Most iPWR SMR designs aim to balance the use of proven LWR technology with the novel solutions necessary to exploit unique characteristics and potential advantages of SMRs. Thus, it comes as no surprise that developing, analyzing, licensing and ultimately deploying SMRs require testing and validation beyond and on a scale larger than that for ‘traditional’ large loop PWRs.

Testing of components and systems may be hierarchically divided into:

• engineering development tests;

• separate effects component tests;

• integral effects tests;

• integral primary configuration test facilities;

• prototypes.

Engineering development tests aim to demonstrate feasibility and verify engineering capability before fabricating final components. Separate effects component tests examine the design, fabrication, operation and qualification of large-scale prototypic components. They may include accelerated aging, irradiation, seismic testing, etc., and establish performance of components. They also provide data for validation of computer codes. Integral effects tests examine and demonstrate integrated performance of combined systems or features, typically in a scaled setup. They may be used to show interaction between systems, including safety and non-safety systems. They also may provide thermal-hydraulic performance parameters for models and analysis, and be used to validate codes. Integral primary configuration test facilities are clearly of particular interest for iPWR SMRs since the integral primary configuration is the main difference to the existing, operating loop PWRs. They employ electrically heated rods to simulate the reactor core and are used to demonstrate the overall

Table 8.3 Summary of safety-related characteristics for selected integral designs CAREM25 IRIS mPOWER NuScale RITM-200 SIR SMART W-SMR Argentina International USA USA Russian Federation USA, UK Republic of Korea USA CNEA Consortium Babcock & Wilcox NuScale Power OKBM Afrikantov Combustion Engineering KAERI Westinghouse Power level (MWth) 100 1000 530 160 175 1000 330 800 Power level (MWe) 27 335 180 45 50 320 100 225 Primary circuit circulation Natural Forced Forced Natural Forced Forced Forced Forced Fully internal pumps n/a Yes No n/a No No No No Soluble boron-free Yes No Yes No Yes Yes No No core Internal CRDMs Hydraulic Electromag. Electro­ Hydraulic No No No No Electromag. Safety systems Passive Passive Passive Passive (*) Passive Active and passive Passive DHRS Passive Passive Passive Passive (*) Passive Passive Passive CDF Target 1.0 X 10-7 ~1.0 X 10-8 ~10-8 ~1.0 X 10-8 (*) (*) 1.0 X 10-6 Target 1.0 X 10-7 (*) LERF Target 1.0 X 10-8 ~1.0 X 10-9 (*) (*) (*) (*) Target 1.0 X 10-8 (*) NOTES: 1. Table prepared based on public information, mainly from the IAEA ARIS database (IAEA, 2012a). 2. Single unit power level quoted. Most designs consider multi-module siting. 3. CDF = core damage frequency, per reactor-year. 4. LERF = large and early release frequency, per reactor year. 5. n/a = not applicable. 6. (*) = information not available in considered references.

normal and off-normal performance of the whole system and validate system codes. For the same reason, several iPWR concepts are considering or have decided to build a scaled-down prototype. A prototype uses nuclear heat, i. e. it is a critical reactor. Notably, CAREM-25 (IAEA, 2012a) is a 27 MWe prototype for a larger 100-200 MWe commercial version. According to IAEA (2012a), site excavation work for CAREM-25 was completed at the end of August 2012, and construction has begun. As quoted by the World Nuclear News (http://www. world-nuclear — news. org/), in December 2013, the contract for the reactor vessel was awarded, and, according to the Comision National de Energia Atomica (CNEA), the unit is currently scheduled to begin cold testing in 2016 and receive its first fuel load in the second half of 2017.

Engineering development tests for iPWR SMRs are driven by the novel components, or components used in a novel way, as compared to loop PWRs. Depending on the specific iPWR design, this may include, among others: fuel and fuel assembly, internal control rod drive mechanism (electro-magnetic or hydraulic), fully immersed pumps, integral steam generators (frequently with helical coils or multi-stage), integral pressurizer or self-pressurizing systems, and novel instrumentation to address specific needs of integral systems, e. g. flow measurements and nuclear safety instrumentation (Petrovic et al., 2005).

Illustrative examples (listing only a portion of the intended testing) include the following:

• mPower has invested over $100M in a component testing program and integrated system test (IST) facility. It is conducting or planning tests on reactor coolant pumps, CRDMs, fuel, steam generator and emergency high pressure condenser (Azad, 2012; www. babcock. com/products/Pages/IST-Facility. aspx).

• NuScale planned or is performing tests that include steam generators, CRDMs, fuel bundles (Ingersoll, 2012). NuScale has also commissioned a multi-module control room simulator laboratory with 12 independent module simulators, to demonstrate multi-module operation, since the basic configuration of NuScale power plant will include 12 45 MWe modules (Ingersoll, 2012; www. nuscalepower. com).

• Westinghouse is planning a similar series of tests, has already built two full-scale fuel assemblies and has been testing internal CRDMs for its SMR (Kindred, 2012).

Separate effects component tests also reflect iPWR SMR technical features. They may be related or extend engineering development tests beyond the development, and may consider operation and qualification of large-scale prototypic components, including accelerated aging and irradiation testing. Some typical examples include:

• verifying heat transfer characteristics if novel heat exchanger type(s) are considered for primary or decay heat removal;

• steam generators’ long-term inspectability and maintenance;

• main coolant pump operability and long-term performance;

• in-core instrumentation performance and long-term operability;

• fuel assembly performance (vibrations, seismic response).

Integral effects tests are intended to verify coupled performance and interaction between systems and may include (depending on the iPWR design):

• testing coupled performance of steam generator and emergency heat removal system

(EHRS);

• reactor vessel and containment or guard vessel interaction;

• reactor coolant system and ADS (automated depressurization system) coupled

performance.

Of particular importance for iPWR are phenomena related to natural circulation (IAEA, 2005b). This is due to the fact that most of the concepts incorporate passive, natural circulation-driven, decay heat removal systems. Some of the lower-power concepts (e. g. CAREM-25, 27MWe; NuScale, 45 MWe) also employ natural circulation for heat removal in normal full-power operation. A number of tests, related to specific passive systems, are planned, aiming to better understand the phenomena, demonstrate performance of the systems, and validate codes and methodologies needed for design and licensing.

As already mentioned, integral configuration test facilities are indispensable for validation of system models and accurate simulation of the whole system, and as the basis for licensing. Proper scaling is perhaps the most important preparation task for integral testing; it allows replicating correct physics and validating codes even though the geometry itself is not necessarily prototypical in all aspects, and the tests are electrically, not nuclear heated. A hierarchical, two-tiered scaling analysis (H2TS) (Zuber, 1991) provides a framework for systematical decomposition that includes the system, subsystems, modules, constituents, geometrical configurations, physical phases (gas, liquid, and solid), fields and phenomena. Some examples of such facilities are provided below.