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.

Developments to monitor whose achievement would indicate the future strength of

the SMR program are as follows:

• Russia: sustained construction and deployment of SMRs for specific terrestrial and ocean missions.

• USA: design certification by the US NRC of an SMR design; continued authorization of SMR development funding to the DOE by the US Congress and administration; firm commitment of a US utility to construct an SMR; continued development of the Next Generation Nuclear Plant by the DOE and the Next Generation Nuclear Plant (NGNP) Industry Alliance to further high-temperature gas reactor technology.

• China: evaluation in 2018 of the completed pebble bed reactor to assess whether cost and performance targets for electricity production based on its experimental HTR-10 steam cycle design have been achieved.

• Worldwide: announcement of firm interest by a developing country in an SMR compared to a large Generation III+ water-cooled unit.

1.7 Conclusion

It is likely that, given the operability and licensing experience of LWRs, the prospects for deployment of these reactors, and principally the PWR, are the most promising. However, while SMR deployments for specific missions as is occurring in Russia and China will undoubtedly continue, the prospect for large-scale deployment of SMRs for electricity production in the US and in developing nations is as yet uncertain. The current resolution of this uncertainty awaits achievement of regulatory certification of at least one design and more certainty in the costs, both overnight capital cost as well as the delivered electricity cost.

The major components in an I&C system include the primary or sensing element, the transmitter, the processing electronics, and the actuation devices. The primary/sensing element is the device that senses the process. For example, a sensing element may be the temperature sensing device, or the pressure sensing device. The transmitter is the device that converts the physical parameter being sensed to an electronic signal that can be transferred to follow-on processing electronics. The processing electronics perform various operations on the signal, which could be a simple as a applying a gain, or as complex as a filtering algorithm. The actuation device is the device that reads the electronic signal and performs the final action. The actuation device could be a control board indicator, a computer display, or an actuation signal sent to some other mechanism such as a control valve or an electronic device. The cabling is the wiring that ties it all together. The following discussion on major components breaks down into six sub-categories: safety systems I&C, nuclear steam supply system (NSSS) I&C, balance of plant (BOP) system I&C, diagnostics/prognostics, processing electronics, and cabling.

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 ALM process can provide a number of advantages, both business and technical, over traditional manufacturing methods. The justification for considering ALM arises from the volume of the market. For a small reactor with product lifespans of 40 to 60 years it is clear that no single supply chain can support the surge of production volumes at product launch and then sustainment for replacement parts towards the tail end of the product life with the same supply chain. This again is a new challenge for the nuclear industry that has evolved around a culture of bespoke engineering, where support for a plant through life from the same bespoke supply base is acceptable. For a small reactor delivered as a volume product the sustaining engineering challenge to the manufacturing supply base is different. Sustaining the product through life can no longer use the same original equipment manufacturer (OEM) supply chain economically. Automotive manufacturers do not supply replacement door panels for 10-year-old vehicles using the same line that delivers for their current year models. The small reactor supply chain faces the same set of challenges. Techniques such as ALM that have lower volume applications come into play offering significant economic advantages over the initial OEM supply chain. This is part of a strategy to maintain the competitive support of the plant through its operating life.

More specifically the attributes of ALM can be considered as two groups, OEM benefits and through-life benefits. ALM-OEM benefits include the following:

• Unit and/or through-life cost saving from reduced material quantity and/or machining costs offered by the ALM process.

• Unit and/or through-life cost savings from a reduced part count, e. g. manufacturing an assembly of multiple parts as a single component.

• The availability of welding test pieces, non-destructive examination (NDE) test pieces and other assembly and manufacturing aids significantly ahead of lead units can greatly reduce development programmes.

ALM — through-life benefits include the following:

• ALM can provide an alternative strategic sourcing route to the traditional forging, casting or fabrication route. It is highly suited to the low-volume, high-quality requirements of supplying nuclear-grade components. It can therefore be used to mitigate the risk of an existing manufacturing route that is threatened and/or may not be viable in the future for through-life sustainment.

• Where the existing manufacturing route is causing significant difficulties in supporting build, due to length of the manufacturing timescales.

By manufacturing components in layers, geometries that could not previously be

manufactured can now be produced. This enables a number of potential benefits:

• Optimisation of design definition for improved performance.

• Assemblies can be consolidated into a single component, thus simplifying manufacturing processes, reducing through-life costs, removing welds and fabrication, reducing inventory.

• Multi-functional parts can be produced by integrating cooling channels, electrical controls and instrumentation and/or cable management channels within structures.

• A structural integrity improvement may be realised, e. g. elimination of welds.

• High stiffness to weight ratio parts can be manufactured with internal lattice structures driven by finite element analysis (FEA) optimisation algorithms. These structures have thicker lattices where loading is high and thinner lattices where loading is low.

• Graded structures can be produced, where the material type is varied within a single structure, e. g. a tube can be manufactured that is Type 316L stainless steel at one end and Inconel 625 at the other, without the need for a transition weld.

12.3.1 Electron beam melting (EBM)

Additive manufacture by electron beam manufactures parts by melting metal powder layer-by-layer using an electron beam in a high vacuum environment. Parts produced by electron beam melting (EBM) are usually smaller than those produced by the laser process, but the EBM process does yield components that are fully dense, void-free and extremely strong.

As with ALM, CAD geometry, a power source and metal powder is required. However unlike ALM, EBM-fabricated components do not require heat treatment because of their high densification and operating temperature of typically 700-1000 °C during the fabrication phase. EBM is used in the aerospace sector where titanium and titanium-alloy components are produced, although systems do exist which can produce components up to 450 mm X 100 mm X 100 mm in a small variety of high — value metals.

Nuclear component materials in nickel-based alloys could be manufactured by the EBM process, but a cost-benefit analysis should be made to determine the viability when compared to existing fabrication techniques.

Synthetic gasoline (syngas) may be produced from natural gas or coal via the conventional methanol-gasoline process. These processes produce methanol as an intermediate product, synthetic gasoline and liquefied petroleum gas as end products, and significant GHG emissions. The conventional coal and natural gas cases differ in the approach to generate syngas; however, from the syngas to gasoline via methanol production, the processes are the same.

The nuclear heat integration cases for methanol to gasoline are slightly different in their integration points for the coal and natural gas feedstocks. For the coal-to — gasoline process, hydrogen from nuclear-driven HTSE is used in the gasification process. Power from the reactor is used for compression and sulfur removal. For the natural gas-to-gasoline process, nuclear heat is used for the reforming process and electric power is used for compression. Nuclear integration provides significant reduction in carbon dioxide emissions relative to the conventional (non-nuclear) case [3, 21, 22]

A performance test of the major components such as the RCP, steam generator (SG), and control rod drive mechanism (CRDM) was carried out. In the SMART standard design approval program, additional performance tests for the RCP and CRDM are scheduled to be performed to verify the final design models.

Figure 15.2 Schematic diagram of the VISTA facility.