The aim with this master thesis is to identify similarities and differences between the UK and Swedish safety requirements for hazards at the plant level. It is also to investigate the underlying requirements for the safety documentation of those hazards. The method in the report is picked from literature studies, such as internal documents and the information published by the UK´s and Sweden’s countries' nuclear authorities. Semi-structure interviews have been conducted. The report is strictly dealing with internal and external hazards. In addition, the study is only made on one Light water reactor in each of the following countries, Sizewell B in the UK and unit O2 at OKG, Sweden. An important conclusion is that the main differences are based on different ideological approaches to managing risk in the law and how each country assesses the hazards. The similarities are above all, the identified hazards as well as the safety analysis that has to be done, both deterministic and PSA. Moreover, those who own the risks are ultimately responsible for preventing a nuclear accident.