Arnold Energy Center NextEra Energy Duane Arnold, LLC

Attachment:

Response to Second Request for Additional Information, License Amendment Request to Adopt National Fire Protection Association Standard 805, Performance-Based Standard For Fire Protection For Light Water Reactor Generating Plants cc: NRC Regional Administrator NRC Resident Inspector NRC Project Manager M. Rasmusson (State of Iowa)

Attachment to Response to Second Request for Additional Information, License Amendment Request to Adopt National Fire Protection Association Standard 805, Performance-Based Standard For Fire Protection For Light Water Reactor Generating Plants 15 pages follow

Second Audit (5/12) of DAEC - Question 1 DAEC Second Audit Question 1

a. A): Request that licensee notifies staff when remaining cables have been identified and analyzed. Licensee noted that the expected timeframe to complete data gathering and determine impact on PRA analysis is approximately the end of September 2012.

b. C): During audit discussions, the staff understood that this statement meant that the increased heat release rate and fire propagation associated with thermoplastic cables did not result in the identification of any additional targets. Staff requests that licensee confirm that understanding at the conclusion of the RAI response.

RESPONSE

The two RAI items above will be addressed as Items A and B.

A) DAEC identified or assumed unqualified cables in plant locations included in the fire PRA due to the inability to retrieve qualification documentation on some cables. For these plant locations self ignited cable fires were postulated consistent with NUREG/CR-6850 guidance. Table 1 presents the estimated additional fire risk from postulated self ignited cable fires. From Table 1, the contribution of self ignited cable fires to total plant risk is estimated to be less than one percent of total CDF and LERF.

DAEC identified or assumed thermoplastic cables in plant locations included in the fire PRA. For the applicable raceways in these plant locations, cable damage threshold, heat release rate, and flame propagation for thermoplastic cables were used consistent with NUREG/CR-6850 guidance. In those plant locations where a bounding fire scenario was used in the fire PRA instead of fire modeling, the presence of thermoplastic cables did not change the results of the fire PRA. For other areas with identified thermoplastic cables, additional walkdowns were performed to identify new targets or changes in the fire scenario input. Table 1 presents the estimated additional fire risk given thermoplastic cables. From Table 1, the presence of thermoplastic cables resulted in approximately two percent increase in total plant CDF and LERF.

Table 1 presents the updated total plant fire CDF and LERF. Incorporation of the unqualified and thermoplastic cables into the fire PRA for DAEC results in an overall increase in total CDF and LERF of approximately two percent.

Due to their association with fire scenarios involving VFDRs, the identified or assumed unqualified cables and thermoplastic cables in the Cable Spreading Room (PAU 11A, fire area CB1) and the Division 1 Essential Switchgear Room (PAU 1OF, fire area CB3) result in increases in the delta risk for those fire areas, as well as for the total plant. Table 2 presents the resulting changes in delta risk. The updated delta CDF and LERF for fire area CB1 and CB3 results are acceptable. Additionally, the updated delta CDF and LERF for the total plant results are acceptable.

Therefore, inclusion of the identified or assumed unqualified cables and thermoplastic cables does not change the conclusions of the fire PRA or the LAR.

Rev B. Page 1 of 2

Second Audit (5/12) of DAEC - Question 1 The new self ignited cable fire scenarios and the change in input for fire scenarios with thermoplastic cable targets will be included in the fire PRA at the next update.

Table 1 Increase in Total Plant Risk from Unqualified and Thermoplastic Cables Percent Percent CDF (/yr) Increase in LERF (/yr) Increase in CDF LERF DAEC Base 4.36E-5 n/a 1.59E-5 n/a Unqualified Cable Risk 4.47E-8 0.10% 9.61 E-9 0.060%

Increase thermoplastic Cable Risk 6.85E-7 1.5% 3.93E-7 Increase Updated Total 4.43E-5 1.6% 1.63E-5 2.5%

Table 2 Updated Delta Risk Based on Unqualified and Thermoplastic Cables Fire Area Base Delta CDF Updated Delta Base Delta Updated Delta CDF LERF LERF CB1 1.49E-8 2.02E-8 1.49E-8 2.02E-8 CB3 1.43E-8 1.95E-8 1.28E-8 1.74E-8 Total Plant 1.11 E-7 1.22E-7 5.55E-8 6.54E-8 B) Based on NUREG/CR-6850 Appendix R, the presence of thermoplastic cables results in increased heat release rate and fire propagation. Additional walkdowns were performed in plant locations with thermoplastic cables considering the increased heat release rate and fire propagation. The walkdowns did not result in the identification of additional targets.

