Small Nuclear Power Reactors.

  • There is revival of interest in small and simpler units for generating electricity from nuclear power, and for process heat.
  • This interest in small and medium nuclear power reactors is driven both by a desire to reduce the impact of capital costs and to provide power away from large grid systems.
  • The technologies involved are very diverse.

As nuclear power generation has become established since the 1950s, the size of reactor units has grown from 60 MWe to more than 1600 MWe, with corresponding economies of scale in operation. At the same time there have been many hundreds of smaller power reactors built both for naval use (up to 190 MW thermal) and as neutron sourcesa, yielding enormous expertise in the engineering of small units. The International Atomic Energy Agency (IAEA) defines ‘small’ as under 300 MWe, and up to 700 MWe as ‘medium’ – including many operational units from 20th century. Together they are now referred to by IAEA as small and medium reactors (SMRs).  However, ‘SMR’ is used more commonly as acronym for Small Modular Reactors.

Today, due partly to the high capital cost of large power reactors generating electricity via the steam cycle and partly to the need to service small electricity grids under about 4 GWe,b there is a move to develop smaller units. These may be built independently or as modules in a larger complex, with capacity added incrementally as required (see section below on Modular construction using small reactor units). Economies of scale are provided by the numbers produced. There are also moves to develop small units for remote sites.  Small units are seen as a much more manageable investment than big ones whose cost rivals the capitalization of the utilities concerned.

This paper focuses on advanced designs in the small category, i.e. those now being built for the first time or still on the drawing board, and some larger ones which are outside the mainstream categories dealt with in the Advanced Reactors paper.   Note that many of the designs described here are not yet actually taking shape.  Three main options are being pursued: light water reactors, fast neutron reactors and also graphite-moderated high temperature reactors. The first has the lowest technological risk, but the second (FNR) can be smaller, simpler and with longer operation before refueling.

Generally, modern small reactors for power generation are expected to have greater simplicity of design, economy of mass production, and reduced siting costs. Most are also designed for a high level of passive or inherent safety in the event of malfunctionc. A 2010 report by a special committee convened by the American Nuclear Society showed that many safety provisions necessary, or at least prudent, in large reactors are not necessary in the small designs forthcomingd.

A 2009 assessment by the IAEA under its Innovative Nuclear Power Reactors & Fuel Cycle (INPRO) program concluded that there could be 96 small modular reactors (SMRs) in operation around the world by 2030 in its ‘high’ case, and 43 units in the ‘low’ case, none of them in the USA.  (In 2009 there were 133 units up to 700 MWe in operation and 16 under construction, in 28 countries, totaling 60.3 GWe capacity.)

A 2011 report for US DOE by University of Chicago Energy Policy Institute says development of small reactors can create an opportunity for the United States to recapture a slice of the nuclear technology market that has eroded over the last several decades as companies in other countries have expanded into full‐scale reactors for domestic and export purposes. However, it points out that detailed engineering data for most small reactor designs are only 10 to 20 percent complete, only limited cost data are available, and no US factory has advanced beyond the planning stages. In general, however, the report says small reactors could significantly mitigate the financial risk associated with full‐scale plants, potentially allowing small reactors to compete effectively with other energy sources. In January 2012 the DOE called for applications from industry to support the development of one or two US light-water reactor designs, allocating $452 million over five years.   Other SMR designs will have modest support through the Reactor Concepts RD&D program.

In March 2012 the US DOE signed agreements with three companies interested in constructing demonstration SMRs at its Savannah River site in South Carolina. The three companies and reactors are: Hyperion with a 25 MWe fast reactor, Holtec with a 140 MWe PWR, and NuScale with 45 MWe PWR. DOE is discussing similar arrangements with four further SMR developers, aiming to have in 10-15 years a suite of SMRs providing power for the DOE complex. DOE is committing land but not finance.  (Over 1953-1991, Savannah River was where a number of production reactors for weapons plutonium and tritium were built and run.)

The most advanced modular project is in China, where Chinergy is starting to build the 210 MWe HTR-PM, which consists of twin 250 MWt high-temperature gas-cooled reactors (HTRs) which build on the experience of several innovative reactors in the 1960s and 1970s.

Another significant line of development is in very small fast reactors of under 50 MWe. Some are conceived for areas away from transmission grids and with small loads; others are designed to operate in clusters in competition with large units.

Already operating in a remote corner of Siberia are four small units at the Bilibino co-generation plant. These four 62 MWt (thermal) units are an unusual graphite-moderated boiling water design with water/steam channels through the moderator. They produce steam for district heating and 11 MWe (net) electricity each. They have performed well since 1976, much more cheaply than fossil fuel alternatives in the Arctic region.

