Aus Carbohydrazid und Orthocarbonsgureestem erhillt man 4-Amino-I .2.4triazolone-(5), die auch bei lgngerem Erhitzen rnit aliphatischen Carbonsauren entstehen. Nach kurzer Reaktion rnit den Carbonsauren fallen 1.5-Diacyl-carbohydrazide an, die sich in saurer Lbsung partiell zu 1-Acyl-carbohydraziden verseifen lassen. Die 1 -Acyl-und die 1.5-Diacyl-carbohydrazide werden alkalisch zu 4-Amino-1.2.4-triazolon-(5) cyclisiert . Auch No-Acyl-carbazinsiiure-Hthylester ergeben z. T. bei der Umsetzung rnit Hydrazin 4-Amino-l.2.4-triazolone-(5). -Methylierung der 4-Amino-1.2.4-triazolone-(Z) in alkalischer Lbsung fuhrt zu KRBGER, HUMMEL. MUTSCHER und BEYER Jahrg. 98

This paper presents aspects of site decommissioning and clearance of a former fuel fabrication facility (development and production of fuel assemblies for research reactors and HTR) at Hanau (Germany). The main pathways for environmental contamination were deposition on soil surface and topsoil and pollution of deep soil and the aquifer by waste water channel leakage. Soil excavation could be done by classical excavator techniques. An effective removal of material from the saturated zone was possible by using advanced drilling techniques. A large amount of demolished building structure and excavated soil had to be classified. Therefore the use of conveyor detector was necessary. Nearly 100000 Mg of material (excavated soil and demolished building material) were disposed of at an underground mine. A remaining volume of 700 m3 was classified as radioactive waste. Site clearance started in 2006. Groundwater remediation and monitoring is still ongoing, but has already provided excellent results by reducing the remaining Uranium considerably.

We examined the suitability of taking smear tests (DIN ISO 7503.1) to evaluate surface activity. Special respect was given to mixtures of nuclides typical for the nuclear industry. We analysed the nuclides of samples of different fuel pools to evaluate the smear test measurement technique. Special calculations were carried out to examine the amount of nuclides that are difficult to measure due to their low maximum decay energy of less then 0.15 MeV (e. g. 55Fe, 63Ni). The response characteristic, detection sensitivity and the influence of the nuclide used for calibration were examined in detail on the basis of the nuclide vectors of fuel pool samples. We learned that especially the isotope standard used for calibration has a major influence for the suitability of the measurements. Calculation of the amount of these nuclides in relation to the effective dose (inhalation, ingestion) and the skin dose showed that they contribute little to the complete exposition.

Clearance levels for building structures normally are defined surface-specific (Bq/cm2) by the projection of the specific activity onto the surface. This proceeding led to the actual release criteria for buildings in the EC, which were also used for the actual draft of the new German RPO. The practical ability of collimated in-situ spectrometry verifying the keeping of these revised nuclide-specific clearance levels and the corresponding radiological averaging area of 1 m2 will be demonstrated. A completely different approach performing clearance measurements in building structures with poor remaining artificial activity was sketched in an earlier work, by performing a set of in-situ measurements without collimation. For this purpose, the spectrometer is calibrated for the measurement of the gamma dose rate at a very low level. The direct measurement of this value and its comparison with the fundamental, dose-based release criteria is a large advantage of this procedure. The sensitivity of a commonly used high-purity germanium detector is sufficient for this purpose with short measuring time; or in other words the detection limits are much smaller than 1 nSv/h. Therefore this presentation is dealing also with a complete new concept for the release of building structures of NPP’s. It is not supported by the actual release criteria basing on conversion factors from effective dose to surface-specific activity. The concept shown here, does not need this conversion, the effective dose is evaluated directly. On the other hand, it might be a basis of a fast, simple procedure in the projects of the next decades. The basic theoretical work is finished. In future, a practical check in an actual decommissioning project has to be done and the experiences gained by this work have to be documented.

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