3.4.1 Individual Protection

There are approximately 11 million radiation workers worldwide, (IAEA/NSR/2002, 2003). Standards of radiological protection in the nuclear industry are very high and are probably more advanced than those in practice in the non-nuclear industry. The science is also very mature although there is some need for greater harmonisation of terminology, quantities and units. The IAEA works closely with employers, regulators and workers through the International Labour Organisation (ILO) in the continuing development of safety standards for occupational protection. The agency is also involved with radiological protection of individuals in general, including for example the protection of patients undergoing radiology.

5.6.3.1 Present

Magnox and AGR. The objective of UK fuel cycles has been to maximise energy production, while minimising costs and effects on the environment. To this end UO2 is recycled in AGRs and the AGR and Magnox fuel cycles have been harmonised. About 15,000 t of reprocessed Magnox uranium has been recycled, re-enriched and used in the production of 1500 t of AGR fuel (Ion and Bonser, 1997). Considerable experience has therefore been amassed on manufacturing fuel from recycled spent fuel.

Advanced plant designs are being developed to meet the requirements of utilities and regulators discussed above. They aim to provide significant improvements in performance and safety over current generation plants.

As stated earlier, advanced power plant designs are often separated into two categories, evolutionary and innovative, see for example (Juhn, 1999). Evolutionary plants are based on an evolution from an existing design through relatively small changes. The aim is to remain with design features that are proven and hence to reduce technological and other risks. Evolutionary reactors have been developed through the 1990s taking advantage of lessons learned from existing plants. These designs are, therefore, at an advanced stage of development. A number of designs have already received design certification.

Innovative designs incorporate much more radical changes in design compared with existing plants. They may include features that need verification and hence give rise to

less quantifiable risk. By definition these designs are not likely to be available for at least several decades. Table 7.6 gives some indication of the relative investment that is needed between the two categories of plant, before reaching commercial operation.

Sweden currently has 11 nuclear power reactors operating, producing about a half of the country’s electricity (World Nuclear Association, 2003). In 1980, a referendum was called to examine different options for phasing out nuclear energy. It was decided to continue the operation of existing plants and to complete those under construction provided that it remained economic to do so. The anticipated time period was assumed to be for 25 years, the end of their planned operating lives. At the time, the Swedish Parliament decided against any further expansion of nuclear power with an aim of decommissioning all reactors by 2010.

There had been political manoeuvrings over the last few decades to close Barseback 1 and 2. These are several 600 MWe BWRs operating within about 30 km of Copenhagen and therefore close to the Danish border. In 1997, an agreement was forged between the various political parties to close one unit by mid-1998 and the other unit by mid-2001. In return, the remaining 10 reactors might be allowed to run for 40 years. In practice, unit one was closed in 1999 but unit 2 continues in operation.

Public opinion has been largely supportive to nuclear energy. In a 2001 poll, 75% of people gave the restriction of greenhouse gas emissions as the top environmental priority, only 10% voted for phasing out of nuclear power. On nuclear power matters in general about 76% voted for some degree of nuclear power continuation in Sweden.

Environmental quality is of very high importance in Sweden with commitments to stabilise carbon dioxide emissions at 1990 levels by 2000. A full nuclear power phase out would in fact increase carbon dioxide emissions by about 50% above the 1990 level.

With regard to waste management, there has been an intermediate level waste repository near Forsmark since 1988. For high-level waste, there is the CLAB repository at

Oskarshamn that has been operating since 1985. This is a temporary solution; the fuel will be stored under water in an underground rock repository for about 40 years. It will then be encapsulated in canisters for burial in a 500 m deep repository. Research is underway at the Aspo Hard Rock Laboratory; candidate repositories are at Oskarshamn and Osthammar, at Forsmark.

12.2.1.1 SCWR (Gen IV). The Generation IV supercritical water cooled system is a thermal reactor aimed at electricity production as the primary option (Figure 12.1).

Pump

Figure 12.1. Supercritical water reactor. Source: NEA Annual Report (2002).

The option is, however, retained of converting the core design to a fast spectrum to enable actinide recycle.

The reference plant has 1700 MWe power at an operating pressure of 25 MPa above the thermodynamic critical pressure of water. The outlet temperature has a reference level of 510°C but this could range up to 550°C. The system has a high efficiency of 44% (The US Generation IV Implementation Strategy, 2003). This results in good economics, further enhanced via a simplified plant design. However, due to its corrosive high-temperature water environment, the SCWR requires significant materials development. Further developments are also required to address a number of operational safety issues.

12.2.1.2 SCLWR. The study (Squarer et al., 2001) takes the University of Tokyo’s Super Critical Light Water Reactor (SCLWR) as one of the most likely economically competitive of the proposed designs. It can also be designed as a fast reactor that could be fuelled with MOX fuel of around 12% enrichment.

The high-performance LWR size scales considered by Japan (Squarer et al., 2001) are based on the following parameters for core and fuel design, reactor pressure vessel, containment, turbine and balance of plant. The scale is that of a large 1000 MWe power output, at 25 MPa pressure and 500°C outlet temperature. It has 4.2 m active core height, 121 fuel assemblies with 8 mm OD fuel pins, and control rods inserted from the top, 3.380 m RPV ID and 27.5 MPa design pressure, a cylindrical containment with a turbine frequency of 50 cycles s_1. It can be seen that this design is consistent with the Generation IV reference design.

