Yu. V. Mironov

A procedure for performing a statistical analysis of the uncertainties in thermohydraulic calculations

A methodology is developed for performing statistical analysis of the uncertainties in thermohydraulic calculations on the basis of the idea of the GRS method. The coefficients, which are to be varied, in the semiempirical closure relations are determined for the RELAP5/MOD3.2 and MELCOR 1.8.3 codes; their distribution functions and variation ranges are chosen. In the RELAP5/MOD3.2 code, input of the coefficients is built-in in order to be able to vary the closure relations. The procedure makes it possible to estimate with a prescribed degree of reliability the confidence interval for the calculations of key parameters for experimental stands and operating setups and to determine the dominant factors influencing the computational results.

An analysis of the dynamics of the RBMK-1000 reactor for rupture of the pressurized collector at low power

In order to evaluate the safety of the RBMK-1000 reactor, one must study the behavior of the reactor in emergency situations at low power. In this case the core is filled with water, close to the saturation state, and disturbances producing steam in the core may for a positive void coefficient lead to an appreciable power increase. In this article, the authors consider the maximum projected emergency; rupture of the pressurized collector under conditions close to those reached at Power Plant 4 of the Chernobyl Nuclear Power Station just before the 1986 accident. The objective is to determine the possible consequences of the maximum projected emergency at lower power and to estimate the effectiveness in such situations of the measures taken since 1986 to increase the safety of nuclear power stations with RBMK reactors. A numerical analysis was performed on the basis of a general-loop thermohydraulic program Relap5/mod2, including in the algorithm the inverse effect of coolant density on the reactor kinetics, using a precise model with six groups of delayed neutrons.

Role of separate factors in the development of the Chernobyl accident

Immediately after the accident in the fourth power unit of the Chernobyl nuclear power plant many computational and analytical investigations of the development of the accident and the values of separate factors in this situation were performed at the NIKIET and other research centers. Foreign research centers, where, in particular, the modern general-loop programs of the type Relap 5, Retran 02, and others were employed for modeling the thermohydraulic processes in the circulation loop of the reactor where the accident occurred, also participated in this process.

Analysis of transient processes in nuclear-reactor loops

An algorithm is presented which may play a significant role for real nuclear-reactor loops in multivariant calculations by its economy. The TRANS7 algorithm has been developed for the solution of this problem; the TRANS7 algorithm performs the numerical integration of the thermohydraulic equations of one- and two-phase flows and the heattransfer equations in the fuel elements. A mathematical model is presented which is closed by empirical relations for slipping and friction in the two-phase flow and for heating of the water in the nonequilibrium-boiling zone. The thermophysical properties of water and steam are calculated using a bundle of programs and introlduced in the computer memory in tabular form, which is suitable for interpolation with respect to the pressure and heat ontent. When considering a group of experiments, the TRANS7 algorithm gives completely satisfactory agreement of the theoretical and experimental data.

Thermohydraulic calculation of multirod heat-liberating piles cooled by single-phase heat carrier

The PUCHOK-BM program was used for a thermophysical analysis of the HLP of a gas-cooled fast reactor, considering 217 rod fuel elements arranged in a triangular lattice with relative step s/d equal to 1.32, and relative distance to the wall equal to 1.33. The numbering scheme adopted for the rods and elementary cells together with curves of the energy distribution in the cassette cross section, is given. The cassette is cooled by helium with an initial pressure of 160 bar. In the calculations, the equation of state of an ideal gas and the temperature dependence of the viscosity and heat conduction of helium were used. 10 refs.