The current commercially available nuclear reactors all have cores with solid fuel rods and are cooled either by light water or heavy water. These reactors are collectively known as Generation 3 reactors.
There are a series of major issues associated with the current 3rd generation nuclear power plants that are being deployed in a number of countries, many of which stem from the adoption for commercial power producing reactors of the Uranium/Plutonium (U/P) fuel cycle, and in particular, the use of solid fuel contained within fuel rods.
This choice was driven some 50-60 years ago by the needs of the military, both for plutonium for bombs and high-powered compact reactors for nuclear submarines.
The use of a solid form of fuel imposes limits on the degree of burn-up that can be achieved, due to the progressive build up of fission products within the fuel rod, which in turn dictates the frequency of re-fuelling shutdowns. It also has an adverse effect on the fuel costs and the quantity of high active waste created. The use of water as the coolant requires very high pressure coolant systems and highly engineered safety measures to eliminate the risk of a Loss of Coolant Accident (LOCA).
A number of challenges arose when these technologies were adopted for civilian use. For example:
– Very expensive and complex engineered safety systems, as borne out by the UK licensing experience with the EPR safety control systems;
– Complex and regular re-fuelling arrangements, requiring plant shutdowns for PWR and BWR, and on-line refuelling machines for HWR’s due to the limits on the achievable burn-up;
– Low thermal efficiencies caused by the low steam temperatures due to the temperature limits placed on the fuel rods canning material and the very high coolant pressures required for higher temperatures;
– The need for large quantities of cooling water in order to maximise the poor thermal efficiency;
– Sophisticated fuel fabrication facilities for new fuel;
– Construction of the necessary large primary pressure vessels and forgings, to the highest engineering standards;
– Complex and costly secondary containment systems, due to the large amount of stored energy within the primary loop and core;
– Long-term storage of irradiated fuel: The US has some 70,000 Te of irradiated waste fuel in surface storage (both wet and dry);
– Long-term storage of the actinide wastes if re-processing is undertaken to recover the uranium and plutonium. The US has recently abandoned development of its YUCA Mountain long-term repository;
– Diversion of technology and fissile material for illicit weapons manufacture;
– Transport of high active waste for re-processing and storage;
– Questionable economics due to construction cost escalation and program delays, open-ended decommissioning costs, and unknown long-term storage costs for the large quantities of highly active waste produced;
– Increasingly complex and arduous consenting of new plants and regulation of operating plants, and;
– The unit sizes have increased to 1600 MW in the case of the AREVA EPR, and 1000MW in the case of the Westinghouse/Toshiba AP1000, based on the claimed, but not delivered, improved economics.
The adoption of what have been called 3rd generation nuclear reactors has made the scale of most of these problems even greater than before. AREVA’s recent experience with their first three EPR type reactors under construction bears testament to this, with large cost escalation and major construction delays.
In recognition of these fundamental constraints and problems associated with the current reactor systems, 12 countries are participating in the Generation IV International Forum (GIF), to further research theoretical reactor designs that offer improvements in nuclear safety, proliferation resistance, waste production, resource utilisation, and overall economics. The designs under consideration are grouped as either Thermal Reactors or Fast Reactors.
The Thermal reactor systems under investigation are:
– Very High Temperature Reactor (VHTR)
– Supercritical Water Cooled Reactor (SCWR)
– Molten Salt Reactor (MSR)
The Fast Reactors under investigation are:
– Gas Cooled Fast Reactor (GFR)
– Sodium Cooled Fast Reactor (SFR)
– Lead Cooled Fast Reactor (LFR)
All these reactor types seek to achieve much higher burn-up of the fuel, thereby reducing the magnitude of the waste disposal and re-processing challenges, along with better resource utilisation. However all but the MSR rely on solid fuel, either in fuel rods or in the form of ceramic fuel (usually the carbide forms of uranium or plutonium) dispersed in a graphite matrix. Once again the use of solid fuel introduces limits and constraints on both the reactor designs and the maximum achievable burn-up.
In the case of the MSR, the coolant is a mixture of molten salts and the fuel is dispersed in a homogeneous manner throughout the coolant. This removes all the major limits and constraints on the maximum burn-up that can be achieved. It also offers the best way of using thorium as the main fuel component for the reactor without the need for very complex fuel reprocessing that the use of solid Thorium requires. The MSR studies show that it is capable of breeding more thorium fuel than it consumes, even though it is a thermal reactor.
The origins of the thorium fuelled molten salt reactor (TFMSR) date back to a very successful development program at the Oak Ridge National Laboratory (ORNL) in the USA, culminating in almost five years of successful operation of an 8 MW thermal MSR during the period 1965 to 1969. This program demonstrated the many advantages of the MSR, such as very high temperature operation (650 degrees centigrade), high power densities, the online removal of fission products, and online re-fuelling. This work has been extended in the intervening years to develop designs that breed the fuel from naturally occurring thorium.
