Is Zaporizhzhia safer now?

What is “cold shutdown”? And what about the fuel pools?

Cold shutdown reduces risk of disaster at Zaporizhzhia nuclear plant – but combat around spent fuel still poses a threat

By Najmedin Meshkati, University of Southern California

Is Zaporizhzhia safer now? — Beyond Nuclear International Energoatom, operator of the Zaporizhzhia Nuclear Power Plant in the Ukrainian city of Enerhodar, announced on Sept. 11, 2022, that it was shutting down the last operating reactor of the plant’s six reactors, reactor No. 6. The operators have put the reactor in cold shutdown to minimize the risk of a radiation leak from combat in the area around the nuclear power plant.
The Conversation asked Najmedin Meshkati, a professor and nuclear safety expert at the University of Southern California, to explain cold shutdown, what it means for the safety of the nuclear power plant, and the ongoing risks to the plant’s spent fuel, which is uranium that has been largely but not completely depleted by the fission reaction that drives nuclear power plants.

What does it mean to have a nuclear reactor in cold shutdown?

The fission reaction that generates heat in a nuclear power plant is produced by positioning a number of uranium fuel rods in close proximity. Shutting down a nuclear reactor involves inserting control rods between the fuel rods to stop the fission reaction.

The reactor is then in cooldown mode as the temperature decreases. According to the U.S. Nuclear Regulatory Commission, once the temperature is below 200 degrees Fahrenheit (93 Celsius) and the reactor coolant system is at atmospheric pressure, the reactor is in cold shutdown.

When the reactor is operating, it requires cooling to absorb the heat and keep the fuel rods from melting together, which would set off a catastrophic chain reaction. When a reactor is in cold shutdown, it no longer needs the same level of circulation. The Zaporizhzhia Nuclear Power Plant uses pressurized water reactors.

How does being in cold shutdown improve the plant’s safety?

The shutdown has removed a huge element of risk. The Zaporizhzhia Nuclear Power Plant is a pressurized water reactor. These reactors need constant cooling, and the cooling pumps are gigantic, powerful, electricity-guzzling machines.

Cold shutdown is the state in which you do not need to constantly run the primary cooling pumps at the same level to circulate the cooling water in the primary cooling loop. The International Atomic Energy Agency (IAEA) has reported that reactor No. 6 is now in a cold shutdown state like the facility’s five other reactors, and will require less power for cooling. Now, at least if the plant loses offsite power, the operators won’t have to worry about cooling an operating reactor with cranky diesel generators.

And by shutting down reactor No. 6, the plant operators can be relieved of a considerable amount of their workload monitoring the reactors amid the ongoing uncertainties around the site. This substantially reduced the potential for human error.

The operators’ jobs are likely to be much less demanding and stressful now than before. However, they still need to constantly monitor the status of the shutdown reactors and the spent fuel pools.

What are the risks from the spent fuel at the plant?

The plant still needs a reliable source of electricity to cool the six huge spent fuel pools that are inside the containment structures and to remove residual heat from the shutdown reactors. The cooling pumps for the spent fuel pools need much less electricity than the cooling pumps on the reactor’s primary and secondary loops, and the spent fuel cooling system could tolerate a brief electricity outage.

One more important factor is that the spent fuel storage racks in the spent fuel pools at the Zaporizhzhia Nuclear Power Plant were compacted to increase capacity, according to a 2017 Ukrainian government report to the IAEA. The greater number and more compacted the stored spent fuel rods, the more heat they generate and so more power is needed to cool them.

There is also a dry spent fuel storage facility at the plant. Dry spent fuel storage involves packing spent fuel rods into massive cylinders, or casks, which require no water or other coolants. The casks are designed to keep the fuel rods contained for at least 50 years. However, the casks are not under the containment structures at the plant, and, though they were designed to withstand being crashed into by an airliner, it’s not clear whether artillery shelling and aerial bombardment, particularly repeated attacks, could crack open the casks and release radiation into the grounds of the plant.

