ACCIDENT TOLERANT FUEL | SPECIAL REPORT U3Si2 U3Si2
USA-Westinghouse + SiC/SiCf cladding
+ Cr coated Zr cladding USA-EPRI Lined Mo cladding USA-ORNL
FeCrAL cladding SiC/SiCf cladding
USA-GNF FeCrAL cladding KOREA-KAERI AFRICA
SOUTH AMERICA
Cr doped + FeCrAL cladding SiC/SiC cladding Microcell fuel
AUSTRALASIA & OCEANIA
SPAIN-ENUSA Cr coated Opt ZIRLO
FRANCE-FRAMATOME CEA Cr doped + Cr coated Zr SiC/SiC cladding
NORTH AMERICA EUROPE ASIA JAPAN
FeCrAL cladding SiC/SiCf cladding
GB-NNL (with W) U3
Si2 fuel RUSSIA
Cr coated Zr SiC/SiCf
CHINA
FeCrAL cladding SiC/SiCf cladding
Coated Zr cladding UNSiy
fuel
FCM Fuel (Fully Ceramic Microencapsulated matrix)
Left, figure 1: Map showing ATF fuel projects from different vendors and the different types of advanced fuel Source: Nicolas Waeckel
The origins of ATF Nuclear fuel has been subject to continuous development over the past 40 years and has reached a stage where it can be safely and reliably irradiated up to 65 GWd/tU in commercial nuclear reactors. During this time, there have been many improvements to the original designs and materials, but the basic design of uranium oxide (UO2
) fuel
pellets clad with zirconium (Zr) alloy tubing has remained the fuel of choice for the vast majority of commercial nuclear power plants. However, severe accidents, such as those at the Three Mile Island plant in 1979 in the US and at Japan’s Fukushima Daiichi NPP in 2011 showed that, under extreme conditions, nuclear fuel will fail. Under certain circumstances, high temperature reactions between zirconium alloys and water will lead to the generation of hydrogen, with the potential for explosions to occur. During the earthquake and tsunami that seriously
damaged the Fukushima Daiichi plant in 2011, the reactors shut down immediately but fission products in the fuel continued to release decay heat. Zirconium alloys in the cladding of the fuel assemblies oxidise rapidly at temperatures a few hundred degrees higher than normal operating temperatures, leading to disintegration of the fuel rods and rapid corrosion of the cladding. This process released hydrogen causing explosions that further damaged the plant. This disaster prompted researchers to begin developing
accident-tolerant fuel solutions which would allow more time before active cooling is required in a loss of coolant accident (LOCA) or, even better, would be able to indefinitely withstand the sustained high temperatures created by decay heat and insufficient cooling, thus preventing or delaying the release of radionuclides during an accident. Research, focused mainly on the design of fuel pellets and cladding, as well as interactions between the two, almost immediately got under way in key nuclear countries such as the USA, Russia, France the UK, South Korea, Japan and China. This research has been supported by international bodies such as the International Atomic Energy Agency (IAEA) and the OECD’s Nuclear Energy Agency (NEA).
ATF and the IAEA The IAEA has been supporting international co-operation among member states in fuel development since the 1980s, long before the Fukushima accident. This included efforts to enhance the capacities of computer codes used for predicting fuel behaviour, within the framework of Coordinated Research Projects (CRPs). However, the Fukushima accident demonstrated the need for adequate analysis of all aspects of fuel performance to prevent a failure and to predict fuel behaviour in accidents, as well as the need to test and model the behaviours of ATFs. The IAEA works through technical meetings, consultancy
meetings, conferences, and CRP activity. Two CRPs were organised in the wake of Fukushima to focus on the modelling and testing of nuclear fuels and ATFs in design basis and severe accidents. The first CRP on “FUel Modelling in Accident Conditions
(FUMAC)” (2014-2018) sought to better understand fuel behaviour in accident conditions by identifying best practices in the application of relevant physical models and computer codes, used by different member states, and the enhancement of their predictive capacities. Well checked results of accident simulation experiments and their analyses with advanced fuel performance codes were carried out in the CRP and the results published in an IAEA technical document in 2019. The second CRP on “Analysis of Options and Experimental
Examination of Fuels with Increased Accident Tolerance (ACTOF)” (2015-2019) dealt with the acquisition of data through experiments on advanced technology fuel types and cladding materials. It also looked at development of modelling capacity to predict the behaviour of the components and the integral performance of ATF designs under normal and transient conditions and sought to demonstrate improvements under severe accident conditions. These results were published in an IAEA technical document in 2020. Based on recommendation of an IAEA Technical Meeting
(TM) on Modelling of Fuel Behaviour in Design Basis Accidents and Design Extension Conditions in May 2019, a new CRP on Testing and Simulations of ATF was launched
www.neimagazine.com | January 2024 | 37
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45
