New methods and mathematical simulation software are under developing at SPE RESST during years for the support of radiation sustainable technologies [26–33].
In 2006 the specialists of SPE RESST have finished the development of a new (third) version of the multipurpose RaT 3 code for the Monte Carlo simulation of the radiation transport and irradiation effects in the complex heterogeneous media [26,27]. The RaT code, based on the open-source code of Geant4.8.0 (CERN) libraries, provides the consistent statistic simulation of electromagnetic and hadronic processes in the interaction of different radiations with material, including the high-precision models of photonuclear reactions and the evaluated ENDF/B-VI data driven methods of the neutron transport simulation with taking into account the S(α,β)-treatment in the thermal energy region. In the RaT code implemented are new four-dimensional (4D) methods of the Monte-Carlo simulation of nonstationary radiation effects [27,28], as well as, the double Monte-Carlo methods for simulation of the radiation transport in the random and parametrized media [29,24]. The code involves the developed tools for analysis of simulation and calculation results on the cross-section and rates of different secondary processes of radiation effect on the materials including the radiation damage of structural materials.
Such performances, quite comparable with potentialities of the recognized world leaders - the codes MCNP(X) (USA) and MCU (Russia) - determine the ranges of the code RaT 3 application in the dosimetry, electrophysical and γ-radiation technologies, medical physics (radiation therapy of cancer, production of medical isotopes), neutronics of multiplicating systems and radiation materials science. Therefore the RaT 3 code can be considered as a prototype of the first national code for the computed support of the atomic power engineering, nuclear fuel cycle and applied nuclear and irradiation technologies.
In 2006 we applied the RaT code  for simulation of dose effects due to the heterogeneity and stochasticity of the arrangement of typical objects subjected to the irradiation sterilization, namely, disposable syringes. However, the main attention was given to the investigation, by the simulation methods, of radiation properties of new radiation sources for applications in irradiation and nuclear technologies [30–33]. For example, previously, jointly with the Russian State Science Center "Research Institute for Nuclear Reactors", a work package for designing of new industrial γ-radiation sources based on europium radionuclides was developed. The code RaT was used to calculate  radiation fields (see Fig.1), as well as, operating and storage thermal conditions for optimized europium sources having in their structure Eu-15x isotope mixtures with a maximum specific activity of ~80 Cu/g reachable under direct reactor irradiation. It has been established, that the short terms (less than 100 FPD - full-power days) of neutron europium activation to the maximum activity makes such sources to be unique renewable industrial γ-sources.
Fig.1. Radiation fields of the γ-radiation air-kerma rate for the optimized design of a cylindrical γ-source with Co (left) and Eu (right) loadings of the active core.
In 2006 the researchers started investigations of a new object - the promising neutron sources based on the subcritical assemblies driven by the high-power electron accelerators being widely discussed in the context of the development of nuclear technologies and materials science [31–33]. Using the code RaT the specialists of NSC KIPT firstly performed detailed comprehensive calculations of the neutron-physical characteristics of a model subcritical (keff = 0.98) system (see Fig.2) controlled by the beam of 100 MeV electron and 100 kW power on the neutron-production target. In cooperation with the Scientific-Technological Complex "Nuclear Fuel Cycle" at NSC KIPT the calculations were confirmed by comparison with the independent simulation data obtained using the codes MCNPX 2.4 and SCALE5 certified by Nuclear Regulation authorities.
|Fig.2. 3D-model of the subcritical assembly for the code RaT 3 (a) and simulated spatial distributions of the neutron-flow density (b) and power (c) in the assembly at a level of the neutron-producing target.|
For the first time by means of the code RaT 3 it has been succeeded to calculate the characteristics of the primary radiation damage of materials being irradiated in the research channel of this assembly and to investigate, by the methods of 4D-simulation, unsteady effects of neutron flux and power oscillations, temperature jumps of materials and thermal elastic stresses in the structural parts of the subcritical system in the case of application of a pulsed electron accelerator as its driver.