الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 83 |  |  |
| | | from | 83 | | |
Abstract
The current research is based on studying the effect of changing heavy water percentages in the moderator in central and peripheral fuel cells in a mixed heavy/light water reactor, the resonance of absorption in fertile material can be adjusted to give best neutronic properties and high inventory of the fissile material- by varying D2O/H2O ratio in the moderator and increasing thermal neutron flux- at the peripheral fuel cells, in which mixed moderator is more effective for breeder thorium fuel. Monte-carol N Particle code (MCNP5) is used to model a Czech research reactor (LR-0) which is a benchmark research reactor with fuel assemblies the same as the Russian reactor type (VVER- 1000), but LR-0‟s assemblies are shorted in length. Eleven-different heavy/light water mixtures viz.; 0%, 10%, …., 90%, 100% heavy water percentages in the moderator were investigated by studying the effect of changing the D2O/ H2O ratio on the Neutron flux in Fuel, Moderator, and Control rods, Besides studying Neutrons‟ interactions with Fuel, Moderator and Control rods. Tallies of (MCNP5) Code were used to study varying of D2O/H2O ratio in Thorium fuel to calculate the conversion ratio of 232Th to 233U at the eleven-different heavy water ratio. Burn up calculations‟ results of the fuel are obtained using (MCNP6) in (LR-0) reactor model to study the effect of changing the D2O/ H2O ratio on the reactivity coefficient. The parametric research study showed that: the optimal ratio of heavy water/ light water for using thorium fuel in closed fuel cycle as a breeder of 233U is at 100% heavy water, at the beginning of the first fuel loading cycle. The burn up results showed that: changing heavy/light water ratios leads to change the reactivity coefficient “k-effective” by days due to change neutrons‟ absorption cross-section in heavy water and light water.