Neutron flux monitoring equipment

Neutron flux monitoring equipment (NFME) is intended for:

  • monitoring of main neutron-physical parameters of the reactor plant: power, period (speed) of power change, reactivity;
  • generation of protection signals (emergency reactor shut-down), and control signals at normal operation conditions, at disturbance of safe operation conditions and during accidents ;
  • presentation of information on monitored parameters at control panels;
  • transfer of signals and information to other subsystems of the control and protection system (CPS) of NPP power Unit.

In compliance with classification of NP-001 (OPB 88/97) by influence on safety NFME is related to elements of control safety system - class 2 (2NU). In compliance with NP-026-04 NFME is related to functional group 2UK2.

NFME, depending on a project, consists of two or three sets; each of them in its turn consists of three or four monitoring channels.

NFME ensures the following:

  • monitoring of neutron flux density in the channels of reactor plant ionization chambers, on its basis the calculation of power within the range from 1·10-9 to 150 % of nominal value of the reactor power is ensured. The monitoring of neutron flux density is performed by means of neutron flux detection units from composition of detection devices UDPN.
  • automatic correction of readings within the power range from 10 to 150 % of nominal value of the reactor power by compensating the influence of factors distorting the power reading of NFME channels (density of heat transfer fluid in downcomer region of the reactor, shape of height power density field, etc.) – function of automatic correction of power readings (ACPR);
  • calculation of reactor period value within the limits from 5 to 999 s;
  • generation of setpoints by power and period, which may be performed in two ways: the automatic generation (“floating setpoint”)  or manual setting of setpoint values by operator by means of setpoint setting unit BKC;
  • generation of discrete signals on exceeding of setpoints by reactor power and period by current values of monitored  parameters, and transfer of information on generation of these signals;
  • transfer of discrete signals to adjacent systems (SLPE, Teleperm XS, automatic power controller (APC), refueling machine, etc.) via standard schemes with possibility of changing the communication parameters without improvement of modules;
  • calculation of reactor reactivity value – function of reactivity monitoring equipment (RME);
  • generation of unified analogue signals, proportional to the value of power, period and reactivity for transferring to other CPS subsystems;
  • automatic check of intrinsic good condition;
  • automated check of monitoring channels with delivery of the check results for processing to digital carrier;
  • logging and displaying of information at digital displays, light and sound signaling at panels and control boards;
  • archiving of intrinsic information and information of adjacent systems – function of data displaying and logging hardware (DDLH).
  • monitoring of neutron flux density and speed of its change during reactor refueling – function of refueling monitoring system (RMS);
  • generation of control signals during monitoring of refueling.

The composition of NFME includes:

  • neutron flux detection devices (types and amount are determined during development of specific project);
  • data acquisition and processing devices (DAPD), performing the role of central part of NFME channel, executing receipt, processing and transfer of information.
  • data displaying, archiving and logging devices, or gateway devices of NFME sets, realizing the functions of acquisition and exchange of information of NFME set with the systems of top level system of Unit, and also the functions of short-term archiving of information on NFME set operation;
  • information submission and control devices;
  • reactor internals state monitoring hardware (RISMH). 

NFME technical means (NFME TM) are divided into three categories by metrological characteristics:

  1. those being measuring means subjected to metrological monitoring and supervision, being initially calibrated after manufacturing before delivery to NPP, and calibrated periodically during operation;
  2. those being measuring means not subjected to state metrological monitoring and supervision, and being initially calibrated after manufacturing before delivery to NPP, and calibrated periodically during operation;
  3. those which are not measuring means.

NFME has fail-free redundant electric supply circuit, which makes it possible to input various voltage for supplying NFME channels (220 V of alternative or direct current, 48/24 V of direct current) depending on a project. All the devices and units related to NFME channels are supplied from data acquisition and processing devices DAPD. 

NFME is built-up on the basis of limited amount of unified modules. Functions of module are determined by configuration of microcontrollers software and of programmable logic arrays (PLA) being configured. PLA are configured at the stage of manufacturing. Programming and configuration environments contain the procedures of checking the configuration for presence of errors and instrument for simulating the configuration operation with generation of reports.

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