Wyden is an ignorant alarmist who is exploiting the Fukushima accident for political gain. Below is a link to an authoritative refence on the radioactive decay of nuclear wastes over time.
http://www.nucleartourist.com/basics/sfdecay1.htm
Unfortunately, these well refenced charts do not document the massive reduction of radioactivity that occurs during the first year after a reactor is shut down. The general rule of thumb is that the radioactivity decreases by ninety percent for every seven fold increase in time since shut down. There are of course adjustments for how long a reactor has been operating and accumulating longer lived fission products.
The bottom line is that while the spent fuel pool for Unit#4 contains a batch of spent fuel rods that had only recently been removed from the reactor before the earthquake, after a years time the spent fuel rods in the unit #4 pool are not significantly more radioactive than the spent fuel inventory in the other pools.
The bloviating about the alleged dangers of Plutonium is rediculous. To many ignorant people, including Senator Wyden, presume the Plutonium is exceptionally dangerous because it has an extremely long half-life of 24,000 years. Actually, there are several isotopes of Plutonium in nuclear wastes with half-lives ranging from a few seconds to 24,000 years. More importantly, the radioactivity of any isotope is inversely proportional to it's half-life. The longer the half-life, the less radioactive it is. Most of the radioactivity of Plutonium is caused by the Pu-238 isotope with a half-life of 87 years. However; the total radioactivity of Plutonium is trivial compared to that of the fission products whose half-lives typically range from a few minutes to a few years.
The big news about Fukushima is that the worst danger is over. The reactors have been successfully shut down in spite of failures of control rods to fully insert. The radioactivity of the reactor cores has decayed to the point that natural circulation can keep the cores cool without any need for pumps. The radioactivity of the reactor cores has decayed to the point that you could flush all of the reactor cores as well as the spent fuel pools into the ovean without significantly increasing the radioactivity naturally
present.
The point being you have scrutinize where the information is coming from, from retailers trying to sell survivalist products or a politician who's out
for his own political gains.