The Effect of Gamma Irradiation on the Physiochemical Properties of Caesium-Selective Ammonium Phosphomolybdate–Polyacrylonitrile (AMP–PAN) Composites

Abstract

Managing certain by-products of the nuclear fuel cycle, such as the radioactive isotopes of caesium: 134Cs, 135Cs and 137Cs is challenging due to their environmental mobility and radioactivity. While a great many materials can isolate Cs+ ions from neutral or basic aqueous solutions via ion exchange, few of these, with the exception of ammonium phosphomolybdate (AMP), function effectively in acidic media. The use of AMP, and its porous composite in polyacrylonitrile (PAN) for management of Cs radioisotopes in various nuclear wastes have been known for decades and are well studied, yet the effects of radiation on the physiochemical properties of such composites have only received limited attention to date. In a previous publication, we demonstrated that a 100 kGy gamma irradiation dose has negligible effect on the ion exchange performance of AMP and AMP–PAN with respect to capacity or kinetics under the Cs+ concentrations and acidity found in spent nuclear fuel (SNF) recycling. As a continuation of this prior study, in this publication we explore the effects of gamma irradiation on the physiochemical properties of AMP and AMP–PAN using a range of characterisation methods. The effects of the same gamma dose on the oxidation state of Mo in AMP and AMP–PAN, the thermal degradation of both AMP and AMP–PAN, combined with a first study into the high-temperature degradation AMP, are reported. The implications of irradiation, its possible mechanism, the conditions present in SNF recycling, and for the end-of-life disposal or recycling of these materials are also discussed.

Metal Ammonium Phosphates Ion Exchangers for the Remediation of Low-Level Nuclear Wastes

“…24 The pH of the model liquor increases to a neutral equilibrium value of between 7 and 8 within 5 minutes of the addition of the MAP adsorbents and maintains this throughout the duration of exposure, though the slightly acidic conditions are maintained with SnHP. The adsorption of the cations from the model liquor onto the tested adsorbents are believed to occur via exchange with ammonium ions as for AMP, [17][18][19][20] with the exception of SnHP, where H + ions are exchanged instead. The behaviour of molybdate (MoO 4…”

“…15 Several of our previous publications have explored the use of AMP for, heterogeneous isolation of Cs + in reprocessing flowsheets, granting a direct recovery and disposal route to this energetic fission product, which could mitigate many of the challenges within the recycling of spent fuel. [17][18][19][20] For decontamination purposes however, selectivity is unnecessary, rather an ability to absorb a wide range of radionuclide contaminants is often preferred.…”

Accessible Statistical Regression, Extrapolation and First-Principles Modelling of Nuclear Data for Spent Nuclear Fuel Composition and Decay Heat Calculations in Short-Term Storage and Recycling

“…With this in mind, and for the purpose of complementing ongoing research into advanced spent nuclear fuel (SNF) recycling technologies, [16][17][18][19][20] we have developed a simplified model for calculating SNF isotopic, and thus elemental, compositions and the decay heats of unknown spent Gen III(+) Pressurised Water Reactor (PWR) fuels with respect to burnup (BU) and post-reactor cooling times up to a decade. This is achieved by interpolating within and extrapolating beyond the known burnup data range on an isotopic level, 21 and serves to address the lack of specific data required.…”

“…4 To our knowledge, this represents the first instance of this approach being applied to nuclear data and could be adapted to other complex datasets in a range of academic fields, alongside applications in the wider nuclear fuel cycle. This information will be utilised to discern the effects of separations on downstream processes, conversion, and storage in SNF recycling, [16][17][18][19][20] expanding beyond the available source data 5 and extrapolating to cover Gen III+ reactor systems. We believe this could contribute to improvements on the design of new SNF recycle and waste management facilities, 22 to facilitate wider, cost-effective management of the vast quantities of SNF stored worldwide and that produced by advanced Gen III(+) reactors, such as the EPR, which are coming online at the time of writing.…”

Metal Ammonium Phosphates Ion Exchangers for the Remediation of Low-Level Nuclear Wastes

“…2,3 In this publication, we undertake an initial assessment of several inorganic mixed-metal phosphate adsorbents with potentially high capacities for radionuclides in the remediation of such decontamination solutions and with a promising end-of-life disposal strategy to address these challenges. [17][18][19][20] For decontamination purposes however, selectivity is unnecessary, rather an ability to absorb a wide range of radionuclide contaminants is often preferred. 21 We previously demonstrated 22 an efficient, scalable continuous flow synthesis method 23 for the quantitative preparation of metal ammonium phosphates (MAPs) and related compounds with a small particle sizes (< 24 μm), narrow size distributions, and high surface areas (up to 50 m 2 /g, see .…”