Small modular reactors that are being developed or had been developed by the Russian ‘Afrikantov Experimental Design Bureau for Mechanical Engineering’ (OKBM Afrikantov) include:

• KLT-40S reactor for the twin unit barge-mounted (floating) NPP with a co-generation option;

• ABV reactor for the twin unit barge-mounted or land-based NPP with a co-generation option;

• RITM-200 reactor for a new generation multi-purpose nuclear ice-breaker, with a potential of being considered further for the barge-mounted and land-based NPPs.

All of the above-mentioned designs are indirect cycle PWRs. In most cases twin units with such reactors are being considered as standard plant configurations. Multi-module plant configurations are not being considered for any of the OKBM Afrikantov designs. The design and operating characteristics of these SMRs are summarized in Table 17.1, and the core and fuel design characteristics in Table 17.2.

The most mature of the SMR designs by OKBM Afrikantov is the KLT-40S reactor of 38.5 MW(e) per module. It has a submarine prototype experience of several thousands of reactor-years and an ice-breaker prototype experience of nearly 300 reactor-years. The KLT-40S design appears to be similar to a conventional PWR reactor with separate vessels accommodating the reactor core and internals, the main circulation pumps, the pressurizer and the steam generators (see Figure 17.1). Control rod drives are external and located above the reactor vessel lid. However, in the KLT-40S case all separate vessels are compact and connected by short pipelines with vessel penetrations in the hot legs. The piping is double wall and incorporates so-called narrowing devices near the penetrations. All modules are connected with brackets fixed by bolts and nuts to restrict possible leaks in the case of a pipe rupture (not shown in Figure 17.1). All primary coolant systems are located within the primary pressure boundary. The above mentioned features effectively reduce the scope and magnitude of possible loss-of-coolant accidents (LOCAs). The refueling is performed in batches every 45-46 months.

The ABV design shown in Figure 17.2 is also backed by some prototype operation experience, the details of which have not been disclosed. It incorporates an integral primary circuit design with in-vessel steam generators. However, the pressurizer and the control rod drives are external. The core design and dimensions are similar to those of the KLT-40S. The reactor is refueled at the factory each 12 years (whole core refueling). To support achieving a long refueling interval, chromium-nickel alloy is used as cladding material instead of the traditional zirconium alloy. The newer version of the ABV reactor employs pumps for the primary circulation, while the older version relied on natural circulation of the primary circuit (ARIS, 2013). The RITM-200 — the newest of all SMR designs presented in this section — has a

Table 17.1 Design and operating characteristics of SMRs from OKBM Afrikantov Characteristic KLT-40S (ARIS, 2013) ABV (ARIS, 2013) RITM-200 (Kessides and Kuznetsov, 2012) Electric/thermal power, MW 2 X 38.5 (non­electrical applications disabled)/2 X 150 2 X 8.5/2 X 38 2 X 50/2 X 175 Non-electrical products Heat for district heating: 2 X 25 GCal/hour, or potable water: 20 000-100 000 m3/ day Heat for district heating: 2 X 12 Gcal/hour, or potable water: 20 000 m3/day 30 MW(e) of shaft power per module; 248 t/h of steam at 295 °C, 3.82 MPa Plant configuration Twin-unit for a barge-mounted NPP Twin-unit for a barge-mounted NPP land — based plant option Twin-unit nuclear icebreaker reactor NPP option to be considered Construction period, months/mode of operation 48/load following 48/load following <48/enhanced load following Thermodynamic cycle type/efficiency Indirect Rankine steam condensing cycle/23.3% Indirect Rankine steam condensing cycle/21% Indirect Rankine steam condensing cycle/28.6% Primary circulation Forced Forced Forced Primary pressure, MPa 12.7 15.7 Increased against KLT-40S Core inlet/outlet temperatures, °C 280/316 248/327 280/312 Mode of reactivity control in operation Mechanical control rods with external drives No liquid boron. Mechanical control rods with external drives Liquid boron. Mechanical control rods with external drives No liquid boron Reactor vessel diameter x height, mm 2176 X 4148 2135 X 4479 Increased against KLT-40S Secondary pressure, MPa 3.82 3.14 Not specified, but similar to KLT-40S Steam generator (SG) secondary side inlet/outlet temperatures, °C 170/290 106/290 Not specified, but similar to KLT-40S (Continued)

