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Progress in Nuclear Energy 50 (2008) 242e250www.elsevier.com/locate/pnucene

Options for small and medium sized reactors (SMRs) to overcomeloss of economies of scale and incorporate increased proliferation

resistance and energy security

Vladimir Kuznetsov*

International Atomic Energy Agency (IAEA), Wagramer Strasse 5, P.O. Box 100, A-1400 Vienna, Austria

Abstract

The designers of innovative small and medium sized reactors pursue new design and deployment strategies making use of certain advantagesprovided by smaller reactor size and capacity to achieve reduced design complexity and simplified operation and maintenance requirements, andto provide for incremental capacity increase through multi-module plant clustering. Competitiveness of SMRs depends on the incorporated strat-egies to overcome loss of economies of scale but equally it depends on finding appropriate market niches for such reactors. For many less de-veloped countries, these are the features of enhanced proliferation resistance and increased robustness of barriers for sabotage protection thatmay ensure the progress of nuclear power. For such countries, small reactors without on-site refuelling, designed for infrequent replacementof well-contained fuel cassette(s) in a manner that impedes clandestine diversion of nuclear fuel material, may provide a solution. Based onthe outputs of recent IAEA activities for innovative SMRs, the paper provides a summary of the state-of-the-art in approaches to improveSMR competitiveness and incorporate enhanced proliferation resistance and energy security.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Small and medium sized reactors; Competitiveness; Proliferation resistance; Energy security; Small reactors without on-site refuelling

1. Introduction

As of 2006, 138 small and medium sized reactors (SMRs)1

were operated worldwide, accounting for 61.6 GW(e) or16.7% of the world nuclear electricity production, and 10more were under construction2 (IAEA, 2006a) to add another3.6 GW(e). This fact points to an ongoing interest in MemberStates in the development and application of SMRs. In thenear term, most new nuclear deployments are likely to be evo-lutionary plants building on proven systems while incorporat-ing technological advances and often the economies of scale,

* Tel.: þ43 1 2600 22820; fax: þ43 1 2600 29598.

E-mail address: v.v.kuznetsov@iaea.org1 According to the classification used by IAEA, small reactors are reactors

with an equivalent electric power less than 300 MW, medium sized reactors

are reactors with an equivalent electric power between 300 and 700 MW.2 The total number of nuclear power plants (NPPs) operated in 2006 was

442, and 28 new NPPs were under construction.

0149-1970/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.pnucene.2007.11.006

resulting from the reactor outputs of up to 1600 MW(e). Forthe longer term, the focus is on innovative designs aimingto provide increased benefits in the areas of concern associ-ated with further expansion of nuclear power, as well as to of-fer a variety of energy products and flexibility in siting andfuel cycle options. Many innovative designs are reactorswithin the small-to-medium size range (IAEA, 2005a, 2006b).

About 60 concepts and designs of innovative small and me-dium sized reactors (SMRs) are analyzed or developed withinnational or international programmes in Argentina, Brazil,China, Croatia, France, India, Indonesia, Italy, Japan, the Re-public of Korea, Lithuania, Morocco, Russian Federation,South Africa, Turkey, USA, and Vietnam (IAEA, 2006b). In-novative SMRs are under development for all principal reactorlines and some non-conventional combinations thereof. Theprojected timelines of readiness for deployment are between2010 and 2030. Innovative design approaches aim to provideincreased benefits in plant competitiveness and proliferationresistance, and to offer increased energy security.

243V. Kuznetsov / Progress in Nuclear Energy 50 (2008) 242e250

2. Market potential of SMRs

Having foregone the economies of scale at the outset, de-signers of SMRs are targeting those customers to whom largeeconomy of scale plants would be ill suited. Notwithstandingthe fact that SMRs may still have higher specific capital costs,they offer other features that could be beneficial for certaincategories of customers, such as:

� Countries with small and medium electricity grids;� Villages and towns and energy intensive sites in off-grid

locations;� Rapidly growing cities in developing countries;� In a more distant future, perhaps, merchant type plants3 for

non-electric energy services.

