[en] China LEAd-based Research Reactor (CLEAR-I) is a 10 MW lead-bismuth cooled research reactor, which serve as ADS and Lead cooled Fast Reactor technology verification platform. The evaluation of radioactive source term is needed for reactor decommissioning, worker and public dose rate. In this contribution, radioactive source term of CLEAR-I was calculated for normal operation in reactor core, primary coolant, cover gas and secondary coolant by CAD-based Multi-Functional 4D Neutronics and Radiation Simulation System (Visual-BUS) developed by FDS Team. This calculation is a guidance for reactor decommissioning, worker and public dose and radioactive waste disposal and transportation. (author)

[en] In order to predict the dispersion of radionuclides both in atmosphere and aquatorium, a new model was established to couple the Gaussian puff model and Eulerian model. The results of the coupling model presented good agreements with the references, which demonstrated the validity of all the modules. The coupling model was applied to simulate diffusion and concentration distribution of ¹³¹I in atmospheric and aquatic medium in the fuel assembly meltdown accident of China lead-based experiment reactor. The results showed that the distribution range of atmospheric pollutions was within 10 km 2 h after accident, meanwhile distribution range of aquatic pollutions was between 10 km and 20 km. Under the fuel assembly meltdown accident, the contaminant concentration in atmospheric and aquatic are still below the national standard limit. (authors)

[en] Accelerator Driven subcritical System (ADS) was recognized as an effective nuclear waste transmutation device. Target in liquid or solid in an independent loop bombarded by the charged particle beam was considered as the neutron source. Heavy metal was chosen as target material or coolant. The present work was to discuss the possibility of taking Minor Actinides as part of spallation target material, for a better transmutation performance of entire ADS. According to the thermal cooling and irradiation time limitation, a conceptual design of target for transmutation was proposed. And preliminary neutronics analysis for target performance assessment including neutron flux, neutron yield as well neutron spectrum is shown in this work. (author)

[en] Highlights: • Evaluating the migration of ²¹⁰Po outside primary loop during normal operation. • Activation calculations have been performed using the MCNP and FISPACT-2007 codes. • The Raoult's Law was used to characterize the evaporation model of ²¹⁰Po. • The level of ²¹⁰Po in the reactor building of China LEAd-based Research Reactor could not be harmful to workers. - Abstract: An important issue should be considered for liquid lead–bismuth eutectic (LBE) cooled reactors, which is the accumulation of radioactive ²¹⁰Po generated by neutron-irradiated LBE. It could cause problems during maintenance or refueling operations. Considering the safety of China LEAd-based Research Reactor (CLEAR-I), the activity of ²¹⁰Po in LBE coolant was calculated by VisualBUS system developed by FDS Team. The evaporation process from LBE to cover gas and migration to containing room and reactor building during normal operations were evaluated in this present work. According to preliminary analysis, there is little ²¹⁰Po contamination diffusing into the reactor building and its level in gaseous effluent was within the limits of NRC Regulation (10 CFR). It could not lead to problems during normal operations.

[en] The neutronics reference model of the international thermonuclear experimental reactor ITER only defines the tokamak machine and extends to the bio-shield. In order to meet future neutronics analysis needs, it is necessary to create a reference model of the ITER building beyond the bio-shield. With the help of Monte Carlo automatic modeling program MCAM and based on the engineering CAD model, the neutronics simulation model of ITER building complex was created. This model is the first neutronics model of ITER building complex and will be distributed to the world as a reference model. (authors)

[en] ITER equatorial port cell outside bio-shield plug is a place for allowing free personnel access after shutdown which accommodates various sensitive equipment and pipes. To ensure the personnel safety in port cell after shutdown, the distribution of dose rate in port cell was studied. Based on VisualBUS (CAD-Based Multi-Functional 4D Neutronics Simulation System), dose rate calculations were completed in port cell after shutdown. The result showed that dose rates in port cell are still 2 orders of magnitude more than desired limit (10 μSv/h) after one day shutdown. The optimization of bio-shield was needed. (authors)

