ABSTRACT This paper describes how the neutronic characteristics of a very demanding research reac... more ABSTRACT This paper describes how the neutronic characteristics of a very demanding research reactor facility impact on the mechanical design of the reactor core. The Replacement Research Reactor (RRR) for the Australian Nuclear Science and Technology Organization is described making emphasis in the mechanical solutions to improve the core performance. The compact core is located inside a chimney, surrounded by heavy water contained in the Reflector Vessel. The whole assembly is at the bottom of the Reactor Pool, which is full of de-mineralized light water acting as coolant and moderator and biological shielding. The core is an array of sixteen plate-type Fuel Assemblies (FAs) and five absorber plates, which are called Control Plates (CP). The coolant is light water, which flows upwards. The final design of the core layout and control guide boxes was adopted to minimize the flux and PPF perturbation during the normal operation. The four lateral control plates are used mainly to shutdown the reactor and to compensate large reactivity transients. The central and cruciform regulating plate is used to compensate the reactivity change during the cycle operation. The regulating plate does minimize perturbation on PPF and irradiation fluxes. The design of the reflector tank fulfils all the flux requirements for the irradiation facilities and also the flux perturbation between irradiation facilities. Keywords: Neutronic, Research Reactor, Mechanical Design.
ABSTRACT This paper describes how the neutronic characteristics of a very demanding research reac... more ABSTRACT This paper describes how the neutronic characteristics of a very demanding research reactor facility impact on the mechanical design of the reactor core. The Replacement Research Reactor (RRR) for the Australian Nuclear Science and Technology Organization is described making emphasis in the mechanical solutions to improve the core performance. The compact core is located inside a chimney, surrounded by heavy water contained in the Reflector Vessel. The whole assembly is at the bottom of the Reactor Pool, which is full of de-mineralized light water acting as coolant and moderator and biological shielding. The core is an array of sixteen plate-type Fuel Assemblies (FAs) and five absorber plates, which are called Control Plates (CP). The coolant is light water, which flows upwards. The final design of the core layout and control guide boxes was adopted to minimize the flux and PPF perturbation during the normal operation. The four lateral control plates are used mainly to shutdown the reactor and to compensate large reactivity transients. The central and cruciform regulating plate is used to compensate the reactivity change during the cycle operation. The regulating plate does minimize perturbation on PPF and irradiation fluxes. The design of the reflector tank fulfils all the flux requirements for the irradiation facilities and also the flux perturbation between irradiation facilities. Keywords: Neutronic, Research Reactor, Mechanical Design.
The improvements in the computational systems (increasing the memory and storage capacity and the... more The improvements in the computational systems (increasing the memory and storage capacity and the enhancement of calculation power) allows the development of innovative methods for reactor calculations, including not only more accurate theories and numerical methods, but also adding more prediction capabilities and additional engineering information to perform the numerical analysis of the system. As an example, nowadays it is possible to integrate different tools with interdisciplinary or multi engineering information allowing an integrated approach to the problem to be solved. The INVAP calculation line is used in a wide range of applications (mainly MTR, CAREM and CNA-2), where some of them requires a thermal hydraulic model to evaluate the distribution of the fuel, coolant and moderator temperatures and the coolant and moderator densities. For those cases, such parameters are needed for a proper evaluation of neutronic behavior of the core. Currently CITVAP has several thermal-hydraulic models depending on the geometry considered; 1D geometry, to calculate each channel of the reactor core, and a 3D geometry to use more complex thermal-hydraulic model of the core. The models are for MTR and NPP. The simulations involve natural convection and forced circulation. In the last upgrade of CITVAP, the possibility to use any external thermal hydraulic model was added. All these models are used for the thermal hydraulic feedback of the neutronic calculation, but in some cases can be used for further key analysis in reactor design. Accordingly, there is the possibility to evaluate thermal margins to critical phenomena, perform the evaluation of the temperature distribution for the oxide layer growth calculation and perform the calculation of the power feedback coefficient.
INVAP uses computational tools to predict the behavior of the reactor to be built. Every new reac... more INVAP uses computational tools to predict the behavior of the reactor to be built. Every new reactor needs increasingly detailed analysis from different points of view, as nuclear safety and fulfillment of user requirements (flux and production levels, spectra requirements, perturbations, etc). Furthermore, this analysis must be modeled with a consistent level of detail from all the engineering variables. INVAP has been on continuous development of the calculation system used for design and optimization of nuclear reactors. The calculation codes have been polished and enhanced with new capabilities as they were needed for the reactor design, improving its safety, fuel economy and performance. Nowadays, this calculation line is divided in two main codes: Cell (CONDOR) and Core (CITVAP) codes. The homogenized and condensed macroscopic Cross Section (XS) is one of the main parameters used as interface between both codes; which are calculated by the Cell code and they are used as input by the Core code. The present work summarizes the different theories, algorithms and numerical approaches used by CONDOR to generate the required parameters. The description covers all the calculation stages from the geometrical input up to the generation of the output parameters, describing the different methods used in the different stages.
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