TEPCO fails to pinpoint melted fuel at Fukushima No. 1 nuclear plant

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A photo capturing contaminated water at the Fukushima No. 1 nuclear plant, which was taken by a robot on March 21, 2017.

Tokyo Electric Power Co. (TEPCO) failed to locate melted nuclear fuel inside the No. 1 reactor at the disaster-stricken Fukushima No. 1 Nuclear Power Plant in a robot probe, though it found higher levels of radiation toward the bottom of the reactor container vessel, the utility said on March 27.

TEPCO made the announcement after analyzing data obtained from a probe conducted from March 18 through 22, in which a remotely controlled robot was sent into the No. 1 reactor’s container vessel for research.

The power company is set to finalize a decision to take out melted fuel from the No. 1 through No. 3 reactors as early as this coming summer, accelerating work to decommission the facilities. Like a similar robot probe inside the No. 2 reactor last month, however, the latest survey on the No. 1 reactor also failed to obtain data necessary to extract melted fuel, such as where the fuel is located. Therefore, the utility is compelled to consider fetching melted fuel in the absence of sufficient data.

TEPCO injected a robot that can move on a running belt into the container vessel of the No. 1 reactor. The robot hung a wire holding a camera and a dosimeter at its tip from a metal grating for workers and measured the condition of the contaminated water below. From March 18 to 22, the robot examined an area near a slot from which the device is injected into the vessel and measured 1.5 to 11 sieverts per hour of radiation. Between March 20 and 22, the robot explored an area around the openings for workers at the bottom of the container vessel, which is close where melted fuel is believed to be situated, and detected measurements of 3 to 9.4 sieverts of radiation.

Sand-like sediment was found to be spreading across the bottom of the container vessel. Because of accumulated sediment near the openings, the robot could gauge radiation doses only up to a height of 90 centimeters from the bottom of the vessel. Compared to the radiation levels at the same height of an area where melted fuel is believed not to exist, the area near the openings showed higher radiation readings.

It is believed that most of the melted fuel at the No. 1 reactor has spread across the contaminated water accumulating at the bottom of its container vessel. TEPCO believes that melted fuel is likely leaking from those openings.

Naohiro Masuda, head of TEPCO’s Fukushima Daiichi Decontamination & Decommissioning Engineering Co., told a press conference on March 7, “The results of this probe will be precious resources for us to make a decision on our plan.”

http://mainichi.jp/english/articles/20170328/p2a/00m/0na/014000c

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Nuke watchdog critical as robot failures mount at Fukushima plant

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Some Nuclear Regulation Authority members are skeptical of continuing to send robots into reactors in the crippled Fukushima No. 1 nuclear plant to collect vital data on the locations of melted nuclear fuel and radiation levels.

These regulators are increasingly calling for a new survey methodology after recent investigations utilizing robots controlled remotely generated few findings and were quickly terminated.

We should come up with a method that will allow us to investigate in a short period of time and in a more sensible way,” said a senior member of the NRA, the government watchdog.

The suggestion followed the failure of the latest probe from March 18 to March 22 in which a robot was sent in the No. 1 reactor to ascertain the location of fuel debris, information crucial to preparing for the decommissioning.

Tokyo Electric Power Co., the operator of the plant, said on March 23 the robot was unable to deliver a camera to planned spots from where images of nuclear fuel debris could be taken.

The utility cited the piping and deposits of what looked like sand accumulating on the piping as impediments that hindered the robot surveyor’s path.

The survey was designed for the robot to reach numerous locations inside the No. 1 reactor to determine the location of nuclear fuel debris and their radiation levels.

The lower part of the reactor’s containment vessel is submerged in water where deposits of fuel debris are believed to reside below the surface after melting through in the 2011 nuclear disaster, triggered by the Great East Japan Earthquake and tsunami.

At one location, the robot succeeded in placing a camera, which is combined with a dosimeter, to a depth 0.3 meter from the containment vessel floor.

The probe measured underwater radiation levels from 3.0 to 11 sieverts per hour during the five-day survey. But it was unable to take images of the debris in the water.

TEPCO and the government hope to start removing molten nuclear fuel from 2021. But they have yet to collect information on the location, amount and condition of the melted fuel.

In a survey of the No. 2 reactor in February, a robot became stuck in deposits and other debris after traveling only 2 meters inside.

Surveyor robots for the No. 1 through No. 3 reactors have been developed by the International Research Institute for Nuclear Decommissioning since 2014, a project costing 7 billion yen ($62 million) by the end of March 2018.

It takes time to develop such multifunctional robots, but the surveys centering around the robots so far have failed to produce meaningful results.

No survey has been conducted at the No. 3 reactor.

http://www.asahi.com/ajw/articles/AJ201703240064.html

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

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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