Nuclear Power Reactor Designs: From History to Advances

By Wang Jun

Nuclear Power Reactor Designs: From History to Advances analyzes nuclear designs throughout history and explains how each of those has helped to shape and inform the nuclear reactor designs of today and the future. Focused on the structure, systems and relevant components of each reactor design, this book provides the readers with answers to key questions to help them understand the benefits of each design. Each reactor design is introduced, their origin defined, and the relevant research presented before an analysis of its successes, what was learned, and how research and technology advanced as a result are presented.

Students, researchers and early career engineers will gain a solid understanding of how nuclear designs have evolved, and how they will continue to develop in the future.

• Presents reactor designs through history to present day, focusing on key structures, systems and components
• Provides readers with quick answers about various design principles and rationales
• Includes new approaches such as the micro-reactor and small-modular reactors

• Language: English
• Publisher: Academic Press
• Release date: Dec 1, 2023
• ISBN: 9780323999465

Book preview

Section 1

Nuclear power plant history

Outline

Chapter 1 History of nuclear power plants development

Chapter 2 Early graphite-moderated reactors

Chapter 3 Future challenges

Chapter 1

History of nuclear power plants development

Andrea Bersano¹ and Stefano Segantin²,    ¹ENEA, Bologna, Italy,    ²Massachusetts Institute of Technology (MIT), Plasma Science and Fusion Center (PSFC), Cambridge, MA, United States

Abstract

Almost 80 years ago, on December 2nd, 1942, the first nuclear plant (Chicago Pile-1) reached its first criticality in the secret context of the Manhattan Project. After the end of the second World War, the Atoms for Peace program supported the exploitation of nuclear energy for civil purposes. Therefore, nuclear power plants (NPP) based on different technologies started to be designed, constructed, and operated. The present chapter follows the history of NPP development from the early prototypes to the current days, considering the historical and socio-economic context and the major nuclear power accomplishments and accidents.

Keywords

Nuclear engineering; nuclear power plant; nuclear history; energy engineering; nuclear fission; nuclear fusion

1.1 Introduction

The development of Nuclear Power Plants (NPP) has been strictly connected with the historical context, similarly to other technologies. In particular, extensive investments on nuclear technologies boosted the development of the nuclear sector in specific historical events (e.g., the second World War, the energy crisis in the 1970s, etc.). In light of this, the goal of the present chapter is to describe the history of NPP developments in parallel with the main events of recent human history that affected such developments. The chapter starts from the first prototypes to the present days, covering almost 80 years of progress. This time frame has been divided into three main periods (Fig. 1.1):

• The early development, from Chicago Pile-1 (1942) to Shippingport nuclear power station’s first criticality (1957).

• The golden age, with the majority of NPPs built worldwide, up to the Chernobyl accident (1986).

• The last decades up to the present days.

Figure 1.1 Chapter timeline. Nuclear power plant development timeline.

For each period, a brief historical overview is provided, covering the most significant facts related to the development of nuclear energy. Then the main progress and features of fission NPPs are described. In addition, the main advances of nuclear fusion research in each period are also briefly reported. While the historical overview covers both civil and military facts since they are relevant to nuclear energy development, the NPPs described in the present chapter are restricted to those devoted mainly to civil purposes, with only minor mentions of military applications relevant also to the civil development of nuclear energy.

1.2 The early development: from Chicago Pile-1 to Shippingport

1.2.1 Historical context

The beginning of nuclear science can be tracked down at the end of 19th century with the pioneering research on radioactive decay. The advances in nuclear sciences, not covered in this chapter, enabled the development of NPP, whose beginning could be identified on December 2nd, 1942, with the first criticality of the Chicago Pile-1 reactor. The Chicago Pile-1 marked a significant milestone in the Manhattan Project, devoted to the development of nuclear weapons during World War II (Fermi, 1954; Rhodes, 1986), and more widely on mankind’s technological history.

At the end of the war, the tremendous potential of nuclear energy for military and civil purposes became evident. Therefore, a few months after the establishment of the United Nations (UN) on October 24th, 1945, the UN Atomic Energy Commission (UNAEC) was founded on January 24th 1946 by the very first resolution of the UN General Assembly to deal with the problems raised by the discovery of atomic energy (United Nations, 1946). On the same year, the UNAEC was established by the US Congress and President Harry S. Truman signed the McMahon/Atomic Energy Act on August 1st, 1946, for the exploitation of atomic energy for civil purposes (US 79th Congress, 1946).

