Lifting Platform Supply - Turn-key

A turn-key project of installing a lifting platform for transporting equipment and material in the turbine building was established. The project was ordered by NPP Krško and it includes project documentation, purchase of equipment, installation, testing and education of NPP Krško personnel for operation and maintenance of the lifting platform.

Picture 1: Entrance gate into Lifting Platform on elevation 115.55

Picture 2: Lifting Platform for material transport 

Modification is labeled 531-AB-L. It is not found as Nuclear Safety Related. The lift was manufactured by ALIMAK, Colle di Val D'Elsa, Italija, type CM15/60. The load bearing capacity of the lifting platform is 1500 kilos and the dimension of transport platform is 1.5 x 6.0 m. It will be used for transporting material in three floors, to the maximum height of 15m. The project contains electrical supply, automation, construction statics, safety at work and is in compliance with all regulations based on the local legislation for lift using as well as the regulations of NPP Krško.

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

Replacement of Thermal Insulation on Pipe-work in the RB

In Sipro we have established project documentation for the replacement of thermal insulation on piping in the reactor building of Nuclear power plant Krško. Companies placing the order were TRANSCO Products Inc. Chicago, USA and Numip Ltd. Ljubljana, who was the performer of the installation. Modification is labeled 542-RC-L and constitutes solution to the requirements of NRC Bulletin 2003-1 »Potential Impact of Debris Blockage on Emergency Sump Recirculation at Pressurized Water Reactors«.

Picture: Transco Drawing of MRI Segment

The above mentioned report notes that classic insulation materials (deliquescent and fibrous materials, like calcium silicate, glass wool etc.) are removed due to the possibility of blocking the suction of recycling pumps in the case of containment emergency cooling needs.

Picture: MRI Segment

The replacement insulation is known as MRI (Metal Reflective Insulation), constructed of stainless steel material. On the basis of heat calculations the thickness of MRI was defined, considering particular piping thermal requirements and construction conveniences. Seismic calculation of mechanical insulation integrity for operation during postulated earthquake was made, as demanded for all nuclear safety related systems in NPP Krško. Insulation was replaced on the following Safety Related systems operating in temperature range between 110 and 325 degrees Celsius: RC (Reactor cooling), CS (Chemical and volume control), SI (Safety injection), RH (Residual heat removal), WP (Waste processing), AF (Auxilliary Feedwater), FW (Feed water) and BD (Blow down). Project was performed during the outage R2007.

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

New purification line for RWST and SFP water

A turn-key project, which was ordered by Nuclear power plant Krško, was established. This project included installation of a new process line for filtration and purification of process water from the rad-west storage tank (RWST) and spent fuel pit tank (SFP). Filtration technology is based on ion-exchange resins and mechanical filtration by means of "Johnsonscreen" system and special 5 micrometer cartridge filter.

Picture 1: 3D Image of Piping Layout of RWST System 

Picture 2: 3D Image of Demineralizer

Picture 3: 3D Image of Filter

The project is labeled 546-WS-L and is classified as Nuclear Safety Related. It is a case of project documentation, fabrication of equipment, installation, testing and education of NPP Krško personnel for operation and maintenance of the new process line. Within this project the pressure vessels have been designed in accordance with Euronorm AD Merkblatt 2000 and certified by TUV body. The pipe-work has been constructed by ASME B31.1 and ASME Section III Class 3 standard. Modification will shorten and accelerate purification of radioactive water and so improve existent treatment of radioactive water from both technology and the aspect of nuclear safety growth.

