Characterization of Data on Putting A Facility Damaged by An Accident into A Safe State

Period: 2003-2004

Customer: Nuclear Safety Research Association of Japan (NSRA)

Project objective: study physical and chemical properties of lava-like fuel-containing masses (LFCM) of ChNPP Unit 4 that was damaged as a result of the Chornobyl accident; obtain new data on the processes of melted fuel interaction with the damaged reactor structural materials.

The following activities were accomplished within the framework of the project:

• research of LFCM imitators obtained as a result of applying the following methods: nuclear microanalysis, crystal optics, X-ray structure analysis, focused-beam electronic microscopy, metallography;
• series of experiments to synthesize LFCM imitators under laboratory conditions with the objective to specify LFCM formation scenario; research of the synthesized samples by means of various instrumental methods;
• 51 samples were made from a prepared mixture to further obtain a glass-ceramic melt;
• impact of cooling rate on the process of fuel containing masses (FCM) formation in vacuum was studied;
• impact of burning time on the FCM formation process was studied;
• process of FCM formation in aerial atmosphere at the temperature of ~1500 ⁰ C was studied;
• thermal and physical characteristics of some LFCM imitators samples were studied.

Research results:

• identification of density, thermal and physical characteristics of synthesized LFCM;
• new data on temperature of LFCM imitators formation, on LFCM imitators phase and elemental composition were obtained;
• it was determined that during the experiments, the fuel material intensively interacts with graphite, which results in a great loss of material (up to 60% of mass) due to its carrying out of the interaction zone;
• it was proved that during a long-term burning (~20 hours) at the temperature of ~1500 ⁰ C in vacuum, an intensive (up to 84% of mass) evaporation of initial mixture components takes place; the similar results were obtained for the low cooling rate (~0.5 ⁰ C/min) (the ratio amounts up to 79% of mass);
• it was determined that brown ceramics with glossy finish is obtained at high temperature (~50 ⁰ C/min); chocolate-brown ceramics with flat finish is obtained at low temperature (~0.5 ⁰С/min and 4.5 ⁰ C/min) – this confirms the suppositions about different speeds of LFCM solidification in different premises during the ChNPP accident.