Turbine Control System Replacement at NPP Krško, Turbine Emergency Trip System and Moisture Separator Super Heater Control

Purpose of the project was the replacement of Turbine Control System (TCS) at Nuclear Power Plant (NPP) - Krško. From the plant construction time and the first plant start-up in 1981, the NPP TG (Turbine Generator) set was controlled and monitored by DEH (Digital Electro Hydraulic) Mod II Control System designed in 70's, based on P2500 CPU and number of I/O controllers and modules. The P2500 CPU and associated controllers were built with discrete TTL components (TTL logic chips) and the P2500 CPU had 64k of 16 bit words of ferrite core memory. For that time, DEH Mod II had sophisticated MCR (Main Control Room) HMI (Human Machine Interface) based on digital functional keyboards, one alphanumeric black & white CRT monitor and printer.

After twenty-eight years of operation and because of several other reasons, NEK decided to replace the old DEH Mod II Control system with the new Emerson Ovation' based DCS (Distributed Control System) on redundant platform for the control and monitoring of secondary plant systems in the NPP Krško, and the new system was named PDEH (Programmable Digital Electro Hydraulic) TCS.

The project enveloped implementation of PDEH system on three application platforms: BG KFSS (Background Krško NPP full scope simulator), FG KFSS (Foreground full scope replica Krško NPP full scope simulator) and PDEH system installed in the plant. The HMI for the BG KFSS platform constitutes only of soft panels or monitor graphics (all MCB - Main Control Board and its controls are available as graphic images on workstations), while the HMI for FG KFSS includes full scope replica of NEK MCR and MCB.

The new PDEH system was installed on two KFSS platforms (BG and FG) in October-November, 2008; pre-outage or on-line field installation work was performed in the January-March 2009 timeframe; while the old DEH Mod II was decommissioned and the new plant PDEH system was installed during the outage in April, 2009 and tested with the plant on line in May, 2009.


Picture 1: Old DEH and turbine monitoring NEK MCB HMI equipment before project implementation with marked-up equipment that will be removed


Picture 2: New PDEH MCB HMI equipment

The scope of project was enveloped with the basic DEH turbine control system replacement and additional functional items as listed below: 

  • Replacement of the existing DEH Mod II Turbine Control System with the new PDEH (Programmable Digital Electro Hydraulic) system built by Westinghouse Electric Corporation on Emerson Ovation DCS platform. Several functional, reliability, and HMI improvements were implemented against the existing DEH Mod II TCS (Turbine Control System).
  • Replacement of the existing Turbine ETS (Emergency Trip System) with several functional, reliability and HMI improvements against the existing Turbine ETS. Included were also replacements of hydraulic control system – single transmitters replaced with manifolds with double or triple sensors, permitting redundancy and on-line maintenance of failed sensors.
  • Replacement of the existing MSR (Moisture Separator Reheater) Control System with several functional, reliability and HMI improvements against the existing MSR Control.
  • Controls and indicating lamps that were used for remote control and testing of 12 EX (Extraction Steam) valves were removed from one of the MCR operator panels and integrated within the new PDEH. Also several reliability and HMI improvements against the existing manual controls on the MCR operator panel located behind the MCB (Main Control Board) Section A.
  • Remote control and monitoring of the main electric generator hydrogen purge system for which the new PDEH system provides HMI platform and programmable digital platform on which HMI and control algorithms have been implemented.
  • Implementation of the new PDEH system on background and foreground KFSS. 

The Sipro scope of services was electrical, I&C and mechanical engineering and design required for the development of Design Modification Package; engineering support to Westinghouse during design, installation and testing phases; as-built drawings; preparation of modification Turnover Package.

Project Manager: Marko Šegula, B.Sc.E.E.


Enhancement of the Emergency Power Supply

Enhancement of the Emergency Power Supply for the Nuclear Power Plant Krško provided a new 4,5 MW Diesel Generator (DG3) and its supporting components housed in a new Seismic Category I Bunker Building 1 (BB1). The building is protected against aircraft crash, against potential spill of combustible aviation fuel and against flooding with use of watertight doors and sealed underground connections. The BB1 houses the DG3 generator with its supporting electrical equipment, including 6.3 kV switchgear, battery, battery charger, motor control centers, various distribution panels, and miscellaneous electrical/mechanical equipment.   

           BB1 building

                                                                           Picture 1: BB1 building 

4,5 MW DG3 is intended to operate either as an Alternate AC (AAC) source in case of a total loss of on site and off site power or as a backup to either of the existing plant Emergency Diesel Generators (DG1 or DG2).

A seven day supply diesel fuel storage facility consisting of the Main Storage Tank located in a seismic Category I safety-related below grade concrete watertight and a fuel oil truck unloading facility are located nearby.

The new electrical underground duct bank from BB1 to IB building was constructed for cabling connections between BB1 and Main Island.

