This 1986 aerial view of the Chernobyl shows damage from an explosion and fire in reactor four on April 26, 1986. Volodymyr Repik/AP

April 26 marks a morbid historic anniversary. Thirty years ago to the day in 2016, the Chernobyl nuclear power plant melted down outside Pripyat, Ukraine.

The resulting explosion killed 31 people almost immediately, and the spray of radioactive fallout forced the permanent evacuation of at least 100,000 people nearby — though, in a gross oversight on the part of officials, the evacuation of Pripyat didn't begin until 36 hours after the initial explosion.

While exact figures are still disputed, it's estimated that the explosion has caused thousands of deaths in the intervening years, likely with more still to come.

But that wasn't the end of Chernobyl's story.

Despite setting a 19-mile exclusion zone and building a huge concrete "sarcophagus" to cover the melted-down (and still radioactive) Unit 4 reactor, officials kept three reactors operating in the wake of the aftermath — nearly 14 years altogether.

At the time of the incident, a fifth and sixth reactor units were under construction. Those projects were quickly halted, but Units 1, 2, and 3 kept producing power.

The troubles continued as well. Unit 2 shut down in 1991 after being damaged by a fire. Unit 1 closed in 1996 amidst international outcry about the health effects radiation poisoning, including elevated rates of thyroid cancer among children.

The last unit, Unit 3, operated until 2000, when international negotiations finally shut down the plant for good.

Why did it take so long?

One reason was power shortages. In 1987, the LA Times reported that, while the Soviet Union had advanced in the previous year under its final leader, Mikhail Gorbachev, technology was "years behind" the US.

The Soviet economy wasn't doing too well, either — and after Chernobyl, it only got worse.

Even in the contemporary world, nothing about nuclear is cheap: Not the labor or materials needed to build a plant, not the uranium, and certainly not the expense of decommissioning a multi-unit power producer.

No non-nuclear replacement could come close to generating the same amount of power, and building a new power plant would take money and time the struggling nation didn't have.

Decommissioning a nuclear power plant isn't easy, either. In fact, Chernobyl is shut down but not fully decommissioned, meaning that the reactors still need to be taken apart and decontaminated. They also need remove the depleted uranium fuel rods, which are highly radioactive.

The current plan, laid out by the international organization the Nuclear Energy Agency (NEA), will have to find solutions for not only the depleted uranium, but treatment and storage for every piece of equipment used in Chernobyl and the decommissioning process.

Remember, this is nuclear waste we're talking about: You can't just toss it. The NEA is building storage facilities on-site to house the waste.

The original 1986 sarcophagus around Unit 4 was only meant to be temporary. So at the moment, a $2.3 billion USD structure is being built to encase the unit for decades to come.

Things are happening rapidly, however, thanks to some international help. Officials expect the site could be decommissioned as early as 2022.