ML101450047
| ML101450047 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 05/24/2010 |
| From: | Cowan P Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| TAC ME2159 | |
| Download: ML101450047 (8) | |
Text
Exelon Nuclear www.exeloncorp.com ExeIn.
Exelon.
200 ExeJon Way Nuclear Ken nett Square, PA 19348 10 CFR 50.90 24, 2010 May 24,2010 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Peach Bottom Atomic Power Station, Unit 2 Renewed Facility Operating License No. DPR-44 NRC Docket No. 50-277
Subject:
Response to Request for Additional Information - License Amendment Request for Type A Test Extension
References:
- 1) Letter from P. B. Cowan (Exelon Generation Company, LLC) to U.S. US. Nuclear License Amendment Request - Type A Test Regulatory Commission, "License -
28, 2009 Extension, dated August 28,2009 Extension,"
- 2) Letter from J. D. Hughey (U.S. (US. Nuclear Regulatory Commission) to C. G.
Pardee (Exelon Generation Company, LLC), "Peach Peach Bottom Atomic Power Station, Unit 2 - Request for Additional Information Regarding License Amendment Request For One~Time One-Time Five-Year Containment Type A ME2159), dated Integrated Leak Rate Test Interval Extension (TAC NO. ME2159),"
February 23, 2010
- 3) Letter from P. B. Cowan (Exelon Generation Company, LLC) to U.S. Nuclear Response to Request for Additional Information -
Regulatory Commission, "Response -
Extension, dated February 25, License Amendment Request for Type A Test Extension,"
2010
- 4) Letter from J. D. Hughey (U.S. Nuclear Regulatory Commission) to C. G.
Pardee (Exelon Generation Company, LLC), "Peach Peach Bottom Atomic Power Station, Unit 2 - Request for Additional Information Regarding License Amendment Request For One-Time Five-Year Containment Type A ME21 59), dated May Integrated Leak Rate Test Interval Extension (TAC NO. ME2159),"
19, 2010 19,2010
Response to RAI - License Amendment Request ForFor Type A Test Extension 24, 2010 May 24,2010 Page 2 In the Reference 11 letter, Exelon Generation Company, LLC (EGG) requested a proposed Primary Containment Leakage Rate change to modify Technical Specification (TS) 5.5.12, "Primary Program. Specifically, the proposed change will revise TS 5.5.12 to reflect a one-time Testing Program."
extension of the containment Type A Integrated Leak Rate Test (ILRT) from 10 to 15 years.
pertormed no later than October This one-time extension will require the Type A ILRT to be performed 2015.
In the Reference 4 letter, the U.S. Nuclear Regulatory Commission requested additional information. Attachment 11 contains our response to this request for additional information.
No regulatory commitments are contained in this response.
Should you have any questions concerning this letter, please contact Tom Loomis at (610) 765-5510.
II declare under penalty of perjury that the foregoing is true and correct. Executed on the 24th of May 2010.
Respectfully,
'ij Olr ~!Uf Pamela B. Cowan Director, Licensing & Regulatory Affairs Exelon Generation Company, LLC
Attachment:
- 1) 1) Response to Request for Additional Information - License Amendment Request for Type A Test Extension cc: USNRC Region I, Regional Administrator USNRC Senior Resident Inspector, PBAPS USNRC Project Manager, PBAPS R. R. Janati, Bureau of Radiation Protection, Commonwealth of Pennsylvania S. T. Gray, State of Maryland
Attachment 1 C) 3CD C
00 30 Response to Request for Additional Information CD 0
CDCD 0 CD CD0 V
CD :
C)
CD 00 CD IA 00 License Amendment Request for Type A Test Extension CD CD CD 0 0
RM DOCUMENTATION APPROVAL FORM RM DOCUMENTATION NO. PB-LAR-07 PB*LAR*07 REV: 0 PAGE NO. 1I STATION: Peach Bottom Atomic Power Station UNIT(s) AFFECTED: 2 TITLE: Response to an additional NRC RAI Related to the License Amendment Request for a Type A Integrated Leak Rate Test Interval Extension for Unit 2
SUMMARY
This document contains responses to an additional PRA related RAI obtained from the NRC for the PBAPS Unit 2 LAR for a one-time extension to the containment Type A integrated leak rate test (ILRT).
(ILRT),
This is a Category II RM Document lAW ER-AA-600-1012, which requires independent review and approval.
(( )) Review required after periodic Update
((X]
X] Internal RM Documentation (( ] External RM Documentation Electronic Calculation Data Files: N/A Method of Review: X J] Detailed (( ]j Alternate (( ]j Review of External Document
((X This RM documentation supersedes: N/A in its entirety.
