Proton-induced He production cross sections, (p, He), for Al and Ni have been measured up to 16MeV by using a He accumulation method.
The reliability of the present experiment was confirmed by performing three kinds of experiments for the Al(p, He). The sample structure or the manner of measuring the number of bombarding protons differs in each experiment. A comparison of their results shows that it is valid to install an Al sample in a Faraday cup for determination of the absolute number of incident protons and to sandwich a sample sheet by two Au foils to catch outgoing α-particles from the sample surface layer for measuring the all He produced in the sample.

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We have evaluated the cross sections of ¹²C for neutrons up to 80MeV, paying more attention to the intermediate energy range above 20MeV. For energies below 20MeV, the evaluated data of JENDL-3.2 were adopted with some modifications. In the energy range above 20MeV, total cross section and its covariance matrix were evaluated using a generalized least-squares method with available experimental data. The spherical optical model was used to evaluate reaction and elastic scattering cross sections. Inelastic scattering to the first 2⁺ state was calculated based on the DWBA. The optical potentials used in these calculations were obtained by means of the microscopic folding model based on the Jeukenne-Lejeune-Mahaux theory. Double-differential emission cross sections for neutron, proton, deuteron, triton, ³He, alpha-particle and other heavier products were calculated using the Monte-Carlo method by which three-body simultaneous breakup process and two-body sequential decay process were taken into account in n+¹²C multibody breakup reactions. Kerma factors calculated from the evaluated cross sections were also compared with measurements and other evaluations.

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Crack generation and propagation through the first wall of a fusion reactor under cyclic thermal stress caused by pulsed reactor operation has been studied analytically, and the results have been compared with experimentally acquired data. The analysis first covered the transient heat transfer through a test specimen pulse-heated on one face and constantly cooled on the reverse face. This was followed by elastoplastic stress analysis to estimate the stress-strain relation that prevails during pulsed heating. Finally, the crack propagation behavior was analyzed applying the non-linear fracture mechanics parameter termed "extended J-integral", and calculated with the three-dimensional finite element code "MARC". The results agreed well with experimental data obtained on a test specimen of type 316 stainless steel plate that was subjected to cyclic electron beam heating. This indicated the possibility of validly predicting the crack propagation behavior of a fusion reactor first wall.

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Calculated photon responses of LiF TLDs based on Burlin's cavity theory were compared with those measured using the TLDs sandwiched between two Teflon, aluminum, copper and gold foils for 30 to 200keV X-rays. The discrepancies between the calculations and the measurements were within 48% for gold, while 15% for the other media. In the cavity theory, the weighting factors related to the electron attenuation are used. The factors differed largely from those calculated with a Monte Carlo transport code ITS, of which the validity was confirmed by comparison with the response measurements. The ITS calculations also showed that the attenuation coefficients of electrons from the foils did not necessarily agree with those from the cavity theory, and the coefficients largely depended on the media. To obtain the more accurate response easily, another method are proposed, noticing that the electrons incident on the LiF are absorbed completely below 200keV. In the new method, total dose in LiF is calculated using energy transmission and reflection coefficients for the dose given by the electrons from the foils and using the mass energy absorption coefficients for the dose by the electrons generated in LiF. Responses calculated with this method agreed with those of the ITS within a difference of 6%.

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The post-dryout flow regime transition criterion from inverted annular flow (IAF) to agitated inverted annular flow (AIAF) is suggested based on the hyperbolicity breaking concept. The hyperbolicity breaking represents a bifurcation point where a sudden flow transition occurs. The hyperbolicity breaking concept is applied to describe the flow regime transition from IAF to AIAF by the growth of disturbance on liquid core surface. The resultant correlation has the similar form to Takenaka's empirical one. To validate the proposed model, it is applied to predict Takenaka's experimental results using R-113 refrigerant with four different tube diameters of 3, 5, 7 and 10mm. The proposed model gives accurate predictions for the tube diameters of 7 and 10mm. As the tube diameter decreases, the differences between the predictions and the experimental results slightly increase. The flow regime transition from AIAF to dispersed flow (DF) is described by the drift flux model. It is shown that the transition criterion can be well predicted if the droplet sizes in dispersed flow are evaluated appropriately.

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Actinides, mainly responsible for the long term risk of spent fuel, are the principal candidates to transmutation due to their large absorption cross sections.
Systems driven by particle accelerators have been investigated in the past to produce fissile material. Recently these systems have been reconsidered to destroy minor actinides (MA) and long-lived fission products (LLFP), reducing the need for the traditional final confinement of radioactive waste.
Two Monte Carlo calculation models have been developped to determine the criticality safety conditions and the burning capability of MAs and of Pu.
A Pu burner, whose core is poisoned with Th to compensate by producing ²³³U the burnup reactivity due to the even Pu isotopes, can operate at a low proton current using perhaps a cyclotron, incinerating 70% of the charged Pu; its burning capability would be the production of about 1.5 PWRs.
Liquid fuel accelerator driven systems can be used in the future (due to the accelerator dimensions) for MA burning using D₂O as carrier in a homogeneous core; such a system can burn the production of more than 15 PWRs.
In the future, also the problem of LLFP burning could be solved definitively using a system with D₂O as carrier.

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When a gas mixture consists of isotopes and squares of relative mass differences among the isotopes are small enough to be negligible, an approximation to a thermal diffusion factor in a 3-component mixture was derived analytically and was found to be the same as the binary thermal diffusion factor. Relative errors between exact and the approximation of the thermal diffusion factor in a 3-component argon 36-38-40 isotope mixture were less than 0.01.