The closest analogy to this scenario could be a terrorist attack that, according to a seminal study by the National Research Council, could breach a dry cask and potentially result in the release of radioactive material from the spent fuel. This could happen through the dispersion of fuel particles or fragments or the dispersion of radioactive aerosols. This would be similar to the detonation of a “dirty bomb,” which, depending on wind direction and dispersion radius, could result in radioactive contamination. This in turn could cause serious problems for access to and work in the plant.

Next steps from the IAEA and UN

The IAEA has called on Russia and Ukraine to set up a “safety and security protection zone” around the plant. However, the IAEA is a science and engineering inspectorate and technical assistance agency. Negotiating and establishing a protection zone at a nuclear power plant in a war zone is entirely unprecedented and totally different from all past IAEA efforts.

Establishing a protection zone requires negotiations and approvals at the highest political and military levels in Kyiv and Moscow. It could be accomplished through backchannel, Track II-type diplomacy, specifically nuclear safety-focused engineering diplomacy. In the meantime, the IAEA needs strong support from the United Nations Security Council in the form of a resolution, mandate or the creation of a special commission.

Najmedin Meshkati, Professor of Engineering and International Relations, University of Southern California

September 21, 2022 Posted by Christina Macpherson | safety, Ukraine | Leave a comment

Offsite power supply to Zaporizhzhia nuclear plant destroyed

Offsite power supply to Zaporizhzhia nuclear plant destroyed

Guardian Isobel Koshiw in Kyiv, 10 Sept 22,

A vital offsite electricity supply to the Zaporizhzhia nuclear plant has been destroyed by shelling and there is little likelihood a reliable supply will be re-established, the United Nations’ nuclear watchdog chief has said.

Rafael Grossi, the director general of the International Atomic Energy Agency (IAEA), said shelling had destroyed the switchyard of a nearby thermal power plant.

The plant has supplied power to the nuclear facility each time its normal supply lines had been cut over the past three weeks. The thermal plant was also supplying the surrounding area, which was plunged into darkness.

Local Ukrainian officials said work was under way to restore the connection, which has been cut multiple times this week.

Grossi, who said he had been informed of the situation by IAEA representatives at the plant, called for an “immediate cessation of all shelling in the entire area”. “This is an unsustainable situation and is becoming increasingly precarious,” he said, without apportioning blame for the shelling.

Ukraine and Russia have blamed each other for shelling near Zaporizhzhia in southern Ukraine and within the perimeter of Europe’s biggest nuclear power plant, which has six reactors.

The thermal supply has been cut and restored multiple times this week and Enerhodar, the nearby town, has suffered several complete blackouts.

When the thermal supply has been cut the plant has relied on its only remaining operating reactor for the power needed for cooling and other safety functions. This method is designed to provide power only for a few hours at a time. Diesel generators are used as a last resort. The constant destruction of thermal power supply has led Ukraine to consider shutting down the remaining operating reactor, said Grossi. Ukraine “no longer [has] confidence in the restoration of offsite power”, he said.

Grossi said that if Ukraine decided not to restore the offsite supply the entire power plant would be reliant on emergency diesel generators to ensure supplies for the nuclear safety and security functions.

“As a consequence, the operator would not be able to restart the reactors unless offsite power was reliably re-established,” he said…………….. https://www.theguardian.com/world/2022/sep/09/offsite-power-supply-to-zaporizhzhia-nuclear-plant-destroyed

September 21, 2022 Posted by Christina Macpherson | safety, Ukraine | Leave a comment

All 6 reactors at Zaporizhzhia nuclear plant now completely stopped operating

 Operations at the Russian-held Zaporizhzhia Nuclear Power Plant in Ukraine
have been fully stopped as a safety measure, Energoatom, the state agency
in charge of the plant, said. The plant “is completely stopped” after thec
agency disconnected the number 6 power unit from the grid at 3.41am (local
time), it said in a statement. “Preparations are under way for its cooling
and transfer to a cold state.”

