Methods for Decontaminating Radionuclides from Neutron-Irradiated Carbon And/or Graphite Materials

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This patent describes innovative methods for the decontamination of radioactive isotopes (radionuclides) from carbon and graphite materials that have been exposed to neutron irradiation, commonly found as waste from nuclear reactors. It employs mechanical processes (such as crushing, shaking, and sieving) combined with advanced chemical treatments using gases or liquids under controlled conditions (like pressure cycling, heating, and the use of activation energy). Key to the invention is the use of non-constant pressure (including alternating overpressure and vacuum) and temperature phases to increase the penetration and effectiveness of the decontaminating agents, resulting in much faster and more thorough removal of radionuclides compared to conventional methods.

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• Processing and decontaminating radioactive graphite moderator blocks or carbon waste from decommissioned nuclear reactors.
• Reducing radioactivity in carbon-based components to allow safe disposal or downgrading to lower waste categories.
• Preparing neutron-irradiated graphite for long-term storage in nuclear waste repositories by minimizing residual radioactivity.
• Potentially reclaiming and recycling carbon or graphite materials that have been exposed to radiation, after decontamination.
• Decontaminating laboratory or industrial graphite equipment that has unintentionally become radioactively contaminated.

BenefitsContent extracted from patent full text and abstract with AI.

• Greatly accelerates the removal of radionuclides compared to traditional methods, reducing treatment time from days to a few hours.
• Reduces mass loss of treated material, preserving more of the original waste for potential reuse or easier handling.
• Enables more complete decontamination, often allowing radioactive waste to be reclassified to less hazardous categories (e.g., from intermediate-level to low-level waste).
• Improves the long-term safety and stability of stored waste by removing those radionuclides most likely to leach or outgas over time.
• Allows for flexible adaptation to various chemical agents and processing conditions, maximizing efficiency for different types of contaminants or waste forms.
• Reduces costs and logistical challenges associated with long-term storage of high-activity radioactive waste.

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Patent Abstract

The present invention relates to methods for decontaminating radionuclides from neutron-irradiated carbon and/or graphite materials, comprising mechanical and/or chemical treatment methods. The mechanical treatment methods comprise the steps of fracturing, shaking, and sieving, and the chemical treatment methods comprise the supplying of activation energy and the addition of gaseous decontaminating agents. The addition and treatment with decontaminating agents are performed in a heatable pressure- and/or vacuum-resistant reaction vessel or in reaction chambers arranged one after the other. The methods are characterised by the following steps: a) adding gaseous decontaminating agents, the gaseous decontaminating agents being added at a charging pressure that lies above the atmospheric pressure or with pressure alternations, such as alternations between overpressure with respect to atmospheric pressure and vacuum with respect to atmospheric pressure, so that the ingress of the decontaminating agents into the inner pore system of the neutron-irradiated carbon and/or graphite material is accelerated with respect to addition at constant atmospheric pressure, b) flushing the reaction vessel or the reaction chamber with inert gas at preferably the same charging pressure as in step a) or at pressure reduced down to the atmospheric pressure in order to largely leave the decontaminating agent in the pore system, c) heating to T > 300 °C under atmospheric pressure conditions, d) extracting the formed gases from step c) by applying a vacuum to the reaction vessel or the reaction chamber and capturing the released radioactive gases, e) iteratively repeating at least one of steps a) to d) until radionuclides cannot be detected or can be detected only up to a desired concentration in the gas analysis of the extracted gases from step d). The invention further relates to a method in which a liquid decontaminating agent is used.