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Offline Rennhack

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Press Question
« on: Dec 28, 2002, 09:28 »
If anyone can help this guy, please send me an email.
Mr. Rennhack--
I'm a reporter at the St. Paul Pioneer Press, and I came across your website and found it interesting. I'm trying to track down some generating figures for Xcel Energy's nuclear and conventional power plants, though, and I was having difficulty reconciling some numbers, so I'm writing to you to see if you might be able to provide some insight.

In particular, I'm trying to figure out how to determine "net capacity factor." FERC seems to have one formula, NERC has another and it appears the individual utilities may even have their own.

Since you cite the '97 "average capacity factor" numbers on the plant pages of your website, I'll use that year as an example. If you look at the NRC's 2002 annual report, it shows that in '97, Monticello had a capacity factor of 83.6; your site lists it as 76.7. Similarly, the '97 NRC figures for Prairie Island's Unit 1 and 2 capacity factors are 98.9 and 91.1 respectively; your site lists the '97 figures as 78.4 and 81.2 respectively. I checked with the NRC and they said they use the capacity factors that are provided by the licensee.

Compounding the problem is that when I use figures that NSP provided to FERC in its Form 1 covering '97 and plug them into the equation that FERC told me to use, I come up with a capacity factor of 97.1 at Monticello, and a combined capacity factor of 76.8 for Prairie Island. (In the FERC Form 1, all figures for the two units are combined into a single total.)

The raw numbers from the Form 1 that FERC said are relevant are Total Installed Capacity (Max. Gen. Nameplate Ratings-MW), Plant Hours Connected to Load and Net Generation Exclusive of Plant Use. Given that, the relevant figures for Monticello for '97 are:

Total Installed Capacity: 631.2 MW
PHCL: 6776
Net Gen.: 3,876,322 MW

I guess this is a rather long-winded way of asking:

-- Where did you get your figures?
-- If you came up with them on your own, what equation did you use and what were the raw numbers for it?
-- Are you able to provide any insight into how to come up with figures that would be considered reliable by the industry?

Thanks. I appreciate your help.

I borrowed the statistics from the Nuclear Energy Institute ( And the EIA
EIA states 2001 AVERAGE capacity factor as 74.1% (Monticello) NEI states 76.5 Net Capacity Factor…

I would say that the term ‘average’ and ‘net’ might have something to do with the difference.

I have found no ‘formula’, just a definition:

Capacity factor (gross)
The ratio of the gross electricity generated, for the period of time considered, to the energy that could have been generated at continuous full-power operation during the same period.

Capacity factor (net)
The ratio of the net electricity generated, for the period of time considered, to the energy that could have been generated at continuous full-power operation during the same period.


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Re: Press Question
« Reply #1 on: Dec 29, 2002, 03:00 »
It is also interesting to note that a utility can produce beyond 100% capacity with cold injection water for cooling the condenser. I believe there are actually 2 capacity factors, one is for operability, one is for power generation, although I may be wrong about this. The numbers would be similar, but slightly off.

Offline HydroDave63

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Re: Press Question
« Reply #2 on: Dec 29, 2002, 07:28 »
Mike, your definition of

Capacity factor (net)  
The ratio of the net electricity generated, for the period of time considered, to the energy that could have been generated at continuous full-power operation during the same period.

is essentially correct, when you also subtract out power used by the generating station on its aux loads, like air conditioning/HVAC loads, HP break trailers, lighting, etc.
It can exceed 100%, for factors like colder ultimate heat sink temps, turbine efficiency, nuclear instrument rating increases,etc. The last two factors have become more and more commonplace throughout the industry in recent years. The baseline number of what the plant should produce is based on its original year of manufacture rating. Several utilities have changed turbines for greater efficiency, and many have recalculated some statistical properties of their nuclear instruments, and allowed to run at 102% rated thermal power. So, in a good year, at a top performing plant it is not impossible to have a 103% capacity factor year. Hope this helps!


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Re: Press Question
« Reply #3 on: Dec 29, 2002, 08:15 »
There are many versions of "Capacity Factor", utilities customize the stats to meet their needs. I have seen "Net Dependable Capacity Factor" which considers age related de-rates, usually provided to State Commerce Commissions for rate case analysis in regulated states. More applicable to fossil boilers accumulating scale and slag, many nukes are owned by fossil utilities and use these numbers for corporate conformity.