Much of the world’s land mass supports sparse populationsand is unsupportable by an electric grid (US-DOE-NE, May2002). The northern extremes of the North American andEurasian continents are sparsely populated; the villages andtowns are widely separated and are un-serviced by road, rail,or electrical grid. Examples include northern Alaska, Canada,and Siberia. For example, two-thirds of Russia’s territory areoff-grid and can be expected to remain so for decades if not for-ever. Nonetheless, population centres, such as villages and smalltowns, and industrial sites in these off-grid areas require energy,both as electricity and as district heating.

Island countries face a similar challenge for electricity de-livery to widely dispersed population centres located on scat-tered islands separated by miles of ocean. Indonesia, a countryof 13,700 islands, is perhaps the most dramatic example(Su’ud, 2003). Many island villages require more thanelectricity e desalinated water often comprises an additionalnecessary energy service.

The potential market for support of off-grid villages andtowns is not confined to arctic and island regions. The govern-ment of India has identified 80,000 villages that are likelynever to be connected to the grid (Webb, 2005). The vast rea-ches of Brazil and Argentina contain hinterlands of low popu-lation density where grid emplacement is not cost effective.

For customers of this category, the difficulties attendant tofuel supply cause busbar energy cost to significantly exceedthe rates experienced on well-developed urban grids. For ex-ample, in northern Canada, busbar costs of 9e13 US$ cent/kW(e)-hour are typical; across Alaska the rates vary between9.3 and 45 US$ cent/kW(e)-hour (US-DOE-NE, May 2002).These exceed typical costs in the U.S. contiguous 48 statesby factors of 3e10.

Harvesting of natural resources is among the first steps forattracting foreign investment and initiating economic develop-ment in many developing countries and/or in sparsely settledregions. The economic activity of a majority of the remote

3 Merchant generation companies who operate outside the regulatory frame-

work of regulated utilities and sell their product on a competitive market (i.e.,

they receive no guarantee of profitability in exchange for a guarantee of pro-

viding services to consumers).

villages is tied to harvesting of natural resources, such as min-ing, drilling, logging, fishing, etc. Along with permanent vil-lages, dedicated work camps can be established temporarilyto staff those harvesting activities.

Because of their remoteness and constrained transportationinfrastructure, economic competitiveness of the harvested re-source may require energy not only to harvest but also toadd value to the raw product prior to shipping. For example,mines invest energy to mill the ore prior to shipping; fisheriesuse energy to process and pack the catch prior to shipping;loggers employ energy to produce paper, etc.

A market niche for nuclear power plants with SMRs could,therefore, also be that of off-grid industrial applications, sup-porting the energy intensive processes, which harvest andadd value to natural resources.

It is expected that the growth of developing countries wouldtake place faster in the coming decades (Nakicenovic et al.,1998; Bugliarelo, 1999). Nuclear energy may be required tofill a growing market share of world’s primary energy supplyin the future because its large resource base and its avoidanceof greenhouse gas emissions are favourable features for sus-tainable development. Whereas in the past, nuclear deploy-ments have been predominantly in developed countries, allprojections forecast that the dominant energy capacity addi-tions will occur in the currently developing economies (Naki-cenovic et al., 1998). SMRs can be designed to meet the needsof these emerging energy markets where industrial/technicalinfrastructure is generally poor. They could also provide addi-tional assurances of energy security without exacerbating therisk of proliferation.

The truly massive future growth in energy demand wouldbe for support of cities throughout the developing world;that is where energy infrastructure deployments could domi-nate throughout the 21st century. The projection for massiveenergy demand growth in cities of the developing world canbe understood as the product of population growth, rural-to-urban demographic migrations, and economic development(Bugliarelo, 1999). By 2015, there would be more than 903cities in Asia; 225 cities in Africa, and 25 cities in Latin Amer-ica. More than 368 of these cities will have more than 1 mil-lion people each. Collectively, these cities would account forabout 1.5e2.0 billion people.

