Power plant design

Small is not new

13 November 2009

B&W's mPower reactor is not the only small reactor to hit the market. By Judith Perera

Some 28 small reactors (<300MWe) are currently in operation worldwide, and six new units with small reactors are under construction: three 220MWe PHWRs in India, one 300MWe PWR in Pakistan, and a floating NPP with two 35MWe KLT-40S reactors in Russia.

According to the International Atomic Energy Agency, there is continued interest from member states in small and medium reactors (SMRs) i.e. those rated at less than 700MWe. SMRs are often aimed at niche markets such as countries with small electricity grids, to supply energy to remote areas or for special applications, such as heat supply for district heating, desalination of seawater, enhanced oil recovery and coal conversion. These markets differ from those in which large nuclear power plants operate in that they have different investment requirements, siting flexibility and grid/infrastructure restrictions. Comparing a single SMR to a larger plant on an economies-of-scale basis is irrelevant. However a series of SMRs combined to achieve the same power capacity could be considered comparable.

The IAEA is preparing a report highlighting the economics and investment-related factors affecting SMR competitiveness, as well as the tools available to judge these factors. ‘Approaches to Assess Competitiveness of SMRs’ is due to be finalized before the end of 2009. In parallel the agency is conducting case studies to highlight the benefits of SMRs versus larger reactors for different deployment strategies and conditions. These case studies are also due to be finalized before the end of the year.

Vladimir Kuznetsov of the IAEA Nuclear Power division told NEI that small reactors have a number of benefits. These include: the small absolute capital outlay; adaptability the conditions where larger reactors do not fit (due to grid constraints, infrastructure restrictions, investment requirements etc); a robust safety case owing to the incorporation of inherent and passive safety design features; and smaller source term (hazard) resulting from smaller fuel inventory and smaller non-nuclear energy stored in the reactor.

“There are no specific drawbacks but generally small reactors will have higher specific overnight costs in $/kWe. To a certain extent that could be counteracted by the effect of accelerated learning, etc. when several small reactors are build in series to reach the same capacity as that of a large reactor,” says Kuznetsov.

Some 40 SMRs are now at different stages of development or design. About a dozen are at advanced design stages and could be deployed within the next decade. These include integral PWR designs (IRIS, SMART, CAREM), floating NPPs (KLT-40S), high temperature gas reactors (PBMR, HTR-PM) and India’s advanced heavy water reactor (AHWR).

Small contenders


The International Reactor Innovative and Secure (IRIS) is a 335MWe pressurised light water cooled reactor. The reactor vessel houses not only the nuclear fuel, control rods and neutron reflector, but also all the major reactor coolant system components including pumps, steam generators and pressurizer. IRIS has been under development by an international consortium (led by Westinghouse) since 1999.


SMART is a 330MWt pressurised water reactor with integral steam generators and advanced passive safety features. Developed by the Korea Atomic Energy Research Institute it is designed for generating electricity up to 100MWe and for cogeneration applications.


Argentina is developing an indigenous SMR known as CAREM and plans to build a 27MWe prototype (CAREM-25) in 2011 to demonstrate the technology. The distinct design features of the CAREM are: integral primary cooling system with in-vessel steam generators, control rod drives, and pressurizer; self-pressurization; and passive safety systems.


Twin KLT-40S reactors will be used in Russia’s first floating NPP, Akademik Lomonosov, scheduled for completion in 2011. The factory-built PWRs, similar to those used in Russia’s nuclear powered icebreakers, can produce 300MWt/70MWe for electricity generation or cogeneration of electricity and heat. The KLT-40S was developed by Russia’s OKBM (experimental design bureau for machine building).

Toshiba 4S

In Japan, the 4S (super-safe, small and simple) reactor is under development by Toshiba, with outputs of 30MWt and 135MWt. It is a pool type sodium cooled fast reactor with a core lifetime of about 30 years. The 4S has reached detailed design stage and pre-licensing negotiations with the US Nuclear Regulatory Commission were started in 2007.


China’s 200MW modular HTR-PM is a high temperature gas cooled reactor with pebble bed fuel and indirect supercritical steam energy conversion cycle. Full-scale demonstration is planned for 2013. Two-module plant configuration is foreseen for the commercial version.

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SMRs on the radar in the USA
B&W to open mPower test centre in Virginia
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