A major advancement in the civil use of nuclear energy was represented by the election of U.S. President Dwight D. Eisenhower in 1952, who held the famous Atoms for Peace speech at the UN General Assembly on December 8th, 1953. This was followed by the First Atoms for Peace conference (Geneve, Suisse) on August 8–20th 1955. Two years later, on July 29th, 1957, the International Atomic Energy Agency (IAEA) was officially created by the US. Ratification of the Statute by President Eisenhower (IAEA, n.d.). In addition, in Europe, the Treaty establishing the European Atomic Energy Community (or Euratom Treaty) was signed on March 25th, 1957, together with the signing of the Treaty establishing the European Economic Community.

In parallel the civil development of nuclear power, military applications continued to be pursued. Significant events were the first H bomb tests in the U.S. (1952) and in the Soviet Union (1953); in the same year, Nikita Khrushchev was elected First Secretary of the Central Committee of the Communist Party after Joseph Stalin’s death. Another military milestone is the launch of the USS Nautilus (SSN-571) on September 30th, 1954. It became the first nuclear-powered submarine with a nuclear reactor built by Westinghouse Corporation (The National Museum of American History, 2000). Designed under the supervision of Admiral H. G. Rickover, it can be considered the precursor of current pressurized water reactors (PWR).

1.2.2 Fission plants development

Chicago Pile-1, constructed during the Manhattan Project below the University of Chicago’s Stagg Field athletic stadium, can be considered the first manmade nuclear reactor Fig. 1.2.

Figure 1.2 Chicago Pile-1. Drawing of the Chicago Pile-1 reactor. Source: Melvin A. Miller of the Argonne National Laboratory, Public domain, via Wikimedia Commons.

It was fueled by natural uranium and moderated with graphite. Cadmium control rods were adopted. Its first criticality, reached at 3:25 pm (Chicago time) on December 2nd, 1942, marked the beginning of the nuclear age (US Department of Energy, 1994). From that moment on, nuclear reactors started to be built initially in the US and then worldwide for military and civil applications. In the early life of this new technology, right after the end of World War II, nuclear reactors were mainly built for the production of fissile material (e.g., Plutonium-239) for military applications.

1.2.3 Experimental prototypes

At the beginning of the 1950s, the first nuclear reactors for electricity production started to operate. Initially, they were mainly research prototypes with an almost negligible electrical output, but the power rapidly increased enabling the construction of the first commercial nuclear plants. One of the first reactors producing electricity was the Experimental Breeder Reactor I (EBR-I) in Arco (Idaho, US). It became the world’s first breeder reactor. At 1:50 pm on December 20th, 1951, it produced sufficient electricity to power four 200 W light bulbs; the following day EBR-I produced enough electricity to power its whole building (ASME, 1979; US Department of Energy, 1994). EBR-I used uranium metal fuel and liquid sodium–potassium alloy as the primary coolant. Its main goal was to demonstrate that a breeder reactor (generating more fissile material than the consumed one) could be feasible (ASME, 1979).

A relevant series of experimental prototypes was the BORAX reactors, which allowed the development of boiling water reactors (BWR). BORAX reactors were used to study the feasibility of directly boiling water in a nuclear reactor in a safe way. They were designed by Argonne National Laboratory and built on the National Reactor Testing Station in Idaho (U.S.). BORAX-I reactor tank was located in a pit in the ground and was designed for a pressure of around 2.1 MPa (300 lbs/sq. inch). The fuel was in form of aluminum rectangular boxes containing a group of thin concave aluminum plates with the uranium fuel between them. Primary cooling was provided by free convection. BORAX-I started operation in the summer of 1953 and a series of tests were conducted on intentional power excursions and steady boiling operation. In the final test, in July 1954, the reactor was deliberately destroyed by a very fast power excursion, which caused a steam explosion. In the test, the majority of the fuel plates were melted and this provided valuable experimental data (Argonne National Laboratory, 2019; Haroldsen, 2008). The subsequent version BORAX-II was built in late 1954, with an increased power of 6.4 MW(t). The operating pressure was around 2.1 MPa (300 psi). A final intentional destructive test was conducted also on BORAX-II bringing the reactor into prompt critical condition (Argonne National Laboratory, 2019; Haroldsen, 2008). BORAX-I and II showed that the BWR concept was feasible and it was decided to proceed with the construction of a power reactor, BORAX-III. The construction began in 1955, almost after BORAX-II final test. A new reactor pressure vessel was placed below ground level in a concrete cell, while some equipment from BORAX-II was restored and installed. To demonstrate the possibility of electricity production, a dismissed Westinghouse 3.75 MW turbo-generator was connected to the reactor together with the auxiliary equipment (e.g., cooling tower, etc.). On July 17th, 1955, Arco (Idaho, U.S.) became the first town completely powered by a NPP. BORAX-III produced around 2000 kW for 2 hours (Argonne National Laboratory, 2019; Haroldsen, 2008). BORAX-III remained in operation until 1956. Then, with the reactors BORAX-IV (started on December 3rd, 1956) and BORAX-V (started in 1962) additional tests have been performed on different fuel designs (e.g., fuel elements made from ceramics of uranium and thorium, operation with fuel element defects) and the possibility of steam superheating directly within the reactor (Argonne National Laboratory, 2019).

