Category Archives: Nuclear Reactors 1

Sodium cooled fast reactors

In the second half of 2010, there were only two operating sodium cooled fast reactors worldwide, the BN-600 in the Russian Federation and the restarted MONJU in Japan. In the past, there were more sodium cooled fast reactors (the last of the two units in France was shut down early in 2010), and several such reactors are expected to start operation in the coming years (in China, India and the Russian Federation) [4.4].

There are two advanced SMR designs in the sodium cooled fast reactor category — the Japanese 4S of 10 MWe and the US PRISM reactor of 311 MWe (840 MWth). The 4S is a pool-type reactor with an intermediate heat transport system and metallic U-Zr fuel. The basic characteristics of the 4S and PRISM are given[27] in Table 4.5. The PRISM reactor is intended to be fuelled with metallic UPuZr fuel using plutonium and depleted uranium from used light water reactor fuel.

The 4S is different from typical past and present sodium cooled fast reactors in that it is being designed for:

• 30 years of continuous operation on a site without reloading or shuffling of fuel;

• whole core refuelling on the site after the end of a 30-year operation cycle.

Подпись: Box 4.3. Sodium fast reactors Sodium has high heat capacity, allowing linear heat generation rates in the reactor core as high as 485 W/cm, but reacts exothermically with air and water. For this reason all sodium cooled fast reactors incorporate an intermediate heat transport system with secondary sodium as a working fluid. Primary sodium delivers heat generated in the reactor core to an intermediate heat exchanger located within the reactor vessel (pool type reactor) or outside (loop type reactor). Secondary sodium delivers core heat to the steam generators located reasonably far from the reactor in a dedicated premise to localise the impacts of still possible steam-sodium reaction. Indirect Rankine cycle on superheated steam is used for power conversion. Using three circuits is not favourable to the plant’s economics, but operation at relatively high temperatures (~530oC at core outlet) gives higher thermodynamic cycle efficiency in sodium cooled fast reactors, ~42% compared to 32-36% in PWRs. Primary and intermediate sodium circuits operate at a very low pressure of ~0.3 MPa. The space over the sodium pool surface in the reactor pressure vessel is typically filled with a low pressure inert gas, such as argon. Conventional sodium cooled fast reactors use forced circulation of the primary and secondary sodium in normal operation. The systems of decay heat removal are typically active. To be competitive economically, sodium cooled reactors target high fuel burn-ups of up to 130 MWday/kg. In most cases they are being designed in view of operation with the future closed nuclear fuel cycles. Positive experience of operation of fast sodium cooled reactors with oxide and metallic (U-Zr, U-TRU-Zr) fuel exists [4.12].

Although it has a very long core lifetime, the 4S offers a very small linear heat rate of 39 W/cm in the core and yields an average fuel burn-up of only 34 MWday/kg at the end of a long operation cycle. Correspondingly, the Rankine cycle efficiency is only 33% compared to 42% reached in other sodium cooled fast reactors.

The 4S uses non-conventional mechanisms of reactivity control in operation and reactor shut down, and utilises decay heat removal systems that are all passive and operate continuously. These mechanisms and safety design features of the 4S are described in Section 8.6.

The reactor vessel is thin and tall (3.55^24 m) and the containment, provided by the guard vessel and the concrete silo with a top dome in which the reactor is located, is compact.

Table 4.5. Basic characteristics of advanced SMR designs — sodium cooled fast reactors

SMR Design Principal designer, Country

Thermal/Electric output, MW (gross)

Availability/ Plant lifetime

Construction period/ Land-based or floating

Mode of refuelling/ Refuelling interval

Mode of deployment/ Plant configuration



50 MWe option

12 months on the site

Distributed or concentrated

Toshiba Corporation,

95%/ 30 years

Whole core/30 years

Japan [4.2]


General Electric, USA [4.44]

840/311 WMe


In batches/12-24 months

The 4S is designed for both distributed or concentrated deployment. Different from other known sodium cooled fast reactors, the 4S provides for an option of hydrogen (and oxygen) co-production with high temperature electrolysis.

