Great discussion, thanks. Nuclear reactors are so much more flexible than they are allowed to be. Regulations have boxed them into a niche and made them so expensive that utilities have to keep them at full power 24/7 in order to make any profit at all. Nuclear light water designs can easily accommodate the entire spectrum of grid requirements from blackstart to fast ramps to baseload. Regulations, with LNT and ALARA at their root have put a stop to all of that. Thanks so much for the great article.
I remember something about steam bypass as a way of allowing reactors to change generation output. I think the heat output from the reactor remains the same, but less steam is sent to the turbines? Is this a feature that must be built into a reactor?
Right. When the grid load is lost the steam turbine-generator can't extract energy from the steam being heated by fission, the thermal source. It may take many minutes to reduce the fission heat generation. The hot steam, normally sent through the turbine then condenser, is sent directly to the condenser, increasing the heat it must remove to the ultimate heat sink: air, evaporation, or water flow. If the plant can remain in this state for a while, it can quickly reconnect and generate power if the grid load reappears.
Could this method also be used to reduce generator output in order to load follow without having to adjust fission rate or allowing slower fission rate adjustment?
Perhaps, but we'd need advice from a steam turbine expert. It increases rejected heat into the river or whatever ultimate heat sink is used, possibly exceeding environmental limits. I think it also increases water circuit losses in the deareator.
These are how the large CANDU units in Canada are built and operated. They can lower turbine output rapidly while maintaining the same reactor power, by discharging steam to the condensers, if the event will occur over a longer period of time, we can then lower reactor power while maintaining the unit available to recover. If a grid fault occurs, I don't know about PWR/BWR, but the CANDU will go into an islanding mode supplying power to itself and remain available to reload to the Grid as the situation settles out. We learned a lot during the 2003 blackout, but a number of the units survived in this mode and help allow for the speedy recovery of the Ontario Grid.
I have it on good authority that the AP1000 is capable of operating in islanding mode. However will the NRC allow that operation mode? Dunno if ALARA-driven regs prevent such operation.
Surprised that you missed that Natrium's design for handling load following is to put excess heat in thermal salt storage and then use that for load following. So, the reactors will be at 300 MWe, but the plant is capable of 500 MWe due to adding heat from the thermal salt.
Superior way for load following.
Hopefully, they ARE going to design the plant to handle 2-3 thermal sources, but start it with Nat Gas boilers. They can then build out the power plant in several years, and while generating power, revenue and hopefully profits, add the Natrium SMR(s).
You seem very knowledgeable about nuclear power plants, but you are misusing the term ALARA.
ALARA refers to keeping radiation doses as low as possible to the plant workers, not to the general public. Nuclear safety is regulated by the NRC and its rules about redundancy, separation, and single failure criteria. It’s all documented in the Federal CFR 50 and each plants license and final safety analysis report, FSAR.
I worked at a nuclear power plant for 36 years and I never heard the term ALARA used when discussing dose to the public.
I understand your point about over regulation and trying to make nuclear power as safe as possible, and how that should be relaxed to allow nuclear power to flourish.
The key thing that needs to change is the NRC’s use of the linear no threshold model, LNT, when it comes to determining dose limits for the public. That’s the key item to change to allow nuclear power plants to become less expensive.
See the Gordian Knot Substack by Jack Devanney for more information.
My nuclear plant also had three independent Emergency diesel generators per unit to provide redundancy and separation. My plant was designed to handle a full load rejection, meaning a total separation of the grid and to keep running and providing power to plant auxiliary systems.
What happened in Spain was an under frequency condition which directly led to reactor trip signals due to lower flow conditions in the reactor.
When the grid experiences voltage and frequency oscillations like what happened in Spain, every reactor and electrical generator is going to trip out on a protection signal.
That’s why grid inertia is so important, to have these large rotating machines connected to the grid to help stabilize the oscillation. Solar plants and wind farms don’t do that.
This was a failure of the ridiculous green energy policies.
I know NRC prevents US nukes from participating in primary frequency control, but is Bob right that they set the frequency tolerances which if exceeded force a trip, or are these set by the plant vendor? In either case, do you recall what Diablo's frequency limits were?
I had to use my Operator Information Manual to get these
Standard Westinghouse Gen 2 setpoints
Reactor Trip at 54 Hz at 0 seconds
Generator Unit trip at
57.5 for 7 seconds
557.9 for 31 seconds
58.3 for 92 secs
We wanted to give the grid time to settle out before we tripped the generator, if the grid was at 54 Hz it was basically gone and so was the reactor.
For the Unit trips, the reactor might stay critical to provide plant loads but that was a very unsure outcome. So we considered it unlikely and instead we always assumed we used our emergency diesel generators to cool down the reactor.
Diablo was a very strange place for off site power design and licensing requirements.
At the time of the transmission outage, Spain was exporting power. The Spain frequency went too high.
The nuclear reactors may have tripped off due to over frequency. Or they may have withstood the over frequency, then too much solar tripped off - causing under frequency, and ultimately causing the reactors to trip off.
We won't know until the system operator publishes a study.
Unfortunately, the Spanish government has already stated that renewables didn't cause the outage, so the public version of the study is likely to be BS.
"New nuclear power plants such as the Terrapower Natrium reactor and the Thorcon 500 MSR can load-follow..." No such plants exist. They are just designs in the eyes of their creators. They may or may not work as you say. Why address them as though they are working and all we need is more?
Great discussion, thanks. Nuclear reactors are so much more flexible than they are allowed to be. Regulations have boxed them into a niche and made them so expensive that utilities have to keep them at full power 24/7 in order to make any profit at all. Nuclear light water designs can easily accommodate the entire spectrum of grid requirements from blackstart to fast ramps to baseload. Regulations, with LNT and ALARA at their root have put a stop to all of that. Thanks so much for the great article.
