LIC-12-0135, Responses to Requests for Additional Information License Amendment Request 10-07 to Adopt NFPA 805, Performance-Based Standard for Fire Protection for Light Water Reactor Generating Plants, 2001 Edition, at Fort Calhoun Station
| ML12276A046 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 09/27/2012 |
| From: | Cortopassi L Omaha Public Power District |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LIC-12-0135 | |
| Download: ML12276A046 (14) | |
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OmahaPublic Power DisAict 444 South 16"' Street Mall Omaha, NE 68102-2247 September 27, 2012 LIC-1 2-0135 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001
References:
- 1. Docket No. 50-285
- 2. Letter from OPPD (J. A. Reinhart) to NRC (Document Control Desk), License Amendment Request 10-07, Proposed Changes to Adopt NFPA 805, Performance-Based Standard for Fire Protection for Light Water Reactor Generating Plants (2001 Edition) at Fort Calhoun Station, dated September 28, 2011 (LIC-1 1-0099) (ML112760660)
- 3. Letter from the NRC (L. E. Wilkins) to OPPD (David J. Bannister), Fort Calhoun Station, Unit No. 1 - Request for Additional Information Re: License Amendment Request to Adopt National Fire Protection Agency Standard NFPA 805 (TAC No. ME7244), dated April 26, 2012 (NRC-12-0041)
- 4. Letter from OPPD (D. J. Bannister) to NRC (Document Control Desk),
Responses to Requests for Additional Information Re: License Amendment Request 10-07 to Adopt NFPA 805, "Performance-BasedStandard for Fire Protection for Light Water Reactor Generating Plants," 2001 Edition, at Fort Calhoun Station, dated July 24, 2012 (LIC-12-0083)
- 5. Letter from OPPD (D. J. Bannister) to NRC (Document Control Desk),
Responses to Requests for Additional Information Re: License Amendment Request 10-07 to Adopt NFPA 805, "Performance-BasedStandard for Fire Protection for Light Water Reactor Generating Plants," 2001 Edition, at Fort Calhoun Station, dated August 24, 2012 (LIC-12-0120)
SUBJECT:
Responses to Requests for Additional Information Re: License Amendment Request 10-07 to Adopt NFPA 805, "Performance-Based Standard for Fire Protection for Light Water Reactor Generating Plants," 2001 Edition, at Fort Calhoun Station This letter provides the Omaha Public Power District's (OPPD's) responses to the remaining Nuclear Regulatory Commission (NRC) requests for additional information (RAIs) transmitted in Reference 3 regarding the license amendment request (LAR) to adopt National Fire Protection Association (NFPA) 805 at the Fort Calhoun Station (FCS). Specifically, OPPD's responses to the Fire Modeling RAI 05 c.i. and Probabilistic Risk Assessment (PRA) RAI 07 a.,
b., and c. are provided in the enclosure to this letter.
Employment with Equal Opportunitv 0Ao 4'
U. S. Nuclear Regulatory Commission LIC-1 2-0135 Page 2 of 2 In Reference 2, OPPD requested an amendment to Renewed Facility Operating License No.
DPR-40 for FCS, Unit No.1, to adopt NFPA 805, Performance-Based Standard for Fire Protection for Light Water Reactor Generating Plants (2001 Edition). The NRC staff reviewed the information provided in OPPD's application and determined that additional information was required in order to complete its review. Reference 3 provides the NRC's RAIs which were received on April 26, 2012. References 4 and 5 provided the responses to a majority of the RAIs and a commitment schedule for submitting the remaining RAI responses.
In addition, OPPD committed to supplement the NFPA 805 transition LAR, as delineated in References 4 and 5 to reflect OPPD's responses to the NRC's RAls, at a time mutually agreeable between the NRC technical reviewers and OPPD project management.
There are no new regulatory commitments being made in this letter as a result of the enclosed NFPA 805 RAI responses.
If you should have any questions regarding this submittal or require additional information, please contact the Supervisor - Nuclear Licensing, Mr. Bill R. Hansher at 402-533-6894.
