Versatile Oxide Films Protect FeCrAl Alloys Under Normal Operation and Accident Conditions in Light Water Power Reactors

JOM, Dec 2017

The US has currently a fleet of 99 nuclear power light water reactors which generate approximately 20% of the electricity consumed in the country. Near 90% of the reactors are at least 30 years old. There are incentives to make the existing reactors safer by using accident tolerant fuels (ATF). Compared to the standard UO2–zirconium-based system, ATF need to tolerate loss of active cooling in the core for a considerably longer time while maintaining or improving the fuel performance during normal operation conditions. Ferritic iron-chromium-aluminum (FeCrAl) alloys have been identified as an alternative to replace current zirconium alloys. They contain Fe (base) + 10–22 Cr + 4–6 Al and may contain smaller amounts of other elements such as molybdenum and traces of others. FeCrAl alloys offer outstanding resistance to attack by superheated steam by developing an alumina oxide on the surface in case of a loss of coolant accident like at Fukushima. FeCrAl alloys also perform well under normal operation conditions both in boiling water reactors and pressurized water reactors because they are protected by a thin oxide rich in chromium. Under normal operation condition, the key element is Cr and under accident conditions it is Al.

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Versatile Oxide Films Protect FeCrAl Alloys Under Normal Operation and Accident Conditions in Light Water Power Reactors

JOM February 2018, Volume 70, Issue 2, pp 176–185 | Cite as Versatile Oxide Films Protect FeCrAl Alloys Under Normal Operation and Accident Conditions in Light Water Power Reactors AuthorsAuthors and affiliations Raul B. Rebak Open Access Accident Tolerant Nuclear Fuels and Cladding Materials First Online: 15 December 2017 913 Downloads 2 Citations Abstract The US has currently a fleet of 99 nuclear power light water reactors which generate approximately 20% of the electricity consumed in the country. Near 90% of the reactors are at least 30 years old. There are incentives to make the existing reactors safer by using accident tolerant fuels (ATF). Compared to the standard UO2–zirconium-based system, ATF need to tolerate loss of active cooling in the core for a considerably longer time while maintaining or improving the fuel performance during normal operation conditions. Ferritic iron-chromium-aluminum (FeCrAl) alloys have been identified as an alternative to replace current zirconium alloys. They contain Fe (base) + 10–22 Cr + 4–6 Al and may contain smaller amounts of other elements such as molybdenum and traces of others. FeCrAl alloys offer outstanding resistance to attack by superheated steam by developing an alumina oxide on the surface in case of a loss of coolant accident like at Fukushima. FeCrAl alloys also perform well under normal operation conditions both in boiling water reactors and pressurized water reactors because they are protected by a thin oxide rich in chromium. Under normal operation condition, the key element is Cr and under accident conditions it is Al. Introduction Worldwide, the generation of electric power has several sources of energy that can be grouped as: (1) fossil fuels (coal, petroleum and natural gas), (2) nuclear and (3) renewable (wind, solar, hydroelectric, geothermal, biomass, etc.) sources. Figure 1 shows that the world energy consumption in the next two decades will be still dominated (~ 80%) by the burning of fossil fuels (liquid, gas and coal). Nuclear energy represents only 6% of the energy consumed worldwide. In the USA, 30% of the consumed natural gas is used to generate about 20% of electrical power produced in the country. On the other hand, 100% of the nuclear energy produced is used to generate electricity. This nuclear electricity also represents about 20% of all the electrical power produced in the country. The president of the Nuclear Energy Institute in the US said that one of her top priorities is to ensure the continuous “safe, reliable operation of the US commercial nuclear reactors” to avoid their premature retirement, which would be replaced by the burning of more natural gas, increasing the emissions of greenhouse gases.2 Currently, there are 99 operating power reactors in the US, 34 boiling water reactors (BWR) and 65 pressurized water reactors (PWR).3 Figure 2 shows in which year these power reactors were connected to the grid, affirming that 89% of the current reactors are at least 30 years old and 45% of the reactors are at least 40 years old. Only one new reactor was connected to the grid in the last 20 years. Currently, four new reactors are under construction in the USA. The existing nuclear power plants (NPP) in the USA are an aging infrastructure, which are investing a bare minimum in upgrades and maintenance.4 It is important to make these NPP safer in their operation for the remaining of their useful life. Open image in new window Fig. 1 World energy consumption by fuel (US Energy Information Administration 2016). Reproduced with permission from Ref. 1 Open image in new window Fig. 2 The age of the operating NPP reactors in the USA. Reproduced with permission from Ref. 3 After the Fukushima NPP black-out following the tsunami on March 2011, the international community has been dedicated to finding a fuel configuration that will be more resistant to a loss of coolant accident (LOCA) than the existing zirconium/UO2 pellets. The massive building explosions at the Fukushima plant were caused by the ignition of hydrogen gas formed by the fast-exothermic reaction of zirconium with water (or steam). $$ {\text{Zr}} + 2{\text{H}}_{2} {\text{O}} = {\text{ZrO}}_{2} + 2{\text{H}}_{2} + {\text{Heat}} $$ (1) There is currently an international research effort to delay the generation of hydrogen gas and to expand the coping time allowed for quenching or cooling the reactor after a severe LOCA. There are several proposals on how to design an accident tolerant fuel (ATF) or an advanced technology fuel (ATF) that will permit for a safer operation of the existing light water reactors.5,6 The ATF proposals include the use of iron-chrome-aluminum (FeCrAl), silicon carbide (SiC), and coated zirconium or molybdenum (Mo) claddings. FeCrAl is the concept that would provide the fastest implementation for the safe operation of the remaining NPP for another 40 years.7 The proposed ATF configuration will use the (...truncated)


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Raul B. Rebak. Versatile Oxide Films Protect FeCrAl Alloys Under Normal Operation and Accident Conditions in Light Water Power Reactors, JOM, 2017, pp. 176-185, Volume 70, Issue 2, DOI: 10.1007/s11837-017-2705-z