The conflicting reports being given to the Japanese public and the world leave any positive assessments tinged with more than a touch of doubt. Early Tuesday, Japan’s nuclear agency raised the severity rating at Fukushima from Level 5 on the International Nuclear and Radiological Event Scale (INES), indicating an “accident with off-site risk,” to Level 7, a “major accident” on par with the 1986 Chernobyl disaster. The Washington Post writes that the upgraded severity reading does not reflect a recent deterioration at the plant. Rather, it suggests Japan’s evolving understanding of the damage that occurred there one month ago and the contamination that has been leaking since.
However, from there the confusion continues with each passing news conference. Hidehiko Nishiyama, deputy chief of the Nuclear and Industrial Safety Agency, states that radiation released from Fukushima Daiichi amounted to less than one-tenth the total released from Chernobyl. Then at another conference, an official from Tokyo Electric Power Co. turns around and says that the amount of radiation leaked could surpass Chernobyl.
Reuters makes this interesting evaluation: Nuclear experts say Fukushima will go down in history as the second-worst nuclear accident ever. Not as bad as Chernobyl in the Ukraine but definitely much worse than Three Mile Island in the United States.
Nuclear energy was seen as a means of supplying an almost limitless supply of electricity while being green and combatting global warming. However, the extent of the nuclear disaster brought about by the natural disaster is amking everybody across the globe re-assess the wisdom of investing in something which has so quickly turned into a nightmare. Nevertheless, many countries already have a huge investment in nuclear energy and despite public outrage over this incident, nobody is going to make nuclear power go away anytime soon.
Will public trust come back? Reuters talks of new designs meant to avoid the flaws of Fukushima by using passive safety systems rather than electric pumps and motors to shut the plant in an outage.
Passive Safety Systems
Third generation designs improve on early designs by incorporating passive or inherent safety features which require no active controls or (human) operational intervention to avoid accidents in the event of malfunction, and may rely on pressure differentials, gravity, natural convection, or the natural response of materials to high temperatures.
In some designs the core of a fast breeder reactor is immersed into a pool of liquid metal. If the reactor overheats, thermal expansion of the metallic fuel and cladding causes more neutrons to escape the core, and the nuclear chain reaction can no longer be sustained. The large mass of liquid metal also acts as a heatsink capable of absorbing the decay heat from the core, even if the normal cooling systems would fail. (Wikipedia)
The Wall Street Journal reports that TEPCO is looking at compensating residents around the Fukushima plant. However as shares have dropped 78% from their value before the March 11 earthquake, just how the company will pay residents remains uncertain. Speculation has been that the Japanese government will eventually have to nationalize the company but no decision has yet been made. Kyodo news agency adds that TEPCO will be considering selling some of its assets and cutting its workforce to free up money for payments.
Melted nuclear fuel likely settled at bottom of crippled reactors
Kyodo news agency is reporting that according to an analysis by the Atomic Energy Society of Japan, nuclear fuel has partially melted and settled at the bottom of the pressure vessels. While a large buildup of melted nuclear fuel at the bottom could become a molten mass so hot it could damage the critical containers and eventually leak huge amounts of radioactive material, temperature readings are showing the fuel is being kept at a relatively low temperature. The society has also said that the fuel grains with a diameter of between several millimeters and 1 centimeter are believed to have settled flatly at the bottom of the vessels, leaving almost no possibility of a nuclear chain reaction called ”recriticality.”
Kyodo goes on though to explain that small amounts of plutonium have been detected in soil samples taken at the nuclear complex. This is the third time plutonium has been found in the soil at the plant. Workers are injecting nitrogen into reactor number one in an effort to stop another hydrogen explosion and will probably do the same for reactors two and three. TEPCO has removed another 660 tons of highly radiactive water that was the result of the company pouring water into the reactor buildings in an effort to cool the reactors.
Telegraph – Apr 12/2011
New video of Fukushima plant
The operator of Japan’s damaged nuclear plant releases new video of the reactors as Japanese Chief Cabinet Secretary Yukio Edano promises to give up-to-date information on the nuclear issue to its worried neighbours.
Wikipedia: Passive nuclear safety
Passive nuclear safety is a safety feature of a nuclear reactor that does not require operator actions or electronic feedback in order to shut down safely in the event of a particular type of emergency (usually overheating resulting from a loss of coolant or loss of coolant flow). Such reactors tend to rely more on the engineering of components such that their predicted behaviour according to known laws of physics would slow, rather than accelerate, the nuclear reaction in such circumstances. This is in contrast to some older reactor designs, where the natural tendency for the reaction was to accelerate rapidly from increased temperatures, such that either electronic feedback or operator triggered intervention was necessary to prevent damage to the reactor.
A scram or SCRAM is an emergency shutdown of a nuclear reactor – though the term has been extended to cover shutdowns of other complex operations, such as server farms and even large model railroads (see Tech Model Railroad Club). In commercial reactor operations, this emergency shutdown is often referred to as a “SCRAM” at boiling water reactors (BWR), and as a “reactor trip” at pressurized water reactors (PWR). In many cases, a SCRAM is part of the routine shutdown procedure, as well.
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