Sorption (K d ) Measurements in Support of Dose Assessments for Zion Nuclear Station Decommissioning -14228

Abstract

ABSTRACT The Zion Nuclear Power Station is being decommissioned. ZionSolutions proposes to leave much of the below grade structures in place and to fill them with "clean" concrete demolition debris from the above grade parts of the facility. The Brookhaven National Laboratory (BNL) conducted a study commissioned by ZionSolutions to provide site-specific data for performance assessment calculations to support the request to terminate the NRC license and allow unrestricted use of the facility. Specifically, the distribution coefficient (K d ) for five radionuclides of concern using site-specific soils and groundwater was measured by following ASTM C1733-10, Standard Test Methods for Distribution Coefficients of Inorganic Species by the Batch Method. The radionuclides of concern are Fe-55, Co-60, Ni-63, Sr-90, and Cs-137. In the testing, Sr-85 was used as an analogue for Sr-90 because it behaves similarly with respect to sorption and has a gamma emission that is easier to detect than the beta emission from Sr-90. Site-specific soils included disturbed sand (sand removed during construction and used as backfill), native sand, silt/clay and silt. In addition, two concrete cores from the Unit-1 Containment Building and the Crib House were broken into particles less than 2 mm in size and tested to obtain distribution coefficients for the five nuclides. For Fe-55 and Co-60, the soils and the concretes removed almost all of these radionuclides in solution. For Ni-63, K d values in the soils ranged from 62 to 331 with the disturbed sand having the highest sorption for Ni. The results indicate values of K d much greater than 1000 for Ni-63 exposed to concrete. Strontium-85 exhibited very little sorption in all media with K d values ranging from 2 to 6 in the soils and 10 to 20 in the concretes. Cesium-137 exhibited substantial sorption in the soils with K d values ranging from 500 to 3000 in the soils. The high K d value for Cs occurred in the silty/clay soil. Clay is known to have a high affinity for Cs. The sorption for Cs was far lower in the concrete with K d values ranging from 45 to 85