The Status of Nuclear Power Technology-An Update

Transcription

1 Public Disclosure Authorized INDUSTRY AND ENERGY DEPARTMENT WORKING PAPER ENERGY SERIES PAPER No. 27 The Status of Nuclear Power Technology-An Update Public Disclosure Authorized April 1990 Public Disclosure Authorized The.World Bank Industry arm Public Disclosure Authorized The~~~~., Ban ndstr Wol an Enrg Dea:mn,PR

2 THEi STATUS OF NUCLEAR POWER TECHNOLOGY - AN UPDATE by Spyros Traiforos, A/ Achilles Adamantiades (EMTIE) and Edwin Moore (IENED) April 1990 Copyright (c) 1990 The World Bank 1818 H Street, NW Washington, DC USA This paper is one of a series issued by the Industry and Energy Department for the information and guidance of World Bank staff. The paper may not be published or quoted as representing the views of the World Bank Group, nor does the Bank Group accept responsibility for its accuracy and completeness. A/ President of SAT Consultants, Washington, D.C.

3 i ABSTRACT This paper traces the development of nuclear power over the past 30 years, briefly explains the presen- designs and new trends in nuclear power technology, and gives an overview of nuclear power costs. As of the end of 1988 there were 429 nuclear reactors in operation and an additional 105 units under construction or in planning around the world, providing almost 20% of the world's electricity supply. In some countries, over half of the electricity is derived from nuclear power; in France it is 70%. Three reactor designs account for 82% of the existing nuclear reactors--pressurized water reactors (PWRs), boiling water reactors (BWRs) and pressurized heavy water reactors (PHWRs). Other reactor types in use for power production include gas cooled reactors (GCRs) (10%), light-water-cooled graphite-moderated reactors (LWGRs) (6%), and liquid metal fast breeder reactors (LMFBRs) (2%). Development work is underway to both improve existing reactor designs and develop new concepts for nuclear reactors. The aim is to increase safety, improve availability and simplify maintainability, including fail-safe features such as gravity supply of emergency cooling water and natural circulation to provide core cooling even if pumps fail to operate in case of accidents. Over the past 30 years nuclear plant construction times have on average increased from less than four years to about nine years due to many factors including larger sizes, complexity of design and increasing regulatory action. Some reactors have taken 14 years to construct from first concrete to grid connection. Capital costs have increased accordingly and typical estimates of base generating costs for future nuclear power plants indicate a nuclear kwh cost would be higher than those for coal, oil, or gas thermal power, at least for the near term. Given the heightened anxieties from the prospect of increasing fossil fuel use, the prospects of nuclhir power in industrialized countries have a modest potential. These prospects will be mainly determined by the increasing world concern over the global warming effect from carbon dioxide emissions, the development of new inherently safe nuclear designs at a cost competitive with other options, and a publicly acceptable resolution of the radioactive waste management problem. In developing countries prospects look much less promising owing to the ready availability of less expensive alternatives, the shortage of investible capital, and the stringent requirements with nuclear power for competent, vigilant -.id effective management of plant operations and strict adherence to rules and regulations. The situation in developing countries may change if modular, factory assembled, inherently safe, operationally tolerant, and cost effective designs appear in the market and gain wide public acceptability.

4 ii ABBREVIATIONS ABB ASEA BROWN BOVERI AEG ALLGEMEINE ELEKTRICITAETS - GESELLSCHAFT AGR BWR CANDU DOE EPA FBR FRG GAO GCHWR GCR GE HTGR HWR IAEA IDC ADVANCED GAS-COOLED REACTOR BOILING WATER REACTOR CANADIAN DEUTERIUM URANIUM DEPARTMENT OF ENERGY (USA) US ENVIRONMENTAL PROTECTION AGENCY (USA) FAST BREEDER REACTOR FEDERAL REPUBLIC OF GERMANY GENERAL ACCOUNTING OFFICE (USA) GAS-COOLED, HEAVY-WATER-MODERATED REACTOR GAS-COOLED REACTOR GENERAL ELETRIC HIGH-TEMPERATURE GAS-COOLED REACTOR HEAVY WATER REACTOR INTERNATIONAL ATOMIC ENERGY AGENCY INTEREST DURING CONSTRUCTION IEA INTERNATIONAL ENERGY AGENCY, AN ARM OF THE ORGANIZATION FOR ECONOMIC COOPERATION AND DEVELOPMENT (OECD) kwh KILOWATr-HOUR

5 iii LMFBR LWGR LWR MHTGR MW NEA NRC ORNL PAH PHWR PWR RBMK SNUPPS THTR TMI UK U0 2 LIQUID-METAL FAST BREEDER REACTOR LIGHT-WATER COOLED GRAPHITE-MODERATED REACTOR LIGHT WATER REACTOR MODULAR HIGH TEMPERATURE GAS COOLED REACTOR MEGAWATTS NUCLEAR ENERGY AGENCY, AN ARM OF THE ORGANIZATION FOR ECONOMIC COOPERATION AND DEVELOPMENT (OECD" NUCLEAR REGULATORY COMMISSION (USA) OAK RIDGE NATIONAL LABORATORY POLYCYCLIC AROMATIC HYDROCARBONS PRESSURIZED HEAVY WATER REACTOR PRESSURIZED WATER REACTOR RUSSIAN TERM EQUIVALENT TO LWGR STANDARDIZED NUCLEAR UNIT POWER PLANT SYSTEM THORIUM HIGH TEMPERATURE REACTOR THREE MILE ISLAND UNITED KINGDOM URANIUM OXIDE US OR USAUNITED STATES OF AMERICA WER RUSSIAN VERSION OF PWR

