The Robot Probe Cannot Confirm Where is the Melted Fuel of Unit 1

24 03 2017

 

Tokyo Electric Power Company announced on February 23 that it had completed a robot probe survey lasting five days in the reactor containment vessel of Fukushima Daiichi nuclear power plant Unit 1.

Its goal was to confirm the whereabout of the melted nuclear fuel, but it was blocked by piping and could not put the camera in athe place where nuclear fuel could be seen.

Information necessary for taking out the nuclear fuel to decommission the reactor remains inadequate, and some voices began to question the robot conducted investigation method.

During the 5-day survey, there was also a point where the measuring instrument with an camera and a radiation dosimeter integrated together was hung up in a range from 0 to 3 meters from the bottom of the containment vessel, pipes and debris blocking its path in many points. The radiation dose in the water is from 3.0 to 11 Sv. Per hour. It was not possible to directly check the melted nuclear fuel.

TEPCO and the country are facing the decommissioning of a furnace …

http://www.asahi.com/articles/photo/AS20170323005483.html

Tepco robot failed to capture images of melted fuel in reactor 1

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A photo taken by a robot on Wednesday shows an underwater image of water pool on the bottom of the containment vessel of the reactor 1 at the Fukushima No. 1 plant

Tokyo Electric said Thursday that it failed to get any photos of potential fuel debris during a five-day probe of the primary containment vessel at reactor 1 of the Fukushima No. 1 power plant.

Tokyo Electric Power Company Holdings Inc., however, stressed that the investigation was worthwhile because its robot was able to take underwater images in the pool of water at its bottom and gauge its radiation level, which will help it estimate where the melted fuel lies.

The monstrous tsunami of March 11, 2011, tipped reactors 1, 2 and 3 into core meltdowns. The molten fuel rods then penetrated their pressure vessels before apparently dropping to the bottom of the giant containment vessels.

There is about a 2.5-meter deep water pool at the bottom of the primary containment vessel of reactor 1, and Tepco believes most of its melted fuel rods fell into it. Thus the main mission of the robot investigation this time was to capture underwater images.

The robot traversed gratings set up several meters above the vessel’s bottom and lowered a wire with a camera and dosimeter on its tip at 10 locations in the water.

Yet none of the images disclosed by Tepco showed anything resembling fuel debris, while parts of machinery, such as a valve, were captured.

When the robot dangled the camera on spots where Tepco thought there was a higher probability of locating the fuel, it instead found a 90-cm pile of sediment.

Tepco spokesman Yuichi Okamura said the sediment is probably not fuel debris, given the relatively low radiation readings, which ranged from 5.9 to 9.4 sieverts per hour.

Although the readings indicate extreme danger to people, Okamura said the readings would have been much higher had they been melted fuel rods. He said Tepco had no idea what the sediment is but added that there was a possibility it was covering the fuel.

According to Okamura, radiation readings get weaker by a hundredth if blocked by a meter of water. Since the robot detected readings from 5.9 to 9.4 sieverts per hour about 90 cm above the pool’s bottom, there might be something down there emitting strong radiation.

Tepco plans another investigation this month to pick up samples of the sediment.

While no fuel debris was recognized, Okamura said Tepco would review the data and analyze it further. By comparing radiation readings from various locations, the utility might be able to roughly pinpoint where the melted rods lay, he said.

He added that it was an achievement that the robot lasted for five days in the deadly radiation and that Tepco was able to retrieve it.

http://www.japantimes.co.jp/news/2017/03/24/national/tepco-robot-failed-capture-images-melted-fuel-reactor-1/#.WNQ_hBh7Sis

Survey under way of Fukushima Daiichi 1 vessel

Fukushima Daiichi 1 PCV robot survey - 20.03.2017

The PMORPH robot within unit 1’s PCV

A robot has entered into the primary containment vessel of the damaged unit 1 of the Fukushima Daiichi plant and provided Tokyo Electric Power Company (Tepco) with radiation and temperature measurements within it. The company hopes the data, together with video footage, will enable it to locate the molten fuel in the unit.

On 18 March, Tepco inserted the PMORPH robot into unit 1 in the first of a series of four planned robot explorations of the basement area of its primary containment vessel (PCV) around the pedestal, on which the reactor pressure vessel sits. The investigation is part of preparatory work for the eventual removal of fuel debris.

