MR ROBERT J. DUSSOL  So fiaco International  Former Consultant to Framatome ANP

SUMMARY. In recent years interest has increased in small and medium sized nuclear power reactors for  generating electricity and process heat. This interest has been driven by a desire to reduce capital costs, construction  times and interest during construction, service remote sites and ease integration into small grids. The IAEA has  recommended that the term “small” be applied to reactors with a net electrical output less than 300 MWe and the term

“medium” to 300-700 MWe. A large amount of experience has been gained over 50 years in the design, construction  and operation of small and medium nuclear power reactors. Historically, 100% of commercial reactors were in these  categories in 1951-1960, reducing to 21% in 1991-2000.  The technologies involved include pressurised water reactors, boiling water reactors, high temperature gas-cooled  reactors, liquid metal reactors and molten salt reactors. Details will be provided of two of the most promising new

designs, the South African Pebble Bed Modular Reactor (PBMR) of about 110 M e ,  and the iRIS (International  Reactor innovative and Secure) reactor of about 335 MWe. Their construction costs are estimated to be about  US$l,OOO/kWe with a generating cost for the PBMR of about US 1 .6c/kWh. These costs are lower than estimated for  the latest designs of large reactors such as the European Pressurised Reactor (EPR) designed for 1,600 W e  for use

in Europe in the next decade.  It is concluded that a small or medium nuclear power reactor system built in modules to follow an increasing  demand could be attractive for generating low cost electricity in many Australian states and reduce problems arising  fkom air pollution and greenhouse gas emissions from burning fossil fuels.

1. Introduction

A total of 441 nuclear power plants were operating in  30 countries at the end of 2002 and producing 16% of  global electricity. These plants represent a mature  technology with over 10,000 reactor operating years of

experience. in addition, the construction of seven new  reactors started in 2002 bringing the total under  construction to 32.  The International Atomic Energy Agency (IAEA)

has recommended that the term “small” be applied to  reactors with a net electrical output of less than  300MWe and the term “medium” to 300-700MWe.  Historically, 100% of commercial reactors were in  these two categories in 195 1-1960,55% in 1961-1970,

16% in 1971-1980, 25% in 1981-1990 and 21% in  199 1-2000. In addition, a large number of nuclear-  powered ships were built with reactors of < 300MWe  and many research reactors of < 100MWe.

Interest has increased in recent years in small and  medium reactors for generating electricity and process  heat. This interest has been driven by a desire to  reduce capital costs, construction times and interest

during construction, service remote sites and ease  integration into small grids. The present paper reviews  past work and recent work on new advanced designs  of small and medium power reactors and suggests that

one of these systems may be suitable for generating  low cost electricity in Australia.

2. Technology of Small and Medium Reactors

The technologies used in small and medium nuclear  reactors over the last 50 years have been diverse:  0 Pressurised water reactors;

Boiling water reactors;  * High temperature reactors;  0 Liquid metal reactors; and

* Molten salt reactors.  Many of the early designs were improved and  increased in power output in an evolutionary way, and  a power output of 1,300MWe became common in  many countries. The safety systems of these evolved  systems were largely “active” in the sense that they  involved electrical or mechanical operation on

command. Some engineered systems operated  passively, eg. pressure relief valves. A high level of  redundancy was built into all of these reactors.  In recent years and in new designs, inherent or  passive safety has been given greater attention. In  these systems safety depends only on physical

phenomena such as convection, gravity or resistance  to high temperatures, not on the functioning of  engineered systems. It has been possible at the same  time to reduce the complexity of the many sub-systems  and thereby reduce capital costs and maintenance  costs. The evolution to larger sizes to reduce costs has

been replaced with simplification, modular  Construction and passive or inherent safety concepts,

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3. Review of Small and Medium Reactors

A list of small and medium reactors with development  well advanced is given in Table 1. The list includes  four types: pressurised and boiling water reactors, high  temperature gas-cooled reactors, liquid metal cooled  reactors, and molten salt reactors.

