Long-Term Aging Of Chernobyl Fuel Debris: Corium And "Lava"

Samples of Chernobyl fuel debris, including massive corium and "lava" were collected inside the Chernobyl "Sarcophagus" or "Shelter" 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 "lava" were affected by static leaching at temperatures of 25, 90 and 150 degrees C in distilled water. A normalized Pu mass loss (NLPu) from corium samples after 140 days was noted to be 0.5 g/m(2) at 25 degrees C and 1.1 g/m(2) at 90 degrees C. For "lava" samples NLPu was 2.2-2.3 g/m(2) at 90 degrees C for 140 days. The formation of secondary uranyl phases on the surface of corium and "lava" samples altered at 150 degrees 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).