Nuclear criticality safety considerations for CASTOR casks with spent fuel of the Rossendorf nuclear devices

The spent fuel of the shut down Rossendorf nuclear devices is to be loaded into storage and transport casks of the type CASTOR-MTR-2. According to the variety of different nuclear devices at the Rossendorf site, the Rossendorf fuel is characterized by a great variety with regard to geometry, material, enrichment, and burn-up. According to the special loading conception, the fuel is embedded in aluminium bodies that the fill the CASTOR. The void fraction within the CASTOR is very small resulting in a small water fraction if water flooding is assumed. The criticality safety is proved by MCNP and OMEGA calculations. These are independent codes that use a completely different data base. The results of both codes agree very well demonstrating the reliability of the calculations. Apart from the proof of criticality safety, some interesting features were found mainly as a result of the very small water fraction.