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This study considers a deliberate hypothetical release of radioactive material over an inhabited urban zone. The event is initiated by the activation of a radiological dispersion device. The main threat is the deposition of radioactive material onto the soil's surface. The radiation represents the threat-defining risks, which depend on the main variables, i.e. soil surface roughness, sex, age of the exposed individuals and the moment of the release (day or nighttime). This study aims to evaluate the effect of soil surface roughness on the radiological risk. The simulation was performed by an analytical method using the HotSpot Health Physics code within the first 100 h. The results found relevant elements that allow for differentiating consequences as a function of the time of release (whether daytime or nighttime), thus allowing decision-makers to be supported with a little more detail about the situation, although in a critical initial phase.

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This study evaluates the risk assessment of a hypothetical scenario where an off-site radioactive release occurs at a nuclear power plant. By using the code Accident Reporting and Guiding Operational System (Prolog Development Center - PDC/ARGOS) a numerical simulation was performed to simulate exposure conditions in an atmospheric plume of contamination. Crews on a rescue mission traverse the plume through a pre-defined path to evaluate the risk from a hypothetical radiological exposure. Applying a sophisticated epidemiological assessment methodology, radiation doses and risks on the teams were evaluated. Core variables such as gender, age and radiation dose were considered in relation to specific morbidities. It was possible to propose a methodology capable of contributing to the reduction of risks to the personnel involved by connecting the results from the computer simulation and the epidemiological risk assessment.

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The application of nuclear technologies in a cargo and container inspection facility can increase the risk of accidents. Estimating the radiation dose in the controlled area generates critical information for elaborating routines aimed at establishing more effective safety procedures. For radiological protection purposes, mapping ambient dose equivalent H*(10) levels is crucial. The radiation source used was a fixed linear accelerator of 4.5 MeV. Five RadEye PRD-ER (Thermo Fisher Scientific) personal radiation monitors and five Geiger-Müller MRAD 111 (Ultra Radac) personal radiation monitors were used for the radiation measurements. The highest ambient equivalent dose rate and dose per scan were found with the Geiger-Müller monitors at values of 5.76E-01 mSv/h and 1.12E-03 mSv, respectively. The results showed that for public individuals, the number of scans at the point of highest dose rate value cannot exceed 893-unit operations. Additionally, the risks involved in the abnormal situation (increased H*(10)) were estimated by using a model to predict the development of solid cancer as a result of occupational radiological exposure. This procedure highlights the risks involved, hence providing initial support to the decision process.

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This study focusses on the risk of potential exposure to radiation for personnel driving a truck as well as illegal individuals being transported in cargo containers. Inspection facilities usually use a high energy linear accelerator (linac) in order to inspect the cargo. Since this type of equipment has associated health risks due to potential unwanted exposure, the occupational and public dose limits should be calculated in order to develop safer work conditions. This work used a computation model running the code MCNPX to simulate a typical cargo inspection facility which used a linac operating at 4.5 MeV. Two scenarios were considered: (1) exposure of the driver to the primary beam due to a potential failure of the safety sensors; and (2) dose received by an illegal individual being transported inside the cargo container. The results show a dose of 0.8514 mSv per scan for the driver exposed to the primary X-ray beam, and 0.1997 mSv per scan for an individual transported in the cargo box. In conclusion, both the individual and the driver received a dose below the acceptable limit considered safe for an individual (1 mSv/year). However, that was the value of one scan; in a case in which multiple scans would be performed, the dose limit can be quickly exceeded. In that case, the limit would be exceeded by the driver faster than by the individual in the cargo.

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RESUMO

The National Council on Radiation Protection and Measurements (NCRP) Report No. 151 is an essential document for bunker design commonly applied for radiotherapy treatment rooms. This document is used as a reference by several countries, including Brazil. The objective of this study is to evaluate the shielding dimensioning methodology recommended by NCRP 151, and compare it with the one adopted by the Brazilian regulatory authority. Radiotherapy rooms and respective doors were designed to use linear accelerators operating at 6, 10, 15, and 18 MeV under two different ways: (a) applying exclusively the methodology recommended by the NCRP 151, and (b) taking into consideration the complementary recommendations from the Brazilian authorities. The results suggest that designers in Brazil can count on at least 4 and 11% safety margin for dimensioning primary barriers in controlled and free areas respectively. Also 8% for secondary barriers in controlled areas, 9.7% for secondary barriers adjacent to the primary belt of free areas, and 6.6% for the lead of the doors.

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