REVIEW: Planning ahead for decommissioning
22 February 2019
Nuclear plant decommissioning is simpler, faster, and less expensive when taken into consideration during the siting, design, construction, and operation phases of the nuclear plant life-cycle. This is also true for radioactive waste management.
Managing Material and Waste from Nuclear Decommissioning is written by past and present members of the Waste Management & Decommissioning Working Group of World Nuclear Association: Michel Pieraccini (Waste Management & Decommissioning Working Group Chair), Mikhail Baryshnikov, Georg Brähler, Klaus Büttner, Olga German, Douglas Kerr, Arne Larsson, Geoffrey Rothwell and Evgeny Zhurbenko. Here, Stephen Tarlton, writer & analyst at World Nuclear Association, reviews the newly published report.
One of the main factors in the successful management of any large infrastructure project is careful planning. According to the report, when it comes to decommissioning a nuclear power plant, planning should ideally begin before the plant is even built. It could be well over 60 years before it ceases operation and decommissioning can begin.
That is not to say that such long-term planning is a result of nuclear decommissioning being especially complicated or difficult to execute. While this may have been true for some early projects, decommissioning is now well understood and can be safely managed. Nevertheless, just as with any other large-scale project, there are several potential stumbling-blocks that can lead to unnecessary cost escalation and delay.
A substantial amount of experience has now been accumulated and solutions based on actual cases have been developed. Methodology to Manage Material and Waste from Nuclear Decommissioning summarises this wealth of experience that has been acquired during more than 50 years of decommissioning projects. By outlining international good practice and describing the potential methodologies for decommissioning and dismantling waste management programmes, the report is intended to serve as a practical guide to decommissioning nuclear plants.
Sequence for success
Successful decommissioning planning requires clear direction (decommissioning strategy), a defined end point, planning time, upfront resources, investment and communication. The best technical and engineering solution can be worthless if it does not provide a financially, socially and politically acceptable solution to delivering the selected decommissioning strategy whilst achieving the selected end state.
Although there are differences between individual countries (such as in regulation, available resources and infrastructure) as well as between the objectives of different operators, the report recommends a sequence to best manage decommissioning and waste management:
- Define the end state and future use of the site at the beginning of the life-cycle of the plant, i.e. during the planning phase.
- Establish radiological, physical and chemical inventories as early as possible. These should be updated throughout the operational phase right up to plant shutdown.
- Continuously assess and improve decommissioning and waste management techniques, operator training, as well as public engagement.
- Sort and segregate material from decommissioning in order to maximise the quantity of material to be recycled in a cost-effective and sustainable way. At the same time, the quantity of radioactive waste to be sent for disposal should be minimised in order to preserve waste storage capacity.
End state
The decisions on strategy and end state will have a direct and major impact on decommissioning planning and associated costs. However, end state objectives are not normally determined by the plant operator but according to national goals, policies and regulations that relate to a mix of political, economic and technical criteria.
At the ultimate end of the plant’s life, there is a choice of two end state objectives. The ‘brownfield’ option results in the retention of a certain amount of regulatory control, i.e. the site is re-used with some restrictions, the nuclear plant is removed and the associated radioactive inventory is removed as radioactive waste. Any remaining inventory is normally associated with subsurface structures and low levels of ground contamination.
The ‘greenfield’ option results in the removal of all regulatory control, where the site is released from all regulatory monitoring with no restrictions on its future use. The site is cleared of its radioactive inventory.
Decommissioning strategy selection requires a wide range of influences - including national policy, space requirements, funding, waste disposal availability, fleet closure programmes, future use of the site (including re-use as a nuclear plant) - to be taken into account. The selection and application of a decommissioning strategy will influence the quantity and category of radioactive waste generated during decommissioning.
Deferred decommissioning will reduce the activity level of the generated radioactive waste due to decay and may allow more manual (as opposed to remote) handling. This will lead to lower disposal costs, but potentially higher overall decommissioning costs due to the longer post-operational duration.
Immediate decommissioning will lead to higher activity levels of the generated radioactive waste due to the lack of time in which decay can occur. Nevertheless, it will shorten the overall duration of the decommissioning project by reducing the amount of work required (less maintenance, fewer surveys, fewer inventory updates required) and therefore lower overall costs are expected.
Finally, entombment uses the existing structure to contain the decommissioning waste in situ. The resulting entombed structure effectively becomes radioactive waste within its own disposal site requiring ongoing institutional controls commensurate with the associated categories of waste. Due to social, political and land scarcity concerns, national policies on decommissioning civil nuclear plants do not normally support entombment.
The impact on the overall cost resulting from the decision on the decommissioning strategy is illustrated in the figure below.
Company structuring and organisation
It would appear that companies that are structured and organised on an integrated model find it easier to manage entire projects. Worldwide experience has shown that companies involved in all aspects of a decommissioning project (planning, operation, maintenance, waste characterisation, treatment, disposal, etc.) have faced less difficulty in planning and managing the project - including optimising their human resources and skills - than ones dealing with a number of separate organisations. Several examples of integrated organisations have demonstrated that they have been able to avoid the conflicts of interest that can arise between plant owners and waste treatment and disposal facilities when responsibilities are separated.
This approach is also advantageous in terms of public acceptance, particularly in gaining the support of the local community, as the operator remains responsible for the site throughout its life-cycle.
Ongoing decommissioning challenges
Managing Material and Waste from Nuclear Decommissioning presents decommissioning and the minimisation of waste in global terms on the basis of several interconnected key parameters: specific national policies; availability of resources and technological capabilities; economic considerations; and site and locality characteristics. The lessons learned in these areas from several countries have been drawn upon in preparing the report. However, a number of issues remain.
In particular, the lack of harmonisation of regulations between countries is hindering multinational approaches to decommissioning and waste management. Not only does this prevent innovation and improvements in efficiency, but also could confuse the public and put its acceptance at risk. Regulatory discrepancies prevent stakeholders from benchmarking the efficiency of decommissioning and waste management strategies between countries, making it difficult for them to identify the best available techniques.
Another challenge relates to the fact that the main structures of a nuclear plant (i.e. the concrete buildings and the site infrastructure) can last significantly longer than the critical components, in particular the reactor vessel. Therefore more consideration should be given during nuclear plant design to the replacement of those components.
The benefits of replacement of such components include:
- Shorter project time to the re-use of the site compared with a new-build project.
- A significant decrease in the overall project cost.
- A reduction of the waste amount since complete plant demolition is not required.
Should all plant components - including the reactor pressure vessel - be replaceable, then a full plant replacement could be carried out within a few years of shutdown, accelerating site re-use and reducing the overall cost of nuclear power generation. Solving this issue would be a major improvement, transforming decommissioning from a costly project lasting 20-30 years to a maintenance period of no more than five years.
According to the report, decommissioning and waste management should not be seen as separate from the operation of a nuclear facility, but simply as the last of the three normal phases of its life-cycle, after design and operation. Overcoming the financial and technical challenges of decommissioning and the associated waste management is a key part of demonstrating to the public and policy-makers that nuclear power is an essential and practical form of low-carbon generation.