Nuclear entombment (also referred to as "safe enclosure") is a method of

nuclear decommissioning Nuclear decommissioning is the process leading to the irreversible complete or partial closure of a nuclear facility, usually a nuclear reactor, with the ultimate aim at termination of the operating licence. The process usually runs according to ...

in which radioactive contaminants are encased in a structurally long-lived material, such as

concrete Concrete is a composite material composed of aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactur ...

. This prevents radioactive material and other contaminated substances from being exposed to human activity and the environment. Entombment is usually applied to

nuclear reactor A nuclear reactor is a device used to initiate and control a Nuclear fission, fission nuclear chain reaction. They are used for Nuclear power, commercial electricity, nuclear marine propulsion, marine propulsion, Weapons-grade plutonium, weapons ...

s, but also some

nuclear test Nuclear weapons tests are experiments carried out to determine the performance of nuclear weapons and the effects of their explosion. Nuclear testing is a sensitive political issue. Governments have often performed tests to signal strength. Bec ...

sites. Nuclear entombment is the least used of three methods for decommissioning

nuclear power plant A nuclear power plant (NPP), also known as a nuclear power station (NPS), nuclear generating station (NGS) or atomic power station (APS) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power st ...

s, the others being dismantling and deferred dismantling (also known as "safe storage"). The use of nuclear entombment is more practical for larger nuclear power plants that are in need of both long and short term burials, as well as for power plants which seek to terminate their facility licenses. Entombment is used on a case-by-case basis because of its major commitment with years of surveillance and complexity until the radioactivity is no longer a major concern, permitting decommissioning and ultimate unrestricted release of the property. Considerations such as financial backing and the availability of technical know-how are also major factors.

Preparation

The first step is to cease operations and stow any spent fuel or waste. Nuclear reactors produce

high-level waste High-level waste (HLW) is a type of nuclear waste created by the reprocessing of spent nuclear fuel. It exists in two main forms: * First and second cycle raffinate and other waste streams created by nuclear reprocessing. * Waste formed by vitr ...

in the form of

spent nuclear fuel Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor (usually at a nuclear power plant). It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor and ...

, which continues to release

decay heat Decay heat is the heat released as a result of radioactive decay. This heat is produced as an effect of radiation on materials: the energy of the alpha particle, alpha, Beta particle, beta or gamma radiation is converted into the thermal movement ...

due to its powerful radioactivity. Storing this waste underwater in a

spent fuel pool Spent fuel pools (SFP) are storage pools (or "ponds" in the United Kingdom) for spent fuel from nuclear reactors. They are typically 40 or more feet (12 m) deep, with the bottom 14 feet (4.3 m) equipped with storage racks designed to hold ...

prevents damage and safely absorbs the radiation. Over a period of years the radioactivity and heat generation declines, until the spent fuel can be removed from the water and stored in casks for burial. When a reactor is decommissioned, partially spent fuel can be treated the same way. The reactor is sealed in order to allow no escape of radioactive particles or gases. Lastly the heating water is then pumped out and put in containers to await proper decontamination. Decontamination is the process of removal of radioactive contaminants on the remaining surface. Washing and mechanical cleaning are processed during the decontamination process by using the chemical reactors, and the global objective is to protect public safety and the environment. The coolant is also removed and stored for proper disposal. This procedure is often performed by the company that owns the plant, and if the company is unable to then properly qualified contractors are brought in. After this procedure comes the next one which deals with the

radioactivity Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

and

radioactive waste Radioactive waste is a type of hazardous waste that contains radioactive material. It is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, nuclear decommissioning, rare-earth mining, and nuclear ...

. The second procedure is the dismantling of the site. The decommissioning project is for removing the radioactive materials. Thermal cutting and mechanical cutting are two technical ways to dismantle and demolish. Thermal cutting is used for the metals by burning with high energy in one concentration area. The mechanical cutting takes place in the workshop with mechanical force and cuts reactive materials into two parts or in small pieces. The most dangerous waste is placed inside radioactive-resistant containers, after which the containers are transported to storage facilities. The rest of the site can then be decontaminated. The site is then checked thoroughly for any signs of radiation. Most of the remaining waste onsite can be disposed of normally as it is either not contaminated or radioactivity levels have dropped to within safe limits. This process is often completed using robots, which are able to access the difficult to reach areas deemed too radioactive for human workers. The robot was made by WWER-440-type-NNR and is mostly in central and Eastern of Europe, Russia. The main idea of using robots in decontamination is to reduce the radioactive to a level, therefore workers can be exposed. The robot's energy was provided from the robot control system and was placed in the manipulator. The manipulator can be controlled by the remote. The “Decomler” robot works in decontamination by using the wheel system and track system. Also, the robot needs to be strictly licensed by national regulating authorities, because the materials processed by the robot need to ensure they are not discharged to outside. Otherwise, it will cause nuclear pollution to both the environment and humans.

