Question

1. What kind of nuclear units were affected in the Fukushima accident?

2. What are the fission products produced in nuclear reactors like Fukushima and Chernobyl?

3. What happened to the nuclear fuel rods in the units 1-4 at Fukushima? How does this compare to Chernobyl?

4. What happened to the spent fuel rods in these units?

5. Which of the four units do you think is the one that poses the biggest danger (for the next million years)? Give reasons.

6. What is the radiation dosage at the edge of the closed zone today at Chernobyl and how does it compare to the dosage at Fukushima? You should look up the wikipedia entry on Chernobyl Exclusion Zone. A nice account of a trip to Chernobyl is given here: http://www.pureearth.org/blog/virtual-tour-of-chernobyl/. How long do you think that these closed zones will be needed? Give reasons.

Answer 1

1. The Fukushima Daiichi Nuclear Power Plant comprised six separate boiling water reactors originally designed by General Electric (GE) and maintained by the Tokyo Electric Power Company (TEPCO).

2. boiling type reactors use Low Enriched Uranium which forms daughter products Barium 141 and Krypton 92 on fission reaction

3. nuclear fule rods in fukushima were removed from the nuclear reactor to shut the reactor down, but the cooling backup genertators shut doen due to the tshunami causing the meltdown of the core reactor. in chernobyl, where as there was no change in normal use of the reactor rods, but with the safety test running underway, the inherent flaws inthe design of the nuclear reactor led to the meltdown of the reactor , when power was tried to shut off and it did not .

4. the spent fuel rods in these cases melted and reacted with other nearby elemts to form radioactive waste which was then thrown to a large surrounding area by the overwhelming steam explosion along with the plumes ( in case of chernobyl) where as it mixed with the flood water in case of the fukushima power reactor distster

5. In Reactors 1, 2, and 3, overheating caused a reaction between the water and the zircaloy, creating hydrogen gas. On 12 March, an explosion in Unit 1 was caused by the ignition of the hydrogen, destroying the upper part of the building. On 14 March, a similar explosion occurred in the Reactor 3 building, blowing off the roof and injuring eleven people. On the 15th, there was an explosion in the Reactor 4 building due to a shared vent pipe with Reactor 3.

The amount of damage sustained by the reactor cores during the accident, and the location of molten nuclear fuel ("corium") within the containment buildings, is unknown; TEPCO has revised its estimates several times.[114] On 16 March 2011, TEPCO estimated that 70% of the fuel in Unit 1 had melted and 33% in Unit 2, and that Unit 3's core might also be damaged.[115] As of 2015 it can be assumed that most fuel melted through the reactor pressure vessel (RPV), commonly known as the "reactor core") and is resting on the bottom of the primary containment vessel (PCV), having been stopped by the PCV concrete. In July 2017 a remotely controlled robot filmed for the first time apparently melted fuel, just below the pressure vessel of Unit 3.

hence, unit 1 is supposed to be most dangerous for the next million years given the significant amount of radioactive waste it had deposited, and has reached till 30 cm close leaking into the ground

6. From the graph on wikipedia page

the chernobyl radiation doses were about 50 Siverts per hour where as from fukushima were about 0.4 Sv per day