Preliminary Analysis of Postclosure DPC Criticality Consequences

ORNL Input to GDSA Repository Systems Analysis FY21

“…Numerical challenges associated with this class of subsurface simulation are well known. The model configuration of interest here with high-resolution explicit representation of the DPC is particularly challenging based on our previous experience [3]. Unfortunately, the addition of the temperature-dependent thermal conductivity appears to make it even more difficult for PFLOTRAN to converge for this model configuration.…”

“…Previous analyses [3] of DPCs containing 37 pressurized water reactor (PWR) assemblies showed that for dry conditions like those typically associated with unsaturated alluvial deposits in the US Basin and Range Province [4], decay heat alone is sufficient to prevent water from accumulating to sufficient depths to initiate a criticality event for many thousands of years after repository closure. Moreover, even small levels of power produced by a criticality event are sufficient to drive water out of a breached waste package and thus terminate the criticality event.…”

Simulations of Water Flow in Relation to a Steady Criticality in an Unsaturated Alluvial Repository

“…The existing literature has documented several scenarios under which to consider the possibility of DPC criticality (Price et al, 2019a;Price et al 2019b;Painter et al, 2019;Furtney et al 2021). Broadly speaking, they can be categorized using the following parameters  Dynamic behavior: pulse/cyclical/slow transient…”