Principal properties of the magnetic helicity are reviewed with pointing out its basic roles in the fusion plasma theory. Approximate conservation of the total helicity in a toroidal plasma characterizes a typical MHD relaxation process which leads to a force-free plasma equilibrium. The distribution of the plasma current is determined by the helicity transport. Transformer induction injects helicity flux into a toroidal plasma system. Oscillating field can also transport the helicity with driving a parallel (force-free) current.

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How the Japanese nuclear reactor safety has been during the past 35 years since the very beginning of her nuclear energy development is described. Safety study first through literature investigation started in later '50s and the experimental work related to reactor safety started in early '60s. Japanese safety standard and criteria were authorized around '60 referred the US systems, but some modifications were made to make them better fitted to the Japanese situations. The results of the experimental study started in the field of thermal hydraulics, fuel and aseismics followed by other fields of activity have been reflected to the brushing-up work of the standard and criteria, including the proposal of doublet type (PCT plus oxidation fraction) in ECCS criteria, which later accepted world wide.
Regulatory experiences especially in the first decade of Japanese LWR operation, the response to which afterwards contributed the elimination of the significant troubles are overviewed. The Japanese response to two greatest accident of Three-Mile-Island and Chernobyl is also briefed. Japanese concept as the base for maintaining reactor safety in such an excellent way has been explained with the author's recommendation along with the so-called Safety Culture.

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A method is described to predict radiation hardness of general purpose logic ICs using device parameters measured by total dose testing of "elemental ICs" selected from an IC family. The total dose degradation on ICs can be predicted by simulations using their back-fitted device parameter shift data and circuits data. This method was applied to CMOS logic ICs of the HD74HC series. The HD74HC04 inverter was selected as the elemental IC, and irradiated up to 300 Gy to determine the threshold voltage shifts of n- and p-channel MOS FETs. Using the back-fitted threshold voltage shifts of the n- and p-channels, the degradation of the static characteristic and propagation delay time of the HD74HCO4 were predicted up to a large total dose, 2, 000 Gy, at functional failure.

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The present work describes the design of a high efficiency thermal neutron detection system, and the measurements performed with it on electrolytic cells containing LiH dissolved in D²O with palladium cathodes. A procedure involving the use of a non-stationary (pulsed) current through the cell caused a correlated neutron production to be observed in a repeatable manner. These patterns are strongly dependent on the previous charging history of the cathodes. The technique employed seems to be very useful as a research tool for a systematic study of the different variables governing the phenomenon.

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An equivalent linearization method has been introduced for density-wave oscillation analysis. Unlike the frequency domain approach with linearized equations assuming an infinitely small amplitude, the present method can deal with large amplitude oscillations with the nonlinearity effect on limit cycle amplitudes taken into account in the frequency domain.
Equivalent linear equations have been derived based on a one-dimensional separated flow model. A profile fit model was adopted for subcooled boiling. The characteristics of the equivalent linear equations and factors to limit the amplitudes were phenomenologically examined.
Analyses of the experimental data by Saha et al. using the present method revealed that, given an appropriate set of two-phase flow correlations, the equivalent linearization method can predict limit cycle amplitudes after instability initiation as well as the stability boundary.

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From a view point that the maximum separation factor (αβ)_max attainable in total reflux operation of thermal diffusion column depends on temperature difference ΔT between hot T_h and cold T_c surfaces in the form of ΔT/T_c as
(αβ)_max=exp[ΔT/T_c•3√6(2+Inδ)αTZ^*/2 In δ√15(In δ)²+56 In δ+53/{1-δT/T^c•4+3Inδ/4Inδ(1+In δ)}].
where δ (≡r^h/r^c) is the ratio of hot wire to cold-wall radii, αT the thermal diffusion factor and Z^*(≡Z/r^c) the normalized column height, remarkable enhancement of separation factor is expected through an adoption of "Cryogenic-Wall" (ex. 77.35 K) instead of "Ordinary Cold-wall" (ex. T^c=288.15 K). The effect of "Cryogenic-Wall" was analyzed on the basis of approximate formulae involving explicitly design parameters for the column constants. In the case where r_c=1.5 cm, Z=150 cm and ΔT=1, 000 K, (αβ)_max for H2-HT through "Ordinary Cold-wall" TD column is 63.4, while that through "Cryogenic-Wall" TD column is 885, for which ΔT=2, 430 K is required in the "Ordinary Cold-wall" TD column and it is impossible for the hot-wire to be at so high temperature because of its melting. The magnitude of enhancement is, however, smaller than that expected from the ratio of ΔT/T_c, because (1) the value of a T decreases in lower temperature region, and (2) the argument of the exponential function for (αβ) _max is not proportional directly to αT•ΔT/T_c but to αT•ΔT/T, where T is the reference mean temperature higher than T_c. The optimum pressure of "Cryogenic-Wall" TD column is considerably smaller (0.024 MPa for the case above) than that of "Ordinary Cold-wall" TD column (0.103 MPa).