The PMORPH robot was developed by Hitachi-GE Nuclear Energy and the International Research Institute for Nuclear Decommissioning (IRID). It can assume a long, straight shape for passing through narrow spaces, such as pipes. Alternatively, it can rotate its crawlers by 90 degrees in relation to its central body to assume a U-shape, with the crawlers providing better stability when travelling over flat surfaces.

The robot features a combined total of five cameras and also includes a winch used for lowering and raising a sensor unit that incorporates an underwater radiation-resistant camera, LED and a dosimeter.

In the latest investigation, the robot travelled along a section of the first floor grating, on which it measured a radiation dose of 7.8 Sieverts per hour. The robot also lowered its sensor unit into the water that has collected at the bottom of the primary containment vessel. At a height of about 1 metre above the PCV basement floor, Tepco recorded a dose level of 1.5 Sv/h. The robot also recorded temperature measurements within the PCV of 14-23°C.

Last month a “scorpion-shaped” robot developed by Toshiba and IRID was sent into the primary containment vessel of unit 2 of the Fukushima Daiichi plant. “In that case,” Tepco said, “although the robot was obstructed from reaching all the way into the pedestal area, important information was obtained about the conditions at the base of the reactor.” Readings indicate the temperature within the area of the containment vessel where the robot stopped was around 16.5°C and the dose rate was about 210 Sv/h, significantly higher than those measured in unit 1.

Tepco said the latest reading and images obtained from unit 1 will now be examined in greater detail. “The conditions of the PCV basement floor will be examined later,” it noted.

The insertion of the PMORPH robot follows an investigation of the unit’s containment vessel by another shape-changing robot in April 2015. That was the first time a robot had entered the containment vessel of any of the damaged units. However, after taking several images and measurements, that robot got stuck in the grating and stopped working.

Tepco is preparing to conduct similar investigations using a robot in unit 3 at the plant.

http://www.world-nuclear-news.org/RS-Survey-under-way-of-unit-1-vessel-2003174.html

Progress of Unit 1 PCV Internal Investigations – March 18. 2017

Preliminary report of March 12 investigation 1/2

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Preliminary report of March 12 investigation 2/2

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Impact to the surrounding environment :

The radiation level of 7.8 Sv/h was measured by a dosimeter during the March 18 investigation, but the radiation impact has been reduced by the shielding of PCV concrete walls and steel. No radiation impact has been observed in the surrounding environment.

The investigation is conduced while creating a boundary around the guiding pipe to prevent the air inside the PCV from leaking to the outside.

No significant changes have been observed at the monitoring posts and dust monitors after the investigation, compared to the before.

Real-time data of the monitoring posts and dust monitors along the site boundary are available on the website.

Reference URL:

http://www.tepco.co.jp/en/nu/fukushima-np/f1/index-e.html

http://www.tepco.co.jp/en/nu/fukushima-np/f1/dustmonitor/index-e.html

Monitoring of the plant parameters:

Although the radiation level of 7.8 Sv/h was measured by a dosimeter during the March 18 investigation,it does not mean that a new phenominonhas occurred but rather the area that has not been investigated since the March 2011 accident was investigated for the first time.

Plant parameters are monitored all the time during the investigation, and no significant changes have been observed in the PCV internal temperatures after the investigation, compared to the before.

The condition of cold shutdown has not been changed. Temperature data inside the PCV are available on the website.

Reference URL: http://www.tepco.co.jp/en/nu/fukushima-np/f1/pla/index-e.html

Robot probe of No.1 reactor to continue until Wed.

The operator of the crippled Fukushima Daiichi nuclear power plant says a robotic survey of fuel debris at the No. 1 reactor is being hampered by plumbing and other structures. The utility says it will extend the probe by one day, until Wednesday.

So far engineers have detected strong radiation of about 11 sieverts per hour in the water inside the containment vessel.

Tokyo Electric Power Company on Saturday started sending a remote-controlled robot into the reactor’s containment vessel to look at the state of debris — a mixture of melted fuel and reactor parts. The robot is equipped with a camera and a dosimeter.

