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Non-nuclear energy

Innovative concepts

Fission and radiation protection
Fusion
   

This area of research examines the potential of innovative design concepts to develop improved and inherently safer processes for nuclear power production and for other novel processes that can exploit the unique features of nuclear energy. Background on different nuclear power plant designs can be found here.

The main research focus in FP6 is on the design and development of new reactor concepts in particular reactors capable of operating at higher temperatures. Higher temperature operation of nuclear reactors would increase the efficiency of power conversion and assist in direct application to industrial processes such as hydrogen production.

Four generations of nuclear reactor technology can be defined. The first and the second generations of reactors met the need for intensive energy production, at low costs and acceptable levels of safety. The third generation of reactor technology was conceived after the Three Mile Island and Chernobyl accidents, and has focused on an even higher level of safety. An example of third generation reactor is the European Pressurized water Reactor (EPR) designed to meet the European Utility Requirements with stringent safety requirements.

A world wide collaboration, the Generation IV International Forum (GIF), has selected six nuclear energy systems (including VHTR/HTR systems) to be developed and to be deployed by 2030. GIF believes that these systems can deliver long-term benefits to the energy industry and ensure that nuclear energy plays an essential role in energy generation worldwide. GIF has published ‘A Technology Roadmap for the Generation IV Nuclear Energy Systems’ that can be accessed here.

High temperature reactors are one of six concepts considered in Generation IV reactor concepts . The Generation IV International Forum is a United States-led initiative with some European involvement. Generation IV designs focus on improving safety, economics, better use of fissile materials and minimization of waste generation.

The concepts being developed by GIF (in addition to HTR/ VHTR designs) are described below.

High Temperature Reactors (HTR)

Nuclear reactors produce heat and the maximum thermodynamic efficiency in heat conversion is improved by operation at higher temperatures.

Operating nuclear reactors at temperatures above 850ºC would permit higher efficiency and also lead to direct process applications such as hydrogen production, which is also more efficiently produced at higher temperatures.

In a HTR helium gas is used as the coolant and is passed directly through the core and over the fuel rods. In most advanced designs the hot helium gas directly drives a gas turbine in a direct cycle (Brayton cycle) to produce electricity at high efficiency. The use of a direct cycle dictates that the fuel and other reactor components are of high integrity.

Fuel elements in a HTR are arranged in a vertical coolant passages in the graphite moderator. The cylindrical core containing the fuel elements is surrounded by a graphite moderating reflector. The control rods for the reactor are located vertically in the outside wall of the core. The core fuel configuration of a HTR may use a pebble bed reactor or, prismatic block configuration.

Small HTRs have been operational for some time, but more recent technology developments are making larger HTRs possible. HTR design is most advanced in South Africa, China, Japan and the EU. However, high temperature operation requires the resolution of many technical issues including:

  • Fuel technology. Fuel for HTR operation is in the form of particles less than a millimeter in diameter, each with a kernel of enriched uranium oxycarbide (9%+ U-235) surrounded by layers of carbon and silicon carbide. This gives containment for fission products which is stable up to 2000ºC.
  • Reactor physics, waste and fuel cycles.
  • Materials studies
  • Components and systems requirements.
  • Safety approach and licensing.

Very High-Temperature Reactor (VHTR)

A graphite-moderated, helium-cooled reactor with a once through fuel cycle that operates at an even higher outlet temperatures of 1000°C. This enables use of reactor heat for process applications via an intermediate heat exchanger, with electricity cogeneration, or direct high-efficiency driving of a gas turbine for electricity production. Modules of 600 MW thermal power are envisaged. The core can be built of prismatic blocks, or it may be a pebble bed. The VHTR system is designed to be a high efficiency system that can supply heat to a variety of high temperature and energy intensive non-electricity production processes. For hydrogen production, the system supplies sufficient heat to use the thermochemical iodine-sulphur process.

