Evaluation of seismic qualification requirements for in-line components (active valves) following the seismic design load change

Most valves installed in Optimized Power Reactor 1000 (OPR1000) have been qualified using the required response spectra or zero period acceleration (ZPA) having maximum 5.0g for safety shutdown earthquake (SSE) loads. The ground acceleration for the SEE loads in Advanced Power Reactor 1400 (APR1400) has increased to 0.3g from 0.2g which has been applied to OPR1000. This increase would result in higher response acceleration in piping system as well as in-line components such as active valves. If pipe and equipment interface requirements are checked during the design stage, the equipment allowable rather than the pipe stress allowable seems to be exceeded. In order to reduce the interface loads to an acceptable level, many supports need to be added to the piping systems. It became a sensitive issue to set the appropriate acceleration value for the active valve qualification to a reasonable level since an increase in the seismic loads may cause an extra expenditure to the equipment suppliers in qualifying these components. Furthermore, in the process of compromising between piping stresses and pipe/equipment interface loads, it is a challenge to keep a good balance between adding supports and not losing flexibility of the piping system. Because of these concerns, various kinds of case studies have been performed to evaluate the effect of the increased seismic design loads associated with the qualification of in-line components (valves) of the APR1400. As a result of analyzing more than 430 cases studies, the maximum seismic response accelerations are ranged from 5.0g to 5.7g. In this regard, 6g acceleration value could be regarded as an appropriate acceleration value for the equipment qualification considering 20% margin to take account for possible deviation from the design condition that could happen during the construction stage. (author)