The road to a zero carbon future?

Nuclear energy can provide centralised stable power.

Small, modular nuclear reactors will expand the use of nuclear power in remote or mobile applications.
Fusion, which promises a limitless energy supply without harmful wastes, is still far in the future. Extending the life of current reactors, the safe operation of new reactors, the successful implementation of advanced reactor designs, and viable solutions to nuclear waste disposal are all crucial to the continued expansion of nuclear power. Small, modular nuclear reactors will expand the use of nuclear power in remote or mobile applications, but security issues must be addressed before these power sources can be implemented securely.

According to statistics from the International Atomic Energy Agency, there are currently 441 nuclear power plants worldwide, with a total installed capacity of 375 gigawatt electric, five power plants that have been shut down, and 60 more that are under construction. In France, nuclear power already has a major share of the energy market. China has plans for nuclear power on a massive scale, aiming to develop more than 100 power plants in the next two decades. A resurgence of interest in nuclear power is being experienced in the United States, where 80 reactors are having their licences renewed and many new licence applications are under consideration.

To date, with the exceptions of Sweden and Finland, no country has managed to find a technically and politically acceptable solution for permanent waste disposal. Temporary storage of spent fuel near reactor sites postpones the need to find a permanent solution, and increases safety and security risks at each site. The reprocessing of spent fuel and use of breeder reactors may create, in addition to waste, materials that could be used in weapons.

Life extension and risk management
In the next decade, almost all the reactors in the US will have exceeded their original design life of 40 years. By 2030, nuclear electricity generation is expected to decline, unless additional life extension or new constructions take place. Several major issues are involved: (1) the safety of operating reactors, especially from hitherto unknown failure modes; (2) fuel reliability and performance; (3) obsolete instrumentation and controls; (4) design and risk analysis tools based on legacy knowledge and computational tools, and; (5) loss of a trained workforce.

Reactor pressure vessel material degradation through continued radiation damage is an issue for any life extension process. Since some of the current failure modes had not been anticipated in the past, there is concern regarding the occurrence of new failure modes over time. Efforts are under way to develop multi-scale models that link the properties of fundamental materials at an atomic level to failure modes, and attempt to predict future failure modes.

Improved understanding of materials degradation mechanisms will prompt the development of suitable monitoring systems. For example, monitoring reactor components for temperature, radiation, and corrosion using networked wireless sensors will improve the safety of systems through redundancy. But the reliability of wireless systems and their proper function in a radiation environment are among the key uncertainties.

In addition to improved technologies, human factor designs will be enhanced and a safety culture implemented. The loss of experienced workforce due to retirement will be addressed through expanded educational, training and 
research programmes. 

Advanced reactor designs
Advanced nuclear reactors with standardised designs and passive safety features are being developed to ensure reduced construction time, increased safety, and improved operating efficiencies. Over the next 10 years, it is likely that new reactor designs will be incremental improvements on existing water-cooled reactor designs.

Beyond 2030, radically new designs, called Gen IV reactors, may come on-stream. These will be either small, modular reactors (SMR) with 10 megawatt electric to 311 megawatt electric capacity that can be used in a much more flexible manner or high temperature reactors that use helium as a heat transfer medium. 
The SMR may be returned, completely sealed, to its original factory for dismantling and disposal following usage. Small reactors may be employed in remote locations for power production or other applications such as desalination. 

Monitored storage system
The spent fuel from nuclear reactors contain some of the original U-235, depending on the burn-up of the fuel. In total, these account for about 96% of the original uranium and over half of the original energy content. This fuel is reprocessed in Europe and Russia to separate the uranium and plutonium from other high-level radioactive wastes that are recycled as mixed oxide fuel. A new reprocessing plant is being commissioned in Japan, which has been shipping its spent fuel to Europe for reprocessing.

In the US, reprocessing was prohibited due to concerns about proliferation of plutonium. There are currently about 270 000 tonnes of fuel in temporary storage with annual contributions of about 12 000 tonnes. With a 20% increase in capacity, this would rise to 14 000 tonnes per year.

Nuclear fusion
Nuclear fusion, which could potentially provide a limitless supply of energy without significant waste production, has been the dream of scientists for decades. Two approaches to fusion energy are being pursued: the ITER programme uses a toroidal Tokomak reactor to confine plasma by a magnetic field to obtain the high temperatures needed for fusion. 
The NIF (US) and HiPER (Europe) programmes use intense lasers to compress pellets of deuterium and tritium to generate fusion. The heat from the fusion is then used to generate steam to power turbines. Recent progress by NIF has been encouraging, but commercial application is still at least two decades away.    

This article is an extract from the DNV report, “Technology Outlook 2020”. Reproduced with permission.
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