Oak Ridge DD Plan 3515 Project - Technology Review (2007) and GammaCam? Technology Demonstration for Characterizing Building 3515 at Oak Ridge (2007)Oak Ridge DD Plan 3515 Project - Technology Review (2007) and GammaCam? Technology Demonstration for Characterizing Building 3515 at Oak Ridge (2007)

摘要

This paper presents the results from the Characterization, Decontamination and Decommissioning (CD&D) Study performed by MSE Technology Application, Inc. (MSE) to assist the U.S. Department of Energy (DOE) and Oak Ridge National Laboratory (ORNL) in the preparation of a Project Execution Plan and Remediation Plan for Building 3515 at ORNL. Primary objectives of this study were to identify innovative CD&D technologies and methodologies and recommend alternatives applicable to the CD&D of Building 3515. Building 3515 is a small heavily shielded concrete and cement block structure centrally located in the Bethel Valley portion of the ORNL. The building's interior is extensively contaminated with Cesium 137 (Cs-137), the primary contaminant of concern. A previous attempt to characterize the building was limited to general interior area radiation exposure level measurements and a few surface smears gathered by inserting monitoring equipment into the building on long poles. Consequently, the spatial distribution of the gamma radiation source inside the building was not determined. A subsequent plan for D&D of the building presented a high risk of worker radiation dose in excess of as low as reasonably achievable (ALARA) because the source of the interior gamma radiation field is not completely understood and conventional practices required workers to be in close proximity of the building. As part of an initial literature search, MSE reviewed new generation gamma source characterization technologies and identified the GammaCam? portable gamma ray imaging system as an innovative technology applicable to locating the dominant gamma ray sources within the building. The GammaCam? gamma-ray imaging system is a commercially available technology marketed by the EDO Corporation. This system consists of a sensor head with a co-aligned camera and a portable computer. The system is designed to provide two-dimensional spatial mappings of gamma ray emitting nuclides in real time. The gamma radiation sensor and camera can be set up within or outside of the radiation field while the system operator and PC can be located 30 to 60 m (100 to 200 ft) from the sensor head. The system has been used successfully at numerous DOE and commercial nuclear facilities to precisely locate gamma radiation sources. However, literature attesting to the ability of this technology to detect radiation sources within heavily shielded structures was not available. Consequently, MSE was not certain if this technology would be capable of locating gamma ray sources within the heavily shielded Building 3515. To overcome this uncertainty, MSE sent two individuals to the EDO Corporation for training. At completion of the training, MSE leased the GammaCam? portable system and brought it to ORNL to evaluate the capability of the system. An overview from this evaluation is summarized in this paper.