Increase the safety margin for nuclear plants

TRME NuclearIAEA experts depart Unit 4 of Fukushima Daiichi Nuclear Power Station on 17 April 2013 as part of a mission to review Japan’s plans to decommission the facility after the accident in 2011. Earlier this year, lethal levels of radiation were detected at the plant. (Image source: Wikipedia Commons)Rising electricity demand has prompted several Middle East and North African (MENA) countries states to turn towards nuclear power to diversify their sources of energy and reduce their carbon footprint

The Barakah nuclear plant in the UAE is currently under execution whilst projects in Egypt, Jordan and Saudi Arabia remain at the planning phase. By 2030, MENA is expected to have added 15.8 GW of nuclear capacity. At present, 2.4 GW of nuclear power facilities in MENA are complete - of which only 1 GW is operational, 5.4 GW are under construction and a further 8 GW are planned by 2030.

As more and more countries such as the UAE, Saudi Arabia, Turkey and Egypt are opting to go nuclear as a key source of power in their energy mix, a number of technical aspects are coming to the fore. Safety is, quite naturally, chief among them. While nuclear power has widely been acknowledged as the safest type of power generation, its constantly evolving technology means that nuclear power plants are becoming ever safer.

A systematic approach to safety margins and the subsequent margins management options represents a vital input to the licensee and regulatory analysis and decision making that will be involved.

Specifically, one of the areas the nuclear industry has been intensely focused on is developing different types of reactor fuels that are more robust and have improved performance during normal and accident conditions. The resulting technology has been dubbed accident tolerant fuel (ATF) – a term used to describe new technologies that further enhance the safety and performance of nuclear materials.

ATF technologies have been under development since the early 2000s. However, it received a marked boost in the wake of the Fukushima accident in March 2011. These technologies create opportunities to modernise the industry and regulatory oversight and improve safety. Earlier this year, at the International Forum ATOMEXPO-2018, which took place in Sochi (Russia), vice-president for R&D of Rosatom, Alexander Ugryumov announced that a new tolerant fuel resistant to accidents would be tested at the Scientific Research Institute of Atomic Reactors (SSC RIAR) in Dimitrovgrad later this year.

Speaking about ATF, Ugryumov said, “First of all, we exclude and try to reduce the amount of hydrogen produced during a severe accident – which was the initial reason for the explosion at the Fukushima nuclear power plant.”

The representative of the fuel division of Rosatom outlined three directions of developments designed to improve the safety of the fuel element cladding.

The first direction is represented by the use and modernisation of heat-resistant chromium-based coatings for traditional zirconium alloys used as the main material for fuel cladding. In the framework of this solution, it is proposed to isolate zirconium from the coolant, thereby preventing the steam-zirconium reaction with the release of a large amount of hydrogen in the event of an accident.

The second direction of tolerant fuel development is the use of the 42CNM alloy (chromium-nickel-molybdenum) instead of zirconium alloys for the fuel element cladding, which should in principle exclude the problem of hydrogen production during a beyond design basis accident. Ugryumov noted that this solution has proved effective in the transport sector (in nuclear icebreaker reactors) and also as a shell of absorbing elements in VVER reactors.

The third key area of research is focused on the implementation of a fuel matrix based on uranium-molybdenum (today the most common option is the use of uranium dioxide). This fuel composition has a higher density and, as a consequence, a higher thermal conductivity, increasing the stability of the reactor core during design basis accidents. Due to a significant reduction in the temperature of the course of accidents, it is planned to exclude beyond design basis accidents – that is, accidents with core meltdown – as a category, Ugryumov said.

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