Emergency and Preventive Reactor Protection Systems

Introduction

SHC E&PRPs used as a technical base in the reconstruction of existing and creation of new emergency and preventive reactor protection systems, perform the following:

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  The data storing on provided by the design operational limits and conditions of the normal and safe unit operation, ERP and PRP algorithms of control signal (commands) forming, which initiate the actuation of emergency or preventive reactor protection accordingly;

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  The reception of technological process control parameters and equipment condition data from sensors and/or adjacent instrumentation and control systems;

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  The forming and output from ERP or PRP commands to adjacent I&C systems in case of any conditions regimented in the appropriate algorithms of emergency or preventive reactor protection;

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  The archiving, display and data registration on the technological process controlled parameters, equipment condition, reactor protections actuations, and the reasons of such actuations;

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  The continuous monitoring (diagnostics) of its technical state, fault detection and identification, archiving, display and registration of diagnostics results;

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  The data output into unit computer information system (CIS) and personnel warning facilities in the main control room.

The preventive reactor protection is the function of normal operation (category B), aimed to prevent the possibility of emergency in case of the deviation of technological process parameters beyond the admissible operational limits and/or in case of normal operation conditions violation set by the project. It is achieved by forced power reduction and / or blocking of any commands, which could initiate power increase.

The emergency reactor protection belongs to the safety functions (category А) and activates in the case of the violation of the provided design limits or conditions, which cannot be eliminated with the help of a relevant systems of normal operation (e.g., due to its failure), or in the case of the events, which could lead to technical parameters variation, being too fast for adequate response of the systems of normal operation, and also in case of violation of unit design conditions safety operation. In such cases, ERP command should be output, which initiates simultaneous insertion of all control rods into the core, causing a reactor subcritical state and power unit shutdown. It defines an essential role of the emergency reactor protection in NPP safety assurance as the last way to avoid the accident.

On the other hand, the cost of “false” power unit shutdowns (unnecessary) due to false operation of the emergency reactor protection, which can be the result of failure or SHC E&PRP malfunction, is obvious.

It would lead to the necessity to regulate the technical specification in such a way to provide quality of the development, production, testing and operation of SHC E&PRP, which correspond to its role in safety assurance, and to make certain that such correspondence is actually achieved. Thus, one of the fundamental safety principles was considered, according to which I&C systems and its equipment should be designed, produced and maintained in such a way, that their specification, verification and validation, quality assurance, quality control and reliability met their safety classification.

Background

Chapter 9 provides a short description of the devices and systems performance, which fulfill emergency and preventive reactor protection functions, being a part of the reactor control and protection system at the Ukrainian NPPs. This chapter provides more detailed information about the purpose, performed functions, technical specifications, composition and structure of E&PRP systems, as well as functional safety assurance on the system life cycle stages.

The requirements to E&PRP systems and SHC E&PRP are determined by common properties of safety important I&C systems and their components, outlined in Chapter 3, and consider the purpose, categories of performed functions and safety class.