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

By: Donald Jones, retired nuclear industry engineer, 2018 July 21
Ontario`s electricity power grid can have surpluses of baseload generation. On windy, sunny, low demand days, a large surplus. This means that the baseload generators, nuclear, run-of-river hydro, wind and solar, need to be manoeuvred. In 2016 Ontario’s Independent Electricity System Operator allowed the curtailment of most of the wind and solar generation before the manoeuvring of nuclear. Before this other generators on the grid had to reduce power to accommodate the generation from wind and solar even though it made no environmental, economic or technical sense to do so since nuclear and hydro supply most of Ontario’s electricity. 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.

Can nuclear power plants deliver on all the attributes U.S. energy secretary Rick Perry claims

By: Donald Jones, P.Eng., retired nuclear industry engineer, 2017 October 11

The U.S. has finally recognized the potential attributes that nuclear  power generation brings to the power grid. “US energy secretary Rick Perry has called on the Federal Energy Regulatory Commission (FERC) to act swiftly to address threats to grid resiliency through market reforms to recognise the attributes of baseload generation sources including nuclear”, and, “Traditional baseload generation, with on-site fuel supplies and the ability to provide voltage support, frequency services, operating reserves and reactive power, is essential to provide resiliency during events like the Polar Vortex of 2014, and more recently hurricanes Harvey, Irma and Maria, Perry said”. Also, “Perry’s proposed rule would allow for the recovery of costs of “fuel-secure generation units that make our grid reliable and resilient”. To be eligible, units must be located within FERC-approved organised markets; be able to provide “essential energy and ancillary reliability services”; and have a 90-day fuel supply on site. They must also be compliant with all applicable environmental regulations” (Reference 1).
 
Question is, can U.S. nuclear generation deliver on those attributes.

This is what the United States Nuclear Regulatory Commission (U.S. NRC) says, (Reference 2)

“Nuclear Power Plants (NPPs) are designed as base load units and are not designed to load follow (either by plant operator action or automatically via external control signal). While operators can adjust power in general, rapid changes are difficult and power changes are most problematic near the end of a fuel cycle (typically 18 months) where reactor power control is more complicated.
NPPs control systems will not be interfaced with or controlled from grid network control systems. Control of a NPP has to be handled by the NRC licensed operators to ensure nuclear safety.”

Thus in the U.S. it looks as if nuclear plants are not licensed to provide attributes like dispatchable load-following, automatic generation control (AGC) and primary frequency response although they would provide reactive power and voltage support and they certainly have adequate on-site fuel supplies. They also provide highly reliable baseload with a 92.5 percent capacity factor in 2016. Since nuclear units are operated at 100 percent full power they would not provide operating reserves. This is not to say they cannot do all the things that energy secretary Perry claims it just means the U.S. NRC prohibits them from doing so.

The impact of fuel cell vehicles and electric battery vehicles on Ontario’s electricity grid

By: Donald Jones, P.Eng., retired nuclear industry engineer, 2014 November 24

Major automobile manufacturers are continuing their development of cars powered by fuel cells using hydrogen (reference 1). Like cars powered by electric batteries the cars themselves will emit no greenhouse gas (GHG). Bulk quantities of hydrogen are mainly derived from natural gas (increasingly frackgas) but the process results in the production of carbon dioxide, a GHG, so fuel cell cars will not reduce overall GHG emissions. However hydrogen can also be produced from the electrolysis of water using electricity. If this electricity is generated from a power grid of non-fossil fuelled generation then zero overall GHG emissions can be achieved – this applies to battery cars as well as fuel cell cars.

Since fuel cell cars and battery cars can significantly reduce GHG emissions in at least part of the transportation sector the market for such vehicles could expand and one of the key questions will be how will these cars affect the demand for electricity and the stability of the grid. Battery cars and fuel cell cars will affect the power grid in different ways. Battery charging is uncontrolled and people will charge their car batteries when convenient, day and night. Fast battery charging at home from a dedicated house circuit can overload the street transformers. Smart controls at the distribution level may alleviate this but ultimately the distribution system might need upgrading to handle the extra demand. All ratepayers will pay for this including those without battery cars. Increasing the day time peak loads on the grid by uncontrolled battery charging will require an increase in generating capacity, likely from frackgas-fired GHG emitting units. Ideally battery charging should be done overnight when surplus generation is available at the lowest carbon dioxide emission intensity and at lowest cost.