The melted fuel is believed to still be at the bottom of the vessel, where about 2 meters of contaminated water accumulates.

TEPCO released the results of the ongoing survey on Tuesday. It said the robot moved to a location believed to be just above the debris and lowered the camera and dosimeter into the accumulated water.

The dosimeter detected radiation of 6 sieverts per hour one meter from the bottom. But piping prevented the device from reaching deeper, and it has yet to confirm the debris.

TEPCO also said the robot recorded about 11 sieverts of radiation per hour about 30 centimeters from the vessel’s bottom at another location. Officials believe the radiation may be coming from contaminated fragments that fell to the bottom, as they expected no debris there.

Through the extended probe, TEPCO hopes to collect more data on conditions inside the vessel.

https://www3.nhk.or.jp/nhkworld/en/news/20170321_33/

 

Clearer water inside reactor 1 should help find melted fuel at Fukushima plant

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A robot on March 18 took this image of a valve and a pipe in cooling water at the bottom of the containment vessel of the No. 1 reactor at the Fukushima No. 1 nuclear power plant.

Cooling water in the No. 1 reactor of the Fukushima No. 1 nuclear plant has improved in transparency, which should make it easier to pinpoint the location of melted nuclear fuel, the plant’s operator said.

The improved transparency, compared with the level two years ago, was confirmed on March 18, when a research robot took an image that clearly showed a valve and a pipe in the water at the bottom of the reactor’s containment vessel, Tokyo Electric Power Co. said March 19.

Devices on the robot measured radiation levels of 7.8 sieverts per hour on a metal stage for workers and 1.5 sieverts per hour in the water.

The research robot on March 20 and 21 will study areas where the melted nuclear fuel could exist.

http://www.asahi.com/ajw/articles/AJ201703200028.html

Robot Probe Forays Inside Fukushima Daiichi Reactor 1

robot probe reactor 1 march 19 2017 2.jpg

Grating inside the containment vessel of the No. 1 reactor at the crippled Fukushima No. 1 nuclear plant is seen in this handout image captured by a robot Saturday.

Robot makes foray into reactor 1

Tokyo Electric on Sunday confirmed lethally high radiation levels inside the primary containment vessel of reactor 1 at the heavily damaged Fukushima No. 1 nuclear plant but found they were not nearly as high as those recently logged in reactor 2.

Using a camera-equipped robot on Saturday, Tepco logged 7.8 sieverts per hour on some grating inside the vessel and 1.5 sieverts per hour in water pooled at its bottom.

Those figures are far lower than the 210 sieverts per hour measured at one spot in the PVC of the No. 2 reactor last month, but they are still extremely high.

The four-day probe launched by Tepco on Saturday is aimed at locating the melted fuel rods inside the No. 1 reactor building.

The primary mission of the robot is to investigate the bottom of the containment vessel to see if it can capture images of the melted fuel. Debris is believed to have penetrated the vessel and fallen into the surrounding containment vessel as a result of the heavy damage inflicted by the March 2011 tsunami that devastated eastern Tohoku.

The pressure vessel is the main component of the reactor and contains the fuel rod assemblies. Finding the exact location and condition of the melted fuel is considered critically important to dismantling the reactors.

However, the high radiation inside poses a daunting challenge for those involved in the decommissioning work.

In photos handed out to the media, a valve is shown covered in a yellowish substance that the utility said could be rust.

Another photo shows the grating that the robot, which is attached to a cable, was traveling on.

The utility had sent the robot into the PVC of reactor 1 two years ago but it could only capture images of the grating at the time.

Tepco said the robot can withstand up to 1,000 sieverts before malfunctioning. It traveled about 5 meters on Saturday and will eventually make its way to the other side of the concrete structure through a space that runs beneath the pressure vessel, which houses the core.

If the robot reaches its goal, computer simulations by Tepco show that there is a chance that melted fuel rods could be found there, Tepco said.

In January and February, Tepco investigated the containment vessel of the No. 2 reactor.

It is now preparing to conduct a similar robot probe of the reactor 3.

http://www.japantimes.co.jp/news/2017/03/19/national/robot-makes-foray-reactor-1/#.WND_z6KmnIV

robot probe reactor 1 march 19 2017