Fukushima Update: Unit 2 temperature rises, Water leaks proliferate on site

Fukushima Update #77, February 6, 2012

by Nelle Maxey

Problems at Fukushima continue to mount.

Water leaks have proliferated around the site for the last couple of weeks. Water lines (which are lying on the ground all over the site) and exposed pumps for the water decontamination and reactor cooling systems have been freezing. See here for pictures and here for layout with 14 leaks in layout map on Jan 29. See here for layouts with latest leaks noted and pictures of leak "mitigation" (like a tarp over the pump truck and light bulbs to heat the equipment. Just like my neighbours do for their chickens.)

This freezing was inevitable, but TEPCO has been scrambling to insulate pipes and pumps and to stop the leaks. As further mitigation, TEPCO replaced the flex pipe lines which were supplying decontaminated, recirculated cooling water to Units 1, 2, and 3 with solid plastic pipe over the last couple of weeks. In the process, they have been changing the flow amounts into the reactors as I showed in a chart for Unit 2 in a previous post. Lower flow amounts were stabilized last week, but now Unit 2 is heating up, so water volumes have been increased.

TEMPERATURE AT BOTTOM OF UNIT 2 RPV

The temperature at the bottom of the reactor pressure vessel (RPV) in Unit 2 has been rising for the last week. The latest published reading today says it is at 71 degrees C.

The green line in today's plant parameter report graph shows this temperature rise at the bottom of the RPV. The partly obscured yellow line shows another RPV temperature measurement of the supporting skirt which you can see is also rising.

Source: http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/12020612_temp_data_2u-e.pdf

The second page of this report shows the temperature reading chart. The 2 readings of interest are the ones labelled RPV Bottom Part (Wall Above Bottom Head), RPV Supporting Skirt Upper Part. Both show rising temperature readings.

For comparison, here are the temp readings on Jan 31 at 11:00 am and Feb 6 at 11:00 am as recorded on this chart over a 6 day period. The chart only records two readings a day.

Bottom of RPV (green line)

Jan 31 shows 50.4C and Feb 6 shows 71.0C, a rise of 20.6 degrees.

RPV Supporting Skirt (yellow line)

Jan 31 shows 42.8C and Feb 6 shows 49.3C, a rise of 6.5 degrees.

A more complete temperature reading chart of all 3 sensors on the bottom of the RPV for the last 5 days is found in the media handout here. The first temperature sensor on this chart is the reading published on a twice daily basis in the parameter report above.

SKF carried this story yesterday on the temperature rise at Unit 2:

Fukushima I Nuke Plant Reactor 2 RPV Temperature: 71.7 Degrees Celsius as of 4PM on 2/5/2012

"The data is not entered yet in TEPCO's plant parameter page. The last measurement of the location – RPV Bottom Part – is at 11AM on February 5, at 68.6 degrees Celsius (as reported in the previous post).

So it went up 3.1 degrees Celsius in 5 hours, the sharpest rise yet since February 1.

From Jiji Tsushin (8:16PM 2/5/2012): [Japanese text removed, emphasis mine]

Reactor 2 RPV temperature at Fukushima I Nuke Plant risen above 70 degrees Celsius, TEPCO increases water injection

TEPCO announced on February 5 that one of the thermometers on the bottom of the Reactor Pressure Vessel of Reactor 2 at Fukushima I Nuclear Power Plant registered 71.7 degrees Celsius at 4PM. The location is one of several temperatures that [the company uses] to gauge the situation. The temperature there has risen sharply since it registered 52.0 degrees Celsius at 11PM on February 1. However, at two other locations at the same height, the temperatures remain steady around 45 degrees Celsius. TEPCO is considering the possibility of instrument failure, but in the meantime has increased the amount of water injected into the reactor by 1 tonnes, to 9.6 tonnes/hour and see if it makes difference.

The new safety regulation approved by the Nuclear and Industrial Safety Agency after the March 11, 2011 accident specifies that it is considered "deviation from operational limit" when the temperature taken at the standard locations reaches 80 degrees Celsius or the amount of injection water is increased by 1 tonnes per day, and the local municipalities have to be notified. TEPCO is planning the analysis of the gas inside the reactor in order to maintain the "cold shutdown state" where the temperature remains 100 degrees Celsius and lower and to prevent "recriticality" where the melted fuel starts nuclear chain reaction."

Source: http://ex-skf.blogspot.com/2012/02/fukushima-i-nuke-plant-reactor-2-rpv.html

Today the government media, NHK, is carrying the story as well. Here is the latest one with updated temperature data. There is a good short video at the link showing a temperature data graph with the 73.3 degree high temperature recording. Note the temperature is falling off at the time of this report, which is the only good news about this development. Although the increased amounts of cooling water being used to lower the temperature only adds to TEPCO's problems. Currently they are injecting and spraying 10.4 cubic meters per hour into the reactor core. This is the highest volume I have seen to date.

Temperature Rises at Fukushima No.2 Reactor

Attempts to cool the temperature in the No. 2 reactor of the disabled Fukushima Daiichi nuclear power plant have only partially succeeded despite the injection of more cooling water.

The temperature in the reactor has gradually risen from about 45 degrees Celsius registered on January 27th.

In the past 4 days, the temperature has climbed more than 20 degrees to above 70 degrees.

The plant operator, Tokyo Electric Power Company began pumping more water into the reactor at around 1:30 AM on Monday. But at 7 AM, the temperature stood at 73.3 degrees and at 5 PM, 69.2 degrees.

