COLUMBIA — The design for AmerenUE's proposed second nuclear plant in Missouri isn't that different from its existing plant, officials from the utility say.
AmerenUE submitted an application to the U.S. Nuclear Regulatory Commission in late July for a license to build and operate the proposed plant, which would be built next to its existing plant in Callaway County.
The existing and proposed plants are both known as four-loop pressurized water reactors. In this type of reactor, normal water - kept at high pressure so it doesn't boil - both moderates the reaction and cools the reactor core, much like a car's radiator cools the engine. The exhaust heat boils other water in four large steam generators, and the resulting steam rotates turbines to generate electricity.
The proposed plant, known as Unit 2, will be about 30 percent larger than the existing Unit 1, said Scott Bond, AmerenUE's manager of new plants.
Design documents previously submitted to the commission state Unit 2 is designed to generate 1,600 megawatts of electrical power. AmerenUE spokesman Mike Cleary said Unit 1 produces 1,190 megawatts.
Bond said most of the differences between the two plants' designs have to do with additional safety equipment.
"Probably the biggest difference is that the new design has four safety trains," Bond said, referring to the independent sets of safety equipment designed to cool the reactor core and prevent damage to it in an emergency situation.
The existing plant only has two such trains, he said.
Bond also said the new design's additional safety equipment would help the plant spend less time offline for refueling than its older neighbor.
Because Unit 1 has only two safety trains, each one can be out of service for maintenance for only 72 hours at a time, he said. If maintenance on a safety train takes longer than that, AmerenUE's operating license requires the entire plant to be shut down.
Unit 2's four safety trains, however, would let plant operators take a train down for up to 120 days at a time, Bond said. This would allow workers to perform maintenance work while the plant is still running instead of waiting until the plant is already offline for refueling.
Bond said this feature would shorten the new plant's refueling outages to 14 days instead of Unit 1's typical 30 days.
"With Unit 2, there would be a lot more maintenance that you can do while the plant's operating, instead of having to do it when the plant is shut down," Cleary said.
If the water surrounding the reactor core were to be lost - termed a "loss-of-coolant accident," during which the core would overheat and possibly melt, Bond said both plants would inject an emergency supply of extra water into the core to cool it down.
"Actually, they handle it very similarly," he said.
Such accidents have occurred before, including the Three Mile Island accident in 1979. In that accident, which the commission's Web site calls "the most serious in U.S. commercial nuclear power plant operating history," part of the core melted but stayed within the main reactor vessel.
Unit 2's design includes space below the reactor vessel intended to catch and cool any melted core material should it escape. Like Unit 1, the reactor vessel would also be surrounded with a large concrete containment building to prevent any possible releases of harmful radiation.
Bond said the new plant would also be built with digital control systems instead of the analog systems that were originally installed in Unit 1.
Other improvements in the new design include more efficient turbines and use of fuel, he said.
"Compare a car that's built in 1980 versus a car built today," he said.
Cleary said that Unit 1 has been upgraded numerous times since it first went online in 1984.
"Due to all the upgrades and modifications, this isn't the same plant that it was when it was first built," he said.