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An NES comparison can be carried out at both the technological and scenario levels. This section discusses some specific issues related to the KI selection to compare NESs at the technological level. The next section will focus on issues related to the selection of KIs for an NES comparison at the scenario level. Creating a universal set of KIs for comparative evaluation of NESs is not possible owing to the need to take into account the specifics of the situation for which experts want to work out a decision, as well as the availability and affordability of appropriate information and data from experts and a decision maker.

Despite the fact that the specific sets of KIs can vary depending on the problem, it is possible to state that agreement on the evaluation areas that need to be considered within comparative evaluations of NESs is achieved among the different groups of experts involved in NES performance and sustainability evaluations. They are as follows: safety, economics, waste management, proliferation resistance and physical protection, environment, maturity of technology and country-specific area. For each of these evaluation areas, taking into account the available information and datasets, the KIs that best represent issues of practical interest for a specific problem need to be defined.

When comparing NESs at the technological level, it is crucial to keep in mind the maturity level of the options under consideration. It is necessary to distinguish situations in which several systems with the same maturity level are being compared and situations in which the experts compare systems with different maturity levels. Certainly, the less mature technologies are characterized by greater uncertainty than the more mature options; as a result, not all KIs can be quantified for less mature options owing to the lack of required information. Therefore, when forming the set of indicators, it is essential to recognize that consideration is only to be given to those indicators that can be adequately evaluated with acceptable accuracy for the entire set of alternatives. With technically less mature concepts, often the most knowledgeable experts are also the concept proponents.

When comparing NESs at the technological level, it is advisable to represent all NFC material flows in specific units (per unit energy production) in order to bring them to a comparable form (e.g. the specific cost of producing electricity, the specific natural uranium requirements, the specific rate of plutonium/minor actinide accumulation, etc.). NES comparisons at the technological level allow the peculiarities of the systems to be considered in selected areas; it is possible to evaluate the financial performance (net present value, internal rate of return, etc.), the likelihood and risks of unfavourable events arising from the commissioning, operation and decommissioning of the systems (e.g. the probability of a core meltdown, reactor core damage frequency, the risks associated with the theft of fissile materials or the misuse of NFC facilities, etc.) and R&D needs, as well as the utilization of NESs for different purposes and so on.

Because a number of KIs are evaluated solely in terms of scores (e.g. the technology maturity level), it is necessary to provide an opportunity to interpret the corresponding indicators and their values for the different alternatives being compared in areas and using concepts that are familiar to a decision maker (e.g. economic risks).

The following is a concise general description of possible indicators for specific evaluations that were discussed by various expert groups within the framework of corresponding case studies on the comparative analysis and evaluation of the NES performance and sustainability.

2.4.1.1. Safety

In general, sustainability evaluations in the area of safety are applicable to more mature designs, and a given set of KIs for safety cannot be applied simultaneously to existing systems and innovative systems where many details are not well known. Proponents of innovative concepts speak about multiple inherent and passive safety features, but the absence of full safety analysis often makes it impossible to evaluate their importance. Should primary hazards and measures to cope with them be identified, the safety case for the system would be presented in the evaluation report, and compliance with the national safety norms and IAEA safety standards could then be used as a ‘go/no go’ KI for safety.

Such potential performance measures as ‘non-nuclear (mechanical, chemical) energy that is stored in and could potentially be released from the reactor system or fuel cycle system’, ‘time constants for transients’, ‘core damage frequency’, ‘large (early) release frequency’, ‘frequency of individual effective dose at site boundary’,

‘source term’, ‘dose versus distance curve’ and others may potentially be useful to specify KIs for sustainability evaluation in the safety area, but it may only be reasonable to use them in cases where all the options being compared may be evaluated by corresponding KIs. Additional indicators may also address other safety aspects:

worker safety, public safety and investment safety (an event that leaves a facility useless, but harms no one, etc.).

2.4.1.2. Economics

The most often used economic KI is LUEC, which includes all the aspects that affect the total cost and views them over system commissioning, operation and decommissioning. At the same time, other economic or financial metrics may also be potentially interesting, such as net present value, total discounted cost, internal rate of return, discounted payback period and overnight capital costs. The need to utilize this kind of KI is caused by the fact that the liberalization of energy markets has given high decision making autonomy to business entities, which in the new conditions first of all seek to maximize their profits. The cash flow theory has come into use as the main tool for choosing efficient investment projects, where the mentioned KIs are used as the prime criteria for decision making efficiency.

Risks associated with the loss of capital investment may also potentially be interesting for decision makers.

As a measure of the risk of capital investment loss, the concept of value at risk (i.e. a measure of loss that will

not exceed the expected loss with a specified probability equal to a given confidence level) could be used. Other possible risks metrics (expected shortfalls, tail value at risk, etc.) may also be considered.

Risks associated with a long term burden for future generations resulting from decisions made in the present could be evaluated by cash flow analysis with declining discount rates.

