Capacity factor of nuclear: US v Japan

[kristopher]

Capacity factor of nuclear: US v Japan

The capacity factor (CF) of a generating unit is a measure that compares the actual amount of electricity produced over time (say one year) to the maximum amount that would be produced if the plant runs full capacity 100% of the time. So a plant that is designed to produce 100 units over a year, but only produces 80, would have a capacity factor of 80%.

The nuclear power plant operators in the US are proud of the fact that they have pushed the CF of their plants to about 93%.

One of the ways they do this is by running past maximum rated output to compensate for the times they must shut down. The other way they do this is to defer maintenance until they shut down for refueling - a possible delay of months or even years.

One of the lessons of Japan and fukushima comes from this. Their fleet of reactors has a capacity factor that, before Fukushima, was just nudging above 80%. Nuclear enthusiasts here explain that as being due to their need to shutdown frequently due to earthquakes. That is true to a point, but it only justifies a fraction of the difference. The real reason IMO is that compared to the US, the Japanese are fanatics about maintaining their equipment properly. Again in comparison to the prevailing US ethos, as a culture they are completely dedicated safe operation of their entire infrastructure. Bridges there are not rotting; roads that are crumbling are repaired promptly. They are not perfect, and they are subject to human greed and folly just like anyone else. BUT - THE PHILOSOPHY THE PUBLIC JUDGES PERFORMANCE BY INCLUDES PLACING A HIGH VALUE ON QUALITY - INCLUDING MAINTAINING QUALITY OVER TIME.

Think about that as you ponder the pride of the US nuclear plant operators in their 93%+ capacity factor.


One final note. The use of capacity factor as a measure of the "best technology" is a frequent red herring designed to deflect attention from a wide array of very important considerations that score poorly for centralized thermal generation. Large scale centralized thermal generation refers to systems that burn fuel to heat water to produce steam to run a generator. Coal nuclear and natural gas all have the potential for high capacity factors. Since wind and solar both have significantly lower capacity factors, this is the favorite point of attack by those supporting Republican energy plans.

What that attack ignores is that actual capacity factor a system operates under is as more a function of the designed system of the grid than an unchangeable characteristic of how a grid must be operated. It is entirely possible to design and operate a grid with a combination of technologies ALL having low operational capacity factors.

Simply comparing capacity factors alone tells us nothing of value until it is placed in proper context. If you want to compare which carbon free techs are best, the way to do it is to look at the result of the full formula where CF is used - the final price of electricity that the generator produces.

And, if transitioning to a carbon free economy is important to you, you'll also want to compare how long it takes to start producing electricity.

[phantom power]

1. As long as we don't also simply ignore them.

[kristopher]

2. Ignore what? nt

[Turbineguy]

3. Where did you get this part?

"One of the ways they do this is by running past maximum rated output to compensate for the times they must shut down. The other way they do this is to defer maintenance until they shut down for refueling - a possible delay of months or even years."

[kristopher]

4. That's an odd question...

I wrote it. What are you wanting to actually say? Do you think it is wrong?

[GliderGuider]

5. It's certainly surprising.

93% capacity allows for 25.5 days per year of down time. Do you have some evidence that American reactors are normally over-run to obtain more down time? A link? If they're doing that I'd agree it's dangerous, but I would have thought that doing that would violate their operating license in some way.

[kristopher]

6. We have many nuclear supporters here. Let's hear them deny it or not. nt

They will not.

[Throckmorton]

8. You made the statement, the burden of proof is on you

So, how do we run a reactor at a higher power level than allowed?

I deny it categorically, exceeding our rated thermal power, even for a moment, is reportable and a violation of our license. The resident inspectors watch that area very closely, and comparisons to rated electrical output and reactor power levels are checked regularly.

Our fuel cycle is 18 months long, we shutdown to refuel for about 1 month out of 18 months. Most maintenance is performed on-line.

[kristopher]

11. What is the margin?

When you say "exceeding our rated thermal power" what are you talking about? (I know but I'd like you to explain so we don't have a bunch of nitpicking)

Would you relate that to the rated output of the generators, which is the relevant metric for what I was talking about in the discussion on capacity factor?

