Technology characteristics can be grouped into two main categories — technical characteristics and context of use.

7.6.2.1 Technical characteristics

These are concerned mainly with the advantages and disadvantages of specific technologies and the human factors considerations. These would include the performance criteria listed below. Most advantages and disadvantages of technology can be evaluated objectively simply by comparing features and performance measurements. However, such measures are often meaningless if not performed with reference to the specific context of use, described below.

Other practical aspects of technology choices would include the following:

• cost of ownership (including cost to maintain and replace);

• availability (is the product actually available and how long will it take to procure?);

• technical performance (how does the product perform on specific measures such as accuracy, sensitivity, resolution, reliability, etc.?);

• environmental constraints for operation (can the product withstand rough handling, dirty environments, etc.?);

• compliance (does the technology meet applicable standards, such as Occupational Safety and Health Administration (OSHA)?);

• Training required (how difficult is it to learn?);

• system variables (processing power, memory size, power requirements).

In addition to these characteristics, we can identify a number of complementary categories that must also be considered when selecting technologies. These application criteria are called the engineering ‘ilities’:

• Usability — As defined in ISO 9241-11 (1998), the effectiveness, efficiency, satisfaction and safety with which specific users can perform specific tasks in defined contexts.

• Maintainability — This is the ease with which a product can be maintained. It is also a

characteristic of design related to the amount of time taken to return a failed piece of equipment back to its normal operable state.

• Accessibility — This is a measure of how easy it is to obtain the device, tool, function or information when needed.

• Operability — This refers to a device being ready for use or to be placed into service, or the ability to keep equipment or system in a safe and reliable, functional condition.

• Reliability — This is the ability to consistently perform an intended or required function and mission and the probability that a given item will perform its intended function for a given period of time under a given set of conditions.

• Durability — How well a device is able to perform and withstand a variety of conditions by resisting stress or prolonged use.

• Simplicity — How easy it is to understand, explain and operate a device or system. We can also associate simplicity with intuitiveness and usability of a device or concept.

The B&W mPower IST facility located in Bedford County, Virginia, USA, includes a scaled prototype of the B&W mPower reactor. All of the technical features of the B&W mPower integral reactor are included in the IST. The multi-year testing will collect data to verify the reactor design and safety performance and support B&W’s licensing activities with the NRC. The reactor prototype was installed in July 2011 and reached full operating conditions in July 2012 (www. babcock. com/products/ Pages/IST-Facility. aspx).

To evaluate the construction costs that, as said, represent the main component of nuclear LCOE, two approaches are usually adopted: top-down cost estimation and bottom-up cost estimation.

• Top-down estimation. The cost is calculated starting from a reference, known cost value, then considering the most important cost drivers that characterize the economics of that specific technology to derive scaled or proportional costs. Regarding the power plant industry, these drivers are: the plant size, the number of units to build, the site location, etc. This procedure is particularly appropriate when the plant design is still in the early phase of development, or when the plant design is characterized by a high level of complexity and number of systems as to make the cost estimation of each of them a hard task with a decrease in the reliability of the end result. An application of top-down cost estimation to SMRs is presented in Carelli et al. (2010).

• Bottom-up cost estimation. The cost analysis is carried out at ‘component level’ and the final cost is the sum of all of the costs related to the components manufacturing, assembling, operation, etc.

Once estimated through the above-mentioned procedures, the life-cycle costs, together with the cost of financing (equity and debt) and tax burdens, may be elaborated to perform a discounted cash flow (DCF) analysis. The DCF analysis provides the most relevant indicators of economic performance, such as the internal rate of return (IRR), the net present Value (NPV), the (LUEC) and the payback time (PBT) (see Figure 10.1). Several studies indicate that optimism in the cost estimation of large projects, such as civil and transport infrastructures, power plants, etc., is a common characteristic. This phenomenon may be observed in the case of NPPs, which are historically characterised by delay in construction and cost escalation (Locatelli and Mancini, 2012a). In order to provide a reliable cost estimation of SMRs, it is important to understand why the estimations of NPP costs, as well as large engineering projects, are usually so inaccurate and how to improve this process. Under this perspective,

Flyvbjerg et al. (2003) show that the availability and reliability of data about large projects affect the estimation. The authors identify two macro-categories of causes to explain inaccuracy in the cost forecast: (i) inadequacy of the methodologies and (ii) strategic data manipulation. The latter, combined with ‘optimism bias’, is responsible for most of the cost escalation.

