NMP1L3467, License Amendment Request - Revision to Alternative Source Term Calculation for Main Steam Isolation Valve (MSIV) Leakage and Non-MSIV Leakage

License Amendment Request - Revision to Alternative Source Term Calculation for Main Steam Isolation Valve (MSIV) Leakage and Non-MSIV Leakage

ML22180A020
Person / Time
Site:	Nine Mile Point
Issue date:	06/29/2022
From:	David Gudger Constellation Energy Company
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NMP1L3467
Download: ML22180A020 (9)

Text

200 Exelon Way Kennett Square, PA 19348 www.constellation.com 10 CFR 50.90 NMP1L3467 June 29, 2022 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Nine Mile Point Nuclear Station, Unit 1 Renewed Facility Operating License No. DPR-63 NRC Docket No. 50-220

Subject:

License Amendment Request - Revision to Alternative Source Term Calculation for Main Steam Isolation Valve (MSIV) Leakage and Non-MSIV Leakage at Nine Mile Point, Unit 1 In accordance with 10 CFR 50.90, "Application for amendment of license, construction permit, or early site permit," Constellation Energy Generation, LLC (CEG) requests approval of proposed changes to the Post LOCA Alternative Source Term analysis for containment leakage at Nine Mile Point Nuclear Station, Unit 1 (NMP1).

The proposed changes include corrections to the chemical group assignment for various radionuclides modeled in the RadTrad 3.03 code and updates to the modeling of both Main Steam Isolation Valve (MSIV) leakage and non-MSIV leakage. This change is in response to an NRC Inspection Finding where it was discovered changes were made to the original 2007 AST analysis that when taken consecutively, would not have been allowed via 10 CFR 50.59. provides an evaluation supporting the proposed change.

CEG requests approval of these changes by February 28, 2023, to support the NMP1 refuel outage. This license amendment will be implemented within 60 days of approval.

The proposed change has been reviewed by the NMP Plant Operations Review Committee in accordance with the requirements of the CEG Quality Assurance Program.

There are no regulatory commitments contained within this letter.

In accordance with 10 CFR 50.91, "Notice for public comment; State consultation," paragraph (b), CEG is notifying the State New York of this application for license amendment by transmitting a copy of this letter and its attachments to a designated State Official.

License Amendment Request - Revision to Alternative Source Term Calculation for Main Steam Isolation Valve (MSIV) Leakage and Non-MSIV Leakage June 29, 2022 Page 2 Should you have any questions concerning this letter, please contact Ron Reynolds at (610) 765-5247.

I declare under penalty of perjury that the foregoing is true and correct. This statement was executed on the 29th day of June 2022.

Respectfully, David T. Gudger Senior Manager - Licensing Constellation Energy Generation, LLC

Attachment:

1. Evaluation of Proposed Change cc: NRC Regional Administrator, Region I NRC Senior Resident Inspector, NMP NRC Project Manager, NMP A. L. Peterson, NYSERDA

ATTACHMENT 1 EVALUATION OF PROPOSED CHANGE License Amendment Request Nine Mile Point Nuclear Station, Unit 1 Docket No. 50-220

SUBJECT:

License Amendment Request - Revision to Alternative Source Term Calculation for Main Steam Isolation Valve (MSIV) Leakage and Non-MSIV Leakage at Nine Mile Point, Unit 1 1.0

SUMMARY

DESCRIPTION 2.0 DETAILED DESCRIPTION

4.0 REGULATORY EVALUATION

4.1 Applicable Regulatory Requirements/Criteria 4.2 Precedent 4.3 No Significant Hazards Consideration 4.4 Conclusions

6.0 REFERENCES

Attachment 1 Evaluation of Proposed Change Page 1 1.0

SUMMARY

DESCRIPTION In accordance with 10 CFR 50.90, "Application for amendment of license, construction permit, or early site permit," Constellation Energy Generation, LLC (CEG) requests approval of proposed changes to the NMP1 Post LOCA Alternative Source Term (AST) analysis for containment leakage at Nine Mile Point Nuclear Station, Unit 1 (NMP1).

The proposed changes are in response to an NRC Inspection Finding where it was discovered changes were made to the original 2007 AST analysis that when taken consecutively, would not have been allowed via 10 CFR 50.59. The first change was performed where corrections to the chemical group assignment for various radionuclides modeled in the RadTrad 3.03 code were needed. The second change involved updates and recategorizations to the modeling of both Main Steam Isolation Valve (MSIV) leakage and non-MSIV leakage.

2.0 DETAILED DESCRIPTION The NMP1 Post LOCA AST analysis is proposing two changes since the 2007 NRC approval of Amendment 194 (ML073230597) (Reference 6.1). NMP1 is a BWR/2 reactor design with two main steam lines.

The first proposed change consists of correcting errors in the source term used by the RadTrad 3.03 code to calculate the dose consequences to the control room personnel and offsite.

Specifically, 20 radionuclides out of the 63 modeled were assigned the incorrect chemical group.