How large is the margin left by the thermal output required to achieve the rating for maximum output of the generators and the maximum thermal output of the reactors?

Was routinely operating within that margin part of the ORIGINAL evaluation of the system?

In your opinion is the regulatory process for approving changes of this nature weighted in favor of the economic benefits, or the safety considerations?

[kristopher]

16. I take it from the silence this point has been accepted? nt

[Throckmorton]

20. No, but you asked a lot of questions

and I am a slow typer.

[Throckmorton]

17. OK, Ill try

When you say "exceeding our rated thermal power" what are you talking about? (I know but I'd like you to explain so we don't have a bunch of nitpicking)

OK, every power reactor in the United States is licensed for a specific maximum thermal power output, in megawatts thermal. This thermal power is monitored continuously using a calorimetric that measures feedwater flow and temperature to determine the thermal power of the reactor. The instruments that measure these parameters are calibrated to an accuracy +/- 2.5% of full instrument scale. The reactor power level is kept at a level the takes into consideration these measurement uncertainties, and therefore it is assumed that the calorimetric is under-reporting power by 2.75% (2.5 plus 10% uncertainty margin) The reactor is operated at a power level, such that if the instruments are wrong, the reactor thermal power level does not exceed the level allowed by your license. There are usually 8 to 16 flow measurement devices, and 12 to 24 temperature measurement devices inputting to this calculation. They are rules checked against each other automatically, and points that are more than 1% away from there companion points are flagged for calibration checks. This mechanism is controlled by 10-CFR-50 Appendix K.

This is for power operation purposes, there is also the Reactor Protection System which monitors reactor power based on an entirely separate set of instrumentation, and automatically shuts down the reactor if the safety limits are approached. The absolute ceiling for reactor power (both thermal and nuclear power, which ever is greater) as measured by the reactor protection system is set at 103% of the rated licensed thermal or nuclear power. yes, we actually measure neutron flux as an index to nuclear using neutron detectors (inside and outside the core).

Would you relate that to the rated output of the generators, which is the relevant metric for what I was talking about in the discussion on capacity factor?

The steam turbines are slaves to the carnot cycle, as such the maximum mechanical power they can extract from the steam supply system is about 33.67 of the available thermal power, and there is no way the change that. So a 2700 Megawatt Thermal Reactor Plant produces around 909 Megawatt Electric of gross Generation, and about around 870 megawatts of net generation, which is what is available to the grid. The remaining 39 megawatts is used to power the house loads inside the plant. This gross generation number is compared to the thermal generation number, to verify plant efficiency, as a drop in this number indicates wasted energy going somewhere. Any attempt to generate more power that that, will cause a rise in thermal reactor power.

How large is the margin left by the thermal output required to achieve the rating for maximum output of the generators and the maximum thermal output of the reactors?

The margin left before the licensed thermal power limit is exceeded around 2.75% of measure thermal power, or the measurement uncertainty + 10% of the measurement uncertainty.

Was routinely operating within that margin part of the ORIGINAL evaluation of the system?

Yes, the plants were designed to operated at 100% of rated power as base load from the start. Now several, but not nearly all, plants have received power up rates since construction.

In your opinion is the regulatory process for approving changes of this nature weighted in favor of the economic benefits, or the safety considerations?

There have been two methods used to increase the electrical output of units, one is the Appendix K up rate and the other is stretch power up rates.

Appendix K up rates take advantage of the major improvements that have occurred in the ability to measure flow over the past 40 years. This allows the measurement uncertainty of the feedwater flow measurements to be reduced by about 50%. reducing the error margin and allowing plants to run closer to their rated thermal power. Instead of running 2.75% away from the limit, they can run about 1.5% away from the limit, due the the increased accuracy of the instruments.

