Ontario’s IESO prefers Enhanced CANDU 6 over AP1000 for new build at Darlington

By: Donald Jones, P.Eng., retired nuclear industry engineer, 2013 August.

This article will appear in the 2013 September edition of the Canadian Nuclear Society’s “BULLETIN” 

The Independent Electricity System Operator (IESO) prefers the Enhanced CANDU 6 (EC6) over the Westinghouse AP1000 for new build at Darlington. Well, it is inferred anyway.

On page 6 of the IESO’s written submission to the Ontario Power Authority’s (OPA) 2005 December 9 Supply Mix Advice Report to the Minister of Energy (MOE), Volume 5 – Submissions and Presentations Received, it states,

“To bring supply and demand into balance under Unutilized Baseload Generation (UBG) conditions, baseload generation must be shutdown. For example, if a nuclear unit is unable to perform power reductions it will be shutdown, typically resulting in a 48 hour “poison” outage. Such shutdowns, which assist with low demand concerns, can adversely impact the ability to meet demand during subsequent peak periods until the unit(s) return to service. Any consideration of nuclear generation additions should examine the ability of the different nuclear options to reduce power under UBG conditions, with preference going to those technologies which can better accommodate this requirement”. (author’s emphasis)

Note that the IESO now uses the term “Surplus Baseload Generation” (SBG) instead of “Unutilized Baseload Generation” (UBG). Since the EC6 is much more flexible than the AP1000 (reference 1) it is clear that the IESO preference would be the EC6 for new build at Darlington. Bruce Power’s eight units have already demonstrated what even a limited amount of flexibility can achieve, so much so that they are classified as “flexible nuclear” by the IESO (reference 2). The EC6 will have much more steam bypass capacity than the Bruce units and in addition will be able to do reactor manoeuvring when necessary.

The IESO requirement for more flexibility in future capacity additions to the Ontario grid appears regularly in its “18-Month Outlook” series, for example,

“The existing coal fleet, though running at vastly reduced levels from previous years, provides the IESO with desirable flexibility, such as quick ramping and operating reserve, under all market conditions. As Ontario’s coal-fired generation is shut down over the next two years, its associated flexibility will be lost. Therefore, future capacity additions should also possess this flexibility to help facilitate the management of maintenance outages, provide effective ramp capability, supply of operating reserve and even provide regulation when necessary”.

The EC6 can meet these requirements (reference 1).

The OPA’s 2005 December 9 Supply Mix Advice Report to the MOE, Supply Mix Summary, Part 1.1, page 3, states,

 “Planning supply mix would be simple if a single source were superior to others in all areas – environmental impact, reliability and costs – and could meet equally well the needs of base, intermediate and peak load. The reality is that no such single resource exists – a combination of resources and technologies is needed, and tradeoffs and synergies among them must be considered”. 

This false premise resulted in the government’s 2010 Long-Term Energy Plan (LTEP) restricting nuclear to 50 percent of generation because of perceived nuclear inflexibility. On the contrary flexible nuclear can provide reliable base, intermediate, and peak load if necessary with no emissions at stable and competitive cost (reference 3).  France gets over 75 percent of its electricity from its flexible nuclear plants and its electricity prices are among the lowest in Europe. France has achieved this with nuclear units that are much less flexible than the EC6. New nuclear build should not stop at the 12,000 MW in the government’s LTEP. Much more nuclear capacity must be built (references 4 and 5). The future is with nuclear and hydro, not with frackgas and wind, though with climate change even hydro is not a sure thing. Unlike frackgas a nuclear energy supply is almost inexhaustible and will be available for thousands of years. Other countries can only wish for Ontario’s nuclear and hydro infrastructure and potential.


1. Contenders for nuclear flexibility at Ontario’s Darlington B, AP1000 and EC6, and the winner is….., Don Jones, 2013 January, see item 19 of, https://thedonjonesarticles.wordpress.com/articles/

2. Ontario’s already “flexible nuclear” CANDU even better by satisfying IESO requirements to replace flexible coal, Don Jones, 2012 October, see item 18 of https://thedonjonesarticles.wordpress.com/articles/

3. Dash for gas: Will Ontario repeat the UK’s mistake?, Don Jones, 2013 May, see item 27 of, https://thedonjonesarticles.wordpress.com/articles/

4. Ontario needs more than 2,000 MW of new nuclear despite what the Long-Term Energy Plan says, Don Jones, 2011 January, see item 5 of,  https://thedonjonesarticles.wordpress.com/articles/

5. An alternative Long-Term Energy Plan for Ontario – Greenhouse gas-free electricity by 2045, Don Jones, 2011 May, see item 2 of, https://thedonjonesarticles.wordpress.com/articles/ 

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