SAFETY P R A C TIC E S - gnssn - International Atomic Energy Agency

This publication is no longer validPlease see http://www-ns.iaea.org/standards/Assessment questions(1) Has the equipment or components been qualified for the intended service anddoes the documentation verify the qualification?(2) Have the environmental conditions been identified for all components importantto safety?(3) Have the components been type tested according to a recognized standard orhave some components been qualified by analysis?(4) Is there an exchange programme for components qualified for a life shorterthan the expected plant life?3.4.2. Stand-by power supply units and support systemsStand-by power supply units are essential to enable the EPS to fulfil their safetyfunction on failure of other power sources. Consequently, it is important that thestand-by power supply units be of high quality and reliability. The prime movers ofthe stand-by power supplies may be hydroturbines, gas turbines, steam turbines,diesel engines, etc. The stand-by unit is acceptable if it is sufficiently reliable, hasadequate capacity and performance characteristics, can start and deliver the requiredpower to the loads in the required time, and is appropriately qualified.Design documents, specifications, load balance calculations, including worstconditions during anticipated operational occurrences and accident conditions,should show that the unit will perform according to the required power output, takinginto account startup time and the load sequence programme.The calculations concerning cooling water system, combustion air supply,preheating power supply, starting power supply, installation room ventilation andfuel and lubrication oil consumption should be reviewed to prove that the unit canstart and operate as required.The power supply units include diesel and steam turbine driven pumps andgenerators but because the stand-by power supplies which are most often installedin nuclear plants are diesel generators, greater emphasis is given to them in thefollowing guidance. In some cases units combine pumps and generators. (‘Unit’refers to the prime mover plus the electrical generator, pump, etc. in the followingquestions.)Basis for acceptanceSafety Guide 50-SG-D7, Sections 3 and 4, paras 523-526, 587-591.27