U1.04/05A - Plant Improvement Project at Khmelnitsky NPP - Upgrading of Reactor Control and Protection System & Neutron Flux Monitoring System Electrical Equipment

Khmelnistky nuclear power plant (NPP) consists of two VVER 1000/320 units that belong to a standard VVER 1000 reactor design. Unit 1 was commissioned 1987. Despite the Unit 2 construction started shortly after the Unit 1, its construction was put on hold in 1990 because of the Moratorium on building nuclear facilities raised by Ukrainian parliament after break down of former Soviet Union. Construction of Unit 2 was eventually completed in 2004 in the framework of K2R4 Euratom loan that was provided to Ukraine for the completion of two remaining unfinished VVER 1000 units whose construction was on hold for about 16 years.

RCPS is a multifunctional system including subsystems for reactor control during normal operation, as well as power limiting and emergency subsystems. RCPS consists of the following subsystems:

• Automatic Reactor Power Controller (ARPC).
• Unload and Power Limitation System (UPLS).
• Signal generating systems: Emergency Protection System (EPS), Preliminary Protection System (PPS-1, PPS-2), and Accelerated Preliminary Protection System (APPS).

NFMS involves the ex-core neutron flux monitoring system which ensures monitoring of the entire neutron flux measurement range, and is typically subdivided into three sub-ranges with an overlap of at least two decades. The ionization detectors for the source range and intermediate range were originally designed with moving mechanisms to allow their removal from the area of significant neutron flux after transfer the reactor into the energy range.

A replacement strategy considered a new digital technology available in the European market for nuclear application, i.e. I & C systems important to safety, and in NFMS, application of the wide range ionization chambers, which allows fixing position of ionization chambers in the specific core height and thus avoiding any moving parts in the NFMS.

A replacement of RCPS and NFMS was planned in three consecutive plant outages under the assumptions that the same equipment has already been installed and successfully tested at Unit 2.

This project aimed at upgrading the existing Reactor Control and Protection System (RCPS) and Neutron Flux Monitoring System (NFMS) at Unit 1 of Khmelnitsky NPP.

The original RCPS and NFMS were based on the old analogue technology that become obsolete and had rather low reliability record. Also, the availability of spare parts was another limiting factor for which the plant needed an upgrade project.

The IAEA issue book for VVER 1000 reactors indentified a low reliability of I & C systems important to safety, which provide essential controls of the plant nuclear and conventional processes, as well as inadequate accident monitoring instrumentation which is used to inform the operator of the status of safety related parameters as an important safety issue.

Khmelnitsky Unit 2 already replaced the original analogue RCPS and NFMS in the framework of K2R4 completion project that was financed from the Euratom loan.

Consequently the European Commission launched a project to address this issue in the framework of TACIS 2005' nuclear safety programme.

The overall objective of this project was to procure and install the new RCPS and NFMS at Khmelnitsky Unit 1.

The Ukrainian Consortium Radiy-Impuls has been chosen to supply the new digital equipment through the open tender. Both Consortium members have been known among manufacturers of specialized electronic equipment for a long time. For example, Impuls delivered the original electronic equipment in the frame of Soviet Union space programme. After break down of former Soviet Union, both companies started developing their own programme, primarily focusing on replacement of the control and process monitoring system at Ukrainian nuclear fleet (14 reactor units). Despite both companies are competitors on the market, they joined their forces for the delivery of digital systems as follows; Radiy delivered equipment for RCPS while Impuls delivered equipment for NFMS.

A digital equipment for RCPS was based on field-programmable gate array (FPGA) technology, which is an integrated circuit designed to be configured by the customer or designer after manufacturing hence "field-programmable". All digital and control systems manufactured at Radiy have an integrated system of self-diagnostics which allows detecting minor deviations in system’s operation as well as prevention of failure growth at earliest stages. Besides that, the application of information and control platform allows:

• Decreasing risks related to personnel mistakes and common-cause failures
• Providing a flexibility of integration during equipment commissioning
• Decreasing a time period of upgrade of out-to-date equipment to the minimum

RCPS and NFMS functional diagrams and algorithms remained the same as originally designed, i.e. all assumptions used in safety and accident analysis of the Final Safety Analysis Report (FSAR) remained unchanged. Nevertheless, respective FSAR chapters related to reactor control and protection were modified so that to reflect the design and functional characteristics of the new digital equipment.

Initial project schedule considered implementation of the two-train RCPS and NFMS in the three plant outages; nevertheless, the Consortium was able to manufacture, test, install and commission the entire system within two plant outages.

Key contract data are as follows; the supply contract was signed on 8 December 2006. The supplier manufactured the equipment, performed factory acceptance tests and installed the equipment of the 1st train (RCPS and NFMS) in 2007 outage. Consequently, the equipment of the 2nd train was installed and commissioned in 2008 outage. The Final Acceptance was signed after the end of Warranty in 2010.