Nuclear may eventually play a major role here; however,the features of nuclear deployments must be tailored to thecustomer’s situation. Local grids can be small as city develop-ment starts. Economy of scale deployments may be inappro-priate to the initially small needs. The financial conditionsfaced by many developing cities may favour small initial cap-ital outlay, with incremental additions deployed as populationgrows, as energy input per capita increases, and as the city be-comes wealthier. To accommodate rapid growth but shortageof initial financing, a ‘‘just-in-time’’ capacity growth planwould be appropriate. Therefore, the SMR reactor plantsmust be designed to be easily expandable into clusters com-prising ever-larger power installations.

The non-electric markets for nuclear energy potentially in-clude seawater desalination, district heating, low temperature

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

1,1

0 1 2 3 4 5 6 7 8 9Number in the series

La

bo

r in

te

ns

ity

, re

l. u

nits

year 1

year 2

year 4

year 4

year 5

year 6

year 7

year 8 2 years

Fig. 1. Impact of production process continuity on labor intensity in serial pro-

duction of marine-propulsion reactor plants e there was a 2-year interval be-

tween the production of the second and third plants; the third and fourth plants

were produced in the same year (OKBM, Russian Federation).

244 V. Kuznetsov / Progress in Nuclear Energy 50 (2008) 242e250

process heat, and high temperature heat (including a potentialfor hydrogen manufacture by water splitting). These marketsare likely to be served by commercial entities, which are sep-arate from electric utilities, and for which financing relies oncommercial bank loan rates or usual rates of return on investorequity. Design requirements for extreme levels of reliabilityand safety apply to the non-electric applications because ofthe necessity to site process heat sources close to population(and industrial) centres.

The business opportunities for non-electric nuclear energyservices do not necessarily fall under the governance of elec-tric utilities. At least in the more distant future, deployments ofsuch plants could be made under merchant plant financing ar-rangements, for which payback period must be short, internalrate of return on investment must be high, and financial riskminimization would be at a premium. This would make the fi-nancing needs very similar to those of fast growing cities indeveloping countries.

A survey of the market potential for SMRs indicates thatmarket penetration requires:

(a) The initial buy-in cost and the ongoing cost of energy tobe competitive with the prices of the competition that isavailable to the customers (in general, costs in developingcountries are higher or even much higher than found in de-veloped countries serviced by interconnected grids andmassive customer bases).

(b) Beyond cost considerations, market penetration requiresthat SMRs meet the customer’s non-cost-related needsbetter than does the competition available to them.

3. Strategies for SMR competitiveness in targetedmarkets

To achieve plant competitiveness in targeted markets, de-signers of innovative SMRs worldwide follow several com-mon strategies in plant design, such as (IAEA, 2005a, 2006b):

� To reduce plant complexity by eliminating as many possi-ble accident initiators and/or consequences as possible bydesign, taking advantage of small-to-medium reactor ca-pacity and size;� To reduce operation and maintenance (O&M) costs by re-

ducing operating staff number and required skill levelthrough:

- Reducing the number of systems, structures and com-ponents that require maintenance;

- Relying more on reactor self-control in normal opera-tion and in accidents; in some cases, using passiveload follow control;

- In some cases, outsourcing the refuelling operations toa specialized vendor team;

� To increase energy conversion efficiency by applyinghigher core outlet temperatures and advanced energy con-version cycles, such as the Brayton cycle;� To incorporate bottoming cogeneration cycles, in some

cases, based on the use of heat otherwise rejected in

thermodynamic cycle, to produce and co-sell marketablenon-electrical energy products, such as heat for districtheating or potable water, along with the electricity.

The designers also pursue several strategies regarding plantdeployment (which are in turn supported by certain strategiesin plant design), such as:

� To transfer risk from the customer to the vendor, e.g.:- Customer would receive a standard pre-licensed turn-

key plant delivered and assembled by a skilled vendorteam with a shorter interval between securing financ-ing and the start of a revenue stream;

- Thevendor has a start-up risk of building a factory for massproduction and creating a logistics and installation ca-pability, but could spread his cost of risk over many plants;

� To reduce site construction time and/or construction costand achieve an early start of a revenue stream by:

- Sizing the reactor for transportability (or transportabil-ity of modules);

- As an option, increasingly relying on local participa-tion in plant construction;

