MELCOR 1. 8. 1 assessment: LACE aerosol experiment LA4

MELCOR 1.8.3 assessment: CSE containment spray experiments

“…Also, the accuracy and reasonableness of the predicted results generally improve as more MAEROS components and sections are used to model the aerosol size distributions, as would be expected. These CSE results confirm the previous MELCOR assessment guideline [3] that water drops in the atmosphere should be represented by a separate component in transients with a humid atmosphere.…”

“…(The iodine was predicted to exist as a vapor, not an aerosol.) This approach was taken because sensitivity studies in our earlier MELCOR assessment using the LACE LA4 aerosol test [3] indicated that at least two components (one for fog) were needed to correctly account for condensation and evaporation effects. As a sensitivity study, calculations were run for test A-9 using a single aerosol component for all classes, which is the normal MELCOR default assumption, and using two components, one for the water fog and the other for both the cesium and uranium aerosols, for comparison with the reference calculation results presented in Section 4.…”

“…[26] MELCOR models condensation/evaporation effects on aerosol particle size, but does not include any model for such hygroscopic effects. The lack of such a model has been noted in previous MELCOR assessments of aerosol behavior in humid atmospheres [3,27].…”

“…The lack of such a model has been noted in previous MELCOR assessments of aerosol behavior in humid atmospheres [3,27]. However, in our reference calculation, condensation/evaporation was specified to take place only on water aerosols and not on all aerosols present (as in the code default), to avoid other modelling problems.…”

1994 MCAP annual report

“…This is a known problem with the VANESA formulation. Such problems are more likely to occur with MELCOR 1.8.2 than with NELCOR 1.8.1 both because of the higher structure retention 32,970.0 s (9.16 hr) 14,778.9 s (12.44 hr) 90,000.0 s (25 hr) due to the eutectic model seen in these calculations and because the greater robustness of MELCOR 1.8.2 allows calculations to be carried to later times. Users are cautioned to carefully examine radionuclide releases when vanishing metallic layers are predicted in CORCON.…”