US-based Orano Decommissioning Services (Orano DS) is implementing an innovative method for rapid reactor dismantling at unit 3 of the Crystal River NPP (CR3). The patented Optimised Segmentation process aims to reduce the volume of waste for disposal and the amount of segmentation work on the reactor structures. Orano says this has substantial benefits in overall execution schedule, dose, and cost.
The process first segments, extracts and separates underwater all of the reactor internals into two categories. These are Greater-than-Class C (GTCC) waste and highly contaminated and activated internal structures. GTCC can be handled, packaged, and stored using conventional methods.
The empty reactor vessel is then repacked underwater using a precisely engineered placement of the highly contaminated and activated waste based on each piece’s characterisation. This concentrates the highest waste category components in the middle of the vertical vessel, while less activated waste is placed in the bottom and top sections. Orano says the reactor vessel and repackaged internals are then drained and immobilised in grout specifically prepared to achieve the ALARA (as-low-as-reasonably-achievable) goal.
Next, the solid, grout-filled reactor vessel packed with waste is segmented into three large sections (bottom, middle, top), in line with with the optimised waste distribution. Each section is packaged and shipped individually in a tailor-made container designed to safely transport and dispose of the waste in compliance with relevant regulations and the disposal site’s waste acceptance criteria.
Only the middle section requires a Type B package approved by the Nuclear Regulatory Commission (NRC). The design of this Type B package was completed in August 2021, and the licence application is now being reviewed by NRC. The optimised waste characteristics in the bottom and top vessel segments will only require shipping containers to comply with industrial package regulations.
Reactor dismantling operations started at CR3 in 2021. Components of the reactor cooling system (steam generators, main coolant pumps and motors, the pressuriser, and large bore piping) have been removed from the containment building and shipped off-site for disposal. Segmentation of the reactor internals took place in 2022 and removal of all reactor structures from the containment building will be completed in 2023.
Orano DS notes that “decommissioning a nuclear plant is significantly different from other industries”, but it is a safe and well-defined process with NRC oversight. The first action following closure of a reactor is to remove all the used fuel from the reactor and its storage pool, and transfer it to dry storage. This significantly reduces the radiological risks to the public.
The accelerated decommissioning process involves removing, packaging, and shipping low-level radioactive materials, such as the reactor vessel, to an off-site licensed disposal facility and then demolishing the reactor building. Non-radiological buildings and structures can be demolished at any time as the project progresses. Twenty-four-hour security, emergency response, and radiological and environmental monitoring programmes continue during and after the decontamination and dismantlement process is completed.
Once all the buildings have been cleared from the site, the only remaining structure will be the dry storage facility with the used nuclear fuel. The fuel will remain as a securely guarded facility until the it can be removed to a national used fuel repository or a consolidated interim storage facility (CISF). Currently the USA has neither a repository or a CISF.
The timeline for CR3 is as follows:
- 2020: Start planning and engineering
- 2021-2026: Remove components
- 2026: Shrink regulated land area and partially terminate the licence
- 2026-2027: Demolish all structures except the dry cask storage facility
During 2020-2037, Orano says a dry cask storage facility will provide a safe, proven system that stores used nuclear fuel assemblies in sealed steel canisters housed in robust concrete structures.
After 2037, Orano will move canisters of used fuel assemblies off-site to a licensed repository; decommission the dry cask storage facility; fully terminate the licence; and return the property to Duke Energy for reuse.
CR 3, an 860MWe pressurised water reactor, began commercial operation in 1977, but was closed in 2009 after complications arose related to the reactor's containment structure following steam generator replacement work. It was permanently shut down in 2013 and decommissioning was originally expected to take 50 years and to be completed by 2074, with dismantling starting in 2067.
By 2018, all the plant's used fuel had been transferred to an on-site Independent Spent Fuel Storage Installation. NRC approved the transfer of the nuclear plant's licence from Duke Energy to Accelerated Decommissioning Partners (ADP) in April 2020, and the Florida Public Service Commission subsequently approved the transaction. ADP is a joint venture between NorthStar Group Services and Orano USA. In October 2020, ADP and Duke Energy to begin decontamination and dismantlement of CR3 in 2020 instead of 2067.
Image: Crystal River nuclear power plant (courtesy of Duke Energy)