IESO – The only diverse generation Ontario needs is CANDU and hydro

By: Donald Jones, P.Eng., retired nuclear industry engineer, 2014 September 24

This comment by Kim Warren, VP of Operations and Chief Operating Officer at The Independent Electricity System Operator (IESO), under the title “Powering Ontario Through Energy Literacy”, appeared in a sponsored feature by Mediaplanet in a “Green Living” supplement to the Toronto Star of 2014 September 24, “There are distinct advantages to having diverse fuels. No system operator likes to see all of their eggs in one basket because every fuel has its advantages and disadvantages, and behaves differently in certain seasonal or weather conditions.” Right, except for nuclear!

Wind obviously depends on the weather. So does solar and both are expensive on a $/kWh basis. Only a small fraction of the installed wind capacity is credited by the IESO to be there when needed at peak times and even then there are no guarantees. Wind can be plentiful when not needed and in short supply when it is needed. Embedded solar tends to fade when needed during the late afternoon peak demand and needs more ramping capacity from generators on the grid. Wind can do the same during the morning peak. People living near the huge wind turbine installations will continue to object to their presence. Despite what the IESO says wind puts a lot more stress on the system operators who have to juggle output from other generators on the grid to compensate for wind’s irregularities. If these are gas-fired units it increases greenhouse gas (GHG) emissions above what might have been expected from the reduction in gas-fired MWh due to the wind generation.

Energy storage flywheels and batteries needed to help out wind on Ontario’s electricity grid

By: Donald Jones, P.Eng., retired nuclear industry engineer – 2014 August

Ontario’s Independent Electricity System Operator (IESO) has a pilot project that uses motor/generator flywheels, batteries, and aggregate loads as short term energy storage to, it says, provide regulation services (reference 1). These short term energy storage systems should not be confused with longer term storage systems like pumped water storage, compressed air, thermal etc. Regulation is secondary frequency control (reference 2) and can be automatic (AGC – automatic generation control) or manual and brings grid frequency back into its narrow control band after an under frequency or over frequency event has been arrested and the grid stabilized by fast acting primary frequency control/response. This regulation service is normally supplied by selected hydroelectric units at Niagara Falls and even by Ontario’s coal fired units before they were shutdown. Combined cycle gas turbine (CCGT) units can also be used to provide regulation service.

The addition of large amounts of unreliable wind generated electricity to the Ontario grid will/has caused a deterioration in frequency control (reference 3). Wind does not provide any passive inertial response/energy storage capability or active primary frequency control. The wind generation displaces conventional generation on the grid, initially the CCGTs and then some hydroelectric, with the consequent loss of the passive inertial response (energy storage capability) of the rotating masses of the conventional units to help limit frequency perturbations from such things as wind gusts on the wind generators. As well this results in the loss of the active primary frequency control capability of the conventional units. Primary frequency control is automatic and is provided by the speed governors of individual generating units to very rapidly arrest any drift in frequency due to mismatches in supply and demand on the grid. Primary frequency control is essential for grid stability. Reduced amounts of primary frequency response on the system can result in under-frequency load shedding and cascading outages. Since the nuclear units are presently operated in their turbine-following-reactor mode of operation they cannot provide primary frequency control and only provide passive inertial response (reference 2). This means that during periods of surplus baseload generation (SBG) that usually occur when demand is low and wind conditions are favourable all the large CCGT units and some hydro units are shutdown so frequency response on the Ontario grid will solely depend on the primary frequency response of the operating hydroelectric units with enabled speed governors and the energy storage (inertial response) capability of the nuclear and hydroelectric units. This results in a jittery grid caused by wind gusts and larger swings in frequency after an upset resulting in the need for more megawatts of secondary frequency control/regulation to return grid frequency back into its narrow control band. During periods of SBG without wind generation the grid would still not have the inertial response of most of the gas-fired generators but would be more stable because it would not be subject to the rapid frequency upsets from wind. The shutdown of the CCGTs and some hydro because of SBG, with or without wind generation, also means that the reactive power support and voltage control provided by these units is no longer available with, apparently, little if any affect on grid voltage? If voltage support were a concern and the CCGTs and hydro units did not have a synchronous condenser mode of operation, which they likely don’t, then other equipment that provide local voltage support would have to be used.