Reactor noise analysis method based on information dimension is applied to the monitoring and diagnosing of power oscillation. The method focuses on the utilization of the slope of the correlation integral (SOCI) which determines the information dimension of attractors. For practical application, the information dimension is expected to be the same as the fractal dimension of attractors ; it can be used to classify different asymptotic regimes of nonlinear dynamical systems.
We examined a real power oscillation using SOCI and the results implied that the oscillation was just a noisy limit cycle, although it is not possible to assert that there is no chaotic character in the oscillation because large oscillatory time-series data sets are not available. In addition, the application of SOCI to the realtime monitoring of power oscillation is proposed and examined.

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This paper describes the results of transient experiments using a low enriched uranium silicide miniplate fuel for research reactor. The pulse irradiation was performed in the Nuclear Safety Research Reactor (NSRR) at the Japan Atomic Energy Research Institute (JAERI).
The results obtained in this study are summarized as follows :
(1) The tested fuel plates were damaged with energy depositions above 94 cal/g-fuel, but remained intact below 82 cal/g-fuel. A failure threshold should therefore exist between these two values.
(2) Four of the fuel plates that showed peak cladding surface temperatures <330°C were damaged by the thermal stress during quenching. These damaged fuel plates revealed small intergranular cracks that propagated perpendicularly to the axial direction of the plate, from the Al cladding surface to the fuel core, without significant dimensional changes. On the other hand, when peak cladding surface temperatures were >400°C, the test fuel plates were damaged mainly by melting of the Al cladding, accompanying significant dimensional changes.
(3) The thermal stress of the damaged fuel plates calculated on the basis of the maximum transient temperature drop during quenching was greater than the tensile stress that occurred during fabrication.

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Existing models for estimating fission gas release rate usually have fuel temperature as independent variable. Use of fuel temperature, however, often brings an excess ambiguity in the estimation because it is not a rigorously definable quantity as a function of heat generation rate and burnup. To derive a mathematical model that gives gas release rate explicitly as a function of design and operational parameters, the Booth-type diffusional model was modified by changing the character of the diffusion constant from physically meaningful quantity into a mere mathematical parameter, and also changing its temperature dependency into power dependency.
The derived formula was found, by proper choice of arbitrary constants, to satisfactorily predict the release rates under a variety of irradiation histories up to a burnup of 60, 000 MWd/t. For simple power histories, the equation can be solved analytically by defining several transcendental functions, which enables simple calculation of release rate using graphs.

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Measurements of multiphoton absorption of 16 fern Raman laser radiation in static UF₆ (with 99.3% ²³⁸UF₆) have been performed at room temperature and -35°C. The laser fluence has been varied between 10 and 300 mJ/cm² for six laser frequencies in the range from 615 to 629 cm^-1. Laser frequency and fluence dependence of energy absorbed by UF₆ molecules have been investigated. The results indicate that the number of photons absorbed per molecule r;(φ) at a mean fluence φ at several frequencies is in proportion to φ^α where α ?? 2/3.

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A series of constant load & temperature creep tests and varying load and/or temperature creep tests was carried out on a nickel-base heat-resistant alloy Hastelloy XR, which was developed for applications in the High-Temperature Engineering Test Reactor, at temperatures ranging from 850 to 1, 000°C in order to examine the creep behaviors of the alloy under varying load and/or temperature conditions.
The minimum creep rate was not affected by the prior exposure to the load and temperature environment. The life fraction rule showed a good applicability among various prediction rules. Above-mentioned two items, i.e. no change of the minimum creep rate and the good applicability of the life fraction rule were considered to show that the change of the chemical composition and/or the microstructure during exposure to the high-temperature simulated HTGR helium gas environment was not appreciable to affect the creep strength of Hastelloy XR.

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Effects of a short lived radionuclide fixation to minerals during alteration process from a primary mineral (Ml) to tertiary mineral (M3) through secondary mineral (M2) on a decay chain radionuclides migration (DCRM) have been studied based on mathematical simulation studies. The mathematical migration model in which a daughter radionuclide, N2, corresponds to a short lived radionuclide and is fixed to M2 during alteration from M1 to M2, is proposed.
Also, a fraction of the granddaughter radionuclide, N3, is assumed to be released from M2 into a solution during the alteration process from M2 to M3.
The model studies lead the delay in the migration of N3, with the delay becoming remarkably enhanced if the fixation rate constant of N2 is greater than the decay constant of N2.
Whereas, the delay is reduced by the release of N3 with a faster rate than the decay constant of N3. Therefore, it is important clarify decay chain radionuclides fixation and release mechanisms during an alteration process.