At the 6th INPRO Dialogue Forum, the IAEA recommended consideration of international certification of SMRs. This long-term recommendation must recognize and integrate with the preservation of sovereign authority for licensing. The aviation industry is recognized as a credible model for international certification of airplanes. It may be a difficult task for the international nuclear community to develop a similar certification process simply because NPPs are sited at a fixed location within the boundaries of a sovereign nation with governmental responsibility to license and regulate to protect its citizens and neighbors. Difficult as this task may be, the standardized design of SMRs that will be manufactured and deployed internationally presents an opportunity to assess areas of licensing that may benefit from international certification. Possible licensing areas for international certification include:

• SMR operators;

• SMR manufacturing facilities, equipment, and processes;

• SMR standardized operation and maintenance.

The IAEA must take a lead role in assessing international certification projects. Member states need to participate in and approve any certification process. The IAEA must develop the capabilities and processes to review, approve, and inspect international certification requirements. The global deployment of standardized reactor designs that offer significantly enhanced safety and security features provides a great opportunity to integrate traditional country-specific licensing processes into a more international licensing framework.

11.4 Conclusion

SMRs hold the promise for successful commercial deployment in many and diverse global markets. SMRs offer enhanced safety, security, and flexibility for all applications. Most energy and environmental governmental policies support this clean energy alternative. However, this energy alternative and commercial promise must be advanced by enhanced and informed licensing that recognizes the advantages of the SMR safety design, fabrication quality, reduced public risk, and deployment flexibility.

This chapter provides a strategy and framework, based on US NRC SMR licensing processes and decisions, to support effective and timely licensing. It offers recommendations on how this new reactor technology can be licensed in a collaborative international framework but still recognizes the regulatory responsibilities of each sovereign regulatory authority. Successful licensing pathways must be collaborative, based on the uniformity of SMR designs and manufacturing, and yet reflect the safety and siting considerations that are unique for each application. Enhanced SMR characteristics present a new nuclear licensing paradigm that shifts traditional sovereign regulatory authority responsibilities to an international strategy and framework for certification of approved and licensed SMR designs, and attendant fabrication, operation, and maintenance processes.

The long-term resiliency and sustainability of a hybrid system are important but difficult attributes to quantify. NHES that can adapt and compete in an evolving market should account for potential future risks and opportunities. This type of predictive analysis, while based on less certain assumptions, is key to making sound investment decisions that will influence future technology implementations.

Classes of risks and opportunities that should be considered include:

• changes in the regulatory framework, with particular attention to environmental protection;

• volatility and long-term availability of raw supplies (fuel, process application feedstock, chemical compounds, etc.);

• reliance of a community or industry on energy generation or chemical production means exposure to supply chain risks; and

• scarcity in the raw material supply or high fluctuation in feedstock prices that subsequently give rise to volatility in the market and ultimately translates to higher overall prices for the final products.

Generally, these situations represent very low probability events, such as scarcity of oil or gas supply, but the consequences of such a shortage could be so dramatic that the overall risk is not negligible.

Portfolio diversification may be important to the long-term sustainability of an energy solution. A hybrid system may offer opportunity for diversification of the current supplier set for the commodities produced by the system. The need for diversification applies to the broad scope of energy commodities, such as providing an economically viable, domestic option for transportation fuels, or more narrowly to diversifying the energy source for electricity production. Diversification is achieved only if the compared energy sources are not correlated. Successful diversification increases the long-term sustainability of the candidate system and may be crucial to the stabilization of long-term energy prices.

In many cases advanced SMRs represent an alternative route to deliver the same products as are currently available (e. g. methanol) by means of different starting materials, contributing to stabilization of the final product by positive diversification.

Low sensitivity of system efficiency to the ultimate heat distribution (end use) offers system versatility, acting as risk mitigation for unforeseen changes in the definition of the system boundary condition (e. g. variation of the demand volume and heat to energy ratio or heat usage).

Hybrid systems naturally diversify customers. For example, if a much cheaper source of electricity is identified by a customer, reducing the electricity demand from the NHES plant, the NHES owner/operator may be capable of adapting production to refocus on heat utilization processes to respond to the demand changes. This operating mode introduces stability in the economic performance and capability to exploit emerging or growing markets.

