Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident produced much amount of radioactively contaminated water at the Great East Japan Earthquake. ¹³⁷Cs and ⁹⁰Sr have been focused to remove from the contaminated water using zeolite types of adsorbents. Other radionuclides have been treated and removed separately by Advanced Liquid Processing System (ALPS), where resin is used to immobilize anions. However, these kinds of spent-adsorbents are not suitable for long-terms burying because of its instability, and the representative anionic radionuclides (¹²⁹I, ³⁶Cl, ^99mTc and ⁷⁹Se) have quite long half-life (10⁵-10⁷ years). Montmorillonite (Mt) is an useful adsorbent because of its high chemical stability and large cationic exchange capacity. In the present work, surfactant modified Mt (OMt) has been developed using hexadecylpyridium chloride for adsorption of ClO₄^-, which is a surrogate of ^99mTcO₄^-. For stabilization of spent-OMt, cement solidification was examined with varying the ratio of spent-OMt content. To evaluate its chemical and physical stability, soaking and compressive strength tests were conducted. As a result, it was revealed by FTIR and ²⁹Si-NMR that with increase in OMt contents, the linkage of calcium silicate hydrate was more developed.

A numerical simulator is developed as a part of a Japanese National hydrate research program (MH21, funded by METI) to examine performance of methane gas production system from methane hydrate layer under deep seabed. The simulator solves mass and momentum equations of gas-water two-phase flow using one-dimensional drift flux model to trace velocities and volumetric fractions in each phase along a gas production well with various diameters. An automatic control system is devised in the simulator to control methane gas production rate by keeping the bottom pressure constant. Numerical simulations are conducted to examine characteristics of the system by changing pipe dimensions as parameters based on the real system in the field test. Also, in order to increase performance of the automatic control system, an additional component related to estimated water production rate under designed gas production rate is considered in the system. The new control method is tested as well as a standard feedback control system. As the result, it was verified that the simulator could estimate the flow characteristics during operation in the production well. Also, it was clarified the proposed control method is useful to get the designed gas production. One could get useful information by adding necessary functions and further information by doing more parametric studies with it.

To elucidate the effect of solution composition on the passivation of anode in Cu electrorefining, the potentiodynamic polarization curves were measured by polarizing from -0.2 V versus NHE to 1.0 V using the potential sweep method at 1.0 mV·s⁻¹. The diffusion coefficient was measured by rotating disc electrode method under the conditions of 50, 100, 150, 200, 250 and 300 revolutions per minute of disc electrode and polarizing from 0.34 V to -0.40 V at 10.0 mV·s⁻¹. The critical current density for passivation and the passive current density decreased linearly with total concentration of SO₄ in solution regardless of solution composition and the presence of impurities such as As³⁺，Sb³⁺ and Bi³⁺, showing the good correlation between the current density for passivation and the total concentration of SO₄. The diffusion coefficient of Cu²⁺ ions decreased with total concentration of SO₄ in solution. The increase in passivation with the total concentration of SO₄ is attributed to both decreases in solubility of CuSO₄ in electrolyte and the diffusion coefficient of Cu²⁺ ions. On the other hand, focusing on the effect of kinds of cation on the passivation, the harmful effect on the passivation was largest with Cu²⁺ ions, and was larger in the order with Li⁺，Ni²⁺ and Na⁺ ions, and was smallest with H⁺ ions. The diffusion coefficient of Cu²⁺ ions decreased most with Ni²⁺ ions, and decreased secondly with Li⁺ and Na⁺, and decreased least with H⁺ ions. The diffusion coefficient of Cu²⁺ ions decreased with increasing the viscosity of solution.