Chapter 49: Decommissioning of Nuclear Power Plants | A Book: Nuclear Energy

This chapter was published on “Inuitech – Intuitech Technologies for Sustainability” on April 22, 2013.

As of January 2012, 138 civilian nuclear power reactors had been shut down in 19 countries, including 28 in the United States, 27 in the United Kingdom, 27 in Germany, 12 in France, 9 in Japan and 5 in the Russian Federation.

Decommissioning is a complex process that takes years. The United Kingdom, for instance, completed its first decommissioning of a power reactor in 2011. This reactor, located at Sellafield, was shut down in 1981.The backlog of civilian nuclear power reactors that have been shut down but not yet decommissioned is expected to grow. There is also a large legacy of military and research reactors. There are currently 435 such reactors in operation worldwide, with a total installed electrical capacity of 368.279 billion watts (GWe) (Figure 3). Of these 435 civilian nuclear power reactors, 138 are more than 30 years old and 24 are more than 40 years old. The average age of the civilian nuclear power reactors currently in operation is 27 years.

Many civilian nuclear power reactors will continue to operate safely beyond their original design life. Some will have their operating licences renewed for up to 60 or even 80 years. In addition, there are 63 civilian nuclear power reactors under construction with a net electrical capacity of 61 GWe. All nuclear reactors will have to be decommissioned someday, and the resulting radioactive waste will then need to be safely managed and disposed of.

The United States Department of Energy (DOE) has undertaken to decontaminate more than 100 former research and nuclear weapons sites, covering thousands of hectares, by 2025. This will entail the management of millions of cubic metres of debris and contaminated soil, including large areas where groundwater is contaminated. For instance, the Oak Ridge National Laboratory in Tennessee covers 15 000 hectares with more than 100 known contaminated sites. At the larger Hanford nuclear facility in the State of Washington there are significant amounts of radioactive liquid waste.

The DOE has successfully cleaned up complex sites such as Rocky Flats in Colorado. Nevertheless, some sites may never be cleaned up for unrestricted use. In the United Kingdom, the Scottish Environment Protection Agency (SEPA) concluded in 2011 that it would do “more harm than good” to try and remove all traces of radioactive contamination from the coastline and sea bed around the Dounreay nuclear reactor site. In many countries it will be possible to reuse decommissioned sites that are not fully cleaned up for new nuclear applications.

A combination of activities associated with the dismantling and safe removal of a nuclear power plants (NPPs) from service with the focus to reduce residual radioactivity to a level that permits termination of the license is known as decommissioning. These activities include decontaminating, dismantling and removal of radioactive materials, waste, components and structures. Decommissioning allows the licensee to use the site for other activities instead of leaving the radioactively contaminated material on the site which could adversely affect public health and safety and the environment in the future. If nuclear power plants are not decommissioned, they could degrade and become radiological hazards.Nuclear power plants were designed for a life of about 30–40 years depending upon the type of reactor but newer NPPs are designed for a 40-60 year operating life and these trends will continue into the future designs. Typically, NPPs cease operations for a variety of reasons. For instance, the Regulatory Authorities grant a license for a period of 40 years. At the end of the license period, the licensee can seek to renew the operating license of the plant for another 20 years, or can cease operations and begin the decommissioning process. Some licensees choose to cease power operations before the 40-year licensing period has been completed. Reasons for this decision are usually financial. The plant may require upgrades or repairs that are not economically justifiable, or the licensee may find other sources of power that are less expensive than nuclear generation. However, in addition to financial reasons for decommissioning, the Authorities can order the licensee to cease operations for safety reasons.

The time period to the decommissioning activities for nuclear power plants and research reactors may typically range from a few years to decades (for example, to allow for radioactive decay). As a consequence, decommissioning may be carried out in one continuous operation following shutdown or in a series of discrete operations over time (i.e. phased decommissioning).

