The initial step in the PR&PP assessment is the definition of the challenges, i. e., of the threats considered within the scope of the evaluation. To be comprehensive, a full suite of potential threats, referred to as the reference threat set (RTS), must be recognized and evaluated. If a subset of the threat space is to be the focus of a specific case study, the subset must be explicitly defined. Threats evolve over time; therefore system designs must be based on reasonable assumptions about the spectrum of threats to which facilities and materials in the system could be subjected over their full life cycles. The level of detail in threat definition must be appropriate to the level of information available regarding design and deployment.

The definition of a specific PR&PP threat requires information both about the actor and the actor’s strategy. Here, actor is defined by the following factors:

• type (e. g., host state, sub-national, etc.);

• capabilities;

• objectives;

• strategies.

While economic research usually concentrates on capital cost as the dominant driver of the economic competitiveness, operating costs have much lower impact on generation costs. Few estimates are available on SMR O&M costs and fuel costs. Nonetheless some trends and general considerations may be argued:

• The designers of advanced SMRs often indicate that O&M costs might be lower than those of LRs, owing to a stronger reliance of SMRs on passive safety features and to the resulting decrease in the number and complexity of safety features (Kuznetsov and Lokhov, 2011).

• Economy of scale, co-siting economies and learning influence operating costs of multiple SMRs as in the case of construction costs; comparing an LR of 1340 MWe with a fleet of four SMRs of 335 MWe each, the penalty of SMRs on O&M costs due to the loss of economy of scale is mitigated by co-siting and learning effects and the corresponding overall cost increase on LR is limited to +19%; a learning effect on O&M activities of multiple SMRs is also confirmed (Carelli et al., 2008a).

• In general SMRs offer poor neutron economy due to lower reactor core dimensions, which translates into higher fuel cost incidence on generation costs.

• It is expected that long refueling schemes of some SMRs may increase specific fuel costs, due to a less effective fuel utilization, as compared to SMRs with conventional refueling intervals (IAEA, 2006, 2007b).

• Moreover, it is expected that for barge-mounted SMRs the sum of O&M and fuel costs is 50% higher than land-based SMRs, mainly due to a large O&M required by the barge.

Data information on decontamination and decommissioning (D&D) costs of advanced, modular SMR are not available from experience. One possible unbiased way to calculate them is to perform a statistical analysis of the data available from past decommissioning projects. Historical records show that there are several cost drivers that determine the decommissioning cost. Specifically those critical in the comparison between SMR and LR are: plant size, number of units in the site and decommissioning strategy (‘immediate decommissioning’ or ‘deferred decommissioning’). Multiple regression analysis is a powerful tool applicable to these kinds of analysis which is able to quantify exactly the impact of each cost driver; it allows for an in-depth examination of the trend correlation between the dependent and the explanatory variables. The result of this statistical analysis is that the economy of scale also applies to the plant decommissioning activities and represents a disadvantage for SMRs (Locatelli and Mancini, 2010b); the D&D cost for a medium-sized SMR unit may be three times higher than for a large plant. On the other hand, co-siting economies should decrease D&D costs for parallel dismantling of twin units.

It is worth stressing that historical data are related only to GEN I and GEN II reactors (both large and small), not to modern GEN III+ reactors and SMRs. Regarding SMRs, the design layout simplifications and reduced number of components should drive a cost reduction. In the same way as high content of factory fabrication should decrease construction costs by decreasing on-site assembling activities, modular and factory-assembled reactors should be dismantled in a sub-system that could be transported back to a centralized factory, where operations should be cheaper than on-site dismantling (Kuznetsov and Lokhov, 2011; IAEA, 2007b).

As a general, final comment, it can be stated that technical savings from design simplification and standardization and co-siting economies are the competing forces that play against the loss of economy of scale. The balance between these factors should be evaluated on a project-specific basis and supported by data information from actual experience.

Cladding of nuclear components, in particular large vessels, is applied to prevent the corrosion of the vessel substrate by the aggressive nature of the operating environment. The vessel substrate material is typically a low-alloy steel such as SA508 Grade 3 Class 1, which is a commercial-grade pressure vessel steel used across the nuclear sector. This substrate material can be covered or ‘clad’ with a less corrosive, more inert material such as a nickel-based alloy or a grade of stainless steel.

The current cladding technique is weld-based using wire or strip, fused to the substrate via the welding process. This is an expensive, time-consuming and materially wasteful process — to attain the necessary inert chemistry, several weld passes are made to build up the clad thickness. After each pass, a run of NDE is required to ensure that the clad is not only fully bonded to the substrate, or its previous clad layer, but also that there are no excessive defects such as cracks or high levels of porosity. The final clad layer is then machined back to attain the chemistry content and to provide a good-quality surface finish with a geometrically sound profile. In a typical cladding process, up to 60% of the laid-down clad could be machined away, making the current process wasteful.

The ideal cladding technique would lay down material onto the substrate in a single pass and would not require post-clad machining. The cost and time-savings associated with such a technique would be significant. One solution is to adopt an additive manufacturing process, known as diode laser powder deposition (DLPD). Cladding by DLPD is a deposition welding process in which a layer of metal powder (the clad) is deposited on the parent (the substrate) material. The two materials are fused by the energy provided by the laser and a metallurgical bond occurs. Figures 12.7 and 12.8 show the deposition of clad during proving trials.

