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2 - NRC - Workshop3 - Non-LOCA - FFRD - Final
	ML24067A007
Person / Time
Site:	Nuclear Energy Institute
Issue date:	03/08/2024
From:	Markivich A, Pimentel F; Dominion Energy Co, NRC/NRR/DRA/ARCB, Nuclear Energy Institute
To:	;
References
	Download: ML24067A007 (11)
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Engineering & Risk, NEI March 8, 2024 Non-LOCA Release Fractions Impact from Fuel Fragmentation, Relocation, and Dispersal

This RG does not provide guidance related to an acceptable treatment of fuel dispersal during non-LOCA DBAs.

For the remaining non-LOCA DBAs that predict fuel rod cladding failure, such as the PWR reactor coolant pump locked rotor and fuel handling accident, additional fission product releases may occur as a result of fuel pellet fragmentation (e.g., fracturing of high-burnup rim region) due to loss of pellet-to-cladding mechanical constraint or impact loads At the time of issuance of Revision 1 of this RG, no consensus exists on the mechanism or the computation of TFGR for these events; therefore, future applicants should address this using engineering judgment or experimental data.

Current Guidance

©2024 Nuclear Energy Institute 3 Industry views this as a gap in the guidance presented in Revision 1, resulting in lack of regulatory clarity As such, Licensees are at the discretion of NRC review staff on acceptability of analyzing or evaluating fuel pellet fragmentation for non-LOCA DBAs involving fuel failure Industry recommends this lack of guidance be addressed in Revision 2 consistent with the principles of good regulation Industry Comments

©2024 Nuclear Energy Institute 4 Guidance for FFRD is already provided for LOCA (bounded by MHA LOCA) for additional transient fission gas and fuel fragment dispersal Guidance for calculating fission product releases due to pellet fracturing and grain boundary separation are already provided for Reactivity Insertion Accidents Industry views other non-LOCA events as benign in terms of power/heatup transients for ability to increase available activity from FFRD Industry Comments

©2024 Nuclear Energy Institute 5 For the MHA LOCA, FFRD was justified as bounding with no need to consider additional radionuclide releases NRC Internal Memorandum (ML21197A067) was the basis for this conclusion and included some significant justifications In summary, it was determined FFRD was not a concern for LOCA based on:

Significantly lower fuel failures expected to occur than in MHA LOCA guidance modeling Released fuel fragments would not be expected to significantly contribute to source term in containment Current Guidance - RG 1.183, Rev. 1

Fuel damage models are currently conservative and would potentially bound additional releases of fuel gap activity and/or fuel fragments Addition of fission product activity contained in the fuel rod gap due to high burnup and transient conditions would be limited for these more benign transient events Overall contribution for dose from both additional fission gas products and fuel fragments would reasonably be bounded by current conservative modeling guidance Discussion - Application to non-LOCA FFRD

©2024 Nuclear Energy Institute 7 Locked RCP Rotor and Fuel Handling Accident Events do not contain a reactivity insertion event or prolonged heatup, limiting the fuel fragmentation and gas migration from transient conditions Locked Rotor fuel failure estimates are overly conservative, creating a bounding amount of activity release Fuel Handling Accident guidance conservatively models the assembly activity available for release No technical basis supporting application of an additional source term associated to fuel dispersal for these events Discussion - Application to non-LOCA FFRD

©2024 Nuclear Energy Institute 8 Lack of FFRD guidance for non-LOCA transient analysis radionuclide releases represents significant gap for the industry Revision 1 of RG 1.183 provides guidance for LOCA and Reactivity Insertion Accidents (non-LOCA)

Current non-LOCA dose analysis models (Locked RCP Rotor, FHA) are conservative and there is no technical basis supporting application of an additional source term associated to fuel dispersal for these events Summary

©2024 Nuclear Energy Institute 9 NRC to qualitatively assess FFRD for non-LOCA events such that additional conservatisms do not need to be applied to the current modeling practices Consider similar approach as NRC Internal Memorandum (ML21197A067, based on ML21197A069) that was the basis for the MHA LOCA guidance Industry Recommendation for RG 1.183 Revision 2

ML24067A007

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