[en] The approximations of the nonstationary diffusion equation, taking into account the type of the solution, characteristic to the pulse neutron experiments, are considered. In some simple cases the asymptotic stability and method convergence are proved. A short description of the numerical solution program of the two-dimensional multigroup diffusion equations of instantaneous neutrons is presented

[en] Application of the detector efficiency funtion for quantitative description of space effect (dependence on the neutron detector position) when measuring reactor reactivity using the kinetics equation inverted solution, is suggested

[en] The solution of the simplest model problems of neutron transport in P₁ and 2P₀ approximations is considered. On the basis of the analysis of obtained expressions possible errors arising when using the spherical harmonics method for calculation of nuclear reactor parameters are studied. It is concluded that in the case of detailed group analysis (narrow groups) diffusion approximation underestimates a reflector efficiency in upper groups. If the cross sections of neutron leakage in these groups are high enough the reflector thickness increase results in the flux decrease. In the 2P₀ approximation in this case negative fluxes directed from a boundary occur. When calculating the fast reactors this effect effect can result in general underestimating of the reflector role and as a sequence in underestimating of neutron efficient multiplication factor ksub(eff). As the total number of neutrons in a group is provided by the diffusion approximation in general correctly and the number of reflected neutrons is underestimated in the case discussed the overestimating of the number of neutrons slowing-down in a reflector and penetrating through it is to be expected. For thermal reactors the overestimating of ksub(eff) is to be expected if neutron slowing-down in a reflector is essential in the general bahance and the reflector is thick

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[en] Using a muniature pulsed ionization fission chamber employing a layer of ₂₅₂Cf and positioned in the centre of a sphere, 20 cm in dia., of depleted uranium, and also a neutron scintillation spectrometer with an organic crystal, measurements were taken of the neutron flux density on the sphere surface as a function of time in the range of 5x10^-₉ s to 150x10^-₉ s for the energy ranging between 0.175 MeV and 10.5 MeV. The exponential drop in a limited time interval is shown to exist. The attenuation decrement in this case depends on the neutron threshold energy and varies from 8x10₇ s^-₁ to 3.2x10₈ s^-₁. The experimental results are compared with the calculation performed to a 26-group diffusion approximation

[en] Results of calculational and experimental investigations obtained when studying reactivity temperature coefficients (RTC) in uranium-water assemblies with ρ_H/ρ₅ #approx # 130 depending on the way of positing the gadolinium burnable poison rods (BPR) along the core cross section: uniformly in the core centre and at its peripheral parts. RTG is determined in subcritical state by the shooting source method. The calculations are carried out in two-group diffusion approximation using (r, Z)-geometry in the FACTOR-3, DNESTR programs and (r, φ)-geometry taking account of the BPR real position in the RFI-80 program. The investigations displayed a noticeable dependence of RTG value on the way of BPR position in a core under conditions of reflector and absorbing rods concurrent contribution to the balance of assembly reactivities

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[en] The difference between the spectrum of a neutron beam measured by the time-of-flight method and that of neutrons in a critical fast assembly is considered. The authors calculate corrections associated with the effect of an external neutron beam and the neutron port. They present the results of measurements for verifying the corrections introduced

No abstract available