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North Korea claims to have successfully trialled a hydrogen bomb that could be loaded on to a long-range missile.

Dr Chris Smith from the Naked Scientists described how hydrogen bombs work and why such tests are vital.

Making hydrogen bombs is nuclear fusion when you join atoms together Dr Smith explained.

"This is the process that powers the sun," he said. "And we all know that the sun is up there losing about eight million tonnes in mass every second keeping the earth warm, well you're doing that on earth.

"The fusion reaction then releases a devastating amount of energy, the destructive potential is enormous."

This clip is originally from Peter Allen and Jane Garvey on Sunday 3rd September 2017