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On-line z Japonska: Francouzi zveřejnili plán kontroly svých 150 jaderných zařízení (zdroj: THE NUCLEAR COMMUNICATIONS NETWORK)

Publikováno: 11.5.2011
Rubrika: Jaderné, Jaderné palivo

Plné znění informací japonské vlády uvádíme v tomto článku v anglických originálech (zdroj: THE NUCLEAR COMMUNICATIONS NETWORK). Pod tímto článkem jsou kumulovány všechy související informace tak, jak je postupně k této tématice získáváme a doplňujeme.

 

Schéma varného reaktoru BWR

Princip reaktoru typu BWR

Aktuální zpráva, 10. 05. 2011, 17:1: ASN Announces Details Of French Safety Checks

French nuclear regulatory authority ASN (l’Autorité de Sűreté Nucléaire) has announced specifications and schedules for safety checks at some 150 nuclear installations in France. The checks called complementary safety evaluations are intended to test the robustness of nuclear installations against extreme events, in light of the accident on 11 March 2011 at Japan's Fukushima-Daiichi nuclear power plant. In a statement on 9 May 2011, ASN said the checks will be carried out at Electricité de France’s 58 nuclear units and its 59th unit under construction at Flamanville. Other facilities on the list released by ASN include the Osiris research reactor at Saclay; the Jules Horowitz reactor at Cadarache; and large nuclear fuel cycle centres including Areva's La Hague reprocessing complex, its Melox mixed-oxide fuel fabrication plant, and two enrichment plants at Tricastin. The list also includes the International Thermonuclear Experimental Reactor (ITER) at Cadarache in southern France. Operators of nuclear power stations have been asked to submit their proposed methodologies for the checks to ASN by 1 June 2011 and the results of the safety checks by 15 September 2011. For operators of other installations the deadlines are 15 September 2011 and 15 January 2012. The safety checks include analysis of an installations behaviour in the event of seismic events with an impact beyond design limits and of a complete flooding of a site. Operators must also analyse what ASN calls potential cliff effects the impact of a disproportionate accumulation of events on an installation – and combined seismic and flooding events. Operators have been asked to propose practical measures for improving the handling of such events. ASN said it will take two months to review the results and submit its report to the French government.
 

 

 

 

Aktuální zpráva, 05. 05. 2011, 19:40: Workers Enter Unit 1 Reactor Building For First Time Since Explosion

A team of workers has entered the reactor building of unit 1 at the Fukushima-Daiichi nuclear power plant for the first time since a hydrogen explosion the day after the facility was struck by an earthquake and tsunami on 11 March 2011. Plant operator Tokyo Electric Power Company (Tepco) said that, pending air quality testing to be done over the weekend, it will send workers into the containment building starting next week to install a heat exchanger and hook it up to pipes connected to the reactor's containment vessel. Tepco said the system should circulate about 100 tonnes of water an hour in the containment vessel: 10 times the amount that is currently being injected using a temporary system. The company hopes to launch work to circulate water and remove heat from the reactor by 16 May 2011. The Japan Atomic Industrial Forum (JAIF) said two workers entered the building this morning to install an air purifier. Work to install air ducts will take place over the next week, JAIF said. Workers, breathing from air tanks, will be divided into groups of three and each group will work for about 10 minutes to install eight ducts. Their work precedes the planned installation of the system to circulate cooling water within the reactor, although JAIF said because of damage that work could take many weeks. Tepco said it was planning to begin operating the air purifier later today. Tepco said it will take about three days to vent the contaminated air, filter it, and return purified air to the building. It hopes to lower the radiation level so workers can remain inside for longer periods. Efforts are continuing to cool the rector cores at units 1, 2 and 3, the units which were in service when the plant was hit by the earthquake and tsunami. Units 4, 5 and 6 at the plant were already shut down for maintenance and there was no damage to fuel, core or containment. 

Aktuální zpráva, 04. 05. 2011, 15:54: Tepco Releases Provisional Figures On Workers Total Radiation Exposure

Two workers at the Fukushima-Daiichi nuclear power plant in Japan have received total external and internal combined radiation doses close to the maximum recommended limit for emergency situations of 250 millisieverts (mSv), plant operator Tokyo Electric Power Company (Tepco) has said. On 27 April 2011, Tepco also confirmed that the effective exposure dose of two female employees involved in restoration work at the plant was in excess of statutory dose limits. Tepco said evaluating the total whole-body exposure dose of one female employee in her fifties has shown an effective exposure dose of 17.55 mSv. Evaluation of the other female employee, in her forties, has shown a total whole-body dose of 7.49 mSv. Medical diagnosis confirmed there was no impact on their health. However, the legal dose limit for female employees is 5 mSv per 3 months even in an emergency situation. Tepco also published the results of internal radiation exposure doses of
21 workers whose external doses had been higher than 100 mSv during the period from 11 March to 31 March. The group includes two workers who were exposed to more than 170 mSv on 24 March when laying cables in the basement of unit 2. Their whole-body dose was lower than the emergency limit, but the dose on their legs and feet went far beyond the legal limit for extremities. Tepco said that out of the 21 workers, two received total doses of 200-250 mSv, eight received total doses of 150-200 mSv and 11 of 100-150 mSv. Total dose rates were calculated using both external and internal dose rate measurements. The maximum external whole-body radiation exposure dose received so far by a worker at the plant is 201.80 mSv. The maximum internal exposure dose is
39 mSv and the maximum combined rate 240.80. Tepco said it had carried out the measurements as part of its efforts to ensure no worker at the plant is subject to an exposure dose exceeding the statutory limits. Two workers at the Fukushima-Daiichi nuclear power plant in Japan have received total external and internal combined radiation doses close to the maximum recommended limit for emergency situations of 250 millisieverts (mSv), plant operator Tokyo Electric Power Company (Tepco) has said. On 27 April 2011, Tepco also confirmed that the effective exposure dose of two female employees involved in restoration work at the plant was in excess of statutory dose limits. Tepco said evaluating the total whole-body exposure dose of one female employee in her fifties has shown an effective exposure dose of 17.55 mSv. Evaluation of the other female employee, in her forties, has shown a total whole-body dose of 7.49 mSv. Medical diagnosis confirmed there was no impact on their health. However, the legal dose limit for female employees is 5 mSv per 3 months even in an emergency situation. Tepco also published the results of internal radiation exposure doses of 21 workers whose external doses had been higher than 100 mSv during the period from 11 March to 31 March. The group includes two workers who were exposed to more than 170 mSv on 24 March when laying cables in the basement of unit 2. Their whole-body dose was lower than the emergency limit, but the dose on their legs and feet went far beyond the legal limit for extremities. Tepco said that out of the 21 workers, two received total doses of 200-250 mSv, eight received total doses of 150-200 mSv and 11 of 100-150 mSv. Total dose rates were calculated using both external and internal dose rate measurements. The maximum external whole-body radiation exposure dose received so far by a worker at the plant is 201.80 mSv. The maximum internal exposure dose is 39 mSv and the maximum combined rate 240.80. Tepco said it had carried out the measurements as part of its efforts to ensure no worker at the plant is subject to an exposure dose exceeding the statutory limits.