� To benefit from factory mass production through:- A pre-licensed design certification for a standardized

plant with no site-specific modifications;- Serial manufacture and of standardized plant modules,

incorporating unified structures, systems and compo-nents, see Fig. 1;

- Achieving reciprocity arrangements among licensingauthorities in customer and vendor countries;

� To incorporate an option of multi-module plan clusteringto achieve economic benefits of ‘‘just in-time’’ incremen-tal capacity additions with rapid revenue generation; inmulti-module plant clustering strategy, to take a benefitof smaller module sizes to:

- Achieve learning curve acceleration and discount ratesavings per total capacity installed; and

- To minimize investment risk.

245V. Kuznetsov / Progress in Nuclear Energy 50 (2008) 242e250

In addition to this, designers of SMRs target to offer diversespecial features that might be appreciated by customers intargeted markets, such as:

� Higher potential for reduced/eliminated emergency plan-ning zone, considering the total number of reactors thatwould need to be sited in regions with high populationdensity;� Higher potential for enhanced participation of local indus-

tries and use of existing infrastructure in some developingcountries.� Leasing operation e some approaches employ whole core

fuel cassettes with internal conversion ratio of unity thatmaintains fissile loading, ensuring that there no loss of fis-sile mass ‘‘principal’’ by end of life, while in other casesleasing of a complete nuclear steam supply system isforeseen;� In some cases, long refuelling interval and operation with-

out on-site refuelling.

Fig. 2 provides a generic illustration of potential SMR eco-nomic factor advantages.

4. State-of-the-art design and deployment strategiesfor SMRs

4.1. Targeted economy characteristics

Table 1 summarizes the evaluations of capital costs,construction periods and electricity costs as provided by the de-signers of innovative SMRs with conventional refuellingschemes (IAEA, 2006b).

It is worth mentioning that the targeted range of both cap-ital costs and electricity costs for at least nearer-term SMRs iswithin the corresponding range specified in (IAEA, 2005c) forcurrently offered large-capacity reactors.

To meet the needs of targeted customer groups, thedesigners of innovative SMRs all over the world examinenew design approaches making use of certain advantages pro-vided by smaller reactor size to achieve reduced design and

Fig. 2. A generic illustration of potential SMR economic factor advantages

(courtesy of Westinghouse, USA).

operational complexity, simplified maintenance, or to incorpo-rate higher overall energy conversion efficiency. In most cases,the design approaches used for these SMRs are unique, i.e.,cannot be reproduced in reactors of larger capacity and, there-fore, represent alternative strategies to overcome loss of econ-omies of scale (IAEA, 2006b).

4.2. Approaches to reduce plant complexity

Many approaches in this category pursue a ‘‘winewin’’strategy regarding plant safety design and plant economy char-acteristics. Protection of population from consequences of ac-cidents resulting from internal and external initiators andcombinations thereof relies on traditional defence in depthstrategies (IAEA, 2005a, 2006b). However, in addition to ac-tive safety systems, nearly all SMR designs reinforce the firstand subsequent levels of the defence in depth by broad incor-poration of inherent and passive safety features into designconcept. The goal is to eliminate as much accident initiatorsas possible by design, with the remaining part then being dealtwith by appropriate combinations of active and passive sys-tems. The expected outcome is a highly assured level of pas-sive safety response to enable near-urban plant siting withenhanced protection against natural and human-induced exter-nal events. Another expected outcome is reduced plant sim-plicity potentially resulting in the reduction of both capitaland operation and maintenance costs and less requirementsto emergency planning.

Designers of innovative water cooled SMRs pursue an en-hanced prevention or elimination of abnormal operation andfailures by design. For example, they use integral design ofthe primary circuit incorporating the steam generators andthe pressurizer, providing for the elimination of large-diameterpiping and large-diameter reactor vessel penetrations in orderto prevent large-break loss of coolant accidents, Fig. 3. Theyalso apply the in-vessel location of control rod drives to elim-inate inadvertent control rod ejection and to prevent transientoverpower accidents, as well as to reduce the number of reac-tor vessel penetrations.