The second proposed change involved updates to the modeling of both MSIV leakage and non-MSIV leakage. The original analysis modeled a total of 100 standard cubic feet per hour (scfh)

MSIV leakage and 41.5 scfh non-MSIV leakage. The new modeling allows for a total of 191 scfh of combined MSIV and non-MSIV leakage. This flexibility allows for a maximum MSIV leakage to range from 100 - 190 scfh and non MSIV leakage to range from 1 - 91 scfh in any combination as long as the total leakage was < 191 scfh. Cases were run at increments of 10 scfh throughout their allowed ranges to identify the limiting combination. The combination of 100 scfh MSIV leakage and 91 scfh non-MSIV leakage was found to be the limiting combination.

3.0 TECHNICAL EVALUATION

The NMP1 Post LOCA AST analysis is proposing two changes since the 2007 NRC approval of Amendment 194.

The current analysis uses the applicable regulatory criteria of 5 rem Total Effective Dose Equivalent (TEDE) in the Control Room (CR) for the duration of the event, 25 rem TEDE at the exclusion area boundary (EAB) for the worst 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, and 25 rem TEDE at the outer boundary of the low population zone (LPZ) for the duration of the event with the following final dose results shown in Table 1:

Attachment 1 Evaluation of Proposed Change Page 2 Table 1 30-day CR Max 2-hour EAB 30-day LPZ TEDE (rem) TEDE (rem) TEDE (rem)

Dose 4.81 9.02 1.60 Limit 5 25 25 The first proposed change consists of correcting errors in the source term used by the RadTrad 3.03 code to calculate the dose consequences to the CR personnel and offsite. Specifically, 20 radionuclides out of the 63 modeled were assigned the incorrect chemical group. Table 2 below illustrates the impacted radionuclides, the chemical group used, the proposed corrections, to the chemical group, and the release fraction change.

Table 2 Impacted Rev. 0 Corrected In-Vessel Release Radionuclide Chemical Chemical Fraction Change Group Group [Rev. 0 -> Corrected]

(2) Ba Isotopes Sr Ba 2% -> 2%

• Ba-139

• Ba-140 (6) Noble Metal Ba Noble Metal 2% -> 0.25%

• Mo-99

• Tc-99m

• Ru-103

• Ru-105

• Ru-106

• Rh-105 (12) Lanthanum Noble Metal Lanthanum 0.25% -> 0.02%

• Y-90

• Y-91

• Y-92

• Y-93

• Zr-95

• Zr-97

• Nb-95

• La-140

• La-142

• Am-241

• Cm-242

• Cm-244

Attachment 1 Evaluation of Proposed Change Page 3 Based on the change to release fraction, the 2 BA Isotopes are not impacted because the release fraction did not change; however, the six Noble Metal and twelve Lanthanum groups both saw large reductions in their release fractions. Of these impacted radionuclides, the largest dose impacts are Ru-106, Cm-242, and Cm-244 with Ru-106 dominating among these three.

Table 3 illustrates the total impact the corrected release fractions had to dose results using the proposed corrections of the 20 Isotopes:

Table 3 30-day Max 2-hour 30-day CR EAB TEDE LPZ TEDE (rem) TEDE (rem) (rem)

Dose Impact -0.44 -1.59 -0.15 since AOR Change #1 4.37 7.43 1.45 Dose Results The second proposed change includes updates to the modeling of both MSIV leakage and non-MSIV leakage. The original analysis modeled a total of 100 scfh MSIV leakage and 41.5 scfh non-MSIV leakage. The new modeling allows for a total of 191 scfh of combined MSIV and non-MSIV leakage. This flexibility allows for a maximum MSIV Leakage to range from 100 -

190 scfh and non MSIV Leakage to range from 1 - 91 scfh in any combination as long as the total leakage was < 191 scfh. Cases were run at increments of 10 scfh throughout their allowed ranges to identify the limiting combination. The combination of 100 scfh MSIV leakage and 91 scfh non-MSIV leakage was found to be the limiting combination. Table 4 illustrates implementation of this proposed change if taken sequentially after the source term change listed above resulting in the following increase of dose results.

Table 4 30-day Max 2-hour 30-day CR EAB TEDE LPZ TEDE (rem) TEDE (rem) (rem)

Dose Impact from +0.44 +0.57 +0.13 Change #1 Dose Results Change #1 & #2 4.81 8.00 1.58 Combined Dose Results The final results above remain within the limits established in Table 1 and would become the new limiting analysis of record for the NMP1 Post-LOCA AST calculation.

Attachment 1 Evaluation of Proposed Change Page 4

4.0 REGULATORY EVALUATION

4.1 Applicable Regulatory Requirements/Criteria 10 CFR 50.67, "Accident source term," establishes acceptable radiation dose limits resulting from design basis accidents for an individual located at the exclusion area boundary or low population zone, and for occupants of the control room. The analyses performed by NMP1 demonstrate that the calculated radiological consequences of a design basis LOCA with increased leakage through the main steam lines meet the radiation dose limits specified in 10 CFR 50.67.

