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ASTRID: an option for the fourth generation of nuclear reactors

Why focus on the fourth generation of sodium-cooled fast reactors?

​Managing our energy sources is not only a vital need and a growth factor, but also a key issue for tomorrow's world. In this respect, the nuclear industry has a number of solid advantages, even though it is faced with issues of safety, resource sustainability and waste management, which all call for the pursuit of innovation in technology.

Published on 12 December 2016

​Energy issues

Some figures speak for themselves: the global energy demand will have doubled by 2030 due to the combined effect of population growth – we will have reached 9 to 10 billion in 2050 – and the growth of emerging countries. At a time where available resources are dwindling and where it is becoming increasingly urgent to fight climate change more efficiently, it is vital to exploit low-carbon energy sources that are competitive.

Capable of producing massive amounts of electricity without emitting greenhouse gases, nuclear energy has a number of advantages that makes it a promising solution for the future. Nonetheless, this industry as much as the others, is faced with issues of secure supplies and scarcity of raw materials. In 2014, the available uranium resources were estimated at 69 billion tonne oil equivalent (TOE), compared with 160 for gas and 240 for oil.

Last of all, the multiple recycling of plutonium, the future of long-lived radioactive waste such as minor actinides, and the fight against nuclear proliferation are just as many questions that need to be resolved through innovative nuclear technologies.

Fourth-generation reactors

Launched in 2000 following a proposal from the US, the Generation IV International Forum (GIF) has the objective of promoting nuclear systems of the future.

The forum partners* established an official charter in 2001, which kicked off this collaborative R&D organisation that aims to the feasibility and performance of future nuclear reactor systems. Its objective: to develop reactors with improved safety, sustainability (e.g. more efficient use of uranium), and economic viability compared with other energy sources, while fighting nuclear proliferation, being resistant against terrorist attacks, and generating smaller volumes of ultimate waste.
In late 2002, six different reactor concepts were selected. Three of these concepts involve fast neutrons: gas-cooled fast reactors (GFR), sodium-cooled fast reactors (SFR), and lead-cooled fast reactors (LFR). The others are supercritical-water-cooled reactors (SCWR), very high temperature water reactors (VHTR) and molten salt reactors (MSR).
Heavily involved in this initiative, France is both maintaining a technology watch and leading R&D programmes on all technologies relevant to this fourth generation of reactors. France, through the CEA, is also leading the design studies for an integrated technology demonstrator of a sodium-cooled fast reactor called ASTRID.

* In 2016, the Generation IV International Forum had 14 partners: South Africa, Argentina, Australia, Brazil, Canada, South Korea, China, the US, France, Japan, the UK, Russia, Switzerland and Euratom.

Why has France decided to focus its efforts on fast reactors?

This choice is motivated by the multiple advantages offered by this technology.
The first advantage is that fast reactors can use the plutonium produced by both the current light water reactor fleet and themselves indefinitely, which means plutonium stocks can be managed rationally and durably, thereby confirming plutonium's status as a recyclable material from spent fuel.
The second advantage lies in the fact that fast reactors can burn any type of uranium, whereas the current systems can only handle uranium-235 which is a minority isotope. By utilising all of the uranium in the mined ore, fast reactors multiply the energy that can be extracted from a given mass of natural uranium by a factor of about 100.

With the stockpiles of depleted uranium in France, together with the plutonium produced by spent fuel from the current reactor fleet, the fourth generation of fast reactors will be able to operate for several thousand years, foregoing natural uranium completely.

The third advantage comes from the possibility of fast reactors to transform minor actinides such as americium - long-lived high-level waste - into shorter-lived elements. This process - called transmutation – should make it possible to reduce the emission of heat and the inherent radiotoxicity of ultimate waste in the long-term.

Choosing sodium-cooled fast reactors

The sodium-cooled fast reactor (SFR) is the reference technology for those countries having embarked on the development of Generation IV fast reactors. This technology has been the subject of numerous projects throughout the world, which has led to more than 400 reactor years of operation, including 100 years of industrial operation.

In France, studies are being led by the CEA via the ASTRID project, which will benefit from the operating experience of sodium-cooled fast reactors having operated across the globe, while integrating a number of innovative technological breakthroughs.

Sodium was chosen as the coolant following the analysis of multiple criteria. Other than the fact that it does not slow down neutrons (sine qua non for fast reactors), liquid sodium boasts good thermal properties (conductivity, decay heat removal) and low viscosity, which all make for an excellent coolant. It is also only slightly activated by neutrons, which avoids generating large quantities of radioactive waste. It is not very corrosive either, which makes it compatible with steel. Furthermore, liquid sodium offers certain safety features: its high thermal inertia means that any SFR will behave well in the event an external cooling source (atmosphere, water) is lost. Its main disadvantages lie in its opacity, rendering certain in-service inspection and maintenance operations rather complex, and its high chemical reactivity with water and oxygen in air. These issues are sufficiently well known to allow us to work around them with efficient solutions; for this reason, sodium is not an obstacle in reaching the objectives set for the fourth generation of reactors. 

For the sodium-cooled fast reactor project called ASTRID, the CEA is collaborating with a host of private and public partners. Since 2010, the CEA has been the project owner and contracting authority of this 600 MWe industrial technology demonstrator. Currently in its conceptual design phase, the project is moving ahead according to the schedule defined with the ministerial authorities under the agreement signed by the government and the CEA as part of the Future Investments Programme dedicated to future nuclear systems.