Abstract
The manuscript presents the results of the development of new material for high-level waste (HLW) management: the magnesium potassium phosphate (MKP) compound. The possibility of using zeolite (Sokyrnytsya deposit) to increase the mechanical, thermal, and hydrolytic resistance of this compound with immobilized HLW was studied. The main component of the used natural zeolite is a mineral of the clinoptilolite–heulandite series, and quartz, microcline, and clay minerals (illite, sepiolite, and smectite) are present as impurities. The compressive strength of the compound, containing at least 4.2 wt % zeolite, is about 25 MPa. Compound containing 28.6 wt % zeolite retains high compressive strength (at least 9.0 MPa), even after heat treatment at 450 °C. The adding of zeolite to the composition of the compound increases its hydrolytic stability, while the leaching rate of the mobile nuclides 137Cs and 90Sr decreases up to one order of values. Differential leaching rate of radionuclides from the compound containing 28.6 wt % zeolite is 2.6 × 10−7 for 137Cs, 2.9 × 10−6 for 90Sr, 1.7 × 10−9 for 239Pu, and 2.9 × 10−9 g/(cm2∙day) for 241Am. Thus, the properties of the resulting compound correspond to the requirements for solidified HLW in Russia.
Highlights
The nuclear fuel cycle is the main source of radioactive waste (RW) and produces all types of it, including high-level waste (HLW)
We study the influence of zeolite on the physical and chemical properties of the MKP compound, in order to provide the mechanical, thermal, and hydrolytic resistance required for solidified HLW
It was established that the main component of the used zeolite is a mineral of the clinoptilolite–heulandite series (74%), which is consistent with the data that deposits of zeolite tuff in this region are characterized by clinoptilolite content from 60%
Summary
The nuclear fuel cycle is the main source of radioactive waste (RW) and produces all types of it, including high-level waste (HLW). Energy Agency, RW of any activity level must be immobilized—that is, transformed into a waste form by solidification, embedding, or encapsulating [1]. The influence of different HLW types on the properties of the MKP compound was studied, including 99 Tc waste solutions [5], Pu contaminated ash [6], surrogate denitrated HLW from the PUREX process [7], and HLW bottom sediment surrogates [8]. We confirmed the premise of using the MKP compound for HLW solidification of various composition and origin, including historical
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