Some countries have had a considerable experience  in the design, construction and operation of small  reactors for remote sites or for special purposes eg.  desalination. Examples of these are:

0 The Russian KLT-40 reactor which is well

proven in ice breakers and now proposed for  remote areas on land or on barges to produce heat  and 35MWe and to operate for three years  without refuelling. After a 12-year cycle the  reactor would be taken to a central facility for  overhaul and storage of spent fuel.

e

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Technicatome in France has developed the NP-  300 design from its submarine power plants and  is aiming it at export markets for power, heat and  desalination. It can be built with outputs of 100-  300MWe and up to 500,000 m3/day desalination.  Four small reactors are operating at the Bilibino

co-generation plant in Siberia. These four  62MWt units are a graphite-moderated boiling  water design and produce steam for district  heating and 11 MWe each. They have operated

since 1976 and are claimed to be cheaper than  fossil fuel alternatives in the Arctic region.  The TRIGA power system is a PWR concept  developed by General Atomics based on its well-  proven TRIGA research reactors. The power

system is planned as a 64MWt, 16.4MWe pool  reactor operating at relatively low temperature.

Table 1. List of Small- and Medium-Reactors with Development Well Advanced

Name

CAREM 27 MWe PWR CNEA & INVAF', Argentine

KLT-40 I 35 MWe PWR I OKBM. Russia

MRX 30 - 100 W e  PWR JAERI, Japan

IRIS (See section 4.2) 335 MWe PWR Westinghouse, USA, & others

SMART KAERI, Korea 100 MWe PWR

100 - 300 MWe PWR

50 MWe BWR

NP-300 (See section 3) Technicatome, France

GE & Purdue University, USA

ESKOM, South A-Grica, & others

GA, USA, & others

Modular SBWR

PBMR (See section 4.1) 114 MWe HTGR

285 MWe IFTGR GT-MHR (See section 4.3)

BREST

FUJI

TRIGA (See section 3)

300 MWe LMR RDIPE, Russia

100 MWe MSR ITHMSO, Japan, Russia, USA

16.4 MWe PWR GA, USA

700 MWe PWR ACR-700 (See section 4.3) AEXL. Canada

4. Promising New Modular Designs and Secure) reactor of about 335 MWe.  These designs will then be compared with two other

The Advanced CANDUReactor, ACR-700, from  Atomic Energy of Canada Ltd (700MWe) based  on evolutionally development of its successful  CANDU 600MWe design built in recent years in  China and Korea; and  The Gas-Turbine-Modular Helium Reactor, GT-  M H R  (285MWe modules) developed by General  Atomics, USA, and optimised to burn plutonium.

new designs of medium-sized reactors:  *

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In this short review paper, and in the short time  available for presentation in the conference, it is not  possible to provide the details and the relative merits  of all of the designs listed in Table 1. The following

sections will therefore provide outlines of two  promising designs which have attracted considerable  interest worldwide. These are the South African  Pebble Bed Modular Reactor (PBMR) of about 110  MWe, and the IRIS (International Reactor Innovative

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4.1 The Pebble Bed Modular Reactor (PBMR)

The PBMR illustrates the application of advanced  high temperature gas-cooled technology based on  considerable experience in the building of innovative  designs in the 1960s and 1970s, particularly in the

USA and Germany.  The South Afiican Electricity Utility, ESKOM,  currently operates two Framatome-designed 900MWe  PWRs at its Koeberg Nuclear Power Station near  Capetown. ESKOM has been studying the feasibility  of introducing high temperature gas-cooled reactors

into the South African network since 1993 as well as  for export. The initial project was to design a Pebble  Bed Modular Reactor with a 1OOMWe module to  operate at a 900Â°C outlet temperature with helium  cooling coupled to a direct helium cycle turbine. The  fie1 was based on a proven German design of coated  uranium particles contained in moulded graphite  spheres of 60 mm diameter (slightly smaller than  tennis balls).

Further design optimisation occurred such that by  1998 the revised design was for a module of 114MWe  (285MWt) output capable of load-following with on-  load fbel management and a 40 year lifetime. The

capital cost was estimated to be less than US$lOOM  per module and the target generating cost was about  US$l .Gc/kWh.'These costs were remarkably low and  were competitive with electricity production costs in

coal-fired stations close to South Afiican coal mines  and probably anywhere in the world.  The concept involved building the modules in a  centralised factory in 2, 4 and 8-pack layouts (see  Figure 1) and these would allow the modules to be  brought on line successively as they are completed on

site. Four modules are claimed to fit on a site the size  of a football field.  The PBMR reactor consists of a vertical steel  pressure vessel lined with graphite bricks. The vessel  is connected to two turbo compressor units which are  connected to the generator, power turbine and  recuperator (see Figure 2). The he1 balls contain  uranium dioxide particles triple-coated with silicon  carbide and pyrolytic carbon in 60 mm diameter  moulded graphite spheres (see Figure 3). The helium

turbine development has been undertaken with  industry and the University of Potchefstroom where a  test rig was operated successfblly to demonstrate a  closed cycle multi-shaft turbine on a recuperated  Brayton cycle (see test rig in Figure 4).

