Measurement of the subcriticality of power-stressed reactors with an analog reactimeter

Conclusions A technique has been developed for measuring the effects of reactivity in a subcritical reactor with an analog reactimeter. It is based on the compensation of the current applied to the reactimeter input from the neutron detector. The compensation of current produced by neutrons of the subcritical multiplying assembly formalizes the algorithm for reactivity calculation, making it an adequate model of a reactor with a source and making it possible to determine the subcriticality without prior entry into the critical state. In this case the measurements are made in the presence of neutron sources characteristic of power-stressed reactors. The regular devices of the control and safety system could be used to produce unsteady variation of the neutron flux.All of this permits the proposed method to be extended to zero-power reactors and to power-stressed reactors. Once the subcriticality has been measured an analog of the neutron source is introduced into the reactimeter. This instrument measures the effects of reactivity in the subcritical state without the reactor being previously put into the critical state, monitors the entry of the reactor into the critical state by checking the reactivity, and makes all the measurements usually made with analog reactimeters. If the intensity of the source does not change during measurements (5–10 min) when chambers sensitive to rays (e.g., KNK-56 chambers) are used as neutron-flux detectors, then the accuracy of -ray compensation does not affect the results of the measurements.Translated from Atomnaya Énergiya, Vol. 45, No. 5, pp. 375–376, November, 1978.     

Drying of gas—Air mixtures with Vion KN-1 chemisorption fibre

The use of Vion KN-1 chemisorption fibre in hydrogen form as a selective drying agent for a gas—air mixture containing sulfur dioxide, carbon monoxide, hydrogen sulfide, and nitrogen dioxide was substantiated. The optimum conditions of use and regeneration of the drying agent were determined.Scientific-Research Institute of Physics at Odessa State University. Translated from Khimicheskie Volokna, No. 1, pp. 40–43, January–February, 1994.     

Instability of a Crystal 4He Facet in the Field of Gravity

We analyze here the analog of the Rayleigh instability in the field of gravity for the superfluid?Ccrystal ⁴He interface provided that the heavier ⁴He crystal phase occupies the space over the lighter superfluid phase. We find that the conditions and onset of the gravitational instability are different in kind above and below the roughening transition temperature when the crystal ⁴He surface is in the rough or in the smooth faceted state, respectively. In the rough state of the surface the gravitational instability is fully analogous to the classical case of the fluid?Cfluid interface. In contrast, in the case of the crystal faceted surface the onset of the gravitational instability is associated with surmounting some potential barrier. The potential barrier results from nonzero magnitude of the facet step energy. The size and the tilting angle of the crystal facet are also important parameters for developing the instability. The initial stage of the instability can be described as a generation of crystallization waves at the superfluid?Ccrystal interface. In particular, we discuss the experiments (Demaria et al. in J. Low Temp. Phys. 89:385, 1992; Tsymbalenko in Fiz. Nizk. Temp. 21:162, 1995; Tsymbalenko in Low Temp. Phys. 21:120, 1995) which may concern the gravitational instability of the superfluid-crystal ⁴He interface.     

Study of the physical constants of a uranium graphite reactor lattice by means of a sub-critical assembly

It has been shown experimentally that it is possible to study-the physical constants of the uranium graphite reactor lattice by means of a subcritical assembly.The assembly consisted of a uranium graphite lattice of natural uranium rods for a mockup of the lattice of the Beloyarskii GRÉS type reactor. The subcritical assemblies were placed in the central part of a uranium graphite reactor using tubes of 2% enriched uranium rods. Experiments are described which showed that it is possible to measure the physical parameters of the reactor lattice, namely, the resonance escape probability ,the fast neutron multiplication , and the thermal utilization . Together with the assembly the reactor constituted a critical system. The sub-critical assembly was part of the lattice of the reactor under study. The results of the measurements given are in satisfactory agreement with the calculational data.The authors express their deep gratitude to one and all.The authors also tender thanks to A. V. Kamaev, M. E. Minashin, G. Ya. Rumyantsev, I. G. Morozov for their interest in the work, discussion of results, and valuable comments.     

Compressibility effect on the quantum two-dimensional nucleation at low temperatures

We study the quantum two-dimensional nucleation of a stable solid phase during the first-order transition at temperatures down to absolute zero. The key role of the finite compressibility of a metastable liquid phase in calculating the quantum nucleation rate is emphasized. In particular, the nucleation rate proves to be dependent on temperature in the quantum tunneling regime. On the whole, the nucleation kinetics corresponds to dissipative tunnelung through a potential barrier. Energy dissipation is due to emitting sound waves during the growth of a solid nucleus. The features inherent to the quantum 2D growth of steps on the atomically smooth facets of a helium crystal are discussed as well.