Sincerely, Louis P. Cortopassi Site Vice President and CNO
Enclosure:
Responses to Requests for Additional Information c: E. E. Collins, Jr., NRC Regional Administrator, Region IV L. E. Wilkins, NRC Project Manager J. C. Kirkland, NRC Senior Resident Inspector
LIC-12-0135 Enclosure Page 1 of 12 Responses to Remaining Requests for Additional Information Re:
License Amendment Request to Adopt National Fire Protection Association Standard 805, "Performance-Based Standard for Fire Protection for Light Water Reactor Generating Plants," 2001 Edition Fort Calhoun Station, Unit No.1 Docket No. 50-285 By letter dated September 28, 2011 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML112760660), as supplemented by letters dated December 19 and 22, 2011, and March 20, 2012 (ADAMS Accession Nos. ML113540334, ML11363A077, and ML12083A147, respectively), Omaha Public Power District (OPPD, the licensee), submitted a license amendment request (LAR) to transition the fire protection licensing basis at the Fort Calhoun Station, Unit 1, from paragraph 50.48(b) of Title 10 of the Code of FederalRegulations (10 CFR), to 10 CFR 50.48(c), National Fire Protection Association Standard NFPA 805. Portions of the letters dated September 28 and December 22, 2011, and March 20, 2012, contain sensitive unclassified non-safeguards information (security-related and proprietary) and, accordingly, those portions have been withheld from public disclosure.
The U.S. Nuclear Regulatory Commission (NRC) staff has reviewed the information provided in your application and determined that the following additional information is required in order to complete its review. The RAIs are grouped into the following technical review categories: fire modeling (FM), fire protection engineering (FPE),
monitoring program (MP), programmatic, safe shutdown analysis (SSA), radioactive release (RR), and probabilistic risk assessment (PRA).
[The remaining RAIs, FM RAI 05 c.i. and PRA RAI 07 a., b., and c., and OPPD's associated responses follow.]
Fire Modeling RAI 05:
NFPA 805, Section 2.7.3.5, "Uncertainty Analysis," states: "An uncertainty analysis shall be performed to provide reasonable assurance that the performance criteria have been met."
Section 4.7.3, "Compliance with Quality Requirements in Section 2.7.3 of NFPA 805," of the Transition Report states that "Uncertainty analyses were performed as required by Section 2.7.3.5 of NFPA 805 and the results were considered in the context of the application. This is of particular interest in fire modeling and FPRA development."
Regarding the uncertainty analysis:
- c. It appears that in many cases the most conservative model input parameter values were not used. Two specific examples are described below:
LIC-1 2-0135 Enclosure Page 2 of 12 i The soot yield in the FDS analysis for MCR habitability study was assumed to be 0.06 while higher values are reported in the fire protection literature for the same type of cables. Please provide a summary report of the impact of the uncertainty of the soot yield on the Fire PRA results (i.e., perform a quantitative assessment).
OPPD's Response to Fire Modeling RAI 05 c.i.:
NUREG-1805 (Reference 7), Table 18-3, Smoke Particulate Yield, reports soot yields for the following materials similar to cable insulation:
Table 1 - Soot Yields by Material Material Soot Yield Polypropylene 0.059 Silicone 0.065 Silicone Rubber 0.078 Polyethylene (PE) 0.06 Polyvinylchloride (PVC) 0.172 Ethylenetetrafluoroethylene (ETFE; Tefzel TM ) 0.042 The FCS fire PRA applies a 0.06 soot yield for the main control room abandonment study. The value of 0.172 for PVC was excluded due to its negligible use at FCS.
Recognizing the range of reported values and uncertainty associated with assigning one value for the abandonment study (in particular when actual fires are expected to involve several types of materials, as well as composite materials), a sensitivity study was performed in which the modeled soot yield was increased to a value of 0.08. This value was chosen as it bounds the soot yield for material types listed in Table 1 above, with the exception of PVC, which is negligibly used at FOS. Note that this study was performed for electrical cabinet fires, since the 0.06 soot yield is bounding for transient fires (generally consisting of paper in the control room, which burns relatively "clean"). The fire dynamic simulator (FDS) main control room simulation was re-run for peak heat release rates ranging from 100 to 1,000 kW, which covers 99.6% of the modeled heat release rate probability density function (alpha of 0.84 and beta of 59.3). Resulting optical density as a function of time is reported in the following figure. (See Figure FM-RAI-05ci).