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

RB Recirculation Sump Screen Replacement

In Sipro we established project documentation for replacement of Emergency Core Cooling Sump screen, which serves for filtering of pump suction water during emergency cooling of containment in NPP Krško. Companies placing the order were CCI AG Winterthur, Switzerland and Numip Ltd. Ljubljana, who was the performer of the installation.                                      

Picture 1: Supporting Structure

Picture 2: Screen Section and Maintenance Hole

Modification labeled with 531-AB-L has satisfied the requirements USNRC Generic Safety Issue GSI-191. The above mentioned requirements determine the installation of filter screen with a sufficiently large surface to minimize the loss of pumps NPSH but still high filtering quality. The screen is made up of perforated stainless steel sheet metal forming the total filtering area of 350 square meters. A hydraulic calculation has been made for the existing recirculation pumps in operation with the new screen. Mechanical integrity has been calculated, regarding to encumbrance by the hydraulic pressure drop and seismic forces, as it is demanded for the systems in NPP Krško. Installation of the filter screen in the Emergency Core Cooling Sump of the reactor building was performed during the outage 2007.                                                                                                 

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

The design modification package for implementation of EVND

As a subcontractor of Westinghouse, SIPRO provided the design modification package for implementation of Ex-Vessel Neutron Dosimetry (EVND) system for Krško NPP. The EVND is an additional fast neutrons measurement system, which upgrades the reactor vessel material surveillance program.

Basic problem considered is the embrittlement of material due to exposure to fast neutrons. Neutron that strikes the nucleus imparts energy to that nucleus and degrade the metal structure before stopping. Dislocations and defects lead to embrittlement. The phenomenon affects material Nil Ductility Temperature (NDT) causing brittle fracture even at higher temperatures. EVND system is arranged external to the reactor vessel in the annulus gap towards the biological shield, allowing ease of dosimetry removal and replacement. Radiometric sensors are employed at discrete locations to characterize the neutron energy spectrum variations axially and azimuthally. Once the internal surveillance capsules have been removed the EVND based neutron transport calculations will allow the projection of embrittlement gradients through the reactor vessel. Stainless steel gradient chains are used for locating the dosimeters to complete the mapping between the discrete locations chosen for spectrum determinations. Modification is implemented in outage 2009.

Figure 1 - Embrittlement versus Ductility

Figure 2 - EVND system layout

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

Structural Weld OverLay (SWOL) for NPP Krško

SiPRO prepared the design modification package and the 10CFR50.59 licensing package for the implementation of structural weld over-lays over the Krško NPP pressurizer nozzles. The technical problem is the bi-metallic dissimilar metal welds (DMW), which are used in nuclear coolant systems to connect the stainless steel pipe fittings to the equipment made of carbon steel or low alloy steel. Such welds are often implemented using Cr-Ni Alloy 82/182, which ghas been demonstrated thru the use as such sensitive to the Primary Water Stress Corrosion Cracking (PWSCC).

SWOL is a process by which the PWSCC resistant material is deposited by special welding over the outside surface of the susceptible material. Thus, at the same time provide structural reinforcement, joint stress mitigation and new pressure boundary. SWOL is applied on pressurizer nozzles (surge, safety, relief and spray nozzles), which is classified as ASME Code III Class 1 component. Design is provided by AREVA, USA. It includes sizing, residual stress analyses, crack growth analyses, Leak-Before-Break (LBB) concept analyses, piping stress evaluations and code reconcilaiations. Design meets the requirements of original ASME Code III 1971 Edition with Addenda Winter 1972, 1974 Edition Appendix F for Faulted Conditions and Code Case N-740-2. Special technical report titled “Weld Overlay Alternative Repair Technique For Pressurizer Alloy 82/182 Butt Welds for NE Krško” justifies the path of conformance from Code Case N-740-2 to the ASME Section XI Code Cases N-504 “Alternative Rules for Repair of Class 1, 2 and 3 Austenitic stainless Steel Piping” and N-638 “Similar and Dissimilar Metal Welding Using Ambient Temperature Temper Bead Technique” that provides the references. Installation was performed by Numip d.o.o. in outage 2010.

Figure 1 - Surge line SWOL on the pressurizer bottom

Figure 2 - Top head SWOL locations 

Figure 3 - Surge line nozzle (partial section) without SWOL

Figure 4 - Surge line nozzle (partrial section) with SWOL

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