Problems of evaluating the software quality for systems important for the nuclear power plant safety

During the last decade, automated process control systems (APCS) have approached a qualitatively new level of the development; and a consequence of this progress is considerable complicating the APCS software and its life cycle. In 2000, at the V.A. Trapeznikov Institute of Control Sciences of the Russian Academy of Sciences (ICS RAS), software complexes for perspective nuclear power plant (NPP) APCS has been elaborated The required life cycle of the total APCS is not less than 30 years, what leads to a necessity of developing and implementing comprehensive procedures on maintaining and modification of the software complexes. In the paper, an experience gathered in the ICS RAS on maintaining NPP APCS software, assuring quality of the updated software code and forecasting of costs of its modification and maintenance is presented.