The Environmental Impact Assessment process has  been completed and final reports sent to the South  Afi-ican Dept of Environmental Affairs and Tourism.  It is expected that construction of the demonstration

module and associated fuel plant at Koeburg will be  approved shortly. The estimated low capital cost of  about US$l,OOO/kWe and low generating cost are  expected to make the project attractive for export.

Figure2. Layout  of Main Components

Figure 3. PMBR Fuel Balls

Figure  4. Test Rig for Helium Turbine

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4.2 The International Reactor Innovative and

n e  IRIS concept is based on well established PWR  technology but with an integral primary coolant  system and circulation by convection. It is being  offered in single or multiple modules of 1,OOOMWt  (about 33 5MWe).

The IRIS program was started in late 1999 by  Westinghouse and was one of the winning proposals  in the first Nuclear Energy Research Initiative of the  US Dept of Energy. It then moved through the  preliminary design stage and the start ofthe licensing  process and is being considered as one of several  designs for an early site permit by three US utilities.

The IRIS project is based on proven PWR  technology but has a number of innovative features,  one of which is development by an international  partnership of industry (S), academia (12), research

organisations ( 5 )  and power producers (2). The project  was conceived to meet four objectives: enhanced  safety, improved economics, reduced waste, and  improved proliferation resistance.

Some distinguishing characteristics are: an integral  configuration which addresses all four aims; use of  high bum-up fuel and long core life, eg. four years  without shutdown, thus reducing maintenance costs

and improving proliferation resistance; containment  design practically eliminating small-to-medium loss of  coolant accidents; a ‘Safety by Design’ approach to  eliminate or minimise potential accidents.

All of the main primary coolant components - core,  coolant pumps, steam generators, pressuriser, control  rod drive mechanisms - are within the reactor pressure  vessel (Figure 5). Coolant water flow is upward  through the core. Although the reactor vessel is larger  than a traditional reactor vessel, the overall

containment is much smaller.  A unique aspect of the steam generators (SGs) is  that the high pressure coolant flows on the outside of  the tubes. Thus the SG tubes are in compression and

tensile stress corrosion cracking (which is claimed to  be responsible for 70% of SG failures) is eliminated.  The proponents of IRIS believe that its defence in  depth and safety-by-design approach is so strong that

some of the current licensing requirements can safely  be relaxed.  The present planning is to proceed to design  certification by 2008-2010 and to deploy a fulst-of-a-  kind module by 2012-2015. The economic analysis

was stated to be favourable with the capital cost of  multiple modules of 335MWe being in the range  US$1,000-1,200/kWe. It was also believed that the  reactor could compete with other nuclear and non-  nuclear plants in world markets.

A schematic layout of a plant with two twin  modules totalling 1,340MWe is shown in Figure 6.

Figure 5. Layout of Main IRIS Components

Figure 6. Schematic Layout of Two Twin Module  IRIS Plants of 1,340 Mwe Total Capacity

4.3 Comparisons with Other New Designs

The Advanced CANDU Reactor, ACR- 700

This system was designed by Atomic Energy of  Canada Ltd (AECL) as a new 700MWe version of the  most recent CANDU 6 (700MWe) design with  features fi-om the CANDU 9 (900MWe) design. It uses

light water coolant instead of heavy water and 2%  enriched uranium fuel in an advanced fuel bundle  design instead of natural uranium.  These changes have reduced the size of the core  considerably fi-om a diameter of 6.3 to 4.35 m. Heavy  water is still used as a moderator but not as a coolant,

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thus saving 75% of the costs of the heavy water  inventory of the original CANDU 6 design. A simpler  heat transport system also reduces costs. Another  major change is to move to a negative void reactivity

design instead of a positive void reactivity design and  this is expected to strengthen its licensability in  overseas markets more familiar with the negative void  characteristics of PWR reactors. The operating

temperature and pressure of the design have been  increased over the previous CANDU 6 design leading  to increased efficiency. Some passive safety features  have also been used.

