Life cycle costing in radioactive waste packaging has the potential to reduce costs whilst accelerating cleanup. By Mark C. Janicki and Mark Johnson

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"There is considerable evidence to suggest that many organisations, in both the private and public sectors, make acquisitions of capital items simply on the basis of initial purchase cost. With the notable exception of military applications, very few assets seem to be appraised on the basis of their total lifetime costs. Two decades ago it was claimed that, very few firms appear to undertake life cycle costing studies at the acquisition stage of a physical asset’s life, nor do they collect all costs over their life cycles, and apart from isolated examples, the evidence suggests this situation has not radically changed."

“The life cycle cost (LCC) of a physical asset begins when its acquisition is first considered, and ends when it is finally taken out of service for disposal or redeployment (when a new LCC begins). LCC seeks to optimise the cost of acquiring, owning and operating physical assets over their useful lives by attempting to identify and quantify all the significant costs involved in that life, using the present value technique. LCC is concerned with quantifying different options so as to ensure the adoption of the optimum asset configuration. It enables total LCC, and the trade-off between cost elements during the asset life phases, to be studied to ensure optimum selection."

Source: International Journal of Project Management, Vol. 15, No. 6, pp. 335-344, 1997, Elserver Science Ltd and IPMA, Life cycle costing–theory, information acquisition and application David G. Woodward

Instead of considering only the initial purchase cost of items, organisations should try to quantify the costs of acquisition, operation and disposal – the life cycle cost (LCC) of the item. That approach may drive very different decisions on purchasing items.

What is the relevance of LCC to the packaging of radioactive wastes? When evaluating waste packaging options, individual elements (e.g. container costs) may appear cheaper than alternatives. But they may not necessarily be the most cost effective solution when life cycle costs are taken into account and when other benefits offered by alternative strategies are considered.

A thorough LCC assessment is a process that could help strategic planning and decision making for packaging radioactive wastes. These decision-making processes are often guided by legislative requirements, which look to ensure that risks from nuclear operations are ‘as low as reasonably practicable’ (ALARP) and that environmental impact from a waste management strategy offers the ‘best practicable environmental option’ (BPEO). These balance the benefits (reduced risk, most environmental benefit and least damage) of acceptable cost against the benefit offered. The principles of balancing cost and risk reduction in waste management were embodied within Radioactive Waste Management Policy, Final Conclusions, Command Paper 2919 published in 1995 [1].

In any programme, the best opportunities to achieve an optimised solution at the lowest cost occur during the early concept development and design phase, when significant changes can be made for the least cost. At later stages of the project many costs have become "locked in" and are not easily changed. "As over 70% of the total life cycle cost of a product is committed at the early design stage, designers are in a position
to substantially reduce the life cycle cost of the products they design, by giving due consideration to life cycle cost implications of their design decisions" [2]. To achieve the maximum benefit available during this stage of the project it is important to explore all processes and cost elements in the life cycle.

Globally, redundant plant and legacy waste facilities are being decommissioned to reduce the hazard from the wastes they contain. These operations are producing significant volumes of intermediate level waste (ILW). In the UK 2013 Radioactive Waste Inventory it is estimated that about 200,000 ILW packages (existing waste packages and future arisings) will be produced from decommissioning, managing legacy wastes and future operations. These ILW packages comprise three broad categories: unshielded ILW containers (e.g. 500 litre drums and 3 cubic metre boxes or drums); shielded ILW containers (e.g. 2m and 4m ILW boxes and 6 cubic metre concrete boxes); and robust self-shielded containers (RSCs).

To meet disposability requirements in the UK, waste packages must prevent or minimise the release of activity from the waste package in an impact or fire accident. Traditionally containment performance is achieved by a combination of the waste container and waste form, with immobilisation of the waste by encapsulation. In the case of ILW, encapsulation is primarily in a cement matrix in a thin-walled waste container.

Such containers either have additional concrete shielding within the container to form a shielded waste package or no concrete shielding to form an unshielded waste package.

Shielded waste packages can be stored in ‘simple’ stores that allow for controlled man access whereas unshielded waste packages require morehighly engineered shielded stores with remote handling facilities. Preparing wastes for encapsulation often requires some level of pre-treatment (e.g. sorting, segregation), an encapsulation plant to immobilise the waste, a capping station to ‘seal’ the waste, and a shielded store for ‘unshielded waste packages’. For wastes encapsulated in concrete shielded waste packages the main difference would be the additional facilities required to cast the concrete shield lid remotely.

A new generation of waste containers has been introduced to the UK called robust self shielded containers (RSCs) manufactured in ductile cast iron. These containers meet the performance requirements for disposal (e.g. impact and fire) without reliance on the waste form. The benefits of these RSCs [3] are:

savings in terms of reduced programme
duration and lower cost-to-implement through the reduction in capital plant requirements. For example, RSCs eliminate the need for encapsulation plant integral to waste packaging operations, shielded stores, a shielded transport container infrastructure and remote operations;

  • elimination of lengthy and costly research and development programmes required to establish encapsulation processes and underpin the waste properties;
  • acceleration of site clearance, by avoiding the long lead times associated with the design and construction of plant and equipment and heavily shielded stores;
  • achieving rapid hazard reduction, through early retrieval and packaging of legacy wastes;
  • packaging problematic wastes that are not compatible with cement encapsulation techniques;
  • the container provides shielding of the radioactive contents.