Some of the many advantages of a TFMSR are:
– Thorium is three times more abundant than uranium and much cheaper, with Australia having potentially the world’s largest reserves;
– No fuel fabrication are facilities are required since the fuel is not fabricated but dispersed in the liquid salts;
– It can breed its own fissile material within the reactor, thereby obviating the need for enrichment plants as required for uranium, or re-processing plants, with all the nuclear proliferation risks that uranium enrichment and re-processing entails;
– The thorium fuel cycle is very resistant to diversion of fissile material for weapons manufacture;
– It has a very high degree of inherent safety, such that the reactor shuts itself down in the event of any accident or loss of power supplies, without the need for highly engineered safety systems or operator intervention, and is capable of load following;
– The reactor designs have excellent passive safety features thus further obviating the need for complex and expensive back-up diesel generators pumps etc;
– The reactor burn-up of fissile material is not constrained by solid fuel cladding life time, and hence the higher burn-up means that less fuel is required per GW. (One fifth of that in a Generation 3 type reactor);
– The quantity of high active actinide waste is reduced by a factor of between 1000 and 10,000 times that of the current nuclear reactors, due to the very much higher fuel burn-up achieved as compared to solid fuel types of design;
– The small quantity of highly active waste allows cost-effective on-site storage to be considered, thereby removing the need to transport fissile and high active waste materials around the country;
– There are no major stored energy sources within a MSR and hence the secondary containment requirements are reduced both in complexity and cost as compared to a Generation 3 reactor type;
– The fissile inventory required for start up is at least half of that required for a Generation 3 reactor and about a tenth of that required for a fast reactor. Hence the overall fissile inventory for a fleet of MSR’s will be much less that other reactor types;
– No need for very high pressure reactor vessels and coolant loops, since the reactor core and primary coolant loops operate at very low pressures (typically less than 5 atmospheres);
– The molten salt coolant pumping power is much reduced as compared to gas cooled reactors that offer the same high outlet temperatures. This results in a 4-8 per cent gain in thermal efficiency for the same temperatures;
– The high reactor power density results in much smaller and cheaper plants, which can be designed for economic operation at smaller sizes than the current 3rd generation of water-cooled reactors;
– The high temperatures achieved allows the MSR to be considered as the heat source for zero-carbon hydrogen production along with much improved thermal efficiency for electrical power generation;
– The high temperatures achieved make possible the use of dry cooling, and hence allows plants to be sited away from the coast or rivers and lakes;
– Offers a real opportunity to effect a conservative 30-40 per cent capital cost reduction, due to the ability to manufacture the much smaller reactor core and heat exchangers entirely under factory conditions, and shorter construction times;
– The reactor and core can be designed to allow it to burn up actinide waste, thereby reducing the worldwide high active waste disposal problem created by other reactor systems. For instance, the UK has 102 Te of plutonium in storage from its current and past reactor programs. This flexibility to handle different fuels allows a variety of fuel cycles to be used whilst retaining the same basic reactor engineering design.
The successful results of the ORNL experimental MSR form the basis of much of the renewed interest in this type of reactor and establish a foundation of already proven science and technology for the proposed development of a TFMSR reactor system.
The next step is to build a demonstration TFMSR to establish and provide all the scientific information and data required for the design and construction of commercial-sized plants. The results of the ORNL work would form the basis for such design, which would then be revised to incorporate all the current knowledge, and most importantly, the current requirements for improvements in nuclear safety, proliferation resistance, waste production, resource utilisation, and overall economics. A demonstration plant based on such a design would provide the necessary data, construction and operational experience, and scientific knowledge necessary to design and build a commercial-sized power plant.
The costs for such a program have been estimated by a team in Japan as being some $US300 million. Thus with, say, six participating member countries or companies, the individual cost might be circa $US50 million in total over a six year period.
The adoption of the TFMSR as the reactor system of choice for Australia, along with hosting a demonstration TFMSR, offers many benefits that are not available if the existing PWR/BWR systems were selected. Many of these derive directly from the inherent technical characteristics of a TFMSR, but others would derive from the leading role that Australia would play in developing a reactor system that will, in the opinion of many world experts, be the future of nuclear power, due to its ability to overcome the deficiencies of the current reactor systems being deployed.
Set out below are the some of the major benefits that Australia would derive from such an approach:
– Positioning Australia as an international leader in nuclear engineering and science for the future;
– Developing a reactor system that delivers large improvements in nuclear safety, proliferation resistance, waste reduction/ production, resource utilisation, and overall economics;
– Establishing a national nuclear design and construction capability, including advanced manufacturing facilities and competencies;
– Deploying a reactor system with minimal cooling water requirements and hence can be located away from the coast and rivers, etc;
– Reactor unit sizes that are appropriate for the NEM system;
– Opening up the use of nuclear power for direct high temperature chemical processing, such as the production of hydrogen for transportation use, with no consequential CO2 emissions;
– Develop an economic use for Australia’s very extensive reserves of Thorium, and break the 'razor blade' business model used by the current reactor vendors in relation to their supply of new fuel elements;
– Export opportunities in many areas.
In order to progress this proposal the Federal Government will need to develop a detailed policy position, and gain both parliamentary (bipartisan) support and approval, along with community support for such an approach, including the intention to host the DTFMSR.
A number of countries are working in varying degrees on aspects of the TFMSR technologies already, such as the USA, Japan, China, France, India, the Czech Republic, Singapore, Korea, Russia, and Canada. There is currently a “window of opportunity” for Australia to participate with these countries.
In summary, it is time for the federal government to take the lead in initiating a meaningful debate on the commercial nuclear power options open to Australia. The possible adoption and development of TFMSR technology should be part of that debate. It offers Australia the opportunity to establish a leading position in a technology for the future with worldwide export opportunities.
TFMSR – Thorium fuelled molten salt Reactor
DTFMSR - Demonstration Thorium Fuelled Molten Salt Reactor
MSR - Molten Salt Reactor
CCS - Carbon Capture and Storage
U/PU - Uranium/Plutonium
PWR - Pressurised Water Reactor
BWR - Boiling Water Reactor
HWR - Heavy Water Reactor
LOCA - Loss of coolant accident
EPR - The 1600 MW PWR 3rd Generation reactor being built by AREVA
NEM - The Australian National Electricity Market