Stretch Power up rates are a whole different animal, and make use of reanalysis of the primary plant and protective features to increase reactor power 5 to 10%. I am deeply skeptical of stretch power up rates as being weighed too heavily on the economic side. That being said, these uprated plants are still operating within their revised license limits

My unit has not done either of these power up rates, as our main generator cannot produce the additional megawatts electric to perform a stretch power up rate, and Appendix K up rate is still in the planning stage, but at least 3 years away.

[kristopher]

21. Thank you. To be clear

Do you stand by your assertions made earlier?

[Throckmorton]

22. Yes, I do,

Stated Earlier,

"I deny it categorically, exceeding our rated thermal power, even for a moment, is reportable and a violation of our license. The resident inspectors watch that area very closely, and comparisons to rated electrical output and reactor power levels are checked regularly."

In the context in which it was offered, that Nuclear Plants in the United States routinely, in order to improve their capacity factor, knowingly exceed their maximum licensed reactor power, indeed I do.

Overpower events are serious business.

[kristopher]

23. What you wrote

"The absolute ceiling for reactor power (both thermal and nuclear power, which ever is greater) as measured by the reactor protection system is set at 103% of the rated licensed thermal or nuclear power. yes, we actually measure neutron flux as an index to nuclear using neutron detectors (inside and outside the core)."

Does 103 exceed 100?

[kristopher]

24. ROFLMO You went back and erased your admission?

"The absolute ceiling for reactor power (both thermal and nuclear power, which ever is greater) as measured by the reactor protection system is set at 103% of the rated licensed thermal or nuclear power. yes, we actually measure neutron flux as an index to nuclear using neutron detectors (inside and outside the core)."


Good thing I copied it.

I first heard of the practice when I went toured Hope Creek a few years ago. It was a point of pride during the presentation. Since, I've seen it discussed and mentioned in news reports a number of times.

I just did a google search for "operating nuclear plant above rated capacity" and went to the first link where there was a discussion by NEI nuclear fans. Here it is. Note I didn't need to look hard at all to find this. See the discussion after the blog post.
http://neinuclearnotes.blogspot.com/2007/08/npr-steam-cycle-and-nuclear-energy.html

[Throckmorton]

26. No, its still there

You want to believe that nuclear power is dangerous, fine, I agree, for reasons which are now all to obvious.

Just because you don't agree with the license amendments that make power up rates legal, doesn't make it true that plants are run in excess of their licenses to improve capacity factor.

Don't like power up rates, hell, I don't like them either, but that doesn't make me right either.

[kristopher]

29. That isn't what is being talked about at NEI and you know it.

Dude, you guys BRAG about doing this. Look at the NEI blog comments about california.

Now that it is cast in the light of Fukushima and safety though, it suddenly seems more prudent to deny it.

I understand. You are only human; and that's the fundamental problem with nuclear power.

"As was the case during the California heat wave of 2006. By contrast, for the month of July 2006, according to my colleague David Bradish, all of the state's four nuclear reactors were running at above 100% capacity.
"

[Throckmorton]

31. Huh, ok now I am confused,

I posted something in a NEI blog that you are quoting back to me?

I don't even bother to read the NEI site, its too pro-nuke for its own good.

[kristopher]

32. When I said "you guys"

I was thinking of you and the operators that we spent the afternoon with at Hope Creek (PR guy and 2 operators IIRC).

They were quite proud.

You know, I completely understand the attraction of nuclear power. I don't think people who like it are evil any more than I think the people who saw the potential of oil or coal in 1930 were evil. But there is a time to reassess all technologies and nuclear's time is here.

It is a dinosaur that we need to phase out on the path to a sustainable, safe global energy system.

Peace. And thank you for the discussion.

[FBaggins]

27. Did you read what you linked to?

"It is a HUGE violation for a nuclear plant to run above its rated capacity, and hte NRC would be all over anyone who was running above rated capacity. The reason why numbers above 100% might be shown is that the plant received an uprate at some point and that whatever source is showing the reactor above 100% is not aware of the uprate and is using the old number to make their calculations on."

Seems consistent with what he's saying.

[kristopher]

28. That is a cherry picked quote which others immediately shot down.

Part of the article: "As was the case during the California heat wave of 2006. By contrast, for the month of July 2006, according to my colleague David Bradish, all of the state's four nuclear reactors were running at above 100% capacity."

