In order to improve the sensitivity and the reliability of the sodium leak detection system used in the fast breeder reactors, a new type SID (sodium ionization detector) has been developed, in which the monitored signal is only the fluctuating component of the current between the filament and the ion collector. The fluctuating component was extracted by a band pass filter and its root mean square value was calculated as the SID signal. Fluctuation characteristics of the output current were studied by its frequency spectrum. The results revealed that the current spectrum was affected by the particle size distribution of the aerosol and was most clearly distinguished from that of the background current in the frequency region of 0.510 Hz.
Output characteristics of the fluctuation monitor type SID (FM-SID) were obtained as a function of sodium concentration in the gas. The FM-SID sensitivity was lowered by impurities in the gas, such as oxygen and water vapor. Finally, in comparisons with the conventional DC-SIDs, the background noise level of the FM-SID was much lower and S/N ratio was greatly improved. The detectable sodium concentration level was ten times lower than that of the DC-SID.

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For providing background information on the liquid metal cooling of fusion reactors, the MHD effects on heat transfer of flowing lithium was experimentally studied with an emphasis on temperature fluctuations. The test section was constituted of a 15.8 mm I. D., 1.65 mm thick, 316-SS tubing and a 7.6 mm O. D. heater pin with nine 0.5 mm thermocouples. The experiment covered the range of B=01.0 T, U=0.24.0 m/s, T=320390°C and q=0 68 W/cm². The results are summarized as follows :
(1) With increasing magnetic flux density B, Nusselt number Nu decreases to a value of flat flow velocity model : 6.38 but rises in B=0.10.4 T. (2) The RMS of temperature fluctuation has strong dependence on B and presents a peak near B=0.25 T. (3) The singular rise of Nu is inferred to result from enhanced turbulence due to steepening of radial gradient of velocity near the wall as a result of MHD effect. (4) The transit velocity estimated from temperature cross-correlation in the parallel sector coincides with the mean velocity when B=0 but deviates toward a lower value with applying B. (5) Local flow velocity is decelerated in the magnetically-parallel sectors and accelerated in the per-pendicular.

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Effects of irradiation on the dimension and microstructure in (Th, U)O₂ pellets were examined by measurements of lattice parameter and bulk density changes, and observations of pore structures. The concentrations of fission-induced defects and the damage volume were estimated by a simple model. Both macroscopic and microscopic dimensional changes were found to increase initially with fission dose and then fall off. The difference between macroscopic and microscopic ingrowths increased with dose, suggesting that fission-induced interstitials would cluster or go to sinks and the concentration of vacancies would be in excess of that of interstititials. The damage volume for vacancies was estimated to be about 1 × 10^-22m³•fiss.^-1, and almost agreed with that for fission Xe release. Observations of the pore structure indicated that the volume fraction of pores smaller than 23 μm decreases with irradiation and the distribution of pore size shifts toward the larger side.

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The vapor pressures over single phase vanadium monoxide VO_1.022(s) and the two-phase mixture of vanadium metal (β phase) and vanadium monoxide were measured by mass-spectrometric method in the temperature range of 1, 8031, 990 and 1, 7031, 884 K, respectively. The main gas species over both systems were found to be VO(g) and V(g). The vapor pressure of VO(g) over the two-phase mixture of V(s) and VO(s) was a little lower than that over single phase VO(s). The vapor pressure of V(g) over the two-phase mixture was nearly equal to that over single phase. From the vapor pressure data, the enthalpies of vaporization, the enthalpies of formation for VO(g) and V(g) and the dissociation energy of VO(g) were determined. The oxygen partial pressure was calculated as a function of temperature from the vapor pressures of VO(g) and V(g), from which the partial molar enthalpies and entropies of oxygen in both systems were obtained.