Page 2 of 2 B.

Rev B. Page 2 of 2

Second Audit (5/12) of DAEC - Question 2 DAEC Second Audit Question 2 During the audit, staff discussed with the licensee the maximum panel dimension limit of applicability. It is understood that this maximum panel dimension can be exceeded up to a heat release rate of 783 kW without affecting the Generic Treatments assumptions.

The clarification question is what if an ignition source located along a wall or in a corner exceeds these dimensions, and therefore the maximum HRR for which the Treatments are applicable? Staff requests that the licensee explain how this upper limit of applicability is not crossed for ignition sources located along a wall or in a corner.

RAI RESPONSE:

The limitations for the electrical panel Zones of Influence (ZOIs) as deduced in the RAI FMod 4 Response [DAEC, 2012] are applicable to open burn configurations, consistent with the original "Generic Fire Modeling Treatments" report [Hughes Associates, 2008].

This RAI response provides additional discussion on the applicability of the ZOI dimensions for large electrical panels when such panels are located near walls or near corners.

Source fires that are located near wall and corner boundaries will be affected by these features via a reduction in the air entrainment into the fire and thermal plumes. The entrainment reduction results in a lengthening of the flames and higher temperatures within the thermal plume at a fixed elevation when compared to an open burn configuration, when the heat release rate is held constant. One means of assessing the effect of reduced entrainment for wall configurations is to postulate that the wall boundary is an axis of symmetry within a source fire having twice the heat release rate and twice the plan area (i.e., the 'Image' or 'Reflection' method). Because the entrainment is proportional to the surface area of the fire and thermal plume and the plume angle is constant [e.g., Beyler, 1986; Heskestad, 2008; Thomas et al., 1963; NIST-GCR-90-580, 1990], the air entrainment ratio between the wall configuration and the open configuration may be estimated from the perimeter ratios, which is equal to %r2.

A similar argument applies to corner configurations, except there are two orthogonal symmetry planes; the fire size and fire area for this configuration are quadrupled and the ratio of the corner and open configuration perimeters is 2.

The FPRA addresses wall and corner effects for source fires, including electrical panel fires, by using the ZOI dimensions for a source fire that is approximately two or four times greater than the desired heat release rate (i.e., the 'Image' method). The heat release rate per unit area is varied in the original "Generic Fire Modeling Treatments" report [Hughes Associates, 2008] over a constant range that is applicable to the particular source fire; thus, the fire area is doubled or quadrupled when using a fire size that is two or four times greater than the desired heat release rate bin. This is consistent with the 'Mirror' method for portions of the ZOI that are determined from thermal plume or flame length calculations.

The ZOI for the electrical panels is defined by five parameters in the "Generic Fire Modeling Treatments" report [Hughes Associates, 2008]: a fire plume dominated portion based at the top of the electrical panel and a radiant portion extending from the panel base to the panel top. The thermal plume portion uses three measures: a vertical and Rev B. Page I of 3

Second Audit (5/12) of DAEC - Question 2 two orthogonal horizontal components applicable to the narrower and wider sides. The lower ZOI dimensions have two horizontal components: one that corresponds to the narrower side and one that corresponds to the wider side. The five parameter ZOI is implemented in the FPRA as a two component ZOI. This is done by the vertical ZOI dimension extended downward to the panel base and the maximum horizontal dimension among the four that are defined. The net effect is that the fire plume vertical ZOI dimension and the panel height define the vertical ZOI and the lower ZOI dimension corresponding to the wide side defines the horizontal ZOI dimension (i.e., the lower ZOI dimensions bound the upper fire plume based ZOI dimensions).

The fire plume portion of the ZOI is consistent with the NUREG/CR 6850 [2005] and NUREG/CR 6850 Supplement 1 [2010] treatment for electrical panel fires and addresses external burning and flaming through openings in the panel top or upper vents. The radiant portion provides additional conservatism and explicitly addresses combustion that may occur within a vented panel at a panel boundary or that radiates through gaps and openings. As noted, the fire plume portion is correctly assessed in wall and corner configurations when the ZOI for an electrical panel having a heat release rate two or four times the desired heat release rate is assumed.

