A main issue for the future of nuclear power plant operation is capital cost of new build. One way to achieve competitive economics is to increase the unit power rating (Oka, 1999), taking advantage of economies of scale. This approach has been adopted by many of the evolutionary water reactors’ designers. The power ratings of some of the proposed evolutionary LWRs may be as high as 1500-1700 MWe, many exceed 1300 MWe. Examples are given in Chapter 10. Large evolutionary designs of LWRs incorporating both proven active safety protection systems and more recently large plants putting more emphasis on passive safety systems, e. g. AP1000 are being proposed.

6.3.2 China

There are currently 8 nuclear power reactors operating in China and there are a further 3 units under construction (World Nuclear Association, 2003; Table 9.2). They contribute to about 1.4% of the country’s electricity requirement. These include Daya Bay 1 & 2 that are standard Framatome PWRs at 944 MWe, which have been in operation since 1994; more recently similar reactors Lingao 1 & 2 started up in 2002.

Qinshan 1 was the first locally designed and constructed plant. This was a medium-scale PWR. More recently Qinshan 2, scaled up from Qinshan 1 entered operation in 2002, to be followed by Qinshan 3, expected in 2003.

Qinshan 4 & 5 are heavy-water reactors based on CANDU 6 technology, each at 665 MWe. These came on stream in 2002 and 2003, respectively.

There are also 2 Russian designed VVER-91 1000 MWe units under construction, Tianwan 1 & 2, under an agreement between China and Russia. These units are scheduled to be in operation by 2004.

More reactors are planned under China’s Five-Year Plan (2001 -2005). These include a further two 900 MWe units at Lingao and up to six more 1000 MWe plants at Yangjiang.

There are further proposals for two 1000 MWe units for Haiyang, two 1000 MWe units at Hui An, and two 1000 MWe units at Sanmen.

The China National Nuclear Corporation (CNNC) has reported that the Sanmen reactors will be PWRs, there are plans for further reactors but the technologies are yet to be decided. Possibilities include a Chinese standard 3 loop design developed in collaboration with Westinghouse or the Framatome CNP-1000 design.

Uranium resources in China are expected to meet the nuclear programme requirements in the short term. Fuel fabrication and enrichment facilities also exist. However, to meet the Country’s objective of being self sufficient in nuclear fuel supply, some additional capacity will be required.

Regarding spent fuel treatment and reprocessing, a closed fuel cycle strategy is the declared objective. Construction of a centralised spent fuel storage facility is in progress at LanZhou Nuclear Fuel Complex. There is also a pilot reprocessing plant under construction to be followed up by a full-scale commercial plant.

China is also studying the feasibility of high-temperature pebble reactors to supply process heat for heavy oil recovery or coal gasification. A 10 MWt plant (HTR-10) was commissioned in 2000. China has also a 65 MWt fast neutron reactor under construction near Beijing, scheduled to achieve criticality by 2005.

This design has been put forward by General Atomics within their GT-MHR development programme as a future plant to produce electricity at high efficiency. It satisfies Generation IV objectives, having passive safety, good economics, improved proliferation resistance and better environmental attributes than the current generation of nuclear plants, in that it has better fuel utilisation and produces less waste. It has a high outlet temperature of 850°C and therefore has the additional potential for hydrogen production via high-temperature electrolysis or water splitting. The technology could be put forward for development within the next generation nuclear plant (NGNP) demonstration project at Idaho national engineering and environmental laboratory (INEEL). The nominal power for a single unit is envisaged to be about 293 MWe. The timescale for a possible construction would not be until about 2009. In regard to the economics, the overnight capital costs for 4 standard units is foreseen as about $1000 per kWe with 20 year levelled generation costs of

3.1 cents per kWh (based on 2003 dollars).

13.9.1 Scenarios

It can be seen from the earlier discussion that there are different ADS concepts being considered based on a number on different sub-critical reactor types.

Some of these reactor types have attracted considerable levels of safety research in regard to critical reactor operation. In principle, there are similar categories of accidents that could occur in ADS sub-critical reactors as could occur in critical reactors (Wider, 1997), see, e. g. Table 13.5.