There are many factors that have to be addressed to ensure the safety of nuclear reactors during the operational phase. Some of the factors will continue to apply during decommissioning, but decommissioning gives rise to issues that are in some respects different from those prevailing during the operation of the installation. These issues need to be considered in an appropriate way to ensure overall safety during decommissioning.

1. SAFETY:

At all phases of decommissioning, workers, the public and the environment should be properly protected from hazards resulting from the decommissioning process. A thorough safety assessment of the hazards involved during decommissioning (including accident analysis, where necessary) should be conducted to define protective measures, as part of a defence in depth system that takes into account the specifics of decommissioning. In some cases, such measures may be different from those in place during the operation of the installation.

Decommissioning of nuclear installations often involves the removal, at an early stage, of significant quantities of radioactive material, including fuel and operational waste. Even after this step, the total contamination and activation of the installation is significant and has to be taken into account in the safety assessment.The implementation of particular activities such as decontamination, cutting and handling of large equipment, and the progressive dismantling or removal of some existing safety systems are also of importance. These activities have the potential for creating new hazards. An important objective during decommissioning is, therefore, that the safety aspects of these decommissioning activities, such as the removal of existing safety systems, be adequately assessed and managed, so as to mitigate any potential exposure. Integrity of spent fuel, when still stored on-site in a fuel pool, should be considered and maintained. Fire protection and suppression for the complete site should be included in the decommissioning plan.

2. THE FINANCIAL COSTS OF DECOMMISSIONING:

Cleaning-up of a decommission site is typically dictated by governmental regulation. It is satisfying the stringent regulations that prove to be a primary cost driver for decommissioning and waste disposal. Reactor types and sizes, the number of reactors on an individual plant site, and labour costs are among the main factors affecting costs. Mandated long-term site reviews and on-going monitoring and surveillance also drive up final costs, at times beyond original estimates. Further, non-human driven cost factors must be accounted for including classification and type of waste (see above discussion on waste classifications), amount of waste produced availability of waste repositories for the particular type generated and special transport to those locations. Due to the variations in these cost components and the obvious fact that shortcuts cannot be taken, significant differences between planned and actual costs have not been uncommon. As a result of these lessons, it has become highly recommended practice to estimate and include decommissioning costs from the point of project inception, with review onward.

As another consequence of lessons learned, in some cases it is now mandated that a certain level of funds be set aside for decommissioning and waste disposal costs. Funds may be accumulated through a variety of means including revenues from electricity customers, from taxes and imposition of fees, and in select cases by international donors. Given the increasing pressures on governments today, and the projected growth of nuclear energy, a shift is also projected towards more private sectors funding from investors and lenders.

3. REGULATORY FRAMEWORK:

The regulatory framework of a country should include provision for the decommissioning of nuclear installations, in particular nuclear reactors. National regulatory authorities should provide guidance on radiological criteria for the removal of regulatory controls over the decommissioned installations and sites and should ensure that an adequate system is in place for properly managing the removal of controls.Some activities relevant to decommissioning may be carried out after shutdown of the nuclear installation under licence provisions carried over from the operating phase. Such activities may include management of operational waste, measurements to determine the radioactive inventory, removal from the installation of nuclear fuel or other materials related to the original operation, and preliminary decontamination.

In the absence of regulations addressing decommissioning, decommissioning activities should be undertaken on a case by case basis under existing regulations for operational installations. In such cases, the operating organization should consult the regulatory body in the development and implementation of the decommissioning plan. In the plan, the operating organization should be required to demonstrate how compliance with the regulations will be achieved.

The regulatory control of decommissioning can be done by a single overall licence, by separate licences, or by direct control by a regulatory body, whichever is considered to be most appropriate in the circumstances. Within the scope of the regulatory infrastructure, the regulatory body should review and, as appropriate, approve the selected decommissioning option, decommissioning plans, quality assurance programmes and other submissions related to the decommissioning of a nuclear reactor. Moreover, the operating organization should report to the regulatory body on a scheduled basis, as stipulated in the regulatory control mechanism (e.g. licence), any safety related information (e.g. monitoring data, radiological surveys). In the case of abnormal occurrences, the operating organization should report, in a timely fashion, those data that are necessary to evaluate safety during such events.

