Phase 1 PFDR System for Fukushima Reactor

The Challenge

To design, construct and test a remotely controlled, boom-type robotic arm system (PFDR) for validating the techniques and technology for removing small volumes of fuel debris from the highly radioactive and highly contaminated environment of the disabled Fukushima Unit 2 Reactor.

The preceding project (PCVI) created a system to investigate the Unit 2 Reactor environment, including a 21m long articulated boom. The goals of phase 1 of the PFDR (Phased (scaled-up) Fuel Debris Retrieval) project were:

• to verify the effectiveness of a more complex end of Boom (distal) arrangement
• to verify the ability of the Boom to manoeuvre within a mock-up of the Reactor.
• to verify the ability to place the End Tool onto debris
• to verify the ability to apply controlled force to the End Tool

PROJECT: Unit 2 Reactor Investigation

DURATION: 2020 to 2022

CLIENT: Mitsubishi Heavy Industries (MHI)

EXPERTISE: Robotics, Remote Handling and VR simulation

Veolia's Solution

The Distal portion of the PCVI Boom was re-designed with an additional yawing element, the "Lateral Offset Link", between the Telescope and the Wrist elements to allow increased reach and manoeuvrability of the end of the Boom. Significant mechanical re-design and stress analysis was performed to account for the increased loads with the revised Boom geometry and load cases.

The Boom Foot, where the Boom contacts the environment and applies (measured) force, was relocated from the end of the Telescope to the LO-link.

The Test Shape End Tool on the Wand at the end of the Boom was designed to incorporate a 6-axis load cell to evaluate the forces when the End Tool was deployed onto the Pedestal floor and force applied.

Mock-up and Testing

A Factory Acceptance Test (FAT) facility was built in Abingdon (UK) to evaluate the performance of the Distal Boom. An access platform (approximately 5m tall x 3.5m x 6.75m) was designed and built to locate the Distal Boom Assembly at a suitable position for deployment into a mock-up ("Pedestal") of the reactor Primary Containment Vessel (PCV). The total length of the Boom when fully deployed into the Reactor will be circa 21m. The interior of the Pedestal was a representation of the geometric constraints of the PCV with detailed Control Rod Drive (CRD) zone and upper and lower tier grating floors.

The Test Shape was successfully deployed by the Boom onto the floor of the Pedestal through via two different routes through the double layer of congested grating floors. Force was applied in a controlled manner to floor via the Test Shape by extension of the Wand. The force on the floor was measured by the load cell on the Test Shape assembly and the force at the Boom Foot (applying force to the upper grating) was also measured.

There is a separate case study for the design of the End Tools for fuel debris retrieval.

The mock-up test confirmed that the system can be manoeuvred around all of the obstacles to the deserted reactor floor locations. Demonstrating the testing was successful and the system is awaiting confirmation of the next phases leading up to deployment at Fukushima.