The present work is an attempt to develop a simple dosimeter for measuring the pulsed radiation by the counting of the delayed-pulses. According to our recent study, the delayed-pulses are a kind of Geiger-Muller type discharges which occur being delayed after the time of an irradiation due to negative ions produced in the organic quenched GM counter by incident radiations. It was also made clear that the counting character-istics of the main-pulse being produced immediately after the irradiation exhibits the saturating mode against the intensity of the pulsed radiation, on the contrary, the number of counting of the delayed-pulses increases with the intensity of the pulsed radiation, even when its intensity is extremely increased.
We have succeeded in determining the conditions that improve both the counting number of the delayed-pulses and its linearity against the intensity of pulsed radiation. The measurement of pulsed radiation intensity could simply be made by the counting method of delayed-pulses, even when the pulse width of pulsed radiation is smaller than the dead time of the GM counter. Especially, the intensity measurement for one shot pulsed radiation was made possible by this method.
In practice, this simple measuring method made possible to measure fairly well the intensity of the pulsed radiation of the order 10^-4 to 1μR for one burst irradiation by the counting of the delayed-pulses.

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The behavior of neutrons in a highly heterogeneous unit cell consisting of D₂O moderator, H₂O coolant and a 28-pin fuel cluster contained in a pressure tube has been studied through lattice parameter measurements covering three different ²³²U enrichments, four coolant void fractions and two lattice pitches. A single-region core configuration was adopted, with which measurements were made to determine-in relation to coolant void fraction-the critical D₂O level, as well as various lattice parameters.
A strong dependence on coolant void was observed for the critical level and the lattice parameters, in the case of the smaller 22.5 cm pitch lattice, due to the positive effect on core reactivity exerted by the slowing-down faculty of H₂O in the epithermal energy region. With the larger 25.0 cm pitch, however, no meaningful dependence on void fraction was shown by any of the measured values, and this was ascribed to a compensating negative effect due to enhanced thermal neutron self-shielding in the fuel region produced by the H₂O coolant.
The results of cell calculations obtained by means of the METHUSELAH-II code showed generally good agreement with experimentally determined data, for both critical D₂0 levels and lattice parameters, in the case of coolant-filled lattices (0, 30 and 70% void fractions). For lattices devoid of coolant (100% void fraction), however, discrepancies in lattice parameters-particularly in ρ²⁸-produced corresponding deviations in core reactivity amounting to 1% in excess of those incurred with other void fractions.

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Optimization of the program of installation of reprocessing plants is mathematically formulated as problem of mixed integer programming, which is numerically solved by the branch-and-bound method. A new concept of quasi-penalty is used to obviate the difficulties associated with dual degeneracy. The finiteness of the useful life of the plant is also taken into consideration. It is shown that an analogous formulation is possible for the cases in which the demand forecasts and expected plant lives cannot be predicted with certainty.
The scale of the problem is found to have kN binary variables, (k+2)N continuous variables, and (k+3)N constraint conditions, where k is the number of intervals used in the piece-wise linear approximation of a nonlinear objective function, and N the overall duration of the period covered by the installation program. Calculations are made for N=24 yr and k=3, with the assumption that the plant life is 15 yr, the plant scale factor 0.5, and the maximum plant capacity 900 (t/yr). The results are calculated and discussed for four different demand forecasts. The difference of net profit between optimal and non-optimal installation programs is found to be in the range of 50-100 M$. The pay-off matrix is calculated, and the optimal choice of action when the demand cannot be forecast with certainty is determined by applying Bayes' theory. The optimal installation program under such conditions of uncertainty is obtained also with a stochastic mixed integer programming model.

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In order to provide compact and reliable sodium equipments including a steam gener-ator, performance tests are conducted with a potassium heat exchanger, which is featured by the separate construction of primary and secondary coolant systems. A small amount of potassium plays a role as an intermediate media of heat transportation between these two coolant systems. Heat is transfered by evaporation and condensation of potassium on the surfaces of the primary and the secondary coolant pipings, respectively. The tests are performed in the temperature range of 200300°C and the maximum heat transfer reaches 1.3 kW (heat transfer rate at the primary heating source : 8.6 W/cm² at 300°C). The experimental results are analyzed by using Langmuir's and Schrage's equations and close agreement between experiment and theory is obtained.

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Damage structure produced in stainless steel by "in-situ" irradiation with 1MV electron in a high voltage electron microscope has been observed as a function of irradiation temperature. Small hardly resolvable dislocation loops were produced by the irradiation at 300°C and below. Hexagonal-, diamond- and irregular-shaped loops were observed at 400°C irradiation. During prolonged irradiation the diamond-shaped loops directly devel-oped into dislocation network, while the other faulted hexagonal and irregular shaped loops grew to be dislocation networks after unfaulting. At 500°C irradiation, dislocation loops grew rapidly to be dislocation lines and void nuclei appeared with strain field images. On further irradiation, the void grew larger with little increase in the density. Grain boundary migration toward or away from the highly damaged region was observed at 500°C irradiation.

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Streaming neutrons escaping through an air gap located between the pressure vessel and the primary shield of the Nuclear Ship "Mutsu" were measured by applying the two-detector-method. The two detectors consisted of a single BF3 counter provided alter-natively with different covering arrangements-(a) 3 mm thick steel tube + layers of polyethylene sheeting with total thickness of 30 mm +1 mm thick Cd plate and (b) same covering as (a) + polyethylene boxing 20 mm thick.
In order to derive from the count rates obtained with the detectors described above the absolute values of neutron flux and dose equivalent rate, the detectors were calibrated in laboratory by comparison with a reference detector system in neutron fields created around a ²⁵²Cf source and TCA, a light-water moderated critical assembly. The conver-sion from measured counts to neutron flux and neutron dose equivalent rate was estimated to incur errors of ±15 and ±40%, respectively.

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