Zirconia Inert Matrix Fuel for Plutonium and Minor Actinides Management in Reactors and as an Ultimate Waste Form
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1104-NN03-01
Zirconia Inert Matrix Fuel for Plutonium and Minor Actinides Management in Reactors and as an Ultimate Waste Form Claude Degueldre1, and Wolfgang Wiesenack2 1 NES, PSI, OHLD 08, Villigen, CH-5232, Switzerland 2 OECD Halden Reactor Project, Halden, 1751, Norway Abstract An yttria stabilised zirconia doped with plutonia and erbia has been selected as inert matrix fuel (IMF) at PSI. The results of experimental irradiation tests on yttria-stabilised zirconia doped with plutonia and erbia pellets in the Halden research reactor as well as a study of zirconia solubility are presented. Zirconia must be stabilised by yttria to form a solid solution such as MAz(Y,Er)yPuxZr1-yO2-ζ where minor actinides (MA) oxides are also soluble. (Er,Y,Pu,Zr)O2-ζ (with Pu containing 5% Am) was successfully prepared at PSI and irradiated in the Halden reactor. Emphasis is given on the zirconiaIMF properties under in-pile irradiation, on the fuel material centre temperatures and on the fission gas release. The retention of fission products in zirconia may be stronger at similar temperature, compared to UO2. The outstanding behaviour of plutonia-zirconia inert matrix fuel is compared to the classical (U,Pu)O2 fuels. The properties of the spent fuel pellets are presented focusing on the once-through strategy. For this strategy, low solubility of the inert matrix is required for geological disposal. This parameter was studied in detail for a range of solutions corresponding to groundwater under near field conditions. Under these conditions the IMF solubility is about 109 times smaller than glass, several orders of magnitude lower than UO2 in oxidising conditions (Yucca Mountain) and comparable in reducing conditions, which makes the zirconia material very attractive for deep geological disposal. The behaviour of plutonia-zirconia inert matrix fuel is discussed within a “burn and bury” strategy.
INTRODUCTION The deployment of specific Inert Matrix Fuel (IMF) projects has been reported [1,2] over the last 15 years of work devoted to the utilisation of plutonium and the transmutation of minor actinides (MA: Np, Am, Cm) in thermal reactors by applying an (IMF) concept e.g. [3,4,5] based on studies on uranium-free fuel e.g. [6,7,8]. The developments of an inert matrix fuel (IMF) have led to the selection at PSI of yttria-stabilised zirconia (YSZ) doped with plutonia and erbia PSI, Switzerland [4,9]. This IMF could utilise plutonium in LWR and destroy it in a more effective way than possible with MOX. After utilisation in LWR, the residual plutonium isotopic vector in the spent IMF foreseen for direct disposal is devaluated far beyond the standard spent fuel. The physical properties of the material depend on the choice of the stabiliser as well as on other additives such as burnable poison and/or fertile (MA) and fissile material. Among these properties, the behaviour under irradiation is important for utilisation in-pile. This property has been studied utilising accelerator ion beams and observing material changes during irradiation or
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