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No. 1 reactor endoscope mission may cast doubt on cold shutdown status

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In January of this year, Tokyo Electric Power Co (TEPCO) conducted an investigation in the inside of the primary containment vessel (PCV), of the No. 2 reactor at the Fukushima Daiichi nuclear power plant. They had been assuming that the water in the PCV was around OP9500, but were unable to locate the water level inside of the containment vessel and ultimately guessed that the top of the water must be just out of their ability to investigate.

In August, workers began preparatory work at the No. 1 reactor to investigate the inside of the primary containment vessel. This week, workers at Fukushima Daiichi began the four-day investigation at the No. 1 reactor with an endoscope camera.

During investigation, photos will be taken by a camera, data collected on radiation dose, ambient temperature, water temperature and water level will be collected and sampling of accumulated water will be conducted. New PCV ambient temperature thermometers and water gauges will also be installed to improve monitoring.

The goal of the work is to determine the current conditions in the water, and the amount of contaminated water in the vessel, but after the first day of investigation, workers were unable to find the water level in the reactor, and some damage was found.

For reactors 1 to 3, it is assumed that nuclear fuel and core internals have melted and resolidified (fuel debris) and have escaped in varying amounts from the reactor pressure vessel (RPV) and are thought to currently be located in the primary containment vessel. The nuclear fuel can now only be removed while under a pool of water to ensure the temperature and radiation levels are controlled.

As hydrogen concentration and Kr-85 radioactivity density have been changing since April, it is assumed that the hydrogen generated in the early stage of the accident and Kr-85 which remain in the upper part of the suppression chamber are intermittently released into the dry well.

First, the inability to locate the water obviously means that the water being pumped into the containment is escaping, either through a large hole in containment, or a series of smaller holes.

Secondly, if there is no accumulated water, than there is far less shielding and decay heat removal available than TEPCO has accounted for, which would also infer the melted fuel in the containment vessel may be exposed.

The radiation levels inside of the reactor are one of the key indicators used to determine the location and formation of melted nuclear fuel. If the nuclear fuel was exposed, the radiation fields produced by the melted nuclear fuel would’ve produced radiation fields so strong they would be detectable outside of the reactor building, and no radiation levels that high have been confirmed by the utility.

These new findings by TEPCO may suggest that the water is not adequately cooling any melted fuel which may be located in the containment vessel, or may also infer that the melted fuel has relocated to another location and the containment may be working as a shield to block the radiation emitted.

When looking at raw data provided by TEPCO, one can see that there has been no major flux in temps or radiation levels in a while, which may mean that this condition has existed for some time. The key question is how long has the majority of the coolant water pumped into the reactor been escaping and providing little if any shielding to the melted nuclear fuel.

In short, we have been playing the "where is the corium" game since the first week of the disaster, and the recent finding (no water found in containment vessel) is increasing evidence, when verified by the temperature and radiation levels as given by TEPCO, that the fuel may not still be located where they thought it was.

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11 Comments
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cast doubt on cold shutdown status

Told you so?

-1 ( +0 / -1 )

Cold shutdown on a non exploded & leaking reactor is safe.... the current situtation is far from safe

1 ( +1 / -0 )

The video shows concrete and metal debris with the inside of the pressure containment vessel badly damaged probably from the earthquake or meltdowns or both. As with reactors 2&3, there are cracks in the containment vessel and the suppression chamber. Highly irradiated cooling water is leaking into the basement at about 400 tons per day. On site storage of this water is a major problem.

The radiation level is too high to send workers in to try and repair the cracks.

In reactor No1 more than 75% of the fuel melted and burnt through the reactor vessel and onto the concrete base of the containment vessel. It has burnt into the concrete by more than 70 cm.

TEPCO have decided that the level of water inside the containment vessel is greater than they had thought before the probe was inserted.

"Cold shutdowns isn't something which can happen in a meltdown."

4 ( +5 / -1 )

To gently dismantle the reactors, especially nr3 can serve this new machine. Buildings are more reactors damaged by hydrogen explosions, so the design can be cracked, and even a small shock can cause the water to fuel pools can escape ....

http://www.new4stroke.com/fukushima3.jpg

-1 ( +0 / -1 )

Andrzej Feliks, I cannot understand what you are saying. Your machine with a diamond rope can... do what?

And are you saying that water can escape from the spent fuel pools with even a small earthquake? So, therefore we need to dismantle these reactors and buildings ASAP?

0 ( +0 / -0 )

@zichi - thank you for always providing helpful info and insights on issues of radiation and the Daiichi plant.

1 ( +1 / -0 )

And yet the Japan Times, hardly a pro-nuclear source reports Reactor Number one's level is higher than expected:http://www.japantimes.co.jp/text/nn20121012a4.html

-3 ( +0 / -3 )

And yet the Japan Times, hardly a pro-nuclear source reports Reactor Number one's level is higher than expected:http://www.japantimes.co.jp/text/nn20121012a4.html

Newspapers - whether in print or online - can only report what they're told. They aren't an originator of information and they can't certify that what they're told is 100% accurate.

1 ( +1 / -0 )

Well the key data for the author's ruminations is from January, for Reactor 2, the rest is assumption. Whilst the Japan Times cannot say what it is printing is 100% accurate, it at least has attribution: from TEPCO via Kyodo News.

As for the reactor vessel being breached, the October 12th update on this page indicates it either did not happen - or the corium sealed the breach: http://www.hiroshimasyndrome.com/fukushima-accident-updates.html

-1 ( +0 / -1 )

Star-viking,

the Hiroshima Syndrome blog is a very extreme pro nuclear one and even though I do read it from time to time, he also bends the truth when it does not quite fit in with his opinions.

TEPCO have stated, that it believes about 75% of the nuclear fuel in the No1 reactor had a meltdown, first dropping to the bottom of the reactor pressure vessel and burning through and dropping to the base of the containment vessel. It also believes some of it burnt into the concrete base by about 60cm. From the probe into the containment vessel, it also believes the depth of water is 1.5m to 2m deep.

2 ( +3 / -1 )

This is new data Zichi. The Asahi Shimbun also reports on it http://ajw.asahi.com/article/0311disaster/fukushima/AJ201210110078

Some quotes:

The surface of water could be seen 2.8 meters above the bottom of the containment vessel. TEPCO believes that the melted fuel, lying under the water, is being cooled.

Fumiya Tanabe, who was a senior researcher at the now-defunct Japan Atomic Energy Research Institute, said he was surprised that water levels were so high. He added that the water could have been maintained at these levels because the lower parts of the containment vessel escaped severe damage.

Questions also remained about the location of the melted fuel.

The maximum radiation level of 11.1 sieverts per hour was detected at a height of 8.6 meters from the bottom of the containment vessel.

Radiation levels generally fell toward the lower parts of the containment vessel. The reading was 4.7 sieverts per hour near the water surface and 0.5 sievert in the contaminated water.

The company believed that almost all melted fuel fell through the bottom of the pressure vessel and accumulated in the outer containment vessel. Under that scenario, radiation levels would rise toward the bottom of the containment vessel.

0 ( +0 / -0 )

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