Aktuální zpráva, 03. 05. 2011, 17:59: Tepco: 70,000 Tonnes Of Contaminated Water Needs To Be Removed

There is almost 70,000 tonnes of stagnant water with high-level radioactivity that still needs to be removed from the basement of the turbine buildings of units 1, 2 and 3 at the Fukushima-Daiichi nuclear power plant in Japan, according to statistics from plant operator Tokyo Electric Power Company (Tepco). The transfer of highly radioactive water from the unit 2 turbine building to the radioactive waste treatment facilities was resumed on 30 April 2011, according to the International Atomic Energy Agency (IAEA). With the cooling systems at units 1, 2 and 3 still out of order, Tepco has been pumping fresh water into the reactor pressure vessels and spraying the spent fuel pools at units 1, 2, 3 and 4 in an effort to stop nuclear fuel overheating. While this has so far prevented a dangerous over-heating of the reactor cores and spent fuel pools, it has also created a large quantity of contaminated water that Tepco needs to remove before other work can progress. Efforts are continuing to cool the rector cores at units 1, 2 and 3, the units which were in service when the plant was hit by an earthquake and tsunami on 11 March 2011. Units 4, 5 and 6 at the plant were already shut down for maintenance and there was no damage to fuel, core or containment. At unit 1, fresh water is being continuously injected into the reactor pressure vessel through the feedwater line at a flow rate of 6 cubic metres per hour (m3/h) using a temporary electric pump with off-site power. At units 2 and 3, fresh water is being continuously injected into the reactor pressure vessel through the fire extinguisher line at a rate of 7 m3/h using temporary electric pumps with off-site power. On 29 April 2011, Tepco checked the status inside the unit 1 reactor building using a remotely controlled robot and confirmed that there was no significant leakage of water from the primary containment vessel (PCV). Nitrogen gas is still being injected into the unit 1 PCV to reduce the possibility of hydrogen combustion inside the containment vessel. According to the International Atomic Energy Agency, the indicated pressure in the RPV is still increasing. Efforts are also continuing to cool the spent fuel pools at units 1, 2, 3 and 4 by spraying them with fresh water. At units 5 and 6 the spent fuel pools are under control with full cooling function in operation.
 

Aktuální zpráva, 02. 05. 2011, 18:40:  NEA Calls For Fundamental Changes To Isotope Supply Chain

Governments and industry must work together to implement fundamental changes in the molybdenum-99 supply chain to ensure long-term reliability of supply, the OECD’s Nuclear Energy Agency (NEA) has said. The OECD/NEA steering committee for nuclear energy said disruptions in the global supply chain of molybdenum-99 (Mo-99) and its decay product, technetium-99m (Tc-99m) over the past two years have had significant impact on patients, who have had important diagnostic tests cancelled or delayed. Mo-99 and Tc-99m are the most widely used medical radioisotope, used in medical diagnostic imaging techniques that enable accurate and early detection of diseases such as heart conditions and cancer. On 29 April 2011, the steering committee for nuclear energy endorsed a policy to restructure those aspects of the market that are functioning unsustainably and to promote an internationally consistent approach to ensure the long-term, secure supply of medical radioisotopes. In a statement the committee said that although the supply situation has stabilised for the moment, it remains fragile and the underlying problem – an unsustainable economic structure remains to be addressed. The committee is calling on producers to implement full-cost recovery for Mo-99 activities as a way to ensure continued investment in the industry. Payment for reactor irradiation services and processing services needs to be based on the full cost of production, the NEA has said in the past. The committee also wants the industry to source, value and pay for enough reserve capacity to cope with the unexpected loss of key production sources. Other proposals include urging governments to support the conversion to use of low enriched uranium targets for Mo-99 production, wherever technically and economically feasible. The committee warned that unless action is taken to ensure long-term security of supply, shortages could become commonplace over the next decade. Five research reactors produce 95 percent of global Mo-99 supply: the High-Flux Reactor (HFR) at Petten in the Netherlands, BR2 in Belgium, Osiris in France, Safari in South Africa and the National Research Universal (NRU) reactor in Canada. The Organisation for Economic Cooperation and Development (OECD) is to host a G20 meeting on the lessons to be drawn from the accident at Fukushima-Daiichi nuclear power plant, OECD secretary-general Angel Gurría said in Paris on 28 April 2011. The G20 meeting will be held from 7 to 8 June 2011 and will contribute to the International Atomic Energy Agency’s (IAEA) ministerial meeting on nuclear safety from 20 to 24 June. During a joint press conference with IAEA director-general Yukiya Amano and OECD Nuclear Energy Agency director-general Luis Echávarri, Mr Gurría said that a number of lessons would be drawn from the accident at Fukushima-Daiichi, notably on the design, construction, operation and maintenance of existing and future plants. Mr Gurría also said lessons would apply to waste management and the reaction against nuclear power. Mr Amano said public confidence in the safety of nuclear plants had been shaken. We must work hard on improving the safety of nuclear power plants and ensuring transparency about the risks of radiation, he said. More than ever before, our watchword must be safety first. The IAEA’s ministerial meeting on nuclear safety will renew previous discussions on nuclear safety and review the International Nuclear Event Scale (INES) and other standards. The safety standards are an important element, but what is also needed is an international mechanism for implementation and enforcement of safety requirements around the world, said the OECD’s Luis Echávarri, adding that the Nuclear Energy Agency also favours a strengthening of the IAEA Convention on Nuclear Safety.