LIC-1 2-0135 Enclosure Page 3 of 12 1.60 1.40
- Failure 1.20 -100 kW
-200 kW j* 1.00
-300 kW
. 0.80 -400 kW W
_ 0.60 -500 kW "Ri
- 600 kW o0.40 0.
-700 kW
.. 800 kW 0.20
-900 kW 0.00 11000 kW
(
-0.20 Time (Seconds)
Figure FM-RAI-05ci: Optical Density vs Time FCS Main Control Room Time to abandonment (assuming a 0.3 m-1 criterion per NUREG/CR-6850), non-suppression probability (NSP), severity factor (SF), and total non-suppression probabilities are reported in the following table for electrical cabinet fires.
Table 2 - Electrical Cabinet Fire (Qualified Cable, Multiple Bundles)
Aband. Time (min)
Case HRR Soot Yield = 0.08 NSP SF NSP x SF 1 100 20.5 1.15E-03 5.36E-01 6.18E-04 2 200 13.2 1.28E-02 2.04E-01 2.62E-03 3 300 11.5 2.25E-02 1.09E-01 2.45E-03 4 400 10.5 3.13E-02 6.19E-02 1.94E-03 5 500 10.1 3.57E-02 3.61E-02 1.29E-03 6 600 9.3 4.65E-02 2.14E-02 9.94E-04 7 700 8.8 5.48E-02 1.28E-02 7.01 E-04 8 800 8.5 6.05E-02 7.70E-03 4.66E-04 9 900 8.1 6.90E-02 4.67E-03 3.22E-04 10 1000 7.8 7.62E-02 2.84E-03 2.16E-04 Total Probability 1.16E-02 Assuming a 0.08 soot yield, the total probability that operators will fail to suppress a main control room electrical cabinet fire is 1.16E-02. The following table summarizes the abandonment core damage frequency (CDF) and large early release frequency (LERF) results of this sensitivity study.
LIC-1 2-0135 Enclosure Page 4 of 12 Table 3 - Abandonment CDF and LERF Results Calculated Risk Base Fire PRA* Sensitivity Study Increase between (Soot Yield = 0.06) (Soot Yield = 0.08) two Cases Abandnmen CaDF Abandonment CDF 4.59E-06 7.58E-06 2.99E-06
(/yr) II Abandonment 4.59E-07 7.58E-07 2.99E-07 LERF (/yr) I 1 ::_
- Base Fire PRA results as reported in Section W.2 of Reference 1.
Table 4 extends this sensitivity study to the total plant fire risk and total variance from deterministic requirement (VFDR) fire risk.
Table 4 - Total Plant Fire Risk and Total VFDR Fire Risk Base Fire PRA* Sensitivity Study**
(Soot Yield = 0.08)
Net VFDR ACDF for NFPA 805 5.72E-06 8.71 E-06 Transition (/yr)
Net VFDR ALERF for NFPA 805 6.67E-07 9.66E-07 Transition (/yr)
Total CDF (internal, flood, fire) (/yr) 6.01 E-05 6.31 E-05 Total LERF (internal, flood, fire) (/yr) 4.82E-06 5.12E-06
- Base Fire PRA results as reported in Section W.2 of Reference 1
In conclusion, when the soot yield is conservatively increased to a value of 0.08, the VFDR ACDF, VFDR ALERF, total CDF, and total LERF remain within the regulatory guide (RG) 1.174, Revision 1, Region II acceptance criteria. While this study does highlight the fire PRA sensitivity to the assumed soot yield, the 0.06 value used for the base fire PRA is considered appropriate, and the use of a soot yield greater than 0.08 would be considered excessively conservative, especially for a realistic fire PRA.