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Sample specimens of type 304 stainless steel and Zircaloy-2 were exposed to the OWL-1 loop water at 280°C for 23 d. After the exposure, a number of crystallites are distributed either separately or sometimes in agglomerate on the surfaces. The X-ray diffraction analysis and XMA analysis of the type 304 stainless steel surface revealed that more than 95% of the crystallites have a M₂O₃-type of structure, and some are enriched in Cr. In the subsequent radiochemical analysis of the fractions detached by the various cleaning processes (ultrasonic, electrostripping and electropolishing), it is noticed that the ⁶⁰Co/Co ratio de-creases with the depth of the corrosion layer from the value close to that of insoluble crud in the water (crud-P) to that of soluble crud (crud-F).

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The dissolution of Cr-rich oxides in and the decontamination of contaminated specimens by sulfuric acid-Ce (IV) (SC) solution have been investigated. The results have been compared with those by the reported typical decontamination reagents. The SC solution can dissolve simultaneously not only Cr but also Fe and Ni in the Cr-rich oxides. The dissolution mainly depends on Ce (N) concentration (1.310 × 10^-3 M) and temperature (4090°C), but is independent of H₂SO₄-concentration (0.20.5 M at 5 × 10-3 M Ce (IV)). The DF is ca. 33 at 90°C for 24 h with 0.25 M H2SO4 -5 × 10^-3 M Ce (IV). Under electrolytic regeneration of Ce (IV) from Ce (III) during the decontamination, the DF is raised to 460 even at 80°C for 24 h with 0.25 M H₂SO₄ -1.3 × 10^-3 M Ce (IV). The SC solution can be applicable to the decontamination for decommissioning of both BWR and PWR. Furthermore the combination of the chemical cleaning with an additional ultrasonic cleaning provides a promissing cleaning procedure for post-disassembly components.

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The relationship between the motion of drops and mass transfer in a pulsed column was investigated by taking high speed photographs. The rising motion of drops in the column was found to be divided into jetting, forced rising and free rising periods, whereas the falling motion was divided into forced falling and free falling periods. With use of the observed results, it was confirmed that the drop velocity and the distance of moving drop predicted from the equation of drop motion were satisfactorily compared with the corresponding observed values.
On the basis of the results, the overall mass transfer coefficient in the pulsed column was derived, which was found to be valid in the course of calculation of the amount of mass transfer in the pulsed column.

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Column experiments have been carried out on the migration of ⁶⁰Co, ⁸⁵Sr and ¹³⁷Cs in an alkaline solution (pH 12) through a sandy soil layer. Radionuclide-concentration distributions in both an effluent and a sandy soil layer were measured after pouring 200 ml of aqueous solution containing the radionuclides on the layer, followed by eluting with 3, 800 ml of distilled water.
Strontium-85 and ¹³⁷Cs gave a similar distribution pattern in the soil layer, while ⁶⁰Co migrated deeper into the layer. The migration velocity followed the order ; ⁶⁰Co>⁸⁵Sr ?? ¹³⁷Cs. The order was different from that obtained with the radionuclides existed in a neutral solution. This suggested that the migration behavior of the radionuclides is significantly affected by the pH of the solution in which the radionuclides exist.
The sandy soil layer used here is considered as a linear system for the migration of ⁶⁰Co in the solution of pH 12.

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Tritium permeation at 350°C through stainless steel wall of a vessel filled with deuterium-tritium gas of 6.1 × 10⁶ Pa pressure was practically suppressed by Au plating of 20 μm thick applied to the outside surface. The apparent diffusivity of hydrogen through plated Au layer, derived from the experimental data, was 2 × 10^-11 cm²/s for 470°C, which is 10^-510^-6 times smaller than what would be expected from values reported for wrought Au, and the apparent solubility was very significantly higher than similarly expected level. Gas analysis of the Au layer indicated that the effective suppression of tritium permeation is attributable to trapping of hydrogen by C contained in the Au as impurity. Adequate tightness against tritium leakage has been achieved by Au plating on a vessel used for loading glass microspheres with deuterium-tritium gas, intended for laser fusion targets.

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