I remember something about steam bypass as a way of allowing reactors to change generation output. I think the heat output from the reactor remains the same, but less steam is sent to the turbines? Is this a feature that must be built into a reactor?
Right. When the grid load is lost the steam turbine-generator can't extract energy from the steam being heated by fission, the thermal source. It may take many minutes to reduce the fission heat generation. The hot steam, normally sent through the turbine then condenser, is sent directly to the condenser, increasing the heat it must remove to the ultimate heat sink: air, evaporation, or water flow. If the plant can remain in this state for a while, it can quickly reconnect and generate power if the grid load reappears.
Could this method also be used to reduce generator output in order to load follow without having to adjust fission rate or allowing slower fission rate adjustment?
Perhaps, but we'd need advice from a steam turbine expert. It increases rejected heat into the river or whatever ultimate heat sink is used, possibly exceeding environmental limits. I think it also increases water circuit losses in the deareator.
These are how the large CANDU units in Canada are built and operated. They can lower turbine output rapidly while maintaining the same reactor power, by discharging steam to the condensers, if the event will occur over a longer period of time, we can then lower reactor power while maintaining the unit available to recover. If a grid fault occurs, I don't know about PWR/BWR, but the CANDU will go into an islanding mode supplying power to itself and remain available to reload to the Grid as the situation settles out. We learned a lot during the 2003 blackout, but a number of the units survived in this mode and help allow for the speedy recovery of the Ontario Grid.
I have it on good authority that the AP1000 is capable of operating in islanding mode. However will the NRC allow that operation mode? Dunno if ALARA-driven regs prevent such operation.
Island mode is an important feature. You'd hope the NRC would go attend a demonstration and ask questions.
Howdy Doc,
Surprised that you missed that Natrium's design for handling load following is to put excess heat in thermal salt storage and then use that for load following. So, the reactors will be at 300 MWe, but the plant is capable of 500 MWe due to adding heat from the thermal salt.
Superior way for load following.
Hopefully, they ARE going to design the plant to handle 2-3 thermal sources, but start it with Nat Gas boilers. They can then build out the power plant in several years, and while generating power, revenue and hopefully profits, add the Natrium SMR(s).
You seem very knowledgeable about nuclear power plants, but you are misusing the term ALARA.
ALARA refers to keeping radiation doses as low as possible to the plant workers, not to the general public. Nuclear safety is regulated by the NRC and its rules about redundancy, separation, and single failure criteria. It’s all documented in the Federal CFR 50 and each plants license and final safety analysis report, FSAR.
I worked at a nuclear power plant for 36 years and I never heard the term ALARA used when discussing dose to the public.
I understand your point about over regulation and trying to make nuclear power as safe as possible, and how that should be relaxed to allow nuclear power to flourish.
The key thing that needs to change is the NRC’s use of the linear no threshold model, LNT, when it comes to determining dose limits for the public. That’s the key item to change to allow nuclear power plants to become less expensive.
See the Gordian Knot Substack by Jack Devanney for more information.
My nuclear plant also had three independent Emergency diesel generators per unit to provide redundancy and separation. My plant was designed to handle a full load rejection, meaning a total separation of the grid and to keep running and providing power to plant auxiliary systems.
What happened in Spain was an under frequency condition which directly led to reactor trip signals due to lower flow conditions in the reactor.
When the grid experiences voltage and frequency oscillations like what happened in Spain, every reactor and electrical generator is going to trip out on a protection signal.
That’s why grid inertia is so important, to have these large rotating machines connected to the grid to help stabilize the oscillation. Solar plants and wind farms don’t do that.
This was a failure of the ridiculous green energy policies.
Ken,
I know NRC prevents US nukes from participating in primary frequency control, but is Bob right that they set the frequency tolerances which if exceeded force a trip, or are these set by the plant vendor? In either case, do you recall what Diablo's frequency limits were?
I had to use my Operator Information Manual to get these
Standard Westinghouse Gen 2 setpoints
Reactor Trip at 54 Hz at 0 seconds
Generator Unit trip at
57.5 for 7 seconds
557.9 for 31 seconds
58.3 for 92 secs
We wanted to give the grid time to settle out before we tripped the generator, if the grid was at 54 Hz it was basically gone and so was the reactor.
For the Unit trips, the reactor might stay critical to provide plant loads but that was a very unsure outcome. So we considered it unlikely and instead we always assumed we used our emergency diesel generators to cool down the reactor.
Diablo was a very strange place for off site power design and licensing requirements.
Thanks. So the vendor set the numbers subject I assume to NRC approval?
Be interesting to know how long the Spanish NPP's stayed up.
Yes, all reactor trip set points are reviewed and approved by the NRC.
The root cause analysis should be very interesting.
At the time of the transmission outage, Spain was exporting power. The Spain frequency went too high.
The nuclear reactors may have tripped off due to over frequency. Or they may have withstood the over frequency, then too much solar tripped off - causing under frequency, and ultimately causing the reactors to trip off.
We won't know until the system operator publishes a study.
Unfortunately, the Spanish government has already stated that renewables didn't cause the outage, so the public version of the study is likely to be BS.
No, spanish government has NOT said that. Several members of the government said that, but they have nothing to back it up with.
Let the study commence.
"New nuclear power plants such as the Terrapower Natrium reactor and the Thorcon 500 MSR can load-follow..." No such plants exist. They are just designs in the eyes of their creators. They may or may not work as you say. Why address them as though they are working and all we need is more?