The definitions (GenlV International Forum, 2011b) of PR and PP that apply to most nuclear energy systems also apply to small modular reactors (SMRs). They are as follows.

• Proliferation resistance is that characteristic of an SMR that impedes the diversion or undeclared production of nuclear material or misuse of technology by the host state seeking to acquire nuclear weapons or other nuclear explosive devices.

• Physical protection (robustness) is that characteristic of an SMR that impedes the theft of materials suitable for nuclear explosives or radiation dispersal devices (RDDs) and the sabotage of facilities and transportation by sub-national entities and other non-host state adversaries.

Figure 9.1 illustrates the methodological approach at its most basic. For a given system, analysts define a set of challenges, analyze system response to these challenges, and assess outcomes.

The challenges to the SMR are the threats posed by potential proliferant states and by sub-national adversaries. The technical and institutional characteristics of

Handbook of Small Modular Nuclear Reactors. http://dx. doi. Org/10.1533/9780857098535.2.219

Challenges—- ► System response —— ► Outcomes

Threats PR&PP Assessment

Figure 9.1 Basic framework for the PR&PP evaluation methodology.

the SMR systems are used to evaluate the response of the system and determine its resistance to proliferation threats and robustness against sabotage and terrorism threats. The outcomes of the system response are expressed in terms of PR&PP

measures and assessed.

The evaluation methodology assumes that an SMR has been at least conceptualized or designed, including both the intrinsic and extrinsic protective features of the system. Intrinsic features include the physical and engineering aspects of the system; extrinsic features include institutional aspects such as safeguards and external barriers. A major thrust of the PR&PP evaluation is to elucidate the interactions between the intrinsic and the extrinsic features, study their interplay, and then guide the path toward an optimized design.

The structure for the PR&PP evaluation can be applied to the entire fuel cycle or to specific elements of the chosen fuel cycle (reactor, front-end, or back-end of the particular fuel cycle under consideration). The methodology is organized as a progressive approach to allow evaluations to become more detailed and more representative as system design progresses. PR&PP evaluations should be performed at the earliest stages of design when flow diagrams are first developed in order to systematically integrate proliferation resistance and physical protection robustness into the designs of SMRs along with the other possible high-level technology goals such as safety and reliability, and economics. This approach provides early, useful feedback to designers, program policy makers, and external stakeholders from basic process selection (e. g., recycling process and type of fuel), to detailed layout of equipment and structures, to facility demonstration testing.

While modularization deals with a design and fabrication methodology, design factor is related to the specific and peculiar features and enhancements of a given design concept, in order to meet operating requirements with optimized safety, simplicity and economics. Large plants have been optimized for their particular power output. In designing a plant with smaller output, it does not necessarily make sense to just scale down a large system. Usually SMRs are not a mere re-sizing of larger units; they do not represent a way back, but, on the contrary, a further progress in the technology evolution path.

At a smaller size, different design concepts might be possible, which could lead to a more significant capital cost reduction than simple application of the scaling laws from large design would predict (Hayns and Shepherd, 1991). SMR economic rationale also lies on the enhanced passive safety features and design simplifications, often enabled by a small plant scale. The 300-400 MWe safe integral reactor (SIR) in the 1990s and the international reactor innovative and secure (IRIS) in early 2000s paved the way to the understanding of an innovative technological and economic paradigm.

Most Gen III+ reactor designs include some features that may be regarded as passive (i. e. relying on physical laws and not on human intervention for the activation), but small-scale plants can take maximum advantage of such features, due to their physically smaller size or lower power densities, and consequential lower power output. As a result, the elimination of some engineered safety systems might be possible and/or the safety downgrading of some other components. Revised, simplified and more cost-effective plant layout becomes possible, with favourable impact on costs (Carelli et al., 2008a, 2008b).

Along with such design-related cost benefits, the SMR exploit the economics of small ‘mass production’. SMRs are conceived to take the maximum advantage from standardization and economy of replication (Kutznetsov and Lokhov, 2011), also referred to as the ‘economy of multiples’ paradigm. Moreover, SMRs may encompass a broad range of reactor unit sizes. In principle, the lower the size, the higher the loss of economy of scale to be compensated, and the loss of cost effectiveness in terms of generation cost (Figure 10.13).

SMRs rely on the ‘economy of multiples’ but also on the ‘economy of small’ in the sense that design-related cost savings are necessary to recover economic

competitiveness. The smaller the reactor unit size, the higher must be the design cost savings in order to have the same generation costs as LRs. Some general considerations on cost reduction by design may be drawn from several innovative SMR features, such as the integration of primary loop into the reactor vessel, with the elimination of large loss-of-coolant accident (LOCA), the wide use of passive safety systems with natural circulation of coolant in case of accident, and the elimination of some active components and safety systems. Nevertheless, the design-saving factor that is expected to decrease construction costs of SMRs is strictly dependent on the specific reactor concept. A more reliable estimate could come from a bottom-up cost analysis, referred to the specific plant layout and technical features. In the absence of this information, the economic analysis may consider the design-saving factor as a ‘target’ value to be achieved in order to equalize the SMR and LR projects’ profitability. Thus the economic analysis might offer the manufacturer a sort of indication on a technical and economical goal for the SMR design (Boarin and Ricotti, 2011b). As a consequence, ‘very small’ reactors (VSR) must come up with additional saving factors (Figure 10.14). Rather, VSRs do not really compete in the same SMR playground since they have other unique requirements, e. g. emphasis on total capital cost, rather than on cost per KW installed, and may have unique applications, such as very small or scattered user areas.

