Last reactor Zaporizhzhia nuclear power plant shut down after dam collapse
The last reactor still generating power at Europe’s largest nuclear power plant, in southern Ukraine, has been put into “cold shutdown” — a state in which it no longer generates electricity — as a safety measure after the destruction of a nearby dam threatened the facility. water supply, Ukrainian energy officials said.
Five of the six reactors at the Zaporizhzhia Nuclear Power Plant have shut down completely since September, but one – reactor 5 – was kept in what engineers call a “hot state” to help power supply within the plant.
Like the other reactors, reactor 5 was finally switched to cold shutdown on Thursday, state nuclear power company Energoatom said in a statement. That means control rods are placed in the reactor core to stop the fission reaction and the build-up of heat and pressure.
“Cold shut down is the safest state of operation of a nuclear power plant under such conditions,” the company said, citing the destruction of the Kakhovka dam and the rapid loss of water from the dam’s reservoir.
The factory in Zaporizhzhia has been occupied by Russian troops since the beginning of the war, but is still run by Ukrainian personnel.
Water continued to flow from the Kakhovka reservoir after an explosion caused the dam to collapse, leaving less water available to cool the reactors. On Saturday morning, the water level in the Nikopol area, which is on the opposite side of the Dnipro River from the plant, had dropped more than a meter from the previous day, according to state hydropower company Ukrhydroenergo.
Although the plant had been using the reservoir water for cooling, the head of Ukraine’s state-owned nuclear energy company said the loss of the reservoir does not pose an immediate risk of a meltdown.
That’s because the Zaporizhzhia Nuclear Power Plant was designed with a back-up cooling pond on site to allow engineers to shut down the six reactors even if the Kakhovka Dam were to rupture and drain the reservoir, as is happening now.
“Design conditions have been calculated for this event,” Petro Kotin, Energoatom’s president, said earlier this week.
Although the six reactors are now cold shut down, they still require water to circulate in their cores to dissipate the waste heat from nuclear reactions. Each reactor also needs water for a spent fuel cooling pond.
Supplying water to the plant now, and perhaps for years to come, will depend on maintaining the water level in the site’s cooling pond, which used to be fed by the reservoir.