Decommissioning of a Facility that Produced Incandescent Mantles in Berlin, Germany

The facility which manufactured incandescent mantles was operating from about the 1960s up to 2005. Production was stopped because there was no longer a market for incandescent mantles as they had been superseded by electrical street lighting. The facility was licensed by the radiation protection regulator in the end of the 1970s. Prior to this time, no license was needed and the facility was registered as a chemical manufacturer. After the legislation changed and the radiation protection legislation was issued, the company had to obtain a license and establish radiation protection rules. Thorium was not used for its radioactive properties in the production of incandescent mantles. The production of gas mantles included their impregnation with naturally occurring thorium, which contains 232Th as the radioactive isotope of interest. The thorium impregnation was essential to prevent the gas mantles from burning out too soon and to increase their light efficiency. This solution as Th (NO3)4 was delivered by a company which dealt with several minerals and chemicals. This solution was stored in plastic tanks and contained a high specific radioactivity in Bq/g and dose rates up to several hundreds of μSv/hr. Before seeking bids for the decommissioning of the facility (the company must obtain three bids from different decommissioning companies) it was decided to characterize the site to get a detailed overview about the used equipment, the secondary equipment like exhaust fumes and the radiological inventory. The characterization of the site was estimated to require five workers over two days, including one external specialist knowledgeable in free release of material. Boundary conditions and requirements for characterization are described in the following: (1) The owner of the facility planned to sell most of the equipment for reuse at an Indian facility. This necessitated thorough decontamination. Production of secondary radioactive waste was a problem. Equipment had to be packaged for transport to India in compliance with all relevant transport regulations. Dismantling of equipment intended for reuse had to be planned and executed to facilitate reconstruction in India at the new facility. (2) Definition of end state: The required end state of this project was free release of the production floor (third floor of the building) for reuse and the surrender of the site license. The threshold values for 232Th for surface contamination in Bq/cm2 and activity concentration levels in Bq/g established in German radiation protection law had to be met. (3) Characterization planning and data capture: Before starting the characterization, a plan was made. It included planning of the manpower, identifying the required tools, the time required, analysis methods to be used and a list of assignment of who is responsible for what. (4) Identification of infrastructure and resources required for characterization: Because the facility was still operational up until the shut down, all infrastructures were active and maintained; e.g. electricity, main exhaust and ventilation system, water and drainage system, a lift for materials and also radiation protection equipment like aerosol collectors, surface contamination monitors, a hand, foot and clothing contamination monitor and also calibrated dose rate monitors. Additionally measurement equipment, such as an in situ gamma spectrometer was made available for use by a research institution. (5) Dismantling required for characterization: As part of characterization, it was very important to dismantle some equipment to facilitate further sampling and measurement. For example, the furnace where the mantles had been dried had to be opened to perform measurements. Other structures such as gloves boxes, test equipment, impregnation baths, etc had to be partially dismantled to gain access to the most contaminated areas. Even looking behind furniture or heaters or into rubbish drums can be useful as part of characterization. Prior to opening up equipment, assess the prevailing radiological conditions through appropriate measurement. Appropriate protective clothing should be worn when dismantling equipment, including the wearing of respiratory protection as appropriate. (6) Characterization to solve waste management issues. (7) Health and safety considerations during characterization. (8) Final characterization report: Prior to issuing the final report, checks were made that all measurement points were correctly identified, pictures had been appropriately labeled and sorted, samples were properly stored and sample points were covered or closed again. The results were provided in a summary report to the customer.