Fate and transport of unruptured tri-structural isotropic (TRISO) fuel particles in the event of environmental release for advanced and micro reactor applications.

Advanced nuclear reactor designs and advanced fuel types offer safety features that may reduce environmental consequences in an accident scenario when compared to conventional reactors and fuels. One advanced reactor fuel is tri-structural isotropic (TRISO) fuel particles which are approximately 0.9 mm in diameter. TRISO particle mobility, assuming the particle is unruptured and the encapsulated radionuclides are contained, was explored by a theoretical examination of transport through atmosphere, soil and groundwater, surface water, and non-human biota pathways. TRISO particles are too large and dense to travel in the atmosphere except under extreme conditions. TRISO particles are also too large to penetrate most soil profiles and so cannot be transported to or by groundwater. TRISO particles will settle out of the water column in surface waters and thus the transport will depend on the energy of the water body (e.g., waves or floods). TRISO particles could be transported by non-human biota. The size of TRISO particles could allow them to be intentionally ingested by non-human biota as a gastrolith or mimic something typical in an organism's diet. Generally, TRISO particles will have reduced environmental mobility compared to releases of radionuclides in the event of a conventional nuclear reactor accident. The extent of transport has implications in emergency planning zone designations and other considerations for licensing and deploying TRISO-fueled reactors. Further research and experimental work exploring TRISO particle mobility is required to understand the full environmental mobility of TRISO particles in the environment.

Internal Radiation Dose Evaluation for an Unruptured Post Release Tristructural Istropic Fuel Particle for Advanced and Micro-reactor Applications.

ABSTRACT: There are unique benefits from advanced/micro-reactor designs and fuel types that offer safety features in the case of an accident that may reduce environmental consequences compared to conventional reactors and fuels. Tristructural isotropic (TRISO) fuel particles are a robust advanced nuclear fuel type that leads to the unique question of how unruptured, activated TRISO particles will interact with humans. TRISO particles are 900 µm in size, and that particle size restricts internal dose assessment to the ingestion pathway. Activity of the TRISO particle was established by High Temperature Engineering Test Reactor simulations. The TRISO particle encapsulation was assumed to be perfect; exploration of internal dose contribution from radionuclides released from encapsulation was not included. The TRISO particle was assumed to be mixed actively within each alimentary tract compartment such that homogenous distribution could be assumed according to the International Commission on Radiological Protection publication 133. The dose assessment results indicate that the rectosigmoid colon had the highest internal organ dose for both reference male (2.1 Sv) and female (2.3 Sv). The internal dose from ingestion of the scenario-specific TRISO particle was 0.25 Sv for the reference male and 0.29 Sv for the reference female, which exceeds the annual occupational effective dose limit of 0.05 Sv in the Code of Federal Regulations, 10 CFR Part 20 Subpart C. Similarly, the annual occupational limit of 0.5 Sv to any one organ would be exceeded for the left colon, right colon, and rectosigmoid colon for both the reference male and female.

Prediction of sub-surface 37Ar concentrations at locations in the Northwestern United States.

The Comprehensive Nuclear-Test-Ban Treaty, which is intended to prevent nuclear weapon test explosions and any other nuclear explosions, includes a verification regime, which provides monitoring to identify potential nuclear explosions. The presence of elevated 37Ar is one way to identify subsurface nuclear explosive testing. However, the naturally occurring formation of 37Ar in the subsurface adds a complicating factor. Prediction of the naturally occurring concentration of 37Ar can help to determine if a measured 37Ar concentration is elevated relative to background. The naturally occurring 37Ar background concentration has been shown to vary between less than 1 mBq/m3 to greater than 100 mBq/m3 (Riedmann and Purtschert, 2011). The purpose of this work was to enhance the understanding of the naturally occurring background concentrations of 37Ar, allowing for better interpretation of results. To that end, we present and evaluate a computationally efficient model for predicting the average concentration of 37Ar at any depth under transient barometric pressures. Further, measurements of 37Ar concentrations in samples collected at multiple locations are provided as validation of the concentration prediction model. The model is shown to compare favorably with concentrations of 37Ar measured at multiple locations in the Northwestern United States.