Solution‐Derived, Chloride‐Containing Minerals as a Waste Form for Alkali Chlorides

Abstract

Sodalite (Na 8 (AlSiO 4 ) 6 Cl 2 ) and cancrinite ((Na,K) 6 Ca 2 (AlSiO 4 ) 6 Cl 4 ) are environmentally stable, chloride-containing minerals that are a logical waste form option for the mixed alkali chloride salt waste stream that is generated from a proposed electrochemical separations process during nuclear fuel reprocessing. Here, we discuss a low-temperature, solution-based process to make these phases where sodalite particles are produced in the form of a fine powder with particle sizes on the order of 1-10 lm. Due to the small particle size, these powders require additional treatment to form a monolith. In this study, the powders were pressed into pellets and fired to achieve >90% of the theoretical density of sodalite (2.27 3 10 À3 kg/m 3 ). The cancrinite structure, identified as the best candidate mineral form in terms of waste loading capacity, was only produced on a limited basis but was converted to sodalite upon firing. Here, we discuss the specifics of the solution-based approach, the chemical durability of select waste forms as well as the steps taken to maximize the chloride-containing phases, decrease chloride loss during pellet firing, and to increase pellet densities.E. Vance-contributing editor Manuscript No. 31209.

Ceramic Solidification of Salt-containing Waste from Pyrochemical Reprocessing of Spent Nuclear Fuel

“…除了设计 ACWF, 近几年关于 CWF 的研究还集 中在 CWF 容器设计和实验规模扩大上。INL 的 Bateman 等 [20][21] [24] Fig. 3 Schematic of the simplified solution-based process [24] 这种方法对于高 [30] 。SAP 产品与熔融盐接触 时, 磷酸盐的化学键会发生断裂引发反应。在反应 过程中, 金属元素与复合材料中的铝硅酸盐、铝磷 酸盐和磷酸盐发生化学相互作用, 生成具有高热稳 定性的金属化合物 [31][32] 。反应方程式如下 [30] : 图 4 KAERI 凝固工艺流程脱氯-氯化反应系统 Fig. 4 [32] 。U-SAP 固化体在 650~1150 ℃反应和固 结之后, 结构没有很大变化, 仍保持了其亚微米级 的结构尺寸。KAERI 正在计划进行一系列实验以研 究 U-SAP 固化体的形态、元素分布、热性质和化学/ 物理性质等 [33]…”

Options for the Separation and Immobilization of Technetium

“…The purpose of adding a glass binder to sodalite (and for most of the mineral forms) is that it helps reduce the surface area during consolidation, thus improving the chemical durability of the final Tc-laden waste form. This approach has been used successfully to bind sodalite for the baseline ceramic waste form used to immobilize spent electrochemical salt wastes (Bateman et al 2007;Lepry et al 2013;Riley et al 2012). In these studies, the addition of the glass binder was used to decrease the porosity of the final product and to immobilize the fission products from the salt waste that could not be incorporated into the mineral structure of the sodalite, e.g., lanthanide and alkaline earth chlorides.…”

Solution-derived sodalite made with Si- and Ge-ethoxide precursors for immobilizing electrorefiner salt

“…An alternative way to making the sodalite is with a solution-based approach [3][4][5]. One solution-based method [3,4] used colloidal silica, NaAlO2, and a salt solution to make sodalite at near-room temperature (65 °C), and those samples were referred to as S5A pellets. This process had some limitations where the sodalite production was limited at the elevated firing temperatures required to get high density pellets and the high processing temperatures usually led to chloride volatility and, subsequently, nepheline formation.…”