Liquid and wet LLW generated during operation as well as decommissioning of NPPs is treated with different methods and fixed in a suitable fixation matrix so that a final product meets required criteria for its disposal in a final repository. Cementation is an important process used for fixation of liquid and wet radioactive waste such as concentrate, spent resins and sludge. Active cement grout is also used for fixation of low level solid radioactive waste loaded in final packing containers. VUJE Inc. has been engaged in research of cementation for long. The laboratory for analyzing radioactive waste properties, prescription of cementation formulation and estimation of final cement product properties has been established. Experimental, semi-production cementation plant has been built to optimize operation parameters of cementation. VUJE experience with cementation of liquid and wet LLW is described in the presented paper. VUJE has assisted in commissioning of Jaslovske´ Bohunice Treatment Centre. Cement formulations for treatment of concentrate, spent resins and sludge have been developed. Research studies on the stability of a final concrete packaging container for disposal in repository have been performed. Gained experience has been further utilized for design and manufacture of several cementation plants for treatment of various liquid and wet LLW. Their main technological and technical parameters as well as characterization of treated waste are described in the paper. Applications include the Mochovce Final Treatment Centre, Movable Cementation Facility utilizing in-drum mixing for treatment of sludge, Cementation Facility for treatment of tritiated water in Latvia and Cementation Facility for fixation of liquid and solid institutional radioactive waste in Bulgaria, which utilizes lost stirrer mixer.
This paper deals with advanced 3D computer-aided technologies used for modelling and simulation for decommissioning purposes. Within the A-1 NPP decommissioning process a set of activities is needed to perform successful dismantling and decontamination of rooms and equipment. Optimal process of performance of D&D of underground storage tanks and auxiliary rooms were used on the base of simulation outputs. The mockup tests were performed before using remotely controlled manipulators. The human presence during decontamination and dismantling is case by case excluded due to the radiation safety and ALARA approach. Within Bohunice A-1 Decommissioning Project an advanced computer-aided technologies were/are developed and used. Modelling software packages EUCLID and 3Dipsos together with 3D-laser scanner SOISIC are used for creating of 3D models and also for the verification of as-built state of selected systems and facilities. Software IGRIP is used for computer simulations of all D&D tasks. The 3D modelling and simulation of selected rooms and technological equipment of the A-1 NPP are used consequently in the process of decommissioning preparation and implementation. 3D modelling for the verification and simulation of operating steps is presented in the paper and its contribution to avoiding of collisions and non-optimal interventions into the building and technological parts during performing particular works is evaluated. The application of 3D models for the verification and simulation of operating steps significantly contribute to the optimal planning of D&D procedures. Minimisation of occupation doses of realisation personnel is main reason why the 3D modelling and simulations are used. The paper also presented 3D models of rooms chosen to simulate specific operations (decontamination, handling of radioactive wastes and/or dismantling by remote controlled manipulators) without risk accident, high dose rates of personnel etc. Process of selection of optimal operating procedure for decontamination and dismantling is presented as well as achieved experiences and recommendations for further work.
A pilot free-release monitoring post with a 600 L container monitor was developed and metrological tested within the 2nd stage of NPP A1 decommissioning project. In order to reduce the volume of contaminated soil monitoring a conceptual design of fast sorting loader shovel monitor (loader’s spoon) was proposed and tested within the project as well. The free-release monitoring post makes use of a pair of electrically cooled lead shielded semiconductor detectors placed into a mounting rack ensuring measurements in either horizontal (container monitoring) or vertical (drum monitoring) counting geometry. For evaluation of measured HPGe spectra the Canberra – Packard ISOCS detection efficiency calculation code was used. A loader is used to change the measured side of the 600 L container. For metrological certification of this monitor a special prototype test container with 24 rod sources inside a regular grid was necessary to design and to use. The mentioned above vertical counting geometry together with an additional drum rotator ensures standard free release monitoring of materials in 200 l rotating drums. Successful metrological qualification of the both counting geometries at SMU Bratislava showed 20% accuracy class. A pair of NaI(Tl) detectors and a measurement and navigation frame ensuring loader shovel fixation in counting position are used for the fast sorting monitoring. The navigation of loader and its shovel to the counting geometry should be as fast as possible. The monitored results shall be indicated by a prompt light indication system (apart from storing on HDD). MCNP 5 calculation code was used for assessment of gross gamma 137Cs detection efficiency. The estimated MDA for a pair of 2″ × 2″ Na(Tl) detectors and 30 s acquisition time is about 90 Bq/kg. However, due to the counting geometry deviations from calculated values the uncertainty of measurements can be relatively high. Hence, the system is applicable for sorting monitoring only.
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