Alternately, compact loop-type designs with short pipingand reduced physical connections between main equipmentare used, for the enhanced prevention of loss of coolant acci-dents, Fig. 4. Although they may still appear relatively com-plex, such designs are proven by more than 8000 reactor-yearoperating experience of the Russian marine-propulsion reactorsand have a high potential to be deployed in a very near term.Construction of a pilot floating cogeneration plant of400 MW(th)/70 MW(e) with two water cooled KLT-40S reac-tors has been started in the Russian Federation in June 2006;the deployment is scheduled for 2010.

The designers of high temperature gas cooled reactors ex-ploit the outstanding fission product confinement capabilityof TRISO coated particle fuel at high temperatures e an inher-ent safety feature making a very important contribution to theoverall defence in depth concept of such reactors (IAEA,2006b). Proven in previous tests and operation, this capabilityis definitive for the prevention of consequences of severe

Table 1

projections for the specific capital costs, construction periods and electricity costs for innovative SMRs

Name; country Type; MW; designer Specific capital cost,

US$/kW(e)

Construction

period, months

Electricity cost,

US$ cent/kW-h

Water cooled SMRs

SMART Republic of Korea Integral PWR; 330

MW(th); KAERI, MOST

1714 (Construction cost) Less than 36 4.06

IRIS, USA Integral PWR; 335 MW(e);

Intl. consortium lead by Westinghouse

1030e1240;

First-of-a-kind plant

36 or less 3e4

SCOR, France Integral PWR; 630 MW(e); CEA 10% below the specific capital

cost of a standard large loop-type PWR

w36 13% lower than for a

classical PWR

VBER-300 Russia Advanced loop-type PWR;

295 MW(e); OKBM

1084 e Land based NPP 48e60 2.2 e Land based NPP

820 e Floating NPP 1.8 e Floating NPP

AHWR India Advanced PHWR;

300 MW(e); BARC

1170; First-of-a-kind plant 72 e

HTGRs

PBMR South Africa Pebble bed HTGR;

165 MW(e); PBMR Ltd.

<1500 (Construction cost) 30e34

edemonstration

plant; 24 e

commercial

modules

e

GT-MHR USAeRussia Pin-in-block HTGR;

287 MW(e); GA, OKBM

1460; First-of-a-kind plant Less than 36 3.1 (20-year levelized)

w1000; Nth plant

GTHTR300 Japan Pin-in-block HTGR;

274 MW(e); JAEA

<1750* (target) e 3.5* (target)

HTR-PM China Pebble bed steam cycle HTGR;

160 MW(e); INET

<1500 (target) 48 4.5 (target)

Liquid metal cooled SMRs

KALIMER Republic of Korea Sodium cooled FBR;

150 MW(e); KAERI

2300 e First single module e e

1400e1600 eMultiple unit

construction in series

Core

Riser

SGV; Steam Generatorin Vapour

CRDM; Control Rod DriveMechanism

SGL; Steam Generatorin Liquid

Guide Tubes

Fig. 3. Cross section of IMR reactor e integral type PWR of 350 MW(e) with

coolant boiling in primary system (Mitsubishi Heavy Industries, Japan).

246 V. Kuznetsov / Progress in Nuclear Energy 50 (2008) 242e250

accidents and also allows reducing the mitigation measures.Essentially, it may be important to release helium at an earlystage of an accident, and only natural processes of conduction,convection and radiation in the static structures and media theneffectively accomplish passive decay heat removal. This fea-ture is complemented by slow and stable response to transientscaused by both internal and external initiating events, due tolarge heat capacity of core graphite.

All fast reactors offer extended possibilities to ‘build’ thedesired combinations of reactivity coefficients and effects byan appropriate selection of the design parameters of the coreand reactor internals at the design stage. This possibility, re-sulting from a larger leakage rate of fast neutrons as well asfrom high conversion, can be effectively used to eliminate cer-tain accidents by design, to ensure the reactor self-control ina variety of anticipated transients without scram, and to enablepassive load follow capability of the plant or semi-autonomousoperation with power control executed only via feedwater con-trol from the power circuit side, with no control rods beingprovided for this purpose in core design (IAEA, 2005a,2006b).