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An error-functional expression is proposed to describe the adsorption characteristics with respect to the adsorption potential. An attempt is made to apply the expression to electrometric adsorption isotherms for water on aluminum oxide in an external alternating electric field from experiments using a moisture sensing capacitor. As results of the analyses, it is shown that electrometric parameters characterizing permittivities of adsorbent and adsorbed water depend on temperature, and statistic parameters characterizing the potential distribution vary with temperature. The dependency of the electrometric parameters are elucidated as polarizing behaviors of the adsorbent and adsorbed water in influence of temperature. The variation of the potential parameters are deduced from the temperature dependencies of the polar parameters because the polar adsorption force is caused by interaction of both polarizations of adsorbent and adsorbate ; that is proved by linear correlations of the potential parameters with the product of both polar parameters. The expression is available as a calibration method for the moisture sensor ; that is confirmed by evaluating differences between measured and calculated values. Moisture sensors of this type are recommendable for hygrometry in such as a tritium removal system, and its high reliability is obtained from calibration by the present method.

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Diffusive behavior of strontium and certain kinds of divalent cations in Inada granite were studied by a through-diffusion method. In order to examine the effect of sorption onto overall diffusive behavior, two kinds of solutions were used : 0.1 vi KC1 solution and deionized water.
The effective diffusion coefficient (De) and rock capacity factor (α) were (2.0-3.6) ×10^-13 m²/s and less than 0.022 in 0.1 KC1 solution and (0.321.7) x 10^-11 m²/s and 1.52.4 in deionized water respectively. The De and a in deionized water were much larger than those in 0.1 M KC1 solution. These results are well explained by taking into account the diffusion of sorbed ion or the surface diffusion. In support of this mechanism, most De values of Sr reported for various rocks are found proportional to the sorptivity (ρRd). In the case that the sorptivity is low, De, of Sr depends on porosity like that of nonsorbed iodide. The effective diffusion coefficient of Sr in rocks was well explained by taking into account pore and surface diffusion and was expressed as De=2.1 × 10^-10ε^1.3+3.5 × 10^-12ρRd. The effective diffusion coefficient of divalent cations in the granite was found proportional to their diffusion coefficients in bulk solution.

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A neural network model has been developed to learn the local power distributions in a BWR fuel bundle. A two layers neural network with total 128 elements is used for this model. The neural network learns 33 cases of local power peaking factors of fuel rods with given enrichment distribution as the teacher signals, which were calculated by a fuel bundle nuclear analysis code based on precise physical models. This neural network model studied well the teacher signals within 1% error. It is also able to calculate the local power distributions within several % error for the different enrichment distributions from the teacher signals when the average enrichment is close to 2%. This neural network is simple and the computing speed of this model is 300 times faster than that of the precise nuclear analysis code. This model was applied to survey the enrichment distribution to meet a target local power distribution in a fuel bundle, and the enrichment distribution with flat power shape are obtained within short computing time.

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The concrete is an important material to examine the calculation model employed in the evaluation of criticality safety for nuclear fuel cycle facility. Therefore, the data of the reflection and the isolation effects on reactivity were experimentally obtained using the Tank-type Critical Assembly (TCA). Critical experiments were performed for both the single and coupled cores where low-enriched-uranium fuel rods were arranged in a rectangular parallel-piped geometry. For the single core, the concrete slabs were positioned at one side of the core, whereas they were positioned between two cores for the coupled core to measure the reactivity interaction characteristics. Main parameters were selected as the thickness and the boron content of concrete, and the water-level worth method was applied to measure the reflection effect on the single core and the reactivity interaction effect from one core to the other core on the coupled system including symmetric and asymmetric arrangements. Some benchmark calculations were also executed using the SRAC code system to assess the accuracy of this code system. Moreover, the dependency of the reactivity interaction effect on the concrete thickness and the core geometry was examined on the basis of the Avery's two-point model.

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Four He-bonded fuel pins containing uranium-plutonium mixed nitride pellets were fabricated for the irradiation tests in JMTR, aiming at understanding the irradiation behavior and demonstrating the feasibility of mixed nitride as an advanced fuel for FBRs. Mixed nitride pellets were prepared by carbothermic reduction of the oxides. One of the fuel pins was fitted with a set of W-Re thermocouples in order to trace the temperature change of pellet center during irradiation. Moreover, ferritic stainless steel was adopted as a cladding material in one fuel pin besides type 316 austenitic stainless steel. In this report, the design and characteristics of mixed nitride fuel pins are described.

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Thermal diffusion column⁽¹⁾ is a convenient method for the separation of isotopes on a small to moderate scale⁽²⁾⁽³⁾, because the process has advantages such as high separation factors in apparatus of moderate size and a relatively simple system. A "cryogenic-wall" thermal diffusion column⁽⁴⁾, proposed by the present authors, can meet higher throughput and higher separation factor with smaller energy consumption. The process, therefore, attracts attention to purification of tritium in production system and recovery of tritium from used gas mixture of hydrogen isotopes in fusion fuel cycle. In previous papers⁽⁵⁾⁽⁹⁾, we have reported experimental and analytical results for hydrogen isotope separation by the "cryogenic-wall" thermal diffusion column, and have shown pressure dependences of total separation factor with operational parameters, such as temperature of hot and cold walls and feed flow rate, being changed.

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