4. REGULATORY GUIDANCE ON RADIOLOGICAL AND ENVIRONMENT CONTROLS:

Nuclear safety regulators will typically have some shared responsibilities with the environmental regulators during decommissioning, but the basic radiological and environmental standards, especially effluent discharge and material release criteria, should be the same for decommissioning activities as for operations. Since each country’s laws and practices are different, it is not practical in this report to discuss the division of responsibilities between the nuclear and the environmental regulatory authorities. Therefore, when the term “Regulator” is used, it is understood that it may mean either the nuclear or the environmental regulator, depending upon national laws and practices.Specific regulatory guidance will be needed on radiological and environmental controls for decommissioning. The form and content of the guidance will depend on the individual country’s regulatory approach, but the following topics will need to be addressed:

Acceptable duration of decommissioning period – some regulatory bodies place a limit on the length of time that a facility is allowed to complete decommissioning. There can be several reasons for such a time limit, but one important consideration is that the local public may find an indefinite delay to be unacceptable;
Acceptable strategic options – many countries permit a choice of (a) immediate dismantlement, (b) temporary safe storage for a period of years, with eventual dismantlement, or (c) structures encased in concrete and maintained until radioactivity decays to a level permitting removal of regulatory controls, or some combination of these options;
Scope of radiation surveillances – the regulator will want to ensure that the early site radiation survey covers all important buildings, ground locations, potential groundwater contamination and all effluent discharge pathways. Even if all effluent discharges have been within acceptable levels during the operating life of the facility, the cumulative effect over the years could be great enough that remediation of effluent discharge pathways may be necessary. All offsite shipments of waste must be monitored and documented. It will be especially important for the operator to have controls for any gaseous and liquid wastes that may be different from those during normal operation;
Interim storage facilities for radioactive waste, if needed;
Requirements for the scope and duration of maintaining operational and decommissioning records, especially if there is contemplated a long period of safe storage of the facility; and
Acceptance criteria for termination of all licenses.

There are some unique challenges of decommissioning that the operator and regulator must recognize early. The radiological protection and physical safety of workers will be challenged by the decontamination, disassembly and removal of large radioactive components such as reactor pressure vessel, steam generators and pressurizer, large pipes, pumps and valves. Some workers will be sent into areas of the facility that have not been entered for a very long time and whose condition is uncertain. These activities will require careful planning and adherence to sound ALARA principles. Another unique challenge of decommissioning is the large quantity of waste containing only small concentrations of radioactivity, which must nevertheless be surveyed and monitored throughout its movement on the site and offsite to its ultimate disposal location.

Of course there is much other regulatory guidance on radiological and environmental controls during decommissioning activities, such as routine worker monitoring and effluent controls, but this guidance remains largely the same as it was during normal operation.

5. DECOMMISSIONING STRATEGIES:

The following three decommissioning strategies have been defined by the IAEA namely:

a) Immediate Dismantling: It commences shortly after shut down, if necessary following a short transition period to prepare for implementation of the decommissioning strategy. Decommissioning is expected to commence after the transition period and continues in phases or as a single project until an approved end state including the release of the facility or site from regulatory control has been reached;

b) Deferred Dismantling: As an alternative strategy, dismantling may be deferred for a period of up to several decades. Deferred dismantling is a strategy in which a facility or site is placed in a safe condition for a period of time, followed by decontamination and dismantling. During the deferred dismantling period, a surveillance and maintenance programme is implemented to ensure that the required level of safety is maintained. During the shutdown and transition phases, facility specific actions are necessary to reduce and isolate the source term (removal of spent fuel, conditioning of remaining operational or legacy waste, etc.), in order to prepare the facility/site for the deferred dismantling period; and

c) Entombment: Entombment is a strategy in which the remaining radioactive material is permanently encapsulated on site. A low- and intermediate-level waste repository is effectively established and the requirements and controls for the establishment, operation and closure of waste repositories are applicable.