Entombment

Entombment is a more time-intensive process than protective storage and dismantlement as a decommissioning mode. The simplest of the procedures is entombing the radioactive waste source at the site itself. After containment and disposal of lower-level radioactive spent fuel sources, the entombment process of high-level radioactive parts of the plant may begin. The entombment itself is accomplished by numerous layers of sturdy materials, concrete usually among them. The first step is to cover the area with a protective shield which is usually made up of radioactive-resistant materials - this allows workers to continue working with a significantly lower radioactive environment. The second step is the most crucial and time-consuming. Cementitious materials are used to encase the site in

cement A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ( aggregate) together. Cement mi ...

, absorbent

grout Grout is a dense substance that flows like a liquid yet hardens upon application, often used to fill gaps or to function as reinforcement in existing structures. Grout is generally a mixture of water, cement, and sand, and is frequently employe ...

, and/or infills. Each layer of cement, grout or infills must set and cure before the next layer is added. Time and proper testing is required to ensure the safe containment of radiation within the layers of cement. The final step is often to surround the site in a clay or sand/gravel mixture and then soil is laid on top of the site. Entombment designs must be defined and agreed upon by an authorized organization, like the NRC. These designs must also be an approved alternative to other decommissioning methods. Furthermore, because the nuclear facility is often in close proximity to other public environments, the public must accept entombment as a decontamination & decommissioning (D&D) option before proceeding. Small-scale tests will sometimes be performed to prove to organizations like the NRC that a standard process can be transferred. A consortium approach is also necessary to ensure a broader understanding and funding of nuclear entombment. Sites for potential entombment have been identified in the U.K., Japan, Lithuania, Russia, and Taiwan but further research and development of nuclear entombment methods has been called for as of the early 21st century. Sites must be routinely checked for breaches in the containment barrier for decades. Therefore, entombment is often considered as a last resort solution to the decommissioning of a

or nuclear disaster site.

Concerns

Many of the concerns of nuclear entombment center around ethics and long-term reliability. Given the inherently dangerous contents of entombment structures, they serve as a serious disamenity to nearby residents. Once established, entombment structures cannot practically be transported or modified, making disposal sites effectively permanent for their intended lifespan often up to 1,000 years. In addition, the intended permanence of such structures raises the concern of leak integrity over long periods of time. Should a leak occur, the nuclear waste contents could potentially radioactively contaminate nearby water sources, posing a serious health risk to surrounding inhabitants and the biosphere, possibly violating the

polluter pays principle In environmental law, the polluter pays principle is enacted to make the Party (law), party responsible for producing pollution responsible for paying for the damage done to the natural environment. This principle has also been used to put the cos ...

. Public perception plays an important role in the development of nuclear entombment sites and it can be difficult to ensure a steady supply of both funding and willing workers. Constant, thorough monitoring and sanitation of any nuclear entombment site is required to ensure its stability and effectiveness over a long period of time, a significant expense that is not necessarily predictable for the entire life of the site, leaving a financial liability for future generations. The health and safety of workers monitoring the structure is also a concern; for reference Chernobyl Entombment workers receive about 9.2 mSv per month, compared to the average US resident receiving 3.1 mSv per year. Entombment is not a solution for every type of radioactive waste and is not viable for long-lived radionuclides.

Benefits

The surveillance cost will be lower than the surveillance cost for SAFSTOR (safe storage) option. The cost for entombment is less than the cost for dismantling, since it uses for disposal the same facility from which the waste came. However, this cost is eternal and may be higher in the course of years. The use of entombment requires fewer workers and prevents them from being in major contact with the nuclear waste. In some cases, entombment also provides further financial benefits through reducing costs devoted to waste conditioning and management, as radioactive waste can be placed within the vicinity of entombment enclosures to benefit from decay. In addition to reducing cost, it also minimizes public interaction with the project and the amount of nuclear radiation emitted from the waste. By disposing of the nuclear waste in the same facility it will allow engineers to reinforce the facility to ensure safety for the public and the environment. Entombment is also preferable in instances of time sensitive scenarios, in which the deferred dismantling of a nuclear power plant could potentially increase financial burden and/or the hazardous radioactive decay. Beyond direct practical benefits, entombment has also been explored as a step that can benefit the overall decontamination and decommissioning process, though further research and development is needed before it can be deemed a viable option.

