ML20098D508

AST LOCA Approach to Elemental Iodine Removal - NRC Public Meeting on RAI 6 - April 9, 2020

ML20098D508
Person / Time
Site:	Nine Mile Point
Issue date:	04/09/2020
From:	Exelon Generation Co
To:	Marshall M Plant Licensing Branch 1
Marhsall M, NRR/DORL/LPL, 415-2871
References
Download: ML20098D508 (5)

Text

Nine Mile Point Unit 2 AST LOCA Approach to Elemental Iodine Removal NRC Public Meeting on RAI 6 April 9, 2020

Summary of Current Licensing Basis Elemental Iodine Removal

• Current Licensing Basis (CLB) analysis of record, H21C-106 Revision 2, models elemental iodine removal in bypass leakage pathways as follows:

- Main Steam Lines (MSLs):

- Modeled as two pathways in RADTRAD; one for MSIV stuck open and one representing the other three lines

- No compartments; holdup was accounted for with delayed release timing

- Elemental iodine is conservatively capped at a constant 50% (only piping between the MSIVs credited)

- Other bypass leakage pathways

- Grouped together into drywell (DW) bypass, wetwell (WW) bypass, and delayed DW bypass leakage pathways in RADTRAD with the delayed pathway accounting for transit time similar to MSLs

- Elemental iodine in all bypass leakage pathways capped at a constant 50%

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Summary of Current Licensing Basis Elemental Iodine Removal H21C-106, Appendix C, Page C1:

NMP2 SER (ML081230439) Section 3.2.1.2.5.2, Page 18:

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Summary of Changes to H21C-106 Revision 3 to Be Consistent with CLB Elemental Iodine Removal

• Changes will be made as follows to make the models from H21C-106 Rev. 3 consistent with the CLB for elemental iodine removal:

- Time-dependent elemental removal associated with each MSL volume will be replaced with a constant 50% removal in a single pathway for each MSL (DF=2 for each pathway)

- Time-dependent elemental removal modeled in the DW and WW bypass leakage pathways will be replaced with a constant 50%

- Discussion in Sections 2.3.1.4 and 7.10 of H21C-106 Rev. 3 and associated tables and results will be modified or removed to be consistent with the discussion in H21C-106 Rev.

2 with regards to elemental iodine removal in the leakage pathways

• It is expected that the impact of the change will be a slight decrease in doses from those presented in the LAR; elemental iodine removal in leakage pathways is not a significant factor in the offsite and Control Room doses.

3

LAR Impacts with Implementing CLB Elemental Iodine Removal

• Enclosure A (H21C-106 calculation revision) updated

• Attachment 1, Technical Evaluation

• Table 1 on Page 3 of 22

• Discussion on Page 10

• Changes planned to be submitted

• Only updated Enclosure A

• RAI response discussion 4