In April 1955 the BR-1 (Bystry Reaktor, fast reactor) fast neutron reactor began operation in Obninsk (USSR). It was a zero-power reactor, which served as a basis for the subsequent BR-5, which was commissioned in 1959 to carry out research on sodium-cooled reactors (Nuclear Engineering International, 2016; World Nuclear Association, 2020).

Among the early prototypes, it is worth mentioning the Sodium Reactor Experiment (SRE) at Santa Susana (California, US). The SRE was designed and constructed by Atomics International in a joint program with the AEC to develop a sodium-cooled, graphite-moderated, thermal power reactor. Southern California Edison Company operated the SRE to produce electricity. An intermediate sodium loop was present due to the activation of sodium in the primary loop. Slightly pressurized helium (at 3 psig) was present on the top of the primary sodium to prevent cavitation in the suction of circulating pumps. The fuel elements were grouped in clusters of 7 rods, each composed of a column of uranium pellets with a total height of 1.83 m (6 ft) within a stainless-steel cladding having a thickness of 0.25 mm (0.010 in). The thermal power was 20 MW; the first criticality was reached on April 25th, 1957, and the first electricity for the power grid was produced on July 12th, 1957 (Atomics International, 1959; Carrol et al., 1983; US Department of Energy, 1994).

1.2.4 Power plants

In this early phase, it is not straightforward to make a clear subdivision between experimental reactors and NPPs, due to the general relatively low power of nuclear reactors and the fact that some experiments were also used to produce electricity (e.g., the SRE). However, considering the increased power output and the explicit role of electricity production, some pioneering NPPs can be identified.

On June 27th, 1954, in Obninsk (Soviet Union), the Obninsk Nuclear Power Plant started operations, becoming the world’s first NPP to generate electricity for a power grid. It had a thermal power of 30 MWt, with an electric output of 5 MWe, and was an LWGR (Light-Water cooled, Graphite moderated Reactor), which can be considered as a precursor of the following Reaktor Bolshoy Moshchnosti Kanalnyy (RBMK), high-power channel-type reactor (Josephson, 2005; World Nuclear Association, 2021). Water, chosen as the primary coolant, was pressurized at 10 MPa; the fuel elements had an annular shape, with metal uranium enclosed between two concentric stainless steel tubes and water flowing in the inner tube (Kotchetkov, 2014).

Due to the relatively low electric power of Obninsk NPP, Calder Hall (Sellafield, United Kingdom) is usually recognized as the first NPP to provide electricity on a commercial scale connected to a civil grid. The reactor was designed with the double purpose of producing electricity and also to produce plutonium for military applications (Brown, 2003). This is emphasized in the code name Pressurized Pile Producing Power and Plutonium (PIPPA) (Burchell, 1999). The power station was composed of four gas-cooled reactor (GCR) MAGNOX type and gas-cooled graphite-moderated natural uranium reactors, with a net power output of 49 MWe each (IAEA Power Reactor Information System PRIS, 2022; Jensen & Nonbol, 1998). Unit 1 was connected to the grid on August 27th, 1956, and was officially opened by Queen Elizabeth II on October 17th, 1956 (BBC, 2022). Both direct and indirect cycles have been considered for power conversion; in the end, it was selected the adoption of a steam turbine with a double pressure cycle (The Engineer, 1956).