Although evaluation of the prevailing factors could clearly indicate one of the abovementioned strategies, constraints and overruling factors may occur in practice, and these necessitate a combination of strategies or exclude one or more strategies from consideration.

In practice it is often found that a decommissioning strategy for a particular facility has to be selected in the context of a very complex set of influencing factors. Furthermore, the nature of this complexity tends to evolve with time, such that adjustments have to be made to the selected strategy or to important aspects of its implementation.

In many cases, the basic lesson learned is that if the initial strategy has been well chosen (taking comprehensive account of all relevant issues), then it can be adapted to deal with changing circumstances. Sometimes, it has even been possible to adapt a strategy to deal with a potentially severe constraint.

The following may be considered for decommissioning strategies:

All the identified major factors influence decommissioning strategies to a greater or lesser extent. The selection of a decommissioning strategy needs to be based on the evaluation of all relevant factors. Techniques may be used such as multi-attribute analyses that would consider all the relevant factors, constraints and conditions, their interactions and weights to select the appropriate strategy. Other conditions and constraints may exist, which are not dealt with in this report, and are important to include in site specific evaluations;
The constraints associated with funds, the waste management system and human resources could limit the strategies for decommissioning to deferred dismantling independent of other factors. If this is the case, decommissioning strategies that are not necessarily ‘good practices’ may be forced;
Deferred dismantling caused by the above-mentioned overwhelming constraints is generally attributable to lack of decommissioning planning which is in turn due to insufficient legal or regulatory framework. Authorization of facilities that use radioactive material needs to include decommissioning considerations from the design phase to operational and shut down phases;
When the forced decommissioning strategy is deferred dismantling, the problems associated with decommissioning are only delayed and in some cases exacerbated;
Legal and regulatory infrastructures related to decommissioning need to be established as soon as practicable; and
When constraints occur, management has to proactively take steps to remove the constraints or, if that is not possible, to eliminate or minimize their impacts.

If deferred dismantling is forced due to overwhelming constraints, active retrospective activities are required to cover such items as:

Essential actions in the transition period to render the facility ‘safe’ for the extended storage period;
Management of the deferred dismantling phase;
Interim management of waste and spent fuel;
Updating and preservation of the facility history and technical information on radiological surveillance, design and operation; and
Programmes to ensure planning and execution of final decommissioning.

6. DECOMMISSIONING PLANNING:

The basic rule is that decommissioning is considered in the design and operation phases. However, many of the nuclear power plants and research reactors have been operating for many years, and decommissioning may not have been considered at the design stage. The planning of decommissioning for such installations should recognize this, and planning should start as early as possible.

Three stages of planning are envisaged: initial, ongoing and final. For a given reactor, the degree of detail will increase from the initial to the final decommissioning plan. This planning process will result in the production of a decommissioning plan, as described below.

6.1 Initial Planning:

An initial plan for decommissioning should be prepared and submitted by the operating organization in support of the licence application for the construction of a new reactor. Although the level of detail in the initial plan will necessarily be lower than that in the final decommissioning plan. A generic study showing the feasibility of decommissioning may suffice for this plan, particularly in standardized installations. Depending on applicable regulations, the plan should address the costs and the means of financing the decommissioning work.

In cases where an operational plant does not have an initial plan for decommissioning, a decommissioning plan reflecting the operational status of the installation should be prepared without undue delay.

