Session: 05-05: Radiation Science and Nuclear Materials

Paper Number: 134387

134387 - In Situ Measurement of the Solubility, Diffusivity, Permeability and Chemical Form of Hydrogen Isotope in Liquid Lead-Bismuth 

Abstract: 

  The fourth-generation reactors have been proposed to improve the utilization rate of nuclear fuel and reduce the long-lived fission products. Due to the excellent neutron economy, chemical stability, and thermal characteristics, lead-bismuth fast reactor has become a promising concept. From the perspective of nuclear safety, scientists mainly focus on the behavior of highly toxic ²¹⁰Po and fission products, but rarely look at the tritium problem in lead-bismuth fast reactors.

Tritium in the primary loop of the lead-bismuth reactor is mainly from the ternary fission reaction and (n, α) of lithium impurity. The cladding material is intended to be a ferritic-martensitic steel alloy because of the excellent radiation resistance, creep resistance, and high-temperature resistance, but tritium could easily permeate and be released into the primary loop. Then tritium could migrate into the structural material and the cover gas. The tritium in the structural material will decay to stable He³ nuclide. Then helium bubbles will be produced at the grain boundaries and dislocations under the irradiation synergistic effect, which will produce strong local stress, volume expansion, making the material harden, embrittle, and accelerate the failure process of the structural material. In addition, the tritium in cover gas is at risk of leaking into the environment. Tritium in the environment usually exists in the form of HTO, which can easily enter the inside of an organism through adsorption, respiration, and ingestion, resulting in long-term internal irradiation.

In this work, an experimental device was designed and built based on the “permeation pot” method to measure the transport parameters of hydrogen isotopes in liquid metal. Hydrogen and deuterium were used instead of tritium in the experiment, and permeation experiments were carried out in the range of 350-550℃, and each temperature point with four pressure conditions. The experiment results confirmed that hydrogen isotopes are in atomic form in liquid lead-bismuth, and the diffusion, permeation, and solubility of hydrogen in liquid lead-bismuth were obtained as a function of temperature. Then, the transport parameters of tritium were derived from the hydrogen isotope effect. To further study the tritium chemical form and distribution in the real environment of lead-bismuth reactor, a gas phase oxygen control system was coupled to the experimental device to reproduce a real primary loop environment. The experiment used hydrogen and oxygen mixture gas to control the oxygen content in lead-bismuth and used deuterium instead of tritium for diffusion and release research. The deuterium was loaded at the lower end of the permeation pot. It diffused into lead-bismuth alloy, then released into the cover gas, and finally extracted by the sampling system into the gas phase quadrupole mass spectrometer for composition and content analysis. The experiment focuses on the influence of temperature, oxygen content, and deuterium content on the deuterium form and content in the cover gas. The results show that deuterium in the cover gas mainly exists in the form of HD and HDO, and the HDO share reaches more than 90% under various conditions. At the same time, the temperature, oxygen content, and deuterium content have a monotonic effect on the composition of the cover gas.

Now the transport parameters of hydrogen isotopes in the key structural materials involved in the lead-bismuth reactor are measuring. A dynamic numerical model of tritium transport and migration in lead-bismuth reactors will be built based on the above experiment data in the next step, which could accurately and quantitatively evaluate the tritium safety in lead-bismuth reactors.

Presenting Author: Yingwu JIANG Sun Yat-sen University

Presenting Author Biography: I studied at Sun Yat-sen University.
Research interests: Hydrogen isotope transport parameter measurement, model modification, hydrogen isotope separation, tritium safety assessment.

Authors:

Yingwu JIANG Sun Yat-sen University
Jiewei Wu Sino-French Institute of Nuclear Engineering & Technology
Fuhao Ji Sino-French Institute of Nuclear Engineering & Technology
Junkang Yang Sino-French Institute of Nuclear Engineering & Technology
Muyi Ni Sino-French Institute of Nuclear Engineering & Technology