Failure investigation and mitigation after experimental research reactor fuel plate deformation in an irradiation device

Bert Rossaert, Cezary Bojanowski, Ann Leenaers, Guy Cornelis, Earl E. Feldman, Erik H. Wilson, Steven Van Dyck, John G. Stevens, Jared Wight

Research outputpeer-review

Abstract

Experimental research reactor fuel testing is conducted in the Belgian Reactor 2 (BR2) of the Belgian Nuclear Research Centre (SCK CEN) in dedicated irradiation vehicles or rigs. One such vehicle allows flat full-size fuel plates to be irradiated by inserting them into slotted baskets that captures a narrow portion of the longitudinal edges of the plates. The motion of the fuel plates within the baskets is possible within the narrow slots and thus, the plate is considered to be unattached. The design intentionally omits fixing mechanisms of the fuel plates to the baskets to facilitate the inspection and repositioning of the plates between the irradiation cycles and the accommodation of thermal expansion of the plates in the lateral direction. However, loosely inserted fuel plates have weak structural boundary conditions allowing for larger out-of-plane deflections caused by hydrodynamic loads exerted by the flowing coolant, as compared to those of fixed plates. Unexpected large deformations of plates occurred in several irradiation cycles that further resulted in a loss of cladding integrity. These deformations could not be attributed to a single source. This triggered a series of thermal hydraulic, structural, and fluid–structure interaction analyses aiming at understanding the observed phenomenon. The analyses revealed that, for a certain combination of unfavorable manufacturing and assembly tolerances, fuel plate edges could escape out of the slots in the irradiation basket due to the hydrodynamic load. Subsequently, the plate could become wedged inside the basket coolant channel opening. This resulted in reduced coolant flow and accelerated temperature increase and thermal expansion of the plate while under irradiation. This unfavorable feedback loop could then lead to excessive plate surface temperatures, deformed plates and cladding failure, as was observed in the experiments. These analyses not only provided a probable cause of the fuel plate failures, but also resulted in a new and improved design of the irradiation basket to avoid these issues in the future. A series of recent successful irradiations confirm that the sources of failures were identified correctly, and the implemented mitigations were adequate.

Original languageEnglish
Article number113796
Number of pages16
JournalNuclear Engineering and Design
Volume432
DOIs
StatePublished - Feb 2025

Funding

FundersFunder number
National Nuclear Security Administration Office of Defense Nuclear Nonproliferation
U.S. Department of Energy
National Nuclear Security Administration Office of Defense Nuclear NonproliferationDE-AC02-06CH11357
EURATOM - Research and Training Programme754378, 661935

    ASJC Scopus subject areas

    • Nuclear and High Energy Physics
    • General Materials Science
    • Nuclear Energy and Engineering
    • Safety, Risk, Reliability and Quality
    • Waste Management and Disposal
    • Mechanical Engineering

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