Zirconia Inert Matrix Fuel for Plutonium and Minor Actinides Management in Reactors and as an Ultimate Waste Form

Abstract

A plutonia stabilised zirconia doped with yttria 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 zirconia-IMF 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.

Material Performance of Fully-Ceramic Micro-Encapsulated Fuel under Selected LWR Design Basis Scenarios: Final Report

“…about 575 MWd/kg iHM at a temperature range of 1200 -1350 °C, [24]. In comparison, FCM fuel has a higher target burnup of ~700 MWd/kg, but will experience lower temperatures < 650 °C.…”

Fabrication of ZrO2-based nanocomposites for transuranic element-burning inert matrix fuel

“…In terms of the suitability of IMF for waste disposal, the chemical stability of an IMF should make it a suitable and safe option for the geological disposal of radioactive waste [4]. The solubility tests performed on an IMF using a yttria-stabilized zirconia (YSZ) matrix showed that the IMF is three times less soluble than UO 2 fuel under reducing conditions, and about six times less under oxidizing conditions [5]. In terms of the irradiation stability, the irradiation test performed on the IMF using YSZ and calcium-stabilized zirconia (CSZ) as a matrix showed that IMF has good irradiation stability, but they experience a higher centerline temperature, more swelling, and greater fission gas release than the standard uranium oxide fuel (UO 2 ) [6].…”