Additive manufacturing processes differ significantly from traditional formative and subtractive processes. Formative processes, e. g. injection moulding or casting, require the initial manufacture of long-lead, high-cost tooling or moulds into which material is injected or poured. Subtractive processes, e. g. milling or turning, typically require the procurement of a long-lead, high-cost forging from which material is removed to achieve the final component definition.

Additive manufacturing processes create components by the selective addition of material layer by layer to form the component geometry. Material is only added at each layer where specified by the computer-aided design (CAD) definition. This fundamental difference can offer a number of business and technical advantages over traditional process.

Additive manufacturing processes are often sub-divided according to the energy source used and/or the raw material delivery method. There are two energy sources widely used in industry; lasers and electron beam. There are also two material — delivery methods: ‘powder bed’ and ‘blown powder’.

The term additive layer manufacturing (ALM) is typically used and should not be confused with rapid prototyping which infers a rapid manufacture that may or may not be correct and an end use for the component.

Laser sintering is an inaccurate and unofficial definition, and should not be used as a description for this technology. Direct metal laser sintering is a registered trademark of Electro-Optical Systems (EOS) GmbH and should not be used, as it would denote a specific vendor, not a technology or process group.

3D-printing is an increasingly common term within the industry. However, it is predominantly used when referring to a much wider group of technologies including polymer-based systems.

Hydrogen can be produced through several processes, two of which are briefly described here: HTSE and nuclear-integrated steam methane reforming. Hydrogen is a key element for making fuels and other industrial chemicals. Industry is currently making hydrogen from natural gas via steam reforming. Water and methane are feeds for the process in which some of the methane is used to make steam and the remainder is combined with the steam to create hydrogen and carbon dioxide. In the traditional case, natural gas would be used to drive the steam reforming to produce hydrogen. For the nuclear-integrated steam methane reforming case, process heat from the reactor would be added to the steam reformer [19, 20].

Hydrogen can also be produced using a nuclear reactor by way of HTSE. The heat and electrical power from the reactor can be used to split water using solid oxide electrolysis cells to create hydrogen and oxygen. The process heat from the reactor reduces the amount of electricity needed to split the water, thus increasing the efficiency of the process when compared to low-temperature electrolysis [4].

Hydrogen is an important component for many industrial processes. The conventional method of steam methane reforming is the least expensive hydrogen production method, but produces carbon dioxide and requires constant operation. Hydrogen from electrolysis processes can be turned on and off readily and, for hybrid energy systems, offers a means to integrate intermittent renewable resources. HTSE has higher production efficiency than low-temperature electrolysis that results from the addition of thermal energy to split the water molecule. Heat is required, but heat recuperation within the electrolysis process greatly reduces the amount needed. Only 10-15 percent of the heat from a reactor is needed to maintain HTSE temperatures. The remainder of the heat is converted to electricity to run the electrolysis cells. As long as the cells are maintained at the desired temperature, the electrolysis process can be turned on and off as needed. HTSE also has no carbon dioxide emissions.

The early SMART concept adopted an in-vessel pressurizer type with an inherent self-pressure regulating capability designed to operate via the thermo-pneumatic balance between the water, steam and nitrogen gas which are the three fluids that fill the pressurizer. In the event of a rupture of a pipe line connected to the pressurizer at a high system pressure, a mixture of water, steam and nitrogen is discharged through the break at critical flow conditions. The computer codes for the safety analysis of SMART need to use a verified and validated model for this critical flow. To investigate the thermal-hydraulic phenomena of the critical flow affected by the non-condensable gas entrained in the two-phase break flow, a separate effects test facility was designed and installed at the KAERI site. The test facility can be operated at a temperature of 323 °C and pressure of 12 MPa, with a maximum break size of 20 mm in diameter. A nitrogen gas flow-rate of up to 0.5 kg/s can be injected and mixed with a two-phase mixture in the test section to simulate the transient behavior expected during a LOCA. The test data from the facility were used for the development and verification of the critical break flow model for SMART.

Integral effect test

The SMART-P is a pilot plant of the integral type reactor SMART which has new innovative design features, aimed at achieving a highly enhanced safety and improved economics. An experimental verification by an integral simulation for a transient and accident (VISTA) facility has been constructed to simulate the various transient and events of an integral reactor. The VISTA facility (Figure 15.2) has been used to understand the thermal-hydraulic behavior including several operational transients and design basis accidents. During the past five years, several integral effect tests have been carried out and reported, including performance tests, reactor coolant pump (RCP) transients, power transients and heat-up or cool-down procedures, and safety-related design basis accidents. It contributes to verifying the system design of the reference plant.