Aktuální zpráva, 28. 04. 2011, 19:51: Tepco Revises Fuel Damage Estimates For 3 Fukushima-Daiichi Units

Tokyo Electric Power Company (Tepco), operator of the Fukushima-Daiichi nuclear plant in Japan, has revised its estimates of fuel damage in the reactors of units 1, 2 and 3 at the plant. Yesterday Tepco released new estimates of damage after the country’s Nuclear and Industrial Safety Agency (NISA) questioned the accuracy of the initial assessments. Tepco has revised downwards the estimated fuel damage in the reactor core of unit 1 from 70 percent to 55 percent. The percentage refers to the number of fuel rods with damaged cladding and is based on a re-assessment of the radiation levels in the wet well and the dry well of the primary containment vessel. The company also said it acted inappropriately in excluding fuel damage of less than five percent in calculating total damage ratios for units 2 and 3. As a result, Tepco has revised upwards its estimates of damaged fuel in unit 2 and unit 3 by 5 percent each to 35 percent and 30 percent respectively. The company released its initial estimates of fuel damage on 15 March 2011, based on radiation levels in the reactors and their containment vessels. Earlier this month, NISA provisionally rated the level of the Fukushima-Daiichi accident as Level 7 a major threat on the International Atomic Energy Agency’s International Nuclear Event and Radiological Scale (INES). It had originally been provisionally rated as Level 5. Tepco said the corrected fuel damage estimates will not affect the rating.

Aktuální zpráva, 28. 04. 2011, 10:44: Tepco Completes High-Voltage Rewiring at Fukushima-Daiichi

Tokyo Electric Power Company (Tepco) has finished rewiring the high-voltage power grid at the Fukushima-Daiichi nuclear plant in an effort to secure the facility’s electricity supply from both external and internal sources. Tepco said the work had been finished on 26 April 2011. The plant’s six reactors are connected in pairs to external power sources, but Tepco needed to ensure that if any one of the three external sources is cut off – by another earthquake or tsunami, for example – other sources can be used to cool the reactors. Tepco began connecting cables to the grid for units 1, 2, 5 and 6 last week. Work on units 3 and 4 was carried out earlier this week. During the work, external power to the units was interrupted, but diesel generators were used to power the injection of water to continue cooling the reactors.

Aktuální zpráva, 15. 04. 2011, 16:13:  NISA Fears Leak Of Cooling Water From Fukushima-Daiichi Unit 2

Water being used to cool the number 2 reactor at the Fukushima-Daiichi nuclear plant might be leaking into the trench between the reactor and turbine building, Japan’s Nuclear and Industrial Safety Agency (NISA) has said. The plant's operator, Tokyo Electric Power Company (Tepco), transferred about 660 tonnes of highly contaminated wastewater from the unit 2 turbine building installation trench to a turbine condenser on 13 April 2011. As a result, the water level in the trench dropped by 8 cm, but had risen again by 3 cm yesterday morning. The contaminated water needs to be moved because there is a risk it might continue to leak outside the unit’s controlled zone and from there flow into the sea. Contaminated water has also been found in the turbine hall basements of units 1 and 3, although its level of radioactivity is much lower than the water at unit 2. The total amount of water to be removed is estimated at more than 60,000 tonnes, the International Atomic Energy Agency said. The water has been hampering work to restore the reactors’ cooling systems. Tepco also plans to transfer contaminated water to the plant's waste processing facility, but the facility has not yet been made leak-proof. The utility says it does not know when it can start removing water from reactors other than unit 2. Yesterday, workers continued to move emergency diesel generators to higher ground where they would be safe from aftershocks and tsunamis, according the Japan Atomic Industrial Forum. NISA reported that an earthquake that hit Fukushima prefecture on 13 April
2011 had an epicentre 75 km from the Fukushima-Daiichi nuclear power plant and 67 km from Fukushima-Daini, but no unusual events have been reported at either facility. Meanwhile, interim analysis of water from the spent fuel pool of unit 4 at Fukushima-Daiichi shows higher than normal levels of radiation, which suggests some of the fuel assemblies stored there might be damaged. Tepco said analysis of samples collected from the pool on 12 April 2011 showed 220 kilobecquerels per litre (kBq/L) of iodine-131, 88 kBq/L of caesium-134 and 93 kBq/L of caesium-137. The utility also said the water temperature in the unit 4 SFP had risen to about 90 degrees Celsius, significantly higher than the normal temperature range of 20 to 40 degrees Celsius. To cool the fuel, workers sprayed almost 200 tonnes of water on the SFP for six hours on Wednesday morning. The condition of spent fuel in the SFPs at units 1 and 2 is not known, while at unit 3 Tepco says it suspects there might be some damage. Cooling capacity at all four SFPs was lost after the earthquake and tsunami on 11 March 2011 and keeping the fuel cool has been a priority as Tepco works to stabilise the plant.
 

Aktuální zpráva, 14. 04. 2011, 17:06: Tepco Completes High-Level Radioactive Water Transfer From Unit 2 Trench

Tokyo Electric Power Company (Tepco) has completed the transfer of 660 tonnes of high-level radioactive water from a trench in the unit 2 turbine building to a condenser at the Fukushima-Daiichi nuclear plant. Tepco said the transfer, using an underwater pump, began at 19:35 on 13 April local time (00:35 central European time) and ended at 17:04 local time today (14 April). The contaminated water needed to be moved because there was a risk it might have continued to leak into cable trenches and pits outside the unit’s controlled zone and from there flow into the sea. Contaminated water has also been found in the turbine hall basements of units 1 and 3, although its level of radioactivity is much lower than the water at unit 2. The total amount of water to be removed is estimated at more than 60,000 tonnes, the International Atomic Energy Agency (IAEA) said. The water has been hampering work to restore the reactors’ cooling systems. Tepco said it had also completed the task of installing barriers around a breakwater on the southern perimeter of the plant to prevent radioactive water leaking into the sea from units 3 and 4. Efforts are continuing to cool reactors at the plant. The IAEA said today that fresh water is being continuously injected into the reactor pressure vessel (RPV) at unit 1 using a temporary electric pump with offsite power. At units 2 and 3, fresh water is being continuously injected into the RPVs through the fire extinguisher lines, also using temporary electric pumps with offsite power.