12.2.1.3 B-500 SKDI. The B-500 SKDI design from Russia (Silin et al., 1993) is based on a natural circulation, integrated supercritical pressurised water reactor system, at a smaller scale and power; reference power is 515 MWe.

LANL has been studying accelerator driven transmutation technology (ADTT) for the destruction of nuclear waste and for generating power by systems which do not generate hazardous waste, and destroy their own waste. One particular approach called the accelerator driven energy production (ADEP) process, generates nuclear energy from thorium, avoids the production of plutonium and destroys its long-lived high-level fission product waste (Bowman, 1997).

The system is based on 232Th, which is converted by neutron absorption to the fissile component 233U from which the energy is generated. The system contains a target/blanket that contains the fissile material and the waste to be destroyed. A continuous chain of fissions is produced, by an external neutron source that allows for the expenditure of neutrons on waste destruction (there are about 5-10% fewer neutrons than would otherwise be necessary to maintain a chain reaction). Thus without this external source, the system would not be self-sustaining.

In the ADTT, an 800 MeV proton beam is directed onto a lead target in an assembly containing the target and a surrounding blanket including the fissile material. The blanket acts as a moderator and consists mostly of graphite and molten salt containing the fissile fuel as an actinide fluoride. The graphite and molten salt are compatible; this has been established from long-term experience with the molten salt reactor at ORNL (Weinberg, 1970). The system multiplies the neutrons produced by the beam by about a factor of 20 operating at a keff of 0.95. Heat is removed from the blanket by internal heat exchangers, which transfer heat from the primary working salt to a secondary external salt stream, thence to a steam generator for electric power production. The majority of power generated goes to the grid; about 10-15% is used to power the accelerator. The liquid fuel system is continuously fuelled. It is regularly cleaned to enable fission products to be continuously removed.

The accelerator transmutation of waste (ATW) project is part of the ADTT programme. It has the specific objective to destroy the actinide and long-life fission products from waste arising from the commercial nuclear programme. ATWs are considered in the molten salt thermal spectrum, see Figure 13.3, and liquid lead-bismuth in the fast spectrum.

The VGM-P is a pilot industrial modular helium-cooled reactor designed by OKB Mechanical Engineering, Russia (Figure 14.4). It is based on a pebble bed design approach that can be fuelled on line. It is being considered as a heat source for the various applications above (Golovko et al., 1995, 1998).

Oil and coal refining require different temperature levels. The industry requires high-temperature capabilities for the production of diesel from coal and for the production of hydrogen and fertilisers, etc., intermediate temperatures for secondary reprocessing of oil products and cracking, and low temperatures for initial reprocessing of oil products.

15.15.1 Construction

Much has been learnt from constructing the present generation of plants. Clearly, the minimising of time from the start of construction to commissioning is important. Research into finding generic ways of delivery of components to site is important.

There is a move in the evolutionary and innovative designs towards increased modularisation. Simplified designs and composite construction can reduce the amount of site work required, and therefore reduce cost.

There are some novel sitings for certain reactor types that are being proposed, e. g. barge type systems, which may be appropriate for some remote areas.

There may also be lessons that can be learned from other industries.

As noted earlier, the emphasis of the power generation industry in many sectors (e. g. Europe and North America) at the present time is the continued successful operation of existing plant, rather than the building of new plant. The main economic reason behind this position is the high capital cost of new plants, a degree of stagnation in demand, and the availability of cheap gas.

Operation of current plant will continue provided that they remain not only economic but also safe and environmentally compliant with regulatory guidelines. To be economic, a number of factors need to be considered and these are sector dependent. The plant may need to operate in a de-regulated market in competition with other generators. The economics will depend on electricity prices, which may be reducing, and also on other operating costs. These issues are discussed below. Clearly, overall costs have to be achieved against budget and kept to a minimum, without compromising safety of the plant.

The economic competitiveness of nuclear power plants has been the subject of several OECD studies (Wilmer and Bertel, 2000). These studies have analysed the projected costs of generating electricity compared with alternatives. In Wilmer and Bertel (2000), ‘levelled cost comparisons’ are presented from 12 countries, each providing information for at least one nuclear unit and one alternative. The costs were calculated making common assumptions. For nuclear plants, these included a 40-year lifetime and a 75% load factor. For gas-fired plants, the assumptions included the cost of replacing major equipment after around 20 years. The costs were levelised at 1997 costs.

Nuclear generating costs are the most sensitive to discount rates. The above Table 2.2 indicates that at the time of the study, nuclear power is competitive at 5% discount rates but loses its competitive margin at 10%.

There are several safety issues associated with the operation of research reactors that are being considered by the IAEA (IAEA/NSR/2002, 2003). There exist reactors that have been shut down for long periods with no definite plans concerning their future, i. e. whether and how they might be restarted or decommissioned. Most of the reactors within IAEA Member States are in countries where there is an established regulatory regime that covers all nuclear installations.

Another issue that has been identified has been the storage of spent fuel and nuclear waste at research reactor sites. An IAEA international conference on research reactor utilisation, safety, decommissioning and fuel and waste management will take place in 2003. This will provide a forum for all interested parties, reactor operators, vendors and regulators to share experiences and develop priorities (IAEA International Conference, 2003a).