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Chapter05: Small Nuclear Power ReactorsEdited by Dr. Mir F. Ali

The International Atomic Energy Agency (IAEA) defines small as under 300 MWe, but accordingto the World Nuclear Association, in general, today 500 MWe might be, considered an upper limit

to Small Nuclear Power Reactors.

As nuclear power generation has become, established, since the 1950s, the size of reactor units hasgrown from 60 MWe to more than 1600 MWe, with corresponding economies of scale inoperation. At the same time there have been many hundreds of smaller reactors built both fornaval use (up to 190 MW thermal) and as neutron sources, yielding enormous expertise in theengineering of deliberately small units.

In addition to the main interest in small and simpler reactors for generating clean, safe, and cleanelectricity from nuclear power and for process heat is, driven both by a desire to reduce capitalcosts as well as to minimize the dependence upon large grid systems, here are some other reasons:

The flexibility as small reactors may be, built independently or as modules in a largecomplex with the option to increase capacity incrementally as required;

Small reactors are best suited for remote sites; Small reactors for power generation offer greater simplicity of design, economy of mass

production, and reduced sitting costs; and Small reactors are designed for a high level of passive or inherent safety in the even of

malfunction;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 operationaround the world by 2030 in its High case and 43 units in the Low case, none of them in the

USA.

Here are thehighlights of the activitieson small nuclear power reactors:

The most advanced modular project is in China, where Chinergy is preparing to build the210 MWe HTR-PM, which consists of twin 250 MWt reactors;

In South Africa, Pebble Bed Modular Reactor (Pty) Limited and Eskom had beendeveloping the pebble bed modular reactor (PBMR) of 200 MWt (80 MWe), but funding forthis project has been stopped;

A US group led by General Atomics is developing another design the gas turbine modularhelium reactor (GT-MHR) with 600 MWt (285 MWe) modules driving a gas turbine

directly, using helium as a coolant and operating at very high temperatures; 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-moderatedboiling water design with water/steam channels through the moderator. They producesteam for district heating and 11 MWe (net), electricity each. They have performed wellsince 1976, much more cheaply than fossil fuel alternatives in the Arctic region; and

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Also in the small reactor category are the Indian 220 MWe pressurised heavy water reactors(PHWR) based on Canadian technology, and the Chinese 300-325 MWe PWR such as builtat Qinshan Phase I and at Chashma in Pakistan, and now called CNP-300. The NuclearPower Corporation of India (NPCIL) is now focusing on 540 MWe and 700 MWe versionsof its PHWR, and is offering both 220 and 540 MWe versions internationally. These, smallestablished designs are relevant to situations requiring small to medium units, though they

are not state of the art technology.

Small nuclear power reactors are, classified into the following six categories as per the WorldNuclear Association (Updated 12 October 2010):

1. Light Water Reactors (LWR):US experience of small light water reactors (LWR) 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 inAntarctica 1962-72, generating 78 million kWh. There was also an Army program for small reactordevelopment, and 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.

The following designs, the KLT and VBER have conventional pressure vessels plus external steamgenerators (PV/loop design):

1. KLT-40S:Russia's KLT-40S from OKBM Afrikantov is a reactor well proven in icebreakers and nowproposed for wider use in desalination and, on barges, for remote area power supply. Here

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a 150 MWt unit produces 35 MWe (gross) as well as up to 35 MW of heat for desalination ordistrict heating (or 38.5 MWe gross if power only). These are, designed to run 3-4 yearsbetween refuelling with on-board refuelling capability and used fuel storage. At the end ofa 12-year operating cycle, the whole plant is, taken to a central facility for overhaul andstorage of used fuel. Two units will be, mounted on a 20,000 tonne barge to allow foroutages (70% capacity factor). Although the reactor core is normally, cooled by forced

circulation, the design relies on convection for emergency cooling. Fuel is uraniumaluminium silicide with enrichment levels of up to 20%, giving up to four-year refuellingintervals.

The first floating nuclear power plant, theAkademik Lomonosov, commenced constructionin 2007 and is, planned to be located near to Vilyuchinsk. The plant is due to be, completedin 2011;

2. VBER-150:A larger Russian factory-built and barge-mounted unit (requiring a 12,000 tonne vessel) isthe VBER-150, of 350 MWt, 110 MWe. It has modular construction and is, derived by OKBMfrom naval designs, with two steam generators. Uranium oxide fuel enriched to 4.7% hasburnable poison; it has low burn-up (31 GWd/t average, 41.6 GWd/t maximum) and eight-year refuelling interval; and

3. VBER-300OKBM Afrikantov's larger VBER-300 PWR is a 295 MWe unit, the first of which is plannedto be, built, in Kazakhstan. It was, originally envisaged, in pairs as a floating nuclear powerplant, displacing 49,000 tonnes. As a cogeneration plant, it is, rated at 200 MWe and 1900GJ/hr. The reactor is, designed for 60-year life and 90% capacity factor. It has four steamgenerators and a cassette core with 85 fuel assemblies enriched to 5% and 48 GWd/tUburn-up. Versions with three and two steam generators are, also envisaged, of 230 and 150MWe respectively. In addition, with more sophisticated and higher-enriched (18%) fuel in

the core, the refuelling interval can be pushed from two years out to 15 years with burn-upto 125 GWd/tU. A 2006 joint venture between Atomstroyexport and Kazatomprom sets thisup for development as a basic power source in Kazakhstan, then for export.