Aktuální zpráva, 13. 04. 2011, 13:57: Japan Announces Evacuation Plans For More Residents

The Japanese government is to evacuate the population of a number of towns and villages to the northwest of the Fukushima-Daiichi nuclear plant to prevent the accumulation of individual exposure doses over the next 12 months. According to the International Atomic Energy Agency (IAEA), authorities have found that some areas beyond the existing 20 km evacuation zone could be exposed to more than 20 millisieverts (mSv) during the course of the next year, until March 2012. The evacuation will be a “planned evacuation” with authorities aiming to move people within the next four weeks. The evacuation area includes Kutsurao village, Namie town, Iitate village, part of Kawamata town and part of Minami Souma City. The annual dose limit for controlled nuclear workers or medical personnel is 20 mSv per year, but can reach 50 mSv in an exceptional year as long as the five-year average is not higher than 20 mSv per year, according to recommendations by the International Commission on Radiological Protection (ICRP). In a declared emergency, the recommended limit under Japanese regulations is 100 mSv for controlled individuals. The ICRP backs these regulations, but could sanction a maximum accumulated dose of 250 mSv in extraordinary situations. The annual dose limit for the general public is lower, at 1 mSv per year as a general guideline. However, according to ICRP recommendations, the total dose may reach 20 mSv from technical sources in an exceptional year. Japan has adopted these recommendations. Technical sources include fallout from atmospheric bomb tests, fallout from nuclear accidents, radioactive isotopes released by nuclear installations during normal operation, and radiation released by technical devices such as cathode ray tubes, computers and smoke detectors. They do not include radiation from medical diagnosis and treatment. Meanwhile, plant operator Tokyo Electric Power Company (Tepco) said workers are spraying resin on debris at the plant in an effort to avoid the release and spread of contaminated dust. They have started to erect a steel plate in front of the screen of the unit 2 cooling water discharge channel to prevent any further release of highly contaminated water leaking from trenches and pits and the basement of the turbine hall of unit 2. Yesterday, Tepco started transferring highly radioactive water from a utility trench at unit 2 to the condenser and by this morning had moved about 250 tonnes of contaminated water.As a result, the water level in the trench had dropped by 4 centimetres by 07:00 local time today (midnight central European time) according to the Japan Atomic Industrial Forum.

Aktuální zpráva, 12. 04. 2011, 13:57: Fukushima-Daiichi INES Rating Increased To Level 7

The accident at the Fukushima-Daiichi nuclear power plant in Japan has been provisionally increased from Level 5 to Level 7 a major threat on the International Atomic Energy Agency’s International Nuclear Event and Radiological Scale (INES). Level 7 is the most serious level on INES and is used to describe an event comprised of “a major release of radioactive material with widespread health and environmental effects requiring implementation of planned and extended countermeasures. This is only the second Level 7 accident in the nuclear industry. The first was at Chernobyl in 1986. In a report to the IAEA, Japan’s Nuclear and Industrial Safety Agency (NISA) said the accident had been re-evaluated based on data showing the total amount of radioactivity released to the environment from the plant since it was hit by an earthquake and tsunami on 11 March 2011. The report said figures show the total amount of iodine-131 discharged is estimated at 130 petabequerels (PBq) and caesium-137 at 6.1 PBq. NISA said it estimates that the amount of radioactive material released to the atmosphere is approximately 10 percent of the Chernobyl accident. NISA had initially rated the accident at Fukushima-Daiichi as Level 5, which means “accident with wider consequences. The new provisional Level 7 rating considers the accidents that occurred at units 1, 2 and 3 as a single event on INES. Previously, separate INES Level 5 ratings had been applied for units 1, 2 and 3. The provisional INES Level 3 rating assigned for unit 4 still applies.

Workers at the Fukushima-Daiichi nuclear power plant in Japan have finished discharging low-level radioactive water into the sea to make room in storage facilities for highly radioactive water. Japan Nuclear and Industrial Safety Agency (NISA) spokesman Yasuhiro Sakuma told NucNet that the initial discharge of low-level radioactive water had finished. He said there might be other low-level radioactive water elsewhere in the plant. Plant operator Tokyo Electric Power Company (Tepco) has been discharging the low-level radioactive water into the sea to make room in storage facilities for highly radioactive water from the unit 2 reactor complex, where radioactive water 100,000 times the normal level in an operating reactor has been found in the turbine building basement. There is a risk that this radioactive water might continue to leak into cable trenches and pits outside the unit’s controlled zone and from there flow into the sea. Contaminated water has also been found in the turbine hall basements of units 1 and 3, although its activity is lower than the water at unit 2. The contaminated water needs to be moved from the turbine building basements and from a concrete tunnel and trenches to various storage facilities. The amount of water is estimated at more than 60,000 tonnes, the International Atomic Energy Agency said. The water has been hampering work to restore the reactors’ cooling systems. Tepco is working to lay hoses between the turbine buildings and the storage facilities so the water can be removed. Holes have already been bored in the walls of the buildings, but work to install the hoses has yet to begin, the Japan Atomic Industrial Forum (JAIF) said. In addition, waste disposal facilities need to be closely checked before the procedure can begin, NISA said. NISA said facilities must be checked for cracks that might have been caused by the earthquake, and that this could take up to a week.
 

Aktuální zpráva, 08. 04. 2011, 17:31: Removing Contaminated Water Might Take Another Week, NISA Says

Moving highly radioactive water from a turbine building basement at the Fukushima-Daiichi nuclear power plant might not start for another week, Japan’s Nuclear and Industrial Safety Agency (NISA) has said.  The highly contaminated water is from the unit 2 reactor complex, where radioactive water 100,000 times the normal level in an operating reactor has been found in the turbine building basement. There is a risk that this radioactive water might flow into the sea. The water needs to be moved from the turbine building basement to a storage facility. The water has been hampering work to restore the reactor's cooling systems. Plant operator Tokyo Electric Power Company (Tepco) has been discharging lower-level radioactive water into the sea to make room in the storage facility for the highly radioactive water. But NISA said the facility must be checked for cracks that might have been caused by the earthquake, and that this could take up to a week. The agency said the facility was designed to store low-level radioactive water and that every effort must be made to make sure that highly radioactive water does not leak.

