Nonproliferation improvements and challenges presented by small modular reactors
Small modular reactors (SMRs) may provide an energy option that will not emit greenhouse gases. From a commercial point-of-view, SMRs will be suitable to serve smaller energy markets with less developed infrastructure, to replace existing old nuclear and coal power plants, and to provide process heat in various industrial applications. In this paper, we examine how SMRs might challenge and improve the existing nonproliferation regime. To motivate our discussion, we first present the opinions gathered from an international group of nuclear experts at an SMR workshop. Next, various aspects of SMR designs such as: fissile material inventory, core-life, refueling, burnup, digital instrumentation and controls, under- ground designs, sealed designs, enrichment, breeders, excess reactivity, fuel element size, coolant opacity, and sea-based nuclear plants are discussed in the context of proliferation concerns. In doing this, we have used publicly available design information about a number of SMR designs (B&W mPower, SVBR-100, KLT-40S, Toshiba 4S, and General Atomics EM 2 ). Finally, a number of recommendations are offered to help alleviate proliferation concerns that may arise due to SMR design features.
Design of the 4S Reactor
Abstract The Super-Safe, Small and Simple (4S) sodium-cooled fast reactor plant incorporates innovative design features, such as a nonrefueling reactor, passive safety, low maintenance requirements, and inherent security. Major components such as the reflector drive mechanisms, the electromagnetic pumps, and the double-wall tube steam generator have been optimized for efficient and safe operation. The nonrefueling reactor concept is made possible by incorporating a 30-yr refueling interval for the reflector-controlled metallic fuel core. Sodium-cooled, metallic-fueled fast reactors have a good conversion ratio due to fast neutron usage, thus extending the core life. Passive safety is achieved with redundant residual heat removal systems that function using only natural circulation, and a metallic core with a negative reactivity coefficient. Low maintenance requirements are achieved by simplifying the design and minimizing the use of active components, and by using electromagnetic pumps, which have no moving parts. The inherent security of the nuclear materials is significantly enhanced by the nonrefueling reactor concept and the minimal maintenance requirements. In addition, the reactor building is located below ground level, providing substantial protection against an aircraft impact and thus further enhancing the security of the design. The demonstration of key components such as the electromagnetic pumps and the steam generator is part of an ongoing testing program that has already confirmed many of the 4S engineering solutions. This paper describes the current status of design and component tests for the 4S reactor.
Effect of stress conditions on collapse deformation behavior of a rockfill material
A set of saturated and dry-saturated large-scale triaxial tests were conducted in order to explore the effects of stress conditions on the saturation-induced collapse deformation behavior of a rockfill material. Specimens were tested in different confining pressures and for dry-saturated tests the specimens were submerged in various shear stress levels. The results indicate that in all of the dry-saturated tests a sudden reduction in the volume of the specimens was observed during the submerging process. The ratio of the minimum axial strength of a submerged specimen (at the end of the saturation process) to the shear strength of the specimen before saturation is defined as the coefficient of stress recovery, Csr. Results of the dry-saturated tests showed that this ratio increases as the confining pressure increases and decreases by increasing the shear stress level. According to the results of dry-saturated tests the values of internal friction angle reduction caused by saturation (Δϕc), the ratio of the elasticity modulus of the material after saturation to its elasticity modulus in dry condition, i.e., Ewet/Edry, and also the saturation induced sudden volumetric strain (εvc) decrease as the confining pressure increases. However the shear stress level does not have any meaningful effect on the variation of Dfc, Ewet/Edry and (εvc).