The decommissioning of unit 2 at the Oskarshamn nuclear power plant in Sweden has passed a major milestone with the completion of the segmentation of the reactor internals.

Segmentation work at Oskarshamn 2 was carried out underwater (Image: GEH)

Plant operator OKG AB awarded GE Hitachi Nuclear Energy (GEH) a contract in December 2016 to dismantle the reactor internals of units 1 and 2 at the Oskarshamn plant (O1 and O2). The work includes dismantling, cutting and packing the reactor internals for final disposal. All the segmentation work is being carried out underwater.

GEH has now completed segmentation work on the reactors internals of Oskarshamn 2 and segmentation of those of unit 1 is set to begin early this year. The segmentation project is expected to be completed by the beginning of next year.

GEH said the segmentation was mainly conducted using the Primary Segmentation System that was designed by REI Nuclear, a company that GEH acquired last month.

"This is a historical milestone for the decommissioning of OKG units 1 and 2," OKG CEO and Managing Director Johan Dasht said. "Removal and disposal of reactor internals takes place directly after defueling of the units in order to simplify further decommissioning and improve the environment in the plant."

Lance Hall, executive president of GEH, said: "We supported our customer with strong project execution and completed this work on schedule and on budget. Through our experience, expertise and rigour, we will continue to support our customers throughout the nuclear power plant lifecycle."

Although not part of the contract with GEH, the reactor pressure vessels of the units will also need to be segmented. This work, which is expected to start next year, will mark the start of large-scale decommissioning and demolition of O1 and O2.

German utility EOn - which owns a 54.5% stake in OKG - decided in October 2015 that Oskarshamn 1 and 2 would be shut down permanently. Unit 3 was unaffected by the decision. At that time it said unit 1 would close between 2017 and 2019, there would be no future investments at unit 2 and the reactor will not be restarted. Last February, OKG announced the decision to shut down Oskarshamn 1 in conjunction with a planned outage at the end of June 2017.

Oskarshamn 1, a 473 MWe boiling water reactor (BWR), started up in 1972, while Oskarshamn 2 is a 638 MWe BWR which began operating in 1974. Oskarshamn 3 is a 1400 MWe BWR which began operating in 1985.

EOn spun off of its non-renewable assets into Uniper in January 2016. Uniper announced last month a "long-term and common strategy" for the demolition of Barsebäck and Oskarshamn nuclear power plants in Sweden.

Under Uniper's strategy, the radiological demolition of the four reactors - during which all radioactive waste will be removed from each unit - will be carried out between 2020 and 2028. The total cost of decommissioning the Barsebäck and Oskarshamn units is estimated to be SEK10.0 billion (USD1.1 billion).