Engineering news
Fine cracks can occur over time in these bricks, which were installed in the 1970s and ‘80s. Those cracks might not have any effect on day-to-day operation, but what about during an earthquake?
That might seem an unlikely eventuality, but with 200-300 earthquakes of varying intensity hitting the UK every year – and the potential for devastating damage highlighted by the Fukushima nuclear disaster – the University of Bristol and EDF Energy are not taking any risks.
The partners are showing their earthquake research at the Royal Society’s Summer Science Exhibition, which opened in central London this morning (1 July) and runs until Sunday. “Learning from Fukushima we’ve got to make sure we’ve covered everything,” said Dr Jim Reed at the event. The graphite chief engineer at EDF added: “We test far beyond what we’ve ever seen in the UK.”
This testing involves Bristol’s ‘shaking table’, which at 3x3m is the largest in the UK. It can carry up to 15 tonnes and reach acceleration of up to 5g, with maximum displacements of 0.15m. Researchers input different settings to the table, simulating earthquakes up to 7.2 on the Richter scale – the UK’s strongest ever quake was 6.1. It can even replicate the conditions of real-world seismic events.
“You can either put in a simple sine wave or put in real earthquakes, or scale them up,” said Reed to Professional Engineering. “It does both the magnitude and the frequency.”
On to this table the researchers put a quarter-scale model of a jigsaw-like AGR core, including some with cracks similar to faults that appear over time. The collaborators then repeatedly shook the model before lowering control rods into channels between the bricks, checking they were able to descend and were not blocked by broken chunks. Boron control rods are an important tool for shutting reactors down and preventing potentially disastrous meltdowns, and might even need to descend during a quake.
The research is an assessment of the “worst case scenario”, Reed said. “Our UK reactors, the AGRs… will stop generating in the next 10 years or so. We’ve got to make sure, until then, it’s safe and we understand where it fits in.”
Thankfully, data collected by 3,200 embedded sensors in the model showed the cores can withstand severe seismic activity. There was “no impact on the safe operations of the reactor” even in the 7.1 quake, the University of Bristol said.
The £100m+ project will now run experiments with even more cracked and broken bricks, said Reed. Typical graphite cores are 10m high and weigh 1,400 tonnes, and EDF hopes to ensure cracks cannot lead to disasters – even in unprecedented earthquakes.
Other researchers and companies are showing 21 other exhibits at the Royal Society’s exhibition. For more information, click here.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.