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EXAFS (Extended X-ray Absorption Fine Structure) measurement was carried out for the study of the local structure around Zr in precipitates of Zr(IV)-monobutylphosphate and Zr(IV)-dibutylphosphate, which are one of the main species of so-called "The Third Phase". Both gelatinous and dried samples show the same Fourier transform spectra for Zr(IV)-monobutylphosphate and Zr(IV)-dibutylphosphate. The precipitates in Zr(IV)-monobutylphosphate have the bridging phosphate between Zr ions, Zr-phosphate-Zr, as well as the bridging hydroxyl between Zr ions, Zr-OH-Zr, while no bridging phosphate in Zr(IV)-dibutylphosphate. This fact indicates the layer structure with 16 A distance for Zr(IV)-monobutylphosphate described in Part (I) of the present reports. As for the re-dissolution of Zr(IV)-dibutylphosphate precipitates with increasing tributylphosphate observed in Part (I), the absence of the bridging phosphate in Zr(IV)-dibutylphosphate plays an important role. The chemical structures postulated by elemental analysis, infrared spectra, 'H-NMR and X-ray diffraction in Part (I) were confirmed in detail from the present results of EXAFS. It was confirmed Zr0²⁺, zirconyl ion, does not exist in aqueous solutions.

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A new method was developed for the removal of ruthenium from nitric acid solutions. Ruthenium in 3 M nitric acid solution is oxidized electrolytically to ruthenium tetraoxide, and the tetraoxide is extracted into n-paraffin. The ruthenium tetraoxide extracted in paraffin is readily reduced to ruthenium dioxide by the solvent as black suspension, and it can be easily filtered off through an ordinary cellulose fiber filter. By this method, ruthenium, one of the most troublesome fission elements in PUREX Process, can be removed.

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To clarify various kinds of precipitates formation behavior in high level liquid waste (I-ILLW) from the nuclear fuel reprocessing process, undissolved materials generated in concentration step under vacuum evaporation and aging step at various temperatures and nitric acid concentrations using simulated HLLW solution were closely investigated.
Three kinds of material, mixed crystalline salt of barium and strontium (Ba_0.5, Sr_{0.5M/SUB> (NO3)2), phosphomolybdic acid (P2O5•24MoO3•7H2O), and zirconium molybdate (Zr (OH)2- Mo<SUB<2}O₇. (H₂O)₂) were obtained as the precipitates in the simulated solution. Mixed crystalline salt and phosphomolybdic acid were formed during concentration process. Yield of the former depended on solubility of barium nitrate in nitric acid, so the precipitate was redissolved at concentration below 6 M HNO₃ because of a large solubility at low concentration of HNO₃. The yield of the latter depended on concentration factor of HLLW, but the precipitate was not redissolved at concentration of 210 M HNO₃ in HLLW.
On the other hand, the formation yield of zirconium molybdate which was formed during aging step was effected by both temperature and HNO₃ concentration and increased at high temperature and low concentration of HNO₃.

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Sorption of strontium on a number of minerals and rocks has been studied by varying aqueous concentrations of strontium. Distribution coefficients (K_d) of strontium determined by a batch method remained constant at a low concentration level and decreased with increasing concentration at a high concentration level. Values of K_d.tr at trace concentrations were considerably different depending on types of geological samples. A linear relationship was observed between the values of K_d.tr and the cation exchange capacity (CEC) for cesium as : log K_d.tr =log CEC+constant. The values of K_d.tr of strontium changed almost linearly to those of cesium for individual samples suggesting a similarity in physicochemical interactions between geological samples and these ions.

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