A Comparison of Materials Issues for Cermet and Graphite-Based NTP Fuels
This paper compares material issues for cermet and graphite fuel elements. In particular, two issues in NTP fuel element performance are considered here: ductile to brittle transition in relation to crack propagation, and orificing individual coolant channels in fuel elements. Their relevance to fuel element performance is supported by considering material properties, experimental data, and results from multidisciplinary fluid/thermal/structural simulations. Ductile to brittle transition results in a fuel element region prone to brittle fracture under stress, while outside this region, stresses lead to deformation and resilience under stress. Poor coolant distribution between fuel element channels can increase stresses in certain channels. NERVA fuel element experimental results are consistent with this interpretation. An understanding of these mechanisms will help interpret fuel element testing results.
Thermal, Fluid, and Structural Analysis of a Cermet Fuel Element
This paper presents results and interpretation of a high-fidelity, multidisciplinary simulation of a cermet fuel element. The fluid, thermal, and structural equations are solved for a symmetric sub-region of a fast spectrum reactor core; detailed neutronic simulations provide heat deposition rates. Creep effects on stress are also simulated, as stresses are beyond elastic limits. The intent of this work is to predict maximum fuel temperature, variations in coolant exit temperature between channels, coating stress, and stress sources to evaluate and optimize cermet fuel element performance for Nuclear Thermal Propulsion reactors. The sources of mechanical stress in a fuel element are identified and their individual contributions are quantified. Temperature gradients and cladding-fuel thermal expansion mismatch are major sources of stress. Thick fuel element edge walls contribute to high fuel temperatures, high stresses, and low flow through edge coolant channels.
Handbook of Concrete Engineering
Handbook of concrete engineering , Handbook of concrete engineering , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی