Under­water brazing system

Jun 12, 2019

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.

3. Brazing
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.