Estimation of Radiological Consequences at a Proposed Nuclear Power Plant Site Using Atmospheric Dispersion Code

Atmospheric dispersion modeling and radiation dose calculation have been performed for a generic 1000 MW water-water energy reactor (VVER-1000) assuming a hypothetical loss of coolant accident (LOCA). Atmospheric dispersion code, International Radiological Assessment System (InterRAS), was employed to estimate the radiological consequences of a severe accident at a proposed nuclear power plant (NPP) site. The total effective dose equivalent (TEDE) and the ground deposition were calculated for various atmospheric stability classes, A to F, with the site-specific averaged meteorological conditions. From the analysis, 3.7×10−1 Sv was estimated as the maximum TEDE corresponding to a downwind distance of 0.1 km within the dominating atmospheric stability class (class A) of the proposed site. The intervention distance for evacuation (50 mSv) and sheltering (10 mSv) were estimated for different stability classes at different distances. The intervention area for evacuation ended at 0.5 km and that for sheltering at 1.5 km. The results from the study show that designated area for public occupancy will not be affected since the estimated doses were below the annual regulatory limits of 1 mSv.

POTENTIAL ENVIRONMENTAL HAZARD TO THE PUBLIC FROM THE OPERATION OF URANIUM MINING AND MILLING FACILITY

Mining and milling processes could cause potential radiological exposures to the public. The objective of this study was to estimate the off-site radiological doses expected to be received by the public as a result of uranium mining and milling activities at Mkuju River Project in the United Republic of Tanzania. MILDOS-AREA was used to estimate off-site doses along with RESRAD-OFFSITE for comparison and verification. Since the mining has not yet started, the conceptual scenario was chosen. Using the concept of the most exposed individual, the location of the nearest residence (receptor) was chosen at 2.5 km from the site with other receptors being the fence boundary and grazing area being at 1.0 and 1.8 km, respectively. Yellowcake stack (point source), ore pad and two tailing piles where each had an area of 2.5 × 105 m2 were chosen to be the source of radiological contamination. The radiological source term was obtained from the concentration of 226Ra and 232Th in soil obtained from the previous studies of environmental impact assessments. Meteorological and site-specific data were used for this analysis. The estimated total effective dose equivalent (TEDE) for the nearest residence which was calculated by MILDOSE-AREA ranged from 2.5 × 10−2 to 4.45 × 10−2 mSv/y during the operation of 13 y. The result of RESRAD-OFFSITE ranged from 7.19 × 10−2 mSv/y for the first year to 7.43 × 10−2 mSv/y in the final year. This implied all the estimated TEDEs were below the dose limit and dose constraint of 1 and 0.3 mSv/y, respectively, as suggested by the International Atomic Energy Agency. Hence, it was found that there was no potential radiological concern of uranium mining at Mkuju River Project. It was found that using MILDOS-AREA it is possible to estimate dose at different distances from the facility. Therefore, this study apart from estimating the off-site doses, it can be used for planning of public and social premises before the commencement of the project. That is the distance from the facility where the public should be located as well as other locations for social activities.

OFF-SITE RADIOLOGICAL DOSE ASSESSMENT IN A SEVERE NUCLEAR ACCIDENT OF APR1400

Shin Kori unit 3 of Korea Hydro and Nuclear Power Co. is the pressurized water reactor of advanced power reactor 1400 (APR1400) in the Republic of Korea. A hypothetical accident was assumed for Shin Kori unit 3 to perform the time-dependent dose calculations along with the release rates of radionuclides to the environment. In order to assess the accident scenarios, Radiological Assessment System for Consequence Analysis code was used, which is a set of tools for emergency response applications developed by US Nuclear Regulatory Commission. A straight-line Gaussian model was used for the near-field atmospheric calculations and a Lagrangian Gaussian puff model was used for the far-field simulations where released radioactive materials to the environment were transported, dispersed and deposited. In this study, long-term station blackout in spring, summer, autumn and winter season was considered in 2016–2018 based on reactor condition and seasonal effects. It was found that the worst season is the spring and the worst scenario found during the evening time of spring in 2017. The calculated maximum values of total effective dose equivalent (TEDE) and thyroid committed dose equivalent (CDE) are 22 mSv and 390 mSv, respectively, around 5 km of precautionary action zone (PAZ) in 2 days after the accident. According to Korean regulations on urgent public protective actions, for indoor sheltering, the criteria are 10 mSv in 2 days. For public evacuation 50 mSv in 1 week and iodine prophylaxis should be introduced if thyroid protection level is 100 mSv. Calculated values of TEDE are more than double and thyroid CDE is almost four times in the PAZ compared with Korean regulations; hence, it was found that indoor sheltering and supply of iodine prophylaxis should be executed for short/mid-term protective measures. In this situation, indoor sheltering should be decided by off-site emergency management center, which was accountable for emergency decision-making process in nuclear accident under nuclear safety and security commission in Korea.

Impact of Strontium and Krypton Release from Ghana’s MNSR following a Conjectural Accident Scenario

Accidental release of gaseous or liquid effluents is a critical issue and of a greater concern to the nuclear industry when it comes to the protection of the public and the environment. The emphasis becomes paramount when the release involves particulate of radiation particles. This paper provides a comprehensive insight report on an account of a research investigation carried out in addressing a radiological safety issue of Ghana’s Miniature Neutron Source Reactor (MNSR) during its core conversion project. The amounts of Strontium-90 (Sr-90) and Krypton-85 (Kr-85) effluents presumably released from the reactor hall to the surroundings and the consequential emission radiation to the working area within a 200 m radius were analyzed for a six-month working period. The objective was to estimate specifically the approximate total effective dose equivalent (TEDE) of Sr-90 and Kr-85 by considering a conjectural accident scenario using a well-recognized and user-friendly known atmospheric dispersion model before the preparatory period. The maximum TEDE value recorded at a ground deposition value of 4.6E − 01 kBq/m2 was approximately 1.80E − 02 mSv and 4.90E − 4 mSv for Sr-90 and Kr-85, respectively, at a maximum distance of 0.1 km from the source. The estimated dose values recorded were found to be within the recommended regulatory safety limits of 50 mSv for onsite workers and 1 mSv for the general public. No adverse effect was experienced with respect to human health and the environment.

Radiological consequences assessment of a hypothetical accident during transportation of spent nuclear fuel

During the transportation of spent nuclear fuels, the potential release of the radioactive materials into the atmosphere in the case of an accident becomes a serious threat to public health and the environment. In China, a commercial reprocessing plant is planned to be commissioned around 2025 based on the China nuclear roadmap. After being cooled on site the spent nuclear fuels are transported to the reprocessing plant by train or truck. This requires the assessment of radiological consequences of such accidents during transportation, therefore dose calculations under hypothetical accident conditions have been presented in this paper. The total effective dose equivalent and ground deposition are calculated using the HotSpot health physics computer code with site-specific meteorological conditions. The results indicate that the total effective dose equivalent and ground deposition are both decreased with the increase of the downwind distance. The maximum of the total effective dose equivalent is about 1.4?101 Sv, which is larger than the regulation limit for the public. The TEDE counter plot shows that the inner regions marked with dose contours of 1.0?10?3 Sv are higher than the regulation limits for the public, however this needs no intervention but any unnecessary trip to this area should be avoided.