Functional Approach Assessment

One of the ways of nuclear safety enhancement is continuous monitoring of plant performance aimed at detection of unexpected faults indicated by process parameters deviation from expected values before the fault evolves into a serious failure or break. This timely detection would allow taking effective corrective measures, thus preventing significant component damage.

Although the existing NPP control systems can alert control room operators as soon as a problem occurs, they do not provide, in most cases, any information on the cause of the fault. The cause identification then relies fully on the operator, who has to analyse many other data, before he can properly identify the problem and take appropriate corrective action to prevent the minor fault from developing into a serious failure. This “manual analysis” takes certain time, which can delay the cause identification process from the fault occurrence to an operator’s action (based on an appropriate operating procedure).

This inconvenience may be eliminated by an Early Fault Diagnostic System (EFDS) installed in addition to existing operator information systems (parameter display, fixed alarm systems). EFDS would report any deviation from normal plant parameters to the operators along with suggestions on the possible causes, before any threshold is exceeded leading to potentially dangerous plant state. This would give the operator an opportunity to take appropriate and timely actions to control and limit any undesired consequence of the identified fault, malfunction etc.

The EFDS has to be based on thorough knowledge of plant response to various kinds of faults, incidents, component malfunctions and on the capability to identify causes of possible parameter deviations. This is only achievable by using a plant simulator able to adequately reproduce immediate plant response to a deviation and having the capability to quickly generate and evaluate a large number of possible evolution scenarios. The incidents, which should be considered, may include leakages, flow/pressure disturbances, control systems malfunctions including sensors, component failures etc.

This early fault detection concept can be implemented in three steps: (1) identification of the events and operational modes to be covered by the system, (2) simulation of all possible transients to identify unique plant response for each selected event and (3) automatic generation of a set of diagnostic rules to manage the event.

The project R2.07/95 was established to develop the Early Fault Diagnostic System to be implemented (out of the scope of this project) at a VVER-1000 type target (pilot) NPP. The project was implemented in three phases:

• Phase 1: Functional approach assessment
• Phase 2: Conceptual definition of the Frame Product
• Phase 3: Early Fault Diagnostic System, Frame product development
• Phase 4 – “Specific Early Fault Diagnostic System development, Product implementation” was to be implemented out of scope of the R2.07/95 TACIS project at a target VVER-1000 plant selected by the Beneficiary (Rosenergoatom).

The contract No. 24895 was focused on implementation of the Phase 1.

The objective of this contract was to assess applicability of the above-mentioned early fault detection approach to VVER-1000 plants. This approach had been tested on a power plant in Italy.

The project was implemented by FM Consultants Associates in the period from 6 August 1997 to 6 November 1997. The functional approach assessment itself was performed by Russian organizations: Atomenergoprojekt (AEP) and Moscow Institute for Control Science (ICS). The project work comprised two tasks:

Task 1: Development of a functional prototype of EDS to examine its usefulness and feasibility

The prototype developed consisted of simplified VVER-1000 plant simulator, operator man-machine interface (MMI) and software for automatic generation of diagnostic rules. Presentation of the prototype to Rosenergoatom and NPP staff resulted in the following conclusions: (1) the concept was clear and acceptable for the NPP personnel, (2) the presented MMI was mostly accepted, (3) the simulator quality was adequate and (4) there is need of EFDS installation at Russian NPPs.

Task 2: Assessment of the technical and human environment for EFDS integration

This task consisted in recognition of requirements of potential EFDS users and identification of desired functions of the EFDS. It included demonstrations of the EFDS prototype to personnel of Balakovo, Kalinin and Novovoronezh personnel. The task resulted in issuing technical proposals outlining EFDS functions, installation diagrams at the VVER-1000 main control room and integration of the Early Fault Diagnostic System within the existing plant control systems.

The Phases 1 and 2 of the R2.07/95 project were followed by the Phase 3 covered by the contract No. 25306 (formerly 98-0015). For more information about the 25306 contract objectives and results, see the corresponding summary report on “Early fault diagnostic system of technical processes in VVER 1000”.