# A Global Review of PWR Nuclear Power Plants
## 1 Introduction  
Currently, due to the growing demand for energy worldwide, nuclear energy has regained the relevant role it played throughout the past 20 th century, as an alternative to CO\({}_{2}\)-emitting electric power generation technologies. This generation technology presently accounts for 10% of the electrical energy generated in the world. Over the past eighty years, various nuclear reactor designs have been developed around the world, which can be classified according to (i) their configuration and objectives, or (ii) their generation stage. Within the first classification, it is necessary to distinguish between (i) fast reactors and (ii) thermal reactors. The first ones, fast factors, are capable of generating more fissile material than they have consumed. On the other hand, among thermal reactors there are several combinations of moderators--in charge of reducing neutron energy--and coolants--the fluid that transmits the heat generated in the reactor--that have been successfully developed in different nuclear reactor designs. The second classification (thermal reactors) is the most used [1; 2; 3] and allows defining the following generations of nuclear reactors (Figure 1): _Generation I_: prototypes built between 1957 and1963; _Generation II_: commercial production, built from the mid-1960s onward; _Generation III_: advanced reactors--safer and with greater generation capacity, built since the early nineties; _Generation III_+: nuclear reactors with structural safeguards and/or passive safety features, designed from the 21 st century; and finally _Generation IV_: the highly efficient reactors of the future, with advanced safety features and generating small amount of spent nuclear fuel. Throughout history, the most developed nuclear reactor designs have been Generation II (Figure 2), with different fundamental characteristics [4; 5; 6]: (i) PWR (pressurized water reactor): in whose vessel the coolant does not reach boiling temperature. It developed from the 1950s; (ii); BWR (boiling water reactor): uses light water as moderator and coolant. It developed like the PWR from the 1950s; (iii) PHWR (pressurized heavy water reactor): in which heavy water--deuterium dioxide, D20--was incorporated as moderator and coolant. It was developed in Canada from the sixties; and (iv) GCR (gas cooled reactor): the reactor design that uses graphite as a moderator and gas as a coolant. It was developed in the UK after World War II. Table 1 summarizes the main characteristics of these four designs (PWR, BWR, PHWR, and GCR), as they are the most important within Generation II. Furthermore, in this group of Generation II reactors, there is another design known as LWGR (light water graphite reactor) or RBMK in its Soviet variant, from the Russian _Reaktor Bolshoy Moslichnosty Kanalny_. This latest RBMK design is known to be the one that caused the fatal accident at the Chernobyl nuclear power plant (Ukraine) in 1986. The RBMK design is very different from the rest of the power reactors, since it is used simultaneously for both the production of plutonium as for the production of electrical energy. The basis for the data research on Nuclear Power Reactors is the Power Reactor Information System (PRIS) database from the International Atomic Energy Agency (IAEA) [6]. Other authors have taken data from this database for their research in nuclear science [7; 8]. To study the obtained data, a parameter called _operating factor_ (OF) has been used in this paper, which is defined as the relative frequency of PWR reactors operating around the world (in percentage):  
\[\text{OF}=\frac{n_{i}}{N}.100 \tag{1}\]  
where \(n_{i}\) is the number of a specific PWR design \(i\), and \(N\) the total population of operating PWR in the world (\(N=300\) currently, according to [6]). It is worth noting that the parameter OF is different from that known as the operation factor, which is defined by IAEA as the ratio of the number of hour the unit was on-line to the total number of hours in the reference period, expressed as a percentage [6].