Commercially Irradiated, Refabricated Test Rodlet in INL Hot Cell (photo courtesy of INL)
The HERA project is dedicated to the understanding of the performance of light water reactor (LWR) fuel at high burnup under reactivity-initiated accidents (RIA). This project is part of the Second Framework for Irradiation Experiments (FIDES-II), a joint NEA undertaking that allows members to benefit from a portfolio of irradiation facilities around the world.
On 14 May 2025, Idaho National Laboratory (INL) staff at the Transient Reactor Test Facility (TREAT) conducted the first RIA transient test on a commercially irradiated fuel segment, the first test in the HERA project’s high burnup test series and a milestone for the participants. The data from this test and ensuing tests on this type of rods will provide crucial data for new fuel designs that could extend the life of the current fleet of commercial reactors around the world.
Prior to the high burnup test series, HERA (which stands for High Burnup Experiments in Reactivity Initiated Accident) had six tests with fresh fuel samples, four of which were conducted at the INL and two at the Nuclear Safety Research Reactor (NSRR) test reactor by the Japan Atomic Energy Agency (JAEA). The majority of previous high burnup RIA experiments were conducted on vintage cladding materials and tested at conditions that are slightly different than those expected in today’s LWRs. Modern cladding materials are expected to perform better under prototypic reactor conditions; however, the operation of UO2 fuel to higher burnups also presents new unknowns. The HERA tests will provide an opportunity to identify available cladding failure margins in modern claddings and identify any safety impacts from extending the burnup of UO2 fuels.
Operators Loading the TWIST Capsule with the Commercial Nuclear Fuel Rodlet into TREAT (photo courtesy of INL)
Since the restart of operations at TREAT in 2017, an average of 20 fuel irradiation tests have been conducted each year. In each of these tests, the fuel is exposed to highly controlled transient irradiations, which can include short narrow bursts, simulating one of a variety of nuclear fuel accident scenarios. However, the test subjects irradiated previously are either fresh (unirradiated) fuel, or fuel that has been irradiated in an INL test reactor. In contrast, the fuel inside of TREAT in this experiment was irradiated commercial fuel.
The HERA project is part of the NEA Second Framework for Irradiation Experiments (FIDES-II), a joint undertaking that allows members to benefit from a number of irradiation facilities globally and permits a variety of research questions to be pursued together under the framework and Joint Experimental Programmes (JEEPs). So far, five material test reactors, two transient test reactors and one commercial reactor have been performing irradiations for FIDES-II participants.
More information and a list of ongoing JEEPs can be found on the FIDES-II homepage.
Control Room Operators Conduct the Transient at TREAT (photo courtesy of INL)