LIC-1 2-0135 Enclosure Page 5 of 12 Probabilistic Risk Assessment RAI 07:
Deviations from NUREG/CR-6850 beyond the four identified in Section 4.5.1.2 of LAR were noted. Regarding these deviations, please address the following:
- a. The first of these deviations is crediting a hot work procedural non-compliance factor of 0.01 for Compressor Area Room 19 (FC32), Switchgear Room FC36A, and Switchgear Room FC36B. This deviation is the subject of Item #3 in the supplement to the LAR dated December 19, 2011. For this deviation, it appears that the non-compliance factor should be removed since this factor is implicitly included in the hot work fire frequency. Please indicate any other physical analysis units/fire areas in which this factor is applied. For all cases, indicate the effect of removing this factor on CDF, LERF, ACDF, and ALERF.
OPPD's Response to Probabilistic Risk Assessment RAI 07 a.:
Section 4.5.1.2 of the NFPA 805 transition LAR (Reference 1) identifies that the FCS FPRA applied the following four deviations from NUREG/CR-6850:
- 1) Electrical cabinet generic severity factor and non-suppression probability
- 2) Pump fire frequency apportioning based on runtime
- 3) Diesel generator generic severity factor and non-suppression probability
- 4) Use of the draft version of the frequently asked question (FAQ) 08-0050 dated May 30, 2008 Reference 1 documents a sensitivity study in which the above four deviations from NUREG/CR-6850 are removed and replaced with methods-within the guidance of NUREG/CR-6850. The conclusion of this study was that the FCS NFPA 805 transition still met the R.G. 1.174 acceptance criteria total risk and change in risk without the use of Methods 1 through 4 above.
A supplement to the LAR was submitted to the NRC in December 2011 (Reference 2),
documenting a sensitivity study on a procedure compliance factor used to credit a proposed hot work control procedure change disallowing welding and cutting in the overhead of the Compressor Area (Room 19, Fire Compartment 32), thus addressing the noncompliance factor of 0.01. This response to PRA RAI 07 is intended to disposition all deviations from NUREG/CR-6850 beyond those identified in Reference 1.
This analysis is intended to supersede and subsume the sensitivity study documented in Reference 2. The reason for this approach is that modeling of the procedural compliance factor addressed in Reference 2 is interrelated with, and not easily separated from, the methods questioned in this RAI.
Recognizing that there is subjectivity in determining whether particular methods represent deviations from NUREG/CR-6850, OPPD has systematically reviewed the FPRA and identified two methods, beyond the four identified above and in Reference 1, as follows:
LIC-1 2-0135 Enclosure Page 6 of 12
- 5) A non-suppression probability of 0.01 was credited for cases in which a continuous fire watch is expected to be present. The factor was applied to all cable fires caused by welding and cutting (CFWC) and transient fires caused by welding and cutting (TFWC). The factor was applied to the FC32 Compressor Area and FC41 Cable Spreading Room where OPPD had committed to revise their combustible control procedures to require a continuous fire watch if combustibles were stored on the roof of Room 18 (related to FC32) or if the five pound combustible limitation were exceeded in the FC41 Cable Spreading Room. Finally, the factor was applied as a special case to FC28 with the basis that transient fires are most likely to occur in this particular area when scheduled work necessitating the presence of plant personnel occurs in this area.
- 6) A procedural compliance factor of 0.01 was credited for FC32 and FC41 for cases in which OPPD would have to violate a procedure for the general transient fires, transient fires caused by hot work, and cable fires caused by hot work postulated by the FPRA to occur. Note that this factor was also applied to transient scenarios in FC36C, which is an overhead pyrocrete cable shaft, and the factor was intended to reflect the very low likelihood of transient fires in this generally inaccessible shaft.
Methods 5 and 6 are removed from the FCS FPRA and replaced with methods within the guidance of NUREG/CR-6850 and its Supplement 1, as well as new methods endorsed by the NRC in Reference 3. The following paragraphs document the refinements made to compensate for the removal of methods 5 and 6 from the Fire PRA. At a high level, the following refinements were incorporated: re-evaluation of weighting factors for transient fire frequencies, incorporation of hot work revised frequencies, reduced transient heat release rates for two compartments, crediting suppression and severity factors for the revised compartments and detailed treatment of FC28 (previously quantified at full room burnup).
