EnergySolutions announced yesterday the successful completion of the first large commercial reactor vessel segmentation in the USA using oxy-propane. ZionSolutions, a wholly owned subsidiary of EnergySolutions, completed the segmentation of the reactor vessel of unit 2 of Zion nuclear power plant in late June.
|The two-unit Zion plant in Illinois (Image: Exelon)
The first successful completion of a large commercial reactor vessel segmentation in the country was Rancho Seco in 2008. That plant's reactor pressure vessel was segmented into 21 pieces and shipped offsite to a low level radioactive waste facility. However, EnergySolutions said the Zion Station project was the first to use the large-scale application of thermal cutting (oxy-propane) technology, which resulted in a much quicker cutting time - one month versus seven months at Rancho Seco, where abrasive water jet technology was used.
After more than 20 years of operation, Zion's two reactors were permanently shut down on 15 January 1998. Commonwealth Edison (ComEd), owner of the plant at the time, concluded that the continued operation of Zion Station was not financially feasible and the plant was removed from service.
In 2010, the Nuclear Regulatory Commission approved the transfer of ComEd parent company Exelon's licence to EnergySolutions, which in September of that year began the ten-year process of dismantling the site, and which will eventually move away parts of the plant to its property in Utah.
Carol Peterson, Exelon's senior vice president of strategy and planning and lead liaison for the Zion decommissioning project, said completion of the segmentation was a significant milestone in the decommissioning of the Zion plant. "The innovative process is another example of how EnergySolutions continually looks for ways to apply technology to improve safety and efficiency and to protect the environment," she added.
Salt Lake City-headquartered EnergySolutions said the cutting process started on 26 May, with the first of 17 segments of the reactor vessel cut with an oxy-propane torch connected to a robotic fixture external to the vessel. The final cut was completed on 26 June.
This "first-of-its-kind application" for the US nuclear industry required specialized rigging and lifting equipment that were used "safely without incident", John Sauger, executive vice president for ZionSolutions, said in the same statement. "Extensive design, analysis, mockup testing and planning resulted in a fast cutting sequence with no release of radiation to the environment," he added.
David Lockwood, CEO and president of EnergySolutions, said the company was pleased to have completed three major milestones in the Zion Nuclear Power Plant Decommissioning Project in 2015, including used fuel transfer, B and C level radioactive waste removal and vessel segmentation.
Differing from other reactor disposal projects completed in the past, the Zion vessel is shipped in traditional railcars that require no additional actions such as heavy load analysis and custom railcar availability and scheduling.
Zion was the third dual-reactor nuclear power plant in the ComEd network and served Chicago and the northern quarter of Illinois. The first unit of the plant started producing power in December 1973 and the second unit came online in September 1974. Although it was withdrawn from service in early 1998, it had not been in operation since February 1997. The plant is located on the western shore of Lake Michigan shoreline, in the city of Zion, which is in Lake County, Illinois.
The used nuclear fuel was placed in the plant's onsite storage pool. NAC International, the Georgia-headquartered nuclear fuel cycle consulting and technology company, then provided ZionSolutions with 61 storage systems. All casks were loaded, the pools emptied, and all the used fuel transferred to dry storage, by the beginning of this year.
The $1 billion decommissioning project has required an average of 200 skilled workers each year, most of them local, and a peak workforce of 400.
After 18 years, the activation products in the pressure vessel steel have decayed through many half-lives to very low levels, so that it can safely be handled without elaborate precautions.
Researched and written
by World Nuclear News