Aktuální zpráva, 07. 04. 2011, 17:55: Nitrogen Injected Into Unit 1 PCV After Concern About Hydrogen Build-up

7 Apr (NucNet): Nitrogen is being injected into the primary containment vessel (PCV) of unit 1 at the Fukushima-Daiichi nuclear power plant amid concern that hydrogen that has accumulated there could cause an explosion. Because the containment has already been damaged and pressure inside might drop below atmospheric pressure, there is a risk that outside air containing oxygen could leak into the PCV resulting in the build-up of an explosive hydrogen-oxygen gas mix. Injecting nitrogen is intended to displace oxygen inside the PCV, thereby reducing the risk of explosion caused by the combustible combination of hydrogen and oxygen. Plant owner and operator Tokyo Electric Power Company (Tepco) said nitrogen injection started at unit 1 today at 01:31 local time (18:31 on 6 April central European time). Tepco is preparing to take similar measures at units 2 and 3. Yesterday Tepco said workers at the plant had used 6,000 litres of coagulant to stop a leak from a trench next to the unit 2 inlet point that had been causing highly contaminated water to flow into the sea since 29 March. Tepco said they used liquid tracer to find the source of the leak in a concrete utility trench and then used the coagulant to seal it. Additional measures will now be carried out to prevent the discharge of radioactive material from the trench, which holds electric supply cables.
One possible measure is to continue the injection of coagulant, Tepco said. Iodine-131 and Caesium-137 were both detected in water sampled in trenches and in the sea near the water discharge. The leak was discovered on 2 April when workers detected water releasing a radiation dose rate of more than 1,000 millisieverts per hour in a trench and found a crack about 20 cm wide on the trench’s concrete wall.

Aktuální zpráva, 06. 04. 2011, 17:08: Workers Use Coagulant To Stop Fukushima-Daiichi Leak

6 Apr (NucNet): Workers at the Fukushima-Daiichi nuclear power plant have used 6,000 litres of coagulant to stop a leak from a trench next to the unit 2 inlet point that has been causing highly contaminated water to flow into the sea since 29 March. Plant owner and operator Tokyo Electric Power Company (Tepco) said today that they used liquid tracer to find the source of the leak in the concrete utility trench and then used the coagulant to seal it. The company said the leak had stopped by 09:30 this morning, Japan time (02:30 central European time). Additional measures will now be carried out to prevent the discharge of radioactive material from the trench, which holds electric supply cables. One possible measure is to continue the injection of coagulant, Tepco said. Iodine-131 and Caesium-137 were both detected in water sampled in the trench and in the sea near the water discharge. The leak was discovered on 2 April when workers detected water releasing a radiation dose rate of more than 1,000 millisieverts per hour in the trench and found a crack about 20 cm wide on the trench’s concrete wall, from where water was thought to be flowing into the sea. On 2 April, concrete was poured into the trench in an attempt to stop water leaking into the sea, but no significant decrease in leakage was seen. On 3 April, the top of the trench was broken open and polymer was poured into the trench to stop the leak, but this measure was also unsuccessful. Meanwhile, Tepco has begun discharging into the sea low-level radioactive wastewater stored in sub-drain pits at units 5 and 6 and in a reservoir of the central radioactive waste disposal facility. Tepco plans to discharge approximately 10,000 tonnes of low-level radioactive water and about 1,500 tonnes of the low-level radioactive subsurface water into the sea. The discharge is necessary because workers need to use the reservoirs for storing highly radioactive water from the unit 2 turbine building, where radioactive water 100,000 times the normal level in an operating reactor has been found in the turbine building basement. There is a risk that this radioactive water might also flow into the sea. Tepco said it is concerned that vital equipment needed to secure the safety of the reactors might be submerged if this water is not drained. The utility is also monitoring an accumulation of hydrogen gas in the primary containment vessel of unit 1 Measures are being taken to avoid a hydrogen explosion similar to the explosion in the primary containment vessel of unit 2.

Aktuální zpráva, 05. 04. 2011, 19:01: Tepco Prepares Liquid Glass Injection To Stem Leak

5 Apr (NucNet): Tokyo Electric Power Company (Tepco) was today preparing to inject liquid glass into bedrock at the Fukushima-Daiichi nuclear power plant in an effort to prevent a leak of radioactive water that has been flowing into the sea since 29 March. Tepco said it now thinks the water might not be leaking from a concrete trench, but from a joint in piping upstream of the trench, then seeping through a layer of gravel below. The company said today it had arranged for specialist equipment to be delivered to the plant site and the injection of liquid glass into the bedrock was set to begin. On 3 April, workers poured a polymer absorbent into a duct leading to the pit in the hope of blocking the leak. The polymer material expands when it absorbs water. But there was little change in the amount of water flowing into the sea and this morning workers started pouring a coloured liquid into a tunnel linked to the pit in an effort to retrace the exact route of the contaminated water. Tepco also said today that from 3 April the water level in a trench at unit 3 had increased by 15 cm and the route of that leak is not known. There is a possibility that water in the unit 4 turbine building might be running into a trench at unit 3. As a precaution workers yesterday stopped transferring water to the turbine building of unit 4 and the water level in the unit 3 trench stabilised. Also yesterday, Tepco began discharging into the sea low-level radioactive wastewater stored in sub-drain pits at units 5 and 6 and in a reservoir of the central radioactive waste disposal facility. The discharge is necessary because workers need to use the reservoirs for storing highly radioactive water from the unit 2 turbine building, where radioactive water 100,000 times the normal level in an operating reactor has been found in the turbine-building basement. There is a risk that this radioactive water might flow into the sea. Tepco said it is concerned that vital equipment needed to secure the safety of the reactors might be submerged if this water is not drained.  By 19:10 Japan time (12:10 central European time) on 4 April Tepco was using 10 pumps to discharge low-level radioactive wastewater from the central radioactive waste disposal facility into the sea. Tepco plans to discharge approximately 10,000 tonnes of low-level radioactive water and about 1,500 tonnes of the low-level radioactive subsurface water into the sea.The company said the level of iodine-131 in the wastewater is about 100 times the legal limit. If people were to eat fish caught near the plant every day for a year, their radiation exposure would be 0.6 millisievert. The annual permissible level for the general public is one millisievert.