It should be noted that many innovative SMR designs incor-porate certain non-traditional features, such as provisions forreduced emergency planning zone, confinement instead ofcontainment (HTGRs), compact containment designs or/andoperation without on-site refuelling; these features may benon-routine in previous licensing interactions in some coun-tries and may require a departure from traditional licensing

1 Reactor 6,7 Pressurizers 2 Steam generator 8 Steam lines3 Main circulating pump 9 Localizing valves4 CPS drives 5 ECCS accumulator

10 Heat exchanger of purification and aftercooling system

7

510

4

8

9

1

3

2

6

Fig. 4. Modular layout of the KLT-40S reactor plant for a floating NPP (OKBM, Russian Federation).

247V. Kuznetsov / Progress in Nuclear Energy 50 (2008) 242e250

norms used historically for LWRs toward a more technology-neutral and risk informed approach.

4.3. Approaches for multi-module plant clustering

In situations when the initial energy demand is small andfinancing availability is constrained but growth is expected,the economic benefits of ‘‘just in-time’’ incremental capacityadditions with rapid revenue generation could be enhanced us-ing a multi-plant clustering approach. Anticipating growth,a city having an initial need for only a single plant but antic-ipating that additional plants will be added incrementally inthe future could position itself to recover some of the economyof scale benefits of a large installation. Such scale benefitswould derive primarily from anticipating growth in designingthe site infrastructure:

� Setting aside space for future incremental plants;� Sizing the switchyard, water and district heat distribution

pipelines, etc. for growth; and� Sharing of railroad, road, and seaway access facilities

among future increment plants;� Providing multi-module plant configuration with certain

shared components.

There could be other motivations for multi-plant clustering;for example it could efficiently match incremental capacity

addition with incremental demand growth in liberalized en-ergy markets. The designers of many SMRs provide for crea-tion of multi-module plants with certain shared componentsand infrastructure (IAEA, 2006b), Fig. 5.

4.4. Approaches to improve heat transport and energyconversion efficiency

All SMRs have given up economy of scale benefits at theoutset and seek to benefit instead from mass production ofstandardized, modularized plants in a factory, and from rapidsite assembly. But even more can be done on the plant itselfto lower capital cost by other means. One such means is im-proved conversion efficiency per unit of capital cost in the bal-ance of plant.

Almost all of the water-cooled SMR concepts use a Rankinesteam cycle with saturated or slightly superheated steam forenergy conversion. The energy conversion efficiency hasa maximum of w33% based on reactor core outlet tempera-tures from 270 to 345 �C.

In most of the HTGRs, high efficiency of energy conversionw41e50% is achieved through the use of direct Braytoncycles and through purposeful use of the rejected heat(GT-MHR).

The nearer-term sodium cooled and reactor concepts andthe leadebismuth cooled SVBR-75/100 employ conventional

Fig. 5. A plan and a longitudinal section of the clustered modular nuclear steam supply system SVBR-1600 (IPPE-‘‘Gidropress’’, Russian Federation).

248 V. Kuznetsov / Progress in Nuclear Energy 50 (2008) 242e250

core outlet temperatures in the range from 480 to 510 �C anddrive superheated Rankine steam cycles attaining conversionefficiencies near 39%.

On the other hand, for the concepts having longer-termcommercialization targets, alternative heat transport and en-ergy conversion approaches are being considered. In the areaof simplification of heat transport, chemical compatibilityamong heat transport working fluids (e.g., PbeBi and steamor CO2) is introduced so that an intermediate circuit is elimi-nated and integral (in-vessel) steam generators or heat ex-changers can be employed. Natural circulation of theprimary coolant at full power is used for many concepts. Inthe area of heat engines, Brayton cycles are under study.The lead cooled STAR concepts (IAEA, 2005a) considera supercritical4 CO2 Brayton cycle, which can theoreticallyreach conversion efficiencies of about 43% at core outlet tem-peratures of w500e530 �C, ‘‘traditional’’ for sodium andleadebismuth cooled reactors. Since the Brayton cycle rotat-ing machinery is smaller and the component count is smallerthan for the Rankine cycle, the targeted result would be higherconversion efficiency at lower capital cost as well as smallerrequired operating crew and skill level to achieve reduced op-eration and maintenance costs, see Fig. 6.

