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1- Impacts on RG 1.183 for Workshop2
	ML24043A119
Person / Time
Site:	Nuclear Energy Institute
Issue date:	02/13/2024
From:	Broadbent G, Lafountain S, Markivich A, Pimentel F; - No Known Affiliation, Dominion Energy Co, Nuclear Energy Institute, Southern Nuclear Company
To:	David Garmon-Candelaria; NRC/NRR/DRA/ARCB
References
	Download: ML24043A119 (23)
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Corporate Nuclear Analysis, Entergy (Retired)

Sam Lafountain, Lead Engineer, Southern Nuclear Alex Markivich, Engineer III, Dominion Energy Frankie Pimentel, Sr. Project Manager -

Engineering & Risk, NEI February 13, 2024 Impact of SAND2023-01313 on Source Terms and Radiological Consequence Analyses

©2024 Nuclear Energy Institute 2 Increased Release Fractions can have wide-ranging impacts on plant safety analyses Examples will include results from Dose Impacts for 2 BWRs (Mark I and Mark III) 2 PWRs (large dry and subatmospheric)

Examples of Impacts

RG 1.183 Rev. 1 and SAND2023-01313 release fractions and durations Longer release durations necessitate changes to spray removal effectiveness or duration Worst-case X/Q corresponding to period of highest release Assessment of pool scrubbing for BWRs, as described in SAND2023-01313 Table 5-16 What was NOT changed Core inventory (Ci/MW)

Dose Evaluation Changes

MSIV leakage

Containment leakage

ESF liquid leakage into Secondary CMT Main Steam Credit

No credit for MSL deposition past the outboard MSIV

Credit for MSIV Leakage Control System initiation at 20 minutes 99% SGTS filters, ~1 hour holdup

Drywell-Containment Mixing Current RG 1.183, Rev. 0 accepted uniform mixing after 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months Changed to only credit 2000-cfm hydrogen purge system for entire period See Resolution to Comment 6-5 from the BWROG

2 4

6 8

10 12 Exclusion Area Boundary Low Population Zone Control Room Dose (Rem TEDE)

Location Offsite & Control Room Doses Reg Guide 1.183 Rev. 0 Rev. 1 Rev. 1 w/pool SAND2023-01313 SAND2023-01313 w/pool

Impact of New Mixing Guidance Higher drywell activities for longer time MSIV leakage pathway more significant Lower containment activities Spray less effective CMT Leakage not as significant

Spray Effectiveness Longer Credit for higher effectiveness was a significant benefit

Drywell (DW) spray

Aerosol removal/holdup credited in main steam lines (MSL)

Condenser credited for aerosol removal and holdup of MSIV leakage ECCS leakage pulled into RB and processed by Standby Gas Treatment MCR - Leakage from Condenser into Turbine Building (TB) and into MCR via unfiltered inleakage with no dispersion in Environment (MCR in TB)

For offsite doses - No credit for holdup in TB No other input changes were made to offset dose increases due to guidance changes Example 2: BWR-4, Mark-I LOCA Modeling

CLB - Current Licensing Basis

Rev. 1 - Rev. 1 RFs and timing; DW spray credit removed; MSL and Condenser removal aligned with A-5.6.1

SAND2023 - SAND2023 RFs and timing; removal credits same as Rev. 1 case

SAND2023_Scrub - SAND2023 case but release to DW airspace limited to SAND2023 Table 5-16 Excluding SP Inventory fractions (no DW spray)

Impact of Higher RFs Substantial increase in dose significant nuclides (e.g., Iodines) drives doses up

Impact of More Conservative Aerosol Removal Modeling Inability to credit DW spray with the Rev. 1 MSL aerosol removal models leads to higher concentrations in DW as source for MSIV leakage Lower aerosol removal in Condenser leads to higher concentration leakage

Pool scrubbing is a large benefit based on SAND2023 showing most radionuclides are scrubbed by the Pool rather than released directly to the DW