Aktuální zpráva, 04. 04. 2011, 17:07: Tepco Gets Approval To Release Wastewater Into Sea

4 Apr (NucNet): The Japanese government has approved plans by Tokyo Electric Power Company (Tepco) to release low-radioactivity wastewater into the sea from the Fukushima-Daiichi nuclear power plant as part of efforts to stabilise the facility. According to the Japan Atomic Industrial Forum (JAIF), the utility told a news conference today that it hopes to start releasing 11,500 tonnes of wastewater from tomorrow and that the operation will continue for several days. The company said the level of iodine-131 in the wastewater is about 100 times the legal limit. If people were to eat fish caught near the plant every day for a year, their radiation exposure would be 0.6 millisievert.  The annual permissible level for the general public is one millisievert. Wastewater will be released to make room in containers for highly contaminated water from the unit 2 reactor complex, where radioactive water 100,000 times the normal level in an operating reactor has been found in the turbine-building basement. There is a risk that this radioactive water might flow into the sea. Chief cabinet secretary Yukio Edano expressed concern today about the cumulative effects on the sea of possible long-term radiation leakage from the plant. He said he is urging Tepco to act quickly to prevent the spread of contamination. Tepco said today it is still not sure how the heavily contaminated water is flowing into the sea from the plant. The company had thought it was coming from a crack in a concrete pit, but that now seems unlikely. Yesterday Tepco poured a polymer absorbent into a duct leading to the pit in the hope of blocking the leak. The polymer material expands when it absorbs water. But there was little change in the amount of water flowing into the sea and this morning workers started pouring a coloured liquid into a tunnel linked to the pit in an effort to retrace the exact route of the contaminated water. As a temporary measure, Tepco is considering setting up silt barriers near a unit 2 water intake pipe to prevent radioactive elements from spreading in the ocean. Japan’s Nuclear and Industrial Safety Agency (NISA) said a full-scale recovery of cooling systems at the plant is needed to stem the leakage of radioactive substances, but that work will take several months. A senior official of the agency, Hidehiko Nishiyama, made the comments at a news conference yesterday. Meanwhile, external power supply is now being used to power the pumps that are injecting fresh water into the reactor pressure vessels of units 1, 2 and 3 at the plant, replacing temporary electrical pumps. The switch to external power occurred at all three units on 3 April 2011, according to Tepco’s daily plant status report. Tepco also said some lighting has been reactivated in the turbine buildings of units 1, 2, 3 and 4. Two workers were named as the first official deaths at the plant yesterday. Kazuhiko Kokubo, 24, and Yoshiki Terashima, 21, died at the plant while carrying out regular checks of a reactor when the tsunami hit. They suffered multiple injuries. The two men had been missing since 11 March and their bodies were found last week in unit 4.

Aktuální zpráva, 04. 04. 2011, 09:28: Japan Nuclear Operators Announce Range Of Immediate Emergency Measures

4 Apr (NucNet): Operators of nuclear power plants in Japan have announced a range of immediate measures being taken as protection against the possibility of their facilities being struck by a tsunami. On 30 March 2011, Japan’s Ministry of Economy, Trade and Industry (METI) told utilities to implement emergency safety measures at nuclear power plants based on lessons learned from events at the Fukushima-Daiichi and Fukushima-Daini plants. The Japan Atomic Industrial Forum (JAIF) said Hokkaido Electric Power Company has deployed a vehicle-mounted power generator of 320 megawatts at its Tomari nuclear power plant in Hokkaido, northern Japan. Tohoku Electric Power Company has permanently deployed vehicle-mounted power generators at its Onagawa nuclear plant, which automatically shut down when the 11 March earthquake struck. Hokuriku Electric Power Company has deployed five vehicle-mounted power generators for emergency use at Shika nuclear plant on Japan’s west coast. Kansai Electric Power Company, which operates the Mihama, Ohi and Takahama plants, will use 19 vehicle-mounted power generators, in addition to three existing ones, to reinforce preparedness for severe occurrences, JAIF said. Shikoku Electric Power Company (Ikata nuclear plant), Kyushu Electric Power Company (Genkai and Sendai nuclear plants) and Chugoku Electric Power Company (Shimane nuclear plant) are all said to be adding backup vehicle-mounted generators, JAIF said. The Japan Atomic Power Company, operator of the Tokai and Tsuruga nuclear plants, will implement tsunami measures including building a bulkhead to protect seawater pumps, installing temporary power sources to ensure functions in the central control room, and improving overall safety. Many of the problems facing the Fukushima-Daiichi nuclear power plant stemmed from the total loss of electrical power at the site following the massive earthquake and tsunami on 11 March. The earthquake cut off external power to the plant and the tsunami disabled backup diesel generators. Emergency Measures Being Implemented at Nuclear Power Plants in Japan:

Hokkaido Electric Power Company:

Using vehicle-mounted power generator.
Announced measures to strengthen safety, including ensuring power sources, and diversifying and securing cooling function.

Tohoku Electric Power Company:

Measures to strengthen safety at the Onagawa and Higashidori nuclear plants, permanent use of vehicle-mounted power generators.

Tokyo Electric Power Company:
(excluding Fukushima-Daiichi and Fukushima-Daini)

Postponed construction of unit 1 at Higashidori nuclear plant, which had been scheduled to begin this month.

Chubu Electric Power Company:

Plans to build a seawall higher than 12 meters to protect the plant from tsunamis.
Postponing the restart of unit 3 at Hamaoka, which is undergoing a periodic inspection.
Placing additional emergency diesel generators on higher ground at Hamaoka.
Construction of unit 6 will be put back from 2015 to 2016 or later.

Hokuriku Electric Power Company:

Units 1 and 2 at the Shika plant, currently shut down, will not be restarted until tsunami measures are completed, including deployment of vehicle-mounted power generators, backup electric engines and flood measures.

