The Fukushima Daiichi plant has seven pools for spent fuel rods assemblies.
Six of the pools are located at the top of each reactor building and contained 3,450 fuel rod assemblies between them in 2010.
There is one common pool building housed in a dedicated building. The common pool contains 6,291 fuel rod assemblies.
A dry cask is used to store another 408 assemblies. This is a reported total of 10,149 as of March, 2010.
Add another 700 units for the period of March 2010 to 2011 and the current estimated total of fuel rod assemblies at the reactor site is 10,849.
Each assembly contains 63 fuel rods. So at the time of the accident there were almost 640,000 spent fuel rods being stored on site.
A total of 1,760 metric tons of spent nuclear rods are stored above and around the reactors.
Sometime prior to 2010 the holding capacity of the pools above the reactors was increased by re-racking the existing rods. It is unclear if this increase was anticipated in the original design.
What has become clear is that the added storage of spent fuel rods at the Fukushima reactors is greatly increasing the scale and mortality of this current, world-class emergency.
The practice of re-racking is not limited to Japan. Here in the US, the Nuclear Regulatory Commission (NRC) has increased the number of spent-fuel rods allowed per pool partly because a national disposal site for nuclear waste has not been established.
But the main reason that federally sanctioned re-racking has been allowed is because plant operators avoid millions of dollars in costs by delaying moves to safer but expensive dry cask storage. The concerns of the plant operators drown out any opposition bolstered by the immense amount of money and manpower marshaled by the various lobby groups and PACs - most notably the Nuclear Energy institute (NEI).
The NRC insists the practice is safe but many scientists and engineers say the practice is dangerous and warn that the sheer volume of radioactivity in the pools could turn an accident or natural disaster into a cataclysm. JUST LIKE FUKUSHIMA.
A 1997 study by the Brookhaven National Laboratory concluded that a pool fire at a plant like Millstone Nuclear Power Station in Connecticut or Pilgrim Nuclear Generating Station in Massachusetts could kill 100 people instantly and another 138,000 people eventually. Some $546 billion in damage would result, the study said, and 2,170 square miles of land could be contaminated.
After uranium fuel has been used in a reactor for a while, it is no longer as efficient in splitting its atoms and producing heat to make electricity. It is then called “spent” nuclear fuel. About one-fourth to one-third of the total fuel load is spent and is removed from the reactor every 12 to 18 months and replaced with fresh fuel.
Spent nuclear fuel is still highly radioactive and potentially very harmful. Ten years after removal from a reactor, the radiation dose 1 meter away from a typical spent fuel assembly exceeds 20,000 rems per hour. A dose of 5,000 rems would be expected to cause immediate incapacitation and death within one week.
Many of the radioactive elements in spent fuel have long half-lives. For example, plutonium-239 has a half-life of 24,000 years, and plutonium-240 has a half-life of 6,800 years. Because it contains these long half-lived radioactive elements, spent fuel must be isolated and controlled for thousands of years.
Currently, most spent nuclear fuel is stored in specially designed pools at individual reactor sites around the country. The water-pool option involves storing spent fuel in rods under at least 20 feet of water, which provides shielding from the radiation for anyone near the pool.
The fuel pools vary in size from a capacity of 216 to 8,083 fuel assemblies. Most pools were originally designed to store several years worth of spent fuel.
A second hazard of spent fuel, in addition to high radiation levels, is the remote possibility of an accidental “criticality,” or self-sustained fissioning and splitting of the atoms of uranium and plutonium.
The original design and construction of US nuclear plants planned for used fuel storage over a decade or two, not long-term storage.
The nation’s 104 nuclear power plants are now storing some 63,000 metric tons of spent fuel rods, according to 2010 numbers compiled by the Nuclear Energy Institute.
All of these concerns sit atop a shaky foundation where most plants in the US are re-licensed automatically way past their originally designed lifetime.