United States Nuclear Regulatory Commission

The United States Nuclear Regulatory Commission ( USNRC) provides licensing for the entombment process, as well research and development (R&D) programs to help decommission nuclear power plants. USNRC will continue the development of rule making for entombment. NRC asks companies running power plants to set money aside while the power plant is operating, for future shut down and cleanup costs. The NRC has decided in order for nuclear entombment to be possible, a long-term structure must be created specifically for the encasing of the radioactive waste. If the structures are not correctly built, water can seep into them and infect the public with radioactive waste. The NRC has imposed acts such as the

Nuclear Waste Policy Act The Nuclear Waste Policy Act of 1982 is a United States federal law which established a comprehensive national program for the safe, permanent disposal of highly radioactive wastes. * The US Congress amended the act in 1987 to designate Yucca Mo ...

of 1982 and the Low-level radioactive waste policy. These policies help regulate state governments on the procedures and precautions needed to dispose of the nuclear waste. The Nuclear Waste Policy of 1982 states the federal government's responsibility is to provide a permanent disposal facility for high-level radioactive waste and spent nuclear fuel. If states have also agreed to follow §274 of the Atomic Energy Act they may take on the responsibility of disposing of low-level waste and receive facilities from the federal government for this purpose. Other commissions in the pursuit of improving nuclear entombment as a solution include the Cementitious Barriers Partnership (CBP) and the U.S. Department of Energy (DOE). Research facilities such as those at the Savannah River and Lawrence Livermore Laboratory have contributed to the understanding of safe nuclear entombment.

Containment examples

There are several examples of successful entombment procedures completed. In El Cabril, Spain a multi-concrete barrier concept was used wherein the radioactive waste drums are placed inside concrete boxes. Those boxes are then placed inside a reinforced concrete vault sealed with a waterproof coating to prevent any hazardous liquid from escaping the drums. In the

Hallam Nuclear Power Facility The Hallam Nuclear Power Facility (HNPF) in Nebraska was a 75 MWe sodium-cooled graphite-moderated nuclear power plant built by Atomics International and operated by Consumers Public Power District of Nebraska. It was built in tandem with and co ...

, expanding concrete, seal-welding at penetrations, sand, waterproof polyvinyl membranes, and earth were all used to envelop radioactive residuals. At the Piqua Nuclear Power Facility, seal-weldings and sand were again used to seal the internal reactor, and lastly sealed with a waterproof membrane. At the Boiling Nuclear Superheater Power Station (BONUS) in Rincón, Puerto Rico, a concrete slab was constructed to cover the upper surface while seal-welding was used to secure lower surface penetrations. The

Chernobyl disaster On 26 April 1986, the no. 4 reactor of the Chernobyl Nuclear Power Plant, located near Pripyat, Ukrainian Soviet Socialist Republic, Ukrainian SSR, Soviet Union (now Ukraine), exploded. With dozens of direct casualties, it is one of only ...

is one of the worst nuclear disasters. The initial containment building, commonly known as the sarcophagus, did not classify as a proper entombment device. It was difficult or impossible to repair and maintain because of extremely high levels of radiation. A new structure was structurally completed and put in place in late 2016, and was completed in 2019. The structure measures 108 meters tall, with a length of 260 meters and a span of 165 meters. The main arch is composed of triple-layered radiation resistant panels made up of stainless steel coated in

polycarbonate Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate ester, carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, toughness, tough materials, and some grades are optically transp ...

, which will provide the shielding necessary for radioactive containment. The structure weighs over 30,000 tons and completely covers Reactor number 4. This new tomb is designed to last over 100 years, and has special ventilation and temperature systems to prevent condensation of radioactive fluids on the inside which could result in a compromised containment. The new containment structure is still intended to be temporary, with the goal of allowing the Ukrainian Government and the EU time to develop ways of properly decommissioning the plant and cleaning up the site.

Other examples

Lucens Lucens () is a municipalities of Switzerland, municipality in the Broye-Vully District, Broye-Vully district in the Cantons of Switzerland, canton of Vaud in Switzerland. In 2017 the former municipalities of Brenles, Chesalles-sur-Moudon, Cremin, ...

, Switzerland - initially entombed in a cavern and later decontaminated * Dodewaard, the Netherlands - entombed for 40 years, awaiting final decommissioning; also referred to as 'safe enclosure' *

Runit Dome Runit Island () is one of forty islands of the Enewetak Atoll of the Marshall Islands in the Pacific Ocean. The island is the site of a radioactive waste repository left by the United States after it conducted a series of nuclear tests on Enewet ...

, Marshall Islands - large concrete tomb constructed in 1980 in an atomic blast crater, encasing contaminated soil