No abstract

The purpose of the work is to calculate VVER-1200 neutron-physical characteristics that are important for safety using MCU Monte Carlo code for an independent verification of the accuracy of design calculations of the first fuel cycle. The calculations were carried out before the startup of the first VVER-1200 power unit. A full-scale computer model of VVER-1200 was developed using the design documentation of the fuel assemblies and the reactor facility. Special attention was given to the accurate specification of the geometry and material description of the core and its immediate environment. The full-scale VVER-1200 model allows performing Monte Carlo calculation of some safety-relevant characteristics for which it is impossible or extremely difficult to carry out full-scale reactor experiments. In total, more than 110 different states were calculated; five states were calculated taking feedbacks into account. For all calculations, the neutron-physical characteristics obtained by means of the MCU code were used to verify the BIPR-7A and the PERMAK-A codes.

Full-scale three-dimensional computer model describing neutron-physical processes that occur in the VVER-1200 reactor core involves detailed FA geometry description. However, the detailed description significantly complicates input data, increases calculation time and error probability. Consequently, creation of simplified models of the design elements becomes necessary. In present work, simplified geometrical models of FA design elements are suggested. Calculations of simplified models are compared to calculations of exact models that completely correspond to the working general view drafts provided by OKB “Hydropress”. It is demonstrated that in many problems the use of simplified description of FA elements geometry is possible.

A. S. BikeevUDC 621.039.17Highly detailed computational models of the reactors in the Nos. 2 and 3 units at the Rostov NPP and the No. 3 unit at the Tianwan NPP (China) with the fi rst fuel load are briefl y described. Calculations of two states of the reactors were performed with the MCU code, implementing the Monte Carlo method, for each model: at the lowest controllable power and at nominal power. A TPA thermophysical module connected to the MCU code was used to take account of feedbacks in calculating the state of the reactor at nominal power. Analysis of the results obtained using the MCU and BIPR-7A codes showed agreement between the main characteristics of the reactor facilities.In the last few years, a trend has emerged in the nuclear power industry toward using high-precision software implementing the Monte Carlo method in order to calculate the neutron-physical characteristics of reactor facilities in a state with the lowest controllable or nominal power level [1,2]. The Monte Carlo method is universal in numerical modeling of the transport of different forms of radiation, since it does not impose any restrictions on the geometry of the desired system and makes it possible to model the interaction of radiation with matter on the basis of information from an evaluated nuclear data fi le and the most accurate data are used without additional approximations and rough approximations. The accuracy attainable, owing to the use of high-precision software, in the calculations of neutron-physical characteristic of reactor facilities can be used to validate the safety of an NPP. The additional results obtained can be used to refi ne and fi ne tune the engineering software used in designing fuel cycles and validating the safety of nuclear reactors.The problem of the present work is to approbate the MCU software implementing the Monte Carlo method for calculating some neutron-physical characteristics of VVER-1000 [3].Full-scale computational models of the reactor facilities of the Nos. 2 and 3 units of the Rostov NPP and the No. 3 unit of the Tianwan NPP (China) with the fi rst fuel load were developed to solve this problem. The models were developed using the design documentation for fuel assemblies and the reactor facility: reports, blueprints, explanatory notes, and technical validations. Information presented in GOSTs or technical specifi cations for the chemical composition was used to describe the material composition of steel, alloys, and other materials. In model development, special attention was devoted to the accuracy of the description of the geometry and material composition of the fuel assemblies: the geometry of fuel elements and support lattices, measurement and guiding channels, heads, tails, and other structural elements of fuel assemblies, are taken into account and described in detail. The model of a fuel element consists of cladding, fuel pellets, spring lock, and top and bottom end-pieces. The geometry of the models of the head and tail pieces of a fuel assembly corresponds precisely to the ...

Two types of calculations were made to compare BIPR-7A and MCU results for 3D full-scale models. First EPS (emergency protection system) efficiency and in-core power distributions were analyzed for an equilibrium fuel load of VVER-1000 assuming its operation within an 18-month cycle. Computations were performed without feedbacks and with fuel burnup distributed over the core. After 3D infinite lattices of full-scale VVER-1000 fuel assemblies (FA's) with uranium fuel 4.4 % enrichment and uranium-erbium fuel 4.4 % enrichment and Er2O3 1 % wt were considered. Computations were performed with feedbacks and fuel burnup at the constant power level. For different time moments effective multiplication factor and power distribution were obtained. EPS efficiency and reactivity effects at chosen time moments were analyzed.