ADS discussed above have included fast systems with solid fuel and liquid metal (lead or sodium) cooling and fast systems with circulating molten salt/MA. Fast reactors with

gas cooling have also attracted some attention previously. Thermal systems have been considered with circulating molten salt/minor actinide/Pu and graphite moderator. Thermal systems have also been considered with molten salt/actinide/Pu or a water/oxide slurry circulating in pipes with heavy water moderator.

In low-pressure fast or thermal reactor systems, various categories of loss of cooling accidents can occur. Typical examples are loss of flow (LoF) due to pump failure, or loss of heat sink (LoHS) due to pump failure in the secondary heat removal loops, or feedwater pump failure. Loss of decay heat removal is another example.

For high-pressure systems, loss of coolant accidents (LoCAs) are an additional possibility, occurring due to a break or leak leading to a sudden depressurisation, e. g. in a gas-cooled fast reactor.

ADS could also be vulnerable to transient overpower (TOP) in the case of fast reactors. Concerns for fast systems include possible reactivity insertions associated with moderator insertion, or a possible positive void coefficient in the case of a sodium — cooled fast reactor. Under more extreme accident conditions and core meltdown, reactivity insertions could result from fuel movement. Reactivity induced accidents (RIAs) are a possible concern in thermal reactors. In all systems, inadvertent withdrawal of control rods or control rod ejection in pressurised systems are possible scenarios although since ADS are sub-critical there may be fewer control rods than in critical reactors. The accumulation of fissile material in circulating liquid fuel systems or due to extreme perturbations, e. g. due to earthquakes could cause reactivity insertion. Finally there is the question on whether there are scenarios leading to a sudden increase in accelerator power.

As for a conventional critical reactor, a high degree of reliability is required for the operation of the key safety functions. In the case of an ADS, the most important requirements are the accelerator shut-off system and the decay heat removal systems.

The high-temperature test reactor (HTTR) finished construction in 1996 (Figure 14.5). The power rating was 30 MWt and first criticality was achieved in 1998. This reactor includes the annular prismatic fuel design. The core outlet temperature is currently 850°C but may be increased by 100°C following design optimisation. This reactor is one of kind envisaged for process heat applications and, therefore, includes an intermediate heat exchanger with the purpose of supplying process heat.

Research is being conducted at JAERI on the high-temperature engineering test reactor (HTTR) for heat utilisation (Miyamoto et al., 1998). This is the first high-temperature gas reactor (HTGR) to be constructed in Japan. The design is for a 30-MW thermal output and outlet coolant temperature of 950°C. After a satisfactory demonstration period, a hydrogen production system will be fitted. The process will involve steam reforming of natural gas (Hada et al., 1996). It has been demonstrated in out-of-pile tests at 1/30 scale carried out by the Science and Technology Agency (Inagaki et al., 1997).

Nuclear heat of 10 MW at 950°C is supplied from the HTTR to a heat exchanger in a primary helium loop. A secondary helium loop then transfers heat to the steam reformer, which converts steam and methane to hydrogen and carbon monoxide. To provide stability

Steaa

Secondary hetiurn Feed water

Figure 14.5. HTTR hydrogen production system. Source: Miyamoto et al. (1998).

in the event of disturbances in the steam reforming process, a steam generator is installed at the downstream of the steam reformer to keep the helium gas temperature at the steam saturation temperature.

To reduce carbon emissions, further studies are in progress on hydrogen production by water splitting, via a thermochemical iodine sulphur process first proposed by the General Atomic Company (Norman et al., 1982). This is foreseen as an improved potential heat utilisation and hydrogen production process for the HTGR.

In addition to hydrogen production, there are other high-temperature applications being proposed, including the production of gases such as styrene and ethylene.

14.10.1 Generation IV Systems These have been considered in Chapter 12.

Many codes incorporate single rod models, which calculate thermal properties such as stored energy, radial temperature profiles, fission gas release to the gap and mechanical properties such as creep deformation and irradiation growth (NEA/CSNI/R(99)25, 2000). Examples of such codes are COMETHE, FRAPCON, METEOR, TOUTATIS, TRANSURANUS and ENIGMA (Bailly et al., 1999; Table 16.2). For LOCA analysis, it is important to calculate initial stored energy from normal operation conditions. Other parameters that need to be calculated are clad oxidation thickness, the internal gas pressure, and geometrical parameters including the axial clearance between rods and end fittings. It is important to calculate fission gas content in fuel grain boundaries, fuel porosities and fission gas movement between grains and grain boundaries for the analysis of fuel failure mechanisms in RIA transients. Under RIA conditions, pin failure may result if sufficient fuel swelling and grain swelling occur.

