Haruo Natsume

Reaction of lithium and sodium nitrates and carbonates with uranium oxides

Abstract The reactivity and reaction conditions to form lithium and sodium uranates were studied in an attempt to grope some useful head-end processes in nuclear fuel reprocessing. In the reactions between alkali metal carbonates and U 3 O 8 in air at 800°C, the products with Na/U ratios 0.8 and 0.857 gave the same X-ray diffraction patterns in which the peaks of α-U 3 O 8 were almost not detected. The observed peaks for uranates with Li/U = 1.205, 2, 4 and Na/U = 1 are well consistent with the values reported previously. No indication of formation of Li 2 U 6 O 19 , Li 6 UO 6 and Na 4 UO 5 was observed. Thermogravimetric observations on the reactions between the carbonates and U 3 O 8 revealed that they consisted of two processes, i.e. (1) the formation of uranates and (2) the oxidation of the uranates formed. The rate of reaction (1) was higher than that of reaction (2) when the M/U ( M = Li, Na ) ratio was 0.5. When the ratio was 1, the rate of reaction (1) lowered and became rate determining. The reactions between alkali metal nitrates and UO 2 showed that the minimum M/U ratios for obtaining the uranates without U 3 O 8 were 0.667 and 0.8 for lithium and sodium uranates, respectively. They were formed by heating at 600°C for 3 h in oxygen or air. Mixing process of initial materials is not required for these reactions. The uranates formed were found to be dissolved in 1 M HNO 3 within 1 min.

Non-Destructive Gamma-Ray Spectrometry on Spent Fuels of a Boiling Water Reactor

The spent fuels from the JPDR-I reactor were measured by means of a γ-scanning facility installed in the fuel storage pool. The spatial distributions of the fission products (134Cs and 137Cs) were measured and analyzed in reference to the effects of control rod pattern. The ratios holding between the products of neutron capture and of direct fission (134Cs/137Cs and 154Eu/137Cs) were also examined for its relevance to non-destructive burnup determination. The activity ratios of the fission products can be expressed by a linear function of burnup, provided that corrections are made to account for differences in irradiation history and for spatial variations in the neutron spectrum.

Fast Computer Analysis of the γ Spectrum from Ge(Li) Detectors

A method for rapidly analyzing the γ spectrum obtained with Ge(Li) detectors was developed for a medium-size electronic computer. The analysis is based on the first derivative method, associated with a number of peak-shape tests. The effects of data smoothing and of changes in peak width were studied to determine the optimum conditions for spectrum analysis. The resulting computer program was subjected to various quality tests on the predicted values of the peak position and area. The results of the tests showed that the code thus developed works quite satisfactorily. The code requires 10 sec and a memory core of 29 k when using a FACOM 230–60 for the analysis of a 2,047 channel spectrum.

Systematic radiochemical analysis of fission products

A scheme for the sequential separation of fission products has been developed on the basis of ion-exchange techniques. It consists of a main cation-exchange process for group separation and subsidiary processes of cation or anion exchange for further separations or purifications of the individual fission products. By the present method, Zn, Rb, Sr, Y, (Zr), Mo, Pd, Cd, Te, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu and Tb can be separated simultaneously from an irradiated uranium sample. Of these, alkali, alkaline earth and rare earth metal ions are separated quantitatively. A polarographic method was applied to determine the recoveries of Zn, Mo, Pd, Cd and Te, which were not separated quantitatively.

Radiochemical Determination of Fission Rate in JRR-4

The fission rate in the core of the Japan Research Reactor 4 (JRR-4) was determined by a method based on radiochemical analysis of 99Mo formed in the U samples irradiated in the reactor core. The contribution of epithermal neutron fission to the total fission rate was evaluated from the Cd ratio for U fission. The contribution was several percent. For comparison, the thermal neutron flux also was measured, by Au-foil activation. The fission rate determined from the U samples agreed well with the Au-foil data, except at positions in the peripheral region of the reactor core.