This review summarizes the published theoretical and experimental studies of CsI radiolysis in an operating fuel pin. The calculation method, which has been developed based on gas kinetic theory, is effective for the evaluation of the radiation effect on iodine pressure. The iodine partial pressures, which were calculated by the above method, are high enough to cause FCCI in FBR fuel pins and SCC in LWR fuel rods.
The literature data of experiments exhibit that the iodine is liberated through γ-radiolysis of solid CsI, and the Csl vapor irradiated by electron beam also produced high iodine pressures. It has been also confirmed that the radiation effect in gas phase is still significant even in the case of existence of Cs pressure, which causes decrease of the iodine pressure by recombination.
This review concludes that the radiation effect is important for understanding the chemical behavior of iodine in operating fuel pins.

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Uncertainties of decay heat summation calculations are derived for the thermal fission of ²³⁵U and ²³⁹Pu and the fast fission of ²³⁸U through sensitivity analyses using data given in the JNDC FP nuclear data library. The uncertainties analyzed are those relevant to decay energies, fission yields and decay constants among the nuclear data contained in the summation calculation. For nuclides lacking complete experimental data, the uncertainties of the decay energies are theoretically calculated. Thus analyzed, the maximum uncertainties of burst fission are 2.8% for ²³⁵U, 3.2% for ²³⁹Pu and 4.2 % for ²³⁸U in the range of cooling time between 1 and 10⁹s, and in the case of infinite irradiation, the corresponding level of maximum uncertainty is below 1.6% for all three fissioning nuclides.

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Liquid metal fast breeder reactor (LMFBR) plants are necessary to have system components with thin wall structures that are much different from those of LWR plants, and so some reactivity vibrations are induced by seismic vertical movements between the core and the control rod system. Dynamic response analyses during these vibratory transients were performed and the maximum allowable displacements of the core relative to the control rod system were evaluated with a view to avoid fuel failures.
Two two-region homogeneous and axially heterogeneous oxide cores, and a two-region homogeneous metal core were taken as the reference large FBR cores. The amplitude and the frequency of control rod vibrations, three kinds of reactivity coefficients and scram conditions were selected as main parameters for sensitivity analyses, and integrity limits of fuel assemblies were evaluated and the results of reactivity amplitude were converted into vertical displacements to have the target requirements for the aseismic design. The allowable maximum reactivity amplitudes were 1.19, 1.15 and 0.89 $, and the corresponding allowable relative displacements between the core and the control rod system were 44, 52 and 42 mm, respectively for the above-mentioned three cores in the severest condition. Effects of seismic vibration characteristic, control rod scram time and other affecting factors were discussed based on the final results.

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The aims of the study are to correlate instability data in ATR (Advanced Thermal Reactor) channels using dimensionless parameters, and validate the ATRECS- II code. Various kinds of experiments were conducted with the 14 MW Heat Transfer Loop (HTL) and the 6 MW ATR Safety Experimental Loop (SEL). Experimental ranges of parameters are listed below :
- Natural circulation or forced circulation with channel flow rate of 0.53.6 kg/s
- Pressure ranging 0.27 MPa
- Subcooling ranging 570°C
- Outlet pipe of 9 m in length and 5 in. in diameter, or 25.5 m in length and 3 in. in diameter
- Axial power distributions of 3.7 m heaters are uniform, inlet peak and so on.
For relatively high exit steam quality conditions (Type- II ), instability boundaries are obtained as a function of exit quality and Reynolds number at the core inlet by processing various data, and cladding dryout occurs in conjunction with the Type-II instability. There is another type of instability (Type-I) at the nearly zero exit quality region. In this case, dryout of cladding does not occur in conjunction with the flow oscillation. Period of oscillation was processed to a dimensionless parameter, and correlated with dimensionless inlet subcooling. The behaviors of Type-I and Type-II oscillations and boundaries of instability onset were predicted by the ATRECS- II code.

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The reaction rates between iron and tellurium were measured in the temperature range of 8731, 023 K at the tellurium vapor pressure of 350 Pa and in the tellurium vapor pressure range of 66.71, 000 Pa at 923 K. The electron probe micro-analyzer, marker experiment and X-ray diffractometer were used to clarify the mechanism of the telluride scale growth.
The reaction rate between iron and tellurium obeyed the parabolic rate law and the platinum marker was observed at the phase boundary between iron and telluride scale. The telluride scale consisted of an inner and an outer layers : the former was β-iron telluride grown in parallel with a- and b-axes, and the latter consisted of 8-iron telluride above 980 K and δ- and δ'-iron tellurides below 980 K.
By comparing the activation energy for the reaction between iron and tellurium at constant tellurium vapor pressure with those for the diffusion of iron in β-, δ- and δ'-iron tellurides at constant composition, it was found that the rate-determining step of the reaction between iron and tellurium below 980 K was the diffusion of iron in δ'-iron telluride, but that above 980 K could not be determined.
The reaction rate constant at 923 K and the tellurium vapor pressure of 350 Pa obtained in this study was in fairly good agreement with that calculated by Wagner's and Yurek's theories using diffusion coefficient of iron in iron telluride measured by the present authors.

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Breakthrough properties of Cs were examined at 298 K using columns packed with K⁺ forms of ferrierites. Breakthrough curves showed symmetrical S-shaped profiles at lower space velocity (SV) below 50/h. The adsorption zone of Cs increased linearly with flow rate and exceeded the length of packed column over 50/h. The S-shaped curves were obtained at lower HNO₃ concentrations below 1 mol/dm³, whereas Cs readily flowed out through the column in the presence of 5 mol/dm3 HNO₃. The break point was shifted to lower bed volumes with increasing concentration of coexisting cations ; the amounts of Cs adsorbed were lowered in the presence of competing cations in the order, Na⁺>K⁺>Rb⁺. Cesium adsorbed on ferrierites could be quantitatively eluted with 1 mol/dm³ KNO₃ as an eluent. The selective removal of Cs was achieved by passing the simulated radioactive liquid wastes through the ferrierite columns.

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Density of 30v/0 tri-n-butyl phosphate-n-dodecane solution loaded with uranyl nitrate, nitric acid and water was measured. An empirical density equation was derived from regression analysis of the density data. The equation represents the density values well in a wide range of composition and temperature.

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