The boundaries of the system, which will limit the scope of the evaluation, must be clearly defined. Then the analyst must identify the system elements. The term system element is formally defined as a subsystem of the SMR; at the analyst’s discretion a system element can comprise a facility (not just a building, but a facility in the systems engineering sense), part of a facility, a collection of facilities, or transportation within the identified SMR.

Figure 9.3 System response steps.

9.3.1 Target identification and categorization

Targets are the interface between the actors and the SMR and are the basis for the definition of pathways. Clear, comprehensive target identification is an essential part of a PR or PP assessment. Targets can include nuclear or radiological material, as well as processes, equipment, and information.

There are specific niche markets or applications where SMRs are the only applicable option as an NPP. Given their lower capital requirements and small size, which makes them suitable for small electrical grids, SMRs can effectively address the energy needs of small newcomer countries or remote and scattered areas. Their smaller size may better fit co-generation purposes and other energy applications. In these situations, comparison with large units is not applicable. Considering their output size, a 300-400 MWe SMR plant might also be considered as an alternative generation technology to fossil-fueled, base-load small-medium plants, such as coal and combined cycle gas turbine (CCGT).

According to NEA/OECD (2011), nuclear power is generally competitive with many other technologies (coal-fired plants, gas-fired plants, renewables) in Brazil, Japan, Republic of Korea, Russian Federation and the United States. Similarly, some SMRs are expected to be competitive with several projects of coal-fired, gas-fired and renewable plants of various types, including those of small to medium-sized capacity (below 700 MWe). A Monte Carlo analysis comparing SMRs with coal and gas-fired plants (Locatelli and Mancini, 2010a) stresses the fundamental role of the carbon Tax, or the CO2 sequestration cost, on the competitiveness of nuclear generation cost. Without a carbon tax, coal and CCGT may be more attractive then SMRs, in terms of NPV and LCOE. The carbon tax may dramatically increase the generation cost of coal-fired and CCGT plants and transfer its uncertain value to the overall uncertainty of the investment return of fossil-fueled plants, increasing SMR competitiveness (Figure 10.21).

In the open literature, several studies deal with the application of portfolio theory to power generation sector, but only few compare large and small power plants from this point of view. In Locatelli et al. (2011b) and Locatelli and Mancini (2011a) the investigation of the best combinations of base load power plants, for an investor on the basis of different scenarios, is carried out. As far as different Carbon tax and electricity prices are considered, the IRR and the LCOE are calculated using Montecarlo simulations for three base load technologies: nuclear, coal and CCGT. Different plant sizes are considered: for nuclear plants 335 and 1340 MWe, for coal plants 335 and 670 MWe and for CCGT plants 250 and 500 MWe.

Three markets are investigated, referred to as large grid (30 GWe), corresponding to a national-level utility, a medium grid (10 GWe), corresponding to a regional-level utility, and a small grid (2 GWe), corresponding to a municipality or an island. For

each market two types of portfolio are considered: (i) all possible combinations of large plants only and, (ii) small plants combinations only. In both cases the maximum site size is 1340 MWe, i. e. the size of a stand-alone large nuclear power plant, hence economy of scale and economy of multiples are taken into account.

In order to identify the best power plants portfolio mix from the investor point of view, the IRR and LUEC have been assumed as a metric of the investment performance (higher IRR; lower LUEC). The mean value of such indicators, arising from their own specific probability distributions, has been assessed against their respective standard deviation.

