Swedish nuclear technical services provider Studsvik has signed an agreement with Japanese engineering start-up ReNu Industries to adapt its patented inDRUM radioactive waste treatment technology for use at the Fukushima clean-up site. The partnership aims to build a pilot waste treatment plant in Fukushima Prefecture to process low-level, intermediate-level and high-level radioactive waste, specifically targeting problematic transuranic (TRU) waste streams.
The inDRUM system uses a thermal process to treat waste while it remains completely sealed inside its container. Because the drums are neither opened nor sorted, worker exposure and manual handling are minimised.
The original storage container is loaded directly into an electrically heated Container Treatment Vessel (CTV). The vessel is entirely flooded with a nitrogen gas blanket to remove oxygen. The autoclave is heated to high temperatures between 550°C and 650°C. Because there is no oxygen, the materials do not burn (incinerate). Instead, they undergo pyrolysis.
Liquid components are completely vaporised. Carbon-based organic materials (such as plastics, PVC, rubber, and ion-exchange resins) are thermally decomposed into a dry, inert, inorganic char or ash. Corrosive elements or reactive nitrates are safely converted into stable oxides and carbonates.
Volatised organic compounds, carbon monoxide, and traces of hydrogen produced inside the container are drawn out into a specialised ventilation system. These gases pass through a thermal oxidiser and quench scrubbers to neutralise acid gases. Volatile radionuclides like mercury or iodine are fully captured, allowing only safe, treated gases (such as CO2) to be filtered out and released.
The remaining contents inside the original drum are downsized into a fully stabilised, non-reactive volume, making them immediately ready for final compaction or grouting. For spent ion-exchange resins and similar wastes, volume can be reduced by up to 90%. Studsvik operates a full-scale inDRUM demonstration facility in Nyköping and is advancing the adoption of inDRUM for the treatment of radioactive waste from the European Spallation Source (ESS) in Lund.
Decommissioning the Fukushima NPP is governed by the Japanese Government’s Mid- and Long-Term Roadmap. In September 2024, the project entered Phase 3 – the final phase spanning from the initiation of fuel debris retrieval up to total site clearance. The scale of accumulated and projected waste at the Fukushima site is unparalleled in nuclear history.
The Atomic Energy Society of Japan calculated that if aggressive waste-reduction measures are not applied, the decommissioning process will generate up to 5.6m cubic metres of solid waste. Finding a long-term storage solution for this volume is why the partnership is looking to implement Studsvik’s g technology.
ReNu will re-engineer the inDRUM system to ensure compliance with Japan’s strict seismic criteria and nuclear regulatory frameworks.
To adapt Studsvik’s inDRUM system for Japan, ReNu Industries must fundamentally re-engineer the technology to transition it from European standards to Japan’s rigorous, legal-binding nuclear seismic design criteria (JEAG 4601 / Regulatory Guide for Reviewing Seismic Design).
Because the inDRUM process operates at extreme thermal ranges (550-650°C) while handling highly radioactive, uncharacterised waste, a seismic event could trigger containment breaches or explosive gas mixtures if the system structural integrity fails.
Metals lose a significant percentage of their mechanical strength when heated to 650°C. Under continuous high thermal load, structural components suffer gradual deformation under stress. If an earthquake occurs while the system is at peak temperature, standard steel supports could easily buckle or shear.
ReNu must substitute standard European structural steels with advanced, high-nickel superalloys (such as Inconel 617 or Hastelloy X) for the Container Treatment Vessel. They must also apply complex finite element analysis) to calculate the combined load of extreme heat and multi-axis seismic acceleration.
The inDRUM system processes sealed drums containing unpredictable mixtures of liquid and solid waste. During a high-intensity earthquake, liquids inside the drums will undergo dynamic sloshing, creating highly irregular, moving hydrodynamic pressures against the drum walls and the internal vessel shell.
ReNu cannot use static weight calculations. They must model the waste using Computational Fluid Dynamics coupled with structural mechanics to design rugged internal bracing and shock-absorbing dampers that can counteract these unpredictable internal forces.
The process relies on an oxygen-free, nitrogen-blanketed environment to prevent the pyrolysed organic gases from catching fire or exploding. Japan’s regulations require that the containment boundary remain completely airtight during a design-basis earthquake. Standard piping and mechanical seals can easily shear or warp under intense shaking.
Every gas input, ventilation line, and off-gas duct must be re-engineered with custom multi-ply flexible bellows and seismic isolation loops. The vessel doors and flange gaskets must utilize advanced elastomeric or metallic seals rated to survive high-frequency mechanical vibrations without losing pressure.
Nuclear facilities in Japan are engineered to withstand severe design-basis ground motions with peak ground accelerations often exceeding 600 to 1,000 gals, depending on localised fault lines. This is multiple times higher than the seismic baselines used for standard industrial layouts in northern Europe.
The entire pilot facility cannot sit directly on a standard concrete floor. ReNu must design a dedicated seismic isolation pad utilizing lead-rubber bearings or fluid viscous dampers beneath the framework. This foundation will decouple the ground vibrations from the delicate off-gas filtration systems and the primary heating autoclave.
If a major earthquake strikes, the facility will lose grid power. The system cannot simply be turned off instantly. The drums take hours to cool down from 650°C, during which gas generation continues. ReNu must design a seismic-trigger-activated, completely passive cooling and backup nitrogen-purge system. Seismic sensors (gal-meters) must automatically isolate the off-gas lines, initiate a high-pressure nitrogen dump from dedicated backup tanks using gravity-fed or battery-backed valves, and safe-store the volatile off-gases without relying on external electricity.
ReNu has secured a government grant of up to JPY700m ($4.4m) through the Fukushima Subsidy for Projects Promoting Practical Development for Regional Reconstruction, implemented by Fukushima Prefecture under the Japanese Government’s Fukushima reconstruction initiative, to develop a radioactive waste treatment pilot plant in Fukushima. Phase 1 (Fiscal Year 2026) will establish basic design requirements by March 2027. Phase 2 (Fiscal Year 2028) will complete construction of the pilot facility, subject to final agreements and regulatory approvals.
“Fukushima will need radioactive waste treatment for decades. ReNu is based in Okuma, the town that hosts the plant, and brings the local knowledge needed to adapt inDRUM to Japanese conditions. Fukushima is our starting point in Japan and in Asia,” said Studsvik President & CEO Karl Thedéen.
ReNu Industries CEO Ryohei Takahashi noted: “Decommissioning Fukushima requires technology proven around the world, re-engineered to fit Japan’s regulations and site conditions and implemented with local hands. Through our technical collaboration with Studsvik, ReNu will adapt inDRUM to Japanese regulatory and site requirements. We intend to build on our experience in Fukushima to pursue opportunities elsewhere in Japan and overseas.”