In order to calculate these properties fuel performance codes include a wide variety of models for calculating: radial power profiles, thermal conductivity and specific heats of

materials, gap conductance, hydrogen absorption, waterside corrosion, creep properties, mechanical properties, creep properties, stress-strain relationships, fuel densification, and fuel swelling.

In the future, these codes are likely to be called upon to model burn-ups of up to 65 MWd kgU 1 or higher. The FRAPCON code has recently been modified for burn-ups up to 65MWdkgU 1 (banning et al., 1997). Many of the current codes/models were originally developed and validated for more moderate burn-ups of 40 MWd kgU 1 and the applicability of these codes at higher burn-ups is under review. The models will also require review with regard to their application to MOX fuel.

Nuclear power plant operation along with many other industrial plant operations is inextricably linked with a number of environmental issues. These have and are being considered within a global context, e. g. within the UN (Stockholm 1972 and Rio 1992) and also within the EC. National governments are also addressing these issues by charging various government bodies, agencies and commissions to advise on policy and propose discharge consents, etc. to meet national and/or international targets for emissions.

In the UK (Fisk, 1999), a number of enquiries into future nuclear power have addressed environmental issues in their deliberations. For example, within the past few years the House of Lords has conducted an enquiry into nuclear waste, the Environmental Agency has proposed discharge consents for reprocessing at Sellafield and the Royal Commission for Environmental Pollution has considered evidence on energy and the environment. These initiatives have largely been driven to make input to the debate on how the UK can meet greenhouse gas emission targets for the period 2008-2012. This issue has been a consideration in the UK Energy Strategy Review (Performance Innovation Unit, 2002; DTI Energy White Paper, 2003). The greenhouse gas targets are particularly challenging. Figures 2.4 and 2.5 show the dependence on nuclear energy in 2002 with nuclear electricity representing 23% of the total electricity supply. Without new building, the nuclear fraction figure will reduce with the shutting down of all the remaining Magnox stations by 2010, and some of the remaining AGRs by 2020 (Table 2.8).

Fisk (1999) considers environmental issues within the wider context of ‘sustainable development’ to which the UK government is committed. There are a number of definitions of this concept. A common definition is ‘meeting the needs of our generation without compromising the ability of future generations to meet their needs.’ This definition was put forward by the Brundtland at the end of the 1980s. Generally, the term has come to

mean improved welfare for everyone both in the present and the future. The key concept here is ‘improvement for everyone as opposed to improvement for some at the expense of others.’

Sustainable development and nuclear power invoke a number of issues, perhaps the most important is the issue of waste. Nuclear waste can in principle cause harm to future generations, which could certainly result in the future without an adequate waste strategy. Since in most countries at the present time, there is no agreed strategy, the question must be asked whether it is justifiable to continue with nuclear energy power production, thus generating waste in the hope that future generations will be able to solve the problem.

□ Renewable 3%

Different countries may have different levels of acceptability. There are legacies of inadequate waste disposal in some countries that are now posing significant problems (and expense) to resolve. Practices have been adopted that would now not be considered as acceptable, yet were considered so at the time. Thus, levels of acceptability can and do vary from one country to another and will also change with time. Further there may be economic reasons to transport waste from one country to another, perhaps with less stringent environmental standards. Is this acceptable, both from a global environmental standpoint, or indeed from a moral standpoint — clearly the answer should be no.

The liabilities associated with decommissioning nuclear power plants once they have reached end of life are another important issue. These are obviously inescapable for currently operating plant; liabilities are a critical factor with regard to decision-making for the building of new plant. Having adequate decommissioning plans prior to building is now typically a regulatory requirement. In the UK, for example, there must be such a provision. From an economic perspective, there is the issue of whether adequate funds are in place for decommissioning, these may be available through increased price levies, or government underwriting of liabilities.