In the case of the lower horizontal ZOI dimensions, the distances are determined by calculating the radiant heat flux from a panel face heated by flame impingement within the panel or flame extensions from the gaps equal to 012, , where H is the panel height. The internal boundary condition is a 120 kW/m2 net heat flux, which is based on wall heat fluxes measured in corner configurations [Lattimer, 2008]. In essence, it is postulated that a cable bundle is burning within the panel, and the flames from this bundle impinge on the panel side, causing the panel to heat to approximately 1,000°C.

This energy is directed away from the burning electrical panel through the side at which the flames impinge; any side is assumed to be subject to this type of internal exposure and the resulting ZOI extends equally from each side when the maximum dimension is used. This means that when the electrical panel is located in a wall or corner, there is no effect on this aspect of the computation: the radiant energy is either directed outward away from the wall or corner or it is part of the fire plume. When the energy is included in the fire plume, the ZOI is adjusted using the 'Mirror' method as previously described.

No adjustment is necessary for the lower ZOI dimension. However, the "Generic Fire Modeling Treatments" [Hughes Associates, 2008] do not explicitly account for wall and corner effects. When the 'Image' method is applied via increasing the source fire heat release rate, a higher heat release rate bin is used and the heat release rate increase is applied to both the upper and lower ZOI dimensions. Nevertheless, this is conservative and within the limitations of the analysis because both the upper and lower ZOI dimensions increase with increasing source fire heat release rate. It is only necessary for the lower ZOI dimension to be equal to or greater than the ZOI dimension derived from an open configuration panel, and this limit is 783 kW (742 Btu/s) as described in DAEC [2012]. Therefore, the 783 kW (742 Btu/s) limit for large panels effectively translates into a 1,566 kW limit for panels located near a wall boundary and a 3,132 kW (2,969 Btu/s) limit for panels located in a corner configuration.

Page 2 of 3 B.

Rev B. Page 2 of 3

Second Audit (5/12) of DAEC - Question 2

REFERENCES:

Beyler, C. L., "Fire Plumes and Ceiling Jets," Fire Safety Journal, Volume 11, Number 1, Elsevier Sequoia S. A., Lausanne, Switzerland, 1986.

Duane Arnold Energy Center, NG-12-0177, "Request for Additional Information, License Amendment Request to Adopt National Fire Protection Association Standard 805, Performance Based Standard for Fire Protection For Light Water Reactor Generating Plants," April 23, 2012.

Heskestad, G., "Fire Plumes, Flame Height, and Air Entrainment," Section 2-1, The SFPEHandbook of Fire Protection Engineering,4 th Edition, P.J. DiNenno, Editor-in-Chief, National Fire Protection Association, Quincy, MA, 2008.

Hughes Associates, (2008), "Generic Fire Modeling Treatments," Revision 0, Hughes Associates, Inc., Baltimore, MD, January 15, 2008 Lattimer, B. Y., "Heat Fluxes from Fires to Surfaces," Section 2-14, The SFPE Handbook of Fire ProtectionEngineering,4 th Edition, P.J. DiNenno, Editor-in-Chief, National Fire Protection Association, Quincy, MA, 2008.

NIST-GCR-90-580, "Development of an Instructional Program for Practicing Engineers Hazard I Users," Barnett, J. R. and Beyler, C. L., National Institute of Standards and Technology, Gaithersburg,MD, July, 1990.

NUREG 6850, "EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities Volume 2 Detailed Methodology," Electric Power Research Institute (EPRI) 1008239 Final Report, NUREG/CR 6850, Nuclear Regulatory Commission (NRC), Rockville, MD, September, 2005.

NUREG 6850 Supplement 1, "Fire Probabilistic Risk Assessment Methods Enhancements," EPRI 1019259, NUREG/CR 6850 Supplement 1, Nuclear Regulatory Commission, Washington, DC, September, 2010.

Thomas, P. H., Hinkley, P. L., Theobald, C.R., and Sims, D. L., "Fire Technical Paper No. 7, H. M. Stationery Office, Joint Fire Research Organization, London, 1963.

