A Critical Review of High Burnup Fuel Fragmentation, Relocation, and Dispersal under Loss-Of-Coolant Accident Conditions

Engineering Assessment of UO₂ and Cladding Behavior under High Burnup LOCA Conditions

“…The BISON results presented to this point have predicted stresses that greatly exceed typical UO 2 fracture stresses, which have been reported to range from 80-150 MPa [29,30]. Experimental data [36][37][38][39][40][41][42]27] also show fuel cracking before transient testing and significant cracking and pulverization after transient testing of high burnup fuel. Therefore, cracking will occur prior to the transient and will impact the stress state in the pellet fragments because the cracks change the pellet's constraints.…”

“…The reflood phase can be identified by the rapid cladding temperature drop towards the end of the simulation (~775 s). In this work, the fuel temperatures and stresses were only evaluated during the blowdown and refill phases, which is when FFRD has typically been observed to occur [36][37][38][39][40][41][42]27]. A 90° symmetric generalized plane strain planer slice BISON model was developed to perform sensitivity studies at a single axial location along the fuel rod.…”

“…With fuel dispersal in mind, the shape and size of the rupture opening may be an important consideration as fuel fragments are required to be smaller than the rupture opening to physically disperse through the cladding rupture opening. A recent paper by Capps et al [57] indicates that the size of the burst opening is proportional to the amount of fuel dispersal, and it suggests that large amounts of dispersal required the area of the burst opening to be greater than ~80-100 mm 2 . Therefore, quantifying the burst opening may offer the potential to minimize fuel dispersal and its consequence.…”

Advancements in modeling fuel pulverization and cladding behavior during a LOCA

“…With fuel dispersal in mind, the shape and size of the rupture opening may be an important consideration as fuel fragments are required to be smaller than the rupture opening to physically disperse through the cladding rupture opening. Reference [28] indicated that the size of the burst opening was proportional to the amount of fuel dispersal and suggested large amounts of dispersal required the area of the burst opening to be greater than ∼80-100 mm 2 . Therefore, quantifying the burst opening may allow minimization of fuel dispersal and its consequences.…”

“…Historical integral LOCA tests leveraged infrared lamps to heat rodlets at a constant rate of 5°C/s [29,28]. However, this may not be representative of in-reactor LOCA conditions.…”