A breach at the Nova Kakhovka Dam stemming from the destruction of the 351-MW hydroelectric power plant in southern Ukraine on June 6 has triggered massive flooding, prompted an environmental crisis, and raised new perils for a nearby nuclear plant on the frontlines of the Russia-Ukraine war.

Completed in 1956, the Kakhovka hydropower power plant (KHPP) was a run-of-the-river power plant located at the Nova Kakhovka dam, one of six Soviet-era dams that straddle the Dnipro River, which runs from northern Ukraine into the Black Sea. The Nova Kakhovka dam is located about 18 miles east of the city of Kherson. Russia occupies the southern (or left) bank of the war-ravaged Kherson region, while Ukraine controls the northern bank.

The dam is reportedly 30 meters (98 feet) in height and 3.2 kilometers (2 miles) in width, and it holds back a massive reservoir of around 18 cubic kilometers (4.3 cubic miles) of water.

The Kakhovka hydropower plant is located at the Nova Kakhovka dam on the Dnipro River in southern Ukraine. The 5.7-GW Zaporizhzhia nuclear power plant (ZNPP)—Europe’s largest nuclear plant—is located 200 kilometers (120 miles) upstream. The nuclear plant is sited about 10 kilometers away from the 2.9-GW Zaporizhia Thermal Power Plant. The three plants on the frontline of the Ukraine-Russian war are Russian-occupied. Source: POWER

Ukraine and Russia Trade Blame

The facts are difficult to discern given an inundation of conflicting reports about who and what caused the destruction. According to Ukrhydroenergo, the largest hydropower generating company in Ukraine, the Kakhovskaya HPP has been occupied by Russian troops since last year. The company has suggested the cause of the disaster was a detonation inside the engine room at the Kakhovka HPP, which occurred at 2:50 a.m. on June 6.

Ukrhydroenergo claims the explosion, carried out by Russia, completely destroyed the station, including its 16 gates, the hydropower plant building, the earthen dam insert between the power plant building and the lock, and the administration building. “The station cannot be restored,” said Ukrhydroenergo Director General Ihor Syrota.

On June 8, Ukrhydroenergo distributed a quote from Mykola Kalinin, deputy technical director and chief engineer at engineering firm UKRGYDROPROEKT, suggesting that the destruction was caused by “several simultaneous powerful explosions” from inside the power plant. “We completely exclude that the cause of the destruction was an external impact since the Kakhovskaya HPP was designed and built to withstand a nuclear impact,” Kalinin added. “I do not rule out that the occupiers were advised exactly where to lay the explosives by workers of the Russian energy structure who worked there.” Kalinin also noted that while the explosion was not heard, it could be explained “by the fact that the explosives were planted in the depths of the HPP building in the interior, below the water level,” he said.

Russia at a United Nations Security Council meeting on June 6 claimed Kyiv sabotaged the dam to gain a military advantage. In addition, Russian representative Vassily Nebenzia suggested that Kyiv authorities “significantly increased” water discharge from the Dnepropetrovsk Hydroelectric Power Station, a fifth step on the Dnipro River cascade. That led “to even greater flooding of the territories. This indicates that this sabotage was planned in advance to cause the most severe repercussions for the population of the region,” he said.

A breach at the Nova Kakhovka Dam stemming from the destruction of the 351-MW hydroelectric power plant in southern Ukraine on June 6 has triggered massive flooding and prompted an environmental crisis. Courtesy: Ukrhydroenergo

Nuclear Plant Won’t Be Able to Pump Water From the Reservoir if Levels Fall Too Low

What is known is that the dam’s breach has led to devastating humanitarian and ecological consequences. Along with widespread flooding that has prompted mass displacement, a major concern is that the level of the Kakhovka reservoir is falling dramatically. One worry is that it will be too low for water pumps at the war-ravaged and Russian-occupied Zaporizhzhya nuclear power plant (ZNPP), which is located 200 kilometers (120 miles) upstream of the site.

The International Atomic Energy Agency (IAEA) said it was closely monitoring the situation. On June 7, the agency reported that the reservoir had so far declined by around 2.8 meters (m) since the dam was breached on Tuesday, reaching 14.03 m.

If the level falls below 12.7 m, the ZNPP will no longer be able to pump water from the reservoir to the site,” the agency warned. “As the full extent of the dam’s damage remains unknown, it is not possible to predict if and when this might happen. If the current drop rate were to continue, however, the 12.7-m level could be reached within the next two days.” The water height limit is relative to the Baltic Sea (known as the Baltic Heights System), the agency noted.

On June 8, Ukrhydroenergo reported reservoir levels had fallen to 13.05 m. The company, however, highlighted work on a potential solution. “Ukrhydroenergo together with the design institute Ukrhydroproject is working on a project to build a bridge (overlay) of the Kakhov reservoir to restore the water level to the design mark before the blast,” it said. “A list of priority tasks and works is being prepared.”

Zaporizhzhya Nuclear Plant Taking Precautions, Replenishing Water Reserves

Meanwhile, preparing for the worst, the ZNPP has begun continuously replenishing its water reserves, including the large cooling pond adjacent to the power plant, as well as smaller sprinkler cooling ponds and nearby channels, such as the discharge channel from the nearby Zaporizhzhya Thermal Power Plant (ZTPP), which is used to bring water from the reservoir to the ZNPP site. The replenishment is “fully utilizing the water of the Kakhovka reservoir while this still remains possible,” the IAEA noted.

“When full, these water sources will be sufficient to provide the plant with the water it needs to cool its six reactors as well as its spent fuel for several months. Even though the ZNPP’s six reactors are all in shutdown mode, they still require cooling water to prevent fuel melt and a possible release of radioactive material,” said IAEA Director General Rafael Grossi.

The IAEA noted that while five of the ZNPP’s six reactors are in cold shutdown, one unit remains in hot shutdown to produce process steam on site (for operations such as the treatment of liquid radioactive waste, which is collected from the six reactors even during the shutdown state of the reactors).

As the American Nuclear Society Rapid Response Taskforce underscored, ZNPP is currently supplied with electricity from the Ukrainian power grid. “In the event of an extended loss of external power supply, the nuclear plant has 20 backup diesel generators, with 10 to 15 days of fuel on-site, to meet the typical needs of its reactors. The stockpiled diesel should last significantly longer now as the reactors are ‘cold’ in nuclear terms and, thus, would consume the diesel at a significantly slower pace,” it said.

“Even if the water drops in the breached reservoir to pre-dammed levels for the Dnipro River, the nuclear plant has mobile pumping units that can be used to access water from alternative sources. The plant also has special floating water intakes, which allow the facility to draw water when the reservoir is at low levels,” it said. “In addition, non-essential consumption of water is being halted at the nuclear plant to conserve water. Plant operators are discussing further measures to be implemented.”

Power plant groups continue to carefully monitor the afflicted power plants as the bitter war draws on. On Tuesday, the American Nuclear Society specifically commended industry “colleagues at [ZNPP] for their continued bravery and commitment in keeping the plant safe and operational under extraordinarily difficult circumstances.”

Sonal Patel is a POWER senior associate editor (@sonalcpatel@POWERmagazine).