Page 3 of 3 Rev B.B. Page 3 of 3

Second Audit of DAEC (5/12) - Question 3 DAEC Second Audit Question 3

a. Some clarification is required in the definition of 'support role' and technical lead.

Based on discussions at the audit, the staff understood that there were more required internal qualifications than what are discussed in this RAI response.

Also, it is not clear how qualification for Peer Reviewers (NEI-07-12) translates to qualification for users. The staff requests that the licensee provide additional description in this RAI response.

b. Some clarification is required to specifically describe the different processes and procedures that are used for this purpose. Based on the discussions at the audit, the staff understood there were more procedures in place than what was described in the RAI response. The staff requests that the licensee provide additional description in this RAI response.

c. Some clarification is required to specifically identify any procedures used to integrate the process of communication between the PRA and fire modeling groups. The staff requests that the licensee provide additional description to this RAI response.

RESPONSE

a. The term technical lead is used in the context of those individuals experienced and qualified in the tasks that they supervise. ERIN Engineering ensures those that perform the role of technical lead for the fire PRA are qualified through several processes as described in the response to item b.

The term 'support role' is used in the context of those individuals assisting in fire PRA tasks and are supervised by the technical lead. Support role activities include data entry and manipulation, as well as other routine fire PRA activities (e.g., PRA model quantification and compilation of results).

NEI 07-12 Section 2.2 describes the desired experience requirements for Peer Reviewers. Similar qualification was expected of individuals involved in the performance of the DAEC fire PRA.

b. Training and qualification of personnel involved in technical analysis for the DAEC NFPA 805 project is addressed in a 'Project/Quality Plan' for transition of the DAEC Fire Protection Program to NFPA 805. Per this plan, technical leads are expected to be familiar with the 'Project Instruction' document relating to the task or tasks for which they are responsible.

ERIN Engineering has an internal training and certification process in place to qualify those developing fire PRAs. ERIN Engineering certification guides SR-ES-F01 through SR-ES-F05 require that individuals are knowledgeable and experienced in performing the applicable fire PRA tasks. Additionally, ERIN Page 1 of 2 C.

Rev C. Page 1 of 2

Second Audit of DAEC (5/12) - Question 3 Engineering routinely has internal seminars to keep those performing fire PRAs up to date on new and changing industry guidance for fire PRAs.

The DAEC Training Program Description (TPD) for Engineering Support Personnel (ESP) contains a process for determining whether contract staff should participate or be exempt from the DAEC ESP Training program. Using this process, contract personnel responsible for the performance of fire PRA tasks were not entered into the ESP population. Rather, their qualifications were established based on a resume review and an interview conducted by the PRA Program Owner and the Supervisor, Fire Protection.

With respect to application of the Generic Fire Modeling Treatments and the fire PRA, the technical lead for the project supervised all tasks of the fire PRA including the integration of the Generic Fire Modeling Treatments into the fire PRA model. The technical lead was qualified to each ERIN Engineering certification and was qualified under the DAEC qualification process.

c. No specific procedures or processes were required for communication between the fire modeling group and the PRA group given the groups were integrated into a single project team. Informal communication was used throughout the project when clarification was required in applying the generic fire modeling treatments or addressing specific fire modeling concerns outside of the treatments.

Page 2 of 2 Rev C.

Rev C. Page 2 of 2

Second Audit (5112) of DAEC - Question 4 DAEC Second Audit Question 4 Generic Treatments Review: It was discussed at the audit that when calculating the effect of secondary combustibles, presence of two cable trays placed side by side at a height of 1-ft. above the principal ignition source is assumed to ignite after 5 minutes.

Licensee stated that this is likely a conservative approach and a similar overall result will be determined using the FLASH-CAT method. The staff requests the licensee provide additional supporting documentation to justify this statement. The staff requests that the licensee verify that the DAEC configuration is not affected by any non-conservatism in this approach.

