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Tritium Transport Analysis in Advanced Sodium-Cooled Fast Reactors

A tritium permeation analyses code (SFR-TPC) was developed to analyze tritium distributions in Sodium-Cooled Fast Reactors (SFRs) systems. A MATLAB software was used for developing this code. The SFR-TPC is based on mass balance equations regarding various chemical forms of hydrogen (i.e., T-,HT,HTO), coupled with a variety of tritium sources, sinks, and permeation models. In the SFR-TPC, ternary fission and neutron capture reactions of B10 were taken into considerations as tritium sources. Permeation of tritium through pipes, vessels, and heat exchangers were considered as the main tritium transport paths. In addition isotope exchange models were developed to analyze tritium isotopes distribution in water.
The analysis carried out on an under construction SFR plant (Prototype Fast Breeder Reactors) showed that only 0.016% of tritium released from the core is lost into the environment, adopting a suitable combination of two main tritium transport mitigation techniques (sodium cold traps and permeation barriers).
The SFR-TPC has a very user- friendly utilization for system configurations providing a graphical user interface. Unfortunately, no literature results of tritium analysis were found for this type of nuclear plants and, therefore, a comparison with SFR-TPC solution was not possible.However, a verification of steady state mass conservation law was obtained.
This work contains a brief descriptions of SFR pool type design (regarding relevant aspect for tritium analysis study), a wide section in which all theoretical aspects of hydrogen kinetics are described (such as solubility, diffusivity and permeability) and the central part, which is characterized by basic tritium pathways description, tritium transport theoretical aspects, a simple user guide, and visualization, analysis and verification of a SFR-TPC simulation.

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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.

Laurea liv.II (specialistica)

Facoltà: Ingegneria

Autore: Fabrizio Franza Contatta »

Composta da 257 pagine.


Questa tesi ha raggiunto 297 click dal 09/05/2011.


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