Chernobyl Is Heating Up Again, and Scientists Aren’t Sure Why

The disaster at the Chernobyl nuclear power plant is now more than 20 years in the past, but the possibility of another disaster has yet to fade completely. Recently, engineers completed the construction of the New Safe Confinement (NSC). The NSC was supposed to stabilize the site, which is still highly radioactive and full of fissile material. However, some worrying signals have emerged from the sarcophagus covering the Unit Four reactor, suggesting the remains could still heat up and leak radiation into the environment all over again.

A UN analysis says that only about 50 people died during the original meltdown in 1986, caused by a power loss during a key safety test. But the ensuing explosions launched radioactive fallout into the atmosphere across Europe. The UN later estimated that as many as 4,000 people died as a result of exposure to Chernobyl’s fallout.

Ukraine’s Safety Problems of Nuclear Power Plants (ISPNPP) is currently responsible for securing Chernobyl. The organization began construction of the enormous arch-shaped NSC in 2010 (see above) with the aim of keeping the existing remains of the reactor stable for eventual dismantling, and also to keep the site dry. Ever since the meltdown and initial cleanup, engineers have worried that rainwater leaking into the building could cause another nuclear event. As it turns out, keeping it dry might be even worse.

Meltdowns such as the one at Chernobyl, and more recently at Japan’s Fukushima, are the result of a runaway chain reaction. As uranium fuel nuclei split apart, they release neutrons that strike other uranium atoms, causing them to split as well. The ISPNPP monitors neutron levels in the wrecked Unit Four building, which still contains a molten slurry of uranium fuel rods, zirconium cladding, graphite control rods, and melted sand. The room below the Unit Four reactor was once known as 305/2, but now it’s a vat containing tons of this semiliquid nuclear material. The team estimates half of the reactor’s original fuel is still locked up inside 305/2, so it’s not great news that neutron levels have doubled in the past four years.

No one is sure what the mechanism for this escalation of nuclear activity might be. After all, this fissile soup has never existed before and is therefore poorly understood. ISPNPP scientists speculate that some property of the mixture causes it to generate more neutrons as it dehydrates. Over time, that could increase the risk of another self-sustaining nuclear reaction, which could breach the NSC and spread fallout across the region again.

The ISPNPP believes the risk of a catastrophic containment failure in the near term is low, but it’s not going to ignore the problem. The team is exploring the possibility of deploying a robot to brave the radiation and study the material in 305/2. This robot might be able to deploy boron cylinders, which would operate like impromptu control rods. The ultimate goal, however, is to remove all the nuclear fuel and store it in a geological repository. The ISPNPP is working with the European Bank for Reconstruction and Development to finalize a plan to do just that.

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