Numerical investigation of the convection of heat-emitting liquid reactor materials taking stratification into account

Conclusions The calculations for the different levels of volume heat release showed that the integral heat fluxes at the lateral and top surfaces are virtually independent of the scenario of convective flow. However, the maximum of the heat flux on the lateral surface in the homogeneous case is 1.5–1.6 times higher than the maximum heat flux in the stratified case. This could result in larger mechanical loads on the reactor vessel and therefore more stringent requirements on the cooling of the outer surface of the reactor vessel. Institute of Fast Reactors, Russian Academy of Sciences. Translated from Atomnaya énergiya, Vol. 76, No. 5, pp. 406–411, May, 1994.     

BIR and BIGR Upgrade Variants for Enlarging Their Interior Cavities

Computational results are presented for the neutron characteristics of BIR and BIGR fast pulse reactors, specifically, cylindrical systems with a core consisting of an alloy of 90% or 36% enrichment uranium with 10 mass% molybdenum or a composite uranium–graphite material. The purpose of the calculations is to determine the possibility of increasing the size of the interior cavities in reactors without appreciably degrading the time parameters of the pulses.Reactor models with a metal core, which are best for further consideration, are systems with a disk core which have a cavity with a diameter up to 30 cm along the axis and a thickness-limited iron reflector. For reactors with uranium–graphite core, it is best to develop a new pulse reactor with an axial cavity which has a larger volume and is more accessible for sample placement than BIGR.An important problem of the calculations was to determine screen variants for a cavity which would prevent fuel overheating and at the same time be free of autocatalysis manifestations.     

Kinetics of Aperiodic Cascade Boosters: Speed of Operation and Safety

The results of Monte-Carlo calculations of simple spherically symmetric systems, simulating an aperiodic booster, are presented. The purpose of the calculations is to give a clear demonsration of the specific features of the kinetics of cascade reactor systems and the possibilities which the application of the cascade principle in an aperiodic booster adds to increasing safety and improving the time parameters of the pulses. Another goal is to determine the materials for the moderator which are best from the standpoint of optimizing the parameters of the booster. It is shown that for the same total number of fissions the neutron pulses in a cascade booster are generated under conditions of much greater subcriticality and are much shorter in duration than for a single-section booster. The best pulse parameters are obtained in cascade boosters with tungsten, lead, and molybdenum neutron moderators.     

Computational-theoretical model of a wave multiplying pulsed reactor

A computational-theoretical model is proposed for an innovative zero power wave multiplying pulsed reactor (WMPR) for studying the development of a nuclear fission chain reaction near the upper critical state of the system, i.e., in the region where calculations are difficult to perform and on which nuclear explosion-safety of critical systems depends. A scenario of possible accidents is presented.The novelty and special features of the physical scheme of the WMPR required the use of new computational methods. These methods can be used, for example, to calculate conventional pulsed nuclear reactors.Translated from Atomnaya Énergiya, Vol. 97, No. 6, pp. 414–422, December, 2004.Deceased.This revised version was published online in April 2005 with a corrected cover date.     

Formation of Friction Layers and Wear Resistance of Steels under Conditions of Boundary Friction

We studied the influence of the lubricant compositions Grafitol with 10% graphite (1), Aerol containing 17% MoS₂ (2), Limol containing 60% MoS₂ (3), Limol + 10% chlorine-paraffin (4), and Limol + 10% copper powder (5) on the wear rate and formation of the fine structure of surface friction layers of structural steels. We established a correlation between the tribological characteristics of steels and lubricants. The abrasive wear of 40KhFA steel was minimum if it was lubricated with Limol + 10% copper powder. In this case, its wear was smaller by a factor of 10, 2, 1.25, and 7.25 as compared with lubricant compositions 1–4, respectively. In the course of minimum wear of 40KhFA steel, in the surface friction layers, we observed the minimum values of second-kind distortions (a/a) and of the true size of domains of X-ray coherent scattering (D) as well as the minimum difference between the crystal lattice constants (a) of steel before and after friction.     

Model of the Formation and Growth of a Gas-Filled Cavity in Boron Carbide under Irradiation

A model of the formation and growth of gas-filled pores in the cores of absorbing elements under neutron irradiation is described. The model is based on a definite similarity between the mechanisms of radiation damage in boron carbide and oxide fuel. For boron carbide, the key mechanism is radiation-stimulated coalescence of helium bubbles, which gives rise to the much larger swelling of boron carbide as compared with nuclear fuel. Regimes of the coalescence of helium bubbles as a function of the irradiation intensity, neutron spectrum, and radial position are investigated. It is shown that the model describes qualitatively well the basic development of gas-filled porosity under irradiation in fast and thermal reactors.     

The generation of sound in the flow of an excited gas

We examine the development of sonic perturbations in the bounded subsonic flow of a gas excited by oscillations.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 57, No. 4, pp. 562–566, October, 1989.     

Reactivity effects (autocatalysis) in BR-1 and BR-K1 pulsed reactors

Conclusions Manifestations of autocatalysis, caused by neutron-absorbing samples loaded into a cavity in the core, in explosive accidents in BR-1 and BR-K1 reactors were investigated. The investigation was conducted on the basis of calculations using a multigroup neutron-gas-dynamic program for one-dimensional calculations of fission surges in various configurations of the reactors indicated. It was shown that, even though the boron content in the screens is comparatively limited and the natural isotopic composition of boron is used in the BR-K1 screen, in the case of accidents accompanied by a chain reaction of an explosive type strong manifestations of autocatalysis with nine-fold (BR-1) and 520-fold (BR-K1) increase of energy release in accidental surges are possible. However, the analysis also showed that the manifestations of autocatalysis on this scale are possible only if large excess margins of reactivity are present in the reactors. In BR-1 and BR-K1 reactors, where the margin of reactivity is limited, only moderate manifestations of autocatalysis with a 1.5-fold (BR-1) and 4-fold (BR-K1) increase of energy release in a surge can be observed in reality. The indicated manifestations of autocatalysis in BR-1 and BR-K1 reactors do not require a re-examination of the categories of danger for these reactors, but they must be taken into account during reactor operation. The prohibition of any changes in the reactor configurations which can increase the margin of reactivity must be carefully followed. We thank L. A. Kuz'min for assisting in the calculations and S. V. Petrin for providing the data on the characteristics of accident situations in BR-1 and BR-K1 reactors and for a fruitful discussion of the results obtained in this work. Nuclear Center of the Russian Federation—All-Russia Scientific-Research Institute of Experimental Physics. Translated from Atomnaya énergiya, Vol. 85, No. 3, pp. 179–186, September, 1998.