SKB is responsible for disposal of spent nuclear fuel in a safe way.  The selected method for disposal is based on encapsulating the spent fuel in copper canisters which are embedded in a barrier of bentonite clay in underground tunnels deep in the crystalline bedrock. After deposition of canisters the tunnels are sealed with bentonite backfilling. An underground repository facility has been designed and machines are being developed for the disposal work. Work machines are required for a variety of tasks ranging from transportation to bentonite installation and canister deposition. Due to the radioactive radiation these machines shall operate autonomously under remote supervision.

Navitec Systems has been involved in development of automatic control and autonomous navigation systems for several of the repository machines. The main cases are:

Vertical deposition machine

 

The vertical deposition machine Magne is a wheeled machine designed for autonomous transportation of copper canisters from an underground reloading station to vertical holes in the deposition tunnels. Magne transports the canisters inside a horizontal shielding tube which is turned vertical over the hole for canister deposition. Magne is the first application of the Navitrol navigation system. Special features of this application are high driving accuracy and very high deposition accuracy. Magne stops over a deposition hole with ±3 cm accuracy and deposits the canister with millimeter accuracy. The weight of the machine is close to 100 tons. Navitec has provided:

  • On-board control system consisting of distributed CAN controllers
  • Manual operation with visual guidance and supervision for safe operation
  • Navitrol autonomous navigation
  • Collision avoidance and safety monitoring
  • Fully automatic deposition sequence

Horizontal deposition machine

H-machine

 

Horizontal deposition is an alternative method to the vertical deposition which is currently chosen as reference method. Advantages of the horizontal deposition are less excavation and refilling work and a reduction in underground operations due to a factory assembled buffer and canister package. Disadvantages are the narrow working space and the more complicated transporting principle which is making the machine control rather demanding. In 2011 Navitec Systems took the main responsibility for modernization of the machine targeting on improved reliability and performance. Improvements were made on

  • Instrumentation and actuation system
  • Control methods
  • Onboard machine control software
  • Machine to HMI communication
  • HMI

Backfill machine

Åskar
After vertical deposition of copper canisters the deposition tunnels shall be filled with bentonite. The filling is done by building a stack of pressed bentonite blocks and filling the remaining cavities with pellets. A block stacking pattern has been designed for optimal filling degree and stability. A mobile platform with stacking equipment has been designed for the job. Navitec has contributed with:

  • Positioning and levelling of the platform
  • Laser scanner based measurement of working environment
  • Laser scanner based measurement of backfill stack
  • Stacking of backfill blocks with on-board  industrial robot
  • Automatic stacking planner and process control

Navithor fleet control system

navithorkuva

Many different autonomous machines shall operate simultaneously in the repository. To coordinate the machine tasks in the production plan and to monitor the entire operation a control system is required.  The Navithor fleet control provides

  • Route and traffic planning
  • Machine initialisation
  • Task assignment
  • Execution monitoring
  • Traffic control
  • Collision avoidance
  • Operation logging
  • Operator interface