Prepared by: DonaldEVanover Donald E. Vanover / 2)cr~Ld E V~ .. <-V / 5/20/10 Print Sign Date Reviewed by: Robert J. Wolfgang / ,r4tj~~ / 5/20/10 Print Sign Date Approved by:by Gregory gpygL A. Krueger Print I~
T O
/ 5/21/10 Date
RAI-06
The response to RAI-02 in letter dated February 25, 2010, states that explicit consideration of external events is not warranted. The NRC staff notes that explicit consideration of external events, as described in Section 5.7 of the risk assessment (Attachment 4) in the LAR dated August 28,2009, 28, 2009, would require multiplying the change in core damage frequency (LlCDF)
(CDF) and the change in large early release frequency (L\LERF) by a factor of 12.2. Multiplying the LlLERF (LlLERF) ALERF by a factor of 12.2 would put the total LlLERF Region I"I of the Regulatory Guide (RG) 1.174, "An XLERF in "Region An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant Specific Changes to the Licensing Basis,"
Basis, acceptance guidelines (Le.(i.e. -5.5E-7 in the LAR +
+ -3.2E-6 in RAI response = = -3.7E-6).
Please provide additional justification with regard to the February 25, 2010, response to RAI-02 that supports the conclusion that the total LlLERF
\LERF would be in "Region Region II" Il of RG 1.174. NRC draft guidance on containment accident pressure credit is provided in NRC Draft Guidance for the Use of Containment Accident Pressure in Section 2.7 of "NRC Determining the NPSH [net positive suction head] Margin of ECCS [emergency core cooling system] and Containment Heat Removal Pumps," Pumps, (ADAMS Accession No. ML100550869) transmitted by letter to the Boiling Water Reactor Owners Group on ML100550869)
March 1, 2010 (ADAMS Accession No. No, ML100550903).
Response
The RAI-02 response in the letter dated February 25, 2010 addressed the containment pressure credit for pump net positive suction head in a bounding fashion. Three specific scenarios were analyzed (large LOCAs, anticipated transients without scram (ATWS), (ATWS),
and other transients). The potential impact from external events will be addressed for each of these categories, and the impact on the RG 1.174 region in which the bounding analysis results lie are re-examined below:
LarQe LOCAs Large The large LOCA assessment in the RAI-02 response utilized an applicable initiating event frequency value of 2E-4/yr. It was noted that this assumption was conservative compared to the generic large LOCA (7.0E-6/yr)
(7.OE-6/yr) and medium LOCA (1.0E-4/yr)
(1 .OE-4/yr) frequencies available from NUREG/CR-6928 [Ref. 6-1]. An additional contribution from external events in this category would potentially exist from seismically induced Large LOCA (LLOCA) scenarios. However, the choice of the 2.0E-4/yr2.OE-4/yr applicable LLOCA frequency in the original assessment far exceeds any reasonable representation of an additional contribution from seismic events where most reported values for seismically induced LLOCA frequencies are in the E-6/yr range or less (e.g., using the NRC RASP 2
Handbook, Vol. 2 [Ref 6-2] methodologies and data along with the NRC NUREG-1488
[Ref. 6-3] hazard curves for PBAPS results in a seismic induced LLOCA frequency that
<<1% of the internal events LLOCA frequency used in the original RAI response).
is <<1%
Additionally, seismically induced LLOCA scenarios would be of sufficient seismic magnitude that they would also cause significant damage to other components and structures at the site such that the presence of a pre-existing containment leakage would likely be a moot point in the accident sequence analysis.
Therefore, no additional changes to the calculated L1CDF L\LERF values from Large z\CDF and L1LERF LOCA scenarios is warranted to account for an additional external events impact and the values are as was reported in the RAI-02 response.
~CDF =
tCDF ~LERF =
= IxLERF 22E-7/yr
= 2.2E-7/yr ATWS The ATWS assessment in the RAI-02 response utilized an applicable initiating event frequency value of 1/yr. This is also conservative compared to the actual plant experience over the last several years and to the industry average performance which is trending towards much less than 1 1 automatic scram per year [e.g. 1 1 of
[eg. refer to Slide 11 Ref. 6-4]. An additional contribution from external events in this category could exist from fire, seismic, or other external events, but the use of 11 applicable event per year is judged to be bounding as this value far exceeds any reasonable representation of an additional contribution from external events where the initiating event frequencies are typically much less than this.
ACDF and L1LERF Therefore, no additional changes to the calculated L1CDF L\LERF values from ATWS scenarios is warranted to account for an additional external events impact and the values are as was reported in the RAI-02 response.
~CDF IXCDF =EiLERF
~LERF = 2.2E-8/yr 22E-8/yr Other Transients The potential impact from other transients was also handled in a bounding fashion.
However, the impact from these types of scenarios could also be applicable to external events initiated transient scenarios. In a similar fashion as was provided in Section 5.7 57 of the Risk Assessment (Attachment 4) in license amendment request (LAR) dated August 28, 2009, the external events contribution could be estimated by multiplying the change in core damage frequency (L1CDF)
(ACDF) and the change in large early release (z\LERF) by a factor of 12.2. However, to better frequency (L1LERF) beffer account for this added conservatism, further refinement to the initial bounding assessment is needed.
