The effective thermal conductivity of the fuel elements used in nuclear reactors is of significant importance in determining the performance, reliability and operational efficiency of the reactors. This is especially true in sphere-pac reactor fuels, in which the fuel elements are comprised of packed beds of spherical or near spherical particles.
Presented here is a review of the analytical and experimental investigations, conducted to predict or determine the thermal conductivity of beds of packed spherical particles such as those found in sphere-pac reactor fuels. Included are packed beds in which the particles are all of uniform size and beds in which several different sizes exist.
Analytical techniques for packed beds both with and without restructuring are presented, discussed and compared with the existing experimental data.
Based upon this review, it is apparent that additional analytical and experimental investigations are necessary in order to accurately predict the effective thermal conductivity in sphere-pac reactor fuels. Specific areas where this need is greatest are identified and discussed.

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Cross sections of the ²⁷Al(n, α)²⁴Na and ⁵⁶Fe(n, p)⁵⁶Mn reactions were measured precisely by foil activation in the energy range of 14.019.9 MeV. For the lower energies of 14.014.8 MeV, the neutron fluence rate was determined by associated α-
particle counting, while the proton-recoil telescope was used for the higher energies of 15.219.9 MeV. Correction was applied to account for the additional radioactivity brought by d + D neutrons from deuteron implantation in tritium target. The ²⁴Na and
⁵⁶Mn activities generated by the reactions of interest were determined using 4πβ-γ
coincidence counter. In respect of the ²⁷Al(n, α)²⁴Na reaction, the present results agree well with the latest evaluations of Asami and Vonach and with Ryves' measurements, except in the higher energy regions, and in respect of the ⁵⁶Fe(n, p)⁵⁶Mn cross section, with Ryves' measurements. On the other hand, the ENDF/B-V evaluations deviate appreciably from the present results in respect of both reactions, and this applies also to the JENDL-2 evaluations in respect of the ⁵⁶Fe(n, p)⁵⁶Mn cross section.

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The time-dependent neutron spectra from the surface of an externally pulsed finite block (156 mm diameter, 160 mm high) of ice were measured at 86, 35, 26 and 16 K
over an energy range of 0.00060.02 eV and for durations of time extending from 100
to beyond 600 μs following fast neutron injection.
It was found that, at 86 and 38 K, asymptotic equilibrium distribution was established already around 400 μs after neutron pulse injection, whereas at 26 K, even after
800 μs, the average neutron energy of the measured spectrum was still slightly higher than that of Maxwellian distribution corresponding to the moderator temperature, and further at 16 K, 900 μs after neutron pulses, the difference between the averages of measured and Maxwellian distribution remained at about 50%.
These results should usefully serve test in neutron scattering kernels, as well as studies for improving methods of calculation.

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With a view to reassessing the currently established neutron cross sections for Fe,
Ni and Cr, which are the main constituent elements of stainless steel, electron linac time-of-flight experiments were conducted to determine the energy spectra of neutrons in sample piles of the respective elements, in the energy range covering 10⁰10³keV levels.
The spherical symmetry of neutron distribution in the piles was verified by determining through specimen activation the spatial distribution of neutrons in several radial directions around the target.
The neutron spectra thus determined experimentally were compared with theoretical values derived by one-dimensional transport calculation using data contained in JENDL-2
and ENDF/B-IV. The resulting findings are as follows: (1) Both files call for revising the resonance parameters of Fe and Ni in the energy range below 100 keV. (2) For Fe,
ENDF/B-IV requires supplementation in the range below 840 keV with additional cross section data on inelastic scattering. (3) For Cr, both files need reevaluation of the total cross section, notably in the energy range of 48 keV characterized by a series of large resonances. A neutron transmission measurement, performed additionally, proved the total cross section for Cr to be 30 to 40% higher than derived from JENDL-2 and from ENDF/B-IV.