Kansai Electric Power Company:

Capital investments of at least 50 billion yen (JPY) (600 million US dollars, 420 million euro) to be made in new earthquake and tsunami measures for the 11 nuclear plants in Fukui Prefecture on Japan’s west coast.

Chugoku Electric Power Company:

Temporary suspension of preparatory work for construction of the Kaminoseki nuclear plant, which had been scheduled to start commercial operation in 2014.
Unspecified tsunami measures for Shimane-1 and -2.

Shikoku Electric Power Company:

Will establish a committee to draw up earthquake measures.
Is using three vehicle-mounted power generators and has installed backup seawater pump monitors.

Kyushu Electric Power Company:

Postponement of the restarts of the Genkai-2 and -3, which are undergoing periodic inspections.

Electric Power Development Company (J-Power):

Suspended work on the Ohma nuclear plant, currently under construction.

Japan Atomic Power Company (JAPC):

JPY 20 billion (240 million USD, 170 million EUR) in capital investments for earthquake and tsunami measures at the Tsuruga-1 and- 2 nuclear units.
 

Aktuální zpráva, 02. 04. 2011, 20:01: Tepco Finds Source Of Highly Radioactive Water Leak

2 Apr (NucNet): Tokyo Electric Power Company (Tepco) says it has identified a source of a leak of highly radioactive water leaking into the ocean from unit 2 at the Fukushima-Daiichi nuclear plant. The power company said today (Saturday) that water has been seeping from a 20 cm crack in the wall of a two-metre-deep pit that contains power cables near the reactor's water intake. Water between 10 and 20 cms deep was found in the pit. The radiation level has been measured at more than 1,000 millisieverts (mSv) per hour at the surface of the contaminated water in the pit, Tepco said in a statement today at noon local time. Tepco said it is preparing to inject concrete into the cracked pit to stop the leak. Japan’s Nuclear and Industrial Safety Agency (NISA) confirmed the crack could be one of the sources of radioactivity found in seawater near the water outlet. NISA said it has asked Tepco to test samples of seawater at more locations near the plant and analyse them for different radioactive materials. In the past week, the radiation detected in water in the basement of the turbine building at unit 2 has been about 100,000 times higher than the normal level. High levels of radiation were also found in puddles in a utility trench outside the turbine building. Tepco also said it had made errors measuring the composition of radioactive isotopes in samples of contaminated water taken from plant buildings, trenches, and the sea. The total activity and the iodine-131 values were correct, but the tellurium-129 and molybdenum-99 values were too high because of a programming error in their laboratory. The corrected data have since been published on Tepco’s website. Meanwhile, NISA has said radiation dose levels around the plant are now safe in areas such as the village of Iitake, where authorities had earlier urged residents to avoid drinking tap water after tests showed it contained more than three times the maximum standard of radioactive iodine. The International Atomic Energy Agency (IAEA) reported that on 1 April, iodine-131 was detected in seven prefectures ranging from 7 to 74 becquerel per square metre. The level of caesium-137 in nine prefectures ranged from  2.9 to 76 becquerel per square metre. Reported gamma dose rates in the 45 prefectures showed no significant changes compared to 31 March 2011. NISA said that 106,000 people from Fukushima prefecture had been body-scanned for radioactivity and 102 were above the safe level of 100,000 counts per minute (cpm). When re-checked without their clothing, they were below the limit. NISA reported that among the workers at the Fukushima-Daiichi plant, 21 have received doses exceeding the 100-mSv limit. No worker has received a dose above 250 mSv, which is the dose limit for urgent emergency work according to international recommendations.

Aktuální zpráva, 01. 04. 2011, 18:13: Details Released On Exposure Of Fukushima Staff

1 Apr (NucNet): From a combined total of 996 staff working at the Fukushima-Daini and Fukushima-Daiichi nuclear power plants in Japan, 21 have been exposed to radiation doses higher than 100 millisieverts (mSv) and none have been exposed to more than 200 mSv, plant operator Tokyo Electric Power Company (Tepco) has said. Tepco said 370 staff were working at the Daiichi plant, where authorities have been trying to cool reactors and spent nuclear fuel since an earthquake and tsunami struck on 11 March 2011. Fifty-one of the staff were contractors and the rest employed by Tepco. At Fukushima-Daini, which was less affected by the quake and tsunami, and where all four units shut down safely, there were 626 staff at the plant.  Sixty-four were contractors and 562 worked for Tepco.Tepco did not say if it had included emergency services staff in its figures. The annual dose limit for controlled nuclear workers or medical personnel is 20 mSv per year, but can reach 50 mSv in an exceptional year when the five-year average is not higher than 20 mSv per year, according to recommendations by the International Commission on Radiological Protection (ICRP). In a declared emergency, the recommended limit under Japanese regulations is 100 mSv. The ICRP backs these regulations, but could sanction a maximum accumulated dose of 250 mSv in extraordinary situations. In most countries, the natural background radiation level is about 2 to 4 mSv a year. Meanwhile, dose rate levels continue to decrease slowly on the site and at the site boundary with outdoor air samples showing it is safe for staff to breathe onsite air, although protection is still needed inside contaminated buildings. The Japan Atomic Industrial Forum (JAIF) said today that radiation levels were 910 microsieverts per hour (microSv/hr) at the south side of the plant’s main office building, 144 microSv/hr at the main gate, and 65 microSv/hr at the west gate. These readings were taken at 15:00 Japan time (08:00 central European time) on 1 April 2011. Dose rates were highest on 17 March, showing 4,175 microSv/hr near the main office building, 647 microSv/hr at the main gate, and 313 microSv/hr at the west gate. Spraying with fresh water has begun of the spent fuel pool (SFP) at unit 1 of the plant and continues at the SFPs of units 1-4. Tepco said it has been using water from a barge lent by the US military. The barge has been anchored at a pier at the plant. Yesterday Tepco said it is planning to spray resin, a synthetic chemical, over debris at the plant in an effort to fix radioactive materials and avoid the spread of contamination. JAIF said Tepco is hoping the adhesive resin will prevent radioactive dust from being carried away by wind and rain. Work is continuing to remove contaminated water from the basement of the turbine halls at units 1, 2 and 3 by pumping spilled water into the condenser. Preparations have begun to carry out similar work at unit 4, according to Tepco. The delay in removing the contaminated water is hampering work to cool down and stabilise the plant. Japan’s Nuclear and Industrial Safety Agency (NISA) has ordered Tepco to solve the problem of heavily contaminated water that has leaked into trenches outside the controlled zones of units 1 to 3. Work is continuing to transfer water from the trenches to a storage tank and prevent it from flowing into the sea.

