Westinghouse Electric Company yesterday announced the formal launch of its “accident-tolerant fuel solution”, EnCore Fuel, during the company’s Fuel Users’ Group Meeting. EnCore Fuel is intended to offer “design-basis-altering safety, greater uranium efficiency and estimated economic benefits up to hundreds of millions of dollars” to Westinghouse’s nuclear fuel customers.
Delivered in two phases, the initial EnCore Fuel product consists of coated cladding containing uranium silicide pellets, which Westinghouse says distinguishes the fuel from other accident-tolerant fuel solutions thanks to their higher density and higher thermal conductivity.
“We are leveraging the breadth and depth of our resources, combined with US Department of Energy awards, as well as utility funding, to collaborate with respected industry partners in order to deliver EnCore Fuel to the market on an aggressive, accelerated schedule,” Michele DeWitt, Westinghouse’s senior vice president of nuclear fuel, said. “We are on track to manufacture EnCore Fuel lead test rods as early as 2018, with lead test assembly insertion planned starting in 2022,” he added.
The reduced oxidation and hydrogen pickup of the coated cladding during normal operation (250°C to 350°C) is intended to prolong cladding life, provide enhanced resistance to wear and increase margins, the company said. The coated cladding also supports extended exposure to high temperature steam and air (1300°C to 1400°C) during a loss-of-coolant accident, reactivity-initiated accident and beyond-design-basis conditions.
The second phase of EnCore Fuel features silicon-carbide cladding, which is intended to offer significant safety benefits in beyond-design-basis accident scenarios, the company said. This is enabled by its extremely high melting point (2800°C or higher) and minimal reaction with water, resulting in minimal generation of heat and hydrogen in beyond-design-basis accident scenarios, it said.
SiC cladding development will take longer to finalize and make available commercially, but is intended to provide revolutionary safety margin improvements. SiC cladding reacts 10,000 times slower with water and steam than zirconium, resulting in minimal generation of heat and hydrogen in beyond-design-basis accident scenarios.
Since U3Si2 pellets allow significantly more uranium to be packed into the same volume than UO2, reduced fuel assembly loadings or longer fuel cycles also can be achieved while staying below the 5 percent enrichment limit. Due to a higher thermal conductivity than UO2, U3Si2 provides a safety improvement through less stored energy while allowing a much higher linear heat rate before it melts.
EnCore Fuel’s economic benefits come from fuel cycle impacts of replacing UO2 with U3Si2 and from positive impacts on plant core damage frequencies, primarily from incorporating coated zirconium and SiC composite cladding.
Along with the increased safety margins inherent in accident tolerant fuels, utility benefits will be realized from the following:
• Risk-based technical specifications and resulting relaxed requirements for testing, safety class designation of equipment and systems, redundancy (allowing elimination of equipment / systems), procurement;
• Reduction in the emergency planning and evacuation zones; and
• Improved fuel cycle economics estimated at $2.9M for 1000 MWe, 18-month cycles.
Test fuel rods manufactured in 2017 will undergo exposure in the Advanced Test Reactor (ATR) and TREAT reactor at Idaho National Laboratory and the Halden Reactor in Norway to develop the data required for licensing as a prelude to loading lead test assemblies in commercial reactors. The test protocols will include PWR operating conditions and transient tests.
The current schedule targets insertion of LTRs and LTAs in reactors by 2022, with LTRs manufactured as early as 2018.
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