CANDU nuclear generating station response to a blackout of the power grid

September 27, 2018

By: Don Jones, retired nuclear industry engineer, 2018 September 27

This is an overview of how a present day CANDU unit (excludes Pickering Generating Station that does not have turbine steam bypass capability and Bruce A that does not have adjuster rods – see later) responds to the loss of the power grid, a load rejection. The design intent is to keep the unit operating to supply its own service loads (house load) while disconnected from the grid and to be ready to reconnect to the grid when the grid becomes available.

All actions are automatic. When the loss of the power grid is detected the circuit breakers connecting the turbine-generator to the grid open. If house load is normally supplied by the unit service transformer the unit service loads (reactor heat transport circulating pumps, boiler feed pumps, condenser cooling water pumps, and other loads) are not affected by the de-energized grid. If the system service transformer were supplying half the unit service loads an automatic transfer would occur to transfer those loads to the unit service transformer. Reactor power is quickly stepped back to around 60 percent of full power by dropping the four mechanical control absorbers (rods) part way into the core, the valves supplying steam to the turbine-generator are closed, and the condenser steam discharge valves (CSDVs) are fully opened to prevent a rise in boiler pressure sufficient to cause opening of the boiler main steam safety valves. The  CSDVs allow the steam that would have gone through the turbine-generator to go directly to the condenser. As the boiler pressure drops because of the fully open CSDVs the CSDVs are partially closed by the boiler pressure control system to maintain boiler pressure at  setpoint. The turbine governor adjusts to supply just enough steam to take care of the house load, around 7 percent of full power.
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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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Performance of Ontario’s CANDU nuclear generating stations in 2017

April 3, 2018

By: Donald Jones, retired nuclear industry engineer, 2018 March 29

The raw performance data for 2017 are taken from the Power Reactor Information System (PRIS) database of the International Atomic Energy Agency (IAEA). Note that the Load Factor term used in the PRIS database has the same meaning as Capacity Factor (CF). CFs are based on the (net) Reference Unit Power and on the (net) Electricity Supplied, as defined in the PRIS database. For Ontario, at least, the Energy Availability Factor in the PRIS database can be read as the Unit Capability Factor, see later. More information and performance data for 2016 are in references 1 and 2.

The performance of some of Ontario’s nuclear generating stations is affected by the surplus baseload generation (SBG) in the province. The surplus usually arises because of unreliable intermittent wind generation coming in at times of low demand and wind generation is expected to increase even more over the next several years. Some nuclear units saw electricity output reductions during periods of surplus baseload generation (SBG). This means the CFs are not a true performance indicator for those units (reference 3). A better metric of performance in these cases would be the Unit Capability Factor (UCF – used by Ontario Power Generation and by Bruce Power). The Energy Availability Factor (EAF) is another performance indicator and is shown in the PRIS database. The EAF adjusts the available energy generation for energy losses attributed to plant management, planned and unplanned, and for external energy losses beyond the control of plant management while the UCF only includes energy losses attributed to plant management and excludes the external losses beyond control of plant management like load cycling/load following, grid failures, earthquakes, cooling water temperature higher than reference temperature, floods, lightning strikes, labour disputes outside the plant etc.
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CANDU 6 Performance in 2017

March 27, 2018

CANDU 6 Performance in 2017
By: Donald Jones, retired nuclear industry engineer, 2018 March 27

History

The two lead CANDU 6 projects were Gentilly 2 in Quebec and Point Lepreau in New Brunswick and these were quickly followed by Embalse in Argentina and Wolsong, now Wolsong 1, in South Korea and all came into service in the early to mid 1980s. These can be regarded as the first tranche of CANDU 6 build.

The second tranche of CANDU 6 units came with Wolsong 2, 3 and 4 in South Korea, Cernavoda 1 and 2 in Romania, and Qinshan 3-1 and 3-2 in China (the other units at Qinshan site are not CANDU), all entering service between 1996 to 2007. Each of the second tranche CANDU 6 units incorporate lessons learned from operation of the earlier units with changes to meet latest regulatory codes and standards.

Capacity Factor

The Capacity Factors are taken from the PRIS (Power Reactor Information System) database of the IAEA (International Atomic Energy Agency). Note that the Load Factor term used in the PRIS database has the same meaning as Capacity Factor. Capacity Factors are based on the (net) Reference Unit Power and on the (net) Electricity Supplied figures, as defined in the PRIS database.
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Can nuclear power plants deliver on all the attributes U.S. energy secretary Rick Perry claims

October 11, 2017

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.