The maintenance weighting factors assigned for transient fire frequencies developed in Task 6 - fire ignition frequencies were re-evaluated. The maintenance weighting factors used for calculation of hot work fire frequencies were re-binned such that the full range of factors (1-Low, 3-Medium, 10-High, 50-Very High) were used for each generic location. No fractional (e.g., 0.1) weighting factors were applied. This re-binning resulted in most compartments being ranked as 3-Medium. The chart below shows the distribution of maintenance rankings for the Control/Auxiliary/Reactor Building generic location. Note that the distributions for the Plant-Wide and Turbine Building generic locations are more flat as a result of the smaller number of compartments assigned to these areas. (See Figure PRA-RAI-07a.)
LIC-1 2-0135 Enclosure Page 7 of 12 Control/Auxiliary/Reactor Building Maintenance Influence Factors 25
- 20 E
t E . 15 20 E s z
0 3 10 50 Maintenance Influence Factor Figure PRA-RAI-07a - Maintenance Influence Factors During the re-binning process, the following fire compartments were re-assigned to the Control/Auxiliary/Reactor Building generic location: FC36A East Switchgear Room, FC36B West Switchgear Room, FC36C Pyrocrete Enclosure, and FC41 Cable Spreading Room. These compartments had been assigned to the Plant-Wide generic location, but they more appropriately belong in the Control/Auxiliary/Reactor Building generic location as described in NUREG/CR-6850, Table 6-2. Next, the following revised generic fire frequencies (referenced and endorsed by Reference 3) were incorporated into the Fire PRA:
Table 5 - Revised Generic Fire Frequencies Bin Generic Location Ignition Source Type Mean Frequency 5 Control/Auxiliary/Reactor Cable Fires Caused by 2.69E-04 /yr Building Welding and Cutting 6 Control/Auxiliary/Reactor Transient Fires Caused by 353E-03 /yr Building Welding and Cutting 11 Plant-Wide Cable Fires Caused by 4.71 E-04 /yr Welding and Cutting 24 Plant-Wide Transient Fires Caused by 4.69E-03 /yr Welding and Cutting 31 Turbine Building Cable Fires Caused by 4.50E-04 /yr 31 TrieBWelding and Cutting The next method implemented in the FCS FPRA allows for flexibility in the heat release rate (HRR) prescribed for transient fires. The flexibility to assign transient fire heat release rates based on the characteristics of each plant area, as opposed to blanket application of the 317 kW probability density function to all areas, is afforded by Reference 3. The 9 8 th percentile HRR prescribed by NUREG/CR-6850 is 317 kilowatts (kW). The heat release rate probability density function for transient fire scenarios postulated in the FC32 Compressor Area (on the roof of Room 18) and FC41 Cable Spreading Room was changed from the 317 kW to the 69 kW probability density functions prescribed by NUREG/CR-6850 Table G-1.
LIC-1 2-0135 Enclosure Page 8 of 12 The 69 kW probability density function is appropriate for the cable spreading room, which has a procedural combustible loading limitation of five pounds. A search of OPPD corrective action documents over the past five years did not indicate any combustible control violations in the cable spreading room. There is minimal plant equipment in this room (only cable trays, junction boxes, and one small lighting panel are present), and maintenance activities are therefore minimized in this room. Finally, the FCS Operations, Maintenance, and Engineering departments are highly sensitive to fire risk in this area due to a long history of NRC inspection and oversight focus on cable spreading rooms at nuclear power plants.
The 69 kW probability density function is also appropriate for the FC32 Compressor Area. Due to the tall ceiling height of this area (20 feet), the only transient fire location with the potential to damage overhead cable trays (even assuming a larger 317 kW fire) is on the roof of the component cooling water heat exchanger room (Room 18). The likelihood of transient combustible storage in this small area is very remote because there is no mechanical plant equipment present, and the area can also only be accessed with a ladder or scaffolding. As part of the LAR implementation (REC-108),
OPPD plans to enhance the combustible and hot work controls specifically in this area, requiring a continuous fire watch anytime transient combustibles are stored on the roof of Room 18 and disallowing hot work in FC32 while the plant is at power. A search of OPPD corrective action documents over the past five years did not indicate a pattern of combustible control violations in the FC32 Compressor Area.