Regulatory Guide (RG) 1.183, dated July 2000, "Alternative Radiological Source Terms for Evaluating Design Basis Accidents at Nuclear Power Reactors," provides guidance for implementation of 10 CFR 50.67, including assumptions and methods that are acceptable to the NRC staff for performing design basis radiological analyses using an AST.

Regulatory Issue Summary (RIS) 2006-04, "Experience with Implementation of Alternative Source Terms," provides guidance to ensure that the appropriate level of technical detail is considered in AST analyses and included in AST submittals.

4.2 Precedent Letter from M. David (NRC Project Manager) to K. Polson (Vice President Nine Mile Point),

"Nine Mile Point Nuclear Station, Unit No. 1 - Issuance of Amendment RE: Implementation of Alternative Radiological Source Term (TAC NO. MD3896)," dated December 19, 2007 (ML073230597).

4.3 No Significant Hazards Consideration Constellation Energy Generation, LLC (CEG) has evaluated whether or not a significant hazards consideration is involved with the proposed amendment by focusing on the three standards set forth in 10 CFR 50.92, "Issuance of amendment," as discussed below:

1. Does the proposed amendment involve a significant increase in the probability or consequences of an accident previously evaluated?

Response: No.

The proposed changes to the Alternative Source Term (AST) analysis and those plant systems affected by AST do not initiate DBAs. The AST does not affect the design or manner in which the facility is operated; rather, for postulated accidents, the AST is an input to calculations that evaluate the radiological consequences. The AST does not by itself affect the post-accident plant response or the actual pathway of the radiation released from the fuel. It does, however, better represent the physical characteristics of the release, so that appropriate mitigation techniques may be applied. Implementation of the AST has been incorporated in the analyses for the limiting DBAs at NMP1.

The structures, systems and components affected by the proposed change mitigate the consequences of accidents after the accident has been initiated. These proposed changes do not require any physical changes to the plant. As a result, the proposed changes do not

Attachment 1 Evaluation of Proposed Change Page 5 involve a revision to the parameters or conditions that could contribute to the initiation of a DBA discussed in the NMP1 UFSAR. Since design basis accident initiators are not being altered by the proposed change to the AST analysis, the probability of an accident previously evaluated is not affected.

Plant-specific AST radiological analyses have been performed and based on the results of these analyses. It has been demonstrated that the dose consequences of the limiting events considered in the analyses remain within the acceptance criteria provided by the NRC for use with the AST. These criteria are presented in 10 CFR 50.67 and Regulatory Guide 1.183.

Therefore, the proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated.

2. Does the proposed amendment create the possibility of a new or different kind of accident from any accident previously evaluated?

Response: No.

The proposed changes do not alter or involve any design basis accident initiators. These changes do not involve any physical changes to the plant and do not affect the design function or mode of operations of systems, structures, or components in the facility prior to a postulated accident. Since systems, structures, and components are operated essentially no differently, no new failure modes are created by this proposed change.

Therefore, the proposed change does not create the possibility of a new or different kind of accident from any previously evaluated.

3. Does the proposed amendment involve a significant reduction in a margin of safety?

Response: No.

The proposed changes are associated with the licensing basis for analysis of NMP1 DBAs.

Revision to the AST analysis is being requested. The limiting DBAs have been analyzed using conservative methodologies, in accordance with the guidance contained in Regulatory Guide 1.183, to ensure that analyzed events are bounding and that safety margin has not been reduced. The dose consequences of these limiting events are within the acceptance criteria presented in 10 CFR 50.67 and Regulatory Guide 1.183. Thus, the proposed changes continue to ensure that the doses at the exclusion area boundary and low population zone boundary, as well as in the control room, are within corresponding regulatory criteria.

Therefore, the proposed change does not result in a significant reduction in a margin of safety.

Based on the above, CEG concludes that the proposed change presents no significant hazards consideration under the standards set forth in 10 CFR 50.92(c), and, accordingly, a finding of "no significant hazards consideration" is justified.

Attachment 1 Evaluation of Proposed Change Page 6 4.4 Conclusion In conclusion, based on the considerations discussed above, (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commissions regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.

5.0 ENVIRONMENTAL CONSIDERATION

A review has determined that the proposed amendment would change a requirement with respect to installation or use of a facility component located within the restricted area, as defined in 10 CFR 20, or would change an inspection or surveillance requirement. However, the proposed amendment does not involve (i) a significant hazards consideration, (ii) a significant change in the types or significant increase in the amounts of any effluent that may be released offsite, or (iii) a significant increase in individual or cumulative occupational radiation exposure.

Accordingly, the proposed amendment meets the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9). Therefore, pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the proposed amendment.

6.0 REFERENCES

6.1 Letter from M. David (NRC Project Manager) to K. Polson (VP NMP), "Nine Mile Point Nuclear Station, Unit No. 1 - Issuance of Amendment RE: Implementation of Alternative Radiological Source Term (TAC No. MD3896)," dated December 19, 2007.

(ML073230597).