Underwater brazing system
UWBE and NCS45
With the NCS 45 transportation system and the patented underwater brazing system, DAHER NUCLEAR TECHNOLOGIES GmbH offers an innovative solution to faster achievement of the “fuel-free” objective.
There are established solutions for the disposal of intact fuel assemblies. These fuel assemblies can be loaded into transportation and storage casks and transferred to an interim storage facility.
For the small amount of fissile material in damaged fuel rods that has accumulated in the fuel assembly pool in the operational time of the reactor, compared to the total mass,
there are no, or no inexpensive, solutions connected with transportation and storage casks. As a result, the cost of a few kilos of fissile material is kept at the same level as for a storage pool filled with fuel assemblies.
This is where DAHER NUCLEAR TECHNOLOGIES GmbH’s solution comes in. We transport defect fuel rods from a reactor in decommissioning phase to another reactor. This means that the reactor being dismantled is fuel-free and the cost of securing it can be significantly reduced.
The financial benefits have an immediate impact. In case of a subsequent transfer of the collected defect fuel rods to storage quivers suitable for interim storage, further significant financial benefits result from better utilisation of the capacity of the storage quivers.
DAHER NUCLEAR TECHNOLOGIES GmbH has the hardware, software and experience to provide these benefits:
The NCS 45 cask, which is approved in accordance with the currently applicable dangerous goods regulations pertaining to the transportation of damaged uranium oxide and MOX fuel rods and which is in use for the transportation of fuel rods since 2009 in Germany and the rest of Europe;
The patented underwater brazing system, which makes it possible to enclose spent fuel rods and MOX rods in gas-tight sleeves under water in a storage pool for fuel assemblies;
Qualified personnel for the planning and preparation of shipments, including applying for transport permits and cold handling, the loading and unloading and despatching of the cask, the operation of the underwater brazing system and management of the shipments;
Multiple experiences in the removal of irradiated defective rods from a decommissioned reactor that is being dismantled to another reactor that is still in service.
DESCRIPTION OF THE UWBE
The encapsulation of fuel rods by means of the UWBE takes place in a fuel element storage pool, which provides a sufficient water level for shielding purposes during all handling steps. For standard length fuel rods, a water depth of 12m to 14m is sufficient to meet this requirement.
The encapsulation process is performed in the following steps:
1. A tube is inserted into the UWBE, the fuel rod is inserted into the tube and the UWBE is sealed
Before the UWBE is loaded, the cover is opened. The tube with the pre-assembled bottom plug is secured to the handling tool and lowered into the UWBE. The fuel rod is then inserted into the tube using the NPP’s fuel rod handling tool. Next, the top plug is inserted and the UWBE is sealed.
2. The UWBE is emptied and dried, then it is filled with helium
The water in the UWBE is drained into the pool by overpressure. The water inside the tubes flows through the holes in the bottom plug and the slots in the tube. Then the empty space inside the UWBE, the empty space inside the tube and the fuel rod are dried by vacuum drying. Finally, the empty space inside the UWBE and the empty space inside the tube are filled with helium.
Before brazing begins, both plugs are brought into the brazing position by a remote-controlled mechanical system. In addition, the correct position is checked with the aid of underwater cameras through glass panes at the brazing points of the UWBE. The tube is heated around the plugs, by inductive heating, as are the plugs themselves, until the brazing material becomes fluid and flows into the gap between the tube and the plugs.
4. Flooding the UWBE and unloading the brazing sleeves on the UWBE
The UWBE is flooded with water and opened. Then the brazed sleeve is removed using the handling tool and transferred to the test tube.
5. Helium leakage test
The soldering sleeve is then positioned in the test tube. The test tube is sealed, drained and dried. Then the tightness test is performed using the helium leakage test procedure.