Xenon, Re-Wilding Chernobyl, and the Periodic Table of DEATH and Mystery

Have you ever stupidly accepted a challenge, hubris oozing from every pore, because in the back of your smug little mind you’re thinking, I’m pretty smart, strong, in shape, brave, unafraid?

That’s how we got here today, folks, with the periodic table element, Xenon. You see, initially, the focus of this article was going to be on radioecology and wildlife that now live in the Chernobyl Exclusion Zone in Ukraine (1) and the Polesie State Radioecological Reserve in Belarus (2). Instead, I was suckered by a physicist—YOU KNOW WHO YOU ARE—casually shelling and eating peanuts and talking about Xenon poisoning and Xenon pits. My eyes lit up. Pits? Like the Pit of Despair in The Princess Bride (1987)(4)? And poisoning. The perfect fit for the Periodic Table of DEATH and Mystery.

Or was it?

NO, by golly! It was about Xenon poisoning of the nuclear reactor at Chernobyl in 1987 (6), which means decoding the physics. It was about suckering a biochemist into doing physics. And I fell for it.

Well played, Physicist. Well played.

But it’s only hubris if I fail (5). So, buckle up, buttercup. I’m goin’ in.

Biochemistry and the Elements

The reactivity of an element generally has to do with the number of valance or outer shell (12) electrons flying around the nucleus of an atom, and whether the protons (positively charged atomic particles) balance with the orbiting electrons (negatively charged atomic particles. Electrons don’t really orbit the nucleus like planets orbit the sun. It’s just a convent way of imaging). Biochemists tend to focus on this balance of electrons to protons because this has a huge effect on chemical and biochemical molecules and reactions that impact life (bonds, acids, and bases).

Noble gas elements are considered non-reactive. They are found in the right-hand column of the periodic table, and include the likes of helium (8), neon (9), and krypton (10). Xenon (Xe) has an atomic number of 54 protons (positively charged particles) in its nucleus, and 54 electrons (negatively charged particles) in its orbiting electron shells, creating a neutral element. It has an atomic weight of 131.29—that’s the addition of all protons (54) and all neutrons (77) in its nucleus, and is written Xenon 131. While all elements of the periodic table are charge-balanced, Xenon’s valence electron shell is “full” with no unpaired electrons to create bonds to another atom, the ground state of xenon creates a very stable, or “inert” element (3).

Physics and the Elements

But physicists aren’t as interested in the electrons as biochemists. They are more interested in the nucleus. All but one of the periodic table elements (Hydrogen) have two different atomic particles in their nucleus—protons (positively charged) and neutrons (no charge). Protons and neutrons are valuable when harvesting energy from atoms that are forcefully merged (fusion) or split (fission) because A LOT of the energy released in these nuclear reactions is released as heat. By harvesting that heat energy via intermediates like water to steam, which is then used to spin turbines, humans can convert nuclear energy into clean electric power (13).

And then there’s Chernobyl, a nuclear power plant where “clean” nuclear energy became a very dirty word. Xenon played a significant role in the chain of events leading to the Chernobyl disaster, as did human error. Of course.

Here’s some information you’ll need.

The main fission reaction in a Uranium nuclear reactor is:

1-neutron splits Uranium 235 into Barium 141, Krypton 92, and 3 more neutrons.

The 3 neutrons “released” allow the chain reaction to continue. But too many neutrons can cause a runaway nuclear reaction, which could result in a nuclear explosion. So, some of the neutrons are deliberately taken out of the chain reaction cycle. They are absorbed by boron-carbide control rods that are raised and lowered automatically and manually by plant operators to control the rate of fission.

During the Uranium fission reaction, about 3% of the time (14) radioactive Xenon135 is produced. Uranium 235 splits and creates Tellurium 135, which decays to Iodine 135, which then decays to Xenon 135 (15). This reaction is time-delayed based on the half-life of Iodine 135, which is approximately 6.6 hrs.

Xenon 135 is a STRONG NEUTRON ABSORBER. Way stronger than the boron-carbide control rods. During normal operation, the high neutron flux burns off the Xenon 135 as quickly as it’s produced. The key is for the nuclear power plant to balance the production of Xenon 135 vs its “burn” to Xenon 136, which does not absorb neutrons. Too much Xenon 135 build-up in a reactor can cause XENON PITS and XENON POISONING, and dampen the chain reaction by absorbing too many of the neutrons that cause fission.

Got that? Good. Stay with me now because here comes a biochemist’s simplified version of what happened at Chernobyl.

Chernobyl

On April 25, 1986, operators were scheduled to conduct a safety test on Reactor 4. To do this, they would reduce power from 1600 megawatts thermal (MWt) to about 700 MWt. Due to a communication error during the operator shift change, the power dropped to about 30 MWt, much lower than intended. This drastic power reduction drastically decreases the neutron-Uranium fission reaction and produces a Xenon pit – Xenon 135, building up from the continued decay of existing Iodine 135. The Xenon 135 then absorbs even more neutrons and further suppresses the nuclear reaction.

When the operators tried to raise the power back up again so they could start the safety test, they found the reactor unresponsive due to the Xenon poisoning—there weren’t enough neutrons to maintain the chain reaction. To counteract this, they made a critical mistake and huge safety violation: they withdrew almost all the control rods from the core to increase the number of neutrons for fission.

It turns out Chernobyl’s reactor had a dangerous design flaw: as power increased and water turned to steam, the reaction rate increased further—a positive feedback loop. The operators, unaware of the full extent of these flaws, proceeded with the test. When they initiated the final step, the combination of boron-carbide control rods being withdrawn and the Xenon 135 burn off led to a sudden and uncontrollable power surge due to too many neutrons available for fission reactions. Within seconds, the reactor’s power output spiked to around 30,000 MWt, over 100 times its normal operational output. This caused a steam explosion, followed by a second explosion (possibly like a small nuclear bomb), which destroyed the reactor building and released plumes of radioactive material into the environment.

You probably know the rest of the story. Dozens died from acute radiation poisoning. Thousands were permanently evacuated from the radiated zone around Chernobyl but have increased cancer rates from even the minimum exposure to the released radioactivity. A tragedy, except …

The exclusion zone now teems with wildlife rarely seen before the accident, including wolves, European bison, roe deer, black and brown bears, lynx, and more. A living laboratory for radioecologists. Reading about this rewilded zone inspired my De-Extinct Zoo Mystery series because, along with the zoological park, a huge re-wilded section of northern New Mexico and southern Colorado will be imagined in the fifth book in the series, Hunted.