RESPONSE

The approach for addressing secondary combustibles described in Hughes Associates, "Supplemental Generic Fire Model Treatments: Hot Gas Layer Tables," Supplement 2, Revision G [2011], is based on an ignition sequence within the cable trays that is likely to occur and depending on the number of cable trays actually involved, their width, and horizontal separation, the time for a critical condition to be reached, and initial source width may or may not yield a heat release rate that exceeds the value recommended in NUREG/CR-6850 [2005]. In lieu of identifying whether or not the approach used is conservative relative to the guidelines in NUREG/CR-6850 [2005] and NUREG/CR-6850 Supplement 1 [2010] for each fire scenario that includes secondary combustibles within the FPRA, a new set of hot gas layer tables have been developed to replace those documented in Hughes Associates, "Supplemental Generic Fire Model Treatments: Hot Gas Layer Tables," Supplement 2, Revision G [2011]. The new hot gas layer tables are documented in Report 1 EAK27056.000.001-01 [2012] and use the model recommended in NUREG/CR-6850 [2005] as clarified in NUREG/CR-6850 Supplement 1 [2010] to derive the heat release rates in combination with the 9 8 th percentile ignition source heat release rate. The input parameters for the heat release rate per unit area and the flame propagation rate are obtained from NUREG/CR 7010

[2010] for both IEEE-383 qualified/thermoset and non-IEEE-383 qualified/thermoplastic cable materials. The details of the analysis are documented in Report 1EAK27056.000.001-01 [2012]. Key inputs include the following:

" The heat release rate per unit area for the cables is 150 kW/m 2 (13.2 Btu/s-ft2 ) for thermoset cable materials and 250 kW/m 2 (22.1 Btu/s-ft2 ) for thermoplastic cable materials based on full scale tests on horizontal cable trays as recommended in NUREG/CR 7010 [2010].

" The horizontal propagation rate is 0.3 mm/s (0.011 in/s) for thermoset cable materials and 0.9 mm/s (0.035 in/s) for thermoplastic cables based on full scale tests on horizontal cable trays as recommended in NUREG/CR 7010 [2010].

" The ignition time for the first cable tray is 1 minute, the minimum damage/ignition time for cable trays'as recommended in Appendix H of NUREG/CR-6850 [2005].

• The propagation time between the first tier cable tray and the second tier cable tray is four minutes as recommended in Appendix R of NUREG/CR-6850 [2005].

Rev B. Page I of 4

Second Audit (5/12) of DAEC - Question 4

" The initial area of involvement for the electrical panels is equal to the characteristic length of the source fire. A single characteristic length of 1.2 m (4 ft) is considered, which is representative of a large panel such as a switchgear and conservative for a smaller panel such as an MCC.

" The initial area of involvement for the transient ignition sources is based on the 9 8 th percentile heat release rate and the heat release rate per unit area for transient material as described in Report 1EAR27056.000.001-03 [2012].

Based on a review of the fixed and transient ignition sources that can involve secondary combustible materials, the following DAEC specific 'generic' hot gas layer tables are developed:

NUREG/CR- Peak Ignition 6850 [2005] Source Heat Cable Tray Appendix E Release Rate (kW Configuration Case [Btu/s])

Two 0.61 m (24 in)

Single Bundle, IEEE- 211 (200) wide trays, stacked 383 qualified cable (Cable Tray Configuration 1).

Two 0.61 m (24 in) wide trays, stacked; Multiple Bundles, plus one additional IEEE-383 qualified 3 702 (665) 0.61 m (24 in) wide cable tray adjacent to the stack (Cable Tray Configuration 2).

Two adjacent stacks of Transient 8 317 (300) two 0.61 m (24 in) wide trays (Cable Tray Configuration 3).

Each of the three ignition source-cable tray configurations are evaluated in an open, wall, and corner location using the 'reflection' or 'mirror' method as applicable [Report 1EAK27056.000.001-01, 2012]. Cable trays are assumed to be sufficiently long to support propagation for up to one-hour. In addition, the cable trays are assumed to contain a sufficient density of fuel to support combustion at a fixed location for up to one-hour. The methods described in Hughes Associates, "Generic Fire Modeling Treatments," Project Number 1SPH02902.030, Revision 0 [2008], are used to calculate the time the hot gas layer temperature reaches threshold values of 80 0C (1760 F), 2040 C (400'F), and 329 0C (625 0 F). These temperatures correspond to the temperature at which the ZOls are no longer assumed to be independent of the hot gas layer, the temperature at which full room burnout is assumed for non-IEEE-383 qualified/thermoplastic cables; and the temperature at which full room burnout is assumed for IEEE-383 qualified/thermoset cables [Hughes Associates, "Generic Fire Rev B. Page 2 of 4

Second Audit (5/12) of DAEC - Question 4 Modeling Treatments," Project Number 1SPH02902.030, Revision 0, 2008; NUREG/CR-6850, 2005].