In June 2013, the DOE announced it intended to provide a total of $3.5m in funding to address certain technical challenges associated with designing, constructing, and operating advanced reactors in the future. Again, as noted in the preceding section, these R&D projects for SFRs and HTGRs would have applicability to A-SMR versions of these types of reactor. The partnerships associated with the $3.5m include a 20 percent private cost share arrangement upon successful negotiation. The following descriptions [13] identify the four responsible organizations and a summary of the scope of the four projects:

• General Atomics — will conduct R&D on silicon carbide composite material, which could act as a safe and reliable material for fuel rod cladding in advanced reactor designs. Better understanding of silicon carbide composite material will help incorporate this material into such designs and support future licensing efforts.

• General Electric Hitachi — will develop high-temperature insulation materials and robust analysis tools to help design and manufacture electromagnetic pumps for liquid metal-cooled reactors. Electromagnetic pumps have fewer moving parts than traditional mechanical pumps, thus improving reliability and safety, while reducing maintenance needs.

• Gen4 Energy — will conduct R&D on natural circulation designs for advanced nuclear reactors that utilize a lead bismuth coolant. The project will develop computer models that will help visualize natural circulation flow and integrate it into safe, reliable reactor designs.

• Westinghouse Electric Company — will conduct analysis on sodium thermal hydraulics to support advanced nuclear reactor design. The project will provide analytical tools to help quantify heat exchanger performance and improve component engineering for sodium — cooled reactor designs.

The design of the HTGR endeavors to make the maximum use of inherent safety, and boasts the highest level of passive safety features possible. Safe shutdown of the reactor is ensured in an accident condition even without any operator’s emergency actions, by the low power density of the core, the inherent negative fuel temperature coefficient and the large graphite heat capacity. The core afterheat is removed by natural phenomena such as conduction, radiation and convection to the self-actuating reactor cavity cooling system. Such inherent safety features provide advantages in public acceptance.

There are two types of the HTGR designs, depending on the fuel type: the block and the pebble fuel type. General Atomics in USA developed a block fuel design, while Germany developed a pebble fuel design. Two fuel types shares the same basic technology of the coated particle fuel, TRISO, in which the fuel kernel of 0.5 mm diameter is multiply coated by silicon carbide layers. In the block type, TRISO particles are lumped together into compacts that are inserted into a hexagonal graphite fuel block. Fuel blocks are loaded into fixed positions in the core and reloaded periodically. In the pebble type reactors, TRISO particles are lumped together to make pebble fuels each of which is about as big as a tennis ball in dimension. Pebble fuels enter the core at the top, flow continuously downwards, and then exit the core at the bottom. The pebbles that leave the core are measured and then either rejected as waste fuel, or recirculated to be used again in the core. The failure probability of the TRISO particle is so low (~10-S per particle) that it is sometimes referred as a small containment.

15.4 Future trends

15.6.1 iPWR: SMART

15.6.1.1 A fully passive safety system for SMART

The hybrid safety system currently employed in the standard design of SMART is planned to be upgraded with fully passive safety system. The passive safety system will be developed to maintain the SMART plant in a safety shutdown condition following design base accidents such as LOCA and non-LOCA transient events without AC power or operator actions. The passive safety system consists mainly of a PRHRS and passive injection system (PIS). Based on the current SMART SDA design, the capacity of the PRHRS will be increased up to an operation period of at least 72 hours. All of the active safety features will be substituted with passive versions, eliminating the necessity for emergency diesel generator (EDG) or operator actions for at least 72 hours. A program to adopt a fully passive safety system in SMART began in March 2012, and the testing and verification are planned to be completed by the end of 2014.

Many countries that anticipate the development of nuclear technology by deploying NPPs try to develop the optimized projects to minimize the risks in financial and public acceptance. Then, the SMART will be the only viable solution among SMRs to fulfil the demands of such countries, and the KAERI and the Korean government together will create a worldwide strategy to support the construction of a prototype in Korea and global marketing. Middle East and North Africa (MENA), Southeast Asia and typical arid regions could be the potential owners.

