CAN3-N290.4-M82 (R2011)

1. Scope 1.1 The Standard is concerned with two aspects of the reactor regulating system. The first relates to reactor safety; the second is concerned with effective control of the reactor. These two aspects are not separate. This Standard, therefore, addresses itself to two points: (a) To ensure that the reactor regulating system operates to limit, to acceptable values, the frequency and effects of credible system failure modes leading to uncontrolled positive excursions of reactor power requiring shutdown system action; Note: Other types of failures may lead to a negative excursion of reactor power or to an increase in power that is not significant. Failures requiring shutdown system action are a safety concern, while other failures are more related to effective operation; (b) To ensure that the reactor regulating system meets its requirements for effective control of the reactor and is properly interfaced with other plant systems and with the operators. ,, 1.2 The Standard pertains to all components of the system, covering all the engineering disciplines involved including mechanical, process, electrical, and instrumentation and control design. ,, 1.3 All systems in a CANDU nuclear power plant fall into one of the two categories, as follows: (a) Process Systems - These are all the nuclear and conventional systems in the plant required for operation in any defined state expected during the life of the plant; (b) Special Safety Systems - These are systems specifically incorporated in the plant design to limit or mitigate the consequences of failures of plant process systems, thereby ensuring that any resultant release of radioactivity to the environment and the public is kept within acceptable limits. ,, 1.4 The reactor regulating system is a process system. Since its failure may lead to a requirement for special safety system action, it is a safety related system and the failure frequencies and effects must be considered in the design. The philosophy relative to these considerations is given in the pa per Reactor Licensing and Safety Requirements, D.G. Hurst and F.C. Boyd, AECB 1059 (72-CNA-102). ,, 1.5 The functional and performance requirements for the reactor regulating system shall be established by the designers for a particu lar nuclear power plant and shall be documented in the design manual (see Clause 6.2.1). This Standard does not fully discuss what the role of the reactor regulating system should be, nor does it provide the means of assessing the performance capability of the system in meeting that role. It indicates those requirements which the system should meet, in order that it may carry out its defined roles with acceptable assurance.