The cross sections for the reactions ⁹⁰Zr(n, n')^90mZr, ⁹¹Zr(n, 2n)^90mZr, ²⁰⁷Pb (n, n')^207mPb and ²⁰⁸Pb(n, 2n)^207mPb for neutron energy of 14.8 MeV have been measured by means of the activation method. The cross sections were determined with reference to the known ²⁷Al(n, α)²⁴Na reaction cross section. Isotropically enriched isotopes ⁹⁰Zr, ⁹¹Zr, ²⁰⁷Pb and ²⁰⁸Pb were used as target materials. The irradiations and the activity measurements were re-peated 100 times using a fast pneumatic transport system. The following cross sections were obtained :
410 ±40 mb for ⁹⁰Zr(n, n')^90mZr, 775± 65 mb for ⁹¹Zr(n, 2n)^90mZr
160 ± 23 mb for ²⁰⁷Pb(n, n')^207mPb, 1, 220 ± 100 mb for ²⁰⁸Pb(n, 2n)^207mTb.
From the results of the present work, the effective formation cross sections of 90mZr and 207mPb for natural Zr and Pb have also been estimated as 475±40 mb and 900± 80 mb, respectively.

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The steam generator for LMFBR is composed of multiple tubes with the different flow conditions from each other. Most of the computer codes developed to evaluate the stability analyze a representative tube on the basis of the assumption of the constant pressure drop between the feedwater header and the steam one as single channel. Although the method selecting the representative channel has never been investigated, it is one of the purposes of this paper to examine the approximate method to evaluate the stable boundary exactly.
It is another purpose of this paper to research the mechanism of the limit cycle oscilla-tion observed in 1 MW SG without the thermal insulated downcomer of Power Reactor and Nuclear Fuel Development Corp., so that the effect of boiling in downcomer on the flow in-stability is studied experimentally. The slug excursion instability, which does not belong to Boure's classification of two-phase flow instability, is observed in our experimental ap-paratus. Then, this mechanism is studied under the various conditions of heat fluxes of downcomer and riser, liquid temperature and inlet velocity.

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The NH3 consumption by electron beam irradiation has been studied in the moist NO-SO₃-O₂-N₂ mixtures containing NH₃. The [NH₃] decreased linearly with increasing dose at various NH₃ initial concentrations. The G (-NH₃) increased with NH₃ concentration up to about 500 ppm and was held almost constant (G(-NH₃) =5.8 at 750 ppm NH₃) above it. The rate of the NH₃, consumption was about 175 ppm/Mrad above 500 ppm NH₃, The G(-NH₃) increased with H₂O and SO₂ concentrations. On the contrary, the G(-NH₃) decreased with increasing NO concentration and was hardly affected by the presence of 319.5%0₂. The G (-NH₃) became larger with decreasing temperature in the range of 80150°C. An ap-parent activation energy of the NH₃ consumption was -3.82 kcal/mol. The NH₃ is mainly consumed by the reactions of NH₃ with HNO₃ and H₂SO₄, leading to the formations of NH₄NO₃ and (NH₄)₂SO₄ respectively.

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A new crystalline uranium (IV) sulfate has been prepared. Its magnetic susceptibility was measured from room temperature to 1.8 K and revealed broad maximum at 21.5 K. This anomaly was attempted to analyze by one-dimensional magnetic chain model with isotropic exchange interaction.

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Oxygen-free aqueous solutions of 0.01 mol/l ammonium cyanide were exposed to radiations emitted from the inner source of ¹⁰B(n, , α)⁷Li reaction. Measurements were made of the radiochemical yields for the decomposition of cyanide, and for the formation of several amino acids (mainly glycine) generated by acid hydrolysis of the irradiated solutions.
The G-value of cyanide decomposition was reasonably close to twice the sum of the G-values for radiochemical production of the individual amino acids.
The irradiation products were aminonitrile oligomers. The probable mechanism of reac-tion was formation of aminonitrile oligomer by the chain reaction of cyanide with -OH, -H and e^-_aq species resulting from the radiolysis of water.

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A method was established for determining simultaneously ⁵¹Cr, ⁵⁴Mn, ⁵⁹Fe, ⁵⁸Co, ⁶⁰Co, ⁶⁵Zn, ⁹⁵Zr, ⁹⁵Nb and ¹⁴⁰La present in seawater in concentrations corresponding to 5 mrem/yr for whole-body dose, the level set as guideline by the Japan AEC for light-water-cooled power reactor.
Prior to concentration of the sample by precipitation of hydroxides at pH 10.5, chromate ion was reduced to trivalent form by treatment with sulfurous acid and 1 v/o of hydrochloric acid. After the concentration, the sample was found to retain 85% of Zr and Nb, and 95% of the other elements of interest in the original sample. The determination of ⁵⁹Fe, ⁶⁵Zn and ⁹⁵Zr called for removal of Mg, which was obtained by re-precipitation of the nuclides at pH 7.5.
The method thus established by the basic study was applied to trial treatment of 400l of natural seawater, which yielded percentage of recovery practically equal to those obtained in the basic study for Cr, Mn and Co. The proposed method proved to permit determi-nation of concentrations below those specified previously by the authors as needed for effec-tive assessment of the environment to accord with the AEC guideline. The time required for the chemical procedures and the r-spectrometry to determine the nine radionuclides in 400l of natural seawater is about 34 h. The proposed method is practical in terms also of the time required for the determination.

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A description is presented of an experiment performed in the experimental facility of JRR-4 research reactor to obtain useful data for the assessment of shielding calculations for the problem of annular duct of large radius. Distributions of reaction rate and spectrum of neutrons are measured in the annular ducts of 10 and 20 cm gap widths. The reaction rates are obtained for twenty-five kinds of activation detectors within an accuracy of 28520. The neutron spectra are obtained in the energy range from the thermal to the fast by the activation method with the aid of SAND-11 code and by the counter measurement with the aid of SPEC-4 code. Through the check calculations on the SAND-IL unfolding, it is con-cluded that the spectra obtained by the activation method are reliable except in the energy range of 10 keV-1 MeV where those obtained by the counter measurement are supplied. The comparison of the measurement and the P₃-S₈ calculation by DOT-III transport code indicates a fairly good agreement of a factor 2 for the gap width of 20 cm, however, large underestimation of maximum factor 8 is found in the calculation for the gap width of 10 cm.

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