MBase: The Molecular Basis of Advanced Nuclear Fuel Separations

Lead Research Organisation: Imperial College London
Department Name: Earth Science and Engineering

Abstract

Over 95% of used nuclear fuel is uranium and plutonium, which can be recovered and reused. However, because used fuel is intensely radioactive, this requires very complex processes. These processes can also be adapted to the separation of high hazard materials from the residual radioactive wastes, to simplify radioactive waste management. However, industrial reprocessing of used fuel primarily relies on a 50 year old solvent extraction process (Purex), which was originally developed for much simpler fuels. As a result, modern fuels can prove difficult to reprocess. We will therefore explore two different approaches to nuclear fuel separation in parallel, one based on the established Purex technology and the other on a much more recent development, ion selective membranes (ISMs). ISMs are porous, chemically reactive membranes which can bind metals from solutions then release them again, depending on conditions, thus allowing highly selective separations.In the solvent extraction system, we will focus on a common problem in solvent extraction, third phase formation, and on separation of a group of long lived, high hazard waste isotopes (the fission product technetium and the minor actinides). With the ISMs, we will first prove their utility in uranium/plutonium separation, then extend these studies to the minor actinides. Throughout, we will work with the elements of interest, rather than analogues or low activity models and in realistic radiation environments. In both strands of the project, we will explore the underlying physical and chemical processes then, building on this understanding, we will develop a series of quantitative models, building from phase behaviour to unit operations and finally to process flowsheet models. We wil use the resulting models to explore different options for fuel reprocessing, based on scenarios defined with our industrial partners.

Publications

10 25 50
 
Description The key theme of this 15 man-month project (which benefitted from other parallel research projects) was to develop numerical 'multiphysics technologies to model the behaviour of super-critical fissile solutions capable of self-heating to boiling temperatures. The models developed though this project enabled the simulation of both the neutronics and multiphase flows of these solutions together with their heat transfer with external heat extraction systems. It had been hoped originally to maintain contacts with the French Valduc defence site but a management change made this impossible. So we have made use of our contacts in the United States. The key finding and outcomes include: 1) The first full reconstruction of the US Y12 laboratory criticality accident, demonstrating a capability of accurate predictions by demonstrating agreement with the available data for the event. 2) The first detailed modelling of the historic US Los Alamos lab SUPO reactor, a fissile solution reactor with heat extraction systems, for which modelling heat transfer characteristics (using a detailed 2D/3D coupled model) agreed well with experimental data. Such a capability is vital as this reactor can be viewed as a prime benchmark for future designs of solution reactors. These are candidates for medical isotope production of which the US MIPS design has been an example. 3) A new modelling capability of current PWR designs, allowing us to study the safety of a reactor during unintended scenarios including control rod ejection and increased localised cooling/heating.
Exploitation Route The neutronic-multiphase simulator has already attracted attention from the Japanese Atomic Energy Authority, and it is intended that we contribute to their next meeting on the predictions of nuclear fuel solutions - which is to be held next year. This is in addition to the Y12 national Lab who have shown much interest in the project's outcomes and have encouraged the use of the model for studying criticality accidents involving fissile solutions. The immersed body and heat exchange simulation technology has already been used to model conceptual designs of medical isotope production systems (MIPS) which involve fissile solutions with heat extraction coils. There is immediate potential that this technology can be adapted for use in industry for the modelling solid fuel reactors. It enables the fine detail resolution of heat exchange between fuel pins and coolants, and this allows for the simulation of unintended operations (e.g. cold slugs of coolant water entering the reactor or local control rod ejection) and the assessment of local effects, such as increased heating, on the solid fuel pins. The modelling technologies are now forming the foundations for the simulation of severe nuclear accident scenarios, and this has led to new collaborations with IRSN, in France, on investigating the effects of fuel pin melting and core melting events. For non-nuclear applications the multi-phase flow with heat transfer modelling has the potential to simulate and aid the design of large scale fluidized bed coal furnaces, an application that has already attracted the interest of industry. The research developed under the MBASE project has already been exploited through its use in the modelling of conceptual designs of medical isotope production system (MIPS) reactors. Its unique modelling capabilities has led to the Babcock & Wilcox company, based in the US, funding several years of post doctoral positions and EngDoc students. The MBASE project has helped leverage and underpin the technologies required to model and analyse such a design of a reactor. We are not aware of any other technology that is capable of achieving such detailed modelling capability. In addition the technologies developed are valuable in the context of nuclear criticality safety both globally and in the UK, as evidenced by our earlier simulation of the Japanese JCO plant criticality accident. Our work on criticality accident modelling, which has involved a number of elements of the MBASE project, has now linked in with industry and academia across the world including Japan (JAEA) the US (Y12) and France (IRSN) and the UK. Indeed our first steps in developing this technology and the relevant international links were funded by the (now) ONR.
Sectors Energy,Environment

