temperature profiles were studied. The simulation results showed reductions in fuel centerline temperatures and lower temperature drop across fuel rod cross-section under normal fuel operations. It was observed that there was reduction in gas gap pressure and energy stored in fuel. Transient conditions involving cladding rupture were investigated and important performance parameters such as cladding strain were studied. During these transients, the addition of BeO to UO 2 fuel seems beneficiary.22:T4d4,Japan Atomic Energy Agency has conducted a conceptual design of a 50 MWt small-sized high temperature gas cooled reactor (HTGR) for multiple heat applications, named HTR50S, with the reactor outlet coolant temperature of 750°C and 900°C. It is first-of-a-kind of the commercial plant or a demonstration plant of a small-sized HTGR system to be deployed in developing countries in the 2020s. The design concept of HTR50S is to satisfy the user requirements for multipurpose heat applications such as the district heating and process heat supply based on the steam turbine system and the demonstration of the power generation by helium gas turbine and the hydrogen production using the water splitting iodine-sulfur process, to upgrade its performance compared to that of HTTR without significant R&D utilizing the knowledge obtained by the HTTR design and operation, and to fulfill the high level of safety by utilizing the inherent features of HTGR and a passive decay heat removal system. The evaluation of technical feasibility shows that all design targets were satisfied by the design of each system and the preliminary safety analysis. This paper describes the conceptual design and the preliminary safety analysis of HTR50S.23:T51d,Molecular dynamics approach is used to simulate hydrogen (H) diffusion in zirconium. Zirconium alloys are used in fuel channels of many nuclear reactors. Previously developed embedded atom method (EAM) and modified embedded atom method (MEAM) are tested and a good agreement with experimental data for lattice parameters, cohesive energy, and mechanical properties is obtained. Both EAM and MEAM are used to calculate hydrogen diffusion in zirconium. At higher temperatures and in the presence of hydrogen, MEAM calculation predicts an unstable zirconium structure and low diffusion coefficients. Mean square displacement (MSD) of hydrogen in bulk zirconium is calculated at a temperature range of 500–1200 K with diffusion coefficient at 500 K equals 1.92 * 10 −7 cm 2 /sec and at 1200 K has a value 1.47 * 10 −4 cm 2 /sec. Activation energy of hydrogen diffusion calculated using Arrhenius plot was found to be 11.3 kcal/mol which is in agreement with published experimental results. Hydrogen diffusion is the highest along basal planes of hexagonal close packed zirconium.24:T4dd,Light materials with small atomic mass (light or heavy water, graphite, and so on) are usually used as a neutron reflector and moderator. The present paper proposes using a new, heavy element as neutron moderator and reflector, namely, “radiogenic lead” with dominant content of isotope 208 Pb. Radiogenic lead is a stable natural lead. This isotope is characterized by extremely low micro cross-section of radiative neutron capture (~0.23 mb) for thermal neutrons, which is smaller than graphite and deuterium cross-sections. The reflector-converter for a fast reactor core is the structure capable of transforming some part of prompt neutrons leaked from the core into the reflected neutrons with properties similar to those of delayed neutrons, that is, sufficiently large contribution to reactivity at the level of effective fraction of delayed neutrons and relatively long lifetime, comparable with lifetimes of radionuclides-emitters of delayed neutrons. It is evaluated that the use of radiogenic lead makes it possi

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1	Engineering	10	10	235
2	Natural Sciences	2	2	24
3	Applied Physics	2	2	61
4	Chemical Engineering	1	1	10
5	Chemistry	1	1	14

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