6 iv TABLE OF CONTENTS Page No. Section 1. A Brief History of Nuclear Power... 1 Section 2. Nuclear Power Technology Nuclear Power Statistics Review of Existing Reactor Designs Section 3. New Trends in Reactor Designs Improved Designs Evolutionary Designs Passive Designs Modular Designs Standardization.16 Section 4. Nuclear Power Costs Background Nuclear Plant Construction Times Typical Nuclear Power Plant Cost Estimates Comparison of Base Generating Costs.19 Section 5. The Future of Nuclear Power.20 References 22 Bibliography 23 Annexes 25

7 v LIST OF TABLES Page No. 1.1 Fossil Plant Emission Decrease in France Nuclear Power Reactors in Operation Worldwide, 30 MW or Over, by Reactor Type as of December 31, Nuclear Power in the Developing Countries as of December 31, LIST OF FIGURES 2 1..Nuclear Electricity Generation Share of Total Electrical Energy Worldwide for the Period Countries with Highest Nuclear Share of Total Electricity Production in LIST OF ANNEXES 1. Nuclear Power Reactors in Operation and Under Construction, December 31, PWR Nuclear Design BWR Nuclear Design CANDU Nuclear Design Average Nuclear Unit Construction Time Span Estimated 1100 MW Nuclear Power Plant Capital Investment Costs in the US Based on Median and Better Current Experience Comparison of Base Generating Costs for Oil, Nuclear, Coal and Gas Power Plants.34

8 1 THE STATUS OF NUCLEAR POWER TECHNOLOGY - AN UPDATE 1. A BRIEF HISTORY OF NUCLEAR POWER Nuclear fisbion--the production of energy from splitting the nucleus of a uranium atom--was first achieved in an experiment conducted by Otto Hahn and Fritz Strassman in 1939 in Berlin. The event signaled the beginning of the era unleashing the power of the atom. Three years later another major breakthrough came in the US at the University of Chicago's Stagg Field, where Enrico Fermi and his co-workers, experimenting with uranium spheres emplaced in a pile of graphite blocks, proved that a fission chain reaction in uranium nuclei could be sustained and controlled, making it feasible to harness this energy. These two events marked the birth of the nuclear age. The history of the development and use of nuclear power since then can be divided into four periods, as shown below. Period One: Post World War II to Mid-1960s During this period, development followed two paths: weapons production and commercial reactor development. This paper focuses on the latter. In the US, following World War II, a five-year nuclear power research and development program was launched. The program resulted in the first US nuclear power plant tied to an electrical network--the 60 megawatt electric (MWe) Pressurized Water Reactor (PWR) at Shippingport, Pennsylvania, which began operation in This reactor, developed for the Atomic Energy Commission by Admiral Rickover's Navy Reactor Group, was basically a large-scale version of the reactor deployed earlier in the USS Nautilus, the world's first nuclear-powered submarine. The first commercial order for this type of reactor came from a US utility in In Canada, the US McMahon Act, which denied enriched uranium to the US's wartime Manhattan project partners, led Canada, the UK, and France, to develop technologies that allowed the use of natural instead of enriched uranium. This was made possible by the introduction of a much more effective moderator than the regular (light) water used in PWRs. "Moderator" is a material that slows down (moderates) normally fast-moving neutrons to make them more capable of causing chain-reaction fissions. While the European countries chose graphite (a form of crystalline carbon) as the moderator, Canada opted for heavy water 1. The first heavy-water prototype power 1 Heavy water is made of two atoms of deuterium (one proton plus one neutron) and one atom of oxygen.

9 z reactor was completed in By 1966, this kind of reactor was in commercial operation in Canada. In France, indigenous Gas Cooled Reactors (GCRs), and Fast Breeder Reactors (FBRs) 2 were pursued until 1969, when it became apparent that, without significant development work, the GCRs could not compete with the US Light Water Reactors (LWRs). The decision was then made to build PWRs under license with Westinghouse. The French continued with breeders operating on the plutonium cycle and completed the reactor Phoenix in 1976 and Superphenix in In West Germany (FRG), the first commercial order for a Boiling Water Reactor (BWR) was placed in In the subsequent years Allgemeine Elektricitaets- Gesellschaft (AEG) supplied BWRs under a license from GE, and Siemens supplied PWRs under license from Westinghouse. Other technologies, such as gas cooled reactors, were also investigated. The Germans initiated construction of the Thorium High Temperature Reactor (THTR) at Schmehausen with pebble-bed fuel and helium coolant. The plant, which has operated quite successfully, will be closed down because of budgetary constraints. In the UK, the first reactors, which began operation in the late 1950s, were small GCRs used to produce both electrical power and plutonium. These reactors became known as Magnox reactors, owing to their use of magnesium cladding for uranium oxide fuel. In the USSR, a 5 MWe plant with light-water cooled, graphite-moderated reactor was deployed in 1954 as the world's first nuclear power plant to produce electricity for commercial use. Period Two: Mid-1960s to Mid-1970s During this period, the vast majority of reactor orders in the world were placed. The nuclear power industry in France decided to pursue a standardized PWR design independent of its US licensors. The nuclear power industry in the FRG also became independent of its US licensors. In the USSR the graphite-moderated, light-water cooled design was first adopted and deployed for power production (the Chernobyl station had four units of this design). Due to the safety problems and cost record of this design, the Soviets switched to a light-water moderated and cooled design, akin the PWR developed in market economies. 2 An explanation of the various reactor types is given in Section 2.2.

