NE Seminar: “The Nuclear Regulatory Commission’s Research on Fuel Fragmentation, Relocation and Dispersal”

Date(s) - 11/10/2022
1:55 pm - 2:55 pm

Rhines Hall 125


James Corson, Ph.D.

Senior Reactor Systems Engineer
Nuclear Regulatory Commission

Dr. James Corson is a Senior Reactor Systems Engineer in the Office of Nuclear Regulatory Research at the United States Nuclear Regulatory Commission, where he has worked for the past 12 years.  Dr. Corson specializes in the behavior of nuclear fuel during normal operations, anticipated operational occurrences, and design basis accidents, both for operating light water reactors and for advanced non-LWR designs.  He serves as the NRC technical lead for the Fuel Analysis under Steady-state and Transients (FAST) fuel performance code, and he is an active participant in several domestic and international research projects related to nuclear fuel behavior.
Dr. Corson holds B.S. and M.S. degrees in nuclear engineering from the Pennsylvania State University and Texas A&M University, respectively, and a Ph.D. in chemical engineering from the University of Maryland, College Park.


Extensive research has been conducted on fuel fragmentation, relocation, and dispersal (FFRD) during a loss-of-coolant accident (LOCA). This research has shown that FFRD phenomena are correlated with burnup. As the U.S. nuclear industry pursues the operation of plants with higher fuel burnup levels, it is important to understand and account for FFRD-related phenomena and their impact on regulatory figures of merit (e.g., peak cladding temperature) in licensing applications. Recently, the U.S. Nuclear Regulatory Commission’s the Office of Nuclear Regulatory Research (RES) published a research information letter to communicate staff’s interpretation of findings from experimental programs on FFRD and to define conservative, empirical boundaries for FFRD-related phenomena.
The research information letter provides a basis for limiting the analysis of FFRD to regions of the core with specific characteristics. Data from experimental programs conducted to date suggests that fine fragmentation is limited to fuel above 55 gigawatt days per metric ton of uranium (GWd/MTU) pellet average burnup. Axial fuel relocation is limited to regions of the fuel rod that have a local cladding strain greater than 3 percent. Relocated fuel fragments can occupy between 60 percent and 85 percent of the fuel rod cross-sectional area in the balloon region. The propensity for fuel dispersal is correlated with fuel fragment size and burst opening size; however, cladding burst and fuel relocation are prerequisites. This effectively limits fuel dispersal by the same parameters as fine fragmentation and relocation (i.e., pellet average burnup greater than 55 GWd/MTU and cladding strain greater than 3 percent). Finally, data from experimental programs conducted to date suggests that significant quantities of fission gas may be released during a LOCA transient. Transient fission gas release becomes increasingly significant with increasing burnup, with releases as high as 18 percent observed from a fuel rod segment with an average burnup of 70 GWd/MTU. Fission gas released during a LOCA may impact fuel rod ballooning and burst behavior and, thus, fuel relocation and dispersal.