Objectif Previous experiments made by ENEL on small valves, using aggressive chemicals, showed that zones with residual contamination remain inside the components. The present work aims at solving this problem by enhancing the decontamination effectiveness with the action of focused ultrasonic waves. The main objective of the project is to set up and test in real conditions a new decontamination process based on the simultaneous use of ultrasonic waves and aggressive chemicals, with ultrasonic transducers applied outside the components. This decontamination process, if its expected performances are confirmed, could become a useful tool in decommissioning activities. It should permit the increase of the amount of decontaminable parts without having to spend many man-hours and man-Sv (thus, without dismantling before decontamination). The project is based on experimental investigations, mainly at laboratory scale but also in plant scale. It is the continuation of work performed by ENEL in the framework of previous EC programmes on decommissioning (contract DE-B-005, report EUR 9303; contract FI1D0002, report EUR 12878). Previous experiments made by Ente Nazionale per l'Energia Elettrica (ENEL) on small valves, using aggressive chemicals, showed that zones with residual contamination remain inside the components. The present work aims at solving this problem by enhancing the decontamination effectiveness with the action of focused ultrasonic waves. The main objective of the project is to set up and test in real conditions a new decontamination process based on the simultaneous use of ultrasonic waves and aggressive chemicals, with ultrasonic transducers applied outside the components. Calibration and testing of the prototype ultrasound transducer and generator has been completed. Moreover tests with nonactive AISI 304 pipe allowed the determination of the optimum working conditions (coupler, diameter, ultrasound frequency and power) for subsequent decontamination tests. For first tests the selected transducer is of the Langevine type (eg precompressed) and basically consists of a piezoelectric ceramic material disc forced between 2 metallic blocks. It is applied on the external surface of the pipe by a front conic coupler (sized on a 1/4 wavelength).For initial testing AISI 304 material was used both nonactive and radioactive. The external diameter and thickness are 48.3 mm and 3.7 mm respectively. Radioactive material came from BWR Garigliano and it belonged to an auxiliary pipe (draining line) of the primary system.Preliminary laboratory tests on AISI 304 radioactive specimens have been performed in order to evaluate the effectiveness of the decontamination process both on straight pipes and on complex geometry samples. Tests have been performed in flowing chemicals (5 per cent nitric acid plus 1.5 per cent hydrofluoric acid) with the ultrasound transducer directly applied on the external surface of the tested material. Results indicate that the decontamination process can reduce the residual activity of straight pipes well below the limit of 1 Bq/cm{2} with a uniform and minimal base metal remover (less than about 20 um). Furthermore, results suggest that the direct application of a transducer on a component surface can drastically reduce the residual activity in zones such as welds and dead legs where recontamination occurs if only flowing chemicals are used.WORK PROGRAMME 1.Evaluation selection and acquisition of special ultrasonic transducers to be applied to complex components from outside. 2.Decontamination tests on specimens and components in the DECO loop. 2.1.Preparation of the DECO loop for testing; selection and characterization of test specimens and components from Garigliano BWR. 2.2.Decontamination tests on contaminated specimens. 2.3.Decontamination tests on valves: radioactivity measurements, decontamination factor evaluation and secondary waste assessment. 2.4.Data analysis. 3.Decontamination and dismantling of a part of a real system of a nuclear power station 3.1.Preparation of the system part to be decontaminated. 3.2.Initial radioactivity characterization. 3.3.Process design and configuration. 3.4.Decontamination. 3.5.Dismantling and final radioactivity measurements. 3.6.Evaluation of secondary wastes. Champ scientifique natural sciencescomputer and information sciencesdata sciencenatural sciencesmathematicspure mathematicsgeometrynatural sciencesphysical sciencesacousticsultrasound Programme(s) FP2-DECOM 3C - Specific research and technological development programme (Euratom) in the field of decommissioning of nuclear installations, 1989-1993 Thème(s) A2 - Decontamination for decommissioning purposes Appel à propositions Data not available Régime de financement CSC - Cost-sharing contracts Coordinateur Ente Nazionale per l'Energia Elettrica SpA (ENEL) Contribution de l’UE Aucune donnée Adresse Via Monfalcone 15 20132 Milano Italie Voir sur la carte Coût total Aucune donnée