United States (Alaska)

For the third evaluation case, reference [7.7] indicates the generation costs across Alaska (US) vary between 9.3 and 450 USD/MWh (110-540 USD/MWh in 2009 USD), which exceeds the typical costs in the US contiguous forty eight states by factors of three to ten [7.8]. The climatic and siting conditions in Alaska are similar to those in the northern parts of the Russian Federation and Canada and, therefore, the requirements for NPPs would also be similar. From the economic standpoint, it can be seen that all of the SMRs from Table 7.7 that would meet these requirements could be competitive in particular territories of Alaska. For example, the 4S plant (see Table 4.5 in Section 4.2.5) was originally considered for deployment in the city of Galena in the Alaska state.

Current Status, Technical Feasibility and Economics of Small Nuclear Reactors


Larger nuclear reactors typically have lower specific costs due to the economy of scale, resulting in nuclear power plants with reactors of 1 000-1 600 MWe being most commonly commercialised today.

However, there is currently a growing trend in the development and commercialisation of small and medium-sized reactors (SMRs), i. e. reactors with effective electric power less than 700 MWe. The main arguments in favour of SMRs are that they could be suitable for areas with small electrical grids and for remote locations, and that due to the smaller upfront capital investment for a single SMR unit the financial risks associated with their deployment would be significantly smaller than for a large reactor. This offers flexibility for incremental capacity increases which could potentially increase the attractiveness of nuclear power to investors.

This report is a summary of the development status and deployment potential of SMRs. It brings together the information provided in a variety of recent publications in this field, and presents the characterisation of SMRs currently available for deployment and those that are expected to become available in the next 10-15 years. Additionally, it highlights the safety features and licensing issues regarding such reactors.

Particular attention is given to the economics of SMRs, and the various factors affecting their competitiveness are analysed and discussed. Vendors’ data on the economics of different designs are compared with independent quantitative estimates of the electricity generating costs, and the deployment potential of such reactors in a number of markets and geographic locations is assessed.

This report was prepared by Vladimir Kuznetsov, Consultant, and Alexey Lokhov of the NEA Nuclear Development Division.

Detailed review and comments were provided by Ron Cameron and Marco Cometto of the NEA Nuclear Development Division, with other reviews and input from members of the NEA Nuclear Development Committee.

. Economy of multi-module plants

While twin-units of nuclear power plants exist and the cost reduction factors for them are known and defined by equations (6.9) and (6.10), no experience data is currently available for multi-module nuclear plants. The apparent reason is that multi-module nuclear power plants have never been built. However, with reference to the current safety rules that prohibit safety system sharing among different reactor modules [6.10], near term multi-module plants could be reasonably approximated by sequentially built twin-units. Then, the evaluations provided in Sections 6.2.1-6.2.4 would apply.

In addition to this, reference [6.1] mentions that “for a 5-6 unit plant capital costs may be 15-17% lower than for the basic two-unit plant”. If we apply this to a 300 MWe marine derivative or the integral design PWR discussed in Section 6.2.4 and use the same assumptions, a five-module NPP with such reactors may have the overnight capital costs that are about 7 — 38 % higher (at a 5% discount rate) compared to those of a NPP with a single large PWR of 1 500 MWe, see Table 6.10.

Reduced staffing requirements

Simplified operation and maintenance requirements are targeted by the designers of many advanced SMRs [9.2 and 9.4]. Reduced requirements to operation and maintenance are generically translated into reduced staffing requirements, and such requirements may challenge the corresponding national regulatory norms, specifically, if the latter are defined on a capacity-independent basis. For example, in some national regulations the requirements to have security staffing are independent of plant capacity, which is likely to pose a challenge to small NPPs designed for distributed deployment to serve the needs of small local communities in isolated areas. The corresponding revision or amendment of the regulatory norms will be required in such cases, and the updates need to be initiated in due time not to slow down the overall licensing process.

The issue of reduced off-site emergency planning requirements is addressed in more detail in the following section.

Safety features and licensing of SMRs

Safety features of SMRs

The safety aspects of SMRs have been intensively discussed in several recent publications, mostly originating from the International Atomic Energy Agency (IAEA), which are summarised below. However, one should keep in mind that the safety features of SMRs will be re-analysed following the Fukushima Dai-ichi accident in order to take into account the lessons learnt from it.

The major findings regarding SMR safety are the following:

• The designers of advanced SMRs aim to implement safety design options with maximum use of inherent and passive safety features (also referred to as “by design” safety features).

