STEEDMAN — A little over two weeks into a refueling outage at the Callaway Energy Center, the facility buzzed with activity.

From the beginning of April through the end of May, 1,000 temporary workers will call the plant home as they replace about one-third of the facility's 193 fuel assemblies and perform other routine maintenance. Ameren Missouri managers at the power plant said the maintenance ensures equipment will last until the facility's operating license expires in 2044.

Callaway Vice President Tim Hermann stood on the second floor of Callaway's turbine building Tuesday looking at three large pipes that carry water from the plant's cooling tower into its condenser.

"It's not actually replacement, it's just maintenance," Hermann said. "That's how you get the reliability you want, by doing the right preventative maintenance."

Every 18 months Ameren shuts down the facility for 30 to 45 days for refueling. During the process, spent fuel rods are taken from the facility's reactor and placed into the plant's spent fuel rod pool for five years.

In 2015 Nuclear Regulatory Commission granted Ameren a 20 year extension of the facility's operating license until 2044. Callaway had enough room in its spent fuel pool for 40 years worth of nuclear fuel.

At the time of the extension, Ameren built a dry cask storage system, which stores long-cooled spent fuel rods until the federal government builds a permanent storage facility. Currently 18 of the 48 dry cask plots are used.

Each refueling outage costs Ameren about $29 million. Federal Energy Regulatory Commission rules prevented Hermann from divulging the exact date the work will be finished, and the facility will be powered on.

Some of the work at the power plant looks more noticeable than others.

As Hermann walked around the turbine building, temporary pipes and scaffolding sat everywhere. Higher, on the turbine deck, large concrete blocks sat displaced from their usual spot on the floor as temporary railings surrounded large square voids which construction equipment gets lifted through.

Parts of turbines sit everywhere in the building. In one corner, large parts sit on a pair of the concrete blocks, being used as makeshift table. In others, dozens of turbine blades sat laid out on a table. At Callaway, the plant's nuclear reactor heats water, which transfers the heat to a separate closed system until it becomes steam and turns the massive turbine blades.

Callaway produces about 1,200 megawatts of energy and makes up about 19 percent of Ameren's energy load. Steam first enters a high pressure turbine, is then reheated, then sent through low pressure turbines. About 60 percent of the energy produced comes from the high pressure turbines, Hermann said.

Normally the room sounds loud and requires hearing protection to enter. Ameren is refurbishing turbines in the turbine room for the first time since they were replaced in 2005.

"That's where the mechanical energy is converted into electrical energy," Hermann said as he pointed to a turbine under maintenance.

Other upgrades are less noticeable.

Located deep within the turbine room sits the plant's control center. Most of the controls still look like they did when Callaway opened in 1984. Previously Ameren pledged to convert some non-safety dependent controls to digital controls, but the NRC has expressed concern digital instruments. During this outage, a handful of non-safety-dependent controls were being switched to digital controls, but most will remain analog, Hermann said.

Scars of the Fukushima Daiichi Nuclear Disaster also scar Callaway. A water tank sitting outside the turbine room stores 500,000 gallons of water needed to cool the plant in the event of an earthquake or tornado. Ameren built the tank after Fukushima, Hermann said.

"The NRC issued some requirements on what we have to address beyond our design basis," Hermann said. "The netting around it is stopping a vehicle or heavy equipment that's thrown at it through a tornado."

Shift manager Bryan Parker is one of several employees that oversees operations in the control room. Even before Fukushima, shift managers went through simulations, much flight simulations, to practice everyday operations and emergency situations. Fukushima forced nuclear operators to re-examine their emergency preparedness, Parker said while standing in the control room.

Before Fukushima, Callaway had several backup plans in the event of emergencies, Parker said. After Fukushima, Callaway modified the plant so equipment can be used in case its emergency backup systems fail.

"It affected a lot more than just the procedures," Parker said. "We have a whole new supplemental guidelines on redundant and more defense and depth of these systems.

Around the year 2030, Ameren will need to decide whether it wants to seek another license extension or not. If Ameren seeks another extension, it would take the plant past its 60th birthday. Recently, nuclear plants in the northeast applied to operate past their 80th birthday.

Still, other utilities closed nuclear plants recently because of the high cost of continual maintenance, refueling and operations. In June 2016 Pacific Gas and Electric decided to close the two-reactor Diablo Canyon Nuclear Power Plant, near San Luis Obispo, California, by 2025 rather than invest in a new cooling system. Sitting near a cliff-side overlooking the Pacific Ocean, Diablo Canyon sits in an earthquake prone part of California.

At the time, PG&E stated it planned to replace the plant with cheaper forms of renewable energy. Ameren operates just one reactor at Callaway.

In 2008 the utility filed an application with the NRC to build a second reactor at the site, but withdrew the application in 2015 when Ameren did not find funding for the project.

When nuclear projects first came online in the 1960s many environmentalists saw nuclear energy as a form of green energy. Ameren set a goal of slashing its carbon footprint by 80 percent by 2050 and is closing a handful of coal-fired power plants. Already Ameren reduced its carbon-dioxide emissions by 26 percent, its nitrous-oxide emissions by 44 percent and its sulfer-dioxide emissions by 63 percent Hermann said.

Still, environmentalists by and large do not trust nuclear energy because of the long-lasting impact nuclear waste can have on the environment.

"It's low emission of course," James Owen, executive director of Columbia environmental think-tank Renew Missouri, previously told the Tribune. "It's not renewable."

Hermann does not know what the future holds for Callaway beyond 2044. PG&E can replace Diablo Canyon with renewables because the West Coast renewable market is more fully developed than the Midwestern renewable market, Hermann said.

A second reactor at the site could prolong the life of many of the facilities. Still, utilities struggled in recent years to open new new nuclear reactors in Georgia and other parts of the U.S. because of the high costs of building new reactors. Hermann acknowledged, cost could be a barrier to building a new reactor at Callaway.

"That's an economic decision," Hermann said. "Right now the U.S. has struggled with building a plant in a manner that proved to be economic against the other options."

pjoens@columbiatribune.com

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