Tag: Spent nuclear fuel

 

 

 

But how to dispose of  irradiated water?

I have not been able to find information.

Nor people are sure about dumping nuclear waste into the sea.

TOKYO – Workers discovered new pools of radioactive water leaking from Japan’s crippled nuclear complex, officials said Monday, as emergency crews struggled to pump out hundreds of tons of contaminated water and bring the plant back under control.

Officials believe the contaminated water has sent radioactivity levels soaring at the coastal complex, and caused more radiation to seep into soil and seawater.

The Fukushima Dai-ichi power plant, 140 miles (220 kilometers) northeast of Tokyo, was crippled March 11 when a tsunami spawned by a powerful earthquake slammed into Japan’s northeastern coast. The huge wave engulfed much of the complex, and destroyed the crucial power systems needed to cool the complex’s nuclear fuel rods.

Since then, three of the complex’s six units are believed to have partially melted down, and emergency crews have struggled with everything from malfunctioning pumps to dangerous spikes in radiation that have forced temporary evacuations.

Confusion at the plant has intensified fears that the nuclear crisis will last weeks, months or years amid alarms over radiation making its way into produce, raw milk and even tap water as far away as Tokyo.

The troubles at the Fukushima complex have eclipsed Pennsylvania‘s 1979 crisis at Three Mile Island, when a partial meltdown raised fears of widespread radiation release, but is still well short of the 1986 Chernobyl disaster, which killed at least 31 people with radiation sickness, raised long-term cancer rates, and spewed radiation for hundreds of miles (kilometers).

http://news.yahoo.com/s/ap/ap_on_bi_ge/as_japan_earthquake

How to dispose Nuclear Waste.

 

 

 

The spent fuel rods from a nuclear reactor are the most radioactive of all nuclear wastes. When all the radiation given off by nuclear waste is tallied, the fuel rods give off 99% of it, in spite of having relatively small volume. There is, as of now, no permanent storage site of spent fuel rods. Temporary storage is being used while a permanent site is searched for and prepared.

When the spent fuel rods are removed from the reactor core, they are extremely hot and must be cooled down. Most nuclear power plants have a temporary storage pool next to the reactor. The spent rods are placed in the pool, where they can cool down. The pool is not filled with ordinary water but with boric acid, which helps to absorb some of the radiation given off by the radioactive nuclei inside the spent rods. The spent fuel rods are supposed to stay in the pool for only about 6 months, but, because there is no permanent storage site, they often stay there for years. Many power plants have had to enlarge their pools to make room for more rods. As pools fill, there are major problems. If the rods are placed too close together, the remaining nuclear fuel could go critical, starting a nuclear chain reaction. Thus, the rods must be monitored and it is very important that the pools do not become too crowded. Also, as an additional safety measure, neutron-absorbing materials similar to those used in control rods are placed amongst the fuel rods. Permanent disposal of the spent fuel is becoming more important as the pools become more and more crowded.

Dry Cask Storage Containers .

Another method of temporary storage is now used because of the overcrowding of pools. This is called dry storage (as opposed to “wet” storage which we outlined above). Basically, this entails taking the waste and putting it in reinforced casks or entombing it in concrete bunkers. This is after the waste has already spent about 5 years cooling in a pool. The casks are also usually located close to the reactor site.

Permanent Fuel Storage/Disposal:

There are many ideas about what to do with nuclear waste. The low-level (not extremely radioactive) waste can often be buried near the surface of the earth. It is not very dangerous and usually will have lost most of its radioactivity in a couple hundred years. The high-level waste, comprised mostly of spent fuel rods, is harder to get rid of. There are still plans for its disposal, however. Some of these include burying the waste under the ocean floor, storing it underground, and shooting it into space. The most promising option so far is burying the waste in the ground. This is called “deep geological disposal”. Because a spent fuel rod contains material that takes thousands of years to become stable (and non-radioactive), it must be contained for a very long time. If it is not contained, it could come in contact with human population centers and wildlife, posing a great danger to them. Therefore, the waste must be sealed up tightly. Also, if the waste is being stored underground, it must be stored in an area where there is little groundwater flowing through. If ground water does flow through a waste storage site, it could erode the containment canisters and carry waste away into the environment. Additionally, a disposal site must be found with little geological activity. We don’t want to put a waste disposal site on top of a fault line, where 1000 years in the future an earthquake will occur, releasing the buried waste into the environment.

The waste will probably be encapsulated in large casks designed to withstand corrosion, impacts, radiation, and temperature extremes. Special casks will also have to be used to transfer fuel rods from their holding pools and dry storage areas next to the reactor to the permanent geological storage site.

http://library.thinkquest.org/17940/texts/nuclear_waste_storage/nuclear_waste_storage.html

Related:

Highly radioactive iodine seeping from Japan’s damaged nuclear complex may be making its way into seawater farther north of the plant than previously thought, officials say, adding to radiation concerns as the crisis stretches into a third week.

Mounting problems, including badly miscalculated radiation figures and no place to store dangerously contaminated water, have stymied emergency workers struggling to cool down the overheating plant and avert a disaster with global implications.

The coastal Fukushima Daiichi power plant, 220 kilometres northeast of Tokyo, has been leaking radiation since a magnitude-9.0 quake on March 11 triggered a tsunami that engulfed the complex. The wave knocked out power to the system that cools the dangerously hot nuclear fuel rods.

On Monday, workers resumed the laborious yet urgent task of pumping out the hundreds of tons of radioactive water inside several buildings at the six-unit plant. The water must be removed and safely stored before work can continue to power up the plant’s cooling system, nuclear safety officials said. That process alone could take weeks, experts say.

http://www.cbc.ca/news/world/story/2011/03/28/japan-mon-troubles.html?ref=rss