The ²⁵²Cf fission spectrum averaged cross sections for twelve reactions have been measured relative to the cross section for the ²⁷Al (n, α)²⁴Na reaction. The uncertainties of the measurements are analyzed with regard to the covariances of experimental data.It is demonstrated how to generate and combine the experimental uncertainties in the form of a variance-covariance matrix. The result of the uncertainty analysis taking account of correlations between the experimental data is given. A non-diagonal weighted least square fit has been applied to normalize the measured ratios. Comparing with the standard deviation processed previously using variances only, the standard deviation obtained by the present analysis has been reduced to almost half. This may be due to the developed and improved error analysis based on the covariances between measured data. The meas-ured values of the average cross sections presented here are compared with the calculated ones based on the energy dependent cross sections.

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With a view to enhancing the thermal-neutron intensity obtained from a pulsed neutron source, an experimental study has been made to determine the optimum size of a rectan-gular shaped light water moderator provided with fast neutron reflector of beryllium oxide or graphite, and decoupled thermal-neutronically by means of Cd sheet. The optimum dimensions for the moderator are derived for the neutron emission surface and the thickness, for the cases in which the neutron-producing target is placed beneath the moderator ("wing geometry") or immediately behind the moderator ("slab geometry"). The major conclusions drawn from the experimental results are as follows. The presence of the Cd decoupler inserted between the moderator and reflector prevent the enhancement of thermal-neutron emission time gained by the provision of reflector. With a graphite reflector about 14 cm thick, (a) the optimum area of emission surface would be 25 × 25 cm² for wing geometry and still larger for slab geometry, and (b) the optimum moderator thickness would be 5.5 cm for slab geometry and 8.5 cm for wing geometry. It is thus concluded that a higher neutron emission intensity can be obtained with slab than with wing geometry provided that a large emission surface can be adopted for the moderator.

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The calculation of time-dependent stresses in concrete structures operating at elevated temperatures is discussed. The method described is of a direct formulation technique and it is based on the principles of the calculus of variation. The paper mainly deals with the application of the method to a large and infinitely redundant continuum problem. The analytical procedure of the variational principle is also described and the mathematical expressions are developed for uniaxial and biaxial stress problems. The solution for the biaxial state of stress is carried out by a two-dimensional finite element stiffness analysis.
A step-by-step method developed by the author using two-dimensional finite element stiffness analysis is also described in APPENDIX 3. Both methods are then applied to a real problem for which experimental data exist from Ref. (1). Predicted analytical values obtained by both methods are compared with experimental results. The method is suitable for predicting the distribution of stress in the end slabs of containment vessels. These slabs are perforated to permit fuel loading by the charging machine.

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Zircaloy cladding chemical reactions with coolant water and UO₂ fuel at elevated tem-peratures under a reactivity initiated accident (RIA) condition were studied from a metallurgical point of view on the basis of the Nuclear Safety Research Reactor (NSRR) experiments. The cladding-fuel chemical reaction was extensively analyzed and found to be explainable from equilibrium phase diagrams. The systematic estimation methods of maximum cladding temperature were proposed and examined from metallographies. Maxi-mum cladding temperature can be estimated from measured oxidation thicknesses in the temperature range of 1, 0001, 600°C, from melting microstructures in the range of 1, 6001, 950°C and also from the volume fraction of the precipitates, (U, Zr)O₂-x, in once-molten oxygen-stabilized α-Zircaloy in 1, 9502, 400°C. The estimation by the method proposed in the paper is more valid than thermocouple indications at high temperatures, since thermo-couples perturb the temperatures they are measuring or fail at the extremely high tem-peratures. The results are thought to be applicable also to understand general fuel rod behavior under hypothetical accident conditions which cause severe fuel damage.

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Discrete ordinate neutron transport equation is derived for two-dimensional triangular regions by applying the finite Fourier transformation. Assuming that the angular flux on each side of a triangular region is constant and the source term is constant in a triangular region, a zero-th order discrete ordinate equation is derived. It is shown that in this equation, the angular flux can be obtained always positively, as long as the source is positive.

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A rainout-washout model is proposed in order to forecast the variation of the intensity of environmental γ-rays and study the behavior of radioactive nuclei in the atmosphere on rainy days. This model divides the atmosphere into two parts of in cloud and under cloud. Simultaneous differential equations are formulated to give the time variations of the concen-trations of daughter nuclei of 222Rn during precipitation in each state of free atoms or ions, aerosol particles, cloud droplets and rain drops. Coefficients used in the equations for removal of daughter nuclei from one state to other one and for washout by rain drops are estimated from published data. Variations of various concentrations are obtained. Counting rates of a Ge (Li) detector are calculated for 352 keV (²¹⁴Pb) and 609 keV (²¹⁴Bi) γ-rays. They are mainly due to γ-rays from daughter nuclei accumulated on the earth's surface, most part of which is brought by rainout in cloud. Experimental variations of counting rates are well reproduced on rainy days. For the forecast of the variations it is necessary to measure rainfall rates, concentrations of ²²²Rn and cloud base heights at short interval.

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To overcome the impediment against practical utilization of the technically already available process of solidifying low- and intermediate-level radioactive wastes for disposal in ocean bottom, arising from the regulatory minimum density of 1.2 prescribed for such solidified wastes, a method is proposed of thickening the polyethylene with 3638 w/0 sodium sulfate anhydride to raise the density above 1.2. The resulting thickened polyethy-lene loaded with simulated radioactive waste showed a monoaxial compressive strength far exceeding 150 kg/cm², and proved to possess good stability in deionized water in immersion tests lasting 400 days. Polyethylene was also found to provide a volume reduction factor far higher than obtained with cement or asphalt solidification.

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Coherence function is one very important tool of noise analysis and in practice has been widely utilized since long for various studies associated with reactor noise. Re-cently a spectral decomposition technique, the so-called noise power contribution (NPC) analysis⁽¹⁾ based on time series modeling has come into use in the reactor noise field. One of the present authors first made clear the-oretically the relation between the ordinary coherence (OCH) and the NPC functions⁽²⁾. He also proposed a method of noise analysis called "OCH-NPC comparison approach" which evaluates system dynamics by com-parison of the OCH and the NPC functions⁽³⁾. The method has proved to have potentials of clarifying the cause-consequence relation-ship between measured variables, detecting feedback and of extracting the property of a feedback effect if it exists.
In this note, an attempt is made to add further insight into the physical meaning of the OCH-NPC comparison approach by in-terpreting the relation between the OCH and the NPC functions in terms of a vector (phasor) representation on a complex plane. Through the mathematical development, it will be shown that the OCH corresponds to the squared magnitude of a vector represented by the sum of two vectors with magnitudes determined by the NPC ratios. This geomet-rical interpretation will be useful for making clear the significance of the OCH-NPC com-parison approach as a method to evaluate system dynamics.

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In our previous study⁽¹⁾⁽²⁾ the ¹⁰B(n, α)7Li reaction proved to induce an oligomer in the aqueous cyanide solution. The oligomer pro-duces some amino acids in high yield by acid hydrolysis.
The present note covers a similar study on the irradiation of aqueous solutions of thiocyanate, with the intention of knowing whether the presence of SCN- may result in the formation of some S-containing amino acids. The result showed the generation of H₂, SO₂ and an oligomer producing certain amino acids by acid hydrolysis. But no S-containing amino acid was produced.

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