A new method to form a small divergence dc ion beam using a large-area single-hole electrode instead of a multiaperture electrode is described. A distinctive feature of this method is to make use of multiple electron beams in an ion source to control the spatial ion density distribution at the region of ion beam formation; the electron beams play a role to aid formation of the concave plasma boundary, which is required to extract a convergent ion beam from gaseous plasma according to the experimental facts described in Part (I). In this experiment, it was verified with three slab-like electron beams that formation of the concave boundary was possible in a stable and steady state. This electrode system can be applied to some types of the present high current ion sources to obtain large-area dc ion beams.

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The radioactive nuclides ¹²⁴Sb (T_1/2=60.3 d) and ¹²⁵Sb (T_1/2= 2.77 yr) were produced from natural antimony by JRR-3 reactor irradiation of 283.5 h through the single and double capture processes. After cooling of 3.50 yr, the γ-ray spectrum of the antimony sample irradiated was measured by a 50 cc coaxial type Ge(Li) detector, and the photo-peak yield ratio of ¹²⁵Sb (E_γ=428 keV) to ¹²⁴Sb (E_γ=1.691 MeV) was obtained. By using a relation between this photo-peak yield ratio and the ¹²⁴Sb(n, γ)¹²⁵Sb cross section, the reactor neutron capture cross section of 60.3-day ¹²⁴Sb was obtained as 17.4^+2.8_-2.5 b. The thermal neutron flux at the position of antimony sample irradiated was estimated as (4.92±0.38) × 10¹²n/cm²•s by measuring the 1.333-MeV photo-peak yield of ⁶⁰Co, which was activated by reactor irradiation of cobalt impurity contained in the antimony sample.

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Stable parameter identification and adaptive control schemes are considered for a reactor model embodying two temperature feedbacks-slow and fast. This reactor model is liable to see its feedback coefficients change sign in the course of long periods of operation, resulting in nonlinear oscillations of neutron flux, which cannot be described by a linearized model. This nonlinear system is expressed in terms of memoryless non-linear elements in the feedback loop of a linear system, with the aid of linear and non-linear transformations, and the nonlinear elements are here treated without being linearized. A new system representation is introduced, using which, stable parameter identification and adaptive control schemes are developed in the pattern of the Model Reference Adaptive System (MRAS) with use made of the Lyapunov method. Both schemes are shown to be stable, and furthermore globally stable if the input has frequencies sufficiently varied to permit all the excited modes to be considered linearly independent. It is thus shown that the estimated parameters converge to the true values for the parameter identification, and that, for the adaptive control, the output error between the plant and the model tends toward zero.

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The distribution of fission products in various steps of the fluoride volatility process on simulated irradiated nuclear fuels is considered. The ruthenium behavior is similar to that of Zr. This suggests a large percentage of Ru appears as RuF., presumably after decomposition of the instable RuOF4 produced in the fluorination in the presence of oxygen.

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The relation between strain rate and iodine stress corrosion cracking (SCC) was studied on Zircaloy-2 subjected to uniaxial stress under constant extension rate in an iodine partial pressure of 4 Torr and at a temperature of 350°C. The specimens were machined from actual fuel cladding tube. In iodine environment, the tangentially directed specimens registered sharp decreases in stress beyond maximum point ; this is attributed to crack initiation and propagation. Fracture ductility diminished with decreasing strain rate. Severe SCC was observed at strain rates below 2 × 10^-3 min^-1. At high strain rates, the mechanism governing the rate of SCC appeared to be the time-dependent corrosion process. The axially directed specimens showed no signs of embrittlement due to gaseous iodine ; this is attributed to the particular texture of the Zircaloy. Fracture surface observations indicated that transgranular cleavage fracture along the basal plane appeared to play a significant role in the stages of SCC initiation and propagation.

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This paper reports some irradiation effects and recovery behavior of neutron irradiated boron carbide pellets that were used as control rod elements in the Enrico Fermi Fast Breeder Reactor. Measurements were carried out on changes in lattice parameters, thermal expansion, helium release, elastic moduli and microstructure observations by annealing the irradiated pellets at elevated temperatures. The increase in unit cell volume of B4C upon irradiation was found to be 0.22%. The recovery in lattice parameter began at around 500°C and completed at 1, 000°C. It was found that the pellet showed a sharp increase in a dimensional change at about 700 to 800°C with a large amount of helium release, and the pellet which showed larger swelling released smaller amount of helium.

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The computer simulation method has been applied to the analysis of the NO and NO₂ decomposition in the NO-N₂ and NO₂-N₂ mixtures by electron beam irradiation. The calculated results regarding the NO and NO₂ decomposition were in good agreement with the experimental results in both mixtures. The NO and NO₂ decomposition is mainly induced by the radical reactions and is hardly induced by the ion reactions. That is, the NO decomposition in the NO-N₂ mixture is mainly induced by the attack of N formed by the radiolysis of N₂. The NO₂ decomposition in the NO₂-N₂ mixture is induced not only by the attack of N, but also by the attack of 0 formed through the reaction of NO₂ with N at low doses. At high doses, the decomposition of NO formed through the reactions of NO₂ with N and with 0 is mainly induced by the attack of N, in contrast to the NO₂ decomposition by the attacks of N and O at low doses. The G value of the formation of N(G (N)) by the computer simulation was 2.0.

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Large numbers of graphite blocks are involved in the high-temperature gas-cooled reactor (HTGR) core. In the analysis of time history core response, integral time mesh is small so that many integral steps are necessary, because the impact vibration of the core occurs under seismic excitation and the impact between blocks is complete in several 10^-310^-4s. Therefore, time history analysis of the core seismic response requires considerable computational cost. To reduce this cost, a simplified model for core seismic analysis is contrived.
This report describes simplified modeling in the seismic response of HTGR core consisting of graphite blocks. For the model, one degree-of-freedom mass with nonlinear column characteristics is used instead of the stacked column.
Results of the simplified model are compared with those of the experiment and also with a detailed analytical model. The former is in good agreement with both the experimental and the detailed model.

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