 
Description Some of the technology developed in this project has been extended into research in medical isotope reactor designs using fissile solution fuels.
Impact Types Economic

 
Description Collaboration with Babcock & Wilcox: modelling of medical isotope reactors 
Organisation Babcock & Wilcox
Country United States of America 
Sector Private 
PI Contribution The technologies developed under MBASE were naturally extended to the modelling and study of the dynamics of conceptual designs of medical isotope reactors involving critical fissile solutions. With collaboration with the Babcock & Wilcox company we were able to analyse a design of reactor that they were considering building for the purpose of producing these medical isotopes.
Start Year 2011
 
Description Collaboration with Y12 on investigating criticality accidents involving nuclear fuel soultions 
Organisation Oak Ridge National Laboratory (ORNL)
Department Y-12 National Security Complex
Country United States of America 
Sector Public 
PI Contribution The MBASE project enabled us to work with the Y12 National Lab, based in the US, on predicting the dynamics of criticality accidents involving nuclear fuels. As part of this collaboration we were able to provide the most detailed modelling analysis yet on one of their own criticality accidents that occurred a number of decades ago.
Start Year 2010
 
Description Collaboration with the HMS Sultan: Neutronics-fluid flow modelling of Pressure Water Reactors 
Organisation HMS Sultan
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Public 
PI Contribution Through collaboration with HMS Sultan the outcome of the research developed under the MBASE program was extended to the modelling of coolant flows through PWR assemblies and their full cores. This investigation studied the effects of unintended reactor operations - including control rod ejections and localised cooling.
Start Year 2011
 
Description Collaboration with the University of South Carolina: Neutronics-fluid flow modelling of Pressure Water Reactors (PWRs) 
Organisation University of South Carolina
Country United States of America 
Sector Academic/University 
PI Contribution Through collaboration with the University of South Carolina the outcome of the research developed under the MBASE program was extended to the modelling of coolant flows through PWR assemblies and their full cores. This investigation studied the effects of unintended reactor operations - including control rod ejections and localised cooling.
Start Year 2012
 
Description Collaborations with ONR 
Organisation US Office of Naval Research Global
Country United States of America 
Sector Public 
PI Contribution The work of MBASE has led to new collaborations with the ONR on severe accident modelling. The multiphase modelling elements of MBASE led to new investigations into the study of the integrity of structures of pressure water reactors under accident scenarios.
Start Year 2012
 
Description Severe nuclear accident modelling in collaboration with IRSN 
Organisation IRSN, Institut de radioprotection et de sûreté nucléaire
Country France, French Republic 
Sector Public 
PI Contribution The multi-phase modelling components of MBASE has been re-applied to the modelling of sever accidents involving both localised fuel pin melt and full core melt and capture. This element has involved collaborations with the severe accident modelling group based within IRSN - Institute for Radiological Protection and Nuclear Safety ? of France.
Start Year 2011
 
Description Coupled Radiation Transport and Fluid Flow Simulations of Liquid & Solid Fuel Reactors 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience
Results and Impact As an invited speaker, we presented the work conducted through the MBASE project to the University of South Carolina covering the modelling techniques used to model both liquid and solid fuel reactors.
Year(s) Of Engagement Activity 2013