• On their own, the “by design” safety features used in SMRs are in most cases not size — dependent and could be applied in the reactors of larger capacity. However, SMRs offer broader possibilities to incorporate such features with higher efficacy.

• In the case of some technologies (such as high-temperature gas reactors), the incorporation of passive safety features limits the reactor capacity.

• All of the SMR designs considered here aim to meet international safety norms, such as those formulated in the IAEA Safety Standard NS-R-1 Safety of the Nuclear Power Plants: Design Requirements, regarding implementation of the defence-in-depth strategy and provision of redundant and diverse, active and passive safety systems.

• The available information on safety features of advanced SMRs for plant protection against the impacts of natural and human-induced external events is generally sparser compared to that on internal events.

• The core damage frequencies (CDFs) indicated by the designers of advanced SMRs are comparable to, or even lower than the ones indicated for the state-of-the-art, large water — cooled reactors.

Evaluation of SMR deployment potential

7.2.1 SMR designs selected for the evaluation of deployment potential in niche markets

Deployment potential was evaluated for typical SMRs of the PWR type presented in Table 7.1. The independently estimated ranges of LUEC values given in Table 7.3 were used for the evaluation. Table 7.7 summarises the plant configurations with SMRs for which the evaluations were performed. For convenience, letter codes were attributed to each of the SMRs to denote plant configuration. The letter codes are decrypted as follows:

• PWR — pressurised water reactor;

• number, for example, -8 or -335, — electric output per reactor module;

• S — plant with a single reactor module;

• T — twin-unit plant;

• TT — two twin-unit plants;

• M — modular plant (with 5 or 6 reactor modules);

• B — barge-mounted plant;

• L — land-based plant;

Подпись: PWR-125ML five module plant
Подпись: PWR-335TTL two twin-units
Подпись: IRIS (USA) 53-56
Подпись: 1 340 Подпись: n/a 83-90 n/a

The LUEC estimates in Table 7.7 are given for 5 % and a 10 % discount rate, and also with or without taking into account the heat credit from Table 7.6, to enable evaluation of the deployment potential of SMR plants operating in a co-generation mode.

Total electric

LUEC at 5%

LUEC at 5%

LUEC at 10%

LUEC at 10%

Plant configuration

output of the

Based on

discount rate,

discount rate,

discount rate,

discount rate,

plant (net) MWe

USD per MWh

USD per MWh[59] [60]

USD per MWh

USD per MWh*




twin-unit barge-







PWR-35TB twin-unit barge — mounted











single module








Table 7.7. Advanced SMRs (PWRs) for which the evaluations were performed taking into account the

heat credit (where applies)







twin-unit barge-











PWR-302TL twin-unit land — based





34-38 75-81


large interconnected electricity grids (“on-grid” locations). Another segment of electricity markets associated with isolated or remote locations with small, local electricity grids or with no grids at all (“off-grid” locations) will be considered in more detail in Section 7.2.5.

The evaluations were performed for several electricity markets in Brazil, China, Japan, the Republic of Korea, the Russian Federation, and the United States, separately at a 5% and 10% discount rate. The selected countries represent both developed and transitional economies. No countries from the European Union were considered since SMRs are currently not considered for near term deployment in this region of the world.

Safety features of advanced SMRs

The study analyses the most recent publications on SMR safety, in a large part originating from the International Atomic Energy Agency (IAEA). However, one should keep in mind that the safety features of SMRs will be re-analysed following the Fukushima Dai-ichi accident in order to take into account the lessons learnt from it.

The main conclusions regarding advanced SMR safety are as follows:

• The designers of advanced SMRs aim to implement safety design options with the maximum use of the inherent and passive safety features (also referred to as “by design” safety features). [83]

• In the case of some technologies (like high temperature gas reactors) the incorporation of passive safety features limits the reactor capacity.

• All of the SMR design concepts addressed in this study aim to meet the international safety norms, such as formulated in the IAEA Safety Standard NS-R-1 “Safety of the Nuclear Power Plants: Design Requirements”, regarding implementation of the defence-in-depth strategy and provision of the redundant and diverse active and passive safety systems.