The following thirteen nuclear power reactor designs under this category, have, the steam supplysystem inside the reactor pressure vessel ('integral' PWR design). All nuclear power reactordesigns have, enhanced safety features relative to current LWR.

No Reactor Hyperlink to Description

1 RITM-200 OKBM Afrikantov is developing a new icebreaker reactor

2 VK-300 Another larger Russian reactor is the VK-300 boiling water reactor3 VKT-12 A smaller Russian BWR design is the 12 MWe, transportable VKT-124 ABV A smaller Russian OKBM Afrikantov PWR unit under development is

5 CAREM The CAREM reactor being developed by INVAP in Argentina, under

6 SMART On a larger scale, South Korea's SMART (System-integrated Modular

7 MRX The Japan Atomic Energy Research Institute (JAERI) designed the

8 NP-300 Technicatome (Areva TA) in France has developed the NP-300 PWR

9 NHR-200 The Chinese NHR-200 (Nuclear Heating Reactor) developed by

10 IRIS Westinghouse's IRIS (International Reactor Innovative & Secure) is

11 mPower In mid-2009, Babcock & Wilcox (B&W) announced its B&W

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12 NuScale A smaller unit is the NuScale multi-application small PWR, a 160

13 TRIGA The TRIGA Power System is a PWR concept based on General Atomics'

2. High-Temperature Gas-Cooled Reactors (HTR):Building on the experience of several innovative reactors built in the 1960s and 1970s, new high-temperature gas-cooled reactors (HTR), being developed. These reactors will be capable ofdelivering high temperature (up to about 1000C) helium either for industrial application via a

heat exchanger, or to make steam conventionally via a steam generator, or directly to drive aBrayton cycle gas turbine for electricity with almost 50 percent thermal efficiency possible(efficiency increases around 1.5 percent with each 50C increment). Improved metallurgy andtechnology developed in the last decade makes HTR more practical than in the past, though thedirect cycle means that there must be high integrity of fuel and reactor components.

Fuel for these reactors is in the form of TRISO (tristructural-isotropic) particles less than amillimetre in diameter. Each has a kernel (ca. 0.5 mm) of uranium oxycarbide (or uraniumdioxide), with the uranium enriched up to 20% U-235, though normally less. This is surroundedby, layers of carbon and silicon carbide, giving a containment for fission products which is stableto over 1600C.

There are two ways, in which these particles are, arranged: in blockshexagonal 'prisms' ofgraphite, or in billiard ball-sized pebbles of graphite encased in silicon carbide, each with about15,000 fuel particles and 9g uranium. There is a greater amount of used fuel than from the samecapacity in a light water reactor. The moderator is graphite.

HTR can potentially use thorium-based fuels, such as highly enriched or low-enriched uraniumwith Th, U-233 with Th, and Pu with Th. Most of the experience with thorium fuels has been inHTR. With negative temperature coefficient of reactivity (the fission reaction slows astemperature increases) and passive decay heat removal, the reactors are inherently safe. HTR

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therefore do not require any containment building for safety. They are sufficiently small to allowfactory fabrication, and will usually be, installed below ground level.

Here are some major designs, which are, covered under this category:

No Reactor Hyperlink to Description

1 HTTR,GHTR Japan Atomic Energy Research Institute's (JAERI's), High2 HTR-10 China's HTR-10, a 10 MWt high-temperature gas-cooled3 HTR-PM Construction of a larger version of the HTR-10, China's HTR

4 PBMR South Africa's pebble bed modular reactor (PBMR) draws on

5 GT-MHR A larger US design, the Gas Turbine - Modular Helium Reactor

6 EM2 In February 2010, General Atomics announced a modified version of

7 Antares Another full-size HTR design is the Antares reactor being put

8 Adams Engine A small HTRconcept is the Adams Atomic Engines' 10 MWe direct

9 MTSPNR A small Russian HTR which was being developed by the N.A

3. Liquid Metal-Cooled Fast Neutron Reactors:

Fast neutron reactors have no moderator, a higher neutron flux and are normally, cooled by liquidmetal such as sodium, lead, or lead-bismuth, with high conductivity and boiling point. Theyoperate at or near atmospheric pressure and have passive safety features, (most have convectioncirculating the primary coolant). Automatic load following is, achieved due to the reactivityfeedbackconstrained coolant flow leads to higher core temperature, which slows the reaction.Primary coolant flow is by convection. They typically use boron carbide control rods.