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Confusion with the IAEA reactor performance data in the PRIS

July 30, 2017

By: Donald Jones, P.Eng., retired nuclear industry engineer, 2017 July 28.
This article, edited for space, appeared in the 2017 June edition of the Canadian Nuclear Society`s BULLETIN as a Letter to The Editor.

BULLETIN Publisher’s NoteThe CNS Nuclear Canada Yearbook commenced using PRIS data this year. Data was no longer available from the CANDU Owners Group, and data from public sources such as Nuclear Engineering International or Nucleonics Week had become either incomplete or late in publication.

When the author was preparing an article on the performance of Ontario’s CANDU nuclear units (reference 1) he wanted to include some idea of the amount of energy being curtailed by a unit at the Bruce Nuclear Generating Station due to load cycling. To do this required a close look at the  published performance indicators in the Power Reactor Information System (PRIS) database of the International Atomic Energy Agency (IAEA)(reference 2) and this revealed some discrepancies.

The performance of some of Ontario’s nuclear generating stations is affected by the surplus baseload generation (SBG) in the province (reference 1). Some nuclear units saw electricity output reductions during periods of surplus baseload generation (SBG). This means the CFs (Capacity Factors) are not a true performance indicator for those units (reference 3). A better metric of performance in these cases would be the Unit Capability Factor (UCF – used by Ontario Power Generation and by Bruce Power). The Energy Availability Factor (EAF) is another performance indicator and is shown in the Power Reactor Information System (PRIS) database of the International Atomic Energy Agency (IAEA), (reference 2). The EAF adjusts the available energy generation for energy losses attributed to plant management, planned and unplanned, and for external energy losses beyond the control of plant management while the UCF only includes energy losses attributed to plant management and excludes the external losses beyond control of plant management like load cycling/load following, grid failures, earthquakes, cooling water temperature higher than reference temperature, floods, lightning strikes, labour disputes outside the plant etc. The UCF seems a much better indicator of how well the unit is being managed than either CF or EAF. The UCF rather than the CF would also be the more appropriate number to use when calculating the Equivalent Full Power Hours (EFPHs) on the reactor pressure tubes of Bruce units that use steam bypass at constant reactor power since steam bypass operation does not affect the EFPHs on the pressure tubes. Only  reactor power changes would do that.
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CANDU cousins in India – Performance in 2016

April 8, 2017

By: Donald Jones, P.Eng., retired nuclear industry engineer, 2017 April 5

Most of India’s nuclear reactors are of the pressurized heavy water reactor (PHWR) type with horizontal pressure tubes, just like the Canadian designed CANDU. In fact the first PHWR (not the first nuclear reactor) in India was the Rajasthan Atomic Power Project (RAPP) unit and was a CANDU designed by Atomic Energy of Canada Limited (AECL) that used the Douglas Point unit in Ontario as reference design but modified to aid localization. RAPP-1 entered commercial operation 1973 December. While RAPP-1 was being constructed the design of RAPP-2 was started (Author’s note: I know because I was part of design team). However the detonation of a nuclear device by India in 1974 curtailed completion of the design by AECL and India was on its own as far as nuclear technology was concerned. The design was completed by India and RAPP-2 eventually entered commercial operation in 1981 April. Since those early days India has developed its own indigenous designs of PHWRs with net electrical outputs of 202 MW, 490 MW, and 630 MW. They bear little to no resemblance to Douglas Point. All 17 PHWR units operating in 2016 (excludes RAPP-1 which has been shutdown since 2004) were 202 MW (220 MW gross) except for two 490 MW (540 MW gross) units. There were four 630 MW (700 MW gross) units under construction with none in operation. All PHWR power units, except for RAPP-1, are designed, owned, and operated by Nuclear Power Corporation of India Ltd. Several of the country’s PHWRs have been refurbished for extended life operation. For more detailed information on the Indian nuclear program see, Nuclear Power in India (reference 1).

The performance data are taken from the Power Reactor Information System (PRIS) database of the International Atomic Energy Agency (IAEA). Note that the Load Factor term used in the PRIS database has the same meaning as Capacity Factor (CF). CFs are based on the (net) Reference Unit Power and on the (net) Electricity Supplied, as defined in the PRIS database, so capacities referenced in this article are net electrical MW output. The lifetime, or cumulative, CF is based on the date of commercial operation and will include the outage time if the unit has been refurbished. Only the performance of India’s PHWRs is reviewed in detail but India’s three operating non-PHWR units are mentioned. Read the rest of this entry »