10 5 Period ltree: Mid-1970s to 1978 This was a time of mixed activity in the U' No new reactor orders were placed. While some new orders were placed worldwide, some older ones were cancelled, mainly in the US. The reasons for the cancellations stemmed mainly from lower than expected demand for electricity, but included also growing opposition to nuclear power and escalating construction costs. This opposition was fueled by growing concerns about public health and safety, questions on radioactive waste disposal, mismanagement of projects, and a public identification of nuclear power with the proliferation of nuclear explosives. In 1975, a fire at Browns Ferry 1 and 2 nuclear power plants in the US, although not resulting in damage to the reactors, raised concerns about how close these reactors came to a core meltdown. An industry-wide reevaluation of fire protection measures in nuclear power plants resulted in long outages and costly corrective actions. Period Four 1979 to Present In 1979 a watershed event occurred in nuclear power history: the Three Mile Island Unit 2 (TMI-2) accident in a reactor of a Pennsylvania nuclear power plant in the US. It led to massive investigations, public hearings and regulatory actions. The record shows that radioactive releases to the environment and hence impact on public health were minimal. However public concern grew to unprecedented height stemming from ineffectual, distorted, and conflicting messages in public communication; the perceived inability of the US Nuclear Regulatory Commission to promptly and effectively control the crisis; shortcomings in design, operation and maintenance; and the violation of safety procedures. The accident led to a high degree of stress in the area's local population, to a reconsideration of emergency procedures, and to a series of costly design backfits intended to prevent similar accidents from happening in the future. Although there was no harm to the public's physical health, the accident was an economic disaster. An investment in the order of US$1 billion was lost within a few hours; Unit 1 was placed out of operation for about eight years; and the cleanup effort, in which both the Federal Government and the US utilities participated, has cost more than US$1 billion over 10 years, bringing the utility owner to the brink of bankruptcy. Cleanup operations will continue with no prospects that the damaged reactor will ever return to service. Clearly, the negative impact of the TMI-2 accident on the nuclear power industry was very grave. Following the accident, many nuclear power plants were cancelled in the US, including almost completed units. Among them were Perry 2, Grand Gulf 2, WNP- 1, and WNP-3. Another blow was delivered to nuclear power in the US when the owners of Midland, a nuclear power plant 100% complete but plagued by quality assurance and licensing problems, decided to convert the plant to a gas-burning cogeneration station. Another significant setback to the deployment of nuclear power was

11 J1. the decision of the Swedish people to phase out nuclear power by the year 2010, even though nuclear power provided 47% of the country's electricity in It should be noted, howwver, that the practical replacement of nuclear power in Sweden is problematic, and it is not at all certain that the phaseout will take place. The year 1986 was, however, the blackest year in the history of the nuclear power industry. It was then that the most serious accident ever in a commercial nuclear power plant occurred at Unit 4 of the Chernobyl Plant in the USSR. The cause of the accident was gross violation of operating procedures and a design that lent itself to sudden increases of power (positive rather than negative feedback of reactivity) and the presence of graphite that caught firr; and burned uncontrollably. Although the reactor was equipped with some kind of containment structure, this was not sufficiently strong to contain the accident and limit the spread of radioactivity to the environment. Massive amounts of radiation were released to the atmosphere causing the following dallage: o o o O o Thirty-one people died from acute radiation exposure. The population subjected to long-term cancer effects from the accident was estimated in the range of 10,000 to 40,000 although the method of estimation is a matter of controversy, and the number could be lower. Large tracts of land became unusable. About 100,000 people were relocated. Radioactivity was transported as far as the UK, Italy, Spain, and Sweden, causing widespread public concern. It must be noted that although a large amount of radioactivity (about two million curies) was released uncontrollably, the accident was less severe than other serious industrial accidents such as the Bhopal chemical accident in India that caused upwards of 2,000 deaths and tens of thousands of injuries. Although such a release of radioactivity caused serious local damage, it did not have a significant or lasting impact on the world's global environment. However, it did have a detrimental effect on the public's perception of nuclear power and seriously challenged the nuclear power industry's safety record. It is important to note that the flaws of this design had been known for some time. Since the accident, the Soviets have taken several design and operational measures to correct these deficiencies. Moreover, this type of plant has been discontinued in the USSR, and a decision was made to proceed with the deployment of the PWR design.

12 The years following 1986 have been characterised by great uncertainty about the future of nuclear power. In the US, completion of ongoing nuclear units continued while some orders were placed in Korea, France and Japan. On the whole the nuclear power industry is in a period of stagnation. Another important event took place in June, 1989 when the citizens of Sacramento, California, voted by a 53% majority to shut down Rancho Seco, a nuclear power plant operating since 1975 but plagued with operational problems and poor performance. The significance of thic incident in the history of nuclear power in the US is that the opponents of nuclear power attacked the key principle that has helped the nuclear power industry in this country to survive 14 referenda in 13 states. namely, that nuclear power is cheaper than other sources of electricity. In all previous referenda the debate focused primarily on purported threats to human health and safety to the environment; in Rancho Seco the economics of nuclear power were questioned. Lately there has been some shift in the public's view of nuclear power. This change has been spurred by the growing concern over the greenhouse effect, and acid rain, which are caused, at least partially, by the burning of fossil fuels. Recent French experience demonstrated the potential for reducing atmospheric pollution by switching from fossil plants to nuclear. In 1970 France's electricity supply was about 50% fossil, 45% hydro and 5% nuclear. After the oil embargo of 1973, France embarked on a large-scale nuclear program. In 1988 the electricity supply was 70% nuclear, 20% hydro and 10% coal. Table 1.1 shows there has been a ten-fold reduction in fossil power plant emissions in France over an 8-year period due to lower fossil plant operation following the switchover to nuclear, even though the total electricity supply in France grew about 50% during the same period. Table 1.1 FOSSIL PLANT EMISSION DECREASE IN FRANCE Emission Thousands of Tonnes Sulfur dioxide Nitrogen oxide Carbon dioxide Particulate matter 80 2 Total Source: Rl (see List of References).

