Candu Energy Inc. says Enhanced CANDU 6 is flexible – so revise the boilerplate

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

In its media releases on the study of possible use of the Enhanced CANDU 6 (EC6) to burn surplus UK plutonium Candu Energy Inc. has explicitly stated that its EC6 has flexible load capabilities. For example, the media release of 2013 August 1 (reference 1) said,,

“The Enhanced CANDU 6 (EC6) is a 700 MWe class heavy-water moderated and heavy-water cooled pressure tube reactor. It is the only commercialized reactor offering flexible fuelling arrangements from natural uranium to advanced fuels such as recycled uranium, thorium and plutonium mixed oxide (MOX). This fuel flexibility is combined with superior safety and economic performance, high reliability, flexible load capabilities (author’s highlight), very high localization potential and straightforward integration into the existing grid system. CANDU reactor operators currently fabricate or procure their own fuel locally, increasing their energy independence and creating a nuclear fuel infrastructure without the need for enrichment.”

The flexibility attribute was likely mentioned in association with the UK study because new build in Europe has to at least meet the flexibility regulations of the European Utilities Requirements (EUR) that are based on the requirements of the grid operators, subject to licensing approval by the specific nuclear regulator. The EC6 would have to comply with the manoeuvrability specifications of the EUR if Candu Energy wants it to be part of new build in Europe.

Up to now the only references to nuclear flexibility were buried in the EC6 Technical Summary document in the balance of plant section describing the steam and feedwater systems and just said that the EC6 has condenser steam discharge valves designed to discharge up to 100 percent of the steam flow directly to the condenser, bypassing the turbine, and that this provides operational flexibility in support of load-following operation in conjunction with overall reactor control. In the operations and maintenance section it said that in the event of a loss of connection to grid bypass capability would allow a quick return to full power from house load power. This makes the EC6 different from the CANDU 6 and from Bruce and Darlington units since these units cannot presently discharge 100 percent steam flow directly to the condenser. Even so Ontario’s Independent Electricity System Operator now describe Bruce units as “flexible nuclear” despite their limitations (reference 2).  

Various anti-nuclear organizations and individuals label nuclear as inflexible baseload supply. Even pro-nuclear organizations, that should know better, such as the Canadian Nuclear Association and the Organization of Canadian Nuclear Industries, amongst others, continue to promote nuclear as baseload generation with no reference to its flexibility potential and support the government’s false and unnecessary “supply mix” directive. Support of the “supply mix” is support of frackgas-fired generation and wind/solar and implies that nuclear is inflexible. Ontario just needs flexible nuclear and hydro, full stop (reference 3). The incorporation of flexibility into Ontario’s power grid has to be paid for whichever way it is done, by nuclear or by gas (reference 4). Ontario’s present Long-Term Energy Plan restricts nuclear generation to no more than 50 percent (reference 5) because of the perceived inflexibility implied by statements from these authoritative sources. Since 2012 June Candu Energy has stated, with reference to the UK study, that the EC6 does have flexible load capabilities so maybe all these organizations can now face facts and revise their boilerplate.

The author first raised the issue of CANDU flexibility, including a suggestion to improve robustness of the turbine steam bypass system, in a letter in the Canadian Nuclear Society’s BULLETIN, 2005 December edition (reference 6), but, except for the media releases on the UK study, there has been no mention of flexibility capability on the Candu Energy (previously AECL) website or in its literature and presentations. Candu Energy should take steps to highlight this important flexibility attribute in its EC6 Technical Summary, on its website, and in its future presentations. One can only hope that more details on the EC6 flexible load capabilities such as ramp rates, automatic generation control, and dispatchable load-following were included in Candu Energy’s recent proposal to the Ontario Power Generation for new build at Darlington (reference 7).


1. Candu Energy Inc. media release, 2013 August 1, 

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,

3. An alternative Long-Term Energy Plan for Ontario – Greenhouse gas-free electricity by 2045, Don Jones, 2011 May, see item 2 of, 

4. Dash for gas: Will Ontario repeat the UK’s mistake?, Don Jones, 2013 May, see item 27 of,

5. 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,

6. Bring load-following into open, Don Jones, 2005 December, see item 23 of,

7. Contenders for nuclear flexibility at Ontario’s Darlington B, AP1000 and EC6, and the winner is….., Don Jones, 2013 January, see item 19 of,


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