Experienced team preparing for cutting workPublished 2018-02-19 10:32
At the end of April, the first cutting work of project Serin, the segmentation of the reactor pressure vessel's internals, will take place at Oskarshamn 2 (O2), thus initiating the first major decommissioning work at the plant. OKG and the supplier, General Electric Hitachi (GEH), are currently preparing for the upcoming work.
Segmenting internals is nothing new to either OKG or GEH. OKG's Billy Slättengren is the project manager for the project, and this will be his fourth time doing segmentation work.
"We've done this before, most recently when O3 was being modernized," says Billy. "GEH also has extensive experience in the area and this will be their third time doing segmentation work for us. This means that we have valuable experience to draw on and also that we will be able to refine and improve the techniques."
At the beginning of March, GEH will set up in the reactor hall at O2, which has been fuel-free since December last year so that activities such as preparing the equipment that will be used can take place. Since the components to be segmented are radioactive, all the work will be performed underwater. A segmentation station will be set up in the reactor pool into which the components will be lifted, starting with the moderator-tank upper head and the steam separators. Using a circular saw, the components will be cut in two and the parts will then be placed in cassettes. The cassettes will then be placed in steel vessels using a radiation protection hood. Cassettes and steel vessels are manufactured by local supplier Damen Oskarshamnsvarvet.
"The vessels are manufactured in three different versions to satisfy the various requirements," Billy explains. "The vessel with the largest volume has walls that are 50 mm thick, but there will also be vessels with walls that are 100 and 150 mm thick respectively. The most active components will be placed in vessels with a thickness of 150 mm. When full, the heaviest vessel will weigh 43 tons."
Storage in rock cavern
When the steel vessels are full, they will be transported to the underground storage site for active waste at OKG and stored there until SKB's long-term repository is ready, which will not be until 2045 at the earliest.
If all goes to plan, the segmentation of O2 will take approximately one year. After that, during spring 2019, GEH will relocate to Oskarshamn 1 (O1) and do the same work there. The project is expected to be completed at the start of 2020.
Creating better conditions
According to the schedule, the large-scale decommissioning and demolition of O1 and O2 will start in around 2020. Getting started on the initial decommissioning work now has several advantages.
"Once we've completed the segmentation, we can drain the water from the reactor pool, which means that we can turn off certain systems and thus reduce the operating and maintenance costs. Once we've got rid of the radioactive components, the risk level at the plant will also be lowered, and technically speaking we'll have better conditions for the remaining decommissioning work."
The reactor pressure vessels at O1 and O2 will also need to be segmented gradually, but this is not part of the project and will mark the start of the large-scale decommissioning and demolition.
A segmentation station will be set up in the reactor pool into which the components will be lifted. The equipment was tested by the supplier in the U.S. in November and passed with flying colors.