6.2 Ongoing Planning:

During the operation of a reactor, the decommissioning plan should be reviewed, updated and made more comprehensive with respect to technological developments in decommissioning, incidents that may have occurred, including abnormal events, amendments in regulations and government policy, and, where applicable, cost estimates and financial provisions. The decommissioning plan should evolve with respect to safety considerations, based on operational experience and on information reflecting improved technology. All significant systems and structural changes during plant operation should be reflected in the process of ongoing planning for decommissioning; and

6.3 Final Planning:

When the timing of the final shutdown of a nuclear reactor is known, the operating organization should initiate detailed studies and finalize proposals for decommissioning. Following this, the operating organization should submit an application containing the final decommissioning plan for review and approval by the regulatory body. The decommissioning plan may require amendments or further refinements as decommissioning proceeds, and may require further regulatory approval.

If the selected decommissioning option results in phased decommissioning – with significant periods of time between phases – a higher level of detail may be required for the next phase being executed. As a result of executing an individual phase of the decommissioning, some modification to the planning for subsequent phases may be needed. In such cases, subsequent sections of the decommissioning plan may require updating and reviewing. The experience from previous decommissioning should be appropriately taken into account as a matter of principle. The following list of items to be considered for the final decommissioning plan should thus be updated whenever previous decommissioning experience permits:

A description of the nuclear reactor, the site and the surrounding area that could affect, and be affected by, decommissioning;
The life history of the nuclear reactor, reasons for taking it out of service, and the planned use of the nuclear installation and the site during and after decommissioning;
A description of the legal and regulatory framework within which decommissioning will be carried out;
Explicit requirements for appropriate radiological criteria for guiding decommissioning;
A description of the proposed decommissioning activities, including a time schedule;
The rationale for the preferred decommissioning option, if selected;
Safety assessments and environmental impact assessments, including the radiological and non-radiological hazards to workers, the public and the environment;
This will include a description of the proposed radiation protection procedures to be used during decommissioning;
A description of the proposed environmental monitoring programme to be implemented during decommissioning;
A description of the experience, resources, responsibilities and structure of the decommissioning organization, including the technical qualification/skills of the staff;
An assessment of the availability of special services, engineering and decommissioning techniques required, including any decontamination, dismantling and cutting technology as well as remotely operated equipment needed to complete decommissioning safely;
A description of the quality assurance programme;
An assessment of the amount, type and location of residual radioactive and
Hazardous non-radioactive materials in the nuclear reactor installation, including calculation methods and measurements used to determine the inventory of each;
A description of the waste management practices, including items such as:
- identification and characterization of sources, types and volumes of waste;
- criteria for segregating materials;
- proposed treatment, conditioning, transport, storage and disposal methods;
- the potential to reuse and recycle materials, and related criteria; and
- anticipated discharges of radioactive and hazardous non-radioactive materials to the environment;
A description of other applicable important technical and administrative considerations such as safeguards, physical security arrangements and details of emergency preparedness;
A description of the monitoring programme, equipment and methods to be used to verify that the site will comply with the release criteria;
Details of the estimated cost of decommissioning, including waste management, and the source of funds required to carry out the work; and
A provision for performing a final confirmatory radiological survey at the end of decommissioning.

7. SOME REALITIES ABOUT DECOMMISSIONING:

7.1 Waste: A large number of sites will be required to store radioactive waste from decommissioned NPPs and other nuclear reactors over the long term. It is likely that additional buildings and facilities to treat, package and store resultant wastes will need to be constructed to handle output from newly decommissioned reactors. In turn, the infrastructure itself will also eventually have to be decommissioned. Decommissioning activities produce 68 per cent of Low and Intermediate Level Waste – Long-Lived (LILW-LL), of which only seven per cent has been disposed-off to date (Figure: 49-06 and Figure: 49-07).Extensive research indicates that significant numbers of countries have plans in place for disposal of Low and Intermediate Level Waste – Short-Lived (LILW-SL) and some LILW-LL. However, most countries have no designated sites for high-level waste due to political and public perceptions and long-term uncertainties surrounding the issue. The case of the United States illustrates these difficulties in a developed country: Problems associated with the selection of a site for the long-term disposal of high-level waste and spent fuel have been ongoing for many years, leading to an increase in costs as solutions are considered; action is presently suspended. Countries facing greater economic constraints will have even more serious difficulties dealing with radioactive waste disposal. In some cases, no waste management systems exist and the dismantling will be deferred to a later date.

