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Hydride-Dehydride Recycle Process for Plutonium Components

Recent development of a hydride-dehydride recycle process provides a breakthrough plutonium-processing technology for the dismantlement and destruction of nuclear weapons. Past plutonium reprocessing technologies generated copious amounts of mixed hazardous waste that were difficult to dispose of. These past methods are no longer permitted, available, or acceptable for the removal of plutonium from nuclear weapons retired from the stockpile. Indeed, it is currently irresponsible to generate mixed hazardous waste because no repository exists for its disposal. As such, until the development of the hydride-dehydride recycle process, the United States had no easy way to recover plutonium from its nuclear weapons without generating copious amounts of mixed hazardous waste.

The hydride-dehydride recycle process developed at Los Alamos is an environmentally benign process that reduces hazards to workers and the environment and eliminates the generation of mixed hazardous wastes. This recovery process takes advantage of the fact that plutonium reacts easily with hydrogen gas. The principal advantage is the simple, fast, and reversible chemical reaction. Plutonium forms a metal hydride compound by reacting with hydrogen gas thousand of times faster than other metals do. The metal hydride then dissociates readily back to hydrogen and plutonium when heated. The use of hydrogen thus provides a convenient method for separating Pu from other materials within weapon components.

Figure 2. The Los Alamos-developed process for hydriding and dehydriding of nuclear weapon parts for plutonium recovery. It also shows the final product.

This recovery process is initiated by placing a plutonium-containing weapon component in the upper portion of the vacuum chamber (cold zone) as shown in Figure 2. An attached furnace tube and crucible with a resistive heating element (hot zone) is located directly below the nuclear component. A small amount of hydrogen gas supplied by a commercially available uranium hydride (UH3) storage bed is introduced into the evacuated reaction chamber. The hydrogen gas reacts with plutonium from the weapon component to form a plutonium hydride compound (hydriding reaction). This hydride subsequently falls from the component and into the hot crucible where the heat initiates the release of hydrogen gas (dehydriding reaction). Hydrogen gas released from the hot zone is recycled to hydride more of the plutonium located in the cold zone. The hydriding-dehydriding continues between the cold and hot zones until the plutonium is completely extracted from the weapon component.

Melting and subsequent cooling of the plutonium powder produce a solid plutonium metal product that is ready for storage. During the plutonium melting process the hydrogen gas is pumped from the reaction chamber by a uranium powder storage bed. This hydrogen gas is stored at low pressure in the uranium bed and is readily available for future processing of other weapon components. The whole process occurs well below atmospheric pressure and in the absence of any oxidants, which mitigates any possible explosion hazard of hydrogen gas. In addition the correct amount of hydrogen needed for the recycling reaction is easily and safely acquired by raising the temperature of the uranium hydride bed until the desired quantity of gas is obtained. This innovative method of hydrogen reagent supply eliminates the hazard of handling high-pressure gas cylinders within a plutonium facility. The reabsorption of the hydrogen gas by the uranium powder further enhances the safety of this process and prevents hydrogen gas from being released to the environment.

This process enables a key step in the verification and dismantlement of the worldıs nuclear weapon stockpile. Currently, without this technology, the United States has no permissible means of dismantling nuclear weapons and removing plutonium for subsequent bilateral or international inspection and storage. This process is the principal technology for warhead dismantlement and thus contributes to reducing the global nuclear danger. It may be applied to any suggested scenario that requires plutonium retrieval, including vitrification, reactor burning, or geologic storage, before final plutonium disposition. The process itself produces a minimum of waste and mitigates numerous environmental hazards formerly associated with weapon dismantlement operations. This technology eliminates mixed hazardous waste streams for which there is no current U. S. repository.

The hydride-dehydride process has other applications as well. It can be used immediately to clean up plutonium metal from manufacturing equipment such as casting molds, tantalum and ceramic crucibles, ceramic and metal stirrers, and steel furnace tubes. A prototype hydride-dehydride recycle system is currently being used on a production scale to support several LANL programs. These programs include the Surveillance Program (study of aging effects within the nuclear package of a weapon), Fire Resistant Pit Program (develop fire-resistant container for the nuclear package), Waste Minimization Program (develop waste-free plutonium processing technologies) and finally Automated Recovery Integrated Extraction System Program (dismantlement program).


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