[niko12]

who prevents meltdown and the emission of radiation to the environment?

How does training of personnel prevent accidents from occurring? Who monitors that personnel are trained and are used appropriately in a nuclear power plant?


Compare and contrast the accidents at Three Mile Island, Chernobyl, and Fukushima-Daiichi nuclear power plants in terms of release of radiation (health effects on people living in the area). What accounts for this difference?

[Arkcon]

Your questions are very broad, and general.  Yet, highly specialized.  Did you try to Google these concepts to build a basic understanding?  The various news articles on the recent Fukushima event could have the beginnings of the answers for you.  Did you try the local library?  There are surely many books written about the Three Mile Island and Chernobyl accidents over the years.  Let's see what you can do on your own, to start with.

[Borek]

Somehow these questions look like taken directly from a homework. We won't do homework for you, please read forum rules.

[vmelkon]

who prevents meltdown and the emission of radiation to the environment?

Are you talking about a nuclear power plant? Because your title says nuclear chemistry.

Anyway, if it is about producing electricity, the nuclear operator monitors the reactor(s)
http://www.brucepower.com/1809/meet-our-people/nathan-stam/
http://www.tva.com/insidetva/aug_sep09/job_rocks.htm

For the other questions, hunt them down.