Fukushima Radiochemistry

On the 11^th March 2011 at 14:46 Japan Standard Time, a category 9 earthquake was recorded off the northeast coast of Japan. The epicenter was approximately 72 kilometers east of the Oshika Peninsula of Tohoku. The earthquake moved Honshu 2.4 m east and shifted the Earth on its axis by almost 10 cm. The earthquake was recorded as an upper 6 at the prefecture of Fukushima.

6 separate boiling water nuclear reactors make up the Fukushima I power plant. Nuclear reactors numbers 4, 5 and 6 had already been shut down prior to the earthquake for routine maintenance. Nuclear reactors 1, 2 and 3 were shut down after the earthquake but the subsequent tsunami flooded the plant and incapacitated the emergency generators which ran the pumps to cool the reactors. Reactors 1, 2 and 3 suffered partial nuclear meltdowns (melting of the core of the nuclear reactor), hydrogen explosions destroyed parts of the buildings housing reactors 1 and 3, an explosion damaged reactor 2's containment which is designed to prevent the release of radioactivity into the environment, and several fires broke out in reactor 4. As the water levels in spent fuel pools dropped, the spent fuel rods began to overheat.
On 25th March, Japan's nuclear regulator announced a likely breach of Number 3's containment vessel. World wide measurements of wind-born radioactive iodine and caesium vented from reactors suggested a massive increase in these substances which led to bans on the sale of food grown within a 100km radius of the Fukushima I plant

Cesium-137 is a radioactive isotope of cesium that is formed during the nuclear fission of uranium. It has a half-life of 30.17 years and decays by beta emission to metastable barium-137. Cesium-137 is soluble in water, and its behaviour in living things is similar to that of potassium. The biological half-life of cesium is about 70 days. Experiments with dogs have shown that a dose of 44μg/kg of cesium-137 is lethal within 3 weeks. Prussian blue, Fe₇(CN)₁₈.14H₂O, chemically binds cesium-137 and speeds up its expulsion from the body, so it can be used to treat ingestion of cesium-137.

Iodine-131, also called radioiodine, makes up about 3% of the products of uranium fission. It undergoes beta decay and has a half-life of about 8.02 days. High doses of iodine-131 can be less dangerous than low doses since high doses tend to kill thyroid tissues which could otherwise become cancerous as a result of the radiation. Ingestion of iodine-131 is treated by taking iodine supplements containing non-radioactive iodine-127 as iodide ions. This raises the total amount of iodine in the body and therefore reduce the uptake and retention of radioactive iodine-131.

Reference:
http://www.newsdaily.com/stories/tre72l501-us-japan-contaminants/

Further Reading:
Isotopes
Nuclear Decay
Half-life

Study Questions:

1. Explain what is meant by the term nuclear fission.
2. Give the atomic number and mass number for each of the following:
   
   • uranium-235
   • uranium-238
   • cesium-137
   • iodine-131
3. How many protons and neutrons are contained within the nucleus of each of these atoms:
   
   • uranium-235
   • uranium-238
   • cesium-137
   • iodine-131
4. Explain what is meant by beta decay.
5. Write balanced chemical equations for the beta decay of each of the following:
   
   • cesium-137
   • iodine-131
6. What does a Chemist mean by the term half-life?
7. If a 20kg dog ingests 880μg of cesium-137, how much cesium-137 will remain after 3 weeks? (The half-life of cesium-137 is about 30.17 years)
8. "The biological half-life of cesium is about 70 days". What do you think this means?
9. If a 20kg dog ingests 880μg of cesium-137, how much cesium-137 will remain in the dog's body after 70 days?
10. Iodine pills were distributed to people living around the Fukushima power plants on 12^th March. A typical emergency dose is 130 milligrams of potassium iodide. What mass of iodine is contained in each dose?
11. The iodine dose contained in the emergency pills is about 700 times larger than the normal nutritional daily need of an adult. What is the approximate mass of iodine is required per adult daily?