Recent advances in water cooled reactor (WCR) technology include significant improvements in the design of safety systems, changes in fuel designs to improve resource utilization while reducing the volume of spent fuel, and making plants more economical to operate and maintain. Another important aspect is the development, design, testing and construction of small modular, factory-built integral pressurized water reactors.
"More than 90% of the world's operating nuclear power reactors are light water reactors and heavy water reactors," said Dohee Hahn, Director of the IAEA Division of Nuclear Power. "Water cooled reactors will continue to play a major role in nuclear electricity generation, and possibly other applications, for many more years." Also, the majority of nuclear reactors under development and construction are water-cooled.
Member States' activities and international collaboration on developments and innovations in WCR technology were the focus of this year's joint meeting of the IAEA Technical Working Groups on Advanced Technologies for Light Water Reactors (TWG-LWR) and Heavy Water Reactors (TWG-HWR) that met at the IAEA Headquarters in Vienna on 12–14 April 2016.
"It is interesting to note that, in addition to China and Russia, LWRs are also the preferred technology choice in many newcomer countries or countries with smaller nuclear power programmes that are actively pursuing new builds," said David Nicholls, Chief Nuclear Officer of Eskom, South Africa's electricity generating company, and Chair of the TWG-LWR.
Light water reactors are the most common WCRs worldwide and are divided into two types: pressurized water reactors (PWRs), which produce steam for the turbine in separate steam generators; and boiling water reactors (BWRs), which use the steam produced inside the reactor core directly in the steam turbine. All LWRs require uranium fuel that is enriched in the fissile isotope, U-235.
"Although the HWR fleet is much smaller than the LWR one, it is still making an important contribution to electricity production in countries such as Argentina, Canada, China, India, Republic of Korea and Romania," said Rick Didsbury, General Manager for Research & Development Operations at the Canadian Nuclear Laboratories in Chalk River, Canada, who chairs the TWG-HWR. "HWRs have a lot of potential for the future in optimising resource utilization: for example, China is looking at using recycled uranium, India is continuing its thorium programme, and there are also opportunities for the use of HWR technology to dispose of civilian plutonium inventories, as in the UK example."
Heavy water reactors use "enriched" water, the molecules of which comprise hydrogen atoms that are made up to more than 99 per cent of deuterium, a heavier hydrogen isotope. This heavy water, used as a moderator, improves the overall neutron economy, allowing uranium fuel to be used that does not require enrichment.
As advisory bodies on advances in WCR reactor technologies, both working groups proposed new areas of common interest that may form the basis for future IAEA activities. Among the suggested topics, to be harmonized with other ongoing and planned projects, are innovative LWR and HWR concepts to further improve economics and sustainability, recent innovations in digital, prognostic and diagnostic technologies to improve human performance during high-stress situations, reduction of the environmental impacts of nuclear power plants (NPPs) during normal operation, and exploring the use of thorium to optimize current fuel cycles. Also proposed was further work on defining an extended NPP design basis, meaning that existing and new NPPs can prevent and mitigate accident scenarios that might be more severe than those considered at the time of plant design.
Both TWGs are long-standing, with the TWG-LWR established in 1987, and the TWG-HWR in 1997. They comprise experts who, in their personal capacity, provide advice and support for IAEA programme implementation, reflecting a global network of excellence and expertise with the purpose to advance WCR technologies.