Fukushima – Seven years later and water is still problem number 1

On 11 March 2011, tragedy struck Japan. A magnitude 9.0-9.1 earthquake sent shockwaves hurtling through the Pacific Ocean towards the densely populated island nation. The quake was the 4th strongest recorded since the early 20th century, and the largest recorded in Japanese history. As of 2017, a total of almost 16 000 people lost their lives directly to the effects of the quake, and another 3 500 deaths were identified as being earthquake related. Of course, the massive tsunami created by the quake also resulted in the most severe nuclear disaster since the Chernobyl reactor meltdown in 1986.

An area of about 1 260 km2 (i.e. a radius of 20 km) surrounding the Fukushima Dai-ichi nuclear power plant was evacuated after it was realised that 3 of its 6 reactors could no longer be cooled, leading to a meltdown. The reactors had also sustained basement damage, only making the problem worse. Radioactive material was now being leaked into the environment and the ocean – uncontrollably.

100 000 people within a 20 km radius of the power plant were evacuated

What happened?

Nuclear power relies the production of steam created by the heat given off during the process of nuclear fission. This steam is used to drive a turbine that generates electricity. Fission occurs when unstable (radioactive) atoms split and release enough energy to split other unstable atoms in a chain reaction. In nuclear reactors, the extent of the fission process is controlled by rods that can be inserted into the core containing the radioactive fuel. These control rods are also used to stop the fission process: however, even after the reactor has been shut down by the control rods, the fuel rods must still be cooled to prevent a meltdown.

Energy released during the splitting of atoms generates heat, which then creates steam to drive a turbine

In the Fukushima disaster, the reactors used water as a coolant. After the reactors were shut down following the earthquake, electricity from the power grid (used to pump and circulate the vital cooling water) was cut off due to downed power lines. The emergency diesel generators should have started and provided electricity for the pumps, but these were submerged under water brought ashore by the tsunami, rendering them useless. Without the cool water, the reactors’ cores overheated, producing a hot and radioactive lava ripe for environmental devastation.

7 years later, water is still the primary problem

Today, an exclusion zone remains in place, but the continuing contamination of water is the primary problem.

Fukushima is wedged between mountains and the ocean, and when it rains, run off from the mountain range passes the contaminated site (both above and below ground) on its way to the ocean. As the reactors’ basements were cracked during the quake, a central concern relates to the fact that the water now pumped into the reactors to cool the melted cores ends up leaking into the soil. The leaked water is contaminated with radioactive material, and is carried off into the ocean by subsurface rainwater runoff. See the images below:

Water runoff from the mountains passes the plant on its way to the ocean

The runoff water also flows under the plant, mixing with contaminated water used to cool the melted radioactive core material

To deal with this issue as best possible, engineers tasked with damage control and clean-up operations pump ground water into reservoirs constructed onsite. By 2016, almost 1 billion litres of contaminated water had been pumped and stored.

Storing the pumped and contaminated groundwater is unsustainable in the long run

Unfortunately, this alone is not enough to prevent radioactive leakage into the ocean. Authorities also implemented a system in which frozen water is used to create walls of frozen soil around the perimeter of the reactors. This, it was hoped, would prevent water from flowing under the reactors. The long term effectiveness of this system, however, cannot be conclusively proven.

Sub-zero temperature water is used to create a wall of frozen soil meant to act as an impermeable barrier, thereby isolating the dangerous subsurface water directly under the reactors

Given the fact that decommissioning Fukushima will still take another 4 decades, and that radioactive waste remains dangerous for many hundreds of years, the lasting effects of the disaster will be with the Japanese people for some time to come. Moreover, as there are 450 reactors worldwide (with another 160 planned), we can only hope that humanity’s mistakes will be lessons well learnt by future generations.

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