Ruthenium Oxidation in High Temperature Air and Release of Gaseous Ruthenium KFKI-3/2008

The RUSET experimental programme was launched in order to study Ru oxidation and release from fuel in high temperature air. More than forty small scale tests have been performed with mixed powder components of inactive materials and with short fuel rods. The influence of temperature, air flow rate and the presence of other fission products on the gaseous Ru release and the retention role of fuel pellets and cladding have been investigated. The test series indicated that if an air ingress type severe accident occurs most of the initial Ru mass can be released from the reactor core to the containment or environment. Some part of the released gaseous Ru undergoes precipitation and deposits on the cold surfaces, another part is released in gaseous form. The deposited Ru oxides can serve as a secondary source for further gaseous Ru releas

CODEX-CT-2 experiment: Long term treatment in high temperature hydrogen and water quenching of a fuel bundle KFKI-2008-02/G

The simulation of the Paks-2 incident was carried out in the frame of an experimental programme in the CODEX facility with electrically heated fuel rod bundles. The main boundary conditions for the CODEX-CT-2 were similar to the previous CODEX-CT-1 test. The most significant difference between the two tests was the operation of the air let down valve that was open in the first test and closed in the second one. In the second test the hydrogen produced in the Zr-steam reaction could not escape from the test section and it prevented the access of steam to the Zr surfaces and caused much less oxidation than was observed in the first tests. The final quench by water led to temperature excursion in the bundle and in the shroud. The final state of the bundle was very brittle, the fuel rods and the shroud were cracked and fragmented

CODEX-CT-1 experiment: Quenching of fuel bundle after long term oxidation in hydrogen rich steam KFKI-2008-01/G

The cleaning tank incident at the unit 2 of Paks NPP in 2003 resulted in severe fuel damage of 30 assemblies. The fuel rods heated up due to insufficient cooling and the zirconium components suffered heavy oxidation. Opening of the tank and quenching of the assemblies by cold water led to fragmentation of brittle zirconium components. Due to the poor instrumentation there were many open questions concerning the course of the incident and the behaviour of fuel assemblies. In order to improve the understanding of the phenomena that took place during the Paks-2 incident integral tests have been carried out in the CODEX (Core Degradation Experiment) facility. The tests simulated the whole scenario of the incident using electrically heated fuel rods. The final state of the fuel rods showed many similarities with the conditions observed after the incident at the NPP and for this reason it is very probable that the thermal conditions and chemical reactions were also similar in the tests and in the incident. The post-test examination of CODEX-CT-1 bundle indicated that the high degree of embrittlement was a common result of oxidation and hydrogen uptake by the Zr components

High performance passive vibration isolation system for optical tables using six-degree-of-freedom viscous damping combined with steel springs

Mechanical vibrations in buildings are ubiquitous. Such vibrations limit the performance of sensitive instruments used, for example, for high-precision manufacturing, nanofabrication, metrology, medical systems, or microscopy. For improved precision, instruments and optical tables need to be isolated from mechanical vibrations. However, common active or passive vibration isolation systems often perform poorly when low-frequency vibration isolation is required or are expensive. Furthermore, a simple solution such as suspension from common bungee cords may require high ceilings. Here we developed a vibration isolation system that uses steel springs to suspend an optical table from a common-height ceiling. The system was designed for a fundamental resonance frequency of 0.5 Hz. Resonances and vibrations were efficiently damped in all translational and rotational degrees of freedom of the optical table by spheres, which were mounted underneath the table and immersed in a highly viscous silicone oil. Our low-cost, passive system outperformed several state-of-the-art passive and active systems in particular in the frequency range between 1-10 Hz. We attribute this performance to a minimal coupling between the degrees of freedom and the truly three dimensional viscous damping combined with a nonlinear hydrodynamic finite-size effect. Furthermore, the system can be adapted to different loads, resonance frequencies, and dimensions. In the long term, the excellent performance of the system will allow high-precision measurements for many different instruments

Behavior of Zr1%Nb Fuel Cladding under Accident Conditions

The behavior of the VVER fuel (E110) cladding under accident conditions has been investigated at the AEKI in order to study the role of oxidation and hydrogen uptake on the cladding embrittlement and to understand the phenomena that took place during the Paks-2 cleaning tank incident (2003). The test programme covered small scale tests and large scale tests with electrically heated 7-rod bundles in the CODEX (Core Degradation Experiment) facility. Since a hydrogen rich atmosphere could have been formed in the closed tank, the experiments were carried out in hydrogen-steam mixture.JRC.E.4-Nuclear fuel