'Chernobyl' evidence presentation

Jared Harris as Valery Legasov in HBO’s “Chernobyl”

There was recently a smallish but nonetheless startling fire at the Castañeda household. There’s no use pointing fingers, but suffice it to say, mistakes were made. Fortunately, it was quickly doused and there was little damage. And, most importantly, nobody was hurt.

I have new a new perspective on such mishaps these days, after having watched HBO’s “Chernobyl,” a five-part miniseries that dramatically re-enacts the 1986 explosion of the Chernobyl nuclear reactor in the former Soviet Union, as well as the trial of those accused of causing it.

Watching the miniseries yields important lessons on how to present scientific evidence at trial.

Nuclear Physics 101

Chernobyl. Now that was a disaster. Thousands died, many in the immediate aftermath, but many more in later years from radiation-related illnesses. Thousands of square miles in Ukraine and Belarus are still in what’s called The Exclusion Zone, where access is strictly limited and radiation remains at treacherously high levels.

As a litigator, though, what I most appreciated from watching the finale was the way nuclear physicist and Chernobyl investigator Valery Legasov (portrayed by Jared Harris) explained two things to the judges hearing the case: 1) how a nuclear reactor works and 2) why Chernobyl reactor 4 exploded.

Granted, this was all dramatic license, because, in real-life, Legasov didn’t actually testify at the trial of the three men accused of causing the disaster. But, as an illustration of how to explain complex, highly technical facts to a non-technical audience (which, as an energy litigator, I must often do), the “Chernobyl” finale was practically a master class.

It reminded me of the late, great Rick Garza, an engineer who served as my expert witness in the Mesa Petroleum Partners v. Baytech trial in 2016. Rick served as an expert witness in countless trials, and he did a brilliant job of turning headache-inducing technical matters into easy-to-understand concepts that just about anybody could digest. And he did it without PowerPoints or computer-generated graphics. In fact, he was more likely to do his pre-trial prep at a craft or hardware store than in front of a computer.

Which is why I was so impressed with Valery Legasov’s presentation in the “Chernobyl” finale. It was low-tech and simple, but it wasn’t dumbed-down. He used appropriate terminology, but he explained it in a way that someone without a PhD in nuclear physics would be able to understand it. That’s a delicate balance, and I know from experience that it’s an exceedingly hard one to strike.

The question of why the reactor exploded had been the central question of the miniseries. The reactor was designed with a failsafe that, even when everything else had gone wrong, would instantly shut the reactor down and avoid an explosion. An explosion was inconceivable, to hear the plant’s managers and party officials tell it.

But, as Legasov testified, the Chernobyl reactor had a fatal design flaw that actually turned the failsafe into a detonator.

As Legasov approached the witness’ podium, he carried a stack of blue and red plastic cards. A helper rolled up a display board.

‘The Invisible Dance’

As Legasov explained, “The only thing that happens in the nuclear reactor is that reactivity, which generates power, either goes up or it goes down. That’s it. All the operators do is maintain balance.”

Legasov began placing the plastic cards on the display board, with the red plates representing those elements that cause reactivity to go up and the blue plates representing those elements that cause reactivity to go down. I’ll let him take it from here:

“As uranium atoms split apart and collide, reactivity goes up [red card goes on the board]. But if you don’t balance the reactivity, it never stops rising, so … boron control rods … reduce reactivity like brakes on a car [blue card]. But there’s a third factor to consider: water. Cool water takes heat out of the system [blue card].

As it does, it turns to steam or what we call a void. In an RBMK reactor of the type used at Chernobyl, there’s something called a positive void coefficient [red card]. … It means that the more steam present within the system, the higher the reactivity, which means more heat, which means more steam. Which means … it would appear we have a vicious cycle on our hands.

And we would, were it not for this – the negative temperature coefficient [blue card].
When nuclear fuel gets hotter, it gets less reactive, so…

Fuel increases reactivity [red].
Control rods and water reduce it [blue].
Steam increases it [red].
And the rise in temperature reduces it [blue].

This is the invisible dance that powers entire cities without smoke or flame. And it is beautiful. When things are normal.”

Bad Decisions and a Design Flaw

But Chernobyl wasn’t in its normal state, he explained, because the reactor had been held at half power for 10 hours in anticipation of a long-planned safety test that the reactor’s managers were under great pressure from their higher-ups to perform. That reduced power allowed xenon to build up. Normally, xenon (a natural byproduct of uranium splitting) is burned away when the reactor is at full power. Instead, it was building up, essentially poisoning the core.

When the power inexplicably dropped below the engineers’ target, the man in charge, Anatoly Dyatlov (the chief villain), issues a series of orders that make the reactor more and more unstable, including removing almost all the boron control rods and shutting down the water pumps. The reactor immediately begins to heat up, and with nothing to slow it down, conditions quickly become dangerous.

As Legasov relates these decisions, he removes blue cards from the right side of the board and puts red cards back up on the left side of the board. He is soon standing next to a board with nothing but red cards.  The reactor is essentially a speeding locomotive with no brakes.

Once it’s apparent the reactor is in danger, the engineers decide to execute the failsafe: all the boron control rods [blue cards] go back in to the reactor and stop it. Unfortunately, the boron control rods in the Chernobyl reactor (and many other Soviet reactors, as we learn) had graphite tips, which accelerate reactivity.

“Why?” asks one of the judges.

“It’s cheaper,” Legasov answers.

The second the graphite tips enter the core, the temperature skyrockets, and the reaction accelerates, turning Chernobyl reactor 4 into a nuclear bomb.

And that, sadly and tragically, is how a nuclear reactor that supposedly couldn’t possibly explode, exploded. As a viewer, I appreciate how well the science was explained and broken down into understandable concepts. But as an inhabitant of this planet, I can’t help but be unnerved by how quickly and irreversibly the situation went south – and by how many bad decisions went into that happening.

There are a lot of reasons to watch “Chernobyl” – for its window into a terrifying, tragic chapter of history, for the insights to be gained about life in the USSR before its collapse, and, frankly, for some great TV. But, for lawyers, particularly those of us tasked with explaining highly technical facts to non-technical audiences, it was a wonderful illustration of how to present a complex case in an understandable fashion.

Chrysta Castañeda


Chrysta Castañeda, the founding partner of Dallas’ The Castañeda Firm, is a commercial litigator focusing on oil and gas litigation. She was named one of The National Law Journal’s 2018 Elite Trial Lawyers. Chrysta can be reached at chrysta@castaneda-firm.com.