In assessing packaging options for transport, storage and disposal of ILW, cost is not the only factor. Other attributes have to be considered such as safety, technical performance (with practicability and feasibility), social and ethical, security and financial issues. However, cost clearly plays an important part in deciding a strategy for packaging ILW.

The cost of RSCs is higher than for standard containers. But that generally refers only to capital cost. When the cost of storing RSCs in stores that require minimal or no additional shielding, compared to unshielded waste packages in highly engineered shielded stores is factored into an LCC assessment then a different cost relationship emerges.

From Figure 5 it can be seen that the optimum solution from a cost perspective would depend on the packaged volume. As the volume of waste to be packaged increases, the increased cost for an ncapsulation plant and highly engineered store is off set by the lower cost of containers.

Further economic assessment of life cycle costs change further the point at which unshielded packages, or shielded waste packages that require waste encapsulation (2m and 4m ILW boxes and 6 cubic metre concrete box) remain the most economic option. The following factors affect the life cycle cost assessment:

  • costs of continued asset care and maintenance, to maintain the safety of the facility awaiting decommissioning until waste packaging plant and processes are available;
  • cost and programme extension required to design, construct, operate, maintain and decommission an encapsulation plant;
  • cost and programme extension required to design construct, operate, maintain and decommission an engineered shielded store;
  • procurement, maintenance and operation of a fleet of shielded transport containers to move unshielded waste packages (potentially for both on-site and off-site transport movements);
  • maintenance and operating costs for plant and equipment associated with handling unshielded waste packages.

The discussion above largely considers arguments centred on possible effects within an LCC assessment on pre-treatment and encapsulation of wastes for shielded and unshielded boxes. What would also be important in ensuring cost effectiveness of a packaging option is the amount of waste that can be packaged into the container: the higher the packaging efficiency of a container, the lower the overall cost per m3 of contained waste.

Iron is a much more efficient shield material than concrete, because it has higher density and atomic number. When comparing the capacities of containers of the same external package volume that use concrete shielding, for example the 2m ILW box and 6 cubic metre concrete box, to an equivalent RSC, the RSC offers an increase in waste capacity of around 50% for comparable shielding efficiencies. This additional capacity means that RSCs offer the following additional benefits over concrete shielded boxes:

  • fewer containers required;
  • fewer packaging and handling operations;
  • reduction in storage space;
  • reduction in transport movements (based on package volume);
  • reduction in disposal costs (based on packaged volume); and
  • reduced environmental impact due to fewer containers, lower resource usage, and reduced transport operations.

Such reductions may also assist in reducing overall radiation exposures to workers and members of the public due to fewer operations.

Within the industry there is a growing interest in using concrete boxes due to their potential low capital cost to manufacture. However, within the context of a life cycle assessment the initial higher cost of RSCs compared to concrete would be offset by the efficiency in savings when taking into consideration the other elements within the lifecycle, as illustrated above.

Another factor that would need consideration in such an assessment is the technical maturity levels of each option (Technical Readiness Levels). A product at an early stage of development maturity may require considerable research and development effort to bring it up to a technical maturity level suitable for implementation.

There may also be the fundamental issue of the suitability of the container for the proposed waste to be packaged e.g. the use of cementitious encapsulants can give rise to chronic waste evolution in some reactive wastes, potentially threatening waste package containment and performance.

In waste packages where concrete is expected to perform both shielding and containment functions, the properties of the waste form and its evolution characteristics could be highly constraining. Development and capital expenditure may be required to demonstrate that concrete packages are suitable for long term storage, followed by transport and disposal. Risk mitigation may also be required when considering the use of a concrete box in case of non-compliance with transport requirements (for instance an overpack may be required).

There may be a perception that when an individual project element within an overall waste management programme presents a cost saving over alternatives, it represents the most cost effective optimum waste package option; this saving may prove to be illusory when considering all elements within a LCC assessment of that programme.

The examples given comparing RSCs with the more traditional methods are intended to illustrate this point. This is not to say that there is one specific waste packaging solution, and there are other issues than cost to consider. Large volumes of waste are likely to favour the more traditional approaches – that of encapsulation in thin walled containers. However, and as illustrated in this article, although container costs for RSCs are higher than with other options that rely on the more traditional approaches of encapsulation for packaging wastes, they offer reduced life cycle costs whilst providing opportunities to accelerate clean- up. RSCs also offer technical advantages for wastes that are not compatible with the traditional approach of encapsulation and shielding using concrete.

Balancing cost and risk reduction are important regulatory drivers, particularly for dealing with legacy issues. If an economically affordable solution exists that would allow decommissioning of a high hazard facility, then why delay the work on the possibility that a lower cost solution might be available sometime in the future – particularly when considering the uncertainties in achieving a viable solution and those inherent in an extended timescale. Such uncertainties bring project risk, with subsequent cost implications, as do delays in implementing a packaging solution, which can increase radiological risk.

 

About the authors

Dr. Mark C Janicki, business development director, and Mark Johnson, engineering director, Croft Associates Ltd