 RTE 11th Sept 2022

https://www.rte.ie/news/ukraine/2022/0911/1321783-ukraine-russia/

September 21, 2022 Posted by Christina Macpherson | safety, Ukraine | Leave a comment

Ukraine Considers Shutting Nuclear Plant After Loss of Backup Power

After shelling destroys key electricity supply, Zaporizhzhia facility may have to rely on generators with 10 days of fuel left

WSJ, By Drew Hinshaw and Laurence Norman Sept. 9, 2022

Ukraine is considering shutting down the sole remaining reactor at the Zaporizhzhia nuclear plant, the International Atomic Energy Agency said Friday, after shelling left the plant without a safe and sustainable source of backup power.

The plant, which has already shut down five of its six reactors, risks having only one remaining source of electricity to power its systems in case the sixth reactor has to go offline, said Director General Rafael Grossi in a statement..

Normally, if the plant can’t supply itself power,
it can draw electricity from a nearby thermal-energy plant. But shelling
overnight Thursday destroyed a switchyard that carries electricity out from
that coal-fired plant, Mr. Grossi said.

It is unlikely that it will be
repaired, he added, given the constant artillery fire, meaning the nuclear
plant would have no off-site emergency source of power. The plant could
turn to back up generators, but those only have enough fuel for about 10
days, according to Ukraine’s state-owned nuclear company, Energoatom. The
plant, occupied by Russian soldiers who patrol with grenades dangling off
their belts, is still operated by the company’s Ukrainian workforce.

Plant workers, meanwhile, have no electricity in their homes and the
shelling risks accelerating an exodus of essential staff. “This is an
unsustainable situation and is becoming increasingly precarious,” Mr.
Grossi said. “The power plant has no off-site power, This is completely
unacceptable. It cannot stand. ”The Zaporizhzhia plant is now producing a
minimal 250 megawatts, enough to monitor and sustain the temperature of its
cooling ponds, to pump water through the station, to clean the air inside
the plant, and to perform other basic safety functions, said Petro Kotin,
interim president of Energoatom.

If the last operating reactor goes down,
he said, the staff will need to supply 200 tons of diesel daily to the
generators. The IAEA said in a report Tuesday Ukraine had 2,250 tons of
diesel fuel available for the whole site. Procuring more would require
several truckloads of fuel to cross through an active conflict area
subjected to continual artillery fire, many times a day. Nuclear experts
said it could make sense to shut down the last reactor and work off backup
generators, because the earlier that is done, the cooler the reactor core
would be if Zaporizhzhia’s generators run out of fuel and there is an
accident.

Workers reached by The Wall Street Journal have blamed the
artillery fire on Russia. Plant technicians, backed by European officials
and independent nuclear analysts, have said the shelling serves the
Kremlin’s broader goal of severing Zaporizhzhia’s power connection to
Ukraine’s remaining territory and eventually rerouting it into
Russian-held areas. Russian soldiers have laid land mines around the
plant’s cooling ponds, parked heavy artillery near its reactors, and
turned its safety shelters—meant for plant workers to flee to in an
emergency—into a bunker for themselves, workers say.

When IAEA inspectors
visited the plant last week, they found that the alternative emergency
center that Russian soldiers offered the staff didn’t have its own
ventilation system to filter out radiation from the air, or its own source
of power—or even an internet connection.

Shutting down the plant, in the
midst of an active conflict, would pose enormous and unprecedented
challenges for the nuclear industry. Defunct or dormant nuclear plants
still require electricity and careful maintenance by trained staff to
monitor and safeguard spent nuclear fuel, among other safety operations.
The plant currently suffers obstacles sourcing the spare parts and fuel
that would be required. Compounding difficulties, the Zaporizhzhia plant
has seen a considerable amount of its workforce flee, slipping out through
Russian checkpoints to Ukrainian-held ground.