Aside from the concerns of waste disposal, perhaps the major environmental requirement from the public is that the risk of severe accidents is not only small, but also that if such accidents were to occur they can be effectively managed. This is a particular concern for older currently operating plant, which perhaps (and indeed were) licensed under more tolerant licensing regimes than those of the present day. Such plants may have greater vulnerabilities for severe accidents than some modern plants.

It has been discussed above that an important environmental benefit put forward for continued nuclear power plant operation is that it does not contribute to increased global warming and acid rain. The challenge is how to realise this benefit. National governments may set up infrastructures offering incentives to reduce emissions, which might be achieved either by building of new nuclear plant or through life extension of existing plant. In the latter case though, safety must not be compromised. Pressures to continue operation may be very great where no alternative power producers are available. This may be particularly true in the less developed countries. From an environment perspective, clearly safety considerations and the avoidance of adverse environmental consequences resulting from an accident must be paramount.

The experience from nuclear plant operation has shown that effective plant management and organisational structures are essential to support all operations of plant activity including normal operation, maintenance, refuelling, etc. These are also necessary to achieve the economic performance required by the licensee and to meet the environmental and safety standards required by the regulator.

A good description of practices presently adopted by international bodies and the results achieved is given in IAEA Technical Report No. 369. This book is written in the form of a manual describing a number of ways by which interested parties can transfer to their own situation, the experiences of experts from a number of IAEA Member States. Many of these management practices (developed in the remainder of this section) apply across other large industries.

It requires significant managerial skill to achieve the necessary cost reductions and resource allocations against budget limitations without impacting on the operational and safety performance of the plant. To facilitate these, senior managers must define carefully and communicate to their workforce, the objectives, strategies and criteria in order that correct decisions can be made at all levels to achieve balance between the trade-offs of operational excellence and low cost.

To further the implementation of high standards, an approved quality assurance (QA) programme is usually mandatory, which should be periodically reviewed and updated. International standards such as ISO-9000 are required for many plants (or other comparable quality management systems).

To achieve good operational efficiency, it is important to have a positive and well — motivated work-force and this can only achieved via good employee and management relations. Management must be seen to implement its stated programmes in order to command the necessary respect and support from employees. It must also maintain good relationships with contractors.

In cutting costs to improve efficiency, it may be necessary to reduce staffing levels and this situation may impact adversely on staff morale. Technical Support Organisations can also be impacted if the operating companies place less work outside. This situation must be managed to ensure that the resource reduction is achieved via voluntary staff release as far as possible.

Clearly loss of valuable technical expertise may not result in increased efficiency if there is an inadequate quota of technically trained staff remaining. In many instances, it is the more able staff who leave first during uncertainty and times of change. At a later date, there may be increased costs in recruiting and training new staff in the highly specialised and technical nuclear industry.

Efficiency may be improved via new and more innovative management approaches. New management may consider greater empowerment to lower levels of the organisation. Delays in processes (e. g. signing of routine forms) due to the absence of senior management and the burden on senior management in performing such activities are not efficient. A more imaginative management may introduce simpler work processes.

It is important that the consequences of necessary management decisions to improve efficiency are portrayed in a balanced picture. In times of change, employees may dwell on more negative aspects but for example, reduction in work-force and greater empowerment will mean that the remaining employees have greater responsibilities, more rewarding jobs and more opportunities for promotion. Such positive aspects should be recognised in good management teams.

By virtue of the plant operating licence, ageing plant structures must have sufficient integrity to meet all safety requirements during the latter stages of plant life. However, the impact on the structures from decommissioning operations must also be assessed prior to decommissioning. For example, in the case of the containment, there may be a need to erect another structure to meet the required containment safety function.

In the decommissioning of ageing plants, structural integrity of vital components cannot be expected to meet the present day standards. In this case, the adequacy of the components will need to be considered against ALARP principles.

Current plants in Japan are licensed against Japanese regulatory standards, codes and guidelines. The Japanese approach to safety is harmonised with other international activities through participation in IAEA activities. For example, Japanese utilities participate in the US ALWR initiatives.

The requirements for future ALWRs are being established by both regulator and utilities. In parallel, design programmes for future plants are proceeding with improved safety levels. Current Japanese plants such as the APWR and ABWR have core melt frequencies below 1E-6/reactor year, below the International Nuclear Safety Advisory Group (INSAG)-3 target for future plants of 10E-5/reactor year.