Fission Engineering & Fuel Cycle

Modular Pebble Bed Reactor

The research objective of our project is to establish the conceptual design for an innovative modular pebble bed reactor (MPBR) that is cooled by helium and generates electricity using helium gas turbines. The plant would be rated at 120 MWe with a modular design that will allow factory manufacture of most modules, making the plant economically competitive with natural gas, combined-cycle plants.

Our overall objective is to participate in the design, construction, and operation of the Next Generation Nuclear Plant (NGNP) to be built in the next decade at the Idaho National Laboratory (this plant would also be a test bed for hydrogen production). Areas of research include: coated fuel particle design, safety analysis, core optimization, modularity principles of factory fabrication, high temperature intermediate heat exchanger design and overall design optimization. If successful, the modular approach to design and construction will offer enhanced safety and economic competitiveness that could revolutionize production of nuclear-generated electricity.

Nuclear Space Power Reactors

An initiative has been launched to explore potential power systems for large-scale 4 MWe reactors to provide electric power to plasma engines in space. Starting with the Mars Mission design project in 2003, in which several space-based and Mars-based power plants were conceptualized, follow-on work includes optimizing designs for mission requirements. Future work will be coordinated with the MIT Aeronautics and Astronautics Department, NASA, and Naval Reactors.

Risk-Informed Safety Standards

Licensing of next generation reactors will require innovative safety requirements based on an assessment of risk, applying probabilistic and deterministic criteria. This research is focused on developing such a risk-informed approach in the design and, subsequently, licensing of future reactors. This concept will then be extended to allow for “license by test” for new technologies, avoiding years of paper analysis and using the plant itself to demonstrate safety by tests.

Plant Operational Performance

Nuclear power plants in the US have achieved record high capacity in recent years, while the performance of plants in other nations has been relatively stagnant. Research indicates that the new competitive environment in the US and the application of risk-informed tools has improved both performance and safety. Research continues into the effectiveness of risk-informed regulation, and how management and safety culture play a role in making nuclear plants safe and economic.

Nanofluids for Nuclear Applications >>

Nanofluids are engineered colloidal suspensions of nanoparticles (1-100 nm) in a base fluid. Common base fluids include water and organic liquids. Nanoparticles are typically made of chemically stable metals, metal oxides or carbon in various forms. The size of the nanoparticles imparts some unique characteristics to these fluids, including greatly enhanced energy, momentum and mass transfer, as well as reduced tendency for sedimentation and erosion of the containing surfaces. Nanofluids are being investigated for numerous applications, including cooling, manufacturing, chemical and pharmaceutical processes, medical treatments, cosmetics, etc.

The overarching objectives of the research program at the Nuclear Science and Engineering Department are to measure and understand key transport phenomena in nanofluids, and evaluate their applicability to nuclear systems. The program comprises various experimental and analytical activities, including procurement and characterization of water-based nanofluids, thermo-physical property measurements and modeling, single-phase and two-phase heat transfer and pressure drop measurements in nanofluid flow loops, and analysis of the potential impact of the use of nanofluids on the safety, neutronic and economic performance of nuclear systems.

>> More information is available at Center for Nanofluids Technology at MIT

Heat Transfer Enhancement in Gaseous and Liquid Nanofluids

Addition of small (10-100 nm) particle populations to liquids has been found to enhance heat transfer by as much as 100%, without significantly increasing either pressure drop or erosion of exposed surfaces. Such “engineered” fluids are known as nanofluids. Given current interest in helium and carbon dioxide as coolants and working fluids for nuclear plants, it is important to investigate whether a similar approach could work for gases. Gases have low thermal conductivities, thus the relative benefit of heat transfer enhancement could be significant. Open questions regarding use of nanoparticles in gases include a potentially higher rate of both particle deposition on exposed surfaces, and erosion due to the higher velocities at which gases are used. We have started a basic investigation into the key phenomena governing heat transfer in gaseous and liquid nanofluids.

Advanced Light Water Reactors (LWR)

Development of next generation nuclear power depends upon improving performance with regard to economics, safety, waste production, and proliferation resistance. Use of advanced fuels in a once-through LWR fuel cycle has the potential to improve all four areas. Several ideas are being investigated:

Advanced Fuel Design. The use of annular fuel (designed to allow both internal as well as external cooling) substantially reduces both fuel temperature and heat flux to the coolant. This will enhance the safety margin of the fuel in the LWR core if operated at the same power density. In Pressurized Water Reactors (PWR) and Boiling Water Reactors (BWR) cores, use of annular fuels allows extraction of more power from the same vessel and primary system volumes, improving the economics of reactor operations.

Nuclear Fuel Cycle. The development of long-cycle BWRs is being investigated. Extending the refueling interval to fifteen years would make the placement of the plants in less developed areas of the world more attractive, by reducing both the infrastructure necessary for refueling operations and opportunity for diversion of fuel materials to weapons programs. Using thorium as part of the reactivity control is being investigated.

