Abstract :
[en] Nondestructive test (NDT) has been widely used for defects detection, well joints inspection, and material integrity verification in recent decades. Gamma radiography’s applications in industry are known as high risk-related techniques among the nuclear-related industries nowadays. For example, the IAEA safety report about the lesson learned from accidents in industrial radiography reported that around 45 % of accidents in the nuclear industry accounted for industrial radiography in both developed and developing countries [1]. This demonstrates the need to optimize safety and protection measures around gamma sources used in fixed industrial radiography. The present study focuses on the optimization of engineering barriers during the sitting and construction phases of such facilities. Monte Carlo methods-based PHITS are used to optimize the shielding design of enclosures of a radiographic facility to create a safe working environment for both radiographers and the public. The Particle and Heavy Ion Transport code System [2, 3] was used to determine the appropriate concrete wall and dose estimation to keep radiation As Low As Reasonably Achievable (ALARA). As shown in Fig.1, there are many concerns in old built facilities and few in new ones, but the primary objective is to provide radiological protection regulation or to update and optimize the existing regulation, taking into consideration the shielding design of the facility
As the radiation exposure to any given material depends on the thickness of the shielding, the quantity, and the energy of the radiation, both Co-60 and Ir-192 sources were used in our study as they are the most used high-energetic radionuclides used in industrial radiography. The MC code used for computation, PHITS, is a general-purpose Monte Carlo Particle and Heavy Ion Transport code System developed by a collaboration between Japanese institutions and Europe. The version used, PHITS 3.10 with several changes, allows the simulation of photon and other particles of interest transport over a wide range of energy. The design principle here is based on providing enough shielded enclosure to keep the dose rates out of the facility (in the closest adjacent areas to the facility) lower than 2.5 μSv/h, in adherence to the ALARA principle for the public exposure. If not, a large exclusive area should be set, but this part is considered as administrative controls, which are discussed differently. The facility design was based on the IAEA safety report series [7] and the photon flux distribution simulated is presented in Fig. 2 along with the plot of the dose conversion factor used for computation.
Appropriate concrete thickness to shield radiation from isotropic sources was computed prior to the radiographic testing room design. The minimum concrete wall thickness for the facility using Co-60 sources described previously was found to be 120 cm while it was found to be 70 cm for Ir-192 related facility as shown in TABLE 2. To ensure that the radiation dose falls under the recommended limits set either by international organizations as IAEA, or by the regulatory authority of Cameroon, the necessary and appropriate shielding walls and shielding materials shall be installed and regulated by laws.
It is recommended to the government, conjointly with the NRPA of Cameroon, to make a law project in this regard that will be passed in view to facilitate the regulation of the wide-spreading practice of industrial radiography using radioactive sources, especially gamma imaging. The present code could be really helpful to the Government of Cameroon in developing a database for sitting and construction of radiographic testing rooms depending on the radionuclide type, its energy and intensity, and its activity. Appropriate design-based maze technology was developed by Guembou in his thesis [6]. There is a real need for the implementation of the international rules and the adoption of clear and specific national guides for the application of industrial radiography in Cameroon as well as in different other countries. Different IAEA safety standards series, safety reports series, and technical documents were provided to help governments, institutions, and individuals involved in the use of radioactive sources for industrial radiography to develop an appropriate safety culture. In this regard, enclosures of a radiographic room should be properly designed and used for the sources for which they were designed, considering the maximum activity, the type of radioisotope, their energy, and intensity. Developing countries as Cameroon could use MC simulation for national regulation improvement according to their socioeconomic statute and technology-based considerations.
