DURING OPERATION OF CHERNOBYL 1-3 from 1977 to 2000, more than 21,000 used RBMK fuel assemblies accumulated at the station. They are now stored in the ISF-1 wet used fuel storage facility. But ISF-1 was not designed for long- term fuel storage, and its service life expires in 2035. All the stored assemblies must be transported from IFS-1 to a new dry storage facility, IFS-2, using a special transport container.
Construction of the ISF-2 facility was funded by an international donor fund, the Nuclear Safety Account, managed by the European Bank for Reconstruction and Development (EBRD). ISF-2 cost €400 million and was financed with contributions from Belgium, Canada, Denmark, the European Union, Finland, France, Germany, Italy, Japan, the Netherlands, Norway, Russia, Sweden, Switzerland, Ukraine, the UK and the USA.
The project began in the late 1990s but was stalled when the technology provided was shown to be inadequate to meet the facility’s functional and regulatory requirements. US-based Holtec took over the IFS-2 project in 2011, after demonstrating to the EBRD and State Nuclear Regulatory Inspectorate of Ukraine (SNRIU) that it had the technologies to deal with Chernobyl’s RBMK fuel. Holtec then started work to develop a fully functional store using the legacy systems, structures and components supplied by Areva, and by acquiring replacement systems from France, Germany, Italy, the USA and elsewhere.
Holtec handed over the ISF-2 complex to the owner, Chernobyl Nuclear Power Plant, in December 2019. In September the following year it received a permit to carry out hot testing of the facility. Hot testing was completed on 14 December 2020, after the second double-walled shielded canister (DWC) was loaded into the IFS-2. The first canister had been placed in storage on 18 November.
“With the successful transfer of the first two filled DWCs to ISF-2 in November — December 2020 and the licence for operation provided by Ukraine’s Nuclear Regulatory Inspectorate on 26 April 2021, 35 years from the day the horrendous accident struck Chernobyl, we commissioned one of the world’s largest and most complex dry interim storage facilities,” said Riaz Awan, vice president for Ukraine Operations at Holtec.
In April Balthasar Lindauer, EBRD’s director of nuclear safety, welcomed the milestone and described it as “a major step forward in the transformation of the Chernobyl site.” And on 8 June this year, ChNPP officially announced that it had started a 10-year period during which it will transport the spent nuclear fuel from the old storage facility to the new one, where it will be stored for at least 100 years.
Once all fuel has been transferred to the new ISF-2 facility, the existing wet fuel storage facilities, which have been in service well past their initial design life, will be decommissioned, marking another major step towards increased nuclear safety at Chernobyl. All fuel loading operations will be monitored by the International Atomic Energy Agency and the State Nuclear Regulatory Inspectorate of Ukraine.
Innovative technology
The challenges at Chernobyl spurred Holtec to develop several innovative technologies, such as the double-walled canisters. These render any risk of leakage seven orders of magnitude less likely than the risk level required by regulations in the US, which are similar to most other regulatory regimes. Among other innovations, Holtec is using its forced gas dehydrator to extract the last trace of entrained moisture from the fuel for guaranteed storage safety and it is using extruded Metamic tubes to dissipate residual heat from the used fuel efficiently.
Holtec has also commissioned a purpose-built hot cell (one of the world’s largest), among other innovations. Germany-based Bilfinger Noell GmbH supported Holtec with comprehensive services in planning, design, qualification, engineering, manufacturing, delivery, refurbishment and commissioning of this large hot cell at the ISF-2. Inside this hermetically sealed room, all work takes place automatically or remotely, as personnel are not permitted in the cell.
Once they reach the hot cell, the fuel assemblies, which are around 10 meters long, are dismantled into three parts. During this process, the fuel assemblies are suspended vertically in a device specifically developed for the purpose. They are dismantled at the central rod using a specially designed saw. This is a demanding process because, for safety reasons, the cutting blade cannot come into contact with the actual fuel. The extension rod is removed for handling outside of ISF-2 (radioactive material). The fuel bundles are placed in fuel tubes (a fuel tube is a non-leak-tight cylinder designed to accommodate fuel bundles) and are subsequently packed into Holtec’s double-walled canisters. The fuel assemblies are also completely dried in the forced gas dehydrator process (above) specially developed by Holtec to prevent water from causing long-term damage to the canisters.
Finally, 93 fuel assemblies separated into 186 fuel bundles are placed into fuel tubes, then loaded into DWCs which, after complete drying, sealing and backfilling with helium, are stored individually in concrete enclosures in the ISF-2.
“Our services helped ensure that Holtec and Chernobyl NPP were able to provide a reliable process for the safe treatment and interim storage of highly radioactive waste for the Chernobyl Nuclear Power Plant,” says Karsten Osterland, project manager for nuclear technologies at Bilfinger Noell GmbH. “For this technologically demanding project, we were able to contribute our process engineering experience and expertise in the treatment of nuclear waste and, together with Holtec, achieve the demanding qualification procedure required by the Ukrainian and international nuclear regulatory authorities.”
Bilfinger Noell says its scope comprised the process technology for the remote operation of the hot cell with auxiliary rooms, including a special cutting machine, machines for the transport of fuel assemblies and canisters, enclosures, suction devices, shielding windows, manipulators, double-lid airlocks for fuel assemblies and 200 l drums, small-part airlocks, transport carts for shielding casks and 200l drums, wall penetrations with a remote operating plug system, various remote operating gripper systems for crane operation, lighting, a video system, a drum measurement station, the main filter system, shielding plugs, a shielded docking device for the special cask and a system for the complete dismantling of fuel assemblies, if necessary.