Table 17.1 Continued Characteristic KLT-40S (ARIS, 2013) ABV (ARIS, 2013) RITM-200 (Kessides and Kuznetsov, 2012) Turbine type Two condensing — extraction steam turbines, one per each reactor Two condensing — extraction steam turbines, one per each reactor Not specified, electric propulsion Instrumentation and control system Based on the state- of-the-art for PWR and marine reactors Based on the state- of-the-art for PWR and marine reactors Based on the state- of-the-art for PWR and marine reactors Containment type and dimensions, m Primary rectangular steel containment 12 X 7.92 X 12 Secondary containment: rectangular steel system of compartments, 15000 m3 Primary rectangular steel containment 5.1 X 4 X 7.5 Secondary containment: rectangular steel system of compartments Primary rectangular steel containment 6 X 6 X 15.5 Secondary containment: rectangular steel system of compartments Plant surface area, m2 Coast: 8000 Water area: 15 000 Coast: 6 000 Water area: 10 000 Limited to the ice­breaker

per-module electrical output of 50 MW(e). It incorporates the experience in design and operation of many of the Russian marine propulsion reactors. Like ABV, RITM-200 has an integral primary circuit design with in-vessel steam generators (see Figure 17.3). The pressurizer and the control rod drives are again external. The core design and dimensions are modified against those of the KLT-40S (see Table 17.2), but exact data on these modifications is not available. The reactor employs forced circulation of the primary coolant provided by the main circulation pumps, as shown in Figure 17.3. The reactor is refueled at the refueling base each 4.5-7 years (whole core refueling). Chromium-nickel alloy is used as cladding material instead of the traditional zirconium alloy (Veshnyakov, 2011).

The SMR designs from OKBM Afrikantov have the following common design features:

• All reactors are being designed for twin unit plant configurations with individual turbine generators in the power circuits of each of the reactors.

• Flexible co-generation options (production of heat for residential heating or superheated process steam or seawater desalination) are being provided for in the designs as options.

• Construction period is typically 4 years (perhaps, somewhat shorter for the newest RITM — 200).

• All designs provide for load following capability.

• The fuel is UO2 in inert matrix within the cylindrical fuel elements and the fuel enrichment is always below 20%, even for the ice-breaker reactor RITM-200.

Table 17.2 Core and fuel design characteristics of SMRs from OKBM Afrikantov Characteristic KLT-40S (ARIS, 2013) ABV (Aris, 2013) RITM-200 (Kessides and Kuznetsov, 2012) Electric/thermal power, MW 2 X 38.5 (non­electrical applications disabled)/2 X 150 2 X 8.5/2 X 38 2 X 50/2 X 175 Core diameterxheight, mm 1155 X 1200 1155 X 1200 1550 X 1650 Average core power density, MW/m3 119.3 30 ~ 45 Average fuel element linear heat rate, W/ cm 140 65 Several times less than in the KLT-40S Fuel material UO2 in inert matrix UO2 in inert matrix UO2 in inert matrix Fuel element type Smooth-rod, cylindrical Smooth-rod, cylindrical Smooth-rod, cylindrical Cladding material Zirconium alloy Chromium-nickel alloy Chromium-nickel alloy Fuel element outer diameter, mm 6.8 6.9 No information Lattice geometry Triangular Triangular Triangular Number of fuel elements in fuel assembly 69, 72, 75 69, 72, 75 No information Number of fuel assemblies in the core 121 121 199 Burnable absorber Gadolinium Gadolinium Gadolinium Enrichment of the reload fuel, 235U weight % 15.7 18.7 <20 Interval between refuelings, months 45.4 288 54 — first units 84 — serial units Average fuel burn-up, MWday/kg 45.5 49 45-47 Mode of refueling Refueling in batches on the barge Whole core refueling (factory maintenance of the barge is carried out every 288 months) Refueling at a base

Exchanger of i circuits

Hydraulic

accumulator

Figure 17.1 Layout of the KLT-40S reactor (ARIS, 2013).

• All designs, including those with the integral primary circuit, have external control rod drives, external pumps and external pressurizers which use gas as a working medium to ensure a slow response of the primary pressure to rapid changes of the core temperature.

• Mechanical control rods are used for reactivity control in all designs and, additionally, liquid boron system is used in the ABV reactor only.

• The average fuel burn-up is within the range of 45-49 MWday/kg, i. e., below the values achieved in the state-of-the-art NPPs with large reactors.

• All designs employ double containments.

