Idaho National Laboratory (INL) is developing a Molten salt Research Temperature-controlled Irradiation (MRTI) experimental capsule for the Neutron Radiography (NRAD) reactor. The test vehicle is designed to contain actinide-bearing chloride salt, which previously has not been subjected to a neutron field. Fuel-bearing salt irradiation thus far has only been fluoride based. Despite this, there is a strong interest in using chloride salts for Molten Salt Reactor (MSR) concepts in industry due to their higher potential actinide content, and better suitability for a fast spectrum configuration. The main objectives of the experiment are threefold: (1) assess the source term mechanics, (2) study the evolution of thermophysical properties with burnup, and (3) evaluate the impact of irradiation-induced corrosion on materials interfacing with the salt. A conceptual design of this first-of-kind experiment is being completed and will be summarized in this article. Neutronic simulations of the experiment and its surrounding reactor environment were conducted using the Monte Carlo N-Particle Transport code (MCNP). Thermal analysis was conducted using ABAQUS finite element software and COMSOL. Parametric analyses considered: The F-1 vs. C-4 position in NRAD, the capsule wall material choice, overall dimensions, and 235U enrichment level. Suitable design configurations are presented and compared to each other. The salt is double encapsulated to provide insulation and redundancy in the case of leakage. A gas-gap between the inner capsule and the outer container is used to enable tuning of thermal conduction to the NRAD coolant by altering its thickness and its gas-mixture. The selected concepts can reach power densities above 20 W/cm3 (the desired target) and adhere to reactivity insertion limits of the NRAD reactor (below 45 cents). Fine-tuning of parameters such as the Ar/He ratio in the gas-gap ensured the configurations reached a targeted average salt temperature of 600oC, while avoiding salt freezing or exceeding material limits. An immersion heater design was preferred to a furnace-type approach in order to satisfy both the need to melt the fuel before reactor startup, and to dissipate heat when fission energy is being generated within it. The resistive heater is placed within a thermowell and is relied upon to control the temperature of the experiment (both when the reactor is on or off). Mechanical design work focused on generating Computer Aided Design (CAD) models of the overall MRTI experiment layout and evaluating structural/pressure considerations to adhere to American Society of Mechanical Engineers (ASME) standards. The selected configurations can contain over 10 cm3 of fuel-bearing chloride salt, which is sufficient for the purposes of the post-irradiation examination (PIE) and provides sufficient volume for at least one thermocouple to monitor salt temperature. Submersion of additional instruments in the salt (e.g., neutron detectors, needle probes, optic fibers) will also be considered. &nbsp;The experiment will be placed within a NRAD 3-pin cluster with the fourth pin used for the experiment. It will have an open top fitting to allow for instrumentation cables to be connected to the control system outside of the NRAD reactor. The main designs considered are shown to satisfy primary experiment objectives and required safety limits. This work was supported through the INL Laboratory Directed Research &amp; Development (LDRD) Program under DOE Idaho Operations Office Contract DE-AC07-05ID14517.

Conceptual Design of Temperature-Controlled Fueled-Salt Irradiation Experiment to Support Demonstration of Advanced Nuclear Reactors

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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