The FPRA supporting Reference 1 conservatively used a severity factor of 1.0 and a non-suppression probability of 1.0 for the FC32 Compressor Area and FC41 Cable Spreading Room transient fire scenarios. In this sensitivity study, vertical and horizontal distances to the nearest target were used to calculate transient fire severity factors in these areas. Resulting severity factors ranged from 0.21 to 0.95 in these areas. The severity factor is a direct multiplier in the CDF equation and this number represents the fraction of fire sizes that are too small to cause damage to cables or equipment.
In addition, the time to damage the nearest cable tray was also used to calculate a manual non-suppression probability using the welding curve (X = 0.188 /min) from NUREG/CR-6850, Supplement 1. The use of the welding curve to calculate non-suppression replaces the 0.01 NSP that was previously assigned for these areas. The damage times ranged from six to eight minutes, and the resulting manual non-suppression probabilities ranged from 0.22 to 0.32 for the FC32 Compressor Area and FC41 Cable Spreading Room transient fire scenarios. Note that the welding curve (X =
0.188 /min) was used specifically for these two compartments in which OPPD plans to implement procedure changes that would require continuous fire watches in these areas when combustible limitations (5 lbs. for FC41 and 0 lb. for FC32 [roof of Room 18]) were exceeded.
For the FC41 Cable Spreading Room, the FPRA supporting Reference 1 conservatively did not credit the alternative shutdown process. This process is proceduralized for cable spreading room fires in AOP-06. This sensitivity study credits the alternative shutdown process consistent with the main control room analysis by assuming 0.1 and
LIC-12-0135 Enclosure Page 9 of 12 0.01 probabilities for failure to prevent core damage and large early release, respectively, using the alternative shutdown process.
For cable fires caused by welding and cutting (CFWC), the sensitivity study assumed that five minutes would be available for fire suppression prior to any significant damage occurring. This approach is reasonable given that the typical hot work fire scenario involves welding slag falling onto a cable tray. It is expected that it would take at least five minutes for the hot slag to ignite cables in the tray and cause significant damage within the impacted tray. Furthermore, a continuous fire watch is present during hot work such that these fires would most likely be detected very early. Using the welding curve (X = 0.188 /min) from NUREG/CR-6850, Supplement 1 and a damage time of five minutes yields a manual non-suppression probability of 0.39.
Aside from the refinements made for the transients in FC32 and FC41, a more detailed treatment of FC28 (Room 71) is implemented. FC28 was originally quantified at the full compartment burn-up level. In this sensitivity study, the compartment was subdivided into three scenarios: transient fire, transient fire caused by welding and cutting, and cable fire caused by welding and cutting. There are no fixed ignition sources modeled in this compartment. For the cable fire caused by welding and cutting, a non-suppression probability of 0.39 is applied as discussed above. For the transient fire caused by welding and cutting, a time to target damage of five minutes was calculated based on an assumed average distance to the nearest target of one meter, and this corresponds to a non-suppression probability of 0.39 (using the welding curve with X =
0.188/min). Finally, for the transient fire, a time to damage of five minutes was similarly calculated, and this corresponds to a non-suppression probability of 0.53 (using the transient curve with X= 0.126 /min).
The following table summarizes the total VFDR ACDF, total VFDR ALERF, total plant CDF, and total plant LERF for the base fire PRA (Reference 1), a sensitivity study in which methods 1-4 were replaced with methods within the guidance of NUREG/CR-6850, and a sensitivity study in which methods 1-6 were replaced with methods within the guidance of NUREG/CR-6850.
