Safety critical software in nuclear power

The uses of computer systems on nuclear plant are outlined. The development of safety-critical and safety-related uses are described. These are classed as Category A and Category B with C by the International Electrotechnical Commission (IEC), in standard IEC 1226. The key application and reliability requirements are provided, together with the relevant standards. Comments are made on acceptance by the nuclear safety regulators and the consequences for system structures. Expected developments in computer use are discussed, with special reference to Eastern Europe, where Russian designs of reactor are being provided with upgrades and retrofit systems. The expected use of soft, on-screen control of safety plant, the use of commercial off-the-shelf (COTS) software and the increased use of computers for protection are discussed. In conclusion, some of the areas needing R and D are described. (author)