Aktuální zpráva, 01. 04. 2011, 15:49: Doel-4 Feedwater Turbopump Anomaly Rated INES Level 2

1 Apr (NucNet): An incident at the Doel-4 nuclear unit in Belgium that would have resulted in insufficient capacity of an auxiliary feedwater turbopump in the event of an incident has been rated as Level 2 on the International Atomic Energy Agency’s (IAEA) International Nuclear Event and Radiological Scale (INES). After the replacement of the pump during an outage in 2009, its rotational speed was adjusted to a lower level because of vibration problems. In a report on the incident to the IAEA, operators said the pump was tested and met the requisite safety specifications. However, the flow-rate versus pressure curve was not verified as required by regulations. This means the pump might not have delivered the pressure and flow required in the event of an incident. The plant operators’ report to the IAEA said an independent emergency feedwater system would have offered additional capacity in such circumstances. However, defence in depth was reduced between the 2009 outage and the discovery of the anomaly during a test on 18 March 2011, the report said.

Aktuální zpráva, 31. 03. 2011, 19:59: Tepco Plans To Prevent Spread Of Contamination By Chemical Spraying

31 Mar (NucNet): Tokyo Electric Power Company (Tepco) is planning to spray resin, a synthetic chemical, over debris at the Fukushima-Daiichi nuclear power plant in an effort to fix radioactive materials and avoid the spread of contamination. In a statement today Tepco said workers need to wait for improved weather before they proceed. An attempt to carry out the work was abandoned today because of unfavourable weather. The Japan Atomic Industrial Forum (JAIF) said Tepco is hoping the adhesive resin will prevent radioactive dust from being carried away by wind and rain. Meanwhile, work is continuing to remove contaminated water from the basement of the turbine hall at unit 1 by pumping spilled water into the condenser. JAIF said that by this morning work was finished to empty a tank for temporary storage of contaminated water from the turbine building of unit 3. A similar operation to empty a tank had begun at unit 1. The delay in removing the contaminated water is hampering work to cool down and stabilise the plant, JAIF said. The condensers are heat exchangers below the turbines, where low-pressure vapour from the turbines is condensed by removing residual or waste heat to the main heat sink. According to the International Atomic Energy Agency (IAEA), the Nuclear Safety Commission of Japan has suggested that higher activity in the water discovered in the unit 2 turbine building was caused by water which has been in contact with molten fuel rods and directly released into the turbine building via some, as yet unidentified path. JAIF said yesterday that damage and leakage is suspected to the primary containment vessel (PCV) structural integrity at unit 2. Japan’s Nuclear and Industrial Safety Agency (NISA) has ordered Tepco to solve the problem of heavily contaminated water that has leaked into trenches outside the controlled zones of units 1 to 3. Work is continuing to remove contaminated water from trenches outside the unit 1 reactor building. Work also began today to transfer water from the tunnel to a storage tank to prevent it from flowing into the sea. Tepco said the water level in the trench had fallen today by about one meter. The company said it will install monitoring cameras to keep track of the water levels in the tunnels to prevent any overflow. Yesterday the IAEA said that dose rates at the surface of accumulated water found in trenches close to the turbine buildings of units 1 to 3 were 0.4 millisieverts an hour (mSv/hr) for unit 1 and more than 1,000 mSv/hr for unit 2.

Aktuální zpráva, 30. 03. 2011, 13:56: Work Continues To Remove Contaminated Water At Fukushima-Daiichi

30 Mar (NucNet): Work is continuing to remove contaminated water from the basement of the turbine hall at unit 1 of the Fukushima-Daiichi nuclear plant by pumping spilled water into the condenser. But at units 2 and 3 there is not enough free capacity in the condensers and work is taking longer than expected, plant operator Tokyo Electric Power Company (Tepco) said. The condensers are heat exchangers below the turbines, where low-pressure vapour from the turbines is condensed by removing residual or waste heat to the main heat sink.  The Japan Atomic Industrial Forum (JAIF) said no major progress has been reported in efforts to drain the basement water. The delay is hampering work to cool down and stabilise the plant, JAIF said. According to the International Atomic Energy Agency (IAEA), the Nuclear Safety Commission of Japan has suggested that higher activity in the water discovered in the unit 2 turbine building is caused by water which has been in contact with molten fuel rods and directly released into the turbine building via some, as yet unidentified path. JAIF confirmed today that damage and leakage is suspected to the primary containment vessel (PCV) structural integrity at unit 2. JAIF had previously said the PCV’s status was unknown. Removal of water from the turbine building basements is an important step before workers can continue efforts to fully restore power to the plant. Meanwhile, Japan’s Nuclear and Industrial Safety Agency (NISA) said it has ordered Tepco to solve the problem of heavily contaminated water that has leaked into trenches outside the controlled zones of units 1 to 3 at the plant. The IAEA said today that dose rates at the surface of accumulated water found in trenches close to the turbine buildings were 0.4 mSv/hr for unit 1 and more than 1,000 mSv/hr for unit 2. An investigation is under way to discover how the water accumulated in the trenches. Fresh water is being continuously injected into the reactor pressure vessels (RPVs) of units 1, 2 and 3 in an effort to cool the nuclear fuel. At unit 1, the temperature at the RPV’s feedwater nozzle – normally the coldest point of the RPV – has increased from 273.8 degrees Celsius to 299 degrees Celsius. The temperature at the bottom of the RPV remained stable at 135 degrees Celsius. Temperatures at unit 2 appear relatively stable at the same measurement points. At unit 3, the temperature at the RPV feedwater nozzle is about 61.5 degrees Celsius and 120.9 degrees Celsius at the bottom of the RPV. However, Tepco said the validity of the RPV measurements