3
Therefore, rather than use the very conservative factor of 2.0 in the assessment for impacts on Human Failure Events (HFEs). (HFEs), it is more reasonable to assume that at most a 50% increase in the Human Error Probability (HEP) values that contribute to the relevant scenarios occurs. This is still bounding, however, since as noted in the original response, although the pre-existing containment breach may lead to an earlier loss of ECCS injection, the actual available time to respond to utilize alternate forms of injection prior to reaching core damage would not substantially change. For the types of HFEs that would be involved in these scenarios, most HEP evaluation methods would predict minimal or no impact due to these timing changes since the difference between the time of the cue and the available time to respond would be on the order of a few hours in both cases and not minutes. For example, the HEP for refilling the Condensate Storage Tank to maintain long term injection from an external source (which is one of the most important actions that would be needed to respond to these types of events) would in fact not be impacted by the timing changes based on the HEP methodology utilized in the Peach Bottom PRA model (Le. (i.e. the EPRI cause based decision trees). In any event, a bounding assessment is utilized by assuming that all of the relevant scenarios are impacted by a 50% increase as shown below.
CDF base = LERF CDFbase base =
LERFbase = 8.3E-7/yr
yr LRT = 8.3E-7/yr
- 2.7E-3
- 1.5 1 ,5
- 5.0 = 1.7E-8/yr 1 .7E-8/yr LlCDF LERF =
1CDF = LlLERF 1 .7E-8/yr - 3.4E-9/yr =
= 1.7E-8/yr 1 .4E-8Iyr
= 1.4E-8/yr To further account for the potential impact from external events, this value can be multiplied by 12.2 as was done in the August 28, 2009 LAR. As noted in the LAR, the use of this 12.2 multiplier is also judged to be bounding for the external events impact.
LXCDF =
LlCDF zLERF = 12.2 ** 1.4E-8/yr
= LlLERF 1 .4E-8/yr = 1 .7E-7/yr
= 1.7E-7/yr RAI-06 Conclusions The incorporation of these bounding assessment results leads to the following totals for LCDF and LlLERF.
LlCDF LERF.
Contributor ACDF ALERF LAR Submittal Internal Events 0.0 4.5E-8/yr LAR Submittal External Events 0.0 5.1E-7/yr 5.1 E-7/yr Containment Pressure Credit - Large -
LOCAs (Internal and External) 2.2E-7/yr 2.2E-7/yr Containment Pressure Credit - ATWS (Internal and External) 2.2E-8/yr 2.2E-8/yr 2.2E-8lvr Containment Pressure Credit - Other Transients (Internal and External) 1 .7E-7/yr 1.7E-7/yr 1 .7E-7/yr 1.7E-7/yr Total: 4.1E-7/yr 4.1 E-7/yr 9.7E-7/yr 4
In summary, In summary, the the results results of of these these assessments, assessments, although although bounding bounding in in nature, nature, still still indicate that indicate that the the increase increase inin LERF LERF due due to the combined to the combined internal internal and and external external events challenges from challenges from extending extending thethe PBAPS PBAPS ILRT frequency from 3 per per 10 10 years toto 11 per per 15 15 years remains in in Region" Region II between between 1E-7 1 E-7 to 1E-6 1 E-6 per per reactor reactor year ("Small (Small Change" Change in in risk> of risk) of the the Regulatory Regulatory Guide Guide 1.174 1174 acceptance guidelines.
guidelines Additionally, Additionally, the the postulated postulated change in CDF is less than 1E-6 1 E-6 per per reactor year, year which is is in in the less restrictive restrictive Region Region Ill ("Very III (Very Small Change" Change in risk) risk> of the Regulatory Guide Guide 1.174 acceptance guidelines.
References RAI-06 References
[6-1] aL, "Industry-Average Eide, S. A. et. aI., Industry-Average Performance for Components and Initiating U S Commercial Nuclear Power Plants,"
Events at U.S. Plants, NUREG/CR-6928, NUREG/CR-6928, January 2007.
[6-2] USNRC, "RiskRisk Assessment of Operational Events Handbook, Volume 2, External Events, Revision 1, September 2007.
Events",
[6-3] Revised Livermore Seismic Hazard Estimates for 69 Sites East of the USNRC, "Revised Mountains, NUREG-1488, Rocky Mountains," NUREG-1488, April 1994.
[6-4] Borchardt, Bill, Excutive Director of NRC Operations, "An An Overview of NRC Operations, Operations," Regulatory Information Conference, March 9, 2010. 2010 Available at http://www. nrc.gov/public-involve/conference http://www.nrc.gov/public-involve/conference-symposia/ric/past/201 O/slides/openingborchardtbpv.pdf.
symposia/ric/past/201 0/slides/openingborchardtbpv.pdf.
55