[en] Highlights: •The source term and consequences of a simulated leakage accident in the primary gas cover for the China LEAd-based Research Reactor are assessed. •The LBE coolant bound a fraction of the volatile fission products. •Radioactive materials released of the accident were mainly noble gas elements, especially xenon. •The individual effective dose and lifetime thyroid dose decreased exponentially with increasing distance from the reactor and both were less than the control limits. -- Abstract: China LEAd-based Research Reactor (CLEAR-I) is a 10 MWt research reactor cooled with lead–bismuth. The cover gas system on top of the reactor cavity prevents the coolant from being exposed directly to the air and is important for reactors cooled with liquid metal. We carried out a preliminary analysis of a leakage simulation for the primary cover gas as a design basis accident of CLEAR-I. The radioactive sources and the consequences of release of radioactive material for the population around the reactor were determined. The results show that Xe-133 was the nuclide released in the largest amounts. Release of airborne radioactivity under the simulation conditions resulted in a maximum individual effective whole-body dose of only 6.06 × 10⁻⁶ mSv and a thyroid dose of only 3.54 × 10⁻⁶ mSv for adult, which are six and five orders of magnitude, respectively, lower than the upper limits set in Chinese regulation GB6249-2011. The results indicate that the consequences would be very small for such an accident for CLEAR-I, and no emergency actions would be required.

[en] Highlights: ► Equatorial port neutronics model was created according to CAD model using MCAM and inserted into ITER neutronics Alite4 model. ► Distribution of shutdown gamma dose rates in port cell and port interspace was studied using VisualBUS. ► The gamma dose rates in the port cell were higher than the desired limit (10 μSv/h). ► Refinements to the bio-shield plug design are suggested to ensure that dose rates in the port cell are within the design value for maintenance access - Abstract: ITER equatorial port cell outside the bio-shield plug is a place to allow personnel access after shutdown that accommodates various sensitive equipment and pipes. Gamma dose rate after shutdown of 1 day in the port cell should be within 10 μSv/h for occupational safety which is one order of magnitude less than that in the port interspace by the shielding of bio-shield plug. To verify the shielding property of the bio-shield plug, the distributions of gamma dose rates in port cell were studied. Based on the ITER neutronics model Alite4 which is a three-dimensional ITER tokomak neutronics model for MCNP calculations with a 40 degree extent in the toroidal direction and vertical reflecting bounded planes on both sides, the equatorial port was updated according to a conceptual CAD model using Monte Carlo Automatic Modeling Program for Radiation Transport Simulation (MCAM). A 2-step method of gamma dose rate calculation was used for shutdown dose rates in CAD-based Multi-Functional 4D Neutronics Simulation System (VisualBUS). The result showed that gamma dose rates in the port cell were higher than the desired limit. Refinements to the bio-shield plug design were suggested to ensure that dose rates in the port cell were within the design value for maintenance access.

[en] Highlights: ► We created a 3D neutronics model of the ITER building. ► The model was produced from the engineering CAD model by MCAM software. ► The neutron flux map in the ITER building was calculated. - Abstract: The three dimensional (3D) neutronics reference model of International Thermonuclear Experimental Reactor (ITER) only defines the tokamak machine and extends to the bio-shield. In order to meet further 3D neutronics analysis needs, it is necessary to create a 3D reference model of the ITER building. Monte Carlo Automatic Modeling Program for Radiation Transport Simulation (MCAM) was developed as a computer aided design (CAD) based bi-directional interface program between general CAD systems and Monte Carlo radiation transport simulation codes. With the help of MCAM version 4.8, the 3D neutronics model of ITER building was created based on the engineering CAD model. The calculation of the neutron flux map in ITER building during operation showed the correctness and usability of the model. This model is the first detailed ITER building 3D neutronics model and it will be made available to all international organization collaborators as a reference model.

[en] As the main interface components between plasma and vacuum vessel, the divertor is foreseen to be removed to the hot cell for refurbishment during the 20 years of ITER operation. During this process, the activated divertor will cause a large increase of radiation in the ITER building. 3D analysis has been performed to assess the radiation maps throughout the ITER building for assisting the shielding design for personnel and sensitive equipment. The activation of the divertor has been determined by coupled neutron transport and inventory calculations, radiation maps have been obtained from gamma transport calculations. The neutron and gamma transport calculations have been performed by MCNP5 code with FENDL2.1library. The inventory calculations have been performed by FISPACT2007 code with EAF-2007 library. The results of these 3D decay gamma radiation maps are presented by pictures in this paper, including the biological dose maps and maps of heat deposition in electronic equipment.