Crystal River reactor vessel removal completed

Friday, 8 December 2023

The Optimised Segmentation process significantly reduced the amount of segmentation work, accelerated the removal from the reactor containment building, and achieved project completion well within the six-year contract schedule, Orano said.

The reactor vessel internals were cut up underwater and categorised based on radioactivity. Those that were classed as Greater-than-Class-C - one of the four classes of low-level radioactive waste according to the US Nuclear Regulatory Commission's waste classification system - were separated and packaged for long-term storage onsite. The remaining low-level radioactive waste was then repacked into the vessel in a precise arrangement to optimise the transportation and cost-effectiveness of disposal.

The repacked vessel - still in its original upright orientation in the reactor cavity - was then drained, filled with an engineered grout, and separated into three pieces by using a diamond wire saw. The three segmented pieces were lifted out and transferred into custom-built packages, which were also filled with grout to immobilise the contents before welding shut in preparation for shipment to disposal.

The final stage was completed in October with the segmentation, packaging, and transfer out of the reactor building of the bottom section of the three-piece partitioned reactor vessel, followed by a cleanup of the emptied reactor cavity, Orano said. The process resulted in a total of four large packages for shipment and disposal offsite: three Class A industrial-type containers and one Class C Type B container. Two canisters of Greater-Than-Class-C waste were placed in the existing onsite dry storage facility for used nuclear fuel. More traditional segmentation into many small pieces would have required about 80 shipments to a disposal site, the company added.

Pierre Marty, executive vice-president of Orano DS International Operations and CEO of Orano GmbH, said the "outstanding" performance at Crystal River followed on from work at Vermont Yankee and Orano's experience decommissioning several German sites, including at Brunsbüttel, an 800 MWe boiling water reactor (BWR). "At Orano DS, we share our experiences and best practices across all of our projects to always provide our customers with the accumulated benefits of our lessons learned," he said.

Lifting efficiency

Mammoet assisted Orano with the extraction of the sectioned 540-tonne vessel, and said its prior knowledge of the facility from previous steam generator replacement work, combined with early involvement with Orano to plan the process and provide a workable solution for handling the reactor parts, was crucial to the first-time application of the optimised segmentation method.

A strand jack system was used to lift and transfer the segments into specially designed packages for transport and removal (Image: Mammoet)

Mammoet's strand jack system lifted, transferred, and then lowered the segmented reactor vessel pieces into the transport and disposal packages at ground level for removal from the reactor building.

"Altogether, Mammoet completed the reactor vessel removal with a quicker, more cost-effective, and more efficient solution using the strand jacks' greater lifting power and minimal required space to position the equipment inside an already congested containment area," the company said.

Mammoet Project Manager Sidney King said the company put together an expert team with decades of nuclear experience to assemble and operate strand jack system. "Execution of the lifts were performed flawlessly, and it is exciting to see the experience, technical expertise, and Mammoet's innovative thinking come together to be a part of this historic moment in nuclear decommissioning," he said.

Crystal River 3, a single unit pressurised water reactor in Florida, began commercial operation in 1977, but was permanently closed in 2013. In 2020, owner Duke Energy contracted Accelerated Decommissioning Partners - a joint venture between NorthStar Group Services and Orano USA - to begin decontamination and dismantlement of Crystal River 3 in 2020 instead of 2067 as originally planned.

Now that the cooling system, reactor vessel, and vessel internals have been removed, the CR3 reactor building has been turned over to NorthStar for demolition.