During CY2000 ERI was awarded a competitive grant by US Department of Energy (Grant No DE-FG02-00ER) in the development of a Small (50 to 300 MWe) Advanced Reactor Technology (SMART) passive nuclear power plant. The design posses the following characteristics:

• Long refueling cycles (>10 years)
• Modular/transportable
• Proliferation resistant fuel
• Severe accidents an integral part of the design basis envelope
• Indefinite passive decay heat removal capability
• Price competitive

The SMART concept utilizes an innovative BWR design characterized by a large volume containment that is more typical of pressurized water reactors. The use of a BWR design reduces the overall system complexity, and eliminates the need for a secondary steam production system (i.e., steam generators), thereby reducing the overall cost, which should offset the additional cost for construction of a stronger containment.

The SMART core design is based on an innovative concept that uses either low-enrichment uranium or a mixture of low-enrichment uranium and thorium. Both fuels are relatively proliferation-resistant, and in conjunction with advanced fuel pin and core materials, the current design would allow continued operation (with provisions for on-line maintenance) for periods exceeding 10 years, without refueling.

The SMART Emergency Core Cooling System (ECCS) and the containment heat removal system are based on a simple concept using passive natural circulation of water for emergency core cooling, and air flow (aided by evaporative cooling at higher than 100 MW(e) power) for containment heat removal.

The SMART vessel and containment systems are shown in Figure 1. The feedwater system is designed to achieve the desired recirculation, core cooling and power production without the need for internal jet and external recirculation pumps. SMART is equipped with a Core Automatic Depressurization System (CADS). Reactor pressure control will be accomplished by means of relief valves which discharge through spargers submerged in a large In-Containment Water Pool (ICWP). The same discharge lines are used for automatic depressurization of the vessel during accidents. The borated water contents of the ICWP will also be used to reflood the vessel (by gravity) once it has depressurized, as well as to flood the reactor cavity/pedestal region (for vessel lower head cooling), in case of severe accidents. The steel containment will serve as the ultimate heat sink, which will also utilize a passive cooling system based on natural circulation of air on the exterior of the steel containment shell. Note that beyond 100 MW(e), the SMART design uses a combination of air and evaporative cooling (not involving any water sprays on the containment shell and not shown in Figure 1). Steam condensing on the shell’s interior is returned to ICWP, where it is available again for vessel or cavity flooding. Other design features include the use of passive engineered design features that are intended to deal with severe accidents as part of the design basis envelope. The SMART design will also be risk-optimized (eliminating the deficiencies in the current generation designs, through simplifications and innovation), and the ultimate aim is to demonstrate that SMART would meet the U.S. Nuclear Regulatory Commission licensing requirements.

The design feasibility studies that have been performed at Energy Research, Inc. have demonstrated the:

• Overall feasibility of the SMART concept,
• Achievement of very long fuel operating cycles (more than 10 years for uranium and more than 6 years for thorium fuels),
• Relatively slow progression of accidents/events in SMART,
• Effectiveness of the various engineered systems (ECCS and the passive containment heat removal system),
• Effectiveness of the various engineered systems to deal with severe accidents,
• Slow (typically days to weeks) pressurization potential of the reactor containment always remaining below the containment design pressure, and
• Adequacy of the existing technology (except for fuel, that requires additional R&D, if very high burn-ups are to be achieved) to support the design certification, fabrication and ultimate construction of SMART.

Additional benefits that could be realized include provisions in design to build several reactor modules at the lower-end of the power range, within an integrated nuclear plant infrastructure, in a common containment with associated decay heat removal and other systems. This would enable demand-based expansion of a reactor plant site equipped with many SMART modules, over time.