13 6 At the present time, however, it appears that the environmental groups still believe that nuclear power in its present form represents a worse alternative than fossil fuels. Nonetheless, for several reasons, including diversity of energy supplies, energy supply independence from oil exporting countries, hedging against future environmental problems with the burning of fossil fuels, and in some cases, national pride, the nuclear power programs in several countries are continuing, albeit with caution. For example, in the first half of 1989 new nuclear power units were commissioned in the US, Japan and France. Meanwhile, China is also rigorously pursuing both an indigenous nuclear capability and nuclear plant imports; its first indigenously designed and built unit, a 300- MW PWR Quinshan-1, is almost complete and scheduled on line in December 1990 while the second project, Guangdong Units 1 and 2, comprising two 900-MW PWRs imported from Framatome, France are 40% and 30% complete.

14 l 2. NUCLEAR POWER TECHNOLOGY Over the last 40 years nuclear power has evolved into an important source of electrical power, providing today some 18% of the world's supply of electricity. This Section summarizes worldwide data on the status of nuclear power development and also describes the major nuclear power plants in use today. 2.1 Nuclear Power Statistics Over the years, many types of nuclear reactors have been used to generate electrical power. The numbers of these reactors in operation and their capacity are listed in Table 2.1. This table also shows that the pressurized water reactor is by far the dominant design. Table 2.1 NUCLEAR POWER REACTORS IN OPERATION WORLDWIDE, 30 MW OR OVER, BY REACTOR TYPE AS OF DECEMBER 31, 1988 Reactor Type No. of Units of Operation Pressurized Water Reactor (PWR) 238 BoiLing Water Reactor (BWR) 86 Light Water CooLed, Graphite Moderated Reactor CLWGR) 26 Pre -surized Heavy Water Reactor (PHWR) 28 Gas CooLed Reactors, all varieties (GCR) 45 Liquid Metal Fast Breeder Reactor CLMFBR) 6 TotaL 429 Source: R3 (see List of References) and Annex 1. From 1960 to the early 1980s, the growth in nuclear electricity generation as a share of total electrical energy has been quite steep, as shown in Figure 2.1. This remarkable growth has been followed, however, by a slowdown in the late 1980s. Although nuclear power accounted, in for an average of 17% of the total electric generation worldwide, this component is much higher in several countries as illustrated in Figure 2.2. In 1988, nuclear power accounted for 40% or more of total electricity generation in six countries: France (70%), Belgium (66%), Hungary (49%), Sweden (47%), the Republic of Korea (47%) and Taiwan, China (41%). A list of nuclear power reactors in operation and under construction in the world, their capacities, the electricity they supplied in 1988, as well as the total operating experience by country, appears in Annex 1.

15 Figure IIAEA-NENP % I B1. 4 TW.h 12 0~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~0 7 energy f 6 1~~~~797 =WhI W % a~~~~~~~~~~~er c0 2 z7ti 1-. I..IJ- Years Nuclear electricity generation and share of total electrical energy for the period 1960 to 1988

16 9 Figure 2.2 COUNTRIES WITH HIGHEST NUCLEAR SHARE OF TOTAL ELECTRICITY PRODUCTION IN 1988 FRANCE 70 BELGIUM 66 HUNGARY 49 SWEDEN 47 REP. OF KOREA 47 TAIWAN, CHINA (*)41 SWITZERLAND _ 37 SPAIN 36 FINLAND 36 BULGARIA 36 GERMANY, F.R. 34 CZECHOSLOVAKIA 27 JAPAN 23 USA 0 UK 19 CANADA 6 USSR 1 3 ARGENTINA 11 GERMAN D.R NUCLEAR SHARE (x) ('): IAEA estimates LBOO1 Source: R8.

17 10 The status of nuclear power in the developing countries is summarized in Table 2.2. Table 2.2 NUCLEAR POWER IN THE DEVELOPING COUNTRIES AS OF DECEMBER 31, 1988 In Operation Under Construction All Developing Countries, Units MW(e) 21,173 22,160 22,407 Countries in CPE-Europe, Units MW(e) 7,437 7,494 11,206 Countries outside CPE-Europe, Units MW(e) 13,736 14,666 11,201 Source: R4 (1987), R8 (1988). 2.2 Review of Existing Reactor Designs As Table 2.1 above shows, PWRs, BWRs. and PHWRs together constitute 82% of all the operating power reactors in the world. Because of this, these designs will be reviewed in the following descriptions in more detail than the other reactor designs The Pressurized Water Reactor (PVR) About 55% of the operating reactors in the world are PWRs. A schematic outline for a PWR and typical design data are shown in Annex 2. The fuel used in this type of reactor is uranium oxide (UO 2 ) in the form of pellets, enriched to approximately 3.5% Uranium-235. These pellets are encapsulated inside zircalloy tubes which form a cladding. The fuel-cladding arrangement is called the fuel rod. A cluster of about 225 of these rods forms the fuel assembly, and in a typical 1100-MWe reactor approximately 200 of these assemblies form the reactor core. The reactor core is cylindrical, about 3.7 meters high and 3.4 meters in diameter and contains about 90,000 kg of uranium. The core is placed in the reactor pressure vessel which is a massive piece of equipment measuring, for a 1000-MW unit, over 12 meters in height by 4.7 meters in diameter with a wall thickness in excess of 20 cm. It is designed to withstand a pressure of ap- -- imately 175 bar and a temperature of 340 C. The total weight of a large reactor ves.el could approach 450 metric tons. Transportation of the component from the fabrication ;hop to the site is a major undertaking and could take many weeks. The reactor vessel and the piping attached to it constitute a barrier to any radioactive release due to fuel failu:e. In a PWR the heat is generated in the core by the fission of uranium. Light (regular) water is used as both moderator of the fission neutrons and coolant. The term

