Three steam generators from unit 4 of Sweden's Ringhals nuclear power plant have been transported to Studsvik's plant, where they will be processed for recycling and disposal.
The three steam generators, which were replaced during the summer of 2011 as part of an uprating and life extension project of Vattenfall's Ringhals 4, were transported by ship from the port of Videbergshamn on Sweden's west coast to Studsvik's own deep-sea harbour at Nyköping on the country's east coast. Each of the steam generators weighs some 300 tonnes and is about 20 metres long.
|One of the steam generators is offloaded at Nyköping (Image: Vattenfall)
Ringhals 4 – a pressurized water reactor (PWR) - was fitted with new low-pressure turbines in 2007 to increase its power output by 40 MWe. Last summer, the unit also received new high-pressure turbines to add a further 30 MWe to its output and new steam generators to add 200 MWe. The replacement of the three steam generators, large heat exchangers located in the containment of PWRs, was the largest single project in the unit's modernization.
According to Studsvik, scrapped steam generators present a challenge: Due to their size, the disposal of whole components in a waste repository is usually very expensive and complicated.
However, the company has developed a process, with partial funding from Ringhals, for treating steam generators which reduces volumes and saves disposal costs. The generator is segmented and the radioactive tube bundle decontaminated. The tube bundle is either then compacted or melted, depending on the type of alloy and the radioactive content. The steel shell and other low-level radioactive components are melted and can be recycled and sold as conventional scrap. Meanwhile, compacted tube bundles and ingots with an activity content that does not allow clearance are returned to the customer together with residual waste (crushed slag, sorted material, cutting and blasting residues and dust from the ventilation filters). This represents about 10% of the total material in a used steam generator and requires about 40 cubic meters of disposal space rather than 400 per steam generator. These are the only components of the steam generators that require disposal in a repository.
Nuclear power plants replace steam generators as part of regular maintenance and when they are modernized. According to Studsvik, it is estimated that several hundred steam generators and other large components are stored temporarily at nuclear power plants around the world awaiting efficient treatment methods.
Studsvik and Vattenfall signed a memorandum of understanding in 2006 regarding the waste treatment in Studsvik's facilities of eight steam generators and two reactor pressure vessel heads from the Ringhals plant.
Researched and written
by World Nuclear News