Advanced High Temperature Concepts for Pressure-Tube Reactors, Including Co-Generation and Sustainability

The development of advanced concepts for pressure-tube reactor technology and its potential contribution to a sustainable future are presented. We show that, using the pressure-tube reactor advantage of modularity, the subdivided core has the potential for optimization of the core, fuel cycle and thermal performance independently, while retaining the advantage of passive safety heat removal. There is no need to switch to radically different coolants, but instead optimize the steam and fuel cycles. We show that continuous improvement leads naturally to the next phase of CANDU water-reactor development, which examines the CANDU–SuperCritical Water-cooled Reactor (SCWR) concept. This is again conventional water technology, since supercritical and ultra-supercritical boilers and turbines have been operating for some time in coal-fired power plants. Using coolant outlet temperatures of about 625ºC achieves operating plant thermal efficiencies in excess of 40%, using a direct turbine cycle. In addition, the plant has the potential to produce large quantities of low cost heat, which can be used for other industrial processes. Thus, the overall thermal efficiency is further enhanced. Significant cost, safety, and performance advantages result from the CANDU-SCWR concept, plus the flexibility of a range of plant sizes suitable for both small (400 MWe) and large (1200 MWe) electric grids, and the ability for co-generation of electric power, process heat, and hydrogen. By optimizing the channel with a passive moderator cooling system, the passive-safety system is functional with the potential for designing a "walk-away" passive-safety system that does not require any operator action (i.e., core melt and severe core damage can be eliminated). In the interests of sustainability, hydrogen production by a CANDU-SCWR is discussed as part of the system requirements, where the methods for hydrogen production will depend on the outlet temperature of the coolant. For temperatures below 625ºC, electrolysis will likely be the preferred viable choice, perhaps in conjunction with process heat, using the cheap power available from existing non-exotic materials and fuels, including sustainable thorium fuel cycles. We also examine the ultimate limits on the pressure-tube concept, using reheat steam-cooled channels. The even higher efficiency from high temperatures at low pressures allows reactor temperature limits to set by materials choice, and variable hydrogen production can then be by either high temperature electrolysis or direct thermo-chemical methods. AECL's evolutionary approach for water reactors is to establish the technology progressively, and evolve to higher temperatures as the operating experience, energy needs, and technical knowledge base advance together. (author)