Here are the major designs under this category:No Reactor Hyperlink to Description

1 Hyperion PowerModule

The Hyperion Power Module is a 70 MWt/25 MWe

2 ENHS The Encapsulated Nuclear Heat-Source is a liquid metal-cooled

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3 STAR_LM,STAR-H2,SSTAR:

The Secure Transportable Autonomous Reactor

4 ARC-100 Advanced Reactor Concepts LLC (ARC) is commercializing

5 LSPR A lead-bismuth-eutectic (LBE) cooled fast reactor of 150

6 Rapid-L A small-scale design developed by Toshiba Corporation in

7 PRISM GE with the US national laboratories had been developing

8 BREST Russia has experimented with several lead-cooled reactor9 TWR An old design has resurfaced as the Travelling Wave Reactor

10 Korean FastReactor Designs

In South Korea, the Korea Atomic Energy Research

4. Molten Salt Reactors (MSR):During the 1960s, the USA developed the molten salt breeder reactor concept as the primary back-

up option for the fast breeder, reactor (cooled by liquid metal) and a small prototype 8 MWtMolten Salt Reactor Experiment (MSRE) operated at Oak Ridge over four years. U-235 fluoridewas in molten sodium and zirconium fluorides at 860C that flowed through a graphitemoderator. There is now renewed interest in the concept in Japan, Russia, France and the USA,and one of the six Generation IV designs selected for further development is the molten saltreactor (MSR).

In the MSR, the fuel is a molten mixture of lithium and beryllium fluoride salts with dissolvedenriched uranium, thorium or U-233 fluorides. The core consists of unclad graphite moderatorarranged to allow the flow of salt at some 700C and at low pressure. Heat is, transferred to asecondary salt circuit and thence to steam. It is not a fast neutron reactor, but with somemoderation by the graphite is epithermal (intermediate neutron speed). The fission productsdissolve in the salt and are removed continuously in an on-line reprocessing loop and replacedwith Th-232 or U-238. Actinides remain in the reactor until they fission or are converted to higher

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Thermal power can be 50-300 MW at low temperature and pressure, and low enriched uraniumfuel used. However, recovering desired isotopes on a continuous production basis remains to be,demonstrated. As well as those in solution, a number of volatile radioisotopes used in nuclearmedicine can be, recovered from the off-gas arising from radiolytic boiling. For isotopes such aSr-89, this is very much more efficient than alternative production methods.

At the end of 2007, Babcock & Wilcox (B&W) notified the US Nuclear Regulatory Commissionthat it intended to apply for a licence to construct and operate a Medical Isotope ProductionSystem (MIPS)an AHR system with low-enriched uranium in small 100-200 kW units for Mo-99production. A single production facility could have four such reactors. B&W expects a five-yearlead-time to first production. The fuel is, brought to criticality in a 200-litre vessel. As fissionproceeds, the solution is circulated through an extraction facility to remove the Mo-99 and thenback into the reactor vessel, which is at low temperature and pressure. In January 2009, B&WTechnical Services Group signed an agreement with radiopharmaceutical and medical devicesupplier Covidien to develop technology for the MIPS.

6. Modular Constitution Using Small Reactor Units:The IRIS developers have outlined the economic case for modular construction of their design(about 330 MWe), and the argument applies similarly to other smaller units.

They point out that IRIS with its size and simple design is ideally suited for modular constructionin the sense of progressively building a large power plant with multiple small operating units. Theeconomy of scale is, replaced here with the economy of serial production of many small andsimple components and prefabricated sections. They expect that construction of the first IRIS unitwill be, completed in three years, with subsequent reduction to only two years.

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Site layouts have been developed with multiple single units or multiple twin units. In each case,units will be, constructed so that there is physical separation sufficient to allow construction ofthe next unit while the previous one is operating and generating revenue. In spite of thisseparation, the plant footprint can be very compact so that a site with three IRIS single modulesproviding 1000 MWe capacity is similar or smaller than one with a comparable total power singleunit.

Eventually IRIS is, expected to have a capital cost and production cost comparable with largerplants. However, any small unit such as this will potentially have a funding profile and flexibilityotherwise impossible with larger plants. As one module is finished and starts producing electricity,it will generate positive cash flow for the next module to be, built. Westinghouse estimates that1000 MWe delivered by three IRIS units built at three-year intervals financed at 10 percent for tenyears require a maximum negative cash flow less than $700 million (compared with about threetimes that for a single 1000 MWe unit). For developed countries small modular units offer theopportunity of building as necessary; for developing countries it may be the only option, becausetheir electric grids cannot take 1000+ MWe single units.

The next chapter will cover Advanced Nuclear Power Reactors.