2.4.1.3. Waste management

It is desirable to keep the generation of radioactive waste (measured, for instance, in tonnes or in volume units) by an NES and its impact (radiotoxicity, etc.) to the minimum practicable level. Different schemes of waste management may provide benefits to repository programmes, reducing the footprint of a repository. In this regard, the main contributors to heat load during different depletion periods of SNF (transuranic elements, fission products, activation product inventory) may also need to be characterized and taken into account.

Different KIs may be used to characterize waste management issues, such as ingestion radiotoxicity, radioactivity at 100 000 years after discharge (long term repository performance), radioactivity at 10 years after discharge (representative of handling issues), radioactivity at 100 years after discharge (decay storage thermal loading), high level waste (HLW) mass/volume, peak dose rate, decay heat or heat load, and time needed to reach a certain level of waste radiotoxicity. Some of these KIs may be represented per unit of energy produced by the system. The quantity of unique activation and chemically toxic waste products and unique waste forms may also be considered, if necessary, within comparative evaluations.

2.4.1.4. Proliferation resistance and physical protection

Proliferation resistance depends on intrinsic features and extrinsic measures that need to be implemented throughout an NES’s full life cycle to ensure that the system will be an unattractive means to acquire fissile material for a nuclear weapons programme. Both intrinsic technical features and extrinsic institutional measures are essential and when applied to an NES can increase the difficulty of diversion of nuclear material and misuse of the NES on the part of the State. In comparison, physical protection and nuclear security are intended to counter threats from sub-State actors; these are the responsibilities of the host State and not a part of proliferation resistance.

Different metrics may be proposed to evaluate the material inventory and forms (unirradiated and irradiated direct use material, indirect use material, item or bulk form) that characterize the proliferation potential associated with the NES. From a marginal risk perspective, it is important that the host State being considered already possess sensitive technological capabilities for enrichment or separation that are physically capable of producing significant quantities (proliferation goal quantities) of unirradiated direct use material inventories. Metrics such as ‘deployment of sensitive enrichment and reprocessing/separation technology’ may represent a capability to produce unirradiated direct use material in a State.

Since high quality safeguards verification increases extrinsic proliferation resistance, such metrics as

‘safeguards implementation considered from early design stage’ represented by a ‘go/no go’ indicator may be valuable. International interdependence (bilateral cooperation agreement obligations), with non-proliferation assurances and obligations documented in cooperation agreements between States, is a legal requirement to increase extrinsic proliferation resistance.

In general, traditional physical protection metrics might be difficult to evaluate for non-mature NES systems owing to the necessity to have detailed designs for associated facilities.

2.4.1.5. Environment

The environment area traditionally covers aspects related to the utilization of natural resources and the impact of the NES on the environment (not directly related to nuclear waste issues), which may be specified by diverse metrics, such as: the amount of useful energy produced by the system (from mining until disposal, including enrichment, reactor operation and separation) per unit of mined natural uranium/thorium; the supply sufficiency of identified rare non-nuclear materials for a targeted deployment scale; and the amount of water (or other consumables) used or land potentially impacted per unit of useful energy produced.

2.4.1.6. Maturity of technology

The technology provided in an INES needs to be ‘proven’ or ‘mature’ before it is included in a proposed design. For a technology to be considered mature, it needs to have already been applied in a prototype (a system, subsystem, or component), tested in a relevant or operational environment, and found to have performed adequately for the intended application for a reasonable length of time, or be fully licensed and operated by a host country before export to another country. This implies a need for measuring or evaluating maturity and ensuring that only a sufficiently mature technology is included by the technology holders in proposed plant designs. In this regard, NESs that are involved in a comparison may be at different design stages (feasibility study, conceptual design, basic design, site selection, detailed design, pre-licensing) and different amounts of time will be needed to mature the technology.

Less mature technologies are characterized by greater uncertainty owing to insufficient detail in areas such as design information, operational data and cost information, but the expected performance characteristics of the less mature options are usually more attractive than those of the more mature ones. The greater the uncertainty is, the greater the risks associated with the project realization will be. The maturity of technology area characterizes an aggregated risk measure and in such a manner the results of a comparative evaluation of less and more mature options may be interpreted for decision makers. The risk terminology provides a good basis for judgements regarding the risks/benefits associated with less and more mature options to inform a decision maker who is responsible for decisions relating to clear recognition of the risks and risk acceptance.

The cost of the R&D and the research, development and demonstration needed to deploy an nth of a kind unit may be a performance measure of the maturity level of technologies. Other performance measures that may somehow qualitatively characterize the maturity level of technology are as follows: the degree of standardization and licensing adaptability, the degree of validation of basic processes (theoretical, process demonstration, pilot facility demonstration), the share of proven technology (in some innovative systems many proven systems and components might be used, such as standard turbine generators available on the market).

2.4.1.7. Country-specific area

Because some innovative technologies may contribute not only to sustainable energy production, but also indirectly (through spin-off enterprises) to other areas of the national economy for some studies, it may seem reasonable to use KIs characterizing the spin-off potential of an NES. Infrastructural (legal, institutional, industrial, human resource) capabilities, political support and public acceptance issues, flexibility for non-electrical services and energy products, and load following capability are other examples of potentially interesting aspects to be accounted for within comparative evaluations of NESs in different countries using corresponding metrics.