Containment

ESF

RWST Backleakage Containment spray credited; terminated at 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months in CLB (or at decontamination factor cutoffs)

Spray duration modified to cover longer in-vessel release duration ESF leakage outside containment is filtered prior to release RWST back-leakage release included separate from ESF leakage Example 3: PWR, Large Dry Containment

Rev1_ExtSpray - Cont. spray extended to cover in-vessel release SAND2023 - Use of RFs and timing from SAND2023 (2 hrs of cont. spray)

SAND2023_ExtSpray - Cont. spray extended to cover in-vessel release SAND23_HalRF - Halogen release capped at 100%

< 2.0 psig at 1.0 hr (after event initiation)

< 0.0 psig at 6.0 hr i.e., TS containment leakage rate of 0.1% vol/day from 0.0 to 1.0 hrs and 0.04% vol/day from 1.0 to 6.0 hrs ECCS Leakage outside containment is unfiltered prior to release 30,000 cc/hr total ECCS leakage with 10% flashing fraction RWST back-leakage release included separate from ESF leakage External shine contributions were not re-evaluated No other input changes were made to offset dose increases due to guidance changes Example 4: 3-Loop, PWR, Subatmospheric Containment

CLB - Current Licensing Basis

Rev. 1 - Rev. 1 RFs and timing

SAND2023 - Use of RFs and timing from SAND2023

SAND2023_HalRF -Use of RFs and timing from SAND2023; Halogen release capped at 100%

Timing Impacts Much longer in-vessel release durations for SAND2023 (and Rev. 1) can be beneficial If spray is credited, plants may need to extend spray duration to cover the longer in-vessel release duration

RF Impacts SAND2023 RFs drive doses higher than current RFs Could potentially result in reductions in operational flexibility (e.g., lower allowable ESF leakage)

Current guidance (separate leakage runs modeling all iodine release) results in total iodine releases above 1.0

Proposed approach: Rev. 2 would contain three (3) MHA LOCA RF tables containing separate Pool, Containment atmosphere, and Steam Line RFs instead of a single table (e.g., current Table 1)

How are the steam line release fractions identified in ML24005A089 intended to be applied in the downstream dose consequence codes?

Released over the course of the in-vessel release duration, fully released into the steam line source volume at the start of the in-vessel period, or something different altogether?

What is intended in guidance/application space with respect to the information in the red box (see previous slide) discussing potentially keeping concentration constant after the early in-vessel period?

MSL and Condenser Deposition RG 1.183, Rev. 1, presents 3 acceptable models for MSL / Condenser aerosol deposition NRC supplemental work has suggested RFs into MSLs directly based on MELCOR modeling that includes deposition between RPV and inboard MSIV Will the Rev. 1 MSL and Condenser deposition models apply downstream of the inboard MSIV or will updates be made to these models?

Natural Deposition in Containment Rev. 0 points to NUREG/CR-6189 (Powers) as an acceptable model (built into RADTRAD and used widely across the industry)

Rev. 1 states that NUREG/CR-6189 is no longer directly applicable without adjustment and provides no acceptable aerosol natural deposition model Given the information available in MELCOR modeling already performed, will an updated acceptable containment natural deposition model be provided in Rev. 2?

Alternatively, an acceptable method of adjusting the NUREG/CR-6189 correlations would be beneficial and avoid each licensee developing their own for Staff review

RF iodine releases greater than 1.0 Current wording from RG 1.183, Rev. 1, Appendix A:

Add to Position A-4.1: "...in the primary containment sump water (in PWRs) or suppression pool (in BWRs) at the time of release from the core. Given the release fractions in Tables 1 and 2, this guidance, combined with the guidance in A-2.1, would lead to release fractions of >1.0 being analyzed for certain nuclide groups. Licensees need not consider total releases that exceed 1.0 if justification is provided that the split between the containment airspace and the pool is conservative. In lieu of this deterministic approach..."

ML24043A119

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