It has been made clear that the reactivity worth of the central cell may be considered equal to the worth of the leakage neutrons from the cell. Thus, the value may be used to evaluate the results of neutron leakage calculations.
A method is proposed for the experimental determination of k_m⁺, a characteristic value of the reactor cell composition, by making use of the reactivity worth of the cell measured at the core center. The quantity k_m⁺ is a kind of infinite multiplication factor defined in the fundamental mode spectra. Since accurate methods based on the fine group treatment are available for calculating k_m⁺, its measurement is valuable for evaluating the cross section library used for reactor calculations.
As an example, the value of k_m⁺ has been obtained for the FCA Assembly V-2, and the resulting experimental and calculated values are examined.

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Several Te compounds including a new Te oxide Te₅O₁₁ were subjected to dry-distillation after reactor irradiation in order to overcome the difficulties accompanying the ordinary dry-distillation from TeO₂. The release of ¹³¹I from Te₅O₁₁ was examined as function of distillation temperature and the thermal behavior of ¹³¹I released was studied by means of thermochromatography. For comparison, the ¹³¹I release from other Te compounds such as H₆TeO₆, (H₂TeO₄)_n, and TeO₃ was also studied.
The compounds studied in this work were found to release ¹³¹I rapidly at temperatures lower than employed in the ordinary dry-distillation of ¹³¹I from TeO₂, thus obviating all risk of contaminating the final products with Te vaporizing at higher temperatures. The rapid release of ¹³¹I was concluded to be caused by thermal decomposition of the compounds studied. In an attempt to prepare a "dry source" of ¹³¹I, ¹³¹I dry-distilled from Te₅O₁₁ was adsorbed on Molecular Sieve, and the release of ¹³¹I from the Molecular Sieve was similarly studied.

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The dry procedure was applied to the separation of ¹⁴C from either finely powdered AlN or AlN in tablet form after neutron irradiation. The mechanism of the ¹⁴C release from the irradiated materials was studied, and the possibility of using AlN target in tablet form for routine production of ¹⁴C was examined.
Powdery AlN, sintered powder tablet, molded powder tablet, and sintered mold tablet were irradiated for 12 days in the JRR-2 reactor. After irradiation, ¹⁴C was separated in the form either of as dioxide or of monoxide, from the irradiated material at various temperatures under oxygen stream, and the rate of combustion of AlN and that of the ¹⁴C release were determined as a function of temperature and reaction time. The release of ¹⁴C from neutron irradiated AlN was found to accompany the oxidation of AlN which took place in the form of tarnishing reaction. Above 1, 090°C, the release of ¹⁴C obeyed the logarithmic rule, indicating that it is governed by the migration of ¹⁴C in the oxide layer. The chemical yield of ¹⁴C was almost 100%, when powdery AlN was heated for 5hr at 1, 180°C. The yield deteriorated in the sequence of sintered powder-molded powder-sintered mold tablet, the last mentioned form producing a yield of only 50% yield under the same conditions.

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Uranium oxysulfide was prepared from 1-pentanol extract of uranium (VI) thiocyanate by vacuum distillation and calcination of the distillation residue. Thorium disulfide was similarly prepared from thorium thiocyanate complex in aqueous phase.

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Rapid separation using NTA in paper electromigration was applied to the study of the γ-decay of ¹⁴⁸Pr and ¹⁴⁹Pr produced in the fission of ²³⁸U. The γ-ray spectrum was measured with a high-resolution Ge(Li) detector. The γ-transitions found to decay with half-lives shorter than 3min were: 135, 162, 256, 300, 511, 614, 696, 868, 1, 022 and 1, 248keV. Of these, the values of 300keV, and of 135 and 162keV were in fair agreement with those reported for ¹⁴⁸Pr and ¹⁴⁹Pr. The decay plot of the strong photopeak of 300keV presented good linearity and the accurate half-life of ¹⁴⁸Pr could be determined as 2.30±0.03min, which is longer than the 1.98min reported for ¹⁴⁸Pr. Similar decay plots of both photopeaks at 135 and 162keV gave a half-life of 2.9±0.1min for ¹⁴⁹Pr, which again is longer than the reported value of 2.3min. Other low intensity photopeaks at 256, 696, 868 and 1, 022keV decaying with half-lives of 2.1∼2.4min can possibly be attributed to ¹⁴⁸Pr. The γ-transitions of 110, 578 and 742keV reported for ¹⁴⁹Pr could not be observed in this experiment.

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Reactivity and compatibility studies were carried out on some vanadium base alloys with ceramic fuel materials. The vanadium base alloys studied were V-20%Ti, V-15%Ti-7.5%Cr and V-5%Cr. The fuel materials with which these alloys were put in contact were UC, UN, (U, Ce)N and (U, Ce)(C, N). Experiments were carried out at 700° and 900°C for both 500 and 1, 000hr. Within the conditions studied, V-5%Cr showed good compatibility with all of these fuel materials, At 700°C, no detectable interaction was observed between any of the alloy-fuel combinations.

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The γ-radiolysis of water has been studied using a water-loop specially designed for this purpose. The water was circulated without contact with air during the irradiation. The apparent G(H₂) value was found to be roughly 10^-3. However a corresponding amount of O₂, was not found, due to its consumption by corroding reactions of the constituent materials under radiation field. In the presence of O₂, and H₂O₂, the H₂-yield curves vs. the irradiation dose were revealed a very distinctive characteristic: following a rapid increase with initial irradiation a plateau range has appeared. The H₂-yield at this plateau range depended on the initial concentration of additives. Continued irradiation, however, caused a gradual further rise in the H₂-yield above the plateau value at a rate corresponding to that found in the pure water system. These yield curves are discussed on the basis of the free radical model for the radiolysis of water.

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For the purpose of analyzing UF₆ and F₂ continuously in the fluorination of U, a system of differential thermal conductivity cells (TCC), equipped with shock absorber, and also NaF and KCl traps, has been trially constructed.
Mixed flow-through/diffusion type katharometers are used, provided with four and two Ni filaments (∼30Ω) on the UF₆ and F₂ cells, respectively. Based on data obtained from preliminary operating tests, the standard conditions for operating the system were established i. e., 500mmHg abs. Cell pressure, 200ml/min flow rate and 80mA bridge current.
Under these operating conditions and for UF₆ and F₂ concentrations of 2 and 20v/0 respectively, the overall out-put variations are below 1%. The total response time of the system including the transport lag is below 1 and 2.5min for UF₆ and F₂ cells, respectively. The dead time due to blow-back noise is observed to have about the same period as the above response time. The sensitivities for UF₆ and F₂ are found respectively to be 11.5 and 0.37mV/v/0, for which the limits of analytical determination are 0.01 and 0.05v/0, respectively.
By practical application to uranium fluorination, the TCC system thus devised, has proven to possess the requisite characteristics for measurements of reaction rate, fluorine utilization and end of reaction in fluid-bed fluorination of uranium oxides.
The system has possibilities of application to the study of reaction steps.

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