{"id":32336,"date":"2022-05-18T05:43:28","date_gmt":"2022-05-18T05:43:28","guid":{"rendered":"https:\/\/sitepourvtc.com\/?page_id=32336"},"modified":"2023-09-26T10:16:10","modified_gmt":"2023-09-26T10:16:10","slug":"safety-systems","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-safety\/safety-systems\/","title":{"rendered":"Safety Systems"},"content":{"rendered":"

Most nuclear power plants introduce a \u2018defense-in-depth<\/b>\u2018 approach to achieve maximum safety, and this approach is constituted of multiple safety systems supplementing the natural features of the reactor core. Level 3 and level 4 usually rely on various safety systems<\/strong>, structures, and components. Engineered safety features<\/strong> and protection systems<\/strong> are provided to prevent evolution towards severe accidents and confine radioactive materials within the containment system. The measures at this level aim to prevent core damage in particular. Design and operating procedures are also aimed at maintaining the effectiveness of the barriers, especially the containment. For example, the emergency core cooling system (ECCS) is provided to mitigate the consequences of a loss-of-coolant accident (LOCA), even though the first level of defense makes such an occurrence highly unlikely.<\/p>\n

Safety-related<\/h2>\n

In the regulatory arena, the term \u201csafety-related\u201d applies to systems, structures, components, procedures, and controls (of a facility or process) that are relied upon to remain functional during and following design-basis events. Safety-related systems, structures, and components have three characteristics. They ensure:<\/p>\n

    \n
  1. the integrity of the reactor coolant pressure boundary (the reactor vessel and associated piping that circulates the reactor coolant);<\/li>\n
  2. the capability to shut down the reactor and maintain it in a safe shutdown condition; or<\/li>\n
  3. the capability to prevent or mitigate the consequences of accidents that could result in potential offsite exposures<\/li>\n<\/ol>\n

    A containment isolation valve is safety-related, for example, because isolating the reactor coolant lines confines radioactivity to the containment building and performs the functions defined above. It helps keep radioactivity away from the public.<\/p>\n

    An emergency diesel generator is safety-related because providing backup power to safety-related equipment ensures the capability to shut down the reactor and maintain it safely.<\/p>\n

    Class 1E<\/h2>\n

    The IEEE created its term for \u201csafety-related electric equipment,\u201d which is \u201cClass 1E.\u201d In IEEE 308 it gives the definition of Class 1E as follows:<\/p>\n

    The safety classification of the electric equipment and systems that are essential to emergency reactor shutdown, containment isolation, reactor core cooling, and containment and reactor heat removal or that are otherwise essential in preventing the significant release of radioactive material to the environment.<\/p>\n

    See also: IAEA Safety Standards, Safety Classification of Structures, Systems, and Components in Nuclear Power Plants. Specific Safety Guide No. SSG-30, ISBN 978\u201392 \u20130\u2013115413\u20132. Vienna, 2014.<\/p>\n

    Active and Passive Nuclear Safety<\/h2>\n

    Nowadays, the most common nuclear reactors (PWRs and BWRs) rely mostly on active safety systems. Active in the sense that they involve electrical or mechanical operation on command systems (e.g., high-pressure water pumps). But the trend is to introduce more passive design features.<\/p>\n

    Passive nuclear safety<\/strong> is a design approach that is more or less in use in nuclear power plants. Passive safety systems are designed to accomplish safety functions without any active intervention on the part of the operator or electrical\/electronic feedback to bring the reactor to a safe shutdown state in the event of a particular type of emergency (usually overheating resulting from a loss of coolant or loss of coolant flow). These systems take advantage of natural forces or phenomena such as gravity, pressure differences, or natural heat convection.<\/p>\n

    The primary design objective of the advanced passive technology is to provide greatly simplified nuclear plant designs that meet or exceed the latest regulatory requirements and safety goals while being economically competitive with other systems.<\/p>\n

    Passive safety systems include: passive safety injection, passive residual heat removal, and passive containment cooling. These systems have been designed to meet the NRC single-failure and other recent criteria.<\/p>\n

    More recently, however, new reactor designs are making more extensive use of passive safety features for a variety of purposes, for instance, for core cooling during transients, design basis accidents or even severe accidents, or for containment cooling, with the claim that passive systems are highly reliable and reduce the cost associated with the installation and maintenance of systems requiring multiple trains of equipment requiring expensive pumps, motors, and other equipment as well as redundant safety class power supplies.<\/p>\n

    Reactor Protection System<\/h2>\n

    The Reactor Protection System, RPS, is one of the safety systems and provides the following functions:<\/p>\n