JET decommissioning program

Overview

The Joint European Torus (JET) Decommissioning Program is the comprehensive, long-term project managed by the United Kingdom Atomic Energy Authority (UKAEA) to dismantle the JET facility, which ceased operations in December 2023 after 40 years of service. As the largest and most successful tokamak experiment to date, JET's decommissioning is a first-of-its-kind undertaking for a device of its scale and radiological inventory. The program's primary objective is to safely deconstruct the machine, manage the resulting radioactive and hazardous materials, and restore the site. Its secondary, and equally important, objective is to serve as a crucial pathfinder for the decommissioning of future fusion power plants, including ITER and demonstration power plants (DEMOs). The data, procedures, and technologies developed during JET's decommissioning will inform the design, material selection, and end-of-life strategies for the entire fusion energy sector, particularly regarding the handling of tritium-contaminated and neutron-activated components.

Radiological and Engineering Mechanisms

The core challenge of JET decommissioning stems from the radiological inventory created during its operational life, primarily through deuterium-tritium (D-T) campaigns. The underlying mechanisms are twofold: neutron activation and tritium contamination.

Neutron Activation: High-energy (14.1 MeV) neutrons produced during D-T fusion reactions are not confined by the magnetic field and collide with the atoms of the vacuum vessel and surrounding structures. This process, known as neutron activation, transmutes stable isotopes into radioactive ones. In JET, key activated materials include the Inconel vacuum vessel, copper magnetic field coils, and the surrounding concrete bioshield. The resulting radioactive inventory is dominated by isotopes such as Cobalt-60 (⁶⁰Co), Europium-152 (¹⁵²Eu), and Iron-55 (⁵⁵Fe), which have half-lives ranging from years to decades. Characterizing the specific activity of different components is a critical first step, dictating the waste classification—Low Level Waste (LLW) or Intermediate Level Waste (ILLW)—and the required remote handling procedures.

Tritium Contamination: As a hydrogen isotope, tritium readily permeates into and is retained by plasma-facing components (PFCs), particularly those made of carbon, beryllium, and tungsten. During JET's operational life, an estimated several hundred grams of tritium were used, with a significant fraction becoming trapped in the vessel walls and dust. This retained tritium must be removed (detritiated) to reduce the radiological hazard for workers and to minimize the volume of radioactive waste. The primary detritiation technique involves heating components in an oxidizing atmosphere to release tritium as tritiated water (HTO), which is then captured by dedicated processing systems. The efficiency of this process for various materials is a key area of research within the decommissioning program.

Remote Handling: Due to the gamma radiation fields from activated components, direct human access to the JET torus hall is restricted. Decommissioning relies heavily on remote handling (RH) technology, much of it pioneered at JET itself. The program utilizes a sophisticated suite of tools, including the MASCOT telemanipulator and robotic cutting and lifting systems, operated from a control room. These systems are essential for tasks like disconnecting pipes, cutting the vacuum vessel into segments, and packaging waste. The experience gained in operating and refining these RH systems is a direct input for the maintenance and decommissioning plans for ITER.

Historical Development

JET began operations in 1983 and formally concluded its scientific mission on December 21, 2023. Planning for its eventual decommissioning has been an integral part of its lifecycle management for decades.

1991 & 1997: JET's first preliminary D-T experiments (DTE1) provided the first real-world data on tritium retention and neutron activation in a tokamak, informing early decommissioning concepts.
2000s: As JET's operational life was extended, decommissioning plans were refined. The UK's Nuclear Decommissioning Authority (NDA) became involved in strategic planning, recognizing the project's national importance.
2014: The Remote Applications in Challenging Environments (RACE) facility was established at Culham, partly to develop and test the advanced robotics required for JET's decommissioning and future fusion machines.
2021: The UK government committed £100 million to the initial phase of the decommissioning and the construction of new research facilities at Culham, signaling the formal transition toward end-of-life operations.
2021-2023 (DTE2 & DTE3): JET's final D-T campaigns were conducted not only to push fusion performance boundaries—setting a world record of 69 MJ of fusion energy from a single pulse—but also to provide a final, comprehensive dataset on material performance, tritium behavior, and activation relevant to decommissioning.
December 2023: JET conducted its final plasma pulse (pulse #105,842), officially ending its four-decade operational phase.
2024: The post-operational phase began, involving the removal of non-activated, non-tritiated systems and detailed radiological surveys to map out the exact conditions inside the torus hall before remote operations commence.

Current Status (as of 2026)

As of early 2026, the JET Decommissioning Program is in the initial stages of its multi-year plan. The period from 2024 to approximately 2027 is dedicated to post-operational clean-out and preparation for remote dismantling.

