AMNA NAWAZ: The Zaporizhzhia nuclear power plant remains caught on the front line of the war in Ukraine.

This week, the director general of the U.N.'s nuclear agency visited the plant in Ukraine's south to assess its stability and the damage caused by Russia's occupation.

Nick Schifrin spoke to Rafael Grossi about why he's no longer calling for a denuclearized zone around the plant and how conditions could become dangerous.

NICK SCHIFRIN: Across the front line, escorted by Russian military police, the world's top nuclear watchdog arrived at Europe's largest nuclear plant to try and prevent nuclear disaster.

The Russians occupying this Zaporizhzhia nuclear power plant gave IAEA Director General Rafael Grossi a tour.

And in a statement aired by Russian TV, Grossi thanked them.

RAFAEL GROSSI, Director General, IAEA: I think it's important that we can continue our dialogue.

NICK SCHIFRIN: But, earlier this month, Grossi was alarmed.

RAFAEL GROSSI: This cannot go on.

I am astonished by the complacency, yes, the complacency.

What are we doing to prevent this from happening?

NICK SCHIFRIN: This is the threat of meltdown.

Russian forces seized the Zaporizhzhia nuclear power plant more than a year ago.

Ever since, it's been in the crossfire fire.

Buildings have been damaged.

The electricity lines that keep the nuclear reactors cool have been cut six times, forcing the use of emergency generators.

And, today, there's only one remaining power line.

RAFAEL GROSSI: How are you?

NICK SCHIFRIN: After meeting Grossi earlier this week, Ukrainian President Volodymyr Zelenskyy called Russia's occupation of Zaporizhzhia -- quote -- "radiation blackmail."

VOLODYMYR ZELENSKYY, Ukrainian President (through translator): Holding a nuclear power plant hostage for more than a year is the worst thing that could happen in the history of the European and global nuclear energy sector.

RAFAEL GROSSI: The possibility, or the probability, should I say, of an accident or action that could impact the plant has increased.

NICK SCHIFRIN: I spoke to Grossi yesterday as he left Ukraine on a train.

RAFAEL GROSSI: On both sides of the front, there is an -- there is a bigger, much larger number of troops and heavy military equipment.

There are constant detonations and explosions near in the vicinity.

I have to cross a mine field myself to get there, which was not the case before.

At this point in time, anything is possible, attacks from outside, sabotage from inside.

NICK SCHIFRIN: What can the IAEA do if, for example, Russia were to leave the plant quickly during any kind of Ukrainian counteroffensive or if Russia were to use the plant somehow as leverage during the Ukrainian counteroffensive?

RAFAEL GROSSI: This goes to the heart of what I'm trying to do.

Initially, we were working towards the establishment of some sort of zone to protect the plant.

With this increased level of combat and military activity, you will not find any military commander or officer that is going to tell you, I'm not going there, or I am going here or there.

So what I'm focusing is on the things that shouldn't be done.

For example, don't shoot at the plant.

This is achievable.

Or another very important commitment, don't use the plant as a military base.

So, what I want is everybody to agree with me.

Agreeing with each other at this point is impossible.

NICK SCHIFRIN: Aren't the Russians already using the plant as a military base?

RAFAEL GROSSI: Well, I am talking to them.

And I am sure that, if we get to some form of agreement between them and me, and on the other side with Ukraine and myself, we are going to be able to avoid this.

NICK SCHIFRIN: The Russians have troops inside the plant of Zaporizhzhia.

Is that correct?

RAFAEL GROSSI: There are security forces.

And if we get to an agreement, this will also be addressed.

So, I'm trying to be very prudent here, because I don't want to put anybody in a difficulty or to point fingers.

My goal here is to protect the plant.

That is my goal, to prevent a nuclear accident with catastrophic radiological consequences, which, at this moment, is entirely possible.

NICK SCHIFRIN: Ukrainian officials are disappointed the IAEA has failed to evict Russian troops or prevented Russians from abusing the Ukrainian workers.

Have the Russians killed anyone at the plant?

Have they tortured anyone?

Have they threatened anyone?

Last September, we spoke to one of the 4,600 Ukrainian workers that continue to operate the plant, down from 11,000.

He agreed to speak to us if we kept him anonymous.

MAN (through translator): Yes, there is official information about injured employees, about the victims.

Some served in the armed forces of Ukraine before.

Some openly demonstrated their pro-Ukrainian position.

This was enough for the Russians to trap those people in the basement and torture them over several weeks.

RAFAEL GROSSI: One of the pillars of nuclear safety is that the staff should be able to work without pressure, without unnecessary stress.

NICK SCHIFRIN: And are they today able to work without pressure, without stress?

RAFAEL GROSSI: No, there is a lot of pressure.

There is a lot of pressure.

And I would say, even without them being subjected to a specific act of pressure, the whole situation is not sustainable.

NICK SCHIFRIN: Rafael Grossi, director general of the IAEA, thank you very much.

RAFAEL GROSSI: I thank you very much.