Thursday, April 29, 2010

2nd Canada-China Joint Workshop on Supercritical Water-cooled Reactors (CCSC-2010)

The 2nd Canada-China Joint Workshop on Supercritical Water-cooled Reactors was held in Toronto earlier this week. (The 1st workshop had been held in Shanghai, China in April 2008.) The Supercritical Water-cooled Reactor (SCWR) is a Generation IV water-cooled reactor concept that holds the most promise for higher efficiency, on account of its higher operating temperature range, the hoped-for single phase (supercritical) operation (i.e., not having to deal with two-phase flow), the thermophysical properties (especially thermal conductivity and specific heat) of supercritical water, and the resulting saving in balance of plant pumps and compressors and secondary loop tubing and systems. What adds to the attractiveness of the concept is the possibility of realizing it within the Pressure Tube (PT) reactor design envelope, and moreover, the possibility of advanced fuel cycles involving thorium fuel within the concept.

However, a number of challenges also exist, which must be resolved through R&D, before the concept can become a realistic design. Within the Generation IV International Forum, Canada leads R&D work on the SCWR concept, and the purpose of the workshop this week was for Canadian and Chinese researchers to share the results of their respective R&D projects on materials, thermalhydraulics, water chemistry, and fuel cycle issues, in addition to more explicit considerations involving safety and licensing related foresight.

Over the three days of the workshop, there were two broad parallel tracks - sessions devoted to (i) materials issues and chemistry; and (ii) sessions devoted to thermalhydraulics, with an interspersed session each on reactor physics, licensing and safety, and nuclear hydrogen production with SCWR heat. Much of the work presented at the conference comprised sharply focused investigations along pre-established R&D priorities that had been scoped out in the basic SCWR R&D plan - both experimental and simulational investigations were presented. 

A significant departure from standard PHWR (CANDU) design that is being considered in the PT-SCWR (CANDU-SCWR) concept involves vertical pressure tubes (as opposed to the horizontal pressure tubes that are standard in PHWRs). Thus, two papers comparing supercritical and subcritical heat transfer correlations and characteristics in vertical pressure tubes, one each from Canada and China, were of particular interest.

Since supercritical water presents significant operating challenges, experimental work often uses surrogate fluids such as supercritical carbon dioxide. An entire session on the thermalhydraulics track was therefore devoted to surrogate fluids. Use of surrogate fluids then necessitates an understanding of two kinds of scaling issues - between experimental loop and a real reactor; and between surrogate fluid and real supercritical water (the 'working fluid').

Two very interesting papers discussed these issues. One paper, from Canada, discussed the supercritical thermalhydraulic loop currently being constructed at the University of Ottawa, while the other, from China, discussed fluid-to-fluid scaling issues. In developing fluid-to-fluid scaling, similarity relationships are often employed, for example, by using dimensionless variables like the ratio of actual pressure to critical pressure - which directly scales with the ratio of temperature to critical temperature for the two different fluids - in the same way. Although the relevant ranges of temperature and pressure at which the behavior develops can be different - the dimensionless ratio behaves in the same way - thus the behavior of the fluid with more easily reachable temperature and pressures (the modelling fluid or surrogate fluid) can be used to perform detailed experimental studies, while the behavior of the fluid with the more stressful operating conditions (the working fluid) can be inferred from the similarity scaling relationship. (Such invariant scaling relationships occur quite widely elsewhere in physics also, with quantities like the magnetization or the superfluid density, for example, in spin glasses or superconductors.) More details are available here [1].

Prof. David Novog's group from McMaster University, and Prof. Guy Marleau's group from Ecole Polytechnique (Montreal) presented papers on safety issues for the Supercritical Water-cooled Reactor.

Overall, the conference covered significant ground in its three days and also included one side trip to NRCan's Material Technology Laboratory (MTL) at Ottawa and another to AECL's Chalk River Laboratories (CRL).


1. Groeneveld, D.C., Tavoularis, S., et al Nucl. Eng. Technology vol. 40 no. 2, 107-116, 2007.