The major differences between the designs are as follows:

• The KLT-40S employs an older compact modular design of the primary circuit, while the ABV and the RITM-200 employ integral designs of the primary circuit with in-build steam generators.

• The KLT-40S is refueled in a conventional batch mode each four years while the ABV and the RITM-200 provide for factory refueling with a longer interval between refueling of up to 7-12 years.

Reactor

Figure 17.2 Layout of the ABV reactor, reproduced with permission by the IAEA from reference IAEA (2007).

• Chromium-nickel alloy is used as cladding material in the ABV and the RITM-200 to ensure operation with a long interval between refuelings.

• Liquid boron system is used for reactivity control in the ABV design, while no such system is being provided for in the KLT-40S and RITM-200 designs.

Comparison of the SMR designs from OKBM Afrikantov indicates the designers prefer to follow an evolutionary approach within which new components are introduced with caution and that well-proven components are used in new designs whenever applicable. The major new direction is related to the integral design of the primary circuit within which only steam generators are being placed inside the reactor vessel. The integral design makes it possible to increase electric output (compare KLT-40S and RITM-200 in Table 17.1) and reduces the dimensions and the mass of a nuclear island (for a twin unit plant the corresponding reduction in mass is from 1770 t (KLT-40S) to 1100 t (RITM-200)). The core design of the RITM-200 also makes it possible to increase by a factor of 20 the number of cycles of power change allowed during the core’s lifetime (Veshnyakov, 2011).

The overall approach to safety design is similar to that of the state-of-the-art PWRs, with some features borrowed from the experience of the marine propulsion reactors. The designers have attempted to eliminate or de-rate as many accidents as possible ‘by design’ and then dealt with the remaining ones by plausible combinations of the redundant and diverse active and passive systems (IAEA, 2009). A short summary of the safety design features incorporated in the SMRs from OKBM Afrikantov is provided below, in line with the defence in depth strategy defined in the Safety Standard No. SSR-2/1 Safety of Nuclear Power Plants: Design, Specific

Main circulation pump

Safety Requirements (IAEA, 2012a). The focus is on design features specific for the addressed SMRs.

According to IAEA (2012a), cited with permission by the IAEA, ‘the purpose of the first level of defence is to prevent deviations from normal operation and the failure of items important to safety’. For this level the OKBM designs provide ‘sound and conservative designs, siting, construction, operation and maintenance’ and, specifically (IAEA, 2007, 2009; ARIS, 2013; Veshnyakov, 2011):

• negative reactivity coefficients over the whole operation cycle;

• compact modular designs with no long pipelines (KLT-40S) or integral primary circuit designs with minimized reactor pressure vessel penetrations (ABV, RITM-200), to eliminate or de-rate certain groups of LOCA;

• eliminated liquid boron system (KLT-40S, RITM-200).

‘The purpose of the second level of defence is to detect and control deviations from normal operational states in order to prevent anticipated operational occurrences at the plant from escalating to accident conditions’ (IAEA, 2012a). Specific systems and features are provided in the OKBM Afrikantov designs to support meeting the objective of Level 2, including (IAEA, 2007, 2009; ARIS, 2013; Veshnyakov, 2011):

• state-of-the-art I&C systems based on PWR and marine propulsion reactor experience;

• redundant and diverse reactor shutdown systems (e. g., control rods driven by gravity, force of springs and mechanically);

• relatively large coolant inventory and high heat capacity of the primary circuit or nuclear installation as a whole, resulting in larger thermal inertia of the system;

• external pressurizers operated on gas medium to ensure slow primary pressure increase in transients.

‘For the third level of defence, it is assumed that, although very unlikely, the escalation of certain anticipated operational occurrences or postulated initiating events might not be controlled at a preceding level and that an accident could develop. In the design of the plant, such accidents are postulated to occur. This leads to a requirement that inherent and/or engineered safety features, safety systems and procedures be provided that are capable of preventing damage to the reactor core or significant off-site releases and returning the plant to a safe state’ (IAEA, 2012a).

To meet the objective of Level 3 the OKBM designs include redundant and diverse active and passive reactor shut down, emergency core cooling and residual heat removal systems (ARIS, 2013; IAEA, 2007, 2009; Veshnyakov, 2011). In this, they are more on the side of the state-of-the art Russian VVER type reactors, as passive decay heat removal systems are seldom found in the designs of the previous-generation marine propulsion reactors.