Considering the double scope of Calder Hall NPP, used also for military purposes, the Shippingport Atomic Power Station (Pennsylvania, United States) is, in general, recognized as the first commercial-scale nuclear plant devoted only to civil applications. The reactor began operation on December 2nd, 1957, 15 years after the Chicago Pile-1, and was connected to the grid on December 18th, 1957 (ASME, 1980; US Department of Energy, 1994). The reactor configuration was rather unique if compared to current western PWRs; the cold leg nozzles were welded on the lower head of the reactor pressure vessel (Fig. 1.3) and the steam generators were horizontal, with a steam drum above them (Féron & Staehle, 2016). In its initial configuration, Shippingport adopted a core composed of a seed and a blanket design. The seed was made by plates of a metallic alloy of highly enriched uranium (93%), disposed of in an annular shape. The seed was surrounded on both sides by a blanket of natural uranium dioxide fuel rods, made of UO2 pellets in a zircaloy cladding (Clayton, 1993). The electric output with this first core design was 60 MW (ASME, 1980). Later on, the core was modified to increase the power output maintaining the seed and blanket design up to February 1974 and then to prove the feasibility of light water breeder reactor (LWBR) with Thorium breeding from September 1977 to October 1982 (Clayton, 1993; Connors et al., 1979).

Figure 1.3 Shippingport reactor pressure vessel. Photo of Shippingport reactor pressure vessel. Source: Photographer Unknown, U.S. Department of Energy, Naval Reactors Program, Public domain, via Wikimedia Commons.

After the initial development of nuclear science at the beginning of the 20th century and the technological acceleration caused by the Manhattan Project during World War II, the start of operation of Calder Hall in 1956 and Shippingport in 1957 marked the beginning of the commercial exploitation of nuclear energy for civil electricity production.

1.2.5 Fusion plants development

The development history of fusion NPPs shares some common points with fission NPPs development but a rather different timescale. More specifically, commercial fusion NPPs are not expected to be massively deployed before the second half of the 21st century. The cause of such almost one-century-long delay is attributable to the major difficulties found in sustaining the fusion reaction and in the engineering of the reactor itself.

Like fission, and in its same period, fusion reactions have been theoreticized and reproduced. In the decade of 1920s, researchers started finding evidence of the existence of nuclear fusion reactions, the nuclei mass differences strongly suggested such reactions to be hugely exoenergetic (Eddington, 1950). Suddenly, during the 1920s, the hypothesis of the stars being powered by fusion reactions started gaining consensus (Clery, 2014; Eddington, 1950). In the 1930s, the first fusion reactions have been reproduced in the laboratory through the help of particle accelerators (Oliphant et al., 1934). These achievements promptly lead to the conceptualization and engineering of fusion nuclear devices, both for civil and military purposes. Military applications are out of the scope of this chapter and just a few scientific achievements will be shortly named. In particular, fully working nuclear fusion military devices showed up extremely soon with respect to fusion NPPs. The first successful tests were conducted in 1952 by the US and in 1953 by the Soviet Union, with a delay of less than a decade with respect to fission military devices. Military research then mainly focused on raising power and efficiency of such weapons. R&D and testing in this field approached the climax in 1961, when the most powerful thermonuclear bomb ever tested (about 50 megatons), the Tsar Bomba was detonated during a test carried out by the Soviet Union (CTBTO, 2022; Khalturin et al., 2005).

In the same years (1940s–1950s) nuclear fusion research programs for civil application purposes started to arise worldwide. The identification of the thermodynamic conditions at which fusion reactions can take place with relevant rates led to the development of the plasma physics field and complex fusion reactor concepts. Since the very first concepts, nuclear fusion for civil purposes focused on confining the super-hot plasma magnetically.

