5th International Symposium on Supercritical Water-cooled Reactors ISSCWR-5 Vancouver

The 5th International Symposium on Supercritical Water-cooled Reactors (ISSCWR-5) begins on March 14 2011 in Vancouver. The conference gets underway with five plenary addresses by national and international program managers of respective SCWR/HPLWR programs on the morning of the first day, Monday, and then branches off into three parallel technical sessions in the afternoon: on SCWR Core Design; on Materials Issues and on General Thermalhydraulics and Safety, chaired by international authorities in these respective fields. The session on General Thermalhydraulics and Safety will be co-chaired by Sama Bilbao y Leon of Virginia Commonwealth University and Jovica Riznik of the Canadian Nuclear Safety Commission.

This pattern of technical sessions continues also on Tuesday; an important facet of the Tuesday morning sessions will be regulatory considerations: a talk by Alexandre Viktorov of the Canadian Nuclear Safety Commission will be on Regulatory Expectations for Advanced Reactors, while Ima Ituen and David Novog of McMaster University will present on Assessing the Applicability of Canadian Regulations to the SCWR.

On Wednesday morning, there are sessions on Safety Issues and non-Aqueous Fluid Heat Transfer, the latter referring especially to experiments on supercritical carbon dioxide, where considerations on fluid-to-fluid scaling are important in interpreting the results and applying them to the real working fluid, supercritical water. Of the many interesting papers, one which describes a supercritical loop for in-pile testing of materials seemed especially interesting.

On all three days, the pattern of three parallel technical sessions is maintained, testifying to the high level and quality of national and international participation in the conference, and the interesting work on the SCWR that continues apace through the Gen-IV International Forum (GIF). Canada, as the host country [and also the country that formally leads R&D on the SCWR under the GIF] has the highest number of papers - both established groups and newer ones, and both senior researchers and students are presenting papers. Importantly, the Canadian participation shows significant engagement with the SCWR concept, across all major stakeholders: by academic groups, by regulatory authorities, as well as by R&D Labs and industrial firms.

The conference closes on Thursday with a tour of TRIUMF, Canada's national laboratory for nuclear and particle physics, located on the campus of the University of British Columbia. The scenic locale of the conference in Vancouver, and the very interesting papers to be presented, and discussions to be had, plus the social and cultural programs and the tour of TRIUMF promise to make this a most memorable conference in the biannual ISSCWR series.

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).

References

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

Materials Challenges for the Supercritical Water-cooled Reactor (SCWR)

The Supercritical Water-cooled Reactor (SCWR) is the most promising evolution of the water-cooled reactor technology that currently dominates the commercial market for nuclear reactors. Essentially the idea is to increase the thermodynamic efficiency of the reactor type by going to higher temperatures and pressures, and thus also going to the supercritical state. Supercritical water also has a much higher specific heat, enabling a higher heat transfer per unit mass. By going to higher pressures and temperatures, it is also possible to avoid phase changes within the coolant loop altogether. This substantially reduces the requirements for pumps and compressors within the coolant loop, simplifying it considerably and introducing even greater economy in the whole power plant.

The merit of the supercritical coolant idea has been tested and the concept has actually been deployed for fossil fuel power plants (coal-fired) already, where thermodynamic efficiencies have considerably risen as a result. Some jurisdictions have also mandated that all future coal-fired power plants be of the supercritical type. The supercritical water coolant imposes more stringent requirements for plant materials used in fossil fuel-fired power plants as well, and this experience is relevant to the Supercritical Water-cooled Reactor (SCWR) concept.

However, what is different about nuclear reactors, of course, is the radiation dose that reactor materials will experience, in addition to the thermochemical stress that the supercritical water environment might impose. This is even more the case when new fast neutron spectrum fuel cycles are introduced, with radiation doses upto a hundred times higher than the thermal spectrum neutrons that current generation reactors use.

Superior irradiation creep strength, and superior thermomechanical behavior in general then becomes a a very desirable critical property to have for cladding materials. I discuss the Materials Challenges for the Supercritical Water-Cooled Reactor in my paper published in the Canadian Nuclear Society Bulletin, Vol. 29. No. 1 pp. 32-38 March 2008.

The supercritical water environment is also chemically different in that it dissolves organic species but not inorganic ones, the reverse of ordinary water. Thus the supercritical water environment is expected to create novel corrosion challenges as well, and these also must be studied and understood.

Materials such as Oxide Dispersion Steels (ODS Steels) have been proposed for use as structural and cladding materials in the Supercritical Water-cooled Reactor SCWR (as well as other Generation IV Reactor concepts). These materials appear to display very desirable irradiation and thermal creep properties, as well as desirable electro-chemical properties (corrosion resistance). Understanding the physical origin of these properties by developing suitable multiscale materials models (MMM) is the focus of my present research.