Key activities include:

Systems De-energization: All major power, cryogenic, and auxiliary systems not required for safety and decommissioning have been shut down and isolated.
Radiological Characterization: Comprehensive surveys are underway to map radiation fields and contamination levels. This involves deploying remote sensors and taking material samples to validate the activation codes and models used for planning. This data is essential for finalizing the waste management strategy.
Tritium Inventory Removal: The active gas handling system is being used to process the remaining mobile tritium from the torus and connected pipework. The total tritium inventory remaining in the machine is estimated to be in the tens of grams.
Remote Tooling Commissioning: The remote handling systems, including cutting tools and manipulators, are undergoing final testing and commissioning in mock-up environments at the RACE facility. Operators are being trained for the complex tasks of dismantling the torus from a distance.

The main remote dismantling of the JET machine itself is scheduled to begin around 2027-2028, once these preparatory phases are complete and all safety cases have been approved by the UK's Office for Nuclear Regulation (ONR).

Notable Implementations

The JET Decommissioning Program is a singular effort, but it is executed by a collaboration of key organizations and leverages specific technologies.

United Kingdom Atomic Energy Authority (UKAEA): As the host organization and operator of the Culham site, UKAEA has primary responsibility for the entire decommissioning project. It manages the budget, timeline, safety case, and workforce. Its expertise in fusion science and engineering is now being applied to the end-of-life phase.
RACE (Remote Applications in Challenging Environments): This UKAEA center is the technological heart of the decommissioning effort. RACE develops, tests, and operates the robotic systems required to work inside the activated JET torus hall. The lessons learned at RACE are directly transferable to ITER's remote maintenance program.
Waste Management Infrastructure: A dedicated Radwaste Facility has been constructed at the Culham site to process, characterize, and package the radioactive waste generated from decommissioning. This facility is designed to handle the specific material streams from JET, including beryllium, tritiated components, and activated metals.
International Collaboration: Although a UK-led program, the decommissioning of JET remains of high interest to the international fusion community, particularly the ITER Organization and EUROfusion. Data and lessons learned are being shared systematically to benefit future projects and ensure the knowledge from JET's 40-year legacy is fully captured.

Open Challenges

Despite extensive planning, the JET decommissioning presents several first-of-a-kind challenges that require ongoing research and development.

Tritium Removal from Co-deposited Layers: A significant fraction of the tritium inventory is trapped in co-deposited layers of beryllium, carbon, and other elements on the vessel walls. The efficiency of detritiation techniques for these complex, mixed-material layers is uncertain and a key focus of the program. Achieving the target of reducing tritium to levels acceptable for waste disposal is a major engineering challenge.
Beryllium Dust Management: JET's use of beryllium as a plasma-facing material presents both a toxicological and radiological hazard. Beryllium dust, which is also tritiated, must be carefully controlled during cutting and handling operations to prevent its spread. Developing robust remote techniques for dust suppression and collection is critical.
Waste Segregation and Minimization: Accurately segregating waste into different classifications (LLW, ILLW) is crucial for managing disposal costs and repository capacity. Overly conservative classification could lead to unnecessarily high costs, while non-compliance is not an option. The program must pioneer techniques for in-situ characterization of large, complex components.
Remote Cutting of Large Structures: The 80-tonne JET vacuum vessel must be segmented into smaller pieces for removal and packaging. Cutting thick, activated Inconel remotely has never been done on this scale. The program is testing various techniques, including plasma arc cutting and mechanical sawing, to find an optimal balance between speed, reliability, and secondary waste generation (e.g., fumes and dross).

Outlook

The credible 5-15 year trajectory for the JET Decommissioning Program involves a phased transition from preparation to active remote dismantling.

By 2030: The initial remote cuts into the vacuum vessel are expected to be complete. The first segments of the torus, including key diagnostics and PFCs, will have been removed and transferred to the on-site Radwaste Facility for initial characterization and processing. The program will have generated the first large-scale datasets on the realities of dismantling a D-T tokamak.
By 2035: The majority of the in-vessel components and the vacuum vessel itself should be dismantled and processed. The focus will shift to the removal of the large toroidal and poloidal field coils and the main machine support structure. The experience gained will be directly informing the final design of remote maintenance systems for DEMO reactors.
By 2040: The program aims to have the JET torus and its immediate auxiliary systems completely removed, with the torus hall de-classified from a radiologically active area. The project will transition to the final phase of building demolition and site restoration. The complete dataset on waste streams, person-hours, costs, and technological performance will form a global benchmark for the lifecycle cost and sustainability of fusion energy, fulfilling JET's final mission.

References

JET's final fusion experiment is a record-breaker — UKAEA (2024)
Decommissioning JET: challenges and opportunities — Nuclear Engineering International (2020)
An overview of the JET decommissioning studies: from the conceptual to the detailed scheme design — Fusion Engineering and Design (2015)
Tritium, dust and waste management in the JET decommissioning project — Fusion Engineering and Design (2023)
Remote handling in JET decommissioning: An overview of the state of the art — Fusion Engineering and Design (2021)
JET Decommissioning and Repurposing — GOV.UK (2021)
Radiological characterisation for the JET decommissioning — EPJ Web of Conferences (2020)
JET Shutdown Operations Underway — UKAEA (2024)