MELCOR Simulations of the Severe Accident at the Fukushima Daiichi Unit 1 Reactor

A MELCOR model of Fukushima Daiichi Unit 1 accident

“…Perhaps there was no spark, or perhaps the calculation overestimates the hydrogen concentration. Or if the calculation underestimates the steam concentration, the atmosphere may have actually been steam-inerted until just before the explosion, as suggested by Gauntt et al (2014). The decrease of steam concentration in the reactor building before the explosion was caused by decreasing leakage from the containment because the containment was depressurized by venting.…”

“…By 30 h, the Sandia calculation gives about 550 kg of hydrogen from MCCI, while the VTT result is double, 1100 kg. There is a similar difference in CO generation from MCCI: about 800 kg in Sandia calculation and 1600 kg in VTT calculation at 30 h. There are probably differences in the MCCI model parameters and in the way in which the melt in the sump was modeled, but these are not described in the Gauntt et al (2014) paper.…”

“…Also the hydrogen mass in the reactor hall at the time of the explosion is smaller, about 100 kg in the Sandia calculation, compared with 323 kg in the VTT calculation. Gauntt et al (2014) report that 2% of CsI inventory was released to the environment in 30 h. This is not straight-forward to compare with VTT's result because it is unknown, how much of the Cs they have assumed to be in the form of CsI and how much as CsOH or Cs 2 MoO 4 . The best number for comparison may be 0.15%.…”

“…MELCOR model by SandiaGauntt et al (2014) from Sandia National Laboratories have published a MELCOR calculation of the Unit 1 accident. They have calculated steam line failure at 6.2 h, while the current VTT model assumes recirculation pump seal leak at 5 h. The RPV failure Noble gases (% of core inventory) Cesium (% of core inventory) Release of cesium and noble gases to the environment.…”

Insights on Accident Information and System Operations during Fukushima Events

“…Thermal-hydraulic (TH) behavior and the progress of core damage were analyzed by TEPCO using MAAP, as described in the TEPCO report [5]. Sandia National Laboratory performed TH analysis using MELCOR, as described in report [30] and papers [31][32][33]. Accident progression analysis using MELCOR was also performed by Hoshi and Kawabe [34].…”