The risk of a North Korean nuclear meltdown can't be ignored, according to a recent note published on 38North, a project of the US-Korea Institute at Johns Hopkins School of Advanced International Studies.

Longstanding doubts over the hermit kingdom's nuclear safety resurfaced in July, when a video emerged of leader Kim Jong Un smoking a cigarette next to a Hwasong-14 intercontinental ballistic missile.

"Kim's recklessness is certainly notable, and it hints at an under-emphasized and potentially devastating possibility: the threat of a nuclear accident in North Korea," said the 38North note, released late last week.

Adding to the concern, Chinese researchers said in September that North Korea's Punggye-ri nuclear test site was at risk of imploding. That was followed by TV Asahi's October report of a tunnel collapse at the same nuclear site, an incident believed to have killed more than 200 people. Pyongyang, in response, called the report false and dismissed it as misinformation.

The Yongbyon Nuclear Scientific Research Center, the North's major nuclear facility, is so densely concentrated that one fire could lead to a disaster potentially worse than Chernobyl, former South Korean President Park Geun-hye claimed in 2014.

Known as the worst nuclear disaster in history, a 1986 explosion at a nuclear reactor inside Ukraine's Chernobyl nuclear plant spewed tons of radioactive material into the air and resulted in thousands of deaths linked to radiation exposure and cancer.

"While [Park's'] damage assessment is likely an exaggeration — researchers from 38 North assess Chernobyl's power output to have been 3,000 percent greater than Yongbyon — the potential for a nuclear accident is not," the note said.

The North has yet to witness a serious accident, but it's had a couple of close calls.