4.5. Increased proliferation resistance and energysecurity

For many less developed countries, these are the features ofenhanced proliferation resistance and increased robustness ofbarriers for sabotage protection that may ensure the progressof nuclear power.

All NPPs with innovative SMRs will provide for theimplementation of the established safeguards verification pro-cedures under the agreements of member states with theIAEA. In addition to this, many innovative SMRs offer certainintrinsic proliferation resistance features to prevent the misuse,

4 CO2 critical state is at T¼ 31 �C and P¼ 7.1 MPa.

diversion or undeclared production of fissile materials and/orto facilitate the implementation of safeguards (IAEA, 2006b).

For example, many of water-cooled SMRs employ lowenrichment uranium and once-through fuel cycle as basicoptions. Therefore, the features contributing to proliferationresistance of such SMRs are essentially similar to that ofpresently operated PWRs and BWRs. They also includean unattractive isotopic composition of the plutonium inthe discharged fuel, and radiation barriers provided by thespent fuel.

The intrinsic proliferation resistance features common to allHTGRs include high fuel burn-up (low residual inventory ofplutonium, high content of 240Pu); a difficult to process fuelmatrix; radiation barriers; and a low ratio of fissile to fuel-block/fuel-pebble mass. Although several HTGRs make a pro-vision for reprocessing of the TRISO fuel, the correspondingtechnology has not been established yet and, until such timeas when the technology becomes readily available, the lackof the technology is assumed to provide an enhanced prolifer-ation resistance.

All liquid metal cooled SMRs are fast reactors that can en-sure a self-sustainable operation on fissile materials or realizefuel breeding to feed other reactors present in nuclear energysystems. In both cases, and if the fuel cycle is closed, the needof fuel enrichment and relevant uranium enrichment facilitieswould be eliminated, which is a factor contributing to en-hanced proliferation resistance.

Other features to enhance proliferation resistance of fast re-actors are the following:

� No separation of plutonium and uranium at any fuel cyclestage and leaving a small (1e2% by weight) fraction offission products permanently in the fuel;� Denaturing of the fissile materials, e.g., through the opti-

mization of the core design to achieve a higher contentof 238Pu in the plutonium, to preclude the possibility ofweapon production via securing an inadmissibly high levelof residual heat of the plutonium fuel e the 238Pu/Pu rationeeded to achieve this still needs to be defined adequately.

16 m

INVENTORYCONTROL TANKSCO2 LETDOWN

TANKS

GENERATOR CO2 TURBINE CO2COMPRESSORS

16 m

FROM Pb-to-CO2 HX

GEARBOX

TO Pb-to-CO2 HX

RECUPERATORSAND COOLER

SHUTDOWN COOLING COMPRESSOR AND MOTOR

Fig. 6. SSTAR supercritical CO2 Brayton cycle layout (ANL, USA).

249V. Kuznetsov / Progress in Nuclear Energy 50 (2008) 242e250

4.6. Small reactors without on-site refuelling

Broader scale of nuclear power deployment worldwidebrings in the energy security/non-proliferation dilemma. Theessence of this dilemma is how to configure the nuclear energyenterprise in a way that provides each country with energy se-curity while simultaneously providing the international com-munity with greater non-proliferation assurances. Severalapproaches to constrain global dispersal of fuel cycle facilities,which handle fissile material in bulk form, while at the sametime not impeding the global dispersal of nuclear powerplants, which handle fissile material only in a discrete form,amenable to item accountability, are under consideration cur-rently (IAEA, 2005b). Small reactors without on-site refuel-ling e the reactors designed for infrequent replacement ofwell-contained fuel cassette(s) in a manner that impedes clan-destine diversion of nuclear fuel material (IAEA, 2005a) emay offer an attractive solution to balance energy securityconsiderations with non-proliferation concerns.

