Guest Post: The Callaway Coastdown

Tom Kauffman

The following is a guest post written by NEI's Tom Kauffman. Though Tom now works in NEI's media relations shop, he spent 23 years working at Three Mile Island, seven of those as a licensed reactor operator. 

Ameren's Callaway Energy Center in Missouri is in a "coastdown." No, it's not rolling to a stop like a skateboard that's missing its rider, it's actually running low on fuel - exactly as planned.

Nuclear plant operators shut down their units to refuel the reactor (aka refueling outage) and do a lot of maintenance work every sixteen to twenty-four months depending on the unit's operating cycle. The Callaway reactor is on a year and-a-half operating cycle.

The uranium fuel in about a third of the fuel assemblies in the nuclear reactor has been used so those fuel assemblies will be removed for storage. The fuel assemblies have been in the reactor for a few cycles of operation and are now located toward the center of the reactor where the greatest fuel use occurs. Of course the operators don't want any of the valuable uranium to go to waste, so it's important that as much as possible has been used to make electricity. Engineers carefully calculate the fuel loading in the reactor to make sure they have enough for each operating cycle, while minimizing the amount that could be unused.

A refueling outage requires hundreds of contract workers, tens or even hundreds of millions of dollars’ worth of parts and materials, and a tremendous amount of planning. In order to be cost effective, thousands of work hours must be completed in a very structured timeframe. Refueling outages usually take 30 to 40 days, so it's important they start on time. Delaying or extending an outage can cost millions of dollars a day and effect fuel use.

Callaway Energy Center

Outages are normally performed during the spring or fall when demand for electricity is low. Nuclear facilities safely produce large quantities of continuous electricity that is vital for grid stability especially during the summer and winter when demand is high. Therefore, the outages need to be done in a relatively short time window. That's why the workers follow a carefully orchestrated, 24/7, computer-driven work plan.

If during an operating cycle a plant has to shut down or reduce power for some reason, that event might delay the start of the outage. If it's lengthy shut down, it may require removing some unused uranium in the fuel assemblies. It also complicates the fuel loading calculations and outage planning. Ideally there are no shut downs during the operating cycle. But how many million horsepower machines can operate non-stop at full power for a year-and-a-half?

That brings us back to the Callaway nuclear facility. It looks like this operating cycle, like its last operating cycle, the unit will run "breaker-to-breaker." This means they started the Callaway unit and ran it continuously at or near full power until it is shut down for the refueling outage. That's outstanding, but it gets even better. Precisely as anticipated (because of their extremely accurate fuel loading calculations) several weeks before the scheduled start of the outage the reactor has started to slowly reduce power because the fuel in the center of the reactor can no longer support full power operation. When power reaches about 80 percent they will shut the reactor down and begin the outage right when their team scheduled it to start. The bottom line is, the unit has run very reliably and the fuel use was on target. It doesn't get any better than that.

By the way, in 2012 the nuclear industry's average capacity factor (a measure of reliability) was a bit under 90%. Callaway's 2012 capacity factor was 99.4%.

Thanks to Tom for filling us in on these details. I think it's also important to point out that nuclear outages are a real boon to local economies. Earlier this month, Exelon's Quad Cities Generating Station began its own outage that drew an additional 2,000 workers to Cordova, Illinois. What's the bottom line financially: $2.7 million pumped into the local economy.

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Uprates Stymie the Search for Scandal

The Washington Post has an interesting blog post from Brad Plumer on the nuclear energy industry’s stealthy increase of electricity output via uprates. Here’s how Plumer defines an uprate:

According to a new analysis by the U.S. Energy Information Administration, the operators of 98 of the country’s 104 commercial nuclear reactors have asked regulators for permission to boost capacity from their existing plants.

Or, as Plumer points out, the equivalent output of six new reactors (though I would add that it is spread out among 30 or more states instead of six – a net positive. Altogether, there have been 145 instances of accepted uprate application – some reactors have been uprated more than once.)

Uprates aren’t peculiar occurrences, but you knew there had to be a catch:

In recent years, however, nuclear operators have started applying for much larger “extended uprates,” which can increase the output of a plant by as much as 20 percent. This process can include big changes to high-pressure turbines and other equipment.

Do these “big changes” create a danger? Well:

Utilities and regulators have used computer modeling to show that “a properly uprated reactor is no more vulnerable than one operating at its original capacity.”

It’s worth remembering that making a facility “vulnerable” does no one any good, so the conservative approach typically taken at nuclear facilities would dictate that plants avoid uprates if there were multiple instances of their being problematic.

That doesn’t mean there has never been a problem. But where there have been problems, there have been solutions.

In 2002, both reactors at the Quad Cities Nuclear Plant were restarted after having their capacity boosted by 17.8%. Pipes began to shake, and cracks formed in a steam separator, which removes moisture from the steam before it enters the turbines. In one case, a 9-by-6-inch metal chunk broke off and disappeared.

Broken parts were replaced, but the problem continued. Exelon Corp., which owns the three plants, and the NRC were mystified.

Problem.

Eventually the problem was uncovered: acoustic waves caused by the geometry of the steam pipes. The pipes were acting like a musical instrument. Their geometry was modified to "detune" them.

Solution. And the story also notes that the NRC has held up two uprate applications until “steam separator” questions are answered. These are industrial and regulatory issues that are handled in the course of doing business.

To be honest, while Plumer is looking for a way to make uprates newsworthy, building from an L.A. Times story, he’s honest in noting that they have not been problematic so far: the Quad Cities story above comes from the Times may seem to put a more sinister cast on uprates, but still nothing came from the incident. A problem occurred, caused no harm and was fixed.  That’s not very diabolical.

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Let’s be fair here. You want reporters to go after hidden and/or malignant behavior in industry – and nuclear energy facilities have been in the journalistic loop since the accident at Fukushima Daiichi – but the American nuclear energy industry just hasn’t been cooperating by revealing itself as a scandal ridden cesspool run by uncaring monsters.

The AP series last year ran several parts and ended up being about nothing because there was nothing really to find. That was an epic fail. Plumer and the Post more or less admit that the biggest scandal surrounding uprates is that they have supplied some 6500 additional megawatts of cleanly generated electricity. So at least we know that.

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