Prior investigation

of absorber rod Dy2O3TiO2 behavior

after severe accident test

FSUE SRI SIA “LUCH”ICP MAE

Presented by Dmitry N. Ignatiev

Forschungszentrum, Karlsruhe, Germany, October 25-27, 2005.

- Cladding deformation and fuel rod depressurization;- Eutectic interaction of zirconium, B4C and stainless still;- Oxidation and embrittlement of claddings by steam and UO2;- Melting of zirconium and - Zr(O);- Degradation and dissolution of pellets UO2 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

OObjectivebjective of the work of the work

Objective of this work was a study of absorber Objective of this work was a study of absorber rod (Dyrod (Dy22OO33TiOTiO22) behavior) behavior as part of fuel as part of fuel assembly of VVER reactorassembly of VVER reactor under severe under severe accident conditionsaccident conditions

Main tasksMain tasks::- - tests of the absorber with a powdered core made of dysprosium tests of the absorber with a powdered core made of dysprosium titanatetitanate and a cladding made of a stainless steel at the and a cladding made of a stainless steel at the PARAMETR facility (FSU “SRI SIA LUCH");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 studying of interaction products of structural, fuel and absorbing materials being formed at the core destruction materials being formed at the core destruction - studying of the principal physicochemical process, affected on the absorber rod behavior during test.

FA Specification

Disposition of elements in FA

FA

Test Scenario

Temperature of the heated rods

Temperature escalation

Cooling of bundle

time, c

Tem

pera

ture

, C

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

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

Melt between the guide channel and claddings

“Dark”melt (1)

Fe 75%

Ni 15%

Cr 8%

Zr 2%

“Bright”melt (2)

Fe 40%

Ni 25%

Cr 5%

Zr 30%

Interaction between absorber material Interaction between absorber material an stainless steelan stainless steel

1 – absorber rod; 2 – particles of titanate dysprosium; 3 –interaction zone.

Melt, containing stainless steel and dysprosium

“Dark”Melt (1)

Zr 22%

Cr 20%

O 38%

Ti 9%

Fe 5%

Dy 3%

“Bright”melt (2)

Zr 40%

Dy 25%

O 30%

U 3%

Ti 1%

Cr 1%

CONCLUSIONSCONCLUSIONS1. Prior investigation of absorber rod (Dy2O3TiO2) 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 Dy2O3TiO2 powder with stainless steel cladding take place at temperature ≥1400С.

5. In debris drops of melt Zr-Dy-O-U-Ti-Cr were observed.