Light water reactor meaning

In legal and regulatory practice, a light water reactor (LWR) is a nuclear power reactor that uses ordinary (light) water as both the neutron moderator and the primary coolant. The term is a technical, descriptive expression rather than one generally defined in UK or Irish legislation or case law, but it is commonly used in nuclear site licensing, safety documentation, environmental permitting and planning materials. LWRs comprise two main types: pressurised water reactors (PWRs) and boiling water reactors (BWRs), the most widely deployed reactor technologies worldwide. In the UK, operating and proposed large civil stations are PWRs (for example, Sizewell B). Ireland has no nuclear generating stations, though the term may arise in cross‑border environmental assessment, emergency planning and transport regulation. Legal relevance: the reactor type shapes the safety case to the Office for Nuclear Regulation, licensing under the Nuclear Installations Act 1965, Generic Design Assessment, permits for radioactive substances and cooling water under the Environmental Permitting Regulations (or devolved equivalents), planning consent for nationally significant infrastructure under the Planning Act 2008, and strategies for waste, spent fuel and decommissioning. Usage is broadly consistent across England and Wales, Scotland, Northern Ireland and Ireland, notwithstanding differing policy positions on new nuclear build.