The utility firm says 2 other thermometers elsewhere in the reactor gave readings of about 44 degrees.

TEPCO says the rise in temperatures indicate that the flow of water in the reactor may have changed direction after plumbing work, and is no longer able to properly cool down the melted down nuclear fuel.

However, the utility says radioactive xenon has not been detected in gases around the reactor, and that nuclear criticality is not taking place.

The government and TEPCO announced in December that the 3 troubled reactors at the Fukushima plant had reached a state of cold shutdown with their temperatures below 100 degrees. But the situation inside the reactors remains unclear.

New regulations established after the state of cold shutdown was achieved require the utility to keep temperatures inside the reactors below 80 degrees.

TEPCO says it will increase the amount of water being injecting into the reactor to see if the temperature in the reactor drops.

The government's Nuclear and Industrial Safety Agency says there is a need for a comprehensive study to determine whether the reactor is actually in a state of cold shutdown. It says a brief reading of over 80 degrees on one of the thermometers does not necessarily mean there is trouble in the cooling system.

Meanwhile, the Chairman of the Nuclear Safety Commission, Haruki Madarame, says that a recurrence of nuclear criticality is unlikely.

But he criticized TEPCO and the nuclear safety agency for their handling of the matter. He says they are failing to properly explain the state of the reactors to the people.

Monday, February 06, 2012 20:48 +0900 (JST)

You can see puffs of steam being emitted from Unit 2 in this footage from the on-site video camera here.

DEVIATION FROM OPERATIONAL LIMIT

The deviation of the operational limit as described in the press above is in terms of temperature increase above 80 degrees C OR  an increase in amount of water injection by 1 tonne per day.

Under these conditions there is a deviation from operational limit due to water injection increases in Unit 2.

Here are the calculations: 1 liter of water weighs (under most conditions) one kilogram. 1 cubic meter equals 1000 liters. So 1 cubic meter of water weighs 1000 kilograms = 1 metric ton (tonne)

There are other on-going problems at the plant as well.

Unstable temperature at Unit 3 SFP

The spent fuel pool (SFP) at Unit 3 is increasing in temperature according to the latest press handout:

"Cooling of Spent Fuel Pools (As of 11:00 am on February 6)

Unit 3  28 degrees C

Unit 3 Note: Because the pool temperature began to increase, at 9:55 am on February 6, we initiated the secondary cooling tower."

Checking previous handouts I see this temperature rise has been going on since Jan 31st. The cumulative rise in temperature from Jan 30 to today, Feb 6, is 14.9 degrees.

I have noted the day over day temperature rise below.

The largest daily rises were actually between Jan 30 and Feb 1st. However, TEPCO is just noting this in today's handout as they are initiating the secondary cooling tower. Hopefully the temperature will continue to decrease. But this means yet more water to deal with.

Feb 6 28C, +1.5 degrees

Feb 5 26.5C, + 1.8 degrees

Feb 4 24.7C, + 1.8 degrees

Feb 3 22.9C, + 2 degrees

Feb 2 20.9C, +1.9 degrees

Feb 1 19C, +2.9 degrees

Jan 31 16.1C, +3 degrees

Prior to this date the temperatures of the Unit 3 SFP where between realtively stable in the 12 to 13 degrees C temperature range:

Jan 30 12.9C

Jan 29 11.9C

Jan 28 12.1C

Jan 27 12.3C

Jan 26 12.6C

One week earlier on Jan 19 13C

One week earlier on Jan 12 13C

 Storage tanks leaks

Most of the water in the leaks discovered so far was not highly radioactive as it was decontaminated for cooling.  However, the leaks from the storage tanks are a different matter. While the volume of water is very low, the high radioactivity is the problem, especially for the workers.

There are 100 tanks for storing the highly radioactive water from the reactor water desalination system and 3 of them have leaked recently. The tanks unfortunately are bolted together rather than welded (due to the need for haste in installing them on-site in the summer and fall). Picture of tanks and leakage here and here.

These leaks have both gamma and beta contamination at high levels (as stated in the press handout on Feb 3)

22mSv/h of γ-ray [gamma] and 2000mSv/h of β-ray [beta]

 Why I said this is a problem for the workers is shown in this information from wiki [emphasis mine]:

"Shielding from gamma rays requires large amounts of mass, in contrast to alpha particles which can be blocked by paper or skin, and beta particles which can be shielded by foil. They are better absorbed by materials with high atomic numbers and high density, although neither effect is important compared to the total mass per area in the path of the gamma ray. For this reason, a lead shield is only modestly better (20-30% better) as a gamma shield, than an equal mass of another shielding material such as aluminium, concrete, water or soil; lead's major advantage is not in lower weight, but rather its compactness due to higher density. Protective clothing, goggles and respirators can protect from internal contact with or ingestion of alpha or beta particles, but provide no protection from gamma radiation. Source: https://en.wikipedia.org/wiki/Gamma_ray

The gamma ray contamination is to be expected in water pouring over the melted nuclear cores and then concentrated in the desalination process. The leaks were fixed by tightening the bolts on the tanks. Workers walking among the tanks and tightening the bolts are exposed to this gamma radiation. Do workers have adequate protection? This is a very serious problem especially considering the number of tanks storing this highly radioactive nuclear waste water and the now needed constant inspection to stay on top of the leaks. Short-term decision making when dealing with the nuclear disaster is certainly not paying off.

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