15.6.1.2 Further issues for SMR development

The main focus of the Fukushima Daiichi event was the need to remove the decay heat in the reactor after successful shutdown. Although SMRs use the same fuel type and the same light-water cooling as large-scale light-water reactors, there are significant enhancements in the reactor design that contribute to the upgraded safety case. Safety of SMRs tended to rely on the same sorts of features to utilize the technology of large NPP as proven technology, but SMRs have characteristics that may result in significant safety improvements. First of all, there is less heat to remove because of the lower thermal output of the reactors. And the increased water inventory provides more coolant and therefore more time for compensatory actions to take place.

In spite of many safety improvements, some of the concepts being considered introduce new considerations to licensing and safety viewpoints. A skeptical viewpoint on SMRs is that SMRs work almost on the same principle as that of large reactors. Safety characteristics are not significantly better than large reactors due to the introduction of the same sorts of safety features. Some safety benefits also declined as reactor power approached the upper bound of the SMR category. Then, SMRs are expected to face increased regulatory oversight. The SMRs most likely to succeed are designs that use the same fuels and water-cooling systems as the large reactors in operation, because the regulatory authority might be accustomed to regulating those reactors.

The final challenge for SMRs is to guarantee the economic feasibility for potential owners. It concluded that SMRs would not be able to produce electricity more cheaply than large reactors but could fare well against non-nuclear power sources. Whereas the impacts of economies of scale vary according to the relative sizes of the reactors, there still are lots of benefits compensating the economic weakness.

Factors that influence SMRs economic analysis are such as considerably lower total capital cost than large NPPs, reduced on-site construction costs through factory — assembled delivery, less land area and cooling (BOP) requirements, passive designs and other features resulting in fewer staff, additional non-electricity applications providing new markets and income opportunities, and so on.

SMRs are targeting at utilities, companies and countries that are currently uninitiated in the world of nuclear power. To open this new marketplace, developers should provide cost-effective designs covering wide range of site specifics as well as an integrated model of financing, licensing, construction, manufacturing and fuel supply to reduce the risk of economic benefits.

Once an initial estimate has been determined of the enrichment, the number of fuel assemblies to be loaded in the cycle, and the types of BPs that are most suited for the iPWR being developed, the next phase is to determine how to load the core, and which of the assemblies loaded in the previous cycle of operation are available and suitable to be reloaded. A major part of the nuclear design effort is concerned

GTGuide tube [t] Instrument tube ^Gadolinium pin

Figure 4.3 Examples of burnable poison distribution designs.

with this phase, typically referred to as the in-core fuel management, and it brings together many of the key interactions and issues discussed above.

The objective is to load the core to provide a flat/smooth distribution of reactivity across the core, i. e., high and low ^-infinities balancing each other. This distribution of the assemblies in the core, is known as the ‘loading pattern’. If reactivity is too high, then assembly powers will be high, and this in turn will result in power peaking in the fuel rods being too high (see Section 4.2.3). The core is loaded in quarter core symmetry to avoid power and performance tilts in the core, e. g., one quadrant running at higher power than the others. This means that the fuel assemblies are

loaded in groups of four, one in each quadrant. In most iPWRs (and most large PWRs) the fresh fuel is loaded towards the center, and the previously irradiated batches of fuel are loaded towards the edge of the core. This improves the neutron economy by reducing the radial neutron leakage out of the core and is known as a ‘low leakage loading pattern’ (or L3P). This is particularly important for iPWRs because the smaller cores, with a high surface to volume ratio result in a much higher neutron leakage than large PWRs. This does tend to make the iPWRs more prone to power peaking (with all of the higher reactivity at the center of the core), and as such, higher BP loadings are required.

Typically the fresh fuel is loaded in a checkerboard configuration (towards the center as explained above), and the highest ranking in reactivity of the previously irradiated fuels are then loaded into the core design according to ^-infinity ranking. Three-dimensional reactor analysis tools (such as CASMO-SIMULATE) are then used to calculate the assembly, and pin power distribution and to determine if the constraints are met for the fuel. If the peaking is not met, then the fuel can be ‘shuffled’ to improve the power peaking. This can either be done by use of the designer’s skill and experience, or by using loading pattern optimization tools. At the same time as assessing the core loading for power peaking, the energy requirements (cycle length) are also checked to ensure that there is sufficient enrichment loaded in the fresh fuel assemblies. The number and content of the BPs can be changed if sufficiently low peaking cannot be achieved, but the designer also has to be aware that once the BPs deplete in the core the power distribution will change, and can lead to higher pin power peaking during the cycle than at the start.

