Pyrochemical reprocessing of molten salt fast reactor fuel: focus on the reductive extraction step

Abstract

The nuclear fuel reprocessing is a prerequisite for nuclear energy to be a clean and sustainable energy. In the case of the molten salt reactor containing a liquid fuel, pyrometallurgical way is an obvious way. The method for treatment of the liquid fuel is divided into two parts. In-situ injection of helium gas into the fuel leads to extract the gaseous fission products and a part of the noble metals. The second part of the reprocessing is performed by ‘batch’. It aims to recover the fissile material and to separate the minor actinides from fission products. The reprocessing involves several chemical steps based on redox and acido-basic properties of the various elements contained in the fuel salt. One challenge is to perform a selective extraction of actinides and lanthanides in spent liquid fuel. Extraction of actinides and lanthanides are successively performed by a reductive extraction in liquid bismuth pool containing metallic lithium as a reductive reagent. The objective of this paper is to give a description of the several steps of the reprocessing retained for the molten salt fast reactor (MSFR) concept and to present the initial results obtained for the reductive extraction experiments realized in static conditions by contacting LiF-ThF4-UF4-NdF3 with a lab-made Bi-Li pool and for which extraction efficiencies of 0.7% for neodymium and 14.0% for uranium were measured. It was concluded that in static conditions, the extraction is governed by a kinetic limitation and not by the thermodynamic equilibrium.

Defining the Challenges—Identifying the Key Poisoning Elements to Be Separated in a Future Integrated Molten Salt Fast Reactor Clean-Up System for iMAGINE

“…However, the key to the success of the envisaged technology is avoiding the constraints of the existing paradigms of reprocessing technologies, which focus on rigorous, complete and highly selective separation of fissile materials, and taking a strictly demand driven approach for long term reactor operation. Up until now, most of the salt clean-up, polishing, or other related processes are still based on separating fissile materials, e.g., the processes used at MSRE [15], some newer proposals [16,17] and the processes proposed for EVOL [18,19]. The process aimed for here is completely different and could be called "reverse" reprocessing, in that the aim is to leave all fissile materials and all actinides, in the salt, while separating those selected elements which prevent the reactor from long term operation.…”

"Advanced" isn't Always Better: Assessing the Safety, Security, and Environmental Impacts of Non-Light-Water Nuclear Reactors

“…But as discussed in chapter 5, that process has had major problems and would need significant performance improvements to be useful for an MSR. And smallscale experiments on processing the molten fluoride salts that would be used in the European MSFR have found only a "low" extraction efficiency for uranium (Rodrigues, Durán-Klie, and Delpech 2015).…”

“…In 2014, a review article pointed out that fundamental data for the extraction processes are lacking, especially for the separation of actinides from lanthanide fission products (Serp et al 2014). Subsequently, experimental work on separating uranium and neodymium (a surrogate for TRU) from molten fluoride salt found only "low" extraction efficiencies, calling into question the proposed processing approach (Rodrigues, Durán-Klie, and Delpech 2015).…”

Molten salt fast reactor SAMOFAR: Safety issues of the chemical plant

“…To ensure the neutronics properties (limitation of neutron absorbers) and to control the physicochemical properties of the salt (corrosion, deposit...), fission products must be extracted [5]. For this purpose, the chemical plant is composed of four main processes able to perform the chemical separation of the fission products from the fuel salt [6][7][8], i.e. the fluorination, the two reductive extractions and the actinide traps (green boxes in Figure 1).…”