The first and most simple magnetic configuration was conceived by Peter Thonemann in 1938–39, with the "pinch" concept (Dean, 2013). However, the first actual studies started in 1947 in the UK. Sir George Paget Thomson and Moses Blackman, from UKAEA, invented the "z-pinch design, which allowed for the first experimental campaign of this type. A parallel but independent project was started by Lyman Spitzer who, supported by the US AEC and Princeton University, proposed the stellarator concept giving birth to the Project Matterhorn (July 7th, 1951, Princeton, New Jersey) (Sánchez, 2014; Spitzer, 1958; Tanner, 1982). Spitzer’s stellarator began operations two years later (1953) in a laboratory of Princeton University, setting the basis for the Princeton Plasma Physics Laboratory (PPPL), which has been officially founded a decade later (1961) (Tanner, 1982). During the 1950s, the stellarator concept was considered the most advanced and promising configuration for a fusion machine, until the tokamak concept came by. In fact, in the same years, the Soviet Union started its own fusion research program. The first machine with a tokamak-like configuration was built in 1955 by LIPAN and was known under the name of TMF (torus with a magnetic field) (Azizov, 2012; Smirnov, 2009). In just a few years, the toroidal magnetic machine design was perfectioned and it was given the name of tokamak (short for toroidal’naya kamera s aksial’nym magnitnym polem"—toroidal chamber with axial magnetic field). The tokamak design was presented to the World in 1958 at the Second Atoms for Peace conference with the T1 being the first operating machine officially adopting such a design (Arnaux, 2008). From the following decade on, the tokamak configuration started to be considered by experts as the most promising one and it became the most studied configuration (Barbarino, 2020).

1.3 The golden age: from Shippingport to Chernobyl Accident

1.3.1 Historical context

The historical period from the late-1950s to the mid-1980s is characterized by amazing technological development, strong social transformations, and geopolitical conflicts.

Among the most relevant technological advancements, it is worth mentioning the space race between the United States and the USSR. Space exploration was marked by some iconic moments such as the first flight of a man into outer space by Yuri Gagarin (on April 12th, 1961), the famous speech by United States President John F. Kennedy (September 12th, 1962) setting the Moon landing as the main goal within that decade and the actual landing on the Moon by Neil Armstrong and Buzz Aldrin (July 21st, 1969). Several other fundamental technological achievements have been reached in this historical period, for example the invention of plastic by the Nobel Prize winner Giulio Natta, but probably the most significant advancements are related to the development of the information technology sector, marked for example by the invention of the floppy disk by IBM in 1967, the development of the first microprocessor by Intel in 1971, the founding of Microsoft and Apple in 1975 and 1976 respectively, and the invention of the compact disc by Philips and Sony in 1979.

The development of nuclear energy in this period is also influenced by the geopolitical conflicts taking place, such as the Cold War and the oil crisis. The Cold War between the United States and the USSR was characterized by a rise in military expenses also to increase the nuclear weapons power and number to create the so-called nuclear deterrence, based on the mutually assured destruction principle. In this context, dramatic events took place such as the Cuban Missile Crisis in October 1962. However, the Cold War created also the ground for a series of agreements to limit nuclear weapons testing and later on to reduce also the number of warheads. In 1963, the United States, Great Britain, and the Soviet Union signed the Limited Test Ban Treaty. The signature was caused by the concerns of radioactive fallout due to the continuous testing of nuclear weapons in the atmosphere. The treaty banned tests of nuclear weapons and nuclear explosions in the atmosphere, in outer space, and under water. Underground tests were not prohibited if they did not produce radioactive debris to be present outside the territorial limits of the state under whose jurisdiction or control the explosions were conducted (The US National Archives & Records Administration, 2022). This treaty marked a milestone in nonproliferation efforts, however nonsignatory countries (e.g., France and China) continued to conduct nuclear tests in the atmosphere. In 1968, the Treaty on the Non-Proliferation of Nuclear Weapons was opened for signature and entered into force in 1970. The aim of the treaty was to prevent the spread of nuclear weapons, to further the goals of nuclear disarmament and general and complete disarmament, and to promote cooperation in the peaceful uses of nuclear energy (United Nations, 2022).

Another geopolitical conflict that affected the development of nuclear energy is the oil crisis in 1973. The crisis was caused by some members of the Organization of Petroleum Exporting Countries, which imposed an oil embargo against some Western countries. This was intended as a response to their support to Israel in the Yom Kippur War between Israel and a coalition of Arab states led by Syria and Egypt. The oil prices significantly increased reaching a value quadruple than the initial one. The embargo was lifted on March 1974 (Office of the Historian, 2022). This caused a worldwide effort toward energy source alternatives to petroleum products and, for example, was one of the motivations for France to develop a large nuclear industry (Poisson, 2013). A second oil crisis occurred in 1979. The crisis was caused by the beginning of the Iranian Revolution in 1978. Despite a relatively low global reduction in oil production, the price almost doubled due to a booming global economy and a sharp increase in precautionary demand (Federal Reserve, 2013).

