ML21239A021

Teleconference Summary Discussion with the U.S. DOE on Modeling of ET from the Closure Cover for the Sdf in the U.S. DOE Response to the U.S. NRC Request for Supplemental Information

ML21239A021
Person / Time
Site:	PROJ0734
Issue date:	09/01/2021
From:	Chris Mckenney, Ridge A NRC/NMSS/DDUWP/PAB
To:	Melissa Ralph NRC/NMSS/DDUWP/LLWB
A. Christianne Ridge, 301-415-5673
References
Download: ML21239A021 (3)

Text

MEMORANDUM TO: Melissa C. Ralph, Acting Chief Low-Level Waste and Projects Branch Division of Decommissioning, Uranium Recovery, and Waste Programs Office of Nuclear Material Safety and Safeguards THROUGH: Christepher A. McKenney, Chief Risk and Technical Analysis Branch Division of Decommissioning, Uranium Recovery, and Waste Programs Office of Nuclear Material Safety and Safeguards FROM: A. Christianne Ridge, Senior Risk Analyst Risk and Technical Analysis Branch Division of Decommissioning, Uranium Recovery, and Waste Programs Office of Nuclear Material Safety and Safeguards

SUBJECT:

TELECONFERENCE

SUMMARY

DISCUSSION WITH THE U.S. DEPARTMENT OF ENERGY ON MODELING OF EVAPOTRANSPIRATION FROM THE CLOSURE COVER FOR THE SALTSTONE DISPOSAL FACILITY On August 26, 2021, the U.S. Nuclear Regulatory Commission (NRC) staff held a technical call with staff and contractors of the U.S. Department of Energy (DOE) to discuss the DOE model of the closure cap of the Saltstone Disposal Facility (SDF) at the DOE Savannah River Site. The NRC staff held the call to support the staffs review of the DOE 2020 SDF Performance Assessment (PA) (available in the NRCs Agencywide Documents Access and Management System [ADAMS] under Package Accession No. ML2019A055). The discussion related to the revised closure cap model (available in ADAMS under Accession No. ML21160A064) that the DOE submitted in response to the NRC Request for Supplemental Information (available in ADAMS under Accession No. ML20254A003).

CONTACT: A. Christianne Ridge, NMSS/DUWP 301-415-5673September 1, 2021 Signed by McKenney, Christepher on 08/31/21 Signed by Ridge, Alavanja on 09/01/21

M. Ralph

The NRC staff noted that the revised closure cap model projected that the infiltration rate would decrease as the projected thickness of the layer of soil above the erosion barrier decreased due to erosion. The NRC staff questioned that result because the main processes by which an evapotranspiration (ET) cover limits infiltration are water storage and ET, and a covers capacity for both water storage and ET depends on the soil layer thickness. The NRC staff noted that, in the DOE document that describes closure cap model, the DOE indicated that the counter-intuitive result could be explained by increased run-off. However, the NRC staff indicated that in the water balances the DOE provided (available in ADAMS under Accession No. ML21196A077), ET accounts for a much larger fraction of the water balance than runoff does, irrespective of soil layer thickness.

The NRC staff also noted that the DOE model projected significant ET even when the soil layer above the erosion barrier reached zero thickness. The NRC staff questioned that intermediate model result because the DOE also had assumed that plant roots would not penetrate the erosion barrier. Consequently, in the DOE conceptual model, plants could not live and transpire water without a soil layer above the erosion barrier.

The DOE acknowledged the NRC staff concern and proposed that the DOE evaluate plant-related parameters in the closure cap model. The DOE indicated that it expected that correcting the plant-based parameters would decrease projected ET and increase projected runoff without significantly changing the projected infiltration rate. The NRC staff noted that increased projected runoff would affect the NRC staff review of erosion of the closure cap. In response to an NRC question, the DOE indicated that it would inform the NRC staff of the expected date of providing revised information after it had an opportunity to evaluate the effects on the closure cap model.

Call Participants U.S. NRC U.S. DOE U.S. DOE Contractors Hans Arlt Pat Suggs Steven Hommel Christepher McKenney Larry Romanowski A. Christianne Ridge Kent Rosenberger Harry Felsher

Memo ML21239A021 OFFICE NMSS/DUWP NMSS/DUWP NMSS/DUWP NMSS/DUWP/RTAB

/RTAB /RTAB /LLWPB NAME ARidge AR HArlt HA HFelsher HF CMcKenney CM DATE Aug 27, 2021 Aug 30, 2021 Aug 30, 2021 Aug 31, 2021 OFFICE NMSS/DUWP

/RTAB NAME ARidge AR DATE Sep 1, 2021