When decommissioning and dismantling nuclear power plants, disposal of the nuclear fuel is to be regarded as the first priority.
At the time the nuclear power plant units were switched off, there were a total of 5037 irradiated fuel elements at Lubmin in Units 1-5 of the nuclear power plant and the interim store for spent fuel. At Greifswald Nuclear Power Plant there were an additional 860 new fuel assemblies. 235 only partly-used fuel elements from Unit 5 were sold to a nuclear power plant of the same type in Hungary. The sale of the entire new and only partly irradiated nuclear fuel was completed in 1996.
Since there was and still is no final storage facility available in Germany for these materials, the only option is to temporarily store the spent nuclear fuel in the appropriate CASTOR® type casks in an interim storage facility.
With the granting of approval for storing spent nuclear fuel in the dry cask storage hall of the Interim Storage Facility North (ISN) on 5th November 1999 by the Federal Office for Radiation Protection, it was possible to begin with disposal of nuclear fuel from the nuclear power plants in Greifswald and Rheinsberg to the extent provided for.
On 21st May 2006, the last CASTOR® cask with nuclear fuel from EWN was brought from Unit 3 to the ISN. At the moment, there are 74 CASTOR® containers in the ISN, 65 of them from the nuclear power plants in Greifswald (61) and Rheinsberg (4).
Click here for more information about the ISN's dry cask storage hall.
Before starting dismantling, all equipment in the supervised area is assessed radiologically and divided into contamination-free equipment and that where there is suspicion of contamination.
All equipment and systems which have been classified as contamination-free were dismantled as complete components, transported from the machine hall to EWN’s scrap heaps and taken apart there with standard machines.
Equipment which is suspected of being contaminated was dismantled inside the machine hall with standard industrial technology; inaccessible systems were removed with the assistance of thermal separation processes and partly knocked down on site.
Large dismantled parts and components which still need to be broken down were brought to dismantling places within the machine hall and taken apart there. A dismantling place is a separate area which is equipped with air extraction equipment and associated filters.
The parts produced by dismantling were pre-checked for radiation and packaged. They were then measured in the surveillance monitoring system and were able to be disposed of conventionally after approval by the authorities.
After the machine hall equipment had been dismantled, the concrete structures within the hall were demolished. The authority approved the machine hall for further subsequent use.
Following approval of the respective dismantling scope by the authority, cables, electric motors and automation equipment are first dismantled and the thermal insulation is then removed. Dismantling takes place with standard manually used and tested equipment in compliance with radiation protection regulations.
Contaminated plant parts are basically dismantled room by room from plant areas with a low level of contamination to areas with a higher level of contamination.
A radiological assessment of the plant parts and the dismantling locations was carried out at the start of shutting down and dismantling. Measures were taken as necessary to reduce the dose received by staff: decontamination, removal of hot-spots or the setting up of shields.
The dismantled and knocked down plant parts are treated further at various locations. They are knocked down on cutting places in the reactor building, stored as large components or stored temporarily in containers in the Interim Storage Facility North (ISN) or brought immediately to the Central Active Workshop for dismantling and decontamination.
Final plant dismantling is far advanced in the supervised area of the reactor units. The last large component was brought to the ISN in 2013. At the moment, the residual operating systems such as ventilation and electrical technology are being put out of service and dismantled in the reactor buildings following the setting up of alternative measures. Plant dismantling is currently ongoing in the common special building and building decontamination is taking place in other areas.
Activated components are not just contaminated on the surface but emit ionising radiation themselves. These components include the reactors in Units 1 to 5 with their respective assemblies. These components were so heavily activated by neutron radiation whilst the power plant was in operation that they cannot be dismantled and disassembled manually like other components. They can only be dismantled remotely with the aid of manipulators and need to be protected by concrete, steel or water shields. The work is monitored with video technology.
The Disassembly Strategy
The disassembly strategy, in other words the disassembly of the reactor components into segments and their packing into containers for subsequent interim and decay storage, was tested in a model disassembly process in the period from 1999 to 2003. All steps and processes were rehearsed on non-activated components from the unfinished Units 7 and 8.
From August 2004 to July 2007, the internals of the reactor pressure vessels of Units 1 and 2 (core basket, protective pipe block, reactor shaft with shaft base) were disassembled and packed by remote control. Two disassembly facilities were set up for this – so-called wet and dry disassembly facilities.
Less strongly activated parts of the reactor internals were broken up and packed under a protective housing at the dry disassembly facility.
The wet disassembly facility was used for more heavily activated reactor internals. These were disassembled and packed with manipulators underwater in a special tank and then transported under a shielding bell to the designated container for interim storage.
Both thermal and mechanical separating tools, e.g. plasma torches and band saws, were used at each of the disassembly facilities. After disassembly and packing, the filled containers were brought into the ISN. The components are stored there until they can be brought to a final storage facility.
The large component strategy for dismantling activated components, in other words the transport of reactor components with corresponding shielding into the Interim Storage Facility North (ISN), was first tested in October 1999 with the transport of the unused non-activated reactor pressure vessel from Unit 8 into the ISN. In December 2003, the activated pressure container from Unit 5 was then moved to the ISN for interim storage.
This approach proved more expedient than the original dismantling strategy as the large components can first decay in the interim storage facility and then some of these components can subsequently be dismantled manually without special radiation protection measures. For this reason, we decided to transport the reactor pressure vessels from Units 1 to 4, the reactor pressure vessel from Rheinsberg and also the reactor components from Units 3 to 5 for decay storage into the ISN and to dismantle them later.
Only partial shielding is necessary for transporting and dismantling the reactor pressure vessel. The components on the other hand are completely packed into special shielding and transport devices and brought into the Interim Storage Facility North. This work was carried out from 2006 to the end of 2009.
The isothermal containers of the reactors and the annular water tanks were dismantled from their original locations after the reactor pressure vessels had been removed.
The isothermal containers were first dismantled manually and the annular water tanks then dismantled remotely. Dismantling took place under a protective enclosure with a wire saw with diamond cutting technology.
The containers were filled with concrete beforehand for radiation protection reasons. The cut segments were then packed in special containers and also transported to the Interim Storage Facility North for decay storage. Dismantling of these reactor components began in 2008 and was completed in the spring of 2011.