Table 6 - Summary: Reference 1 Base Fire PRA, No-Credit Sensitivity Studies Base Fire PRA Sensitivity Study Sensitivity Study (Reference 1- (No Credit for Methods 1-4, (No Credit for LIC-1 1-0099) Reference 1 - LIC-1 1-0099) Methods 1-6)
VFDR ACDF for NFPA 5.72E-06 8.72E-06 9.OOE-06 805 Transition (/yr)
VFDR ALERF for NFPA 6.67E-07 8.46E-07 7.22E-07*
805 Transition (/yr)
Total CDF (internal, 6.01 E-05 9.40E-05 9.91 E-05 flood, fire) (/yr)
Total LERF (internal, 4.82E-06 8.58E-06 8.68E-06 flood, fire) (/yr) I_ II
- Note that the ALERF without credit for Methods 1-6 is lower than that report without credit to Methods 1-
- 4. This is because the fire PRA model refinements that were made during the sensitivity study assessment of Methods 5 and 6 also reduced the ALERF associated with Methods 1-4, and this benefit is not reflected in the reported ACDF associated with Methods 1-4.
LIC-1 2-0135 Enclosure Page 10 of 12 In conclusion, FCS meets the RG 1.174, Revision 1, Region II acceptance criteria when deviations from NUREG/CR-6850 (Methods 1 through 6 described above) are removed from the fire PRA and replaced by methods within the guidance of NUREG/CR-6850.
- b. The second deviation is crediting a continuous fire watch on storage of combustibles through a non-suppression factor of 0.01. In the case of the roof of FC32, this fire watch credit is applied for all combustible loading; in the case of the Cable Spreading Room (FC41), this fire watch credit is applied for combustibles above 5 lbs. The use of the non-suppression factor must be justified, keeping in mind that the continuous fire watch generally provides detection, but not necessarily suppression. The scenario for the roof should take into account the full range of combustibles that are expected to be located on the roof, as well as the possible locations of those combustibles on the roof. Should the fire watch perform a suppression function, it should be confirmed that one of the fire watch's purposes is to extinguish the fire, that an extinguisher will be readily available, and that the fire watch will have undergone adequate training in the use of extinguishers. Also, the time over which the combustibles are to be placed in each location must be described. Please provide the effect of the second deviation on CDF. LERF, ACDF, and ALERF. For the justification of nonsuppression, address the detection and suppression timing, the combustible storage limit, and any other key assumptions. If this type of non-suppression credit is used elsewhere in the fire PRA, identify and discuss along similar lines, ensuring that the physical analysis unit/fire area in which it is used is identified.
OPPD's Response to Probabilistic Risk Assessment RAI 07 b.:
As described in response to PRA RAI 07a, a non-suppression probability of 0.01 was credited for cases in which a continuous fire watch is expected to be present. The factor was applied to all cable fires caused by welding and cutting (CFWC) and transient fires caused by welding and cutting (TFWC). The factor was applied to the FC32 Compressor Area and FC41 Cable Spreading Room where OPPD had committed to revise their combustible control procedures to require a continuous fire watch if combustibles were stored on the roof of Room 18 (related to FC32) or if the five pound combustible limitation were exceeded in the FC41 Cable Spreading Room. Finally, the factor was applied as a special case to FC28 with the basis that transient fires are most likely to occur in this particular area when scheduled work necessitating the presence of plant personnel occurs in this area.
The 0.01 NSP factor was implemented in the baseline PRA as a result of tight combustible controls for the area, presence of a continuous fire watch and plant sensitivity to the fire compartments in which it was assigned. Hot work activities in FC32 and FC41 are to be performed with the assistance of a fire watch. The fire watch shall have a fire extinguisher checked out for a continuous fire watch. As specified in standing order SO-M-9 (Reference 5), in the event of a fire, the fire watch must immediately report the fire to the control room and attempt to extinguish the fire. Fire watch personnel are trained in accordance with FCS training lesson plan 1065-00 (Reference 4) which includes training on operation and proper use of fire extinguishers.
LIC-1 2-0135 Enclosure Page 11 of 12 FCS maintains that combustibles on the roof of Room 18 would be unusual.