• The available information on safety features of advanced SMRs for plant protection against the impacts of natural and human-induced external events is generally sparser compared to that on the internal events. A certain synergy in coping with the internal and external events is provided by broader incorporation of the inherent and passive safety features (“by design” safety features).

• The core damage frequencies (CDFs) indicated by the designers of advanced SMRs are comparable to, or even lower than the ones indicated for the state-of-the-art large water cooled reactors.

Lead-bismuth cooled fast reactors

There is no operational experience with commercial lead-bismuth-cooled fast reactors in any country of the world. The Russian Federation is the only country that had used the technology of lead — bismuth eutectics coolant and produced and operated small marine propulsion reactors[28] with such coolant, gaining a cumulated 80 reactor-years experience of their operation in nuclear submarines. However, the lead-bismuth-cooled reactors in these Russian submarines were not fast reactors. A moderator (BeO) was used to soften the neutron spectrum.

A principal technical issue with the lead-bismuth eutectics is the corrosion of the fuel element claddings and structural materials in the coolant flow. Corrosion is temperature-dependent and, according to multiple studies performed worldwide [4.12], is easier to cope with at lower temperatures. In the Russian Federation the technology for reliable operation of stainless steel based structural materials in lead-bismuth eutectics was developed, allowing a reactor core continuous operation during seven to eight years within a moderate temperature range below ~500oC[29]. The technology includes chemical control of the coolant.

Another issue with the lead-bismuth eutectics is related to its relatively high melting point of 125oC, which requires continuous heating of the lead-bismuth coolant to prevent possible damage of the reactor internals due to coolant expansion in phase transition. In the Russian Federation they have developed and tested a safe freezing/unfreezing procedure for lead-bismuth cooled reactor cores based on the observance of a particular temperature-time curve.

One more issue with the lead-bismuth cooled reactors is related to the accumulation of volatile 210Po — a strong toxic alpha emitter. Polonium-210 is generated from 209Bi under irradiation and has a

half-life of about 138 days. In the Russian Federation, techniques to trap and remove 210Po have been developed. However, the presence of 210Po is by itself an incentive to consider complete factory fabrication and fuelling for a lead-bismuth cooled reactor.

Otherwise, lead-bismuth eutectics is chemically inert in air and water, has a very high boiling point of 1 670oC, a very high density and a large specific heat capacity which enable an effective heat removal. Also, owing to a freezing point of 125oC, lead-bismuth eutectics solidifies in ambient air contributing to the effective self-curing of cracks if they ever appear in the primary lead-bismuth coolant boundary.

For reasons mentioned above, a typical lead-bismuth cooled fast reactor design concept would be a two-circuit indirect cycle plant. Different from sodium, lead-bismuth cooled fast reactors do not use intermediate heat transport system.

The basic characteristics of the three lead-bismuth cooled SMR design concepts considered in this report are presented in Table 4.6[30]. Of the three SMRs, only the SVBR-100 has reached a degree of maturity with the detailed design development currently being in progress.

image075 image076 image077 image078 image079 image080

Table 4.6. Basic characteristics of advanced SMR designs — lead-bismuth cooled fast reactors


NUTRECK SNU, Republic of Korea [4.14]

Factory fabricated and

Distributed or

70/ 25 per module Not specified

21 months on the site

fuelled/ 10 (5-15)

concentrated/Single or


multi-module plants

100/37 >95%/ 60 years

Not defined Factory fabricated and

fuelled/ 20 years


New Hyperion Power Module

Hyperion Power Generation, USA [4.15]

All SMR designs are within 25-100 MWe range, with the New Hyperion Power Module being the minimum and SVBR-100 being the maximum. All designs are pool type reactors employing an indirect Rankine steam cycle for generating electricity. All designs are factory fabricated and fuelled reactors that are operated at very low, gravity defined primary pressures and are intended for 7-20 years of continuous operation without refuelling on site. Of the three, the Russian SVBR-100 has the shortest burn-up cycle duration of seven to eight years and does not rely on natural convection of the primary coolant in normal operation.

All lead-bismuth cooled fast SMRs are land-based reactors, although a barge-mounted option has been considered for the SVBR-100. Multi-module plant configurations are indicated for the SVBR-100 and the New Hyperion Power Module. For the SVBR-100, two concepts of such plants of a 400 MWe and a 1 600 MWe overall capacity have been elaborated at a design level [4.5].