Overall, the cost reductions are expected to lead to  a capital cost in the region of US$1,000/kWe for  multiple units. The recent experience in constructing  CANDU 6 plants in China and Korea has led to

confidence in the claim that the ACR-700 can be  constructed in 48 months fiom contract signing to  commercial operation and 36 months From fust  concrete pour to fuel loading.

A schematic diagram of the layout of the main  containment building and turbine hall for ACR-700 is  shown in Figure 7.

Figure 7. Containment Building and Turbine Hall

Gas-Turbine-Modular Helium Reactor, GT-MHR

This design is from an international project in which  the main participants are from the USA, Russia,  France and Japan. General Atomics, USA, developed  a modular design of a helium-cooled high temperature

reactor as part of a US DOE program. It initially used  steam turbines but later moved to gas turbines. The  DOE then stopped funding for new reactor designs in  the late 1970s.

GA then proposed that the GT-MHR design should  be optimised to burn plutonium derived from military  decommissioning programs and signed a MOU with  the Russian Minatom in 1995 for this purpose.  Framatome, France, joined the project in 1996 and  Japan's Fuji Electric joined in 1997. The project was  then planned in four stages. The conceptual design

stage was completed in 1997. The detailed design  stage was completed in 2002. The third stage was to  build a prototype in Russia at Seversk but this has  been delayed. The fourth stage would be to develop a

commercial version for world marketing.  The basic design is for a modular plant  of 600MWt  (285MWe). Each module consists of two pressure  vessels mounted side by side in a concrete containment  35m below ground level. One vessel contains the  reactor and the other the power conversion equipment  connected to the reactor by a dual concentric duct. A  cross section of the main components is given in  Figure 8.

Figure 8. Main Components in GT-MHR

The helium coolant outlet temperature is 850Â°C and 70  bar (7Mpa) pressure with the exit gas From the turbine  at 510Â°C and 26 bar (2.6 Mpa). The helium then goes  through a regenerative heat exchanger and a water

cooled heat exchanger before entering a two-stage  compressor with intercooler. The system is expected to  give an overall efficiency of nearly  50%.

The core uses a prismatic design based on standard  GA technology. It has 61 columns of replaceable  graphite reflector blocks containing no fuel arranged  in a hexagon. This is surrounded by 102 columns of  fuel-bearing blocks, ten blocks high, forming an  annular core of 48m outside diameter and 8m height.  This is surrounded by a ring of replaceable graphite  blocks (see Figure 9). The core contains pure  plutonium oxide kernels coated in a triple layer of

porous carbon, silicon carbide and pyrolytic carbon.  These are formed into compacts and the compacts into  hexagonal-shaped fuel elements (see Figure 10).  No uranium is used to dilute the plutonium so that  no secondary plutonium is produced. The GT-MHR

can therefore consume 90% of the plutonium fuel in a  single pass in a period of 840 equivalent full power  days. This is much higher than any other type of  reactor. The core is designed to be recharged in layers  after about 280 equivalent full power days. The result

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Figure 9. Core Layout in GT-MHR

PARllCLES CBWACls FUEL E L E M W

Figure 10. Structure of Fuel Balls in GT-MHR

is that if three four-module plants were built (each  plant producing X,140MWe), they could dispose of  50te of weapons grade plutonium in a 25 year period  as well as producing 75,OOOMW-years of electricity.

Thereactor is claimed to have very good passive safety  features and can withstand loss of coolant circulation  and loss of coolant inventory without operator  intervention or the use of active safety systems.

The cost was estimated in 1996 to be US$3billion,  equivalent to less than US$1,000/kWe, which was less  than an equivalent light water reactor.

