Long-Term Aging of Chernobyl Fuel Debris: Corium and 'Lava'

Samples of Chernobyl fuel debris, including massive corium and &ldquo
lava&rdquo
were collected inside the Chernobyl &ldquo
Sarcophagus&rdquo
or &ldquo
Shelter&rdquo
in 1990, transported to Leningrad (St. Petersburg) and stored under laboratory conditions for many years. In 2011 aged samples were visually re-examined and it was confirmed that most of them remained intact, although some evidence of self-destruction and chemical alteration were clearly observed. Selected samples of corium and &ldquo
were affected by static leaching at temperatures of 25, 90 and 150 &deg
C in distilled water. A normalized Pu mass loss (NLPu) from corium samples after 140 days was noted to be 0.5 g/m2 at 25 &deg
C and 1.1 g/m2 at 90 &deg
C. For &ldquo
samples NLPu was 2.2&ndash
2.3 g/m2 at 90 &deg
C for 140 days. The formation of secondary uranyl phases on the surface of corium and &ldquo
samples altered at 150 &deg
C was confirmed. The results obtained are considered as an important basis for the simulation of fuel debris aging at Fukushima Daiichi nuclear power plant (NPP).