A New Matrix for Conditioning Chloride Salt Wastes from the Electrorefining of Spent Nuclear Fuel

Abstract

A novel method proposed by Korea Atomic Energy Research Institute has been applied to the treatment of chloride salt wastes coming from electrorefining of spent nuclear fuel, which allows to separate uranium from fission products. It is based on a matrix, SAP (SiO2-Al2O3-P2O5), synthesized by a conventional sol-gel process, able to stabilize the volatile salt wastes due to the formation of metalaluminosilicates, metalaluminophosphates and metalphosphates. With this method a higher disposal efficiency and a lower waste volume can be obtained. Eutectic melt LiCl-KCl (59-41 mol%) has been used to simulate the waste salt. The composite SAP has been prepared by using tetraethyl ortosilicate (TEOS), aluminum chloride (AlCl3.6H2O) and phosphoric acid (H3PO4) as sources of Si, Al, and P, respectively. All reagents were dissolved in EtOH/H2O and the mixture, tightly sealed, was placed in an electric oven at 70 C. After a gelling/ageing for 3 days, the transparent hydrogels were dried at 110 C for 3 days and then thermally treated at 600 C for 2 hours. The final product (SAP) was reacted with metal chlorides at increasing temperatures for 20 hours inside an Argon-atmosphere glove-box, after mixing them at a SAP/metal chloride mixing ratio of 2. The obtained products have been characterized by means of density measurements, scanning electron microscopy, thermal analysis, as well as by XRD, FTIR and Raman spectra. Financial support from the Nuclear Fission Safety Program of the European Union (project SACSESS, contract FP7-CP-2012-323282) is gratefully acknowledged.

Inorganic Waste Forms for Efficient Immobilization of Radionuclides

“…Sodalite is a natural aluminosilicate containing iodine/chlorine, hydroxide, and other anions in its composition and is a well-known efficient feldspathoidal mineral for the immobilization of chloride- and iodide-containing wastes (Figure B). , Various synthesis conditions were optimized for the development of sodalite-based matrices, e.g., the application of sodium aluminate and silica precursors using kaolinite, nepheline, or zeolite A (LTA). In South Korea, the Korea Atomic Energy Research Institute (KAERI) also developed SAP as an efficient immobilization matrix for chloride-containing wastes. , The authors proposed that the SAP can be synthesized by the sol–gel method, and it is highly capable of capturing and stabilizing volatile salt wastes in the form of metal aluminosilicates, aluminophosphates, and phosphates . Moreover, the design and synthesis of glassy waste form (U-SAP) was developed as an alternative matrix for other SAP waste forms …”

“…225,226 The authors proposed that the SAP can be synthesized by the sol−gel method, and it is highly capable of capturing and stabilizing volatile salt wastes in the form of metal aluminosilicates, aluminophosphates, and phosphates. 227 Moreover, the design and synthesis of glassy waste form (U-SAP) was developed as an alternative matrix for other SAP waste forms. 228 de Angelis et al reported a detailed experimental investigation of sodalite and SAP matrices (consisting of silica (SiO 2 ), alumina (Al 2 O 3 ), and phosphorus pentoxide (P 2 O 5 )) as potential candidate for the confinement and immobilization of spent chloride salt waste.…”

“…228 de Angelis et al reported a detailed experimental investigation of sodalite and SAP matrices (consisting of silica (SiO 2 ), alumina (Al 2 O 3 ), and phosphorus pentoxide (P 2 O 5 )) as potential candidate for the confinement and immobilization of spent chloride salt waste. 227 The authors synthesized sodalite and SAP in both pure form and mixed with various glass matrices (glass frit and borosilicate glass) and were loaded with mixed chloride salts. The waste form matrices were characterized by XRD, FT-IR, SEM-EDS, and TGA, before and after leaching experiments.…”

An experimental study on Sodalite and SAP matrices for immobilization of spent chloride salt waste

“…The Korea Atomic Energy Research Institute (KAERI) proposed an immobilization matrix for chloride salt wastes, termed SAP, consisting of SiO 2 ,Al 2 O 3 and P 2 O 5 [27,28]. This matrix, synthesized by a conventional sol-gel process, is able to stabilize volatile salt wastes due to the formation of metal aluminosilicates, aluminophosphates and phosphates, generating chlorine gas [29]. Glass can be added to the SAP matrix as a chemical binder giving rise to higher disposal efficiency and to a lower volume of waste compared with other immobilization matrices [27,30].…”

“…This matrix, synthesized by a conventional sol-gel process, is able to stabilize volatile salt wastes due to the formation of metal aluminosilicates, aluminophosphates and phosphates, generating chlorine gas [29]. Glass can be added to the SAP matrix as a chemical binder giving rise to higher disposal efficiency and to a lower volume of waste compared with other immobilization matrices [27,30]. A recent evolution of SAP, the glassy wasteform U-SAP, shows even better performances with respect to other SAP wasteforms [31,32].…”