The distribution ratios of certain inorganic ions were radiochemically determined in systems of ion exchange resin of porous type vs. 0.1∼1.0M hydrochloric acid or water. The resins used were the cation exchange resins Diaion PK-216 and Amberlite IR-200 (H form), and the anion exchange resins Diaion PA-316 and Amberlite IRA-900 (Cl form). The results concurred with those obtained with ion exchange resins of gel-type (Diaion SKN-1 and SAN-1).
The ion exchange behavior of ¹³⁷Cs was examined by means of an ion exchange resin column. The resin bed consisted of a 2:1 mixture of Diaion PK-216 and PA-316. The decontamination factors were determined at a flow rate of 120 and 180 (hr^-1) in space velocity. The values were higher than those obtained with a mixture of ion exchange resin of gel-type (Diaion SKN-1 and SAN-1).

View full abstract

Corrosion and mass transfer behaviors of austenitic stainless steels in a natural circulation sodium loop have been studied over a temperature range from 630° to 230°C for a period of 2, 000hr with the aid of tracer techniques.
The changes with running time were observed in the metal concentrations in sodium by sampling and analyzing the sodium in the loop. The distributions of the corroded metals over various cross sections along the cooling tube were determined by analyses performed on samples of sodium, which had been obtained by quick solidification of the flowing sodium and dessection of the solidified sample. The distribution of radioisotopes, which had been leached into the sodium from irradiated stainless steel foils located in the hot sodium stream, were also measured.
The changes of leaching rate with running time differed between those of the radioactive and the stable metals. Iron and cobalt deposit on the substrate material presumably by atomic diffusion across the sodium stream and by particle formation in the sodium stream prior to accumulation. Chromium, on the other hand, deposits on the substrate material presumably by formation of chemical compounds in the sodium stream prior to accumulation. The mechanisms of deposition of nickel and manganese could not be made clear.

View full abstract

Hydride directionality in zircaloy is reportedly affected by thermal cycling and stress. Experiments were performed to study these effects quantitatively. The first experiment was thermal cycling applied repeatedly on rolled zircaloy-2 plate under tensile load. It was observed that at the first cycle the hydride directionality changed by an amount depending on the stress level, and thereafter, upon repetition of the thermal cycling, the rate of change was slow and steady, and independent of the level of applied stress.
In arranging the data, a new concept, which was termed the "average precipitation angle", is proposed to express hydride directionality, in which account is taken of the length and the angle of precipitation of the hydride platelets. This concept should at times be more suitable than the currently adopted directionality factor Fⁿ for methodically expressing hydride directionality. Based on the results of this experiment, the average precipitation angle in zircaloy-2 cladding in reactors can be estimated with the empirical formula
A_r=A₀+ασ_t+β(C-1),
where A₀ and A_r: average precipitation angles before and after reactor service, σ_t: tangential stress, C: number of thermal cycles, α and β: constants.
Another experiment was carried out to determine the constant α for zircaloy-2 tubing serving in water cooled reactors. This experiment was on thermal diffusion under internal pressure and thermal conditions simulating those of zircaloy-2 fuel cladding in water cooled reactors.
When the specimens were prepared for the foregoing experiments by hydriding, the hydride platelets did not distribute uniformly across the wall thickness. It was clarified by a third experiment that the hydride precipitated preferentially in the zones subjected to large residual tensile stress.

View full abstract

In an earlier paper, a stochastic model of a power reactor has been proposed by the present author on the premise that the coolant-flow through a core is usually accompanied by random variations in the flow-rate, which are eventually largely responsible for the internal reactivity fluctuations.
In the present work, this model is extended to three different reactor systems: (a) where there exists a relaxation process corresponding to the effect of buoyant flow; (b) where a control or fuel element vibrates randomly, due to coolant flow-rate fluctuations; (c) where there are fluctuations in the inlet temperature with a non-white spectrum.
The noise spectra are derived for various state quantities with use made of the Langevin procedure. The theory is illustrated by referring chiefly to the neutron noise spectra, and comparing with the results of observations.
It is shown that the noise sources in question contribute significantly to the spectra, as compared with a low frequency component due to an inherent noise source in the coolant flow. In particular, a strong resonance peak of the spectra arises from the coupling between the random mechanical vibrations and coolant the flow-rate fluctuations.

View full abstract

The amounts of ²⁴¹Am, ²⁴²Cm and ²⁴⁴Cm were determined by means of a radiochemical technique in several specimens taken from the spent fuel of the JPDR-I. The yields of the transplutonium nuclides were examined in connection with the burnup determined by a conventional method. It was found that the burnup correlates well with the yield ratios of various transplutonium nuclides.

View full abstract

The self-diffusion of C in non-stoichiometric UC has been measured, using radioactive tracer and sectioning technique. The diffusion equations finally derived as function of temperature are:
(1) For UC_0H85 D=1.7×10^-2exp(-57.4±1.8/RTkcal/mol)cm²/sec over the temperature range of 1, 270°∼1, 600°C,
D=3.28exp(-77.2±2.2/RTkcal/mol)cm²/sec over the temperature range of 1, 600°∼2, 000°C;
(2) For UC_1.11 D=9.5×10^-2exp(-54.2±2.6/RTkcal/mol)cm²/sec over the temperature range of 1, 640°∼2, 070°C.
The activation energy for migration of C in UC is considered to be about 54kcal/mol. From the dependence of the diffusion coefficient and the activation energy on C content in UC, it was seen that interstitial C atoms significantly influence the C diffusion in UC, and from this the C diffusion mechanism is judged to be either an interstitial or else an interstitialcy mechanism.

View full abstract

It was established that the dynamics of an evaporator show markedly asymmetric responses. These phenomena are closely related to the response of the liquid level which directly affects the heat capacity.
What is more, the time constants of an evaporator are so large that the transfer functions expressing uranium product evaporator are better approximated by a form representing no self-regulation. Examination of the controllability aspects of three different control algorithms, i. e. control by boiling point raising, cascade control and multivariable control, resulted in the conclusion that the last-mentioned algorithm is superior to the two others for controlling the uranium concentration which is the most important element in uranium product evaporation.

View full abstract

A high flux fast neutron was produced by the (d, n) reaction of a lithium metal target. A thick lithium layer for the target was prepared by a simple method of melt-coating on a copper plate. The fast neutron (>9MeV) flux at a distance of 6mm from the target was (9.0±1.6)×10⁶n/cm²sec•μA with use of a 2.0MeV deuteron beam. A flux of 2.7×10⁹n/cm²•sec was obtained by bombarding the target with the deuteron beam of 300μA.

View full abstract