7.2 Soil Contamination:

Based on past decommissioning experiences, it has been shown that the pattern and extent of soil contamination cannot be planned until late into the decommissioning process. The boundary between the bedrock and soil deposits and the flow pathways in the soil will affect the direction and rate in which the radioactive material will be transported. Soil testing below the buildings cannot be carried out until access has been made safe. Depending on the results of these tests, varying amounts of soil might have to be removed, which cannot be determined until the decommissioning process is well underway. For example, in the case of the decommissioning of the Connecticut Yankee NPP in the United States, the soil volume contaminated was higher than expected and 33 000 m³ of soil had to be removed, increasing the cost of the decommissioning. While the case cited is an extreme example, this factor has to be taken into account. Decommissioning should be carried out in steps to avoid such problems disrupting the overall plans.

One of the possible consequences of soil contamination is the subsequent contamination of groundwater, either through migration of the contaminants through the soil to the water table, or through the variation in water table height, since as the water rises; it can come into contact with contaminated soil. Reporting any leaks during the lifetime of the NPP will enable decommissioning plans to be more precise.

7.3 Need for Trained Professionals:

An increased number of trained professionals will be needed and techniques need to be improved to ensure safer dismantling. In France, major progress has been made, although no NPPs have yet been fully decommissioned despite the closure of ten NPPs since 1973. The dismantling of the Brennilis Power Station was meant to be a learning experience to acquire technological knowledge to apply to other sites in France. Operations have been interrupted since 2007, however, due to security issues concerning radioactivity levels and tracing wastes. As some NPP sites will be placed in safe storage for up to 60 years, professionals will have to be trained now to decommission them at a much later date, to avoid losing current knowledge about how to conduct the decommissioning.

The risks associated with radioactive leaks due to human errors might be higher during decommissioning. Indeed, the perception of risk is lower after high-activity inventory, such as spent fuel, has been removed. In fact, the risk is not negligible due in part to the process being unregulated.

7.4 Security:

Once the spent fuel is removed from the reactors prior to decommissioning, the risks to the public and environment are relatively small. But where facilities are under decommissioning, and in particular when they are placed in “safe-store” mode or entombed, site surveillance has to be maintained to protect the contents from theft and malicious use. This is a costly factor that countries will need to take into account. Concerns exist about the risks associated with the possible use of nuclear devices created from stolen nuclear material as well as sabotage of power stations. These concerns have been proven to be real. In 1998 in Kinshasa, Congo, for example, two reactor rods in a temporarily closed-down research station were stolen. Although one was later recovered in Italy, the other has never been recovered. Security at the site is still considered highly unsatisfactory.

7.5 Cost:

Since few NPPs have been fully decommissioned, the exact costs of accomplishing this phase are unknown. Estimates vary from 9 percent to 200 percent of the construction costs. Data are often not made available to the public owing to contractual arrangements, property rights and other reasons. Cost estimates are only accurate from -5 percent to +15 percent. A report estimating the cost of decommissioning a site in the United States shows that for some projects, documentation on the data used to estimate costs is in fact missing. Moreover, the projected trend toward increased private financing of NPPs can be expected to bring with it more extensive and different types of reporting and documentation needs.

Additionally, it is important to note that recent worldwide economic instability could jeopardize these decommissioning funds, as well as premature or “on-time” NPP shutdowns; thus, relevant operators and governments need to act. There are examples of funds for decommissioning plants in the United States losing 10 percent of their value during the financial crises in 2008, resulting in delayed decommissioning plans.

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