Results of the QUENCH-10 experiment on air ingress

Abstract

The QUENCH experiments are to investigate the hydrogen source term resulting from the water injection into an uncovered core of a Light-Water Reactor (LWR). The QUENCH test bundle consists of 21 fuel rod simulators with a total length of approximately 2.5 m. Experiment QUENCH-10 on air ingress conducted at the Karlsruhe Research Center on 21July 2004 was the first of two experiments to be performed in the frame of the EC supported LACOMERA program. It was proposed by AEKI Budapest, Hungary, and defined together with the Karlsruhe Research Center, supported by Paul Scherrer Institut (PSI), Switzerland. The main objective of this test was to examine the oxidation and nitride formation of Zircaloy during air ingress, before flooding the bundle with water. After a 113-min pre-oxidation phase at 1620-1690 K and an intermediate cooling phase from ∼1690 to 1190 K lasting -38 min the air ingress phase was initiated. In this phase the steam flow of 3 g/s was replaced by 1 g/s of air. The duration of this phase was -30 min. Complete consumption of oxygen and partial consumption of nitrogen (about 0.1 g/s) were observed toward the end of this phase. The total uptakes of oxygen and nitrogen were about 84 and 8 g, respectively. Corner rods withdrawn from the bundle toward the end of the pre-oxidation and air ingress phases confirmed that the target oxide layer thickness of -600 μm in the hot zone was achieved. Reflood was conducted by injecting 50 g/s of water at the bottom of the test section. Bundle temperatures at the hot zone were then -2200 K. Cooling was established almost immediately, and complete quenching of the bundle was achieved after about 100-150 s. A modest release of hydrogen, i.e. -5 g, was observed during the early part of the reflood. Additionally, 3.5 g of the nitrogen were released, i.e. 44 % of N 2 previously taken up in the test section. The evaluation of the hydrogen release rates gives 53 g of H 2 in total, 47.3 g of which was generated up to the beginning of the air ingress phase. After the experiment the test bundle and its shroud appear severely damaged, i.e. completely oxidized, in the region between 750 and 1000 mm and is therefore extremely embrittled.