In addition to the generic scenarios, specific scenarios are considered in the Essential Switchgear Rooms [Report 1EAK27056.000.001-01, 2012]. These scenarios consist of the following:

• The two electrical panel fire scenarios evaluated generically; and

" Transient fire scenarios evaluated with a stack of three horizontal cable trays, each 0.61 m (2 ft) wide in an open, wall, and corner locations.

These hot gas layer conditions are computed in the same manner as the generic cases, except that the specific room height and volume for the Essential Switchgear Rooms are used.

The postulated fire scenarios in which secondary combustibles are postulated to ignite were reviewed using the revised tables provided in 1EAK27056.000.001-01 [2012]. The results provided in 1EAK27056.000.001-01 [2012] confirm that the assumptions used and the application of the results in the tables in Section 6 of the Hughes Associates, "Generic Fire Modeling Treatments," Project Number 1SPH02902.030, Revision 0

[2008], and the "Supplemental Generic Fire Model Treatments: Hot Gas Layer Tables,"

Supplement 2, Revision G [2011] in the fire PRA were conservative.

Page 3 of 4 Rev B.

Rev B. Page 3 of 4

Second Audit (5/12) of DAEC - Question 4

REFERENCES:

Hughes Associates, "Generic Fire Modeling Treatments," Project Number 1SPH02902.030, Revision 0, January 15, 2008.

Hughes Associates, "Supplemental Generic Fire Model Treatments:

Hot Gas Layer Tables," Supplement 2, Revision G, Baltimore, MD, October 10, 2011.

NUREG/CR-6850, "EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities Volume 2 Detailed Methodology," Electric Power Research Institute (EPRI) 1008239 Final Report, NUREG/CR-6850, Nuclear Regulatory Commission (NRC), Rockville, MD, September, 2005.

NUREG/CR-6850 Supplement 1, "Fire Probabilistic Risk Assessment Methods Enhancements," EPRI 1019259, NUREG/CR-6850 Supplement 1, Nuclear Regulatory Commission, Washington, DC, September, 2010.

NUREG/CR 7010, "Cable Heat Release, Ignition, and Spread in Tray Installations During Fire (CHRISTIFIRE) Volume 1: Horizontal Trays," Draft Report for Comment, McGrattan, K., Office of Nuclear Regulatory Research, Nuclear Regulatory Commission, Washington, DC, October, 2010.

Report 1EAK27056.000.001-01, "Evaluation of the Development and Timing of Hot Gas Layer Conditions in DAEC Fire Compartments," Revision 0, Hughes Associates, Inc.,

Baltimore, MD, September 21, 2012.

Report 1EAK27056.000.001-03, "Supplemental Generic Fire Modeling Treatments:

Transient Fuel Package Ignition Source Characteristics," Revision 0, Hughes Associates, Inc., Baltimore, MD, September 19, 2012.

Page 4 of 4 Rev B.B. Page 4 of 4

Second Audit (5/12) of DAEC - Question 5 DAEC Second Audit Question 5 Generic Treatments Review: It was discussed at the audit that it is assumed that the secondary combustibles in the cable trays do not affect the applied ZOI. According to NUREG-6850, Section R.4.2, fire will spread at an angle of 35 degrees (see Figure 1 below). It is not clear what happens to the area that is included in the 35 degree sector, but not included in the rectangular ZOI. The staff requests that the licensee provide additional justification for not using the method described in Section R.4.2 of NUREG 6850.