This cladding technique offers high precision, a high level of automation, a robust and repeatable process and a clad-substrate interface with low dilution, thus attaining the necessary chemistry with a thin layer of clad deposit. This cladding technique is significantly quicker (see Table 12.1) than the existing weld-based technique and combined with a single-pass potential and the possibility of including an in-line NDE/process feedback system as a part of the cladding process, cladding of large vessels could be reduced from weeks to hours.

Conventional ammonia production uses natural gas, steam, and air to produce hydrogen and nitrogen using a two-step steam methane reforming process. The ammonia is synthesized using the Bosch process and by adding carbon dioxide from the reforming process to produce ammonia derivatives such as urea, nitric acid, and ammonium nitrate.

Three types of nuclear-integrated ammonia production are envisioned. The first case adds nuclear heat in the sulfur removal process and the primary reformer. The nuclear subsystem also provides power for compression, refrigeration, fans, and expansion. The second process bypasses the reformer and uses nuclear-generated hydrogen via HTSE. The hydrogen is used directly in the ammonia production process and is also combusted with air to produce the nitrogen needed for the process. Power is also applied to compression, fans, and expanders as in the previous case. The final case again uses HTSE to produce hydrogen, but the nitrogen is provided by an air separation unit, which requires power from the reactor. Ammonia production with nuclear integration would provide modest to large decreases in natural gas consumption (depending on the specific case) and very significant decreases in CO2 emissions (up to 99 percent reduction relative to traditional processes) [3, 23].

The basic R&D efforts made at the early development stage have been extended to develop the conceptual designs of KALIMER 150 and 600, and the basic key technologies over the past ten years since 1997 under the revised nuclear R&D program. According to the Nuclear Technology Roadmap established in 2005, an SFR was chosen as one of the most promising future types of reactors which could be deployable by 2030.

The KALIMER-600 features a proliferation-resistant core without blanket and a decay heat removal circuit (PDRC) using natural sodium circulation cooling for a large power system. In addition, a shortened IHTS piping and a seismic isolation are incorporated into the KALIMER-600 design. The KALIMER-600 conceptual design, which evolved on the basis of the KALIMER-150 design, was selected as

Figure 15.3 SFR R&D program (Korea). PRIDE, PyRoprocess Integrated inactive DEmonstration.

one of promising Gen-IV SFR candidates. R&D efforts have been made on the development of advanced design concepts including a supercritical CO2 Brayton cycle energy conversion system, design methodologies, computational tools and sodium technology.

Older large PWRs do not directly employ an automatic depressurization system (ADS). This can make it difficult to respond to a very small LOCA, because coolant pressure can hang above the discharge pressure of the high pressure injection pumps while coolant inventory is lost. Newer large Generation Ш+ PWRs, such as the AP1000 design, utilize ADSs to allow primary pressure to be rapidly reduced following a LOCA allow low pressure injection systems or gravity-fed water sources to supply water to the reactor to keep the core covered.

Smaller iPWR designs incorporate an ADS into the various protection schemes. This automatic depressurization provides the same function as it does for the newer Generation III+ passive reactor designs. In general, the automatic depressurization is initiated by opening valves connected to the pressurizer steam space. The steam is typically sparged into a water-filled storage tank inside containment or collected directly within the containment for recycling back into the core to keep the fuel covered. The contents of the containment water storage tank located high in containment can be gravity-fed into the reactor vessel after pressure has been reduced to atmospheric pressure.

5.2.3 Relief valves

All current large PWRs include safety relief valves to protect the RCS from exceeding the design pressure. The safety valves are connected to the separate pressurizer tank steam space via 6-inch (15 cm) pipe lines (NRC, 2012a). These safety valves relieve the pressurizer relief tank.

All iPWRs have the same need for safety relief valves to protect the RCS from exceeding the design pressure. Integral PWR safety valves are connected to the pressurizer steam space at the top of the integrated reactor pressure vessel. The connecting pipe would be much smaller than the 6-inch lines on a conventional PWR design. As with the ADS valves, the steam relieved from an iPWR is typically sparged into a water-filled storage tank inside containment or released directly into the containment environment. There is no pressurizer relief tank in an iPWR design.

The physical characteristics of new HSIs include devices that support multimodal interaction, such as touch screens, gesture interaction, speech recognition and synthesis, haptic input and output (that is, technologies that use touch and tactile feedback to enable HSI), and even direct body-machine interfaces (sensors). Advanced display and interaction features already available and under development make use of hand­held devices, head-mounted displays, large overview displays, three-dimensional (3-D) displays (with or without glasses), motion and position tracking. To support such extensive interaction capabilities, the whole system is typically driven by high — performance numerical and graphics processors for demanding applications such as high-resolution displays and computationally intensive applications like processing and trending of large amounts of plant data. (Several of the terms mentioned above may be unfamiliar to some readers; they will be explained a later.)