Considerable effort has been put into these innovative concepts in the Euratom FP5 programme and further work will be initiated under FP6.

Gas-Cooled Fast Reactor (GFR)

Features a helium cooled reactor operating with a fast neutron spectrum and closed fuel cycle. The GFR will operate at high temperature (850ºC) to  produce electricity, hydrogen or process heat with high efficiency. In generation mode the helium gas directly drives a turbine and fuels could include depleted uranium and any other fissile or fertile material. Spent fuel would be reprocessed on site and all actinides recycled to minimize long-lived waste.

A state of the art report has been produced by the Euratom project Gas-cooled fast reactor concept Review Studies (GCFR) and further Euratom work is envisaged under FP6.

Supercritical Water-Cooled Reactor (SCWR)

A high-temperature, high-pressure water cooled reactor that operates above the thermodynamical critical point of water. The operating regime (25 MPa, 510-550°C)  gives a thermal efficiency about one third higher than current light water reactors (LWR). The supercritical water directly drives the turbine, without any secondary steam system. Passive safety features are similar to those of simplified boiling water reactors. SCWR is primarily designed for efficient electricity production and may have a thermal or fast neutron - spectrum depending on the fuel cycle option. For a thermal neutron reactor the fuel is enriched uranium oxide in once through fuel cycle. However in the fast reactor option, full actinide recycle based on conventional reprocessing technology is possible.

This reactor system has been assessed in the High Performance Light Water Reactor (HPLWR) Euratom project and further studies are envisaged by Euratom under FP6.

Molten Salt Reactor (MSR)

Produces power in a circulating molten salt fuel mixture with an epithermal neutron spectrum reactor and a full actinide recycle fuel cycle. The fuel is a mixture of sodium, zirconium and uranium fluorides which circulates through graphite core channels to achieve some moderation and produce an epithermal neutron spectrum. Fission products are removed continuously and the actinides are fully recycled. Coolant temperature is 700°C at very low pressure, but 800°C is possible. A secondary coolant system extracts heat from the molten salt via an intermediate heat exchanger and through a tertiary heat exchanger for electricity generation. The attractive features of the MSR closed liquid fuel cycle include: high-level waste comprising fission products only and therefore shorter-lived radioactivity; a smaller inventory of weapons-fissile material; low fuel use and safety due to passive cooling that is scalable to any size. Molten fluoride salts have excellent heat transfer properties and a low vapour pressure, which reduces stress on reactor vessel and pipework.

This technology is being assessed under the Euratom project Review of Molten Salt Reactor Technology (MOST). Further work may form part of the FP6 work programme.

Lead-Cooled Fast Reactor (LFR)

Features a fast neutron spectrum lead or lead/ bismuth eutectic liquid metal-cooled reactor and a closed fuel cycle for efficient conversion of fertile uranium and management of actinides. Fuel is depleted uranium metal or nitride with full actinide recovery and recycle from reprocessing plants. A wide range of sizes is envisaged from, modular 300-400 MWe units and 1400 MWe central plants. Operating temperatures of 550 ºC is easily achievable. The LFR ‘battery’ concept is a factory-built units with a 15-20 years life for small grids or developing countries. It is designed to meet emerging market opportunities where for distributed generation of electricity and other energy products such as hydrogen and potable water.

Research in this area may be subject to future work under FP6.

Sodium-cooled fast reactors

Features a fast neutron spectrum, sodium-cooled reactor and closed fuel cycle for efficient management of actinides and conversion of fertile uranium. The design utilises depleted uranium in the fuel and has a coolant outlet temperature of 550°C enabling electricity generation via a secondary sodium circuit, the primary one being at near atmospheric pressure. Two variants are proposed: a 150-500 MWe type with actinides incorporated into a metal fuel requiring pyrometallurgical processing integrated with the reactor, and a 500-1500 MWe type with normal MOX fuel reprocessed in conventional facilities off-site. The SFR is designed for management of high level wastes in particular plutonium and other actinides.


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