US-based Westinghouse Electric Company has received approval from the US Nuclear Regulatory Commission (NRC) to use its Advanced Doped Pellet Technology (ADOPT) fuel pellets in US pressurised water reactors (PWRs). The approval came after both NRC and the Advanced Committee on Reactor Safeguards (ACRS) verified that ADOPT fuel significantly enhances the safety and reliability of PWRs.

The technology was developed with funding from the US Department of Energy (DOE) with the aim of increasing the accident tolerance of conventional uranium dioxide fuel pellets. An agreement was announced in 2022 with Southern Nuclear Company to load rods using High-Assay Low-Enriched Uranium (HALEU) ADOPT pellets “with licensing and manufacturing in 2023”. Westinghouse said it is contracted to deliver reload quantities of ADOPT fuel for three units beginning in 2025. HALEU fuel is enriched to between 5% and 19.75% – significantly higher than standard fuel used in commercial reactors. Westinghouse says the increased uranium density of ADOPT fuel improves fuel cycle economics and extends fuel operating cycles.

Tarik Choho, Westinghouse President of Nuclear Fuel, said ADOPT fuel has become “the first product within Westinghouse’s EnCore accident tolerant fuel (ATF) programme that is licensed for US PWRs”. He added that ADOPT fuel “is the result of two decades of in-reactor experience and provides our customers with improved fuel cycle economics and safety margins”.

ADOPT fuel is a near-term fuel product within the EnCore Fuel programme. Westinghouse says the fuel’s enlarged grain size and increased density offers key benefits including:

  • Increased density of fissile material
  • Higher burnups
  • Lower transient fission gas release
  • Higher thermal stability
  • Increased Pellet Clad Interaction margins
  • Enhanced corrosion & washout resistance

ADOPT fuel is an improved uranium dioxide (UO2) design, doped with small amounts of chromia (Cr2O3) and alumina (Al2O3). By utilising small amount of alumina, Westinghouse has been able to keep the amount of chromium (a parasitic neutron absorber) to a minimum, thereby improving neutron efficiency. ADOPT fuel can be used in all Westinghouse and Combustion Engineering PWR and boiling water reactor (BWR) designs, and is compatible with all zirconium-based cladding materials and fuel enrichments.

Westinghouse says the ADOPT pellet design achieves greater uranium efficiency through an approximate 2% increase in fissile material, compared with conventional UO2 products. This increased uranium density promotes core design flexibility and higher discharge burnups. ADOPT fuel is also expected to provide additional safety benefits in terms of fuel fragmentation, relocation, and dispersal in an event such as a loss-of-coolant accident. Increased thermal stability allows for more accurate prediction and enhanced control of pellet cladding gap closure. ADOPT fuel exhibits reduced Pellet Clad Interaction under accident conditions due to its enhanced creep rates at high temperatures. With an oxidation rate 50% less than conventional UO2, ADOPT fuel is expected to have reduced wash-out in the event of a fuel rod leaker.

Image: Westinghouse ADOPT fuel enhances the safety and reliability of PWRs and improves fuel cycle economics (courtesy of Westinghouse)