/ *-Unresolved/unaccounte 35 *d area (Lines show n= E:

', Cable tray n= E:: stack Ignition Horizontal ZOI Source Characteristic length Figure 1. Model for Fire Propagation in a Cable Tray Stack (Figure R-5 from NUREG 6850)

RESPONSE

Under some circumstances, the current analysis may have been non-conservative when identifying targets. This is because the approach for addressing secondary combustibles described in Hughes Associates "Supplemental Generic Fire Model Treatments: Hot Gas Layer Tables," Supplement 2, Revision G, [2011] is based on an ignition sequence within the cable trays that is likely to occur and depending on the number of cable trays actually involved, their width, and horizontal separation, the time for a critical condition to be reached, and initial source width may or may not yield a heat release rate that exceeds the value recommended in NUREG/CR-6850 [2005]. When assessing which targets fall into the ZOI, the approach taken in the FPRA is to extend the vertical ZOI dimension to the ceiling if secondary combustibles are located above the ignition source and within the ZOI for the ignition source alone ["Duane Arnold Energy Center (DAEC) Fire Probabilistic Risk Assessment Fire Scenario Report," 493080001.003, 2012]. The underlying assumption in the application is that extending the ZOI to the ceiling of the enclosure coupled with the horizontal electrical panel ZOI dimension is conservatively bounding the ZOI that would be obtained using the detailed tray propagation model. This assumption Page 1 of 4 Rev 0 Pagel of4

Second Audit (5/12) of DAEC - Question 5 may produce non-conservative results under some circumstances relative to the baseline NUREG/CR-6850 [2005] methodology, especially if the tray to tray separation (h ) is large, there are a large number of trays within the stack, and the cables are thermoplastic. In addition, the horizontal ZOI dimension for fire scenarios involving secondary combustibles initiated by transient ignition sources ignition could be more sensitive to the additional heat source presented by the ignition source than is the horizontal ZOI dimension of the electrical panel fires.

In lieu of identifying whether or not the approach used is conservative relative to the guidelines in NUREG/CR-6850 [2005] and NUREG/CR-6850 Supplement 1 [2010] for each fire scenario that includes secondary combustibles within the FPRA, a revised set of ZOI tables were derived using the methods described in Hughes Associates, "Generic Fire Modeling Treatments," Project Number 1SPH02902.030, Revision 0

[2008]. The revised ZOI tables are developed for specific bounding ignition source-cable tray arrangements and are provided in Report 1 EAK27056.000.001-02 [2012].

Horizontal ZOI dimensions are computed using the heat flux methods described in 1 SPH02902.030, Revision 0 [20081. The vertical ZOI dimension is defined as the ceiling height when secondary combustibles are located within the ignition source ZOI [Report 493080001.003, 2012].

The extent of cable tray involvement is estimated for both IEEE-383 qualified/thermoset and non-IEEE-383 qualified/thermoplastic cable materials using the propagation model as recommended in NUREG/CR-6850 [2005] and clarified in NUREG/CR-6850, Supplement 1, and NUREG/CR 7010, Volume 1 [2012]. Key inputs include the following:

• The heat release rate per unit area for the cables is 150 kW/m 2 (13.2 Btu/s-ft2) for thermoset cable materials and 250 kW/m 2 (22.1 Btu/s-ft2) for thermoplastic cable materials based on full scale tests on horizontal cable trays as recommended in NUREG/CR-7010 [2012].

• The horizontal propagation rate is 0.3 mm/s (0.012 in/s) for thermoset cable materials and 0.9 mm/s (0.035 in/s) for thermoplastic cables based on full scale tests on horizontal cable trays as recommended in NUREG/CR 7010 [2012].

• The initial cable tray length involvement for the transient ignition sources is based on the 9 8 th percentile heat release rate and the heat release rate per unit area for transient material as described in Report 1 EAK27056.000.001-03 [2012].

• The initial cable tray length involvement for the electrical panel ignition sources is assumed to be 1.2 m (4 ft). The results are thus limited to panels that have a characteristic dimension of 1.2 m (4 ft) or less.

• The cable tray length ignited in the second and subsequent trays is determined by the tray intersection with an inverted frustum based at the initial tray. The frustum sides are sloped thirty-five degrees from vertical.

The revised ZOI tables were developed using a steady-state calculation over a one-hour time period. The propagation times between cable tray tiers are thus not necessary inputs.

In addition, the results are applicable to fire scenarios that do not exceed one hour.

Rev 0 Page 2 of 4

Second Audit (5/12) of DAEC - Question 5 Based on a review of the fixed and transient ignition sources that can involve secondary combustible materials, the four DAEC 'generic' ZOI tables are summarized in Table 1.