The results show that the nuclear power plants play a fundamental role in portfolio generation and become a convenient option when the carbon tax is included in the economic evaluation. Based on the above-mentioned criteria of IRR and LCOE, large plants may represent the best investment option where large new power capacity is required and small plants are competitive when small power installations are required. In order to achieve the highest profitability with the lowest risk, it is necessary to build several plants of different types and, in the case of small grids, this is possible only with small power plants. Although the choices of the investor will be subjected to the specific needs and the risk attitude, guidelines can be drawn to facilitate the selection process:

• large plant portfolios usually have better performance than small plant portfolios according to the LCOE indicator;

• small plant portfolios may have comparable performance with respect to large plant portfolios, according to the IRR indicator;

• in case of large markets (> 10 GWe), large plant portfolios are the best alternative in most cases;

• in the case of small size markets (2 GWe), small plant portfolios are able to provide a lower investment risk than large plant portfolios for both IRR and LCOE indicators;

• the optimal mix is largely made up with nuclear power plants when a medium/high cost of CO2 emissions or a low electricity price apply;

• in the absence of a carbon tax, the best performances are provided by coal-fired plants;

• an increase in the electricity price or a reduction of the carbon tax decreases the gap between the small and the large plant efficiency frontiers.

Joining of components throughout the nuclear plant is typically performed by fusion welding, more specifically a TIG process, however there is also some local use of Electron Beam welding but this is aimed at thin-section (less than 20 mm) materials.

TIG welding of thick-section materials, such as pressure vessels, is an expensive, time-consuming practice involving extensive pre-work such as fixturing, tooling, pre-heating of components, etc. TIG welding of thick sections is also performed over a number of runs, typically up to 100 runs for sections of 140 mm or above, and multiple runs of NDE throughout the welding process. Welding, inspection and completion of a large vessel therefore takes many weeks, even months, so accounts for a vast proportion of the fabrication cost and component lead-time element.

Development of the electron beam welding process to thick-section welding offers a number of significant potential benefits: single-pass welding of thick sections (40-140 mm), no requirement for pre-heating of the components and no requirement for a weld filler material. These all offer significant process and cost savings over traditional welding systems, but the key game-changing benefit offered by electron beam welding of thick sections is the removal of inter-stage NDE. Table 12.2 illustrates how the removal of inter-stage NDE from the welding of a thick-section component can dramatically reduce the overall time in process — by nearly 75%.

In short, electron beam welding of a complete large pressure vessel, which could consist of up to five thick-section circumferential welds, could be reduced conservatively by a factor of four. However there is one significant drawback: electron beam welding requires a vacuum to eliminate beam divergence which results in poor beam focus and hence loss of welding capability, especially when considering thick sections. Current technology requires the use of a vacuum chamber which houses the components to be welded as well as the electron beam system — vacuum chambers are extremely expensive to construct and are typically built to accommodate the size

of components to be joined, so even small reactor nuclear vessels would require large vacuum chambers.

A viable alternative would be to bring the vacuum environment to the components to be welded. One could envisage the development of a ‘jacket’ which would wrap and seal around the components to be welded and so would provide a local vacuum for the electron beam. The electron beam gun could be attached to the sealing jacket, and the components rotated around the gun to perform the welding process. The key to success for this technique is around the design of the electron beam gun and the sealing jacket or ring. To further benefit from this proposal, the sealing system should employ design-for-assembly philosophies and ensure that consumables such as seals and sealing surfaces, are easily replaceable. It would be further prudent to design the whole system such that a number of electron beam gun manufacturers could be used on the system thus negating a single-source route and the risk associated with such a strategy.

The recovery of bitumen from oil sands deposits using steam is called the steam- assisted gravity drainage (SAGD) process. Traditionally, steam is generated in a boiler fired by natural gas. In the nuclear-integrated case the traditional natural gas combustion would be replaced by reactor-produced high temperature steam. The steam is injected into the oil sands deposit where it heats the bitumen which enables the bitumen to be brought to the surface. Bitumen is blended with naphtha to produce dilbit, which is sent to a refinery for upgrading and conversion to transportation fuels and other petroleum products. In addition to dilbit, the conventional process generates significant GHG emissions [3, 24].

The Korean government set up a long-term plan for the hydrogen economy in 2005 corresponding to the rapid climate changes and heavy reliance on the imported fossil fuel.