[bananas]

34. "all of the state's four nuclear reactors were running at above 100% capacity."

Pretty unambiguous statement.

[kristopher]

35. It is common knowledge.

And those arguing the point almost certainly are aware of it if they are in the industry.

[Confusious]

38. No, it's not

NRC regulates the maximum power level at which a commercial nuclear power plant may operate.

http://www.nrc.gov/reactors/operating/licensing/power-u...

[Throckmorton]

25. The reactor protection system is just that

A system that protects the reactor due to over power events.

It is not used to operate the plant but to protect the reactor. It does generate alarms if the reactor power exceeds 100% of rated thermal power for more than a few seconds.

The reactor itself can operate for periods of time well above the RPS trip set-points without damage, most can operate at 140% of rated power, according to the Core Operating Limit reports I have seen, for up to 4 minutes without damage. The plant automatically scrams at 103% of rated thermal power.

Nice data mining by the way.

Once again, for the purposes of improving capacity factor in any commercial Nuclear Plant in the United States, or for any other purpose for that matter,

I deny it categorically, exceeding our rated thermal power, even for a moment, is reportable and a violation of our license. The resident inspectors watch that area very closely, and comparisons to rated electrical output and reactor power levels are checked regularly.

[kristopher]

30. .

As was the case during the California heat wave of 2006. By contrast, for the month of July 2006, according to my colleague David Bradish, all of the state's four nuclear reactors were running at above 100% capacity.
http://neinuclearnotes.blogspot.com/2007/08/npr-steam-cycle-and-nuclear-energy.html

[Confusious]

36. Of course you ignore the possibility that

The state government might have requested that increase, it was after all, a heat wave, and what do people do in a heat wave? Turn on air conditioning.

The simplest explanation is best, except in your case, where a few plants running at 100% during a heat wave turns into all of them running at 100% all the time.

Which is total bullshit. A circuit has a certain load. pump too little power in, brownouts happen. Pump to much in, blowouts happen.

You don't think the government keeps an eye on the load and the power output from plants?

How about this from sourcewatch? If a plant runs at 100% all the time, why bother asking for a power uprate? They're not refurbishing the plant to make it more powerful.

http://www.sourcewatch.org/index.php?title=Vermont_Yankee_%28Nuclear_Power_Station%29

NRC regulates the maximum power level at which a commercial nuclear power plant may operate.

http://www.nrc.gov/reactors/operating/licensing/power-u...

[Turbineguy]

7. Just a couple of points.

Manufacturers are always firm about running above 100% rated capacity. Don't do it. Especially with steam turbines. Their overload capacity is measured in cumulative hours over their life span. Not only that, but running above rating reduces thermal efficiency. Steam plants by their nature perform better with steady and rated loads. Therefore the norm is to run steam plants at full load and make up with hydro or gas turbine plants. But within modes of steam generation costs vary. This gives nuclear an advantage over fossil fuels. Thus nuclear plants are run as base loads and other forms pick up peak loads.

Outage periods for nuclear have been drastically reduced over the years. A plant that refuels every 2 years can achieve a CF of 91% percent while running at 95% rated output. Nobody needs to cheat to make their numbers. Also with maintenance, a lot has changed with the use of thermographics, vibration analysis and tribology.

Since fossil fuel plants don't need to shutdown for refueling the improvements have skewed the CF numbers toward nuclear. Also since refueling is the critical path for nuclear, other equipment maintenance schedules are geared toward those availabilities.

On edit: your point is obviously just argumentative and to stir up fear. I am not a proponent of nuclear power plants. They are technically interesting but they are scary enough without the gratuitous hysteria and outright misinformation.

[kristopher]

9. Nuclear plants routinely exceed 100% of rated generating capacity - esp. in summer.

Manufacturers of turbines are not the people who operate them. I'm sure there are reasons not to do it, but there are also economic reasons to do it that conflict with what the manufacturer thinks best.

