nuclear plant

Ukraine nuclear plant: what happens if it releases a radioactive plume?

Posted by

0


An atmospheric scientist describes how researchers would track a toxic cloud in the case of an accident at the occupied Zaporizhzhia power station

A serviceman with a Russian flag on his uniform stands guard in front of the Zaporizhzhia nuclear power plant
A soldier with a Russian flag on his uniform stands in front of the Zaporizhzhia nuclear power plant in southern Ukraine.

Officials from the United Nations’ atomic-energy watchdog have this week begun inspections of southern Ukraine’s Zaporizhzhia Nuclear Power Station, where shelling and fighting have raised the risk of a nuclear accident. Russian troops have occupied the nuclear plant — Europe’s largest — since March as part of their ongoing war in Ukraine. The international community has issued stark warnings that damaging some of Zaporizhzhia’s six reactors could lead to catastrophic meltdowns like those that occurred in 2011 at the Fukushima Daiichi Nuclear Power Plant in Japan.

Following that accident, a network of stations around the world — primarily built to enforce a treaty that will ban nuclear-warhead tests across the world — helped to monitor and predict the motion of the radioactive plume emitted by the damaged reactors. The network is being built and maintained by the Preparatory Commission for the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO).

If an accident were to occur at the Zaporizhzhia plant, Jolanta Kusmierczyk-Michulec could be among the first people to know. Kusmierczyk-Michulec is an atmospheric scientist at the CTBTO’s International Data Centre in Vienna, which is equipped to conduct computer simulations of the motion of a radioactive plume, forwards and backwards in time.

Nature spoke with Kusmierczyk-Michulec about how her work could help the world to cope with a possible accident at Zaporizhzhia.

What does the CTBTO’s nuclear-monitoring network do?

The International Monitoring System is a network of stations that are built and maintained by the CTBTO to ensure that no nuclear explosion goes undetected. For that purpose, we use monitoring stations, which are based on three waveform technologies — seismic, hydroacoustic and infrasound — and we also use radionuclide [detection] technology. This technology is the only one that can confirm whether an explosion detected and located by other technology is indicative of a nuclear test.

And how is your work involved?

In case a radionuclide station detects elevated values of radionuclides, we do backwards simulation [of how the air moves] to have information about the potential source of this detection. In special cases, we also do forward simulations.

We use an open-source atmospheric-transport model, and data from the meteorological centre ECMWF, the European Centre for Medium-Range Weather Forecasts, and from NCEP, the US National Centers for Environmental Prediction. Researchers also use this type of model for various other purposes, for example monitoring of volcanic emissions.

How did the CTBTO help to track the plume from the Fukushima Daiichi accident?

The Fukushima Daiichi Nuclear Power Plant released radioactivity into the atmosphere, which the International Monitoring System observed in the Northern Hemisphere for about three months. Radioactive noble gases, such as xenon, and radioactive particulates were detected.

During the Fukushima event, we did atmospheric-transport modelling to show where the air masses were going. I joined CTBTO in 2012, just after the accident, but still I did a lot of simulations related to it. It was one of the cases that we could use for scientific purposes and for research.

How would we find out if there is a detection of radioactivity released from the Zaporizhzhia plant? Does your network have stations nearby?

The fact that a station is close to the source doesn’t mean that this station will observe something, because air-mass trajectories are quite complex.

The CTBTO cooperates with the International Atomic Energy Agency in the framework of IACRNE, the Inter-Agency Committee on Radiological and Nuclear Emergencies [which was established after the 1986 Chernobyl nuclear accident in Ukraine and coordinates international preparedness and response to a radiological disaster].

For the CTBTO, the critical response task in the case of nuclear or radiological emergencies is to provide real-time data. It’s very likely that the international community would find out about the accident via the IACRNE.

Are there prevailing weather patterns around southern Ukraine that would determine how the plume would probably move?

The answer is not so straightforward. Air masses can travel a long way, for a long time. After a few days, they may reach quite a far distance, depending on the weather conditions, wind directions and wind speeds. Prevailing weather patterns are not a sufficient indicator, especially in that region with quite variable wind direction.

