Experimental and Post-Test Calculation Results of the Integral Reflood Test QUENCH-12 with a VVER-type Bundle", Annals of Nuclear Energy 36

Abstract – The QUENCH-12 experiment was carried out to investigate the effects of VVER materials (niobium-bearing alloys) and bundle geometry on core reflood, in comparison with test QUENCH-06 using western PWR materials (Zircaloy-4) and bundle geometry. While the PWR bundle uses a single unheated rod, 20 heated rods, and 4 corner rods arranged on a square lattice, with a heated length of 1000 mm, the VVER bundle uses 13 unheated rods, 18 heated rods and 6 corner rods, arranged on a hexagonal lattice. The test was conducted at the Forschungszentrum Karlsruhe on 27 September 2006 with largely the same protocol as QUENCH-06, in order to demonstrate the effects on the VVER characteristics more readily. The test protocol involved pre-oxidation to a maximum of about 200 µm oxide thickness at a temperature of about 1200 °C, followed by a power ramp until a temperature of 1800 °C was reached, then reflood with water at room temperature was initiated. The total hydrogen production was 58 g (QUENCH-06: 36 g), 24 g of which were released during reflood (QUENCH-06: 4 g). Reasons for the increased hydrogen production may be extensive damaging of the cladding surfaces due to the breakaway oxidation and local melt formation with subsequent melt oxidation, due perhaps to slightly extended pre-quench transient. Post-test videoscope observations and metallographic investigations showed an influence of the breakaway oxidation with extensive spalling of oxide scales o