18 11 "pressurized" derives from the fact that the water is kept at a very high pressure of about 155 bars (2250 psia) so that, at the maximum prevailing water temperature, no boiling occurs. The generated heat is transferred from the fuel to the coolant, which flows into one side (primary) of a steam generator. There, it heats water kept at a lower pressure on the other side (secondary), boiling it to generate steam. This steam turns the turbine and the electric generator connected to it, generating electricity. These reactors are equipped with a variety of engineered safety features to prevent and/or mitigate the consequences of an accident. The reactor, steam generators and associated auxiliary equipment are enclosed in a containment structure that serves as the last bairrier to any radiation release. The majority of the containment structures are made of concrete and are cylindrical, about 37 meters in diameter and 60 meters high. They are designed to withstand internal pressures from a design-basis accident of up to 4 bars (60 psia) The Boiling Water Reactor (BWR) About 20% of the operating reactors worldwide are BWRs. A schematic outline for a typical BWR plant and typical design data appear in Annex 3. In a BWR, as in a PWR, light (regular) water is used as both moderator and coolant. The term "boiling" derives from the fact that due to the heat generated from fission, the water boils inside the reactor vessel. This is because the water is kept at a pressure equal to the saturation pressure at the prevailing water temperature, namely 69 bars (1,000 psia). The generated steam turns a turbine connected to an electric generator, thus producing electricity. The reactor core for a typical, large 1200-MW unit is cylindrical, about 3.7 meters in diameter and 4 meters high. The reactor vessel is even larger than that of PWRs. A typical vessel for the 1200-MW unit is over 22 meters in height and about 6.5 meters in diameter. The wall thickness is cm; somewhat lower than that of a PWR vessel since the pressure it is called to withstand is about half that of a PWR. The reactor pressure vessel and associated equipment are enclosed in a steel containment structure (not shown in Annex 3), called the "primary containment". The primary containment is equipped with a pressure-suppression compartment, partially filled with water, designed to absorb the heat generated after an accident, and serves as a "scrubber" of any radioactive release. The primary containment is enclosed in a concrete structure called the "secondary containment" which serves as a last barrier of radioactive release in an accident The Pressurized Heavy Water Reactor (PHWR) A schematic diagram for the PHWR, also known as CANDU (CANadian, Deuterium, Uranium) reactor, appears in Annex 4. This design was developed and is promoted by Canada but has been deployed in other countries such as Argentina,

19 12 Pakistan, India and Korea. Approximately 6% of the operating reactors worldwide are of this type. In a PHWR heavy water, i.e. water in which the regular hydrogen atoms have been substituted by atoms of deuterium, serves as both coolant and moderator but these functions are kepl separate through two separate loops. The term "pressurized" derives from the fact that t 1 ie heavy water coolant is kept at a high pressure so that at the maximum prevailing heavy water temperature, no boiling occurs. The heavy water moderator is kept at a relatively low pressure. Heavy water has an advantage of being a much weaker absorber of neutrons than light water. Thus, with a better "neutron economy" a reactor can be run with natural instead of enriched uranium. In this way Canada avoided the need to construct complex and expensive uranium enrichment facilities. The disadvantages of heavy water and natural uranium are that, because of the lower neutron flux, larger cores are required. As with PWRs, steam generators are used to transfer the heat from the heavy water, which circulates in the primary side, into the light water which circulates in the secondary side, thus causing it to boil. Because of its larger core, it has been estimated that a CANDU reactor is roughly 20% more expensive to construct than its equivalent LWR. However, this higher construction cost is compensated by a much lower fuel cost for the natural uranium fuel cycle, about one half that of the enriched uranium fuel cycle. A containment houses the reactor, steam generator, and the moderator loop. Design data for CANDU reactors are also give in Annex The Gas-Cooled Reactor and its Variations The Gas-Cooled Reactor (GCR) is a graphite-moderated unit using natural uranium as a fuel. The majority of these reactors were built in the UK, at the start of its nuclear program, originally to produce both plutonium for military purposes and electrical power for commercial use. The choice of natural uranium as a fuel was originally dictated by the unavailability of enriched uranium. But the rather poor capacity of graphite in slowing down neutrons and its relatively high neutron-absorption characteristics resulted in very large core volumes. The choice of coolant for the first generation of gas cooled reactors was carbon dioxide. The oxide fuel is clad with a thin layer of magnesium alloy, hence the name Magnox for these reactors. The heat is transferred to a steam generator. The system uses a concrete pressure vessel and the primary system and associated components are housed in a containment structure. The relatively high percentage of GCRs in operation (10% of the world's reactors) despite their shortcomings, is the result of the initial push for this design by the UK, not a reflection of current trends. A strong motivation to increase the heat output per unit volume of the reactor core led to the development of the Advanced Gas Cooled Reactor (AGR) in which