1.4 Fission plant development

1.4.1 Nuclear maritime propulsion

After the initial developments of NPP, nuclear energy was soon considered for the propulsion of large ships both in the civil and military sectors. After the first applications to submarines (i.e. USS Nautilus, as described previously), nuclear reactors have been designed also for military surface vessel propulsion. The USS Enterprise (CVN-65) was the first nuclear-powered aircraft carrier. It was commissioned at Newport News (Virginia, US) on November 25th, 1961, and it was deactivated in 2012 (Naval History & Heritage Command, 2022). It was remarkably powered by eight reactors, PWR Westinghouse A2W. The reactors were paired and connected to four turbines and shafts. Each reactor had a power of 120 MWth and used highly enriched uranium (at 97.3%). The USS Enterprise (CVN-65) was then followed by the ten aircraft carriers of the Nimitz class, using two A4W reactors (Moore George et al., 2016).

The N.S. Savannah (Fig. 1.4) was the first nuclear-powered merchant ship. It was built in Camden, New Jersey (USA), and was launched on July 21st, 1959. It was powered by a PWR with a maximum power of 74 MWth, supplied by the Babcock & Wilcox Company. It had two primary loops with two pumps each and a steam generator, where saturated steam was produced. The primary pressure was around 138 bar (2000 psi) and the second one was around 55 bar (800 psi) (US Department of Transportation Maritime Administration, 2011). The ship was not designed to be commercially competitive but it was intended as a demonstration of the use of nuclear energy for civil maritime propulsion. It was designed to carry 60 passengers and 124 crew people. The N.S. Savannah retired in 1971 (ASME, 1983). Later on, other three nuclear cargo ships have been constructed: the Otto Han (Germany), Mutsu (Japan), and Sevmorput (Soviet Union, Russian Federation), the only one still in service.

Figure 1.4 N.S. Savannah. The N.S. Savannah, the first nuclear-powered merchant ship. Source: U.S. Maritime Administration, Public domain, via Wikimedia Commons.

Nuclear-powered cargo ships were in general not cost-competitive with traditional ones; however, nuclear propulsion resulted to be economically feasible for icebreakers. In particular, nuclear-powered icebreakers have been constructed by the Soviet Union (and Russian Federation later on). The first one, the Lenin, entered into operation in 1959 and was decommissioned in 1989 (Ølgaard Povl, 2001; Reistad & Ølgaard, 2006). It was powered by three OK-150 reactors, two loops PWR with a power of 90 MWth each. The OK-150 had a channel-type core with the moderator volume separated from the coolant one (Makarov et al., 2000). In 1966 one of the three reactors suffered a loss of coolant accident (LOCA) with the melting or deformation of part of the fuel elements. Following the accident, the OK-150 was replaced by two OK-900 reactors, with a power of 159 MWth each and the number of primary loops increased from two to four. A modified reactor version, the OK-900 A, with a power of 171 MWth, was used in the following Arktika class ships (Arktika, Sibir, Rossiya, Sovetskii Soyuz, Yamal, and 50 let Pobedy) (Makarov et al., 2000; Reistad & Ølgaard, 2006).

1.4.2 Power plants

After the first prototypes and relatively small commercial NPP previously described, this period was the most prosperous for NPP development. Fig. 1.5 shows the number of operating reactors worldwide, which raised up to nearly 400 at the time of the Chernobyl accident, with a maximum increase of 30 units in 1984. Similarly, the total electric capacity, shown in Fig. 1.5, significantly raised due to both growing number of NPP and the gradual increment of their power output. In this period, PWRs and secondly BWR were consolidated as the most common designs, even if research on alternative technologies (e.g., fast reactors) continued to be conducted with some significant achievements.

Figure 1.5 Worldwide cumulative number and capacity of NPP. Cumulative number and capacity of NPP worldwide with the three main nuclear power plan accidents highlighted. Source: From From IAEA. (2022). PRIS. https://pris.iaea.org/pris/home.aspx.

The Soviet Union, the United Kingdom, and the USA were the first nations to build NPPs for civil applications, as previously described. However, from the late 1950s, the adoption of nuclear power for electricity production had a major growth with the development of nuclear programs and built of NPPs in several nations (e.g., France, Germany, Belgium, Canada, Italy, Japan, and Sweden).