[GliderGuider]

10. Could you prove that assertion, please?

I don't believe you.

[Name removed]

12. Deleted message

Message removed by moderator. Click here to review the message board rules.

[GliderGuider]

13. You seem to be in a better mood today!

That's good to see. :thumbsup:

[kristopher]

15. I got my first full night of sleep since the earthquake.

Thank you.

[Throckmorton]

18. My screen name is Throckmorton

Thanks for the personal barb.

[FBaggins]

14. It doesn't need to be a theory... it should be simple enough to prove.

How long (in total) have they had plants down due to earthquake repairs over the last few years (obviously not including the current period). How long do they take to refuel? The balance of any downtime would be your presumed gap for extra maintenance to retain quality levels.

[kristopher]

19. My friend the flight mechanic with a major american airline

That was a while back but one day a friend who was a flight mechanic (they travel with airplanes for onboard servicing) was complaining to me about his employer.

The basis of his complaint was that he felt that all he ever did lately was to spend his time pouring cans of hydraulic fluid into the systems of the plane. The company found it less expensive to put him on the lane with a pallet of hydraulic fluid than to take the aircraft out of service to repair what the mech considered to be serious leaks.

Such trake-offs are unavoidable even when profit isn't the primary consideration. For example, police patrols are often designed to minimize costs while providing a much coverage of high risk areas as possible. But sometimes the consequences of misjudging the line are far more than anticipated.

I don't think people who push for the line of cost savings are evil and I urge others to refrain from that kind of thinking. When resources are more effectively used, people are genuinely helped by and large. But to bring balance to the equation we need to keep the pressure on the safety side of the system even when the payoff is the intangible of a disaster that never happens.

[Name removed]

33. Deleted message

Sub-thread removed by moderator. Click here to review the message board rules.

[Confusious]

37. Total Bull. made up from whole cloth. link

NRC regulates the maximum power level at which a commercial nuclear power plant may operate.

http://www.nrc.gov/reactors/operating/licensing/power-uprates.html

[kristopher]

39. "...all of the state's four nuclear reactors were running at *above* 100% capacity"

Dude, these guys BRAG about doing this. Look at the NEI blog comments above about california.

Now that it is cast in the light of Fukushima and safety though, it suddenly seems more prudent to deny it.

I understand. You are only human; and that's the fundamental problem with nuclear power.

"As was the case during the California heat wave of 2006. By contrast, for the month of July 2006, according to my colleague David Bradish, all of the state's four nuclear reactors were running at above 100% capacity.
"

[Confusious]

40. Of course you ignore the possibility that

The state government might have requested that increase, it was after all, a heat wave, and what do people do in a heat wave? Turn on air conditioning.

The simplest explanation is best, except in your case, where a few plants running at 100% during a heat wave turns into all of them running at 100% all the time.

Which is total bullshit. A circuit has a certain load. pump too little power in, brownouts happen. Pump to much in, blowouts happen.

You don't think the government keeps an eye on the load and the power output from plants?

How about this from sourcewatch? If a plant runs at 100% all the time, why bother asking for a power uprate? They're not refurbishing the plant to make it more powerful.

http://www.sourcewatch.org/index.php?title=Vermont_Yank...

[kristopher]

41. Who said they run at 100% all the time?

I can't understand your discussion points since they simply do not follow from what's been discussed. I'd like to respond better but...

[Throckmorton]

42. Because when you up rate a plant

Nuclear, coal, solar, what have you, the baseline for 100% moves to a new, higher number. A 1000 megawatt/Hour plant that gets 10% up rate, is now an 1100 Megawatt/hour plant.

Nuclear plants for the most part run at nearly 100% power, most of the time. Either that or they are on the way to or from hot standby (Mode 3 in a PWR). In mode 3, the primary plant is at, or near, operating temperature and pressure, but the reactor is sub-critical (Keff <0.99). The Primary System is heated up using decay heat and heat "added" by running the reactor coolant pumps.

[bananas]

43. So what did David Bradish mean when he said the plants were running over 100% ?

[Throckmorton]

44. I Don't know N/T.