20 13 higher gas temperatures prevail. The AGR uses uranium fuel slightly enriched in U Its coolant is carbon dioxide but at substantially higher temperatures and pressures than in the GCR. Because of the AGR's higher power densities and smaller core volumes, the AGR is less costly than the GCR. But even with the AGR's improvements over the GCR, the UK decided to abandon the gas cooled reactors and to adopt the US PWR design to UK conditions and criteria. The first British PWR, the Sizewell B, is currently under construction in the UK. A program to build more units of this type has been recently postponed following the Government's decision to privatize the electric power industry and to break up generation into three corporations. Following successful development and deployment of the GCR concept in the UK, the US developed its own gas-cooled reactor, called the High Temperature Gas- Cooled Reactor (HTGR). The first HTGR prototype was installed at Peach Bottom, Pennsylvania in Its fuel consisted of uranium and thorium carbides, its moderator was graphite, and its coolant was helium, an inert gas. It had a net output of 40 MWe. After eight years of successful operation, it was taken out of service in 1975 for economic reasons. The second HTGR, the Fort St. Vrain built in 1979, has a net output of 330 MWe. Due to continued technical difficulties that forced the plant out of service frequently and limited its output, the owner utility plans to take it out of service in 1992 after only 13 years of service. Another type of gas-cooled reactor is the pebble-bed reactor, which evolved in the FRG. Its fuel, encapsulated in ceramic spheres ( cm wide) is fissile and fertile material in the form of very small particles (0.4mm) dispersed in graphite that serves as a moderator. Its coolant is helium gas. The design was demonstrated in a 15 MWe experimnental reactor (AVR). The scaled-up version of it, a 300-MWe reactor at Schmehausen, FRG, called the Thorium High Temperature Reactor (THTR), has been completed and has demonstrated its technical features. However, it also had construction delays, funding and regulatory problems, so its future is uncertain. However, because of important safety characteristics, this type of design, specifically a 100-MWe modular unit which exhibits passive safety features, is being considered as a candidate for future development. This design can withstand a simultaneous failure of control rod insertion and loss of flow, without damage to the reactor core as has been demonstrated experimentally at the AVR pilot plant in Julich, FRG. The USSR has shown interest in adopting the high-temperature reactor for its generation system and has recently entered into an agreement with the FRG for technology transfer in this area The Light-Water-Cooled, Graphite-Moderated Reactor (LWGR) This is the first design commercially deployed in the USSR, under the Russianequivalent abbreviation RBMK. Chernobyl, the plant that experienced the major accident in 1986, is an RBMK Its fuel is contained in large tubes and cooled by light (regular)

21 14 water that flows through the tubes at high pressure. These tubes are embedded in graphite, which serves as a moderator. This design has several drawbacks which, though widely publicized after the Chernobyl accident, were weli known to the technical community from the start. It is difficult to control, can have a violent steam-graphite reaction following a pressure-tube leak, and does not have a full containment structure. The Soviets corrected some of these drawbacks after the Chernobyl accident but these plants still operate without full containments. The USSR is now postponing plans to deploy RBMKs in favor of deploying VVERs (USSR's version of the PWR) and enhancing their safety features The Fast Breeder Reactor (FBR) The types of reactors reviewed so far are thermal reactors--reactors in which fission is accomplished through neutrons slowed by their collisions with the moderating medium. But the ability of such neutrons to convert fertile material (e.g. Uranium-238), into fissile material (e.g. Plutonium-239), is limited. The "breeder" reactor is an alternative design without this conversion shortfall. Tt produces more fissile material (i.e. fuel) than it consumes, hence the name "breeder'. Breeding is accomplished through fission-generated neutrons that are "fast" (i.e., not slowed by moderators). The Liquid Metal Fast Breeder React.- (LMFBR) which uses a liquid sodium coolant, is the only FBR design yet implemented. Seven LMFBRs are in operation worldwide, five of which are used for commercial power generation. Most are prototypes. A few more are under construction. The LMBFR design is not, however, favored for widespread use because of its high cost, its massive production of fissile plutonium which poses proliferation risks, and a perception that there is no shortage of uranium supplies. The US commercial prototype, the Clinch River reactor, was cancelled after a long and heated debate over its economic and safety performance. The first French FBR, the Phoenix, has operated successfully but its successor, the Superphenix, is experiencing technical problems; however, the USSR and Japan are still both cautiously pursuing the development and deployment of FBRs.

22 15 3. NEW TRENDS IN REACTOR DESIGNS During the evolution of nuclear power over the past 30 years, its strengths and weaknesses have become clearer. The strengths include its insignificant pollution in normal operation, the abundance of nuclear fuel and fuel diversification, and its high electricity output. The weaknesses include the requirement for stringent and costly safety provisions; the unpredictable nature of the regulatory process in the US; the large reactor sizes required for the economies of scale; and lastly, rapidly escalating costs especially in the US, owing to long construction periods, changing safety requirements, and in several cases, poor project management. The nuclear industry has been addressing these problem areas and has proposed and/or implemented solutions to remedy them. They are categorized in five broad areas: A. Improved Designs B. Evolutionary Designs C. Passive Designs D. Modular Designs E. Standardization 3.1 Improved Designs Existing designs have been improved to incorporate features that enhance safety, reliability, availability and maintainability of the power plants. An example of an improved design is the British PWR (Sizewell B), the currently favored reactor in the UK. This is a modification of the Standardized Nuclear Unit Power Plant System (SNUPPS), originally built in the US. The UK design improves SNUPPS with more emergency core-cooling injection pumps, more auxiliary feedwater-system backup pumps, more emergency diesel generators, and a larger containment to make maintenance easier. In another move to improve nuclear designs Westinghouse, Mitsubishi, and the Japan Power Company have joined forces in an effort, now in progress, to incorporate passive safety system features in existing "mature" nuclear reactor designs. 3.2 Evolutionary Designs Proposed new designs would replace add-on safety features on existing reactors with built-in ones. The result is a simpler design, higher reliability and better maintainability. These designs include control rooms with user-friendly diagnostics and other features based on the human factor considerations in research and development. One example is the advanced BWR Unit design by GE, Hitachi and Toshiba, which is