The projected plants lifetimes are 50-60 years, and the targeted capacity factor is 95% or higher.

Owing to full factory fabrication and fuelling of the reactor modules, the targeted construction period is very short, 3.5 years for the SVBR-100 and 1.75 years for the New Hyperion Power Module.

When described, the reactor pressure vessels are compact, with the maximum dimension not exceeding 10 m, and in the case of the SVBR-100 — 7 m. External cooling of the reactor vessel by air is provided in the PASCAR, while the SVBR-100 and the New Hyperion Power Module are immersed in water pools. Safety implications of these and other safety design features of the lead — bismuth cooled SMRs are explained in Section 8.7.

The SVBR-100 and the New Hyperion Power module provide for a start-up fuel load based on the uranium of slightly less than 20% enrichment. PASCAR is being considered to operate with U-TRU fuel loads in a closed nuclear fuel cycle. The fuel burn-ups are reasonably high, 60-70 MWday/kg.

Summary of SMR competitiveness in “off-grid” applications

The evaluation performed in this section has identified several potential niche markets for SMRs, in particular remote areas with severe climatic conditions hosting mining, refinement enterprises or military bases, and the affiliated small settlements.

On a purely economic basis, isolated islands and small off-grid settlements in populated developing countries (e. g. Indonesia, India) could also become potential market[65].

It was shown that a variety of land-based and barge-mounted SMR plants with substantially higher LUEC could still be competitive on these markets on condition that the plants meet certain technical and infrastructure requirements defined by the specific climate, siting and access conditions of the targeted locations.

In these niche markets, SMRs are not competing with large reactors, the competition will be only with the non-nuclear energy options available or possible for the specific locations.

Co-generation appears to be a common requirement for SMRs in niche markets. More niche markets for advanced SMRs could probably be found if the investigations of this kind are continued.

The evaluation performed in this section, which considered the generation of electricity or the production of electricity and heat in remote or isolated “off-grid” locations, has found many cases when small barge-mounted NPPs with the PWR-8 and PWR-35 twin-units (based on the Russian ABV and KLT-40S designs) are competitive.


[7.1] IEA/NEA (2010), Projected Costs for Generating Electricity: 2010 Edition, OECD Publications,

Paris, Table 3.7a on page 59.

[7.2] IAEA (2006), Status of Innovative Small and Medium Sized Reactor Designs 2005: Reactors

with Conventional Refuelling Schemes, IAEA-TECDOC-1485, Vienna, Austria.

[7.3] Babcock & Wilcox Modular Nuclear Energy (2010), “B&W mPower Brochure”:

www. babcock. com/library/pdf/E2011002.pdf

[7.4] IEA (2010), Electricity Information 2010, OECD Publications, Paris, France.

[7.5] Order #216-e/2 of the Russian Federal Tariff Service (22 September 2009):

www .fstrf. ru/tariffs/info_tarif/ electro/0

[7.6] National Energy Board of Canada (2010):

www. neb. gc. ca/clf-nsi/mrgynfmtn/prcng/lctrct/cndnndstry-eng .html

[7.7] US-DOE-NE Report to Congress (2002), “Small Modular Nuclear Reactors”. Available at a

DOE web site: www. doe. gov.

[7.8] IAEA (2007), Status of Small Reactor Designs without On-site Refuelling, IAEA-TECDOC-

1536, Vienna, Austria.

[7.9] IEA (2008), “Energy Policy Review of Indonesia”:

www. iea. org/textbase/nppdf/free/2008/Indonesia2008.pdf

[7.10] PPEN-BATAN (2008), Nuclear Desalination Technology Application Study, BATAN, Indonesia.

[7.11] Webb, J. (2005), “Daring to be different: India has bold plans for a nuclear future”, New Scientist, issue: www. newscientist. com

[7.12] Government of India, ”Northern Regional Power Committee” — Annual Report 2008-2009: www. nrpc. gov. in

[7.13] “The Commercial Outlook for U. S. Small Modular Nuclear Reactors”, U. S. Department of Commerce, International Trade Administration, February 2011. Available at:

http://trade. gov/publications/pdfs/the-commercial-outlook-for-us-small-modular-nuclear-reactors. pdf