Solidification of NPP Cube Residuesby Incorporation Into Magnesium Cement Matrix
Solidification of high-radioactive NPP cube residues containing primarily sodium nitrate with magnesian cement has been investigated. Magnesian cement is defined as hydrated magnesium oxychloride of the gross formula of (MgO)(2-4)∙MgCl2∙(H2O)(10-18). Starting with the 600 g/L sodium nitrate-containing cube residue the solidified compounds have been obtained with the salt content within the range of 0-29% and the mechanical strength in the double-side compression test within the range of 20.5 - 0.4 MPa, respectively. It has been shown that in the 137Cs leach tests of the solidified magnesian cement samples of any composition over 90% of radioactivity is leached out within the first 10 days of the experiment. Selective 137Cs sorbent additives, namely, clinoptilolite, bentonite, and potassium-nickel ferrocyanide reduce the leaching of cesium down to 1.5.10-3 - 3.0.10-4 g/cm2/day. Those results led to the conclusions that the solidified magnesian cement samples containing selective cesium sorbents and up to 20% of salts except borates met the requirements imposed on the safe SRW storage in the concrete block containers. Magnesian cement could be used as a cost-effective substitute for the Portland cement. Four tables, 4 references.