With Power Uprate projects across the industry, many plants are now "Electrically Limited" due to Transformer capacity or grid limitations.

From an operator perspective, the only thing that matters is Licensed Power Level, given in Tech Specs.

For the company, the Megawatt Hour meter is all that matters, that's how the bills get paid.


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Re: Press Question
« Reply #4 on: Dec 29, 2002, 08:56 »
Downtime has to be factored in...the outages in '97 had'nt shortened quite as much as now. emergency outages and scheduled outages should be averaged in to any net or average. 30 days offline can make a difference.

Offline Rennhack

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Re: Press Question
« Reply #5 on: Dec 30, 2002, 10:12 »
I received another email from our friend at the Pioneer Press, I told him I'm just a Radiation Safety guy, and that he should talk to you smart Nucler engineer folks.
Thanks for your replies, and I appreciate you posting the question on your website. The answers are interesting, although I'll have to admit the more I look into this stuff and learn, the more confusing it gets.

For example, reading the FERC Form 1, (Page 403.2 in NSP's '97 filing) it lists Monticello's nameplate MW rating in '97 as 568.8 MW, but then there are two lines with these entries:

When not limited by condenser water:  562
When limited by condenser water:  545

What the heck does that mean?

Also, I'm having trouble finding if there's a difference between the definition of "period hours," which is the term for the hour figure used in some capacity-factor equations, and "plant hours connected to load," which is the term used in other definitions.

It does strike me that there is some "X" factor or some equation known only to Xcel/NMC that they use when computing their capacity factors, because none of the commonly used equations arrive at the figures they gave the NRC. I spent about an hour on the phone with a helpful guy from Allete the other day going over the Form 1 data, and even he eventually threw up his hands and said he was stumped as to how Xcel came up with the figures they came up with. He tried it every which way and couldn't do it. FERC tells me that there are only three stats you need to figure net capacity factor: rated megawatts, actual net generation and plant hours connected to load.

What I'm trying to do is come up with some reliable and defendable figure that can be used across the board to show how a plant (nuclear and conventional) is performing from one year to the next. While I know that some years may have big performance gains or increases because of scheduled outages, is there any reliable measure or gauge the industry uses that shows a plant's performance, over time?

To your knowledge, is there any generally accepted industry theory (or even anecdotal lore) that establishes any correlation between what is spent on maintenance and the kind of performance you get. I know if I don't spend money maintaining my car, it's performance degrades over time, but my car isn't a power generating plant, so I don't want to rely on intuitive belief on this type of thing.

And lastly (for now, anyway) what facts or figures about a plant do you folks in the industry look at to gauge a plant's performance and reliability? What do you consider important for you to know about a plant?

Again, thanks for your help and insights. I appreciate it.


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Re: Press Question
« Reply #6 on: Dec 30, 2002, 10:42 »
I have seen plant output de-rated due to exceeding temperature limits.

Clinton has a cooling lake, during a long, hot, drought back in the early 1990's, we hit about 86 degrees lake temperature.

That de-rated the plant two different ways:
Hot Condensate (about 120 degrees) would cause the Air Ejector Intercondenser Loop Seal to flash which caused Condenser vacuum to head south. This was called Steam Jet Air Ejector Chugging. We had to back off power about 15% to 20% to recover Condenser vacuum and avoid a Turbine Trip / Scram, which was generally considered bad form. Then we would slowly raise power until about 115 degrees Condensate, ending up at about 90%. That's an example of plant thermodynamics forcing a de-rate.

We also had an outfall temperature limit due to our NPDES discharge permit, limiting us to something like 110 degrees over a length of time - I think it was a few weeks. To avoid adverse environmental impact on the lake. Hot lake temperatures affected that. So there are also regulatory imposed de-rates.

Oddly enough - before the plant, there was no lake. Only Salt Creek, which area farmers said, used to occasionally run dry. I am glad nobody overheated it back then...

So, yes the Condenser can be limiting. With Power Uprates going on, you'll see more of that in July and August unless corresponding improvements are made to the Condenser and Circ Water Systems.