23 16 only 70% the size of current BWRs. One of the advantages of this design is the location of coolant pumps inside the reactor pressure vessel. 33 Passive Designs These are smaller and simpler than current generation reactors (about 600-MWe) that rely mainly on passive (rather than man-controlled) safety systems for "fail-safe" shutdown and heat removal. They use natural forces like gravity and convection instead of active controls to ensure safety as used in the currently operating plants. The US has two such proposed designs: Westinghouse's AP-600 and GE's SBWR (Simplified BWR). In both, the emergency cooling water is stored above the reactor pressure vessel, eliminating the need for emergency coolant pumps. Asea-Atom (now part of ABB)'s Process Inherent Ultimate Safety (PIUS) is a Swedish 660-MWe counterpart, and Combustion Engineering has joined forces with Stone and Webster and UK's Rolls Royce to design a passive 325-MWe PWR called Safe Integral Reactor (SIR). The advanced designs have set a goal of 36 months for plant -!onstruction at a cost competitive with that of coal plants equipped with flue gas desulfurization. 3.A Modular Designs These designs are small modular units that a utility can add to a system as the demand for electricity increases. One such design is General Atomic's Modular High Temperature Gas-Cooled Reactor (MHTGR). This is similar to the FRG's THTR-300, which is a 300-MWe "pebble-bed" reactor. General Atomic claims that with the passive safety features of this design, it needs no containment. But there is a difference of opinion in the technical community on this claim. Modular gas-cooled reactors are also under study in the USSR. 3.5 Standardization Standardization is widely regarded as a remedy to many of the problems facing nuclear power because of three key benefits it promises: 1) Economies in manufacture 2) Reduced regulatory procedures, and 3) Lower construction costs. However, those opposed to standardization argue that a single design error would also be standardized, threatening a host of units. Opponents also argue that it may encourage technological stagnation. To date, several countries have implemented standardization in varying degrees. France's state-owned utility, Electricite de France has done so vigorously with very

24 I7 positive results. And since early 1970 the nuclear industry in FRG has used standardization to control costs and siplify licensing. In 1981, FRG initiated ;*s"convoy" system, designed to standardize requirements between similar PWR designs.t various stages of construction and licensing. The main features of the convoy system are: (1) a common set of engineering documents for all projects; and (2) only four licensing steps (three for construction and one for commissioning) in contrast to up to 15 steps that have applied to previous projects. Using the convoy concept, FRG has been able to license several new plants since In the US, the SNUPPS design, with two plants currently in operation, represents a positive but isolated step towards standardization. But even though nuclear reactor vendors have also proposed standardized designs (many approved by the US Nuclear Regulatory Commission), standardization has not found general support in the US. In the UK, however, standardization of a modified SNUPPS design in the Sizewell B reactor and four planned units represents a serious move toward standardization. Further experience in standardization's impact on construction time, licensing, operability and cost will be useful.

25 18 4. NUCLEAR POWER COSTS 4.1 Background The question of future nuclear power costs is clouded by the uncertainties of regulatory requirements varying by country, construction times affected accordingly. and the possible impact of ongoing reactor design changes. It is meaningless to look back at past designs, schedule achievements, and actual nuclear costs, because nuclear plant construction delays in some countries, particularly the US, and public apprehension following the Three Mile Island and Chernobyl accidents, have established a new environment for any power system planning studies that include nuclear power as an option. Any proposal to build a nuclear power plant now must necessarily face opposition, both national and international, given the growing worldwide concern over all aspects of atmospheric degradation. 4.2 Nuclear Plant Construction Times The lengthened nuclear construction times are apparent in Annex 5 which shows the variations in construction time (first concrete to grid connection) for 450 nuclear units constructed between 1956 and The extremes range from a little over three years achieved by France and the UK in the late 1950s to 14 years for an Indian nuclear unit completed in the mid-1980s. However, more important is the trend in construction times. The average construction time was less than four years before 1960 and almost nine years for nuclear units connected to the grid in 1987, thus more than doubling over the 30-year period. 43 Typical Nuclear Power Plant Cost Estimates Given the great uncertainties concerning future nuclear unit designs, regulation, and construction times, any cost estimates for nuclear power can only be approximate. Nonetheless, many references are available (see Bibliography) presenting nuclear cost estimates for a wide range of conditions and sites. One such estimate (by the US Department of Energy) is shown in Annex 6 and presents the "overnight" (excluding escalation and IDC) estimated capital cost for a 1100-MW nuclear unit to be commissioned in the year The results are $1600 per kw capital cost under ideal conditions with an 8-year construction time, or $2700 per kw under typical US experience and a 12-year schedule. If one adds allowances for escalation and interest during construction the total investment requirements (in current dollars) would probably be more than double the above $1600 to $2700 figures, clearly showing that nuclear power plants, based on today's conditions and designs, are extremely capital intensive.

