Synthesis, characterisation and preliminary corrosion behaviour assessment of simulant Fukushima nuclear accident fuel d
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.35
Synthesis, characterisation and preliminary corrosion behaviour assessment of simulant Fukushima nuclear accident fuel debris Clémence Gausse, Calum W. Dunlop, Aidan A. Friskney, Martin C. Stennett, Neil C. Hyatt and Claire L. Corkhill NucleUS Immobilisation Science Laboratory, Department of Materials Science and Engineering, The University of Sheffield, United Kingdom
ABSTRACT
Nuclear fuel debris generated at the Fukushima Daiichi nuclear power plant during the loss of coolant accident in 2011, still resides within the reactor units, constantly cooled by water. Until it is retrieved, the fuel debris will corrode, releasing radioactive elements into the coolant water and the ground surrounding the reactors. To predict the corrosion behaviour of these materials, and to establish parameters for experiments with U-containing and real fuel debris, the corrosion of two surrogate fuel debris materials, with a composition of Ce(1-x)ZrxO2 (x = 0.2 and 0.4), was investigated. Materials were synthesised by a wet chemistry route and pellets were sintered at 1700°C in air atmosphere. Due to the slow corrosion kinetics, aggressive conditions were applied, and corrosion experiments were performed in 9 mol.L-1 HNO3 under static conditions. The incorporation of Zr into the structure of Ce reduced the normalised dissolution rate; from (3.75 s 0.15) × 10-6 g.m-2.d-1 to (4.96 s 0.28) × 10-6 g.m2 -1 .d for RL(Ce) of Ce0.8Zr0.2O2 and Ce0.6Zr0.4O2, respectively.
INTRODUCTION The earthquake and tsunami that occurred on the 11th March 2011 at the Fukushima Daiichi Nuclear Power Plant (NPP) resulted in a loss of coolant accident and the partial meltdown of boiling water reactor Units 1 to 3 [1–3]. The temperature in the reactors rose in excess of 2000°C causing the melting and the reaction of UO 2 pellets with the steam-oxidised zircaloy fuel cladding. The resulting material, known as Nuclear Fuel Debris (NFD), is principally a U1-xZrxO2 solid solution containing a variety of fission products and minor actinides, including a significant proportion of Pu from MOX fuel [4,5]. According to historic nuclear accidents, it is also suggested that the formation of 65
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glassy or ceramic admixtures of fuel, cladding and reactor components, known as Molten Core – Concrete Interaction Products (MCCIs), occurred at Fukushima. Continuous water
injection (firstly seawater, followed by groundwater from the area surrounding the Fukushima NPP and then filtered water) has been used since the accident to cool the NFD and MCCIs, and reduced the temperature below 100°C [2]. In this so-called stable cold shutdown situation, analysis of coolant water effluent evidenced the presence of Pu, indicating the fuel debris is being dissolved. The aqueous leaching of fu
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