Offline radmax

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Re: Press Question
« Reply #7 on: Dec 30, 2002, 10:50 »
Slightly Off Topic...
but THANK THE "Whatever higher power you believe in"(PC) for a reporter who is actually trying to get it right, and is asking questions of the real experts, and not some Hollywood Who.  8)
Quick, lets get the Raeliens to CLONE this guy before Fonda and Brinkley find out about him. ;D ;D ;D ;D ;D ;D ;D ;D
Seriously, this is proof that people other than ourselves read these pages, and we SHOULD try to police our comments and at least appear to be adults.  Not that we can't have fun, but there are a few who tend to get a little out of hand once in a while, and perhaps they might think about how things appear to outsiders.
It's just too damn'd early in the morning to be this damn'd early in the morning!


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Re: Press Question
« Reply #8 on: Dec 30, 2002, 01:36 »
I worked at a plant that was routinely limited by river discharge temperature, they finally set up cooling towers for the discharge water prior to returning it back to the environment. The cost was more than made up by being able to run at full power during the summer.(they also get to charge more for the electricity then)


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Re: Press Question
« Reply #9 on: Dec 30, 2002, 02:47 »
I want to thank all y'all for the responses so far; they're helpful. The more the better. The clone thing would be ok, as long as he didn't do anything I'd get in trouble for. I tend to get blamed for enough things as it is.....

As you've seen, I'm just trying to educate myself on this stuff, and you can go to the NRC and you can go to the industry trade groups and you can go to the licensees, but I've always found that it's generally best to go to the men and women who actually do the work.

I'm just trying to figure out what reliable (and bullet-proof) indicators there are that show a plant's health over time -- or even if that is a valid way to look at things. It may not be, for all I know at this point. That's one of the reasons I'm trying to educate myself.

Trying to track down the capacity factor thing (and we're talking about net capacity here) may give you an indication of why I wanna pull my hair out. Again, using Monticello as an example, the licensee reported to the NRC that the capacity factor in '01 was 81.6. EIA says it was 74.1. NEI says it was 76.5. When I take Monticello's figures from Xcel's 2001 FERC Form 1 and use the equation FERC told me to use, I come up with 90.6. Allegedly, all of them are the same thing. Frankly, I don't give a hoot which one it is. I'm just trying to figure which one is accepted industry-wide.

(Incidentally, I screwed up in my original e-mail to Michael; the '97 figures I gave him for Monticello were actually '01 figures. The real '97 figures are Total installed capacity: 568.8 MW; plant hours connected to load: 6618; and net generation: 3.6 billion KWh. I've since double-checked all my math on everything else.)

I do want to assure you folks that I really try to get things right. When it comes to understanding complex technical stuff, the average reporter really isn't well-prepared, the average editor even less so. (And I'm talking about print reporters here. Maybe it's my bias, but TV reporters seem to be even worse.) Anyway, I know the stuff is technical and there are a lot of "ifs" and "buts" and "maybes" and subtleties and nuances, and I want to try and understand that without simplifying it. I don't want to sound like I'm bragging, but by way of introduction so I'm not a total stranger to y'all, I'll mention that I won a Pulitzer in '89 in the explanatory journalism category. I was working in Dallas at the time, and spent 22 months inside the NTSB, following them as they investigated the crash of a business jet. I was the first and, to date, only reporter the NTSB has ever allowed to view an air safety investigation from the "inside." And believe me, I learned pretty quick that when it came to aviation, journalists screwed up with some frequency, so I had to overcome a lot of anti-media feelings and prove to the folks I was in it for the long-haul and just wanted to get it right and explain what was going on to my readers.

I know all of this is long-winded, but I just want to know what facts, figures and statistics the folks who do the work look at when you're gauging whether a plant is working efficiently or not.

Any help/guidance/insights/warnings would be helpful. Just so we're on the same page, I won't print anything posted on this forum in the paper I work for, the St. Paul Pioneer Press, without first checking with and interviewing the author of the post. So I just wanted to put you guys at ease on that point.
Again, thanks.
David Hanners


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Re: Press Question
« Reply #10 on: Dec 30, 2002, 05:29 »
The best way to measure a plants ability is two fold. Inadvertent scrams and down time past scheduled down time. Capacity factors as you can tell are confusing. Ralph Nader's group, "Public Citizen" has a lot of information on the nuclear plants, although I think they value INPO's opinion to highly.

The lower the injection water or river water the better it is for the heat cycle. The delta t across the turbine is related to enegy transfer to the impeller. The higher the delta t the better.


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