# A Global Review of PWR Nuclear Power Plants
## 1 Introduction
Figure 1: Generations of nuclear reactors throughout the past seventy years. The 447 nuclear reactors operating in the world as of January 2020 are distributed as follows: (i) PWR: 300 operating reactors, representing 67% of the operating nuclear reactors and an electric power generation capacity of 284 GWe; (ii) BWR: 69 operating units, representing 16% of the total and an electrical power generation capacity of 69 GWe; (iii) PHWR: 48 operating units, representing 10% of the total and a capacity of 24 GWe; (iv) other designs: the remaining 7% of the operating nuclear reactors in the world are capable of generating 17 GWe, among which are different designs such as GCR and LWGR (Figure 3). It should be noted that these data correspond to January 2020 and that they may vary from the current ones depending on (i) the start-up of a reactor that was previously under construction or (ii) if there has been a permanent shutdown of a reactor that was in operation. Among the 300 PWR nuclear reactors currently operating in the world [6], there are several design variants. To obtain a safer and more efficient PWR reactor, the different components of this technical system have been taking different forms over time due to various technical factors (performance, safety, availability). Thus, several references have dealt with the evolution of nuclear reactor designs  
Figure 2: Generation II designs: (**a**) Pressurized Water Reactor (PWR); (**b**) Boiling Water Reactor (BWR); (**c**) Pressurized Heavy Water Reactor (PHWR); and (**d**) Gas Cooled Reactor (GCR). globally, analyzing the different factors modified in different generations [9; 10; 11]. Besides, other authors discussed the evolution of the PWR design throughout the different Generations [12; 13; 14] and other references developed the technical evolution of aspects of the PWR design as relevant as control rods or fuel [5; 15; 16]. Given these results, it can be assured that the PWR design: (i) is that which currently has the highest implementation percentage (67%) in the world (Figure 3); and (ii) has given rise to different variants depending on various technical factors. From a simple consultation in SCOPUS on the number of articles that include, in the title, abstract, or keywords, the names of Generation II designs (PWR, BWR, PHWR, and GCR), Figure 4 was obtained. Thus, a total of 22,457 papers in the SCOPUS database include the denomination of the Generation II designs (data collected in April 2020). Among this criterion, 11,762 (around 52%) of the total published papers include \"PWR\" or \"pressurized water reactor\", so this design gets the highest number of papers among Generation II nuclear reactors. On the other hand, approximately one half (48%) of the published research papers are linked with the rest of Generation II designs. In this group, 6341 papers containing \"BWR or \"boiling water reactor\" (approximately 28%); 958 papers containing \"PHWR\" or \"pressurized heavy water reactor\" (around 4%); and 3396 papers containing \"GCR\" or \"gas-cooled reactor\" (around 15%) in the title, abstract or keywords. It should be emphasized here that the GCR design exhibits a higher scientific interest than expected, since its OP is only 4% in the world (Figure 3). This may be due to the GCR nuclear power plants are mainly concentrated in the United Kingdom--where this nuclear reactor design was developed. In this country, approximately