Tritium Transport Analysis in Advanced Sodium-Cooled Fast Reactors

INTRODUCTION - 1 - INTRODUCTION The Sodium-Cooled Fast Reactor (SFR) system is one of six types of plants in Next Generation Nuclear Plant (NGNP). The NGNP [1] is in the pre-conceptual design phase with major design selections (e.g., reactor core type, core outlet temperature, etc.) still to be carried out. SFR features a fast-spectrum reactor and a closed fuel recycle system. The primary mission for SFR is the management of high-level wastes and, in particular, the management of plutonium and other actinides [1]. With innovations to reduce capital costs, the mission can extend to electricity production, given the proven capability of sodium reactors to utilize almost all of the energy in the natural uranium versus the 1% utilized in thermal spectrum systems [1]. One potential problem of using SFR is tritium permeation from the primary coolant through heat exchangers and other plant facilities to the environment. In SFR tritium mostly comes from ternary fission of the fuel and neutron capturereactions inside boron-containing materials, such as control rods and neutron flux shielding blocks, as shown in Chapter 4. Tritium that enters in the primary coolant will be circulated or permeated to the secondary coolant through the intermediate heat transfer loop. The permeated tritium,successively, enters the product steam/water into steam generator through heat exchanger surfaces. The mechanisms of tritium transport are diffusion, bulk transport, and permeation (seeFig. 1). Transport of different chemical species of tritium in the environment (i.e. HT and HTO) is related to physical and chemical processes. Physical processes are bulk transport (tritium moves because of its dissolution inside heat transfer fluids) and diffusional transport (tritium motion is driven by concentration gradient). Reactions and state changes of chemical species are chemical processes [2]. A tritium permeation model, thus is required in order to estimate the total amount of tritium released into the environment and circulating inside the plant. In fact the model is applied to the overall SFR plant, considering all tritium transport processes inside nuclear plant installations and studying systematically tritium transport in each component. The objective in this work is exactly to simulate tritium transport behavior in SFR components (according to reference SFR configuration reported in Fig. 1) and to predict tritium quantities in different SFR devices by means of solving mass conservation laws with computational tools (such as MATLAB packages). The tritium path in a SFR is shown in Fig. 1. Recently, other authors developed a tritium permeation analysis code (TPAC) for Very High Temperature Gas Reactors [3] and the current work was deeply inspirited to this permeation code by the computational and mathematical structure point of view.