On July 21st, 1958, in France, the G-2 reactor reached the first criticality and was connected to the grid on April 22nd, 1959. It was a gas cooled reactor (GCR) with a reference unit power of 39 MWe (thermal power of 260 MWth) and was designed also for the production of Plutonium. It was located in Marcoule and adopted natural uranium fuel, graphite moderator, and CO2 as coolant (IAEA, 1963; IAEA, 2022h). Some other GCR entered into operation in the following years (e.g., G-3 and Chinon A-1, A-2, and A-3) but then from the Sixties, France mainly directed toward PWRs. The first France PWR, Chooz-A, was connected to the grid on April 3rd, 1967, and it became also the first commercial PWR built in Europe. It was designed by Westinghouse and it had a reference unit power of 305 MWe (thermal power 1040 MWth) (IAEA, 2022e; Nuclear Engineering International, 2010). In the Seventies, France significantly expanded its nuclear program after the oil crisis with the Messmer Plan. In addition, it fully committed to PWRs initially based on Westinghouse design and later designed by the domestic company Framatome.

In the USA, the growth of NPP number was very rapid. After Shippingport, several other PWRs with increasing power were connected to the grid for example Yankee Rowe in 1960 and Indian Point-1 in 1962. In parallel, starting from the experience on the General Electric plant in Pleasanton (California) and the series of BORAX experiments, the BWR plants started to be exploited on a large scale. The first one, Dresden-1, was connected to the grid on April 15th, 1960, and was located in Morris (Illinois). It was designed by General Electric with a reference unit power of 197 MWe (thermal power 700 MWth). It had a dual-cycle layout with both an external steam drum and steam generators. This design was adopted due to its -load-following capability. In fact, in case of increasing demand, more steam would have been directed to the lower stage of the turbine, without modifying the primary pressure and steaming rate from the reactor. The higher steam flow rate sent to the turbine would have increased the subcooling of the coolant at the reactor inlet causing lower void formation in the core and higher moderation. This in turn would have caused a higher reactor power to meet the new load. However, this specific configuration needed additional plant capital and maintenance costs and was used in a limited number of NPPs (Fennern, 2018; IAEA, 2022f).

In the same period, between the late Fifties and early Sixties, also Canada started the construction and operation of NPP. Canada followed neither the PWR and BWR designs under development in the USA or the CGR under development in the UK and France. It designed pressurized heavy water reactors (PHWR) called Canada deuterium uranium (CANDU), which adopt heavy water both as a coolant and moderator. Since heavy water (D2O) absorbs fewer neutrons than light water (H2O), it allows the use of natural uranium without enrichment as fuel to avoid the cost of reprocessing and lower the risk of proliferation. In addition, CANDU does not use a traditional reactor pressure vessel but horizontal pressure tubes containing the fuel assemblies and the coolant, surrounded by a large tank (the calandria) containing the moderator. The coolant is pressurized and the steam is produced in steam generators. This configuration with pressure tubes allows also the online refueling of the reactor with dedicated remotely operated machines. The first Canadian reactor was the Nuclear Power Demonstration (NPD), connected to the grid on June 4th 1962. It was located in Rolphton (Ontario) on the Ottawa River. It had a reference unit power of 22 MWe with a thermal power of 92 MWth. It had 132 horizontal Zircaloy-2 pressure tubes within an aluminum calandria vessel about 5.2 m (17 ft) of outside diameter and about 4.6 m (15 ft) long. The NPD served as a prototype for all subsequent CANDU reactors (Canadian Nuclear Society, 2002; IAEA, 2022m).

In the Soviet Union, ten years passed between the connection to the grid of the first NPP in Obninsk (1954) and the following ones. In 1964 two new NPP were connected to the grid: Beloyarsk-1 and Novovoronezh-1. Beloyarsk-1 was an RBMK (model ABM-100) with a reference unit power of 102 MWe (thermal power 286 MWth) (IAEA, 2022c; World Nuclear News, 2014). Novovoronezh-1, in the Voronezh region, was the first VVER (veda-vodyanoi energetichesky reactor)—water cooled power reactor constructed. It was called V-210 and had a reference unit power of 197 MWe, with a thermal power of 769 MWth (IAEA, 2022k; Rosatom, n.d).