4.4 Comparative Electricity Costs

The relative costs of generating electricity from coal,  gas, nuclear and renewables varies considerably  depending upon location and a number of economic  assessment factors, eg. discount rates. Coal is, and will  remain, economically attractive in many countries  which have abundant domestic resources, especially if  these are close to load centres. Gas is competitive in  many countries using combined cycle plants although

there is uncertainty on the future price of gas.  From the outset, the features of nuclear power have  been its relatively high capital costs and low he1 costs  compared with coal- and gas-fired plants. However,  nuclear power has been shown to be competitive with

fossil fbels in many countries, eg. France, Japan,  Korea. A study published by the OECD's Nuclear  Energy Agency in 1998 provided cost projections for

the period 2005-2010. The study showed that nuclear  costs were lower than coal and gas  in France, Russia,  Korea, Spain, Canada and China.

A new French government study has assessed the  cost of electricity in 2003 euro c/kWh for a plant  starting up in 2015 as follows: 3.04 for nuclear, 3.2-  3.4 for coal and 3.5 for gas. If external costs were  taken into account these costs increased to: 3.30 for  nuclear, 4.24 for gas and 4.8-4.95 for coal. The

nuclear plant was assumed to be the new European  Pressurised Water Reactor (EPR) at a basic capital  cost of 1,043 euros/kWe, compared with 569 euros/  kWe for gas and 1276-1,400 euros/kWe for coal.

4.5 The Australian Electricity Situation

Australia relies very heavily (85%) on coal for its  supply of electrical energy for residential and industry  use and on petroleum products for transport. While  renewable sources are becoming used increasingly,

they are unlikely to contribute more than a few percent  over the next two decades.  The Electricity Supply Association of Australia  estimates that electricity demand will increase at 3%  per year to 2020. This represents a 70% increase on

current demand and a need to construct about  50,000MWe of new capacity. If this was to be based  on coal the environmental impact would be  considerable, while if based on gas it would require  the discovery of one or more major new gas resource  areas and still contribute to greenhouse gas emissions.

It is therefore suggested that nuclear power should  be evaluated as part ofAustralia's fbture energy needs,  taking into account cost competitiveness, including all  external costs, and environmental factors.

One of the small- or medium-reactor systems  described in this paper may be appropriate for the  Australfan situation. A modular reactor system with  modules added to the grid system progressively every  two to three years could easily be integrated into the

grid systems of any ofthe Australian states, even those  currently with small grids, eg. Tasmania and the  Northern Territory. These modular plants would also  be suitable for remote towns and areas with large

mining or processing plants.  The estimated capital and generating costs of the  advanced modular plants of about US$1,000/kWe and  US2c/kWh, are equivalent to AUS$1,500/kWe and  AUS3c/kWh. The capital cost is higher than those for

coal-fired or combined cycle gas plants in Australia  and many other parts of the world. However, the  generating cost could be competitive especially as the  future cost of gas over the next two decades is not  known with certainty. The cost would be even more

competitive if external costs were included for coal  and gas. Such plants would also have the advantage of  reducing problems arising from air pollution and  greenhouse gas emissions from burning fossil hels.

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References and suggested sources of information

UIC Nuclear Issues Briefing Paper No. 60, May 2003,  on “Small Power Reactors”.  UIC Nuclear Issues Briefing Paper No. 16, May 2003,  on “Advanced Reactors”.

UIC Nuclear Issues Briefing Paper No. 8, December  2002, on “The Economics of Nuclear Power”.  OECD/NEA PublicationNEA/COM (2002)4 on “The  Role of External Costs in Energy Policy”.

IAEA Nuclear Power Statistics for 2003, IAEA News,  May 2003.  Electricity Supply Association of Australia (ESAA),  “Electricity Sales Forecasts by State and Class to  2020”, 2002.  B.Barre, Cogema, “Les reacteurs de petite et moyenne  puissance d’hier et d’aujourd’hui pow: la production

d’energie”, Revue Generale Nucleaire, No. 6, 2001,  PPS 29-32.

D. F. Torgerson, AECL, “The ACR-700”, Nuclear  News, October 2002, pps 24-32, publ. by American  Nuclear Society.  M. D. Carelli, Westinghouse, “IRIS: A Global

Approach to Nuclear Power Renaissance”, Nuclear  News, September 2003, pps 32-42, publ. by American  Nuclear Society.  D. R. Nicholls, ESKOM, Nuclear Engineering

International, December 1998, pps 12-16.

Acknowledgements

The assistance of Dr Clarence Hardy, ANA, in the  preparation of this paper is acknowledged, and  Framatome ANP and the Uranium Information  Centre, Melbourne, for extracts &om their recent  publications.

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