Safety improvement highlights nuclear construction

JENKINSVILLE – The concrete pour at the Jenkinsville Nuclear Reactor 2 made history as the first for nuclear related construction in this country in 30 years.

The construction took just over 50 hours and was a continuous, no-joint pour. Concrete was made at a batch plant on site. The pour was six feet thick and used around 700 cubic yards of concrete. The operation used four trucks with three pouring at any one time and 16 more trucks that were constantly mixing and carrying concrete back and forth.

The Unit 2 site, shown here, is being constructed in parallel with the unit three site, though some processes must be completed at Unit 2 and construction staggered at Unit 3.
The Unit 2 site, shown here, is being constructed in parallel with the unit three site,
 though some processes must be completed at Unit 2 and construction staggered at Unit 3.

 

After the concrete cured for four weeks, the bottom head of the containment vessel, a 550 ton lift, was placed in the center of the excavation.

That containment vessel was lowered into place by one of the largest cranes in the world. The heavy lift derrick that engineers designed specifically for this project runs on rails, pivots 360 degrees and is strapped to the ground using a universal joint.

That allows the derrick access to Unit 2 and Unit 3 as well as the modular assembly building. The containment vessel is 1.25 inch steel and is assembled on site. Reactor components go inside the vessel. Workers currently are welding ring sections now to stack on the lower level of the containment vessel. Three ring sections go next and two are in construction now. They will be closed in by the top head component.

 Workers do rebar work and form work for a Unit 2 wall in preparation for a concrete pour.
Workers do rebar work and form work for a Unit 2 wall in preparation for a concrete pour.

Portions of components are assembled in the module assembly building, which is 150 feet from ground to eave. During construction, a submodule sits on a table and is lined up and then placed on a loader to transport it on the adjustable dolly-like machine, enabling the section to be driven over to the heavy lift derrick.


From there, the section is hoisted in place and installed. The module assembly building has removable outside walls so the trolley can carry the module straight to the heavy lift derrick.

The reactor two site, shown here, recently was the first concrete pour for a nuclear power plant in the United States in 30 years.
The reactor two site, shown here, recently was the first concrete pour for a nuclear 
power plant in the United States in 30 years.

 
Biggest changes

For all the state-of-the-art equipment, “the biggest change is in passive safety systems,” said SCE&G’s Ron Jones. “In the existing fleet of nuclear plants, which are safe, safety systems are redundant with redundant power supplies. Current plants, in the unlikely event of an accident, operators must take actions with valves and pumps. There are procedures for that and it is safe, but this is a simpler set up.”

The new systems use gravity, evaporation and precipitation to cool the reactor and assorted components. Those systems cost less to maintain as well. Basically, in 72 hours the plant would cool itself and the only thing needed to be done by the technicians next would be to refill a tank with water.

The low profile cooling towers are a hallmark of the new designed AP 1000 power stations, which take up less space than the old technology. Cooling tower 3A contains 16 fan cells. In these towers, evaporated water showers down into a basin and then is deposited to a pumphouse and back up to the cooling tower.

The cooling tower extends underground to conde
nsation tubes where the water goes to dissipate heat before returning to the cooling tower. Cooling tower 2A is 75 percent complete. 2B and 3B are having foundation work done and the pump house is being worked on between the basin.

According to SCANA, the panels are precast for cooling towers in Spartanburg at Kendall Corp., a contract worth over $40 million to the state’s economy.

The AP 1000 reactor contains three low pressure turbine rotors. For Unit 2, the lower level of turbine building is completed and the main condenser for Unit 2 was placed in June. The Unit 3 base mat will be poured this fall as part of the Unit 3 nuclear island, which consists of the containment vessel, auxiliary equipment and batteries. Workers are also erecting the cooling towers and base rebar is under construction in Unit 3.

Steve Byrne, COO and president of generation and transmission for SCE&G, said timing is everything when constructing a nuclear power plant and he noted there are four nuclear projects less than 100 miles apart in the Carolinas and Georgia.

Byrne said about 15 licenses are on file with the NRC. Other utilities have the opportunity to build but the economic downturn resulted in the conservation of electricity in the United States.

“In the southeast, electricity usage remained flat, contrary to that trend, so SCE&G is still adding customers,” Byrne said. “The recession may have changed some utility companies immediate plans but they still are pursuing licenses with the intent to build facilities.”

Byrne said the Chinese plants under construction that SCE&G studies are the same with the nuclear islands, although they use a different turbine manufacturer. Still, that gives the consortium valuable opportunities to learn from issues the Chinese might encounter with construction.

Jobs

Chief Nuclear Officer Jeff Archie spoke of SCE&G’s efforts to cultivate the next generation of nuclear professionals. Over his 35-year career at VC Summer, he was with the plant when it went on line and now has opportunity to be engaged in the new plant projects.

“We like to talk about people and the success of our staff and people especially for a generation of people in nuclear power who are young and new to the industry,” he said.

He said they have had eight interns from local colleges this summer that provided a good pipeline of talent. Archie said the plant employs not just up-and-coming engineers but mechanics, finance workers, chemists and more.

At its peak the construction will employ about 3,000 craft workers and 600 to 800 management staff. About 800 craft workers were on site during media day along with about 200 subcontractors. Construction personnel are trained on a regular basis. At the site one can advance from apprentice to journeyman to foreman. Jobs include linemen, concrete finishers, rood benders, scaffold builders and electricians.

Material arrives from all over the world to the port in Charleston and with rare exceptions is shipped by rail to the Jenkinsville construction site. Right now about 1,600 consortium and 300 SCE&G employees make up the operating staff and the staff trainers are getting licensed now using the reactor simulators. To date approximately $2.5 billion has been spent on the project.

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