1. Prior investigation of absorber rod Dy 2 O 3  TiO 2 behavior after severe accident test FSUE SRI SIA “LUCH” ICP MAE Presented by Dmitry N. Ignatiev Forschungszentrum, Karlsruhe, Germany, October 25-27, 2005.

2. - Cladding deformation and fuel rod depressurization; - Eutectic interaction of zirconium, B 4 C and stainless still; - Oxidation and embrittlement of claddings by steam and UO 2 ; - Melting of zirconium and  - Zr(O); - Degradation and dissolution of pellets UO 2 by molten zirconium, formation of U – Zr – O melt. Interaction of dysprosium titanate with stainless still and zirconium in severe accident conditions? Principal physicochemical process of severe accident reducing to the degradation and melting of bundle

3. Objective of the work Objective of the work Objective of this work was a study of absorber rod (Dy 2 O 3 TiO 2 ) behavioras part of fuel assembly of VVER reactor under severe accident conditions Main tasks: - tests of the absorber with a powdered core made of dysprosium titanate and a cladding made of a stainless steel at the PARAMETR facility (FSU “SRI SIA LUCH"); - estimation of final state of the absorber and model FA as well as absorbing material distribution within FA after testing; - studying of interaction products of structural, fuel and absorbing materials being formed at the core destruction - studying of the principal physicochemical process, affected on the absorber rod behavior during test.

4. FA Specification Disposition of elements in FA FA

5. Test Scenario

6. Temperature of the heated rods Temperature escalation Cooling of bundle time, c Temperature, C

7. Posttest appearance of the test bundle Posttest view of bundle (Z = 900…1200 mm) Posttest view of bundle (Z = 500…700 mm) Tungsten heater Spacer grid Absorber rod Fuel pellet Spacer grid cladding Z = 1200 mm Z = 900 mm

8. 1 – guide channel; 2 – absorber rod; 3,4 – melt on the guide channel; 5, 6 – cladding Microstructure of absorber rod cross section (Z = 950 mm) Interaction between cladding and guide tube

9. Melt between the guide channel and claddings “Dark” melt (1) Fe75% Ni15% Cr8% Zr2% “Bright” melt (2) Fe40% Ni25% Cr5% Zr30%

10. Interaction between absorber material an stainless steel 1 – absorber rod; 2 – particles of titanate dysprosium; 3 –interaction zone.

11. Melt, containing stainless steel and dysprosium “Dark” Melt (1) Zr22% Cr20% O38% Ti9% Fe5% Dy3% “Bright” melt (2) Zr40% Dy25% O30% U3% Ti1% Cr1%

12. CONCLUSIONS 1.Prior investigation of absorber rod (Dy 2 O 3  TiO 2 ) behavior at severe accident test of VVER reactor was carried out. 2. In conditions of the given experiment the basic dodges of destroying of assembly were melting steel constructional elements at a stage of heating and shedding of claddings and fuel pellets at cool-off. 3.The sequence of bundle failure starts with stainless steel melting (absorber rod cladding and guide tube). Most of thus melt react with zirconium claddings. 4.Diffusion interaction of Dy 2 O 3  TiO 2 powder with stainless steel cladding take place at temperature ≥1400  С. 5.In debris drops of melt Zr-Dy-O-U-Ti-Cr were observed.