Wednesday, April 13, 2011

#Fukushima I Nuke Plant: Reactor 4's Spent Fuel Pool Water Analysis

shows that the damage to the fuel rods in the Pool is only partial, if that, says TEPCO.

Asahi Shinbun (in Japanese; 12:58AM JST 4/14/2011) reports that TEPCO released the result of the test that it did on the water sample it had taken from the Spent Fuel Pool of the Reactor 4 on April 12. The result has not been posted on TEPCO's site, but from the Asahi article:

  • 400 cc (0.4 liter) of water in the Pool was taken, using the concrete pump's boom, on April 12;

  • Iodine-131: 220 becquerels/cc

  • Cesium-134: 88 becquerels/cc

  • Cesium-137: 93 becquerels/cc

  • In normal operation of the reactor, these numbers would be less than 1 becquerel.

  • The numbers are low compared to the contaminated water in the turbine building in which these numbers are in several million becquerels, leading TEPCO to conclude that "part of the fuel rods may be damaged, but the majority of the rods in the Pool are intact."

  • Fuel rods were all under water (2 meters under water).

So is everything dandy at the Reactor 4?

Mainichi Shinbun (in Japanese; 10:23AM JST 4/13/2011) may be saying "Not so fast." Why? Because the temperature of the Pool is high, and the radiation level above the Pool is high.

The Spent Fuel Pool's temperature was found to be 90-degrees Celsius, higher than the temperature (84-degrees Celsius) when the hydrogen explosion happened on March 15. In addition, at 6 meters above the Pool, the radiation level was 84 milli-sievert/hr; during normal operation of the reactor, the radiation level there would be 0.0001 milli-sievert.

The Mainichi article says all TEPCO can do is to replenish the water in the Pool as it evaporates from the heat, until the water (coolant) circulation system is somehow restored to remove the heat.

And when will that be? According to TEPCO's president in the presser on April 13 that I watched, "all in good time" and he really doesn't know much of anything.


netudiant said...

The number 4 spent fuel pool has been replenished via a cement mixer pump almost daily since the second half of March. So there is some ongoing dilution of the pool water.
Still, the pool has over 4000 tons capacity and recent injections have been small, about 200 tons/day. So the pool should be fairly quiescent, especially as the fuel had been out of the reactor for some time and should have been relatively cool.
However, we now have clear evidence of fuel damage, which may translate into a pile of loose fuel pellets at the bottom of the pool, warming each other rather than getting cooled by circulating water. This is the simplest scenario and is consistent with the evidence.
The good thing is this also suggests the pool is still structurally intact, an unexpected positive development.

Anonymous said...

My question is why only test for the most volatile isotopes for all we know they may have mostly boiled off in the first few weeks. Remember a large portion of the radiation has been blown out to sea so who knows how much has actually been released. The NRC seemed to be very worried about SFP#4 in their initial assessment. The water in the turbine basement hasn't been constantly boiling off the volatile fraction of contamination like SFP#4 so I'm not surprised at the high concentrations found there. Also from what I understand they should have filled the SFP many times over in the last month and yet it only has 6.5 feet covering the fuel? (it should be about 30' under) I find It hard to believe the coolant loss is through evaporation alone. There may be a pool leak that has allowed the coolant's radiation level to be diluted over the course of time.

Another thing to remember is these radiation readings only reflect the gammma ray component the radiation detector was 6 meters away, too far to detect alpha and beta activity. Have they released the radiation levels for the other SFP's for comparison?

Anonymous said...

Here's more detailed information on how the DOE dealt with the Rocky Flats clean-up. I really think this is what the Japanese have to worry about in the future remediation.

In 2000 it was revealed that Kaiser-Hill, the principal cleanup contractor, had made a deal in 1995 with Congress imposing limits on the cleanup. The secret agreement set deadlines on both time and money, with a Dec. 2006 deadline and a $7 billion spending cap on the cleanup. The deal was made before the contamination was even evaluated.

A breakdown of the cleanup budget reveals that most of the $7 billion goes to site security, relocation of weapons-grade material, removal of bomb-production waste and demolition of buildings. Soil and water cleanup was allocated only $473 million, about 7 percent of the total. Since Rocky Flats is to be designated a wildlife refuge, levels of allowed radiation were determined based on the “maximally exposed individual” for the site: namely, a wildlife refuge worker. The risk factor for a refuge worker is calculated based on 2,000hours per year spent on site. While this may be a reasonable short-term application, the land will be radioactive for billions of years. It is possible that someday people will live there,grow food, and use water contaminated with radioisotopes.

In order to perform a cleanup with a limited budget,the DOE and Kaiser-Hill created separate remediation standards for surface and subsurface soil. Fifty picocuries of plutonium is allowed to remain in the top 3 feet of soil.At a depth of 3 to 6 feet, 1,000 picocuries per gram is permitted, though as much as 6,000 picocuries may be left in small areas. Below 6 feet, there is no limit on how much plutonium is allowed to remain, and controls would be put in place to monitor and contain the contaminants. A National Academy of Sciences study calls such controls“inherently failure prone.” Plutonium-239 has a half-life of 24,400 years and is known to cause genetic mutations,cancer and damage to the immune system.

Anonymous said...

The latest unloading to this spent fuel pool was from a core stopped on 30th November 2010, but the Iodine-to-Caesium ratio proves more recent fission.

Maybe the operators filled #4 pool with cooling water exiting an other reactor, as I had suggested to do to reduce the volume of waste water, in which case radioactivity and composition tell nothing about the fuel in #4 pool.


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