‘The purpose of the fourth level of defence is to mitigate the consequences of accidents that result from failure of the third level of defence in depth. The most important objective for this level is to ensure the confinement function’ (IAEA, 2012a). To meet this objective, all of the OKBM Afrikantov SMR designs provide for in-vessel retention of corium without a core catcher. The following features support achieving this quality:

• relatively low core power density (all designs omit KLT-40S) (see Table 17.1)

• active and passive systems of reactor vessel cooling.

In addition to this, all designs incorporate double containments (see Table 17.1) and active and passive containment cooling systems.

Finally, ‘the purpose of the fifth and final level of defence is to mitigate the radiological consequences of radioactive releases that could potentially result from accident conditions’ (IAEA, 2012a). To meet this objective, all OKBM Afrikantov SMR designs provide for on-site and off-site emergency measures and off-site emergency planning zones. However, the requirements to off-site emergency planning are reduced compared with those in place for conventional NPPs with large reactors. As an example, cited with permission by the IAEA from IAEA (2012a), the on-site and off-site emergency planning measures for a barge-mounted plant with the two KLT-40S reactors are as follows:

• Staff presence in the compartments adjacent to the containment and in other compartments with high radiation level to be excluded;

• To limit radiation dose to the population living within a 1 km radius from the floating NPP, depending on the actual radiation situation, some protection measures such as iodine prophylaxis or sheltering will be implemented;

• Temporary limitation will be established on the consumption of some agricultural products grown within a radius of 0.5 km from the ‘floating’ plant, when contaminated with radioactive release;

• Evacuation of the population is not required at any distance from the ‘floating’ NPP.

The SMR designs from OKBM Afrikantov incorporate protection against external event impacts. The plants are being designed for the design earthquake frequency 10-2/ year and the maximum design earthquake frequency 10-4/year, with maximum design earthquake 8 on the MSK scale (pre-Fukushima Daiichi data) (IAEA, 2009). In this, the equipment, machinery, systems important for safety and their mounting are designed for 3g Peak Ground Acceleration (PGA). They remain operable under inclination and heaving, typical of a floating NPP operation conditions (IAEA, 2009).

In addition to the above-mentioned, the designs of the barge-mounted plants take into account the external events specific of a barge-mounted NPP, such as the following (cited with permission by the IAEA from IAEA, 2009):

• Sinking of the floating NPP;

• Grounding, including that on a rocky ground;

• Collisions with other ships;

• Fall of a military aircraft onto the plant from a high altitude;

• Blockage of water intakes by debris from another ship;

• Helicopter crash-landing on a floating NPP.

Except for a nuclear ice-breaker plant with the two RITM-200 reactors, barge — mounted NPPs are being designed to produce energy only when rigidly moored to a shore (or a shore fixed structure) (IAEA, 2009). Plant mooring devices provide for plant retention at a tsunami wave height of up to 4 m. Barge-mounted plants are being designed to be moored in a bay protected by a dam (Sozonyuk, 2011) (see Figure 17.4).

The probabilistic safety analysis performed for the KLT-40S and ABV-based barge-mounted plants indicates the core damage frequency (CDF) is 10-6/year, while the large early release frequency (LERF) is 10-7/year (ARIS, 2013). These numbers are similar to the values typical of the state-of-the-art large NPPs with large reactors (ARIS, 2013).

In 2013, the pilot barge-mounted NPP with the two KLT-40S reactors, named ‘Akademik Lomonosov’, was under the final stages of construction in St Peterburg, Russia, with no additional R&D for this project being required. Subject to the results of pilot plant operation, the design features and main technical solutions developed for the barge are planned to be used in full in new generations of ‘floating’ NPPs,

equipped with nuclear reactors of other types. Specifically, it is planned to be done for the barge-mounted plant with the two ABV reactors.

The previous design of the barge-mounted plant with the two ABV reactors had already been licensed for construction and operation, but requests of customers in the Russian north indicate that a longer core lifetime is preferable in targeted locations. Negotiations with potential customers are in progress to tailor plant characteristics to their requests. Specifically, R&D is on-going to develop and validate the ABV core design with 12 year refueling interval with the initial enrichment of fuel by 235U not exceeding 20%.

For the new RITM-200 ice-breaker reactor, design has been completed and approved in March 2013, followed by the bidding which has been won in April 2013 by the ZiO-Podolsk Plant of the joint stock company (JSC) Atomenergomash. ZiO Podolsk will construct the nuclear installation, while the rectors will be assembled at OKBM Afrikantov. No additional R&D is needed for this design.