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Technology Factsheet

Compact Sodium-Cooled Nuclear Reactor Facility (KNK2) Remote Dismantling System

Category: Robotics > Dismantling and Retrieval > Bespoke System
Reference # : Model No :

The KNK (Kompakte Natriumgekühlte Kernreaktoranlage) plant was to be decommissioned completely in ten steps (i.e., under the corresponding ten decommissioning permits) to reach green field condition at the end of 2018. To date, nine decommissioning permits have been issued. The decommissioning and demolition activities of steps 1 to 8 have been completed. Under the 9th decommissioning permit, removal of the reactor vessel with its internals was completed in April 2008.

Site:Other
Industry:Nuclear
Size:Very Large (>100kg/200lb, >120cm/48in)
TRL:Operational (9)
TRL2:Operational (9)
Tether: *
Waterproof: *
Payload: *
Reach: *
Manipulator: *

Benefits

Limitations

Comments

The KNK (Kompakte Natriumgekühlte Kernreaktoranlage) plant was a compact sodium cooled reactor with an electrical gross output of 21 MW, erected on the premises of the Karlsruhe Research Center, used to develop sodium technology. Initially, between 1971 and 1974, the plant was operated with a thermal core, referred to as KNK I. From October 10, 1977 onwards, it was run with a fast core under the name KNK II.

Starting in 1993, the plant was to be decommissioned completely in ten steps (i.e., under the corresponding ten decommissioning permits) to reach green field condition at the end of 2018. To date, nine decommissioning permits have been issued. The decommissioning and demolition activities of steps 1 to 8 have been completed. Under the 9th decommissioning permit, removal of the reactor vessel with its internals was completed in April 2008. The following steps of the 9th permission include the dismantling of the heat insulation, the primary shield and the activated part of the biological shield.

The cutting, transport and conditioning steps presupposed the following equipment inside the enclosure:
- Disassembly manipulator (Milling machine).
- Crane to carry the disassembly manipulator within the enclosure and lower it into the vessel.
- Load manipulator for the handling of cut pieces and tools.
- Second crane for the handling of the transport baskets.
- Double lid system to transfer baskets with sodium free pieces directly into containers for further transport.
- Shielding valve to deliver parts to the specially-adapted shielding bell for the transport of sodium-contaminated pieces to the washing facility.
- Shielding lid to close the reactor vessel for manual interventions within the enclosure.
- Master slave manipulators for the handling of mills and other tools.

The dismantling machine was extensively tested at the manufacturer’s test facility using a 1:1 mock-up and approved by the independent technical supervision expert before it was delivered and installed in the KNK reactor vessel. In the course of the mock-up tests, approx. 10% of the total cuts have been tested. Priority and especial attention has been paid to the cutting of overlapping areas and transition spots.

The following tasks and problems were analyzed and resolved:
- Cut/drill tracking system in cylindrical geometry (tank wall, hemispherical head, pipe nozzles) – development of a new two-axle control system.
- Positioning accuracy (reproducibility). – > mechanical measures for the reduction of the axle play, no-load operation test routines for verification, reproducibility of the start coordinates.
- Re-design of the energy supply chain, reduction of the cable diameters to reduce the bending radii.
- Recovery concept – > realization over mechanical direct access (detachment of brackets and fastening to cell crane) with the help of recovery bars with telescopic extensions.
- Improvement of the milling process – > milling concept and cutting plan over 5 cut depths; milling kerfs and milling cutter thickness decrease with increasing depth.
- Vibrations – > development and assembly of shock absorbers as well as development of special drills (adjustment of cutter head and cutting geometry).
- Chip problem (removal, collecting, pollution) – > development of special drills with chip removal slots, installation of encapsulations at the dismantling tool, protection of the spindle and spindle bearing.

During the dismantling at KNK, problems arose concerning the low durability of the milling tools and connected effects. In particular, the cutting of the thickest parts (reflector) took more time than estimated. Investigations showed that the problems were not caused by the milling tool itself but by the insufficient rigidity of the machine. This phenomenon increased with the dismantling progress as the bearings of the axes were suffering under attrition. Taking into account the number of axes, the sum of the single slackness led to a flexibility of the dismantling machine which prohibited an efficient milling process.

As one consequence of that, the milling tool became too hot and started glowing.

Taking a conclusive look at the mock-up tests was very helpful and necessary. In general acceptance tests, qualification and proving of the dismantling equipment and tools is a very important step that should be proceeded with in-depth and very carefully. Also, metrological investigations should be taken into account to identify weaknesses and failures which are sometimes not obvious in practical tests. If possible, well-proven conventional tools should be preferred and customized if necessary.

The dismantling of the reactor vessel was finished in April 2008.

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