Supercritical Water Reactors, operating at pressures higher than 20 MPa, offer the potential for high energy conversion efficiency (above 40%) while minimizing equipment requirements. However, the coolant will undergo a large reduction in density as it flows across the core, giving rise to potential density wave instabilities and requiring special care in the core’s hydraulic design.

Enhanced Nonproliferation Fuel Cycles for Thermal Reactors

Spent fuel from LWRs contains significant amounts of fissile materials that can be recycled as fuel in other reactors, significantly reducing waste and expanding nuclear fuel resources. Using inert fuels that do not produce new fissile materials as hosts for actinides would enable burning of the actinides at the same rate as they are being produced. Thus, long-term storage of actinides in a permanent repository can be essentially eliminated, and the total volume of material sent to the repository greatly diminished. The use of thorium has also been investigated to reduce the production of plutonium in once-through reactors. Reductions of a factor of 3 to 4 might be possible in heterogeneous reactors if high burning of the fuel can be accommodated. This will also reduce the volume of the spent fuel.

Nuclear Energy and Transportation Fuels

Nuclear energy provides a means for production of gaseous and liquid fuels that can reduce if not eliminate the dependence on fossil fuels. For example, production of hydrogen—for use in hydrogen-fueled automobiles­—can be accomplished either through electrolysis or thermochemical means. The design of an efficient integrated plant for production of hydrogen through high temperature steam electrolysis is under investigation. Heat transfer, power conversion efficiency, and optimum temperature and pressure conditions are being investigated using principles of thermodynamics and electrochemistry.

Our projects are being conducted in collaboration with national laboratories and industrial partners under bilateral arrangements, with support from the Department of Energy under the Nuclear Energy Research Initiative Program (NERI).

Hydride Fuel for Water-Cooled Reactors

Introduction of hydrogen atoms into nuclear fuel achieves neutron moderation with a relatively low coolant volume. As a result, the hydride core can have a smaller volume or higher total power in the same volume relative to an LWR core that burns oxide fuel. The net benefit will be increased core life, discharge burnup, total energy generated per fuel load, and capacity factor of LWR cores. Other anticipated outcomes are reduction in fuel cycle electricity costs, along with improved resource utilization, reduction in the volume and hazard of high level waste, and increased proliferation resistance. Finally, the inherent negative temperature coefficient of hydride fuel may lead to improved safety of PWR’s.

The ongoing hydride fuel project has a broad scope including backfitting of existing reactors; design of new core configurations; and evaluation of five test fuels. The MIT focus is on the hydraulic, mechanical and safety aspects of core design. These fuels are also being explored for use in the Generation IV supercritical water reactor.

Advanced Fuel Cycles

The closed fuel cycle is being investigated internationally for its potential benefits to spent fuel management. Thermal and fast burner reactors in various combination with existing light water reactors are being examined to identify optimum strategies for waste fuel management. The optimum strategy must supply the world’s anticipated electricity demand in an acceptable economic and proliferation-resistant manner. The goal of this work is to identify preferred strategies relevant to the current once-through fuel cycle strategy, as well as R&D requirements for reactor and fuel cycle facility characteristics which are necessary to accomplish these strategies. Two strategies are being investigated: a thermal reactor actinide burner using assemblies with a portion of the pins of fertile-free fuel in combination with standard LWRs, and a lead-cooled actinide fast burner in combination with standard LWRs.

The MIT Research Reactor (MITR) is a heavy-water reflected, light-water cooled and moderated research reactor that utilizes flat, plate-type fuel. The reactor is part of the MIT Nuclear Reactor Laboratory, an interdepartmental laboratory that functions as an educational and research center for many MIT departments, as well as local universities and hospitals.

The MITR has a broad research program that encompasses most aspects of neutron science and engineering, including nuclear medicine (especially neutron capture therapy); neutron activation analysis for the identification of air pollutants and isotope ratios in geological specimens; fission engineering, including digital control of spacecraft reactors; materials testing and evolution; and teaching. It is one of six facilities world-wide with the capability to conduct patient trials for boron neutron capture therapy (BNCT) to irradiate both glioblastoma multiforme (brain tumors) and deep-seated melanoma (skin cancer).

Of the many experiments that are being conducted, some of the most prominent include: the design, installation, and characterization of a fission converter that produces an epithermal neutron beam for medical applications; clinical trials of neutron capture therapy; microdosimetry studies to support neutron capture therapy; use of neutron activation analysis for mineral uptake in humans using stable isotopes; analysis of meteorites and lava flows, and identification of origin of air pollutants; in-core loops for the evaluation of water chemistries for pressurized water reactors and boiling water reactors; in-core experiments to evaluate the behavior of next generation nuclear fuels; and the development and demonstration of techniques for the closed-loop digital control of spacecraft and terrestrial reactors.

Our students pursue thesis topics that combine theoretical and experimental components, allowing them to experience the full breadth of the program and facility.