In the Main Control Room (MCR) the controls for DG3 were located on a new Class 1E electrical control board. In existing switchgears the DG3 feeder units ia exuiped with new vacuum breakers and protective relays for cable overcurrent protection and CT for differential protection.

Sipro performed design engineering activities.


 Picture 2: DG3

Project Manager: Božidar Linke, B.Sc.E.E.

Replacement of Voltage Regulators and Control Equipment on DG1 and DG2

To ensure constant AC power supply NEK has three diesel generators – two were installed with original power plant design, additional third diesel generator was installed during the outage 2012. In the event of loss of off-site power, each of them can provide energy for the operation of safety related systems in the plant. To increase reliability of operation and to simplify maintenance as well, the modification of electrical equipment in the original two diesel generators will be performed. During the outage 2015, first diesel generator was modified, and second will be modified during the outage 2016.

Sipro provides project documentation with detailed instructions for replacement of the main control cabinets, reconstruction of smaller control cabinets of auxiliary systems of the generator and additional connections for the NPP process information system. Project documentation contains all necessary BOM’s, instructions and drawings for implementation of new equipment, with modified operating and maintenance procedures and also recognizes impacts on other systems in the plant.



Picture: Control cabinets of diesel generator 1

Project Manager: Matjaž Stanko, B.Sc.E.E.

Modification of Essential Service Water System (SW) Intake Structure and Equipment

Modification of the Service Water System belongs within the set of measures which are necessary to eliminate the consequences of the effects due to increase of the level of the Sava River while constructing accumulation pool of hydro power plant Brežice. Increase of the level of the river will change ability to access the equipment in the NPP Krško intake structure as needed for inspection and maintenance. Sipro designed seismically qualified platforms for accessing to equipment and modifications of supporting systems for fire protection pumps (FP system) and essential service water pumps (SW system). At vertical columns of pumps special guides are installed that allow the pulling out and installation of pumps in terms of increased water level. Additionally, ladders for access to the bottom of the pool are designed in accordance with safety at work standards. Designed are also additional outage gates which will be enable to isolate and emptying pumps compartments for maintenance personnel access. The project also included safety analyses as needed for authorization by nuclear safety authority.

Project Manager: Mladen Debeljak, B.Sc.M.E.

Obstruction Lights Replacement

Our client, Krško NPP has contracted us to do an obstruction lights replacement project at their meteorological measurements tower. This is a 70 m tall antenna like structure that has to be lit at night and in poor weather conditions in order to be visible for nearby air traffic.

Scope of project:

  • examination of existing tower installations
  • designing and planning of new obstruction lighting in accordance with ICAO regulations
  • selection of high performance LED long life lights
  • designing of a control cabinet
  • automatic turn on/off in regards to ambient light conditions
  • propper functioning at low temperatures remote
  • turn-on capability
  • supply from redundant power source

 Picture: Meteorological measurements tower


Project Manager: Marko Šegula, B.Sc.E.E.

Replacement of the Reactor Cooling Pump Motor

In order to preserve the plant availability and reliability NEK has decided to buy a new RCP motor. On the basis of Investment Program and Technical Specification SP-S700A the replacement RCP motor has been ordered as fit, form and function replacement motor to existing KRK-125 motors including certain upgrades to like-for-like replacement.

The new RCP motor was manufactured by Westinghouse / Curtis-Wright EMD at EMD facility in Cheswick, PA, USA. The EMD shop order D039 was assigned to the job and will be used to uniquely identify the motor and trace its design, production and test records and documents to NEK. New D039 motor was connected mechanically, electrically and instrumentally to the plant like the existing one and replaced the KRK-125 motor (S/N 1S86P550) on RCPCPC01-MTR location in 2007 outage.


Detailed design modification package (DMP) for modification 576-RC-L addressed all aspects of the new D039 RCP motor interfaces and/or upgrades of existing interfaces required to properly control and/or supervise motor functions. The existing alarm and/or the trip set-points are not changed by modification. Additional instrumentation devices (oil level transmitters, bearing RTD’s and vibration sensors) were interfaced to the plant Process Information System. The new oil spill protection system has been installed which provides means to collect and store any oil spill from the motor.





Picture 1: The new RCP motor with Oil Spill Protection System


The implemented activities did not present any functional changes from the existing design of RC pump motor basic function which would have negative affect on the normal plant operating parameters nor the safeguards systems actuation or the accident mitigation capabilities of the plant. The same design and construction of the reactor coolant pump motor critical parts are utilized on D039 and 86P550 motors. The inertia of motor and pump rotating parts is equal in D039 motor as it was in the 86P550 motors and thus the coast down flow characteristics is not changed from those analyzed in SAR.








Picture 2: Handling the RCP motor

The plant reliability and availability is increased as in the case of an RCP motor failure the third (spare) motor is available on site. This also allows the refurbishment of the motor exempted from the service. In the same time the DMP 576-RC-L provided solutions for the third (spare) motor long term storage and maintenance activities in FHB 100.300 location.                                            

Project Manager: Božidar Linke, B.Sc.E.E.