For the designer, the other key criterion during this stage of the design process is the economics of the required fuel. The main variables that affect the fuel costs for a given cycle of operation will be (a) the number of fresh fuel assemblies required, and (b) their enrichment. Since the fuel is loaded in quarter core symmetry, an additional new fuel assembly required in a quarter core means the purchase of four assemblies, an increase of the order of several million dollars in fuel price. Similarly, if the core is designed such that there is too much radial or axial leakage (particularly relevant to the small cores of the iPWRs), then additional enrichment in the fuel will be required to achieve the required cycle length and fuel discharge burnup. This results in an increase not only in the enrichment costs, but also the uranium ore required to be purchased.

Reducing the number of fuel and BP rod types is also a means by which the designer can improve the fuel economics. Good practice involves keeping the number of fissile enrichments to a minimum across the assemblies, rather than having multiple enrichments, either within an assembly, or within a reload batch of fuel. For a reload of fuel, two or three enrichments would not be unusual. Similarly for the BP types and enrichments of fissile material in the BP rods and the BP loading itself, minimizing the variations is key to the fuel costs. In this case, good practice may be to use only one BP type (e. g. gadolinium) and, for example, only three different weight percentages across all fuel designs, e. g., four, six and eight. Also, the designer must ensure that the BP burns out fully, i. e., there is no residual absorption of the BP in the fuel, which is particularly important for highly poisoned cores where the
impact would be greater. For those iPWRs that require a high BP loadings (e. g., for long cycles, or single-batch cores), minimizing the residual absorption by using boron rather than gadolinium, or a combination of the two would be warranted.

The compactness of the iPWR combined with fewer assemblies available (in terms of absolute number, variation in burnup, BP types, etc.,) makes the loading pattern design process more challenging and achievement of an optimized core design more difficult. For example, iPWRs have of the order of one-fifth of the fuel assemblies of a large PWR as shown in Figure 4.4.12

Once the cycle length has been achieved with pin power peaking, fuel rod and assembly burnup within the allowed constraints, a brief safety analysis is often completed prior to the full set of detailed analyses and reports being completed. This overall saves time and money in the design process. The usual checks include:

• power peaking through the cycle;

• moderator temperature coefficient at hot full power and hot zero power;

• shutdown margin.

However, certain iPWR designs will have their own nuances that the designers will learn are key to a successful design prior to committing the nuclear design for a full safety analysis, and so ad hoc checks will be identified.

Level sensing and indication are a requirement for NSSS control systems. Several NSSS level measurements come from the protection system (safety system) through isolators, such as pressurizer level, steam generator level, and refueling water storage tank level. Other level indications such as boric acid tank level, volume control tank level, and accumulator tank level come directly into the NSSS processing electronics from field sensors and transmitters. It is expected that iPWR NSSS controls will have similar level signal requirements and a similar split between isolated safety signals and direct field signals as large PWRs. Those signals that come direct from the field, and do not go through the safety system, will have the flexibility of using newer technology for level detection, as the qualification of new devices will not be as rigorous or time consuming as a safety sensor qualification. The new technology discussion in Section 6.2.3 also applies to this section.

Another new technology that might be considered for level sensing is vibrating fork technology. This technology uses the principle of a tuning fork to detect level.

With this technology vibrating crystals are submerged in the medium, so when the density of the medium changes, the frequency of the crystals change. Used primarily as a level switch the crystal is placed at the level of actuation in a tank, and when the medium transitions that level, the oscillation changes and instigates a switch for an actuation. The actuation in many cases is an indication or alarm, but in some cases the actuation would be a control valve. The Rosemount 2120 level switch uses this technology. Although this technology is largely for level switches, a string of vibrating forks along the length of the vessel/tank could act as a level indication, not just a switch.

As mentioned in Section 6.2.3, fiber technology offers some efficient solutions for level measurement, and would likely be considered as a solution for certain tanks and vessels.

There are many different ways to classify HSI technology, depending on the context, as described before. The terms ‘human-system interface’ and ‘human-system interaction’ both suggest that either a technology-centric or a human-centric classification would be possible. This section provides a simple taxonomy that describes both perspectives.