Qualification of safety-critical systems for nuclear power plants using an integrated method TVO SWEP (Software evaluation procedure), based on SPICE and FMECA

Teollisuuden Voima Oy (TVO) operates two nuclear power plant units and has started to build a third one. The current nuclear power units have a continuing need to maintain and update existing instrumentation and parts of their control systems. Each new device shall be classified and qualified according to its safety requirements. Using modern technology means, in practice, that more and more components have programmable features. Standards and rules given by authorities set the acceptance criteria for the components used in the safety systems of nuclear power plants. The reliability of such components has proven to be difficult to demonstrate due to the nature of flaws in software. As a result of development, there has been a clear need for an integrated and effective method to qualify software intensive systems in nuclear power plant units. Integration has three major areas: 1) definition and harmonization of requirements for software intensive systems at different safety classes 2) integration of several approaches like SPICE (Software Process Improvement and Capability dEtermination) and FMECA (Failure Mode, Effects and Criticality Analysis method) to improve confidence in qualification 3) integration of the system acquisition and qualification processes to improve total effectiveness of the acquisition, delivery and deployment processes The first phase of the integrated qualification method in Finland is called TVO SWEP (SoftWare Evaluation Procedure). It consists of detailed qualification processes and related methods for safety category B and C (IEC 61226) and Finnish safety class 3 qualifications. The method is implemented partially in Excel sheets and a database program which generates reports. This method is based on international standards. TVO will use the SWEP method to evaluate suppliers and the conformance of their products/systems against requirements. It has been used in several cases, and it seems to save a lot of qualification resources compared to traditional methods.