Structural and NA-release studies for NZP materials

Abstract

Wiile NaZr2(P04)3 (NZP)- structured waste forms have been suggested for many years as immobilising agents for High-Level Waste (HLW) from nuclear power plant fuel or weapons production, little attention has been paid to Na release from NZP (but see [1]). For example, highly active Na-rich wastes can arise from liquid sodium used in the primary cooling of fast reactors or from radioisotope production; hence Na immobilisation and speciation in HIPed ceramics are the focus of this current work. The structural characterisation of the NZP family of materials (namely and their sodium titanium phosphate (NTP) analogues, will be presented from recently undertaken XRD, SEM and 23Na and 31P MAS NMR studies. For the purpose of Na immobilisation, it would be clearly advantageous from the viewpoint of maximising waste loadings to utilise the most Na-rich version of the NZP structure, namely Na5Zr(P04)3, although useful waste loadings can be achieved with the Na3Zr1.5(P04)3 variant. HIPing at 9000C is used in the production to eliminate volatility in the hot consolidation step, and studies of possible can/waste form interactions will be presented. The solid state 23Na and 31 P MAS NMR studies of these products are particularly useful in detecting problematic phases and undesirable structural aspects which can inhibit waste form performance.