Also in the small reactor category are the Indian 220 MWe pressurised heavy water reactors (PHWRs) based on Canadian technology, and the Chinese 300-325 MWe PWR such as built at Qinshan Phase I and at Chashma in Pakistan, and now called CNP-300. These designs are not detailed in this paper simply because they are well-established. The Nuclear Power Corporation of India (NPCIL) is now focusing on 540 MWe and 700 MWe versions of its PHWR, and is offering both 220 and 540 MWe versions internationally. These small established designs are relevant to situations requiring small to medium units, though they are not state of the art technology.

Other, mostly larger new designs are described in the information page on Advanced Nuclear Power Reactors.

Medium and Small (25 MWe up) reactors with development well advanced

Name Capacity Type Developer
KLT-40S 35 MWe PWR OKBM, Russia
VK-300 300 MWe BWR Atomenergoproekt, Russia
CAREM 27-100 MWe PWR CNEA & INVAP, Argentina
IRIS 100-335 MWe PWR Westinghouse-led, international
Westinghouse SMR 200 MWe PWR Westinghouse, USA
mPower 125-180 MWe PWR Babcock & Wilcox + Bechtel, USA
SMR-160 160 MWe PWR Holtec, USA
SMART 100 MWe PWR KAERI, South Korea
NuScale 45 MWe PWR NuScale Power + Fluor, USA
 CAP-100/ACP100 100 MWe PWR CNNC & Guodian, China
HTR-PM 2×105 MWe HTR INET & Huaneng, China
EM2 240 MWe HTR General Atomics (USA)
 SC-HTGR (Antares) 250 MWe HTR Areva
SVBR-100 100 MWe FNR AKME-engineering (Rosatom/En+), Russia
 Gen4 module 25 MWe FNR Gen4 (Hyperion), USA
 Prism 311 MWe FNR GE-Hitachi, USA
FUJI 100 MWe MSR ITHMSO, Japan-Russia-USA


Light water reactors

These are moderated and cooled by ordinary water and have the lowest technological risk, being similar to most operating power and naval reactors today. They mostly use fuel enriched to less than 5% U-235 with no more than 6-year refueling interval, and regulatory hurdles are likely least of any SMRs.
US experience of small light water reactors (LWRs) has been of very small military power plants, such as the 11 MWt, 1.5 MWe (net) PM-3A reactor which operated at McMurdo Sound in Antarctica 1962-72, generating a total of 78 million kWh. There was also an Army program for small reactor development, most recently the DEER (deployable electric energy reactor) concept which is being commercialised by Radix Power & Energy. DEER would be portable and sealed, for forward military bases. Some successful small reactors from the main national program commenced in the 1950s. One was the Big Rock Point BWR of 67 MWe which operated for 35 years to 1997.  There is now a revival of interest in small LWRs in the USA, and some budget assistance in licensing two designs is proposed.

Of the following designs, the KLT and VBER have conventional pressure vessels plus external steam generators (PV/loop design). The others mostly have the steam supply system inside the reactor pressure vessel (‘integral’ PWR design). All have enhanced safety features relative to current LWRs.  All require conventional cooling of the steam condenser.

In the USA major engineering and construction companies have taken active shares in two projects: Fluor in NuScale, and Bechtel in B&W mPower.
Two new concepts are alternatives to conventional land-based nuclear power plants. Russia’s floating nuclear power plant (FNPP) with a pair of PWRs derived from icebreakers, and France’s submerged Flexblue power plant, using a 50-250 MWe reactor possibly to be derived from Areva’s latest naval design. The first is described briefly below and in the Russia paper, the second is mainly described in the France paper, since details of the actual reactor are scant.


Russia’s KLT-40S from OKBM Afrikantov is a reactor well proven in icebreakers and now – with low-enriched fuel – proposed for wider use in desalination and, on barges, for remote area power supply. Here a 150 MWt unit produces 35 MWe (gross) as well as up to 35 MW of heat for desalination or district heating (or 38.5 MWe gross if power only). These are designed to run 3-4 years between refuelling with on-board refuelling capability and used fuel storage. At the end of a 12-year operating cycle the whole plant is taken to a central facility for overhaul and storage of used fuel. Two units will be mounted on a 20,000 tonne barge to allow for outages (70% capacity factor).

Although the reactor core is normally cooled by forced circulation (4-loop), the design relies on convection for emergency cooling. Fuel is uranium aluminium silicide with enrichment levels of up to 20%, giving up to four-year refuelling intervals.  A variant of this is the KLT-20, specifically designed for FNPP. It is a 2-loop version with same enrichment but 10-year refueling interval.

The first floating nuclear power plant, the Akademik Lomonosov, commenced construction in 2007 and is planned to be located near to Vilyuchinsk. Due to insolvency of the shipyard the plant is now expected to be completed in 2014. 2 See also (see Floating nuclear power plants section in the information page on Nuclear Power in Russia).


OKBM Afrikantov is developing a new icebreaker reactor – RITM-200 – to replace the KLT reactors and to serve in floating nuclear power plants. This is an integral 210 MWt, 55 MWe PWR with inherent safety features. A single compact RITM-200 could replace twin KLT-40S (but yielding l

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