The ZOI tables bound the cable tray configurations identified at DAEC for each ignition source identified [Report 493080001.003, 2012].

Table 1 - Ignition Source - Cable Tray Combinations Used to Developed DAEC Generic ZOI Tables.

NUREG/CR-6850 Ignition-680 S5Peak Ignition Source Ignition Source [2005] Appendix Heat Release Rate Cable Tray Configuration E Case (Ignition (kW [Btu/s])

Source)

Two adjacent stacks of two Transient 8 Small - 69 (65) 0.61 m (24 in)wide trays Large - 317 (300) (Cable Tray Configuration 1).

Three 0.61 m (24 in) wide Transient 8 Small - 69 (65) cable trays in a single stack Large - 317 (300) (Cable Tray Configuration 2).

Two 0.61 m (24 in)wide Single Bundle, IEEE-3831 211 (200) trays, stacked (Cable Tray qualified cable Configuration 3).

Two 0.61 m (24 in) wide trays, stacked; plus one Multiple Bundles, IEEE-383 702(665) additional 0.61 m (24 in) qualified cable wide tray adjacent to the stack (Cable Tray Configuration 4).

Each of the four ignition source-cable tray configurations are evaluated in an open, wall, and corner location using the 'Image' method as applicable [Report 1EAK27056.000.001-02, 2012; NIST-GCR-90-580, 1990]. Cable trays are assumed to be sufficiently long to support propagation for up to one-hour. In addition, the cable trays are assumed to contain a sufficient density of fuel to support combustion at a fixed location for up to one-hour. The methods described in 1SPH02902.030, Revision 0 [2008] are used to calculate the ZOI dimensions for the combined ignition source-cable tray configurations after one-hour. The electrical panels are conservatively assumed to have a one-hour fire duration in this treatment in order to maximize the cable tray contribution.

Each fire scenario in which secondary combustibles are postulated to ignite has been reassessed using the revised tables provided in Report 1EAK27056.000.001-02 [2012].

The review of these postulated fire scenarios did not result in new targets with risk significant cables. Therefore, the application of the new zone of influence does not result in changes to the fire risk and conclusions for the application.

Page 3 of 4 Rev 00 Page 3 of 4

Second Audit (5/12) of DAEC - Question 5

REFERENCES:

1EAK27056.000.001-02, "Combined Ignition Source - Cable Tray Fire Scenario ZOls for DAEC Applications," Revision 0, Hughes Associates, Inc., Baltimore, MD, September, 2012.

lEAK27056.000.001-03, "Supplemental Generic Fire Modeling Treatments: Transient Fuel Package Ignition Source Characteristics," Revision 0, Hughes Associates, Inc.,

Baltimore, MD, September, 2012.

1sPH02902.030, "Generic Fire Modeling Treatments," Revision 0, Hughes Associates, January 15, 2008.

Hughes Associates, "Supplemental Generic Fire Model Treatments: Hot Gas Layer Tables," Supplement 2, Revision G, Baltimore, MD, October 10, 2011.

NIST-GCR-90-580, "Development of an Instructional Program for Practicing Engineers Hazard I Users," Barnett, J. R. and Beyler, C. L., National Institute of Standards and Technology, Gaithersburg, MD, July, 1990.

NUREG/CR-6850, "EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities Volume 2 Detailed Methodology," Electric Power Research Institute (EPRI) 1008239 Final Report, NUREG/CR-6850, Nuclear Regulatory Commission (NRC), Rockville, MD, September, 2005.

NUREG/CR-6850 Supplement 1, "Fire Probabilistic Risk Assessment Methods Enhancements," EPRI 1019259, NUREG/CR-6850 Supplement 1, Nuclear Regulatory Commission, Washington, DC, September, 2010.

NUREG/CR-7010, "Cable Heat Release, Ignition, and Spread in Tray Installations During Fire (CHRISTIFIRE) Volume 1: Horizontal Trays," Final Report for Comment, McGrattan, K., Office of Nuclear Regulatory Research, Nuclear Regulatory Commission, Washington, DC, July, 2012.

Report 493080001.003, "Duane Arnold Energy Center (DAEC) Fire Probabilistic Risk Assessment Fire Scenario Report," Nextera, Palo, IA,2012.

Page 4 of 4 Rev 00 Page 4 of 4