Chemical Analysis of High-Level Radioactive Waste Glass by ICP-AES

Abstract

In a reprocessing plant for spent nuclear reactor fuel, the spent fuel is dissolved in concentrated nitric acid solution, and plutonium and unburned uranium are removed in the chemical separation process. The remaining solution contains more than 99% of the nonvolatile fission product elements, impurities from the cladding materials, corrosion products, traces of unseparated plutonium and most of the transuranic elements. This reprocessing waste is called high-level radioactive liquid waste (HLLW). The HLLW is generally concentrated by evaporation and stored as an aqueous nitric acid solution in high-integrity stainless-steel tanks. Internationally, glass is the material of choice for incorporating and immobilizing the hazardous radionuclides in HLLW because of the good product durability and technical maturity. Recently, the HLLW arising from the commercial reprocessing plants were converted into borosilicate glasses in the vitrification plants in France (in the R7 and T7 Vitrification Plants at La Hague), and in the UK (in the Windscale Vitrification Plant (WVP) at Sellafield).1 Part of the vitrified products produced at La Hague have been already returned to Japan and the products vitrified at Sellafield will be returned to Japan in the near future, according to the agreements between the Japanese electric power companies and Compagnie Generale des Matieres Nucleaires (COGE-MA) or British Nuclear Fuels plc (BNFL) for the reprocessing of irradiated oxide fuel. In these situations, it is necessary to confirm the general characteristics of these vitrified products. At the Japan Atomic Energy Research Institute (JAERI), a series of characterization tests (chemical analysis, heat load measurement, leaching test, homogeneity and devitrification test) on the radioactive samples of vitrified residues were performed in cooperation with Commissariat a l'Energie Atomique (CEA), COGEMA and BNFL with the support of Science and Technology Agency (STA). 2The chemical analysis of the vitrified products produced in the industrial vitrification plant is one of the most important subjects in the characterization tests, because the analytical data are effective for the confirmation of the agreement between the industrial product and designed product. However, the chemical analysis of industrial vitrified product has never been carried out in other countries. In our previous study, an analytical method was developed and evaluated by using inactive samples for supporting the characterization tests of actual high-level radioactive waste glass. 3 The good accuracy of the method was demonstrated by the analytical data of the simulated inactive waste glass sample and several reference materials of glasses (National Institute of Standards and Technology: NIST SRM). Thereafter, this analytical method was modified slightly from the standpoints of the remote sample preparation in the shielded cells (e.g. use of devices and equipment protected from breaking) and the improvement of ICP-AES (e.g. determination of Li and Na by the addition of...

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