The functional requirements of Main Steam Isolation Valves (MSIVs) provided in the Boiling Water Reactor (BWR) nuclear power plants in Japan have been previously evaluated via seismic test and so forth; however, since the response acceleration has increased in line with a recent reassessment of standard earthquake ground motions, it is necessary to evaluate seismic operability with respect to high acceleration. In addition, from the viewpoint of equipment fragility in seismic PRA also, it is necessary to determine practical seismic operability limits.

We used a resonant shaking table in the Central Research Institute of the Electric Power Industry (CRIEPI) \[1\], which is capable of seismic tests at acceleration levels that have been unachievable until now, and in seismic tests carried out on a MSIV, we obtained results confirming that validated seismic operability was possible even at response accelerations as high as 15×9.8 m/s^2^.

 

1\. Introduction

With increasing standard earthquake ground motion, it is necessary to develop evaluation methods that can adequately confirm the operability of nuclear plants and quantitatively evaluate the seismic proof margin.

Seismic operability of MSIVs, which are important pieces of equipment in BWR plants, is specified as validated response accelerations at the valve actuator of 10×9.8 m/s^2^ horizontally and 6.2×9.8 m/s^2^ vertically, in Japanese technical code JEAC 4601-2008 \[2\]. The piping and support systems should be designed so that the response acceleration of the valve actuator in seismic analysis does not exceed the specified validated acceleration. Rational design will be possible if the validated acceleration can be increased.

These specified validated acceleration values were determined by seismic tests carried out in the 1980s, and therefore, it can be assumed that the acceleration was limited by the performance of the shaking tables used, and that the actual seismic ability of MSIVs is higher.

A High Acceleration Shaking Table System Using Resonance Vibration developed by CRIEPI was completed in 2015 \[1\]. Therefore, we carried out high-acceleration seismic tests on a MSIV using this shaking table, with the aim of improving the validated acceleration.

 

2\. Seismic tests

As the MSIV test specimen, we fabricated a full-size MSIV which is provided in nuclear power plants in Japan.

The seismic test includes actuating the test specimen backward and forward, sideward, and upward and downward by changing the installation position of the valve relative to the direction of excitation. After the response acceleration reached the target acceleration, the test specimen performed a quick-closing motion. The target response accelerations are  15´9.8 m/s^2^ at the pneumatic actuator. The duration of the vibration test at the target acceleration was 15 seconds.

Quick-closing motion during the target response acceleration of the pneumatic actuator were achieved.

The test specimen showed no serious damage after all seismic tests, and the structural integrity of the test specimen was verified.

 

3\. Conclusion

From the results of seismic tests, the test MSIV was judged to be capable of maintaining correct function for response accelerations up to 15×9.8 m/s^2^ in all directions, that is, two horizontal directions and the vertical direction.

 

Reference

\[1\] M. Sakai, et al., “Development of High Acceleration Shaking Table System Using Resonance Vibration”, ASME PVP2016-63752(2016).

\[2\] Japan Electric Association, “Technical Code for Seismic Design of Nuclear Power Plants”, JEAC 4601-2015 (2015).


Seismic Test Result of the Main Steam Isolation Valve for Japanese Boiling Water Reactor Nuclear Power Plants

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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