DESIGN STUDY AND OPTIMIZATION OF A MODULAR MODIFIED CANDLE FAST REACTOR BY USING HELIUM GAS AS COOLANT

• Main Author: Pierre Ndayiragije, Jean
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/87999
• Institution: Institut Teknologi Bandung

The gas-cooled fast reactor (GCFR) was selected as one of the Generation IV nuclear reactor systems to be developed due to its potential for sustainability, safety, reliability, proliferation resistance, reducing the volume and radio toxicity of both its own fuel and other spent nuclear fuel. In addition, energy conversion at high thermal efficiency is possible with the current designs being considered, thus increasing the economic benefit of the GCFR. However, research and development challenges include the ability to use passive decay heat removal systems during accident conditions, survivability of fuels and in-core materials under extreme temperatures and radiation, and economical and efficient fuel cycle processes. In this study, the GCFR system is combined with modified CANDLE (Constant Axial shape of Neutron flux, nuclide densities, and power shape During Life of Energy production) burnup scheme to create long life fast reactor with natural uranium as fuel cycle input. Such a system can utilize natural uranium resources efficiently without the necessity of enrichment plant or reprocessing plant. The main objective of this study is to design and optimize a modular modified CANDLE fast reactor using helium gas as coolant. During this research, Firstly, reactor core has been divided into ten regions with the same volume in radial direction and then, the neutronic calculations have been performed. Secondly, the reactor core has been divided into ten regions with the same volume in axial direction and then, the neutronic calculations have been performed. During the shuffling in radial direction, two cases have been considered. The first case was the normal modified CANDLE where the first region is located near to the tenth region and the second case of shuffling in radial direction, the different numbers of regions have been placed on right side and left side of tenth region. One region has been placed on left side of tenth region namely, the normal modified CANDLE and the neutronic calculations have been performed, then, two regions, six regions and seven regions have been placed on left side of tenth region and then, neutronic calculations have been performed. The fuel was loaded in the first region, and after ten years of burnup, it was transported to the second region, and ten years later of burnup, it was transported to the third region and so on. The fuel in tenth region was removed from reactor core. SRAC (Standard Reactor Analysis Code system) was employed for the neutronic analysis. The collision probability (PIJ) method was employed for fuel cell calculations while JENDL-4.0 was employed as a nuclear data library. In the beginning, the power density in each region has been assumed and then burnup and multi-group diffusion equation calculations were carried out. At each step of the burnup, the effective macroscopic cross-section for each burnup step has been obtained. The outcomes have been employed to figure out the multigroup diffusion equation in two-dimensional R-Z using the module of SRAC2006 called CITATION. The results of average power density in each region obtained by using CITATION have been brought back them into the SRAC code for cell burnup calculations. This iteration is performed until convergence is achieved. The comparison of 400 MWth power using helium gas, lead bismuth eutectic and liquid sodium coolants has been also investigated in radial direction. Due to the effective multiplication factor, relative power density and neutron flux, the liquid sodium coolant attained the criticality condition faster than that of helium gas and leadbismuth eutectic coolants. In the first case of modified CANDLE shuffling in radial direction, a 900 MWth power has been designed using various fuel volume fractions and for the second case shuffling in radial direction, a 450MWth has been designed. The lower amount of fuel volume fraction causes an increasing rate of burnup level and a decreasing rate of effective multiplication factor. A 2700 MWth -3100 MWth GCFR employing modified CANDLE shuffling in axial direction strategy have been also designed. UN (Uranium Nitride) and 10% of 232Th have been employed as fuel. The high power level causes an increasing rate of burnup level and effective multiplication factor. The highest average discharge burnup level is about 313 GWd/Ton HM or 31.3% HM (Heavy Metal) for the reactor with high power level. The thermal hydraulic analysis in radial direction of first case has been investigated and the maximum temperature of fuel is about 1700K. The gap temperature, cladding temperature and coolant temperature have been also investigated. The optimization processes have been conducted by adjusting fuel volume fraction and core dimensions. Helium gas has been employed as coolant due to its high thermal conductivity, lower neutron absorption and as a noble gas gives helium unique advantages over any other gas as a coolant. According to those properties helium has been proven to significantly enhance the performance of fast reactors when utilized as a coolant.