IEC 62118 pdf download.Nuclear reactor instrumentation – Pressurized water reactor (PWR) of VVER design – Monitoring adequate cooling within the core during shutdown
1 Scope and object
This International Standard applies to pressurized water reactors (PWRs) of VVER design with configurations similar to those shown in figures 1 and 2, and presents the requirements for monitoring adequate cooling within the core during hot and cold shutdown conditions. Annex B provides more information on VVER operating states. Good international practices to be used when designing new or upgrading existing core cooling monitors for VVER systems are summarized in this standard. This standard does not consider the design details of the different VVER technological systems designs, except to the extent that the design affects the monitoring of core cooling. Requirements are given for core cooling monitoring instrumentation to ensure the safe operation of VVERs during abnormal operation and during and after design basis accidents (DBA). Requirements for core cooling monitoring during conditions beyond a DBA, which could be a specific national requirement or consideration, are not covered here. The core cooling monitoring instrumentation has to function under widely different conditions. The circumstances under which this instrumentation needs to function are described. Descriptions of diverse measuring principles and suitable devices are given along with requirements for the following: • operational conditions; • installation; • operator displays; • testing, calibration and maintenance; • equipment qualification; • documentation; • redundancy.
3 Definitions and abbreviations
For the purpose of this International Standard, the following definitions apply. For terms defined elsewhere, the source is given in square brackets. 3.1 ALARA as low as reasonably achievable 3.2 coolant water and/or steam for heat removal from the core 3.3 DBA design basis accident 3.4 diversity the existence of redundant components or systems to perform an identified function, where such components or systems collectively incorporate one or more different attributes [IAEA 50-SG-D8] 3.5 downcomer annular volume between reactor vessel wall and internals that directs coolant flow to the bottom of the core 3.6 ECCS emergency core cooling system 3.7 LOCA loss of coolant accident 3.8 monitoring means provided to indicate continuously the state or condition of a system, sub-system, equipment or assembly [IEV 393-08-48] 3.9 PAMS post-accident monitoring system 3.1 0 pressurized water reactor (PWR) a nuclear steam supply system in which the pressurized coolant is heated by the reactor core, and process steam is generated in the steam generator by heat transfer from the coolant 3.1 1 reactor containment the structure that encloses the reactor coolant system and parts of specific associated systems, including the pressure containment structures that enclose individual components in some nuclear power plant designs 3.1 2 RCS reactor coolant system 3.1 3 reactor pressure vessel (RPV) the vessel which contains the reactor core 3.1 4 RPS reactor protection system 3.1 5 reduced inventory condition an intentional condition that exists during specific maintenance operations whenever water level in the RPV is lower than the top of the RPV hot leg piping nozzle elevation, plus an allowance for water level measurement uncertainty 3.1 6 redundancy provision of alternative (identical or diverse) elements or systems, so that any one can perform the required function regardless of the state of operation or failure of any other [IAEA 50-SG-D8]
4 Operating conditions
4.1 General The need for adequate core cooling exists for all plant operating modes and states, including normal power operation, operational transients, abnormal conditions and hot and cold shutdown operations. Annex B contains definitions of the various operating modes and plant operating states applied in VVERs. Adequate core cooling is confirmed by measurements of coolant circulation through the RPV at an appropriate temperature, pressure and flow to remove heat from the core. This standard covers instrumentation considerations for monitoring core cooling in PWRs of VVER design with configurations similar those shown on figures 1 and 2. These configurations are similar relative to core cooling monitoring requirements except for the following differences: • Figure 1 (VVER-440): Loop isolation valves allow loops to be isolated from the reactor for maintenance. Core residual heat (VVER-440 first generation) is removed by natural circulation to the steam generators during shutdown operations after the rundown of the pumps in the reactor coolant system. The steam generators are cooled by the secondary auxiliary RHRS. NOTE Some VVER-440 designs (second generation or after modernization) have primary RHRSs similar to VVER-1 000 designs.