 Wall Street Journal 10th Sept 2022  https://www.wsj.com/articles/ukraine-considers-shutting-nuclear-plant-after-loss-of-backup-power-11662747396

https://www.wsj.com/articles/ukraine-considers-shutting-nuclear-plant-after-loss-of-backup-power-1166274739

September 21, 2022 Posted by Christina Macpherson | safety, Ukraine | Leave a comment

Here’s why the risk of a nuclear accident in Ukraine has ‘significantly increased’

https://www.wboi.org/npr-news/npr-news/2022-09-09/heres-why-the-risk-of-a-nuclear-accident-in-ukraine-has-significantly-increased By Geoff Brumfiel, September 9, 2022, The head of the International Atomic Energy Agency is warning that the risk of a nuclear accident at the Zaporizhzhia nuclear power plant has “significantly increased,” following ongoing fighting around the site.

“Let me be clear, the shelling around Zaporizhzhia nuclear plant must stop,” IAEA Director General Rafael Mariano Grossi said in a brief recorded statement released on Friday.

Grossi also warned that the continued fighting might require the plant to shut down its last operating reactor. That would set into motion a chain of events that could intensify the current nuclear crisis. Here’s how.

Nuclear plants need electricity

The Zaporizhzhia nuclear plant is the largest in Europe, capable of producing thousands of megawatts of electricity. But the plant also needs power from the same electricity grid it feeds.

The power is used to run the various parts of the plant, including its safety and cooling systems. Specifically, nuclear power plants require water to be pumped constantly through their cores in order to function safely, and the pumps need electricity.

At Zaporizhzhia, the power is normally supplied by four high-voltage lines, which connect the nuclear complex to Ukraine’s electricity grid, but the conflict has seen those lines systematically cut. The last 750kV line was severed on September 3, according to the IAEA.

A backup line was disconnected two days later due to a fire on the site. In a press conference shortly after returning from Zaporizhzhia, Grossi told reporters that he believed the power lines were being deliberately targeted:

Zaporizhzhia has been making its own power, but that’s a limited solution

Since losing its last connection to the grid on Sept. 5, the nuclear plant has been powering itself in so-called “islanding operation mode.” Under this setup, the Unit 6 reactor has been producing low levels of electricity that are running the rest of the facility.

The reactors at Zaporizhzhia are designed to operate in this mode during startup, according to a nuclear engineer who worked directly with the reactors when the plant began operations in the 1980s, but who was not authorized to speak publicly by his current employer.

“It’s not good, it cannot be done for a long time,” he says. The problem is less to do with the reactor itself than the turbine, generators and other systems–all of which are designed to run at significantly higher power levels than islanding operation mode provides.

Adding to the problem, Grossi said in his statement, is the increasing strain on the plant’s Ukrainian operators. Many of the plant’s current staff of just under 1,000 live in the nearby town of Enerhodar. Its water, sewage and electrical supplies have all been disrupted in recent days by the same fighting that’s damaged the lines around the plant.

“The shelling is putting in danger operators and their families, making it difficult to adequately staff the plant,” Grossi says.

Shutting down the last reactor will trigger emergency generators

With conditions deteriorating, it seems more likely that Ukrainian authorities will decide to power down the last reactor. But in the short term, that could exacerbate the crisis.

That’s because nuclear reactors are more like charcoal grills than gas stoves. Even after they’re shut off, they remain hot for a long period of time. Water must still circulate in the cores to prevent a meltdown.

With its reactors shut down, Zaporizhzhia will switch to backup emergency diesel generators to keep the reactors cool. The emergency generators themselves are a tried-and-true method for cooling a nuclear reactor. In fact, the Nuclear Regulatory Commission requires U.S. plants to switch to emergency diesel generators immediately, bypassing the “islanding operation mode” used in Zaporizhzhia.

“We don’t want to go on the diesel generators, but it’s a situation you can abide by for awhile,” says Steven Nesbit, a nuclear engineer and member of the American Nuclear Society’s rapid response taskforce, which is tracking the current crisis. For example, after losing power during Hurricane Andrew in 1992, the Turkey Point Nuclear Plant in Florida operated for days on emergency diesel power.

If the generators run out of fuel, a meltdown could occur

September 21, 2022 Posted by Christina Macpherson | safety, Ukraine | Leave a comment