Small reactors without on-site refuelling incorporate in-creased refuelling interval (from 5 to 30 years and more), con-sistent with plant economy and considerations of energysecurity (IAEA, 2005a). Both front-end and back-end fuel cy-cle services are assumed to be completely outsourced for suchreactors, i.e., they are either factory fabricated and fuelled orundergo a once-at-a-time core reloading performed at thesite by a dedicated service team provided by the vendor of

the fuel or the reactor itself; such team is assumed to bringin and take away the fresh and spent fuel load and the refuel-ling equipment.

Being designed specifically for operation with the out-sourced front-end and back-end fuel cycle services, small re-actors without on-site refuelling could be employed in anyof the institutional approaches currently considered to con-strain the global dispersal of fuel cycle facilities. For theuser, they could relax the dependence on foreign suppliers,fuel cost changes, political and economic tensions and con-flicts between countries e altogether, increasing the energy se-curity and reducing the obligations for spent fuel and wastemanagement. Factory fabricated and fuelled reactors mayalso appear more environmentally clean, more simple andsafe and secure, just because all operations with fuel are out-sourced and the reactor actually appears as a long-life ‘‘bat-tery’’, perhaps, weld sealed during the whole period of itsoperation on the site.

About 30 concepts of small reactors without on-site refuel-ling are being analyzed or developed within national and inter-national programmes in Brazil, India, Indonesia, Japan,Morocco, Russian Federation, Turkey, U.S.A., and Vietnam(IAEA, 2005a, 2006b). Whether for fast or for thermal neutronspectrum concepts of such reactors, the fuel discharge burn-upand the irradiation of core structures never exceeds standardpractice from the conventional or typically projected designs.The refuelling interval is then extended by derating core

250 V. Kuznetsov / Progress in Nuclear Energy 50 (2008) 242e250

specific power, and the power densities never significantly ex-ceed w100 kW(th)/litre and often are much lower. Burn-up re-activity loss is compensated by using burnable poisons andactive control rods in thermal systems and by designing for in-ternal breeding in fast systems.

The economic characteristics of small reactors without on-site refuelling rely on the same approaches as for conventionalSMRs; however, they are generally less impressive because ofadditionally de-rated power. At the same time, centralizationand streamlining of fuel cycle services under a long refuellinginterval could add economy of scale benefits to nuclear energysystems with such reactors.

5. Conclusion

Continued operation, construction of new power plants, andprogress in design and technology development for futureSMRs indicate the continued interest of many countries tothe development and application of such reactors. Innovativedesign approaches to achieve benefits in plant safety, econom-ics, and proliferation resistance are being explored by SMRdesigners to ensure that such reactors could competitivelymeet the needs of potential users in those markets that cannotbe effectively served by the economy of scale nuclear deploy-ments. The potential users of SMRs are diverse, ranging fromsmall towns and industrial sites in off-grid locations to grow-ing cities in developing countries and future utilities and mer-chant plants for non-electrical applications in deregulatedmarkets. The requirements of these user groups are also likelyto be diverse, protruding from small capital outlay and incre-mental capacity increase to autonomous operation, long refu-elling interval and advanced cogeneration options. Furtherprogress in innovative SMR development and deploymentcould, therefore, benefit from a continuous dialogue amongpossible vendors and potential customers. To facilitate it, theIAEA is carrying out new activities for SMRs that include:

� Assessment of design and deployment strategies proposedto overcome loss of economies of scale, for example, ad-vantages in reduced design complexity, modularity and ac-celerated learning;� Definition of investor requirements for innovative SMRs

and consolidation of methodologies to help public and

private investors in developing countries assess the overallpotential of innovative SMRs;� Systematic re-examination and quantification of needs for

SMRs in countries or certain regions of countries, basedon a country-independent model which will be developedto support such quantification;� Dynamic simulations of energy systems with innovative

SMRs.

Acknowledgements

The author expresses his acknowledgement to D. Wade ofthe Argonne National Laboratory (USA), C. Mycoff of West-inghouse (USA), and K. Veshnyakov of the Experimental De-sign Bureau of Machine Building (Russian Federation) forproviding certain materials and illustrations used in this paper.

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