As an attempt to improve the stability problem of U-carbide fuel, the solid solutions of UC-ZrC and UC-NbC were prepared. Their stabilities against water corrosion and atmospheric oxidation and their compatibility with graphite were compared with those of UC and UC₂.
UO₂+C+ZrC (NbC) mixture was heated in vacuum at around 1, 800°C for 1 hr to form the solid solution. By milling and compacting the reacted carbide and sintering in vacuum at 1, 900°2, 000°C for 1 hr, UC-ZrC or UC-NbC pellets having the density more than 90% of theoretical value were produced.
It was revealed that UC₂ tended to decompose into C and U₂C₃ in the temperature range lower than 1, 500°C and transformed from cubic to tetragonal lattice at about 1, 800°C, although it was compatible with graphite up to 2, 000°C. Whereas, (U. Zr)C or (U. Nb)C showed no lattice transformation up to melting point and more excellent stabilities against corrosion and oxidation, and furthermore, it was compatible with graphite up to 2, 000°C, as long as ZrC or NbC content was more than 72mol/_??_ or 63mol/_??_.
These mixed carbides are promising as a fuel material for a high temperature gas-cooled reactor.

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For the measurement of personal radiation exposure, pocket dosimeters and filmbadges are widely used. As these analog type dosimeters are readily influenced by temperature and humidity, they have some limits on its accuracy and its integrating range. These defects are overcome by digital method. By this reason, we made a digital type dosimeter and studied its characteristics.
The digital type dosimeter is composed by a small type G-M counter, a control circuit, a counter voltage supply, an electronic scaler, a mechanical register and a battery. For miniaturization, micromodule circuits, a watch mechanism and a Ni-Cd-Al cell are used. To reduce the power consumption, the counter voltage is controlled by the counting rate.
The maximum measuring range is 5 r, and the indicating and the alarm level can be set from 0.012 mr to 5 r. The size is 150×90×50 mm and the weight is 500 g.

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Calculations are made of JPDR fuel temperature at loss-of-coolant accident. At the accident, the reactor is scrammed either by a low-reactor-water-level signal or by a high-enclosure-pressure signal, and the core spray system is initiated.
In analyses, a fuel rod and a clad is devided into six and two annulus sections, respectively. Various cases with and without control rods and a core spray system in operation are evaluated. In evaluation of a case without a core spray system in operation, axial heat conduction in UO₂ is neglected before radial temperature distribution is flattened and after that, radial heat conduction is neglected to calculate axial temperature distribution.

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Effects of linear energy transfer (LET) on the product yields of the radiolysis of water have been studied at length and explained satisfactorily by the diffusion theory developed by Magee and his co-workers. If similar discussions are assumed applicable to the other liquid systems than water, the more detailed mechanisms of the radiolyses must be obtained. Though relatively few papers have been published of the LET effects for the non-aqueous systems, some examples, that is, methanol, cyclohexane, cyclohexene, benzene and its derivatives, which were studied systematically to some extent, are reviewed. Special systems are also reviewed briefly.

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