WE often hear about next generation nuclear power plants under development and construction worldwide.
These nuclear power plants are designed from the ground up utilising different philosophies and more importantly, different objectives than conventional light water reactors widely in operation today. Figure 1 illustrates how nuclear power plant designs have evolved since the late 1940s up to early 2030s for both large and small capacity needs.
Figure 1: Generations of nuclear power: Time ranges correspond to the design and the first deployments of different generations of reactors. (Source: Technology Roadmap Update for Generation IV Nuclear Energy Systems)
Conventional light water reactors (covered under Generation I up to Generation III+ in Figure 1) boast an excellent track record regarding safety, reliability and economics. They also produce no greenhouse gas emissions and the waste produced is easy manageable and low in volume (not to mention re-usable through reprocessing).
These plants were, however, designed to produce energy only in the form of electricity. Economics is achieved through economies of scale requiring large capital investments and due to the large plant capacity (1 000MW and more), these nuclear power plants need to be deployed in well-established and appropriately sized electricity grids.
The South African electricity grid meets this deployment criterion; however, to cover electricity needs of areas which do not form part of the main electricity grid and smaller grids in other African countries with smaller electricity grids, an opportunity exists in introducing more suitable nuclear power plants.
For this reason, some Generation IV (Gen IV) nuclear reactors become an essential part of the future energy options. These types of Gen IV nuclear reactors aim to improve on sustainability, economics, safety and reliability, proliferation resistance and physical protection.
What is often not mentioned in this list is the additional energy applications Gen IV nuclear reactors are perfectly suited for the environment. With rising population, mostly in the developing world, and climate uncertainties, we need to find more ways to reduce our burden and even our reliance on the environment.
Gen IV nuclear reactors, such as the Very High Temperature Reactor, are designed to maximize efficiency and utilise the process heat generated by these plants for various energy applications in ways that support the United Nations sustainable development goals to transform our world.
We have to face reality, the climate is changing, world population is growing, and often the environment is unable to sustain the demands we place in it. We see droughts hitting our agricultural sector more often, longer and intense. The dams we built (taking up large areas of valuable agricultural land) are going dry. Our resources of oil, coal and gas are being burned to provide for our energy requirements whilst polluting the environment.
As a scientific community, we need to re-imagine the future. A future, not of energy poverty and limiting resources. A future with vast amounts of excess energy, energy that can be utilised to produce clean water from the sea to irrigate and terraform our desert and semi-desert regions, energy to produce clean fuels to meet all our energy demands. Generation IV nuclear plants can do this, and more.
For this article, we have identified two process heat applications that has the ability to completely change our world for the better.
Hydrogen and fuel production
What is hydrogen economy and why is it important when discussing Gen IV nuclear reactors? A hydrogen economy proposes to make use of hydrogen as an energy delivering source. It can be used in transportation (motive power) and converted into energy by Proton Exchange Membrane (PEM) fuel cells. This however requires hydrogen producing plants and infrastructure to deliver the energy source which in the case of South Africa would require a large investment to deploy it in the use of hydrogen for transportation.
For the use in motive power the mechanisms would require some adjustments in the operation of car engines and on-board hydrogen storage technology readiness level is still a barrier that the hydrogen economy needs to overcome. Another barrier to overcome is low-cost carbon-free hydrogen production.
Over 90% of today’s hydrogen is produced by steam reforming which uses natural gas, oil or coal as source of hydrogen. For every million cubic metres of hydrogen produced per day, 0.3 – 0.4 million cubic metres of CO2 are vented into the atmosphere. This implies that using current energy systems, hydrogen production will be ineffective at combating climate change.
Gen IV nuclear reactors have the potential to change this, as they could use nuclear energy to produce high temperature heat for industry use. The high temperature heat can be applied in thermochemical and electrochemical processes to produce hydrogen.
The benefit in this hydrogen production is the lower electricity usage for hydrogen generation by electrolysis by using high temperature steam electrolysis which operates at high temperatures of between 800 to 1 000 °C.
Other industrial scale hydrogen production processes that are considered to be promising is via thermochemical water splitting, specifically sulphur-iodine and copper-chlorine cycles. Therefore, in the use of Gen IV nuclear reactors, process heat can be used to produce hydrogen through a low-cost carbon free process.
The next step in the value chain is the production of methanol. This would mean instead of storing electric energy in batteries one would store energy as a liquid fuel (methanol). Currently methanol production takes place via coal gasification that uses large amounts of water. For each metric ton of methanol produced, 20 cubic meters of fresh water are used. Another method of methanol production is by using a ruthenium catalyst, carbon dioxide from the air and react with hydrogen to form methanol (depicted in Figure 2).
Figure 2: Methanol and synthetic hydrocarbon production.
Gen IV nuclear plants can therefore be used to capture carbon through the use of process heat to make hydrogen and react it with carbon dioxide to make methanol. Nuclear energy has the potential to be the answer to energy security and carbon capture (making it a carbon negative source) the developing world is looking for. This also allows for another income source from carbon trading in future.
Seawater is the largest water source available. Compared with existing fresh water natural resources, its availability is essentially unlimited. Seawater is still relatively unpolluted compared with natural fresh water sources and in many parts of the world fresh water is not easily available, whereas brackish water and seawater are readily available.