Korea launched a nuclear hydrogen project utilizing very high temperature reactors (VHTRs) in 2004. The preliminary studies in 2004 and 2005 have identified the key technological areas. Based on the studies, VHTR and the nuclear hydrogen program in Korea has started as two major projects; the Key Technologies Development project and the Nuclear Hydrogen Development and Demonstration (NHDD) project. In 2008, the KAEC officially approved the nuclear hydrogen program and the nuclear hydrogen program became one of the national agenda.

The key technologies development project was launched at KAERI in 2006 as a national program supported by the government. Its main aim is the development and validation of key and challenging technologies that are required for the realization of the nuclear hydrogen system. KAERI takes the leading role of the project and the development of the VHTR technologies. Korea Institute of Energy Research (KIER) and Korea Institute of Science and Technology (KIST) take the role of developing the hydrogen production technologies. The project is a 12 year project and run in phase with Gen-IV International Forum and the NHDD projects. The project consists of two stages; the first stage (2006-2011) for the development of technologies and the second stage (2012-2016) for the performance improvement and validation of technologies. The NHDD project is under discussion, aiming at completion of construction in 2026 and demonstration by 2030. The final goal is to commercialize the nuclear hydrogen technology before 2030. The total R&D program for VHTR is shown in Figure 15.4.

5.3.1 Chemical and volume control system (CVCS)

An important support system for current large PWRs is the chemical and volume control system (CVCS). The CVCS functions to purify the RCS, increase or decrease the coolant boron concentration, and maintain the reactor coolant inventory. A continuous flow of reactor coolant is let down to the CVCS where it is cooled, cleaned through filters and demineralizers, reheated and pumped back into the primary system using a charging pump. The chemical shim can be adjusted by adding more borated water or adding more demineralized water back into the primary. Reactor coolant inventory can be adjusted by mismatching the let down flow and the reinjection flow. Reactor chemistry is controlled through the CVCS volume control tank (NRC, 2006).

Because these functions are important for continued long-term operation of the reactor, all iPWR designs will require a similar support system. This will require a system external to the reactor pressure vessel with connections to the primary system in the reactor pressure vessel. These functions are not safety-related, so a dedicated AC backup is not required. However, such systems will need to be isolable from the RCS. The isolation function is safety-related.

Also, because a CVCS support system provides regenerative and non-regenerative heat exchangers to cool the primary fluid in order to protect the demineralizers, some iPWR designs may be able to take advantage of this system to also provide a means to remove decay heat after reactor shutdown. This is feasible due to the lower thermal power generated by the iPWR designs. The CVCS heat exchanger in a larger PWR is not sized for this decay heat removal function.

Functional features of advanced HSIs include standardised as well as user-configurable displays. However, the most important feature would be the organisation of the whole HSI as an operator-centric or task-based system with embedded operator support, including various levels of computer-based procedures. Owing to the inherent complexity of advanced automation systems, the HSI must support intuitive navigation through a display architecture derived from proper task analysis. Advanced HSIs would also provide error-tolerant and resilient operation, support adaptive automation schemes and provide integrated multimedia communication.

As the nuclear power industry transitions to next-generation plant design, processes and advanced control rooms, many new technologies become available to ensure efficient and safe operations. A key component of control room operations is the human operator, who must ultimately use the new technology. All the exciting opportunities offered by HSI technologies confront human factors engineers with some challenging requirements and decisions:

• In-depth task analysis, simulation and prototyping are essential for successful implementation. Next-generation control rooms will offer opportunities to exploit advances in automation system technology that potentially will allow multi-module control rooms to operate with minimal direct human intervention. However, it is vitally important to establish the optimal level of automation for individual system functions as well as for the overall control system. Designers must reconcile an automation philosophy of ‘automate as much as possible’ with the overriding requirement to ‘keep operators in the loop’. A rational task allocation strategy must lead, not to an either/or strategy of allocating function to humans or machines, but to a dynamic, productive collaboration between them. There are many indications that the traditional function allocation methods are no longer adequate to determine what functions can or cannot be automated and the reasons why (Wright et al., 2000).

