Why Ontario’s CANDU nuclear reactors don’t load-follow

July 22, 2018

By: Donald Jones, retired nuclear industry engineer, 2018 July 21
Ontario`s electric power grid has a surplus of power. On windy, sunny, low demand days, a large surplus. Contractually other generators on the grid have to reduce power to accommodate the generation from wind and solar even though it makes no environmental, economic or technical sense to do so.  Since nuclear and hydro supply up to 90 percent of the electricity in Ontario this duty mainly falls on them. Hydro manoeuvring is relatively straightforward, nuclear not so.

For example, an item from Ontario Power Generation’s (OPG) 2009 Annual Report confirms that Darlington and Pickering are, “not designed for fluctuating production levels to meet peaking demand“. Under the definition of Nuclear Unit Capability Factor, page 26, it states, “OPG’s nuclear stations are baseload facilities as they have low marginal cost and are not designed for fluctuating production levels to meet peaking demand……“.  However this is not totally correct. Although not designed to respond to frequent IESO (Independent Electricity System Operator) load-following dispatches the design of the CANDU plants did offer the potential for load-cycling (power reduced overnight/weekends) and this has been demonstrated. In the past some domestic units and off-shore units (CANDU 6) did accumulate considerable good experience with load-cycling by manoeuvring the reactor, with some deep power reductions, but not on a continuous daily basis. For example back in the 1980s several of the Bruce B units experienced nine months of load-cycling including deep (down to 60 percent full power, or lower) and shallow reactor power reductions. Analytical studies based on results of in-reactor testing at the Chalk River Laboratories showed that the reactor fuel could withstand daily and weekly load-cycling. However since then, as will be shown below, regulatory concern has restricted any manoeuvring of the nuclear reactor in order to suit market conditions on the power grid.

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