To provide a reliable answer, we would need to do a forwards simulation using atmospheric transport modelling and actual weather data. It’s likely that if I would repeat the simulation two days later, the air masses would move in a different way.

Have you performed any practice simulations of how a plume coming from the Zaporizhzhia plant would move?

The IDC [International Data Centre] isn’t practicing specifically for any such event, but I did some simulations as an exercise before we spoke, so I know that the wind direction is very variable. As of 29 August, a hypothetical plume would have moved towards the south-east, and after a few days would turn eastward. But this result was based on the forecast data, meaning that in an actual event the simulation should be repeated with the analysed data for higher confidence, once these are available.

‘99% effective’ Fukushima ice wall fails to seal off crippled nuclear plant

Posted by

0


An “almost” watertight ice wall built around the Fukushima nuclear plant in a bid to prevent groundwater from entering the site has, quite predictably, proven to be not good enough, with Japan’s nuclear watchdog now urging TEPCO to find a better solution.
An expert panel with the Japanese Nuclear Regulation Authority examined the latest TEPCO report this week to assess how far and how successfully the project had been implemented, Japanese newspaper Asahi Shimbun reports. The members of the panel concluded that the ice wall was not working and a new plan was necessary to prevent groundwater getting mixed up with radioactive substances.
 A man walks at the empty Yotsukura municipal beach in Iwaki, about 40 km (25 miles) south of the tsunami-crippled Fukushima Daiichi nuclear power plant, Fukushima © Issei Kato

“The plan to block groundwater with a frozen wall of earth is failing,”said Yoshinori Kitsutaka, a panel member and a professor of engineering at Tokyo Metropolitan University.

“They need to come up with another solution, even if they keep going forward with the plan.”

In March, construction company Kajima Corp. began building the frozen wall of earth around the four damaged nuclear reactors and has completed most of the 1.5-km (1 mile) barrier. TEPCO hoped that the frozen earth barrier would thwart most of the groundwater from reaching the plant and divert it into the ocean instead. However, little or no success was recorded in the wall’s ability to block the groundwater during the five-month-period. The amount of groundwater reaching the plant has not changed after the wall was built, experts said.

The problem is said to lie in the wall’s gaps, or parts where the barrier is not frozen. According to TEPCO, 99 percent of their thermometer readings showed that the wall’s temperatures are at or below the freezing point, meaning the wall is mostly solid. However, a remaining one percent of the readings showed temperatures above the freezing point, which means the wall is not solid at those parts.

Those constitute a mere one percent of the 820-meter-long barrier, but these sections, where the earth is not frozen, are enough to ruin the entire project as they were found in areas with high levels of groundwater concentration.

TEPCO however believes that the unfrozen sections can be fixed if coated with concrete.

In April a chief architect of the project said that gaps in the wall and rainfall will still allow for water to creep into the facility and reach the damaged nuclear reactors, which will in turn create as much as 50 tons of contaminated water each day.

“It’s not zero,” Yuichi Okamura, a general manager at Tokyo Electric Power Co. (TEPCO) said referring to the amount of groundwater flowing into the plant. “It’s a vicious cycle, like a cat-and-mouse game…we have come up against many unexpected problems.”

TEPCO has been repeatedly facing criticism for handling of the Fukushima crisis which occurred after a massive earthquake and subsequent tsunami led to a meltdown of reactors at the facility in March 2011.

The company has admitted that it did not act properly during the disaster, confessing in February that it announced the nuclear meltdowns far too late. It also stated in a 2012 report that it downplayed safety risks caused by the incident, out of fear that additional measures would lead to a shutdown of the plant and further fuel public anxiety and anti-nuclear campaigns.

Despite the ongoing problems encountered following the meltdowns, TEPCO has set 2020 as the goal for ending the plant’s water problem – an aim which critics say is far too optimistic. The problem of water contamination is just one of many surrounding the dismantling and containing of the Fukushima plant debris which is estimated to take at least 40 years.