• The variable roles of operators (for example, under reduced plant capacity with varying numbers of operational modules, or during maintenance or emergency conditions) must be analysed and human factors engineers must ensure timely feedback to engineering design from function and task allocation analyses. This strategy must include consideration of the integration of multiple automated systems in the control room, how multiple failures of such automated systems should be handled, and how appropriate task support could be provided to the operator during all modes of operation. An advanced automation system will not only require an adaptive operator support system to match an adaptive automation system (Sheridan, 2002), it will also require extensive self-diagnosis of systems, error correction, intelligent alarm handling and automated event reporting. All of this must be done without leaving the operator out of the control loop.

• Control room design, especially of multi-module control rooms, requires sophisticated analysis, simulation and design methods and tools. In particular, high-fidelity simulators are essential for validation of designs, procedures and operator performance. Once designers have an operational control room they are going to face another challenge: how to keep operators vigilant and engaged in a monitoring role. We can accept that the operator will be involved in a significant amount of extra work related to a FOAK plant during the early stages of operation (for example, tests and diagnostics). Nevertheless, there is little doubt that under normal operating conditions there will be very little for the operator to do, unless we change his or her traditional role. Vigilance and situation awareness under low workload conditions, as well as decisions about the number and duration of shifts are serious concerns still to be resolved through detailed task analysis and studies of human reliability and human performance under various conditions.

• In addition to the changing role of operators, there will be special requirements for the development of a new generation of operating procedures, especially for variable modes of operation. Module-specific operating procedures versus plant-common procedures may require special treatment and this needs to be resolved long before the plant is commissioned. Again, a full-scope simulator will prove indispensable in the verification and validation of many aspects of the operator’s task.

While the many options offered by automation and HSI technology are very exciting, the reality is that designers need to make design decisions that will ensure a licensable, commercially viable plant. Ultimately, they need to focus on what is needed to obtain utility, public and regulatory acceptance of different levels of automation and operator performance in single as well as multi-module plants. Many new HSI technologies, such as augmented reality, intelligent agents or hand-held HSIs, may be of questionable value in the control room because of lack of proof of concept in the nuclear industry. However, the integrated nature of advanced automation systems will dictate an overall integrated approach to the design of the HSI. While advanced HSI technologies may be less important than building safe and commercially viable plants, designers should nevertheless recognise that such technologies offer an opportunity to significantly improve human performance and reliability in the plant and ultimately the effectiveness and efficiency of the whole socio-technical system.

This step decomposes the SMR into a set of system elements and threats to permit pathway analysis. Expert judgment may be used to identify system elements and threats that will be covered under qualitative, coarse pathway analysis and those that should be subjected to progressive refinement with quantitative analysis.

9.4.2.1 Step 5: collect and validate input data (main activity P)

The quantities and sources of input data depend on the scope of analysis. Validation of input data implies either the independent review of the data sources or examination of the consistency and basis for expert elicitation. If information and input data used in the analysis come from classified or sensitive sources, the analyst must ensure that this information is protected appropriately, including the possibility of classified or sensitive evaluation results. Most important in this step is a strong interface with facility designers. Designers should be key members of the proliferation resistance and physical protection evaluation team. Later, when the evaluation is applied to operating facilities, members of the operations team should also be included.

Timely and effective licensing of SMRs is crucial for several reasons. First, utility decision-makers or other applicants must have confidence in a stable, predictable and timely licensing process that will recognize the need to balance the right of all stakeholders to have effective input versus the need for timely and appropriate decisions. Second, common wisdom and logic would suggest that SMRs, which are based on proven LWR technology coupled with safety and security enhancements that are demonstrated through PRA results, testing, and validation, should be channeled into a licensing review that recognizes proven results and risk insights as opposed to a review that is risk averse and demands another layer of validation. Third, timeliness of licensing decisions is critical to investment and financial decisions and results for successful deployment. Fourth, governmental energy policy makers and the public must have confidence that the licensing process will result in timely decisions that can support a government’s energy policy. Delayed nuclear licensing decisions and commercial deployment may result in governmental policies that enhance other energy options to the detriment of a balanced energy policy.