Oh, What a Relief it is…

Located on the west coast of Sweden and producing roughly 25 billion kilowatt-hours of energy per year, the Ringhals Nuclear Power Plant provides approximately one-sixth of Sweden ’s total electrical power. With four reactors, the facility is the largest power plant in Scandanavia. One of these reactors is a boiling water reactor (BWR), while the other three are pressurized water reactors (PWRs), for 3,530 megawatts of total installed power.

The Ringhals plant’s units 2 (875 MW), 3 (915 MW), and 4 (915 MW), which have been in operation since 1975, 1981, and 1983, respectively, are Westinghouse pressurized water reactors (PWRs). The PWR units were suffering, however; the original Fisher and Masoneilan power-operated relief valves (PORVs) were unable to handle Loss of Coolant Accident (LOCA) conditions.

Aware of this situation, Regulating Authorities began watching the power plant closely, and in 1998, Ringhals began studying possible measures to improve its valves’ performance. At this time, the CCI team began working closely with end user Ringhals AB during the study phase and tenaciously provided expert advice for five years.

Ringhals Nuclear’s analysis revealed that the installed pneumatic diaphragm actuators were not qualified for the harsh LOCA conditions inside containment, which was not considered when the units were built. Thus the valves must fulfill an additional function stemming from Anticipated Transient Without Scram scenarios. This function is to bring the reactor coolant pressure down as low as possible and as long as possible in case of a Beyond Design Basis Event.

The old valves were unable to provide this service, and neither Fisher nor Masoneilan could retrofit the valves with qualified actuators. The experts at CCI knew that Ringhals Nuclear needed a qualified valve like the SV50 PORV to handle the various media and their transients.

The CCI solution for Ringhals Nuclear included three new system medium-operated SV50 PORVs on each of the plant’s three PWR units, offering the advantage of pilot control solenoid valves (MV type) fully qualified to IEEE (Institute of Electrical & Electronics Engineers) and KBE (Swedish regulations) requirements. This LOCA-qualified solution is much more reliable and more simple than the old valves, with no safety-related air supply needed.

Since their installation in the first PWR unit, the new PORVs have passed their commissioning tests with flying colors and the valves are leak-tight. Their excellent performance has satisfied the Regulating Authorities, not to mention Ringhals Nuclear – enjoying the peace of mind that comes from first-rate operational safety and reliability. The happy customer is now considering using CCI’s SV design for other safety valve applications.

Published in SOLUTIONS Summer 2005