Tuesday, March 19, 2013

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.

No comments: