J. N. Lillington

During the last century, nuclear power has been established as a reliable source of energy in the major industrialised countries. It has a potentially important role in the future since it does not contribute to the production of ‘Greenhouse’ gases; a growing concern of continued fossil fuel power generation. The time is now appropriate to review the issues surrounding the future operation of current generation nuclear reactors and consider the potential offered by the new advanced reactor designs that have been proposed for the new century. The main purpose of the book is to present in a single volume the main issues of future civil nuclear power plant operation including the justification and incentives for future continuation, safety considerations and existing national strategies. The survey covers the entire major designs and their associated research programmes.

The evolution of the civil nuclear energy programme has seen the development of different generations of nuclear plant. In the US, the different generations have been designated as follows:

I — early prototype reactors in the 1950s & 1960s;

II — commercial power reactors in the 1970s & 1980s;

III — advanced light water reactor designs developed and certified in the 1990s, and;

IV — future generation nuclear energy systems.

Although this terminology has been introduced mainly in the context of US designs, it will be used more generally in this book in referring to the different generations of reactor systems in question.

The first part of the book reviews the commercial plants currently in operation (Generation II) and focuses on the issues concerning the future operation of these plants.

In the main, nuclear power plants have operated very successfully since the 1950s. Water reactors are the predominant type in the world today, mainly pressurised but there is also a significant fraction of boiling and heavy water reactors. The UK is an exception, where gas reactors are predominant. A brief survey of present day reactors is given in the first chapter.

There are wide ranging issues associated with the future of nuclear power. There are also very different perceptions of the benefits compared with the risks. There have been only a very small number of significant accidents, e. g. Three Mile Island and Chernobyl but these have had a major impact in limiting the expansion of nuclear power. The safety of plants for all aspects of operation, including the management of waste, is a public concern that needs to be addressed.

By far the most important pre-requisite for the continued operation of nuclear power plants is that they should remain safe and reliable. Improved safety has resulted from extensive evaluations of the few accidents that have happened together with a general improvement in all aspects of plant management.

Operational efficiency and reliable performance must be achieved to ensure competitiveness in the world market. Operating margins are being optimised, subject to safety limits, to enable maximum power output. Outage times for maintenance and refuelling are being minimised to produce high load factors.

The drive for improved safety and reliability is leading to improved maintenance operations and better monitoring techniques. The contribution of reactor diagnostics, through noise analysis, to both the safety and performance of operating reactors is increasingly recognised. The development of this technology for application to future and/or advanced plants is considered later in the chapters on experimental and theoretical research.

Modernisation programmes are in progress to improve the safety and performance of the older plants in operation. Some of these activities are being carried out in support of life extension, if there is an economic incentive to extend the life of current plants subject to meeting safety constraints. Many of the older VVER reactors are also being modernised. These include replacement of components to improve station performance, but also the back fitting of safety systems, in some cases to extend the design basis accident envelope.

Improvement of the fuel cycle is an important area of current attention. Holistic approaches are being considered to reduce costs over the whole fuel cycle. There is an increasing trend towards the use of high burn-up fuel. Mixed Oxide (MOX) fuels are also loaded into some present day plant. More is likely to be loaded into future reactors, beneficial as a means of reducing plutonium stocks. Advanced fuel cycles based on a thorium cycle could also be considered in place or uranium and plutonium cycles.

Technical solutions have been put forward for the management of waste and spent fuel. The high level waste component is largely contained in temporary on-site storage and some action will need to be taken to ensure continued safe containment. Further, there is a significant number of plants reaching the end of life over the next decade. This will increase the volume of decommissioning activity and the volume of material waste that will need to be managed.

Advanced reactor issues are considered in the second half of the book.

Design objectives are discussed for advanced reactors. There has been a range of different approaches adopted in the development of new advanced reactor designs to simplify the design and hence reduce cost. Evolutionary designs are being proposed, which represent relatively small perturbations from current technology. Other more innovative or revolutionary designs are also being considered that are substantially different from existing technology and these require major development investment.

Advanced reactors will need to meet continued demands for increased safety. Regulatory issues in regard to the potential licensing of advanced plant will be covered in the book. There are likely to be moves towards more harmonised approaches in licensing, perhaps enabled by an increasing tendency from vendors to seek design certification, as has been the trend recently in the US.

There are significant differences in the rates of nuclear power expansion and contraction across the different ‘nuclear’ countries across the world. A snapshot will be provided of the current status of nuclear industry in these individual countries in respect to their position on potential ‘new build’ or otherwise, likely preferred reactor systems, regulatory and political climate etc.

By taking account of operating experience and safety evaluations of current generation reactors, new advanced reactor designs have been proposed which are competitive and more economic than existing designs, incorporating standardised and simpler components. Increased reliability of safety systems will be a further requirement; an objective in many designs is to include a high degree of inherent safety, by taking advantage of the natural forces, e. g. gravity and natural circulation.

Evolutionary water reactor designs (Generation III) are being designed against these objectives and are most likely to be chosen for any ‘new build’ initiatives at least in the short term (e. g. 2005-2015). The book summarises the most likely candidates in a separate chapter.

A major feature of many evolutionary water reactors is a much greater adherence to inherently (passive) safe design principles. Because of their importance in some water reactors, these principles are discussed in a separate chapter. Some of these principles are also a characteristic of more revolutionary water reactor designs. Inherently safe principles are also adopted in some other (non-water) reactors.

Future generation reactors are covered towards the end of the book. These include both medium (e. g. 2015-2025) and long term (2025 onwards) deployment options. The medium term options include some evolutionary designs from reactor systems that have already been prototyped e. g. high temperature reactors). The long term options encompass the Generation IV systems referred to above. A review is provided on these advanced designs including super-critical water reactors, high temperature thermal and gas cooled fast reactors, liquid metal cooled fast reactors (sodium and lead) and molten salt reactors. These reactor systems collectively provide a capability for a wide range of applications, including electricity generation, plutonium and actinide management, heat applications and hydrogen production.

A discussion of Accelerator Driven Systems (ADS) is included in the book. These provide an alternative to the future generation critical reactors described above since they can be used in similar applications. These utilise spallation neutrons, generated from a proton beam incident on a target, in conjunction with a sub-critical reactor. Designs are being considered for electricity applications and particularly for the incineration of plutonium and the transmutation of waste.

Nuclear heat applications reactors, other than for power generation, are also briefly reviewed in a separate chapter. Non-power producing reactors for low temperature applications such as district heating and desalination are already in operation. High temperature applications for hydrogen production and for the chemical and process plant industries are not yet developed commercially but are seen as potentially important in the future. The future generation reactors, referred to above, would be candidates for these applications.

Several chapters towards the end of the book describe the extensive research programmes (experimental and theoretical) that are currently in progress for the purposes of ensuring the safety and reliable operation of current plant and design certification and safety assessment of advanced plant. These include reference to the available published material from reactor vendors and utilities and the more widely available research published by research institutes. Much of present research focuses on present day plant but much is also relevant to the needs of new reactor design developments.

Thus the book considers the significant designs over the range of different advanced evolutionary reactors through to the more exotic reactor designs being proposed, including fluidised bed and burn-up wave type reactors.

The book concludes with a discussion of likely longer term future requirements of a more general nature. This includes such topics as anticipated future energy and electricity requirements. It describes how new nuclear power producing plant could meet the requirements. The book finishes with a brief summary of non-nuclear power options in relation to the projection of possible overall nuclear development strategies in the next few decades.

J. N. Lillington