ActiFlo-Rad® Sludge Retrieval and Processing

PROJECT: ActiFlo-Rad® Sludge Retrieval and Processing of the D-Pit facility at the Fukushima disaster site

DURATION: 2018 to 2026 (planned)

CLIENT: TEPCO

The challenge

Following the 2011 earthquake and tsunami and subsequent meltdown of reactors in Japan, TEPCO was faced with a significant challenge to manage water used to cool the damaged reactors at the Fukushima Daiichi Nuclear Power Plant. In order to mitigate the release of highly contaminated effluent, the treatment of this water was necessary and ultimately achieved by multiple onsite water treatment systems. One of which was the ActiFlo-Rad® system which operated for three months generating coprecipitated cesium and strontium waste in a granular form.

This waste amounted to approximately 34 tonnes at a density of 72 g/l, or over 450m3 of precipitated waste. As part of this critical water treatment process the waste was consolidated in the Process Main Building in the Delta-Pit (D-PIT), a 10m deep by 100m2 subterranean pit located on the Fukushima site.

Over time the waste has settled to a dense sludge with an average density of 750 g/l over 40m3. This legacy waste now presents a significant risk if another tsunami were to impact the site, due to its low elevation and limited tidal protection. The challenge now is to retrieve, de-water, and store this highly radioactive sludge material in a safe condition for future treatment and long-term disposal.

Veolia's solution

In 2018 VNS began working with TEPCO to evaluate the characteristics of the Sludge by performing laboratory demonstration tests of the coprecipitates and reviewed the results against an actual physical sample obtained by the International Research Institute for Nuclear Decommissioning (IRID). A baseline of the material characteristics was developed, and VNS applied optioneering principles to develop a Concept Design for retrieving and treating the sludge, which was subsequently agreed to with TEPCO.

A detailed method of deploying the manipulator system into the contaminated building and to position it above the D-Pit such that the system can 'unwrap' itself and deploy through the access port into the sludge area was highly complex and is unique.

Following the Conceptual Design phase, Veolia led a multi-national and multi-disciplined team to complete the Detailed Design and develop an estimate and schedule for manufacturing and implementation of a complete process system to remotely retrieve, de-water, and store the sludge. This work included: simulant and equipment testing, site access and interference planning, detailed technology assessment, evaluation of codes and standards to ensure compliance with Japanese standards, determination of nuclear safety through Failure Modes and Effects Analysis (FMEA) and Hazard and Operability Study (HAZOP) methods, identification of radiation protection measures, establishment of engineering controls, structural and seismic analyses, and was managed through a comprehensive Project Management Plan for this high profile decommissioning project.

The ActiFlo-Rad® retrieval and processing system approach is based on an innovative decommissioning strategy of customizing fit-for-purpose technologies with a high Technology Readiness Level (TRL - 6 or higher) into a modular system for installation and operational efficiency along with an emphasis on worker safety. The design utilizes a customized Veolia long reach manipulator based on the design for another project at Fukushima. The system had to be transportable (remotely) into and across the highly contaminated building and positioned accurately above the D-Pitt sludge itself. The system effectively comes 'condensed' within a rectangular 'box' which is unique amongst all manipulator deployment systems.

The manipulator will deploy an eductor and waterjet tool that covers all areas of the D-Pit to breakup the high density sludge, as well as a cutting tool for obstruction removal. The eductor allows for the transfer of retrieved sludge to a modular process system which can process the waste. The retrieved sludge is held in a buffer tank prior to being sent to a customized centrifuge for dewatering. The centrate is filtered through a proprietary regenerable filter assembly prior to being recycled through the process system and then transferred to a customized vented storage container, which is compatible with the existing TEPCO interim storage facility.

Special Considerations

This patented approach utilises Veolia Nuclear Solutions proven technologies including expertise from an international supply chain to support what is arguably one of the most challenging decommissioning projects ever encountered in the nuclear industry to date.

VNS expertise:

• Decommissioning Planning
• Remote-Handling/Robotics
• Effluent/Sludge Treatment
• Waste Management
• Characterization/Nuclear Measurement
• Packaging of Waste