Tuesday, April 10, 2012

Fukushima Radiation Alarm Showed Reactors Damaged Before Tsunami Time March 11, 2011 3:29PM

Fukushima Radiation Alarms showed radiation was leaking before tsunami

[Fukushima NukeBlog Index ]

... A monitoring post on the perimeter of the plant about 1.5 kilometers from the No 1 reactor went off at 3.29pm, minutes before the station was overwhelmed by the tide of water that knocked out backup power that kept cooling systems running, according to documents supplied by Tokyo Electric. The monitor was set to go off for high levels of radiation, an official said.

"We are still investigating whether the monitoring post was working properly,'' said Mr Teruaki Kobayashi, the company's head of nuclear facility management said. (translation we don't want to believe it was working properly)  ''There is a possibility that radiation leaked before the tsunami arrived.'' (translation of course radiation leaked, but we want to believe it was possible that it didn't)

Tokyo Electric officials had earlier said the plant stood up to the magnitude-9 quake and was damaged by the tsunami that followed, causing the world's worst nuclear crisis since Chernobyl in 1986.  (translation they said there was no earthquake damage but now they realize they were dead wrong) 
  this from 20th May 2011 http://www.todayonline.com/World/EDC110519-0000704/Fukushima-may-have-leaked-radiation-before-tsunami--Report  

Were the Fuel Rods Damaged by the Eathquake?

Now has anyone figured out exactly what was released to cause such high readings?  I see two failure modes

1. If there is a steam leak, the steam contains trace nucleotides, mostly radioactive N-16, which decays with a 7 second half-life. For this reaon, the turbine needs to be shielded, and for some reactors, the entire building evacuated while it is running (how do they monitor and fix things while is running?)  But there should be no fission products such as Xenon or Iodine 131 as long as the fuel is not damaged.

from http://www.nucleartourist.com/systems/turbine_halls.htm
This photo illustrates the Turbine hall in a BWR facility. Closest to us in the photo is the exciter, generator, 3 low pressure turbine stages, and the high pressure turbine. On either side of the turbine can be seen the moisture-separator reheaters.
Note the shielding around the turbine. Shielding is needed because the steam from the BWR contains radioactive N-16, which decays with 7 second half-life.

Courtesy KKN - Liebstadt NPP

Because the water around the core of a reactor is always contaminated with traces of radionuclides, the turbine must be shielded during normal operation, and radiological protection must be provided during maintenance. The increased cost related to operation and maintenance of a BWR tends to balance the savings due to the simpler design and greater thermal efficiency of a BWR when compared with a PWR. Most of the radioactivity in the water is very short-lived (mostly N-16, with a 7 second half life), so the turbine hall can be entered soon after the reactor is shut down. (from http://www.powerelectricalblog.com/2007/04/boiling-water-reactor-bwr-advantages-ad.html)

2. The fuel rods themselves were damaged by G-forces generated by the earthqake and released radioactive gases like xenon and iodine 131 BEFORE they melted down. This is the scarier scenario which I have not seen anybody else speculate. Each rod is 1 cm (half inch) in diamter and about 4 meters (12 feet) long and weighs about 2 kg or 4 lb. That doesn't sound much stronger than a strand of pasta to me, since it's a length to width ratio of 40 to 1. They are pressurized to 3 atmospheres so we are looking at a very, very tall and narrow soda or beer can. The cladding is probably not much thicker than a beer can as it is only 1 cm in diameter. Even a hairline crack is going to release a lot of the gases into the steam, so this would be in addition to steam leaks.  I can't find any specifications that say what g-forces these rods are supposed to withstand in what direction, or if they have even been tested in an earthquake setup. If they haven't been tested, they should be tested NOW at levels simulating Fukushima and the recent east coast US earthquake.

Here is specifciations of fuel rods from http://www.nucleartourist.com/basics/hlwaste.htm

[These things need to be stored in water for 10-20 years???]

After 3 to 5 years in the reactor, one-third of the fuel assemblies are removed and stored in storage pools for typically about 10 to 20 years. During this period, the fuel loses much of its radioactivity and heat. After that period, the fuel can be stored in large sealed metal casks that can be cooled by air. The spent fuel assemblies are legally referred to as Spent Nuclear Fuel. If the fuel assemblies are reprocessed, the resulting waste is called High Level Waste.

The table below, Table 1.4, entitled IDB Reference Characteristics of LWR Nuclear Fuel Assemblies from the 1996 Integrated Database Report provides the following reference data about PWR and BWR fuel assemblies:

Characteristics BWRa PWRb
Overall assembly length, m 4.470 4.059
Cross section, cm 13.9 x 13.9 21.4 x 21.4
Fuel rod length, m 4.064 3.851
Active fuel height, m 3.759 3.658
Fuel rod outer diameter, cm 1.252 0.950
Fuel rod array 8 x 8 17 x 17
Fuel rods per assembly 63 264
Assembly total weight, kg 319.9 657.9 / 2kg each rod
Uranium/assembly, kg 183.3 461.4
UO2/assembly, kg 208.0 523.4
Zircaloy/assembly, kg 103.3c 108.4d
Hardware/assembly, kg 8.6e 26.1f
Total metal/assembly, kg 111.9 134.5
Nominal volume/assembly, m3 0.0864g 0.186g

a Ref. 5. U.S. Environmental Protection Agency, "Environmental Radiation Protection Standards for Management and Disposal of Spent Nuclear Fuel, High-Level and Transuranic Radioactive Wastes," Code of Federal Regulations, 40 CFR Part 191 (July 1, 1996).
b Ref. 6. U.S. Department of Energy, DOE Order 5820.2A, Radioactive Waste Management, Washington, D.C., Sept. 26, 1988.
c Includes Zircaloy fuel-rod spacers and fuel channel.
d Includes Zircaloy control-rod guide thimbles.
e Includes stainless steel tie-plates, Inconel springs, and plenum springs.
f Includes stainless steel nozzles and Inconel-718 grids.
g Based on overall outside dimension. Includes spacing between the stacked fuel rods of an assembly.

The operator of the crippled Fukushima Daiichi nuclear plant said it is studying whether the facility's reactors were damaged in the March 11 earthquake even before the massive tsunami that followed cut off power and sent the reactors into crisis.
Kyodo news agency quoted an unnamed source at the utility on Sunday as saying that the No. 1 reactor might have suffered structural damage in the earthquake that caused a release of radiation separate from the tsunami.
Apparently, the earthquake had caused a crack in the containment vessel.  http://slashdot.org/story/11/05/18/066250/fukushima-meltdown-might-have-come-with-earthquake-not-tsunami     If the quake...Show full text

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