In order to improve the measuring accuracy of plugging indicators, the effects of operating conditions such as the sodium flow rate and the cooling air flow rate on the measuring error are analyzed.
By this investigation, the measuring error can be evaluated as a function of the Reynolds and Stanton numbers, and suitable conditions which minimize the measuring error are obtained.

View full abstract

Estimation of the spatial distributions of prompt neutrons and delayed neutron precursors has been studied by analyzing the output signals of in-core neutron detectors. In this paper, application of distributed Kalman filter is attempted for a one-dimensional core model having statistical fluctuations. Assuming that their statistics are determined by Schottky formula, the error covariance matrix of estimation is computed in order to evaluate the filter performance. In the computation of this matrix, the algebraic Riccati equation is solved by generalized Newton-Raphson method.
From the viewpoint of estimation accuracy, it is also an important problem to optimize the detector locations. Considering the cases where estimation is focussed on a specified quantity related to prompt and delayed neutrons, the optimum allocations of two detectors are searched numerically. It is inferred that the optimized allocation has a considerable effect on estimating the shapes of the distributions where higher terms of spatial harmonics cannot be neglected.

View full abstract

Measurements of tritium concentration in various media have been successfully performed by detecting with an ordinary NaI(T1) scintillation counter the bremsstrahlung emitted from tritium decay. To distinguish meaningful signals from noises emanating mainly from thermoelectrons present in the phototube, differences in rise time were discriminated by means of an electronic circuit, instead of separation by pulse height analysis. This pulse-shape discriminator successfully reduced noise counts below 18 keV in a multichannel analyzer from 100 cpm to 4 cpm, which permitted direct counting of tritiated water as dilute as 1 μCi/ml, without requiring any complicated preparation.

View full abstract

A method is proposed for conducting power reactor noise analysis without recourse to an actual high power reactor. The basic concept is to simulate the power reactor noise by integrating the different elements constituting the actual reactor noise, such as the random noise-generating force, the zero-power reactor transfer function, and feed-back loops between the reactor power and the noise-generating force.
For the simulation study, a nucleate boiling noise generator and a single feed-back loop were divised to permit experiments with flux-related heater input using the fast neutron source reactor YAYOI of the University of Tokyo.
This report discusses problems encountered in applying the proposed method to the simulation of power reactor noise, and presents some of the results obtained : Two kinds of change in amplitude were observed in the normalized auto power spectral density of the neutron flux, emanating form : (a) fluctuating displacements of the boiling zone bottom boundary, and (b) fluctuating number of passing vapor voids.
Significant differences in the resulting data were observed between the runs performed with constant and with flux-related heater input in the case of step response experiment, but not in steady noise analyses. This apparent ineffectiveness of the feed-back system is due to the relatively small value of the product of the reactivity power coefficient and the reactor power (5×10^-2%Δk/k) in the present feed-back experiment.

View full abstract

The potential energy curves of LiHe⁺, BeHHe⁺ and FHe⁺ in the ground state are calculated with a scale factor optimized STO-6G basis set, and these potential curves are compared with those of HHe⁺, CH₃He⁺, NH₂He⁺ and OHHe⁺ already reported. In the T→He⁺ β^--decay, ground state daughter ions HHe⁺, LiHe⁺ and BeHHe⁺ are found to be bound, whereas CH₃He⁺, NH₂He⁺, OHHe⁺ and FHe⁺ ions dissociate into a He atom and residual fragments.

View full abstract

In a high voltage electron microscope, solution treated Type 316 stainless steel was electron-irradiated at temperatures in the range of 370630°C to a dose of about 30 dpa. The swelling (ΔV/V) induced by the irradiation beyond about 5 dpa is well described by an empirical equation, ΔV/V=A(dpa) ⁿ , under constant void and dislocation densities. With increasing irradiation temperature, the fluence exponent n increases and the pre-exponent term A decreases. At 550°C irradiation, the fluence exponent takes the value of 1.5 due to the diffusion-limited void growth. The value of n larger than 1.5 at higher temperature (>550°C) is attributable to the surface reaction-limited void growth. The smaller value of n for the low temperature ( ?? 500°C) irradiation appears to arise from the dislocation assisted vacancy diffusion. The peak swelling temperature of the specimen irradiated to 30 dpa is about 570°C, which shifts to a higher temperature with increase in electron dose.

View full abstract

Chlorinated benzenes dissolved in deoxygenated alkaline 2-propanol were dechlorinated by irradiating with ⁶⁰Co γ-rays to produce the lower chlorinated benzenes and chloride ion. The yield of dechlorination was found to depend on the number of chlorine atoms on the benzene ring, the G(Cl^-)-values being, for instance, 6, 500, 480 and 2.0 for 0.07 M penta-chlorobenzene, 1, 2, 4-trichlorobenzene, and monochlorobenzene, respectively, in 0.2 M KOH-2-propanol solution. In contrast, the values of G(Cl^-) differed little between the isomers of trichlorobenzene. The large difference in G(Cl^-) according to the number of chlorine atoms can be explained by considering the redox potential of the chlorinated benzenes and the ketyl radical ion.
Trichlorobenzene is dechlorinated to dichlorobenzene and then to monochlorobenzene while producing potassium chloride and acetone, and consuming hydroxide ion. In the experiment, some chlorinated benzene derivatives were observed to be generated in the course of this process--probably dichlorophenyl-2-propanol and monochlorophenyl-2-pro-panol, judging from observation by gaschromatograph-mass spectrometer and from the path-way of formation. The observation also indicated the presence of dichloropheny1-2-propanol in predominant amounts in 1, 3, 5-trichlorobenzene solution, but only in a small fraction in 1, 2, 3-trichlorobenzene.

View full abstract

The problem to optimize the number and locations of environmental radiation monitoring detectors is formulated by taking the specifically defined distance measures as a performance index and solved numerically using heuristic programming such as branch and bound method. An ideal numerical example neglecting noises due to background radiation and so on shows that the desirable number and locations of detectors are determined mainly by the atmospheric conditions and do not so influenced by the variation of the rate and pattern of activity release from the nuclear facility. It is shown also that the appropriate and sufficient number of monitoring detectors to be located around the facility will be from three to six at most, if considered from the viewpoint of pattern recognition.

View full abstract

Precise measurements of burnup and accumulated transuranium elements were carried out on specimens which were taken out from spent fuel of Japan Power Demonstration Reactor (JPDR)-I, by means of chemical analysis and T-ray spectrometry. Results of the measurements are summarized numerically. Core configuration and operational history of the reactor are also described.

View full abstract