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Conference Article: Review of some aspects of radiological interest during the establishment of the safe enclosure of the THTR 300 plant
Stratmann, W. (STEAG Kernenergie GmbH, Essen (Germany)); Baechler, M. (Noell-KRC Energie- and Umwelttechnik GmbH, Wuerzburg (Germany))Abstract
One of the first activities with the establishment of the safe enclosure was the disassembly of the reactor of the burn-up measurement facility. This was a graphite-moderated, air-cooled reactor with strip-shaped fuel elements made of an aluminium uranium alloy. The reactor contained 3.9 kg of high-enriched uranium (93% U-235), the thermal power output was 500 W. Because of the highly cramped conditions, the acceptable dose level and the limited number of fuel stripes, the decommissioning was executed almost exclusively manually. To reduce the collective dose of the personnel, an extensive training with a 1:1 scale mock-up was carried out prior to decommissioning. The removed fuel elements were put into special baskets and were shipped to the interim storage facility BZA in to CASTOR THTR/AVR casks. In order to clear place for the installation of components of the new ventilation system and other systems, the components for high-purity helium compression and storage had to be dismantled. More than 90% of the metal were unconditionally released as iron scrap. Extensive measurements had to be carried out on the dismounting and inspection equipment which had ben mostly already in use during the 3 year time of operation. As a result 3 Mg had to be stored in the remaining controlled area, app. 183 Mg were stored within the supervised area and app. 49 Mg were released as free of contamination. Due to the high tritium inventory, two containers with barrels filled with waste could not be shipped to external storage sites and therefore had to be stored in the remaining controlled area within the envelope of the safe enclosure. Another interesting aspect of the low contamination level of the THTR 300 plant was the release of buildings from the restrictions of the Atomic Energy Act and reduction of the controlled area to a supervised area. Based on statistical methods we were able to prove the low-level contamination status with and acceptable amount of measurements. Finally a new system for monitoring of released radioactivity with the new exhaust air system was designed and built. Government authorities requested a system with advanced sensibility for low emissions of tritium and carbon-14. The design especially had to consider the highest mean time between failures and the lowest mean time to repair possible.
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key words: Gas Cooled Reactor, Nuclear Technology
- Reference:
- Technical committee meeting on technologies
for gas cooled reactor decommissioning, fuel
storage and waste disposal. Juelich (Germany)
8-10 Sep 1997
- International Atomic Energy Agency, Vienna (Austria)
- IAEA-TECDOC--1043, pp:287-294
- International Atomic Energy Agency, Vienna (Austria)