Regulatory requirements for design of safety related computer based control Systems in Indian PHWRs: case study of DPHS-PCS for TAPP-3 and 4

Computer based control systems for safety related applications in nuclear power plants have to meet not only the functional, performance and interface requirements, they in addition, have to meet regulatory requirements like enhanced reliability, safety and security and should provide fault tolerance, diagnostics and self-supervision. The control system architecture, hardware design and software design should meet requirements as specified in design code and guides of AERB. The Dual Processor Hot Standby Process Control System (DPHS-PCS) for TAPP-3 and 4 is a safety related (Class- IB) system. DPHS-PCS regulates PHT pressure, Pressuriser pressure, Pressuriser level, Bleed condenser pressure, Bleed condenser level and Steam generator pressure. The performance, reliability and safety requirements of this control system are met by employing a fault tolerant computer configuration developed for this purpose using hardware designed with facility for on-line diagnostics and software developed under a Software Quality Assurance Plan following AERB guidelines. This paper discusses the design requirements of safety related computer based control systems and how these have been addressed in the design of DPHS-PCS of TAPP-3 and 4. (author)