Decommissioning of a Small Laboratory that Used 14C for Research Activities in Cuba

The International Centre for Neurological Restoration (CIREN) used 14C unsealed sources for radiochemical research. This practice was authorized by the Regulatory Authority through a registration granted in 2003 and valid for 4 years. The institution decided to use an alternative non-radiological technique, so the institution requested release of the radiochemical laboratory from regulatory control. For decommissioning operations, the CIREN contracted the services of the Centre for Radiation Protection and Hygiene (CPHR), which included the collection of radioactive wastes remaining in the facility, the radiological survey and characterization of the facility. It was fortunate that the historical records of CIREN were generally very good. A thorough revision of the available documentation (authorization, source inventories, inspection reports, radioactive waste collection reports) revealed that the only radionuclide used in the last 3 years was 14C; but between 1993 and 1996, other radionuclides, such as: 3H, 51Cr, 125I and 32P were used in the laboratory. The materials containing very short lived radionuclides had decayed to negligible levels. The activity of tritium that had been in use was very low, with the total activity received in the laboratory being only 9.25 MBq in 1993, 268 MBq in 1994 and 37 MBq in 1995. The total decay corrected activity for tritium remaining at the last audit carried out in 2005, based on activity received into the laboratory during 1993-1995 was estimated to be 174 MBq. This activity is below the clearance levels established in Cuban Regulation in terms of annual release rate for liquid discharges. Moreover, most of the materials contaminated with tritium had been previously collected as radioactive wastes. For these reasons, it was considered unnecessary to include tritium in the radiological characterization of the laboratory. From the decommissioning perspective only 14C was considered as the radiological inventory. Because of the radiological characteristics of this radionuclide, the reference levels for decommissioning were considered only in terms of surface contamination (fixed and non-fixed). The unconditional clearance levels for solid materials with low radioactive contents and for liquid and gas discharges to the environment are established in Cuban Regulation (National Nuclear Safety Centre - CNSN) in terms of activity concentration. For 14C the clearance level is 30 Bq/g for solid materials, 2 360 Bq/L for liquids and 47.6 Bq/m3 for gaseous discharges. An annual release of 10 GBq is authorized for liquid discharges. Unconditional clearance levels in terms of surface contamination are not contained in the regulations. For the radiological survey and decommissioning purposes it was necessary to derive surface contamination limits, in order to quantify the exposure risk due to non-fixed and/or fixed surface contamination. It was also necessary to define how to measure the derived surface contamination. The radiological characterization was carried out after all radioactive wastes were collected from the facility and transferred to the waste management facility. This waste consisted of unused solutions in vials and compressible solid waste.