Reactor Vessel Clossure Head (RVCH) replacement and upgrade with Simplified Head Assembly (SHA)

Project is to prevent possible degradation of the material of the Krško NPP reactor head in a manner that is in the nuclear industry known as Pressurized Water Stress Cracking Corosion (PWSCC) phenomenon. Because the original reactor head for the Krško NPP is made using the sensitive material to PWSCC (Alloy 600 material and welds 82/182), the Krško NPP took a proactive approach and decided to replace the head in advance.

The design of the new head uses modern materials based on Alloy 690 and 52/152 quality welds. At the same time modification upgrades the SHA, which will allow for simplified handling. Change is reflected in increased safety and benefit of saving time in future outages. The main contractor of the project is Westinghouse, USA. Local consortium Sipro / IBE has developed design documentation for incorporating the change to the existing plant systems, and for the licensing in accordance with 10CFR50.59 regulations. Reactor vessel head is a nuclear safety related component ASME Code III Class 1. It is forging composed of flange and the dome in one piece. Head is equipped with 33 sets of CRDM, 3 pcs of CETNA, RVHVS and ICCMS piping, DMIMS sensors, removable ductwork for CRDM cooling, CRDM missile shield, cables and connectors, connector panel, ifting cable bridge, lifting seismic tie-rods, thermal insulation and radiation protection. The scope provides a stress calculations per ASME Code, fracture mechanics analysis, analysis of seismic and LOCA accidents, seismic qualification of equipment for the OBE and SSE seismic events, NUREG-0612 analysis, code reconcilations with the original ASME design code 1971 Edition with 1972 Addenda, etc. Modification is implemented in the outage 2012.



Picture 1: Main components of RVCH and SHA


Picture 2: RVCH and SHA in the operating position (3D model by Westinghouse)


Picture 3: New reactor vessel head ready for lifting to Reactor building


Picture 4: Container with original reactor vessel head for permanent and safe disposal in NE Krško

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