Krško nuclear power plantKrško, Slovenia · 2021

Twelve earthquakes on the shaking table, and not a single anomaly

The Silentflex plinth for racks without a raised floor, destined for the Krško nuclear power plant, passed the seismic tests of the nuclear standard IEEE 344 with the servers running and without a single anomaly.

IEEE 344
seismic qualification for nuclear power plants: 12
seismic tests: 10 OBE and 2 SSE: 335 kg
rack and plinth on the shaking table: 0
anomalies at the final inspection

1The challenge
Equipment that must keep working after an earthquake
Equipment in a nuclear power plant is qualified to IEEE 344, the recommended practice for the seismic qualification of Class 1E equipment. For the Krško plant in Slovenia, it had to be shown that a rack on a Silentflex plinth withstands the plant's design earthquakes.
2The solution
The plinth for rooms without a raised floor
The Non-Raised Floor Plinth is all-metal, 600–800 × 1,000–1,200 mm with 135 mm of free height. A Schneider Electric rack of about 235 kg was bolted onto it with 8 M12 bolts. The plinth weighs about 100 kg: some 335 kg in total.
3The test
On the shaking table, with the servers running
VIRLAB, an accredited laboratory, tested the system on 30 March 2021 on a 2.5 × 2.5 m biaxial table driven by two 150 kN servo-hydraulic actuators. The rack was powered at 220 V, with its 19 units switched on to simulate real conditions.
4OBE and SSE
Ten operating-basis earthquakes and two safe-shutdown earthquakes
In each direction (YZ and XZ), five OBE (operating basis earthquake) and one SSE (safe shutdown earthquake) tests of 30 seconds each were applied, in addition to the resonance search in all three axes.
5The result
Not a single anomaly
All the seismic tests were valid, and the final inspection found no anomaly or structural damage, either in the rack or in the plinth.