During a LOCA in a LWR, a containment-sump strainer filters debris, generated from fibrous thermal insulation, from the water collected in the containment sump. The buildup of debris on the strainer and the bypass of debris through the strainer lead to upstream and downstream effects, respectively.
The objective of this research was to create a methodology for obtaining PSDs for this debris upstream and downstream of a sump strainer in multiple size ranges. Fibrous debris was injected into an experimental facility which simulated the conditions in a LWR containment sump. Samples were taken downstream of the strainer during the experiment. Using a NanoSight LM10 and two optical microscope systems, size measurements of particles were made.
The fractional number of particles between 55-188 nm increased from 0.591 to 0.734 upstream to downstream; the number of all other particle sizes decreased. This trend is consistent with Hutten’s [8] statements about the MPPS. For AMIS-1, from upstream to downstream, the fraction of particles smaller than 55 μm increased from 0.77 to 0.89; almost all of the larger particles sizes decreased in number. This demonstrates larger particles being more efficiently filtered. For AMIS-2, from upstream to downstream, the fraction of particles smaller than 340 μm increased from 0.536 to 0.668; all of the larger particle sizes decreased in number. This again demonstrates higher filtration efficiency for larger particles.
Different PDFs provided the best fit for the PSDs in each of the size ranges measured. For the nanometer range, the Johnson’s SB function provided the best fit. For the 10-500 μm range, the upstream and downstream results were fit best with the log-logistic and lognormal functions, respectively. For the 100-2500 μm size range, the Weibull distribution was found to fit best. Changes in the PDFs fit to the upstream and downstream PSDs were similar to what was found when comparing the upstream and downstream PSD histograms.
Size distributions for spherical (tin powder) and angular (SiC F600) particles were easily obtained using the Coulter Counter, however, it didn’t provide reliable results for fibrous debris