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Dose conversion values (DCV: Sv/kg-Tritium release) associated with a release of tritiated hydrogen (HT) to the atmosphere have been studied in the field experiment performed at Chalk River Laboratories in Canada in 1987. For a near ground-level release of HT, DCVs of 2×10^-2 and 3×10^-3 Sv/kg-Tritium were evaluated at distances of 100 and 400m on the mean plume centerline, respectively. An important finding was that less than 1% of the respective doses was attributed to the primary HT plume (by submersion) and the rest to HTO (by inhalation plus skin absorption) which was formed due to conversion of the HT to HTO in the environment. A comparison to a postulated HTO release under experimental conditions predicted that corresponding dose conversion values may reach approximately 90 and 70 times greater than those of the HT release at respective distance. Extrapolation of these experimental dose conversion values into those in maximum-exposed conditions (MEC) was made. It was predicted that the ratios of dose conversion values between HTO to HT releases under the MEC were about 20 at 100m (6 at 400m), though a release of HTO is approximately 25, 000 times more radio-hazardous than a release of HT if no conversion of HT to HTO is assumed to occur in the environment. The present results were compared with those of the French HT release experiment in 1986.

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Control rod columns of the High Temperature Engineering Test Reactor (HTTR) core have each three cylindrical void holes for insertion of the control rods. The reactivity worths of the simulated void holes were measured in the Very High Temperature Reactor Critical Assembly (VHTRC) by the pulsed neutron method with the purpose of evaluating the neutron streaming effect on the reactivity worths of the void holes. The reactivity worths were determined using the revised King-Simmons' formula. The measured results are compared with the calculated ones based on the nuclear data of ENDF/B-IV, using the Benoist's anisotropic neutron diffusion coefficients. It is concluded that the reactivity worths are enlarged up to about twice as large as that obtained using the conventional isotropic neutron diffusion coefficients, and it is also found that the neutron streaming effect that is defined as the relative fraction components exceeding the reactivity worths obtained by the conventional isotropic neutron diffusion coefficients are likely overestimated about 11 and 32% with the void holes being in the core and reflector regions, respectively. Then, the reactivity decrease due to the neutron streaming effect is able to be evaluated around 1%Δk for the initial critical core of the HTTR.

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A study on the sodium void reactivity reduction of 1, 000MWe class fast reactors was performed. The target of this study is to materialize a core concept with a zirconium hydride layer in the internal blanket which satisfies the design criteria; that the possibility of the prompt critical by sodium voiding can be excluded at any time during reactor operation; and that the burnup reactivity is acceptably low, which is less than 2.5%dk/kk'. A series of parametric surveys were performed on the radial size of the internal blanket and the width of the zirconium hydride layer. The width of the layer was set to 3.0cm as the optimized specification which satisfies all the design criteria regardless of the fuel materials; oxide, nitride and metal.
Transient behaviors of the cores were investigated during the unprotected loss of flow accident (LOF). The analyses showed that the oxide core was able to avoid sodium boiling. It was also observed that the cores with nitride and metal fuels had larger tolerance against the unprotected LOF: The outlet temperature were lower by 39 and 60°C compared with the oxide core.

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Benchmark models of the critical experiments which measured reactivity effects of main fission product elements (Rh, Cs, Nd, Sm, Eu, and Gd) and of an important burnable poison element, erbium, were presented. These elements were dissolved in a vessel which was inserted into the central region of a fuel rod array of TCA (Tank-Type Critical Assembly). The atomic number densities of aqueous solutions in the vessel were calculated. Using these number densities, criticality calculations with MCNP 4A, TWOTRAN code, and JENDL-3.2 cross section library were performed for these experiments.

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To understand the distribution of ¹²⁹I trapped in AgS (silver-impregnated silica gel) adsorbent and to determine a calibration curve for measurement of this ¹²⁹I, cartridges containing 10 in-line (arranged in series) filter elements, each packed with a 10-mm thickness of adsorbent, were fed from 20Bq (3.3μg) to 4.6MBq (768mg) of ¹²⁹I at 150°C at a gas velocity of 22cm/s. The ¹²⁹I in each filter element was measured after the adsorbent had been mixed homogeneously until the counting rates at the front and back surfaces of the filter element became equal. The amount of input ¹²⁹I was allocated to each filter in proportion to the counting rates thus obtained.
The first 7 of the 10 filter elements completely confined 4.6MBq of ¹²⁹I. Therefore, the width of the adsorption zone was 7cm. Although each filter element in the cartridge could theoretically adsorb 2.92MBq (485mg) of ¹²⁹I, the first element captured only 1.42MBq, which was 49% of its saturation value. Its DF had dropped to a level of 2.21 for its adsorption of only 17.4% of the saturated amount. As ¹²⁹I continued to be deposited, the DF dropped to 1.45. The high gas velocity causes this phenomenon. Plots of counting rates vs. adsorption quantity provide a calibration curve covering a range of 20Bq to 2MBq of ¹²⁹I with deviation of ±13%. This curve is expressed by lny=-0.57+0.96lnx,
where y is the counting rate (counts/300s) and x the quantity of ¹²⁹I in Bq.

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The elementary chemical reactions of iodine which is a volatile fission product with steam (water) shown in the title are analyzed from the first principle. The activation energies of these reactions are calculated for the first time with a computer program Gaussian94, which is based on the non-empirical molecular orbital theory. The calculated values are expected to agree with those of experiments within an accuracy of a few kcal/mol. Using the values obtained above, the rate constants are also calculated in the framework of the transition state theory. The derived rate constants will allow us to predict the orders of magnitude of experimental values under high temperature conditions (1, 000K or higher). Thus these rate constants are available as input data for the kinetic (non-equilibrium state) study of iodine in severe light water reactor accidents.

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