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Effect of stress ratio on the crack extension rate da/dN was examined for an isotropic nuclear graphite IG-11, using tapered double cantilever beam specimens. Loads were applied to the specimens cyclically at a loading rate of 251 N/s in the load range where the stress ratio R range of 00.8. Here R is defined as the ratio of the minimum stress intensity factor K_min to the maximum stress intensity factor K_max. The rate da/
dN was measured optically using a comparator. Conclusions derived as
(1) For a given value of R, crack extension rate da/dN can be expressed as da/dN-=C(ΔK)ⁿ,
here, ΔK is a stress intensity factor range, i.e. ΔK=K_max-K_min, and C and n are constants and strongly dependent on R value respectively.
(2) Threshold stress intensity factor range ΔK_lh which was defined as the point below which no crack extension more than 10 μm was observed after loadings of 10⁵ cycles was related with R -values as
ΔK_lh/ΔK_lho=(1-R)^0.89, (ΔK_lho=ΔK_lh at R=0).

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The kinetics of the reaction between Np(V) and hydroxylammonium chloride in perchloric acid solution was studied at 70°C. In perchloric acid solutions from 1.0
to 1.5 mol•dm^-3, the reaction rate is described by
-d[Np(V)]/dl = k[Np(V)][NH₃OHCl]^1.6[H+]^2.1,
where the rate constant k= (6.7 ± 0.3) × 10^-2 mol^-3.7 dm^11.1 min^-1. Detailed studies of the dependence of the rate on the concentrations of hydroxylammonium ion and chloride ion showed that the reaction is much accelerated by chloride ion.

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The JT-60 divertor coils produce a separatrix configuration in divertor operations of
JT-60. A suitable separatrix configuration was obtained for a plasma current of 2.1 MA
with coil ampere turns of ± 0.755 MAT. A high primary membrane stress of 52 MPa was permissible at the welded joints of the copper conductor made on the site. The mechanical strength of the joints welded in a factory was also improved by means of a press treatment. Electric insulation materials were selected considering a degradation of withstand voltage characteristics due to high cyclic mechanical strain. Vacuum-tight coil cases were composed of rigid rings and U-shaped bellows made of Inconel-625
alloy, and designed to withstand plasma disruption with a current decay time constant of 3 ms. The maximum temperature of the conductor in the periodic operation of divertor discharges was below 155°C which was the allowable temperature of the coil insulation. Molybdenum armor plates coated with titanium carbide and Inconel-625
bellows cover plates were attached against high heat flux from plasma. Thermal and mechanical load tests were carried out using component models to evaluate their performance in advance of the final fabrication of the actual coils. The satisfactory performance of the divertor coils were demonstrated in the pre-operational power test.

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In a high temperature gas-cooled reactor core consisting of prismatic blocks, leakage flows of the coolant gas occur at the gaps between blocks. Since the leakage flows reduce the effective flow rate in coolant channels, it is important to regulate the coolant flows in a reactor core. In particular, it is necessary to seal the gap between the core support blocks. The seal mechanism, in which the graphite seal elements are installed to cover the gaps between core support blocks, has been devised in the design of the very high temperature gas-cooled reactor. It is estimated that the nonuniform deformation of the core Support structure due to the temperature gradient leads to the creation of the level difference between core support blocks and thus to the malfunction of the seal mechanism. Here, air flow experiments using the models of the core support blocks have been carried out to study the leakage flow characteristics of this seal mechanism under various configurations of the blocks and the seal elements. The pressure loss coefficient factors have been evaluated from the experiments.

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The apparatus previously used for sol preparation under pH control by the aqueous ammonia addition method, was modified for the use of gaseous ammonia. By using this apparatus, starting Th(NO₃)₄ solutions with initial Th concentration of 1 to 2.34
mol/l were neutralized to prepare ThO₂ sols with final Th concentration of 0.94 to 2.0
mol/l. The effects of concentration and neutralization mode on sol properties were studied. In the above range of concentration, the neutralization modes for preparing good quality sols with high colloid fraction and with large-sized colloids were clarified.
Viscosity of the resulting sols was between 1.5 and 2.5 mPa•s, the value is far lower than that of sols produced by KFA workers with a similar method. This discrepancy is discussed.

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