In the same period, three NPPs were connected to the grid in Italy, a MAGNOX in Latina NPP (1963) with a reference unit power of 153 MWe, a BWR in Garigliano NPP (1964) with a reference unit power of 150 MWe, and a PWR at Trino (1964) with a reference unit power of 260 MWe. Trino Enrico Fermi NPP designed by Westinghouse was the most powerful NPP worldwide between 1964 and 1966 and held the record for the longest full-power operation period (322 days) (Bersano et al., 2020; IAEA, 2022i).

The development of NPPs was relatively rapid considering the number of units constructed worldwide, the nations adopting this energy source, and the fast technological advancements. These can be also seen by the rapid growth of the NPP power that in less than twenty years passed from the 60 MWe of Shippingport to around 1000 MWe in some units. For example, in 1973 Leningrad-1 RBMK-1000 at Sosnovy Bor (Soviet Union) was connected to the grid with a reference power output of 925 MWe (IAEA, 2022j). The same year (1973), it was connected to the grid Zion-1 (Illinois, USA), a four loops Westinghouse PWR. With a reference power output of 1040 MWe (thermal power 3250 MWth), it became the first NPP to exceed the 1000 MWe (IAEA, 2022q).

1.4.2.1 Fast breeder reactors

During this period, different technologies were developed in various countries (e.g., PWR, BWR, CGR, and PHWR) and PWRs became by far the most common type of NPP. However, almost in parallel to the development of water-cooled reactors with a thermal neutron spectrum, it started also the development of radically different reactor technologies, which would allow the breeding of the fertile material (uranium-238 and thorium-232).

After the pioneering research on EBR-I, the EBR-II began operation in 1964 in Idaho. EBR-II was a sodium-cooled fast reactor designed and operated by Argonne National Laboratory. Its main goals were to demonstrate the engineering and economic feasibility of fast reactors and the related technology for the on-site recycling of spent fuel (Sackett, 1997; Westfall, 2004). In 1966, the Fermi-1 reactor started commercial operation (after the first criticality reached in 1963). It was in Newport (Michigan, USA) and it had a reference unit power of 61 MWe (thermal power 200 MWth). It was a fast breeder reactor (FBR) cooled by liquid sodium at nearly atmospheric pressure and operated up to 1972 (IAEA, 2022g; US Nuclear Regulatory Commission, 2022).

In 1973, in Kazakhstan, it was connected to the grid of the Aktau NPP (formerly Shevchenko in the Soviet Union). It was a sodium-cooled FBR with a design thermal power of 1000 MWth. However, the plant was operated only up to 750 MWth. The plant type was BN-350 and it was designed to produce electricity (around 150 MWe at the maximum operated power) and thermal power to desalinate Caspian seawater (around 1,00,000 t/day at the maximum operating power). It had a loop-type design with six loops and the primary sodium pumps and intermediate heat exchangers connected to the reactor vessel by pipelines (IAEA, 2002; IAEA, 2007; IAEA, 2022b).

In the same year (1973), it was connected to the grid of the Phénix reactor in Marcoule (France). It was a pool-type sodium-cooled FBR with a capacity of 250 MWe (thermal power 563 MWth). It adopted a mixed plutonium oxide-uranium oxide fuel enclosed in a stainless-steel cladding. The primary circuit, containing around 800 t of sodium, was contained in a stainless steel vessel and it had three primary pumps and six intermediate heat exchangers. The aims of Phenix NPP were among others to demonstrate the feasibility of using sodium as coolant and the reactor breeding. In addition, it was conceived as the prototype for a subsequent 1000 MWe NPP (CEA, 2012; IAEA, 2022l; Sauvage, 2004). Following the overall positive experience of Phénix, at the beginning of 1986, it was connected to the grid of the Superphénix reactor at Creys-Malville (France). It had a reference unit power of 1200 MWe (thermal power 3000 MWth) and it was a pool-type sodium-cooled FBR (IAEA, 2022n). The Superphénix was the largest sodium-cooled FBR ever built and operated worldwide. The primary sodium inventory was around 3500 t and it was circulated by four primary pumps with eight intermediate heat exchangers (CEA, 2016; IAEA, 2007). During its operation (until 1998), it had some minor incidents and several administrative shutdowns and delays also due to political reasons. However, Superphérnix was fundamental to gaining experience in large-scale sodium cooled FBR, which is one of the designs considered for Generation IV