The three commercial seawater desalination processes as identified by the International Atomic Energy Agency (IAEA) which are proven and reliable for large-scale production of desalted water, are: MSF (Multi-Stage Flashing) and MED (Multi-Effect Distillation) for distillation processes, and RO (Reverse Osmosis) for membrane processes.
Nuclear desalination is the principle of coupling on-site a nuclear reactor and a desalination plant in order to produce fresh water. The coupling point is the cogeneration steam turbine conventionally used to produce electrical energy and utilising excess steam for process heat. The electrical energy required by the desalination plant can also be supplied by the on-site nuclear reactor.
The advantage of MED is its low energy consumption compared to other thermal processes, because the vapour produced in each stage is used to heat up the feed water in the next effect. Compared to MSF, this not only reduces the energy required for distillation but also the overall electric power consumption. As a result, this increases the effective energy availability of the plant, as the heat would have been wasted without the desalination application.
The major technology in use and being built today is reverse osmosis (RO) driven by electric pumps which pressurise water and force it through a semi-permeable membrane against its osmotic pressure. This accounted for 65% of 2016 world desalination capacity, up from only 10% in 1999. With brackish water, RO is much more cost-effective though MSF gives purer water than RO. RO relies on electricity to drive the actual process and requires clean (filtered) feed water.
Figure 3: Daily demand and supply pattern in South Africa.
In the case of a more electricity intensive method used (when electricity surplus is available) clean water can be stored, while electricity at utility scale cannot – cost effectively that is. This suggests two synergies with base-load power generation for electrically-driven desalination: undertaking it mainly in off-peak times of the day and week, and load shedding it in unusually high peak times.
Historically, electricity produced by base load power plants, providing minimum power production needs, has been demonstrated to be cheaper compared to peaking and intermediate power plants, by utilising flexible loads in this manner it removes the need for expensive to run (and often polluting) peaking power stations (flexible supply), making a much better case for the use of available energy capacity.
It also removes the requirement for expensive energy storage systems, rather “just-in-time” use of excess energy in value adding applications, resulting in the most efficient use of energy conversion and usage. This is particularly useful for plants with high capital costs and low production costs. This opportunity is depicted in Figure 3.
Small and medium sized nuclear reactors (typically Gen IV) are suitable for desalination, often with cogeneration of electricity using low-pressure steam from the turbine and hot seawater feed from the final cooling system. The main opportunities for small nuclear plants have been identified as the 80-100 000 m³/day and 200-500 000 m³/day ranges.
At the April 2010 Global Water Summit in Paris, the prospect of desalination plants being co-located with nuclear power plants was supported by leading international water experts. As seawater desalination technologies are rapidly evolving and more countries are opting for dual-purpose integrated power plants (i.e. cogeneration), the need for advanced technologies suitable for coupling to nuclear power plants and leading to more efficient and economic nuclear desalination systems is obvious.
In December 2015, the "Global Clean Water Desalination Alliance – H2O minus CO2" initiative was launched at the COP21 climate talks in Paris, and called on its 17-nation membership to use clean energy to power new desalination plants. The call was part of the alliance's aim to tackle the water-energy nexus and climate change.
South Africa is of course not falling behind, due to acute water shortages in the region, Eskom announced in May 2017 that it would install a small desalination plant at its Koeberg nuclear power plant. It will produce water solely for the plant initially. Also, Eskom has agreed to support Cape Town authorities if they choose to progress plans to install a small-scale desalination unit for municipal use at the Koeberg site. It would produce 2 500 to 5 000 m3/day, as a demonstration plant for a larger project.
With the opportunities of utilising the energy security and abundance offered by nuclear power, we might be able to one day see our own arid and desert regions transformed into highly productive agricultural land (see figure 3), providing water security, food security, and ultimately eradicating poverty. As nuclear professionals, this is our vision for the future.
Figure 4: Drip Irrigation in Libya, sourcing water from an underground aquifer. It would be better to use purified seawater, preserving the underground systems. It is already possible to grow forests in the desert with this technology.
Recognising these and other benefits that Gen IV nuclear power systems can hold for South Africa, the country has been a founding member of the Generation IV International Forum (GIF) since inception. South Africa continues to participate actively at the GIF, and in doing so keeps abreast of the latest developments in nuclear reactor technology developments globally.
South Africa will be hosting the Generation IV International Forum in Cape Town from 16 to 20 October 2017, having previously hosted it in 2010.
The Generation IV International Forum (GIF) is a co-operative international endeavour which was set up to carry out the research and development (R&D) needed to establish the feasibility and performance capabilities of the next generation nuclear energy systems (i.e. the Gas-cooled Fast Reactor (GFR), Lead-cooled Fast Reactor (LFR), Molten Salt Reactor (MSR), Supercritical Water-Cooled Reactor (SCWR), Sodium-cooled Fast Reactor (SFR) and the Very High Temperature Reactor (VHTR).
The goals of the next generation nuclear energy systems are to improve sustainability, economics, safety and reliability, and proliferation resistance and physical protection. More information can be found on www.gen-4.org.
* This article was co-authored by, from left Joe-Nimique Cilliers, a SAN-NEST research fellow an Nuclear Engineering lecturer at North West University; Dr. Anthonie Cilliers (Pr.Eng), National Coordinator of the South African Network for Nuclear Education, Science and Technology (SAN-NEST); and Prof Jannie Neethling, a SAN-NEST research fellow and Director of the Centre for HRTEM, Department of Physics, Nelson Mandela University.
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