26 4.4 Comparison of Base Generating Costs 19 Some existing nuclear plants are producing electricity at very low generation costs of only a few US cents per kwh, reflecting the fast construction schedules, limited regulatory action, and "turnkey" construction arrangements that characterized the early nuclear units. However, future nuclear plants will not benefit from such ideal conditions and the generation costs will accordingly be higher. Many generation cost comparis-'ns for various plant types are available with widely differing results, depending to some extent on the particular bias of the estimator. Annex 7 shows a generation cost comparison prepared by the International Energy Agency (IEA), presented in a 1988 report on "Emission Controls in Electricity Generation and Industry". The IEA estimates show that future nuclear generation costs will be about 5 USe (1987)/kWh based on the assumptions shown in Annex 7 including a 10% discount rate, compared to about 4 US /kwh for coal, 5/2 USe/kWh for oil, and 41/2 USe/kWh for gas (presumably combined cycle). The assumed oil and gas prices seem high, but the IEA reference explains that these are average expected lifetime prices. Similarly the coal price band of $40 to $60/tonne used in the report may be high. Nevertheless, the IEA study shows that at 10% discount rate, nuclear is not economic relative to coal or gas thermal, based on the assumptions used, and probably not even economic compared with oil thermal, if lower oil prices continue. However, the IEA figures also show that all the generation costs are in a 3 to 5/2 USe/KWh band, so any significant changes in nuclear construction times, nuclear capital costs or fossil fuel prices could easily change the order of merit in favor of nuclear.

27 S. THE FUTURE OF NUCLEAR POWER 20 For the near and medium term, i.e., for plant commissioning in the next 10 years, the prospects of nuclear power depend strongly on conditions in and perspectives of specific countries. For certain countries such as France, with an excellent record of plant standardization, construction and operation, the deployment of nuclear plants will continue albeit at a reduced pace, given also the fact that, in that country, nuclear energy has already reached 75% of electricity market penetration. Japan, Korea and Taiwan (China), having good experience with their nuclear development will probably continue on this development path, in view also of their heavy dependence on imported energy resources and the need for secure and diversified supply sources. Other countries, such as China, Pakistan, and India have also shown a strong determination to develop nuclear power based on current technology, in particular French technology which, as mentioned earlier, has had an impressive record. These latter countries may have important motivations other than the electricity supply, such as national prestige and a strong desire for indigenous technological development. Outside these specific cases, the prospects of nuclear power based on current technclogy are indeed bleak, given the cost record and safety con'rerns among the public. ' the long term, i.e., beyond the year 2000, the prospects of nuclear power deployere.]i may become much brighter, based on new designs, as described in Section 3. If the new simplified and standardized designs, now being developed by international consortia fc.r PWRs and BWRs, can '5tain a license in the time period , if constructic(;; can be guaranteed at a fixed cost and within a reasonable time period of three to fi. years, if a solution (mostly political and institutional) for the radioactive waste manag ment problem 3 can be established, and if the public and the utilities can be convinced that the plants will be sufficiently robust and resistant to operational transients an-. rmalfunctions 1 including human error, it is quite possible that nuclear power will once againi become a viable option for utilities around the world. It has been argued by technical experts that although the evolutionary designs mentioned above, which will still require the functioning of safety systems for reactor shutdown and residual heat removal from the core to prevent plant damage and the spread of radioactivity to the environment, may be acceptable in developed countries where the technical infrastructure and personnel competence exist at high levels, this could hardly be the case in developing countries where many more scenarios of 3 This is certainly a highly controversial matter. There are those who would argue that the technical solutions proposed have not been adequately demonstrated and that it is impossible to predict waste repository behavior and hence risks, hundreds of years into the future. A separate paper on radioactive waste management is being prepared for publication.

28 21 equipment malfunction and human error, including the consequences of political instability and local conflicts, can be convincingly postulated. For this latter case, revolutionary new designs that can be demonstrated by actual test to sustain the worst possible equipment failure and human error or negligence without significant damage to the reactor core or plant, will be necessary. Such a possibility exists, based on a graphite-moderated, heliumcooled reactor design. The successful tests conducted at Julich, FRG, indicate that a modular, 100-MW (electric) reactor can be built that will satisfy the above stringent criteria. If the cost of such a plant can be contained in the order of US$1,500 in constant 1990 US$ and if its passive safety can be demonstrated by actually testing a full size unit, it is reasonable to assume that the confidence of both the public and investors can be obtained. Although more development work, especially in the area of balance of plant needs to be done, such a development may open the door for world-wide development, including in developing countries, with wide public acceptance. The thrust to develop such a nuclear design for large-scale deployment may, ironically, come from environmental concerns. More specifically from the escalating worries concerning environmental damage from the burning of fossil fuels, particularly the greenhouse effect. Massive environmental degradation from acid rain deposition has been documented and demonstrated beyond doubt in a number of areas including Eastern Europe, Canada, the US, and the Scandinavian countries. Although acid deposition may be controllable to a great extent, through a variety of methods to reduce sulphur and nitrogen oxide emissions, fossil fuels, particularly coal, emit a host of other noxious substances, including toxic trace metals (from arsenic to zinc!), radioactivity, polycyclic aromatic hydrocarbons (PAHs) and carbon dioxide. This latter emission may prove to be, in the long run, the most dangerous substance and the most difficult, if not prohibitively expensive, to control. With grave concerns for the possibility of a global warming trend that may drastically alter the earth's climate and cause massive economic and population dislocations, it seems quite possible that, "clean" and "safe" nuclear power, as defined above, may be found by the public a more acceptable solution and an important component in the future fuel mix for electricity generation. With increasing electrification of the economy, and particularly of the transportation and industrial sectors which are major contributors of greenhouse gases, nuclear power may also displace a good portion of fossil fuels used in these sectors. In this perspective, and assuming the advent of a new generation of nuclear plants, the long-term prospects of nuclear power seem much better than the short- to medium-term prospects. Technical developments in this area merit continuous and careful monitoring.