Results of fission product release from intermediate-scale MCCI tests

A program of reactor-material molten core-concrete interaction (MCCI) tests and related analyses are under way at Argonne National Laboratory under sponsorship of the Electric Power Research Institute (EPRI). The particular objective of these tests is to provide data pertaining to the release of nonvolatile fission products such as La, Ba, and Sr, plus other aerosol materials, from the coupled thermal-hydraulic and chemical processes of the MCCI. Test results have shown first of all that direct electrical heating is a successful method for sustaining internal heat generation in molten core materials for long-term MCCI operation. However, the relatively small scale of these tests permitted a stable crust to bridge the apparatus at the top of the interaction zone, restricting the released gas and aerosol to flow through cracks and pores in the crust. MCCI temperature as high as 2400K was measured resulting in concrete ablation which ranged from 0.8 to 3.9 mm/min. The expected H2O and CO2 decomposition gasses were measured which accounted for peak superficial velocity of ∼ 4 cm/s. With the metallic zirconium present, CO and H2 were also measured; there was no evidence of coking. The aerosol consisted mainly of uranium species plus species of concrete decomposition products. The presence of Zr increased measured release fractions of Ba and Sr species by an order of magnitude, and La species by a factor of three