The implementation of advanced HSIs, as part of the complex socio-technical system of the NPP, requires an integrated approach based on the requirements of

Table 7.2 Continued

Speech recognition Manual scram button Diverse actuation controls

2.3 Output devices

2.3.1 Audio annunciators

Coded

Uncoded

2.3.2 Visual display units

Annunciators Overview displays Process displays Safety-related displays

Flat panel operator displays

Alarm annunciators:

SDCV (spatially dedicated constantly visible) displays

‘Status-at-a-glance’ overviews

Process flow displays

Mode/state displays

Sub-process display

Soft controls

Low-level system status displays

Trend displays

Faceplates

Diagnostic displays

Safety status displays

Event log displays

Dedicated safety-related displays

Post-event display panel

Printers

2.3.3 Hybrid input/output devices

Communication equipment

Intercom

Touchscreens

Intranet

Radio

Telephone

Portable/wearable devices

Tablets

Smartphones

PDAs

Barcode scanners RFID tags

both human and system components. One of the most reliable and effective ways to accomplish either a progressive HSI upgrade or a completely new design, is the integration of HFE with the systems engineering process (SEP) (Hugo, 2012). Systems engineering (SE) is the discipline needed to deliver coherent, cost-effective systems, of whatever nature, but HFE adds an important dimension by helping to integrate the whole system, that is, human plus equipment. The integration of human factors into the SEP considers the role of humans in the selection of HSI technology, and ultimately in the operation and maintenance of the plant at every stage of the system life cycle.

This systematic approach will ensure first of all that the human performance information necessary for engineering design, technology selection and development processes is acquired or developed even before the project starts. Secondly, it will ensure human factors evaluation of systems and operations throughout the project life cycle to identify problems and help engineers to define cost-effective solutions to achieve human and system performance enhancements. A lot of project case studies have proven that it is cheaper and more cost-effective to integrate human requirements early in the project rather than later (Hugo, 2012).

Any evaluation used to support decision-making or planned for wide distribution should include a peer review to ensure product quality. Two types of peer review have been widely used and provide different types of support:

• in-process peer review/steering committee;

• independent peer review of the completed analysis.

In-process peer review brings an expert group of practitioners and decision-makers into the process at regular intervals — perhaps once per quarter — to be briefed on the status of work and any known problem areas. Independent peer review allows objectivity through review of the finished product by independent outside experts who have not been involved in the evaluation. Both types of peer review have a potential role in proliferation resistance analysis.

Current emergency planning requirements for the US were established in NUREG — 0396 (EPA-520/1-78-016), and are incorporated in 10 CFR Part 50, Appendix E, ‘Emergency Planning and Preparedness for Production and Utilization Facilities’. These requirements establish a plume exposure pathway emergency planning zone (EPZ) of 10 miles (16 km), and an ingestion exposure pathway of about 50 miles (80 km) for large LWRs. Appendix E recognizes that certain reactor designs may warrant an exemption from these requirements on a-case-by-case basis. (See footnote 1 of Appendix E.) SMR designs offer a basis to revise these EPZs based on a significantly reduced potential for offsite releases from postulated accidents. The design-specific PRAs will provide a good basis to revise emergency planning requirements based on substantially reduced risk to public health and safety. With expected enhancements to SMR designs for safety, the NRC staff believes that SMRs may develop reduced EPZ sizes commensurate with their accident source terms, fission product releases, and accident dose characteristics.

The NRC staff analyzed the potential for reduced EPZ sizes in SECY-11-0152 (28 October 2011). It considered it acceptable for SMR vendors to establish an appropriately reduced EPZ size based on the factors noted above regarding source terms, releases and dose characteristics. The staff noted a need to further review the ‘modularity’ and ‘co-location’ of SMR reactors. This review will focus on the fact that several SMR designs will be based on multiple reactors being located together in a common facility. Vendors are designing these SMRs so that the reactor modules will be independent — i. e. an accident in one module will not initiate or exacerbate an event at another module. This independence permits smaller source terms and potential releases to the public. Based on these design considerations, the NRC will consider a scalable EPZ size based on offsite dose to the public, and emergency planning measures within the EPZ based on transient time and existing capabilities of federal, state and local response organizations. This approach would not result in a reduction to public health and safety.

Emergency planning size and response measures are important for international consideration and licensing. The NRC’s evaluation of this issue based on offsite dose considerations of new designs and appropriate response measures for the population at risk is instructive for international licensing. International licensing considerations for EPZ size and response measures are unique for extremely remote sites. The NRC has not considered extremely remote sites since there is no pending SMR application with a remote site under consideration.

Important to the US evaluation of reduced EPZ size and measures to be taken within the EPZ, is that response capabilities of offsite personnel and emergency organizations were bolstered significantly in response to the terrorists’ events of 11 September 2001. Federal and state response capabilities are bolstered by better equipment, communications, coordination, and training — all of which are important capabilities to respond to a nuclear event. Additionally, in the post-Fukushima environment, nuclear power operators are considering better coordination and integration of capabilities to respond to an operating plant event. International emergency planning licensing should also consider these factors on a country or regional basis.