Modification of the pressurizer spray system at Trillo I NPP

During the recent Eleventh Refuelling of Trillo I NPP (February-April 1999), the design modification to the Pressurizer Spray System was implemented. This turnkey project which began exactly a year earlier (February 1998) and which was carried out by Empresarios Agrupados included the engineering and design of the modification, the supply of all necessary equipment and components, their assembly and the corresponding tests. The modification, whose purpose was the improvement of the thermohydraulic parameters of the Primary Loop Pressure Control System, consisted of the replacement of the spray valves and lines in order to eliminate the hydraulic transients caused by the closure of the spray valves, and to reduce the impact of the thermal stratification transients, improving therefore the stresses in the old piping. This modification affected the main spray lines (YP) from the primary loop coolant piping, and the auxiliary lines of the Volume Control (TA) and Boron Injection (TW) systems. This paper covers and describes the following topics: Planning the project to meet the very strict deadlines of the project schedule. Establishment of a framework for close and continuous collaboration with Trillo I NPP, and the integration of specific experience from German power plants provided by Preussenelektra. Coordination of the remaining organisations, suppliers and subcontractors participating in the project. Definition of the design criteria in order to fulfill the objective of the modification. Significant technical aspects which arose during the procurement and manufacturing phases of the valves, pressurizer top lid and other components. Performance of the assembly activities and tests to high quality levels and correct application of an adequate Radiological Protection Plan. (Author)