Morihiro Mihara

Development of Low Alkaline Cement Considering Pozzolanic Reaction for Support System in HLW Repository Construction

Cementitious materials have been studied for their applicability as support and lining in the construction of shafts and tunnels of the underground facilities for HLW disposal system. However, in the case of Ordinary Portland Cement (OPC), the buffer materials and the host rock may be altered due to the high alkalinity of groundwater contacting the OPC in the long-term. Low alkaline cements with high content of pozzolanic material were developed in order to reduce such hyper alkaline alteration. This paper shows that the pH of the leaching solution of this cement is about 11, and that it can be applied for full scale lining and for shotcrete.

Thorium and americium solubilities in cement pore water containing superplasticiser compared with thermodynamic calculations

The solubility of thorium and americium in pore water squeezed from a cement paste was investigated by a batch method from oversaturation. The cement paste was prepared by mixing ordinary Portland cement with deionised water; in some cases the deionised water contained a polycarboxylic acid–base type superplasticiser. Following solidification, pore water was squeezed from the cement paste and collected for use in the solubility experiments. The aim of these was to investigate whether there was any effect of superplasticiser on the solubility of thorium and americium in the squeezed cement pore waters. The obtained solubility values in the two squeezed pore waters (with and without superplasticiser present) were similar. Thermodynamic calculations were performed with the thermodynamic database developed by Japan Atomic Energy Agency and compared with the experimental data to verify their applicability. These results showed that the superplasticiser used in the present study after mixing with the cement paste did not have a significant effect on solubility of thorium and americium, and the thermodynamic calculations were applicable in the present system. Size distribution of colloidal species of thorium and americium was also investigated.

The Sorption of Thorium and Americium onto Fresh and Degraded Ordinary Portland Cement and onto Green Tuff

The sorption of thorium and americium has been measured onto crushed samples of freshordinary Portland cement (OPC), degraded OPC (DOPC) and green tuff under a range of aqueous conditions as part of research into the disposal of TRU waste in Japan. Sorption onto OPC was measured from deionised water,3 mol dm −3 sodium nitrate solution and simulated seawater, and onto DOPC from demineralised water; all solutions were pre-equilibrated with the relevant cement. Sorption onto tuff was measured from pre-equilibrated deionised water, 3 mol dm −3 sodium nitrate solution, simulated seawater, OPC leachate and 1 mol dm −3 ammonium hydroxide solution. R D values were determined from the amount of thorium or americium remaining in solution after centrifugation, 0.45 μm filtration and 10,000 nominal molecular weight cut-off (NMWCO) filtration. Centrifugation gave lower R D values than filtration. MeanR D values for sorption onto OPC and DOPC were in the range 4 × 10 4 to ≥1 × 10 6 cm 3 g −1 for thorium, and 3 ×10 3 to ≥1 × 10 5 cm 3 g −1 for americium, after filtration through 10,000 NMWCO filters. Mean R D values for thorium sorption onto tuff increased from2 × 10 3 cm 3 g −1 in tuff-equilibrated deionised water, to ≥ 4 × 10 6 cm 3 g −1 from ammonium hydroxide solution (10,000 NMWCO-filtration). A similar trend was seen for10,000 NMWCO-iltered americium samples where mean R D values increased from 4 × 10 3 cm 3 g −1 in deionised water to 1 × 10 5 cm 3 g −1 in ammonium hydroxide solution.

Effects of Nitrate on Nuclide Solubility for Co-Location Disposal of TRU Waste and HLW

Part of TRU waste includes a large amount of nitrate salt, the effects of which have to be evaluated in a safety assessment of co-location disposal with high level radioactive waste (HLW). High concentrations of nitrate ions from TRU waste might affect the solubility of different radionuclides in the HLW. In the current study, the effects of nitrate salt on radionuclide solubility were investigated experimentally. Solubility experiments of important and redox sensitive radionuclides, Tc(IV), Np(IV) and Se(0), were performed using various concentrations of sodium nitrate (NaNO3 ) and of Np(V) in NaNO3 solutions to investigate complex formation with NO3 − ions. Solubility experiments of Pd(II), Sn(IV) and Nb(V) using ammonium chloride (NH4 Cl) solution were also undertaken to investigate complex formation with NH3 /NH4 + ions. No significant solubility enhancement was observed for Np and Se. Tc solubility in ≥0.1 mol/dm3 NaNO3 solution increased due to oxidation by nitrate ions. An increase of Np(V) solubility was expected by the chemical equilibrium model calculation with JNC-TDB, however, solubility enhancement by complex formation of Np(V) with nitrate ions was not observed. Solubility enhancement by complex formation of Sn and Nb were also not observed, only Pd solubility was increased by complex formation with NH3 /NH4 + ions.Copyright