Nevertheless, the baseline FPRA assumed a transient fire on the roof of Room 18 that would impact the entire overhead area. SO-G-91, Control and Transportation of Combustible Materials (Reference 6), does not allow transients to be stored on the roof of Room 18 (in FC32). Placing transients in this area would be a direct procedure violation. Furthermore, this area is not easily accessible and most of the volume above Room 18 is covered with cables trays, therefore making this an unusual and difficult spot for transient placement. The baseline FPRA's assignment of the procedure compliance factor credits the plant's procedure for prevention of fire sources (transient combustibles on the roof of Room 18).
The sensitivity study documented in OPPD's response to PRA RAI 07a removes this 0.01 factor (originally intended to represent a generic non-suppression probability when a continuous fire watch is present) and sets it to either 1.0 or a calculated value. If a calculated value is used, it is based on the following equation per NUREG/CR-6850, Supplement 1, Chapter 14:
NSP = e*?t where X is 0.188 /min (using the welding curve since a fire watch is present during welding activities) and t is the available suppression time, which is calculated based on the time to target damage given the fire growth profile and the source-target geometry.
The sensitivity study in response to PRA RAI 07 a. concluded that OPPD meets the RG 1.174, Revision 1, Region II acceptance criteria for FCS when all deviations from NUREG/CR-6850 (including the 0.01 non-suppression probability for continuous fire watches) are removed and replaced by methods within the guidance of NUREG/CR-6850.
- c. Please identify and describe any other deviation from NUREG/CR-6850 not already identified and described in this RAI or in Section 4.5.1.2 of the LAR (the subject of another RAI). Please provide a sensitivity analysis of each of these other deviations from NUREG/CR-6850. Also, provide the composite impact on CDF, LERF, ACDF, and ALERF from the sensitivity studies applied upon removal of all deviations identified in this RAI and the four deviations identified in the LAR.
OPPD's Response to Probabilistic Risk Assessment RAI 07 c.:
All methods which OPPD considers to be deviations from NUREG/CR-6850 and its Supplement 1 are declared in response to PRA RAI 07a. The RAI response also provides a composite sensitivity study in which no deviations from NUREG/CR-6850, or other approved guidance, are credited. This study concluded that FCS meets the RG 1.174, Revision 1, Region II acceptance criteria when the deviations from NUREG/CR-6850 are removed and replaced by methods within the guidance of NUREG/CR-6850.
Recognizing that there is subjectivity in determining whether particular methods represent deviations from NUREG/CR-6850, OPPD has systematically identified and evaluated via sensitivity studies all deviations from NUREG/CR-6850.
LIC-1 2-0135 Enclosure Page 12 of 12
References:
- 1. Letter from OPPD (J. A. Reinhart) to NRC (Document Control Desk), License Amendment Request 10-07, Proposed Changes to Adopt NFPA 805, Performance-BasedStandard for Fire Protection for Light Water Reactor Generating Plants (2001 Edition) at Fort Calhoun Station, dated September 28, 2011 (LIC-1 1-0099) (ML112760660)
- 2. Letter from OPPD (D. J. Bannister) to NRC (Document Control Desk), Supplement to License Amendment Request (LAR) 10-07, Proposed Changes to Adopt NIFPA 805, Performance-BasedStandardfor Fire Protection for Light Water Reactor GeneratingPlants (2001 Edition) at Fort Calhoun Station, dated December 19, 2011 (LIC-1 1-0130)
- 3. Letter from NRC (Joseph Giitter) to NEI (Biff Bradley), "Recent Fire PRA Methods Review Panel Decisions and EPRI 1022993, Evaluation of Peak Heat Release Rates in Electrical CabinetFires," dated June 21, 2012 (ML12172A406)
- 4. FCS Training Lesson Plan 1065-00, Nuclear Training Industrial Safety Training Program Fire Watch Duties, Revision 17, February 25, 2008
- 5. SO-M-9, Fort Calhoun Station Unit No. 1 Standing Order, Hot Work Operations, Revision 28, June 13, 2006
- 6. SO-G-91, Fort Calhoun Station Unit No. 1 Standing Order, Control and Transportation of Combustible Materials, Revision 26, December 11, 2009
- 7. NUREG-1805, Fire Dynamics Tools (FDTs) Quantitative Fire Hazard Analysis Methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program (NUREG-1805), December 2004