271-14 Apatite-Induced Cesium Immobilization for Nuclear Waste Management

Session: Geologic Energy Resources and Storage for Now and the Future (Posters)

Presenting Author:

Authors:

Abstract:

Nuclear waste has been a major concern for a long time, but recent advances in scientific research have led to meaningful progress in finding effective ways to manage radionuclides, particularly those found in high-level radioactive waste (HLW) and spent nuclear fuel (SNF). Cesium has several radioactive isotopes, however fission by-products such as cesium-137 & 135 (¹³⁷Cs, ¹³⁵Cs) and strontium-90 account for most of the radioactivity and radiotoxicity generated in HLW after that of uranium (U) and plutonium (Pu). ¹³⁷Cs is the most prevalent cesium isotope in nuclear waste and is highly radioactive, which has a half-life of 30.17 years. Moreover, although in lower quantities, ¹³⁵Cs is another cesium isotope present in nuclear waste. 135Cs, however, has a longer half-life of 2.3 Ma. Therefore, both ¹³⁷Cs & ¹³⁵Cs are of concern at the time for storing, transporting, and/or disposing of them, and must be handled with caution. To protect the environment from the dangers posed by waste generated from this valuable yet sensitive energy source, ¹³⁷Cs & ¹³⁵Cs must be effectively immobilized and securely contained in stable phases or matrices for safer long-term storage or disposal. Several radionuclides, such as uranium, iodine, and strontium, have been studied alongside calcium phosphate minerals, particularly apatite, to assess the minerals’ ability to immobilize them. These studies have shown that the aforementioned radionuclides (U, I, Sr) incorporate well into apatitic structures at hydrothermal conditions. However, understanding the mechanisms between dissolved cesium and apatite remains an important and challenging task, especially at temperatures <300°C, which is the thermal peak of a nuclear waste canister. This study explores how much apatite immobilizes dissolved cesium at different hydrothermal conditions, an area that remains poorly understood. Unlike most ceramic and glass-based techniques that require very high temperatures, in this study we are evaluating temperatures between 160 - 230°C. Three batch experiments were conducted at 160, 200, 230°C (n=6 per temp.). The experimental setup consisted of placing brushite (apatite precursor) into an autoclave together with a 0.5M solution. Aliquots of 1,000 ppm Cesium standard solution were added to make final concentrations ranging from 0.1-15ppm. The analytical techniques in this study encompass XRD and ICP-OES.  This study will provide partitioning data calculated as D^Cs = Cs_apatite/Cs_fluid and will provide insights into the Cs immobilization by apatite

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8043

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.