By Kok Boon CHONG
Fossil fuels dominate the global energy sector, contributing 42 percent of all the carbon emissions for the year 2015 alone, a trend that is likely to persist into the future. As such, given the massive amount of greenhouse gases pumped into the environment, it is almost certain that the targets set for the Paris Agreement will not be achieved if countries fail to adopt, more rapidly, the low carbon technologies as replacement to the current dominant source of energy: the cheap but dirty fossil fuels. In our efforts to decarbonize our energy mix, we have to closely consider multiple low-carbon energy technologies in order to ensure that we maintain energy security, economic viability, environmental concerns, as well as public health and safety. We should be aware however, that while renewables should be heavily emphasized in growth, renewables alone might not fit all our energy demands. Therefore, nuclear energy is a necessary consideration to drive the deep de-carbonization of the energy sector.
As one of the currently available technologies for power generation, nuclear fission is an energy source that is capable of supplying massive amounts of energy at a high capacity factor (a factor of average energy output over time, compared to the maximum possible output). In the absence of rapid breakthroughs in the field of environmentally-friendly energy storage, nuclear energy will be required in the energy mix. However, to maintain nuclear energy as part of the energy mix requires a comprehensive set of technical knowledge and expertise, as well as strict regulations and policy. Therefore, even the pettiest detail involved in its deployment is important for increasing the safety margins of the reactors producing the needed power. Hence, the study described here is part of an ongoing research for future Generation IV reactors, which include reactor designs with potential for commercial applications. Among the objectives aspired towards are improved safety, better sustainability, increased efficiency and lower cost.
Nuclear reactor applications such as fuel cladding (outer containment for nuclear fuel rods) or fuel channel commonly utilize zirconium (Zr) alloys, materials that exhibit a low neutron absorption cross section (important for increasing safety margin during the shutdown of the nuclear reactor) as well as high mechanical strengths and corrosion resistance. This study aims to improve the service duration of the Zr cladder. The goal is not limited to increasing the life span of the nuclear reactor or improving efficiency, but would also reduce the associated environmental issues, especially the high radon emission from loss-of-coolant accidents exemplified by the Fukushima Daiichi Nuclear Power Plant in 2011.
Corrosion in zirconium alloy is a complex electrochemical process influenced by many factors, including the properties of the metal/oxide interface, water chemistry, pressure, irradiation, and time. Tracking the results of the corrosion will aid in the development of slow-corroding alloys required for improving the management of fuel burnup, as well as the efficiency and safety features of the nuclear reactors. Therefore, a study (discussed in the publication below) was made to offer a mechanistic explanation of the interplay between the few essential parameters associated with the corrosion process required for advancing the development of the alloys for sustaining a safer production of nuclear energy.
The study divulges the direct evidence between the probed stress-field and “breakaway” transition in the Zr cladder under the harsh environment inside the reactor, where the ‘’breakaway’’ transition will lead to fuel failure because of the dissipation of the radon gas from the fuel container into the cooling reservoir. Presently, the practice of the nuclear energy industry is to allow for one fuel failure for every one million fuel pin. However, such a failure is not easily predictable, as that requires the exercising of a rather cumbersome in-services reactor inspection, which makes for an extremely challenging situation when predicting the lifetime of the fuel cycle needed for maximizing the economics of nuclear energy without compromising on safety. The study contributes to working around this problem, as an engineer can use the results to improve reliability in the prediction of the lifetime of the nuclear fuel technology through improved design of the alloys deployed in nuclear reactor technology.
The original publication "Evolution of stress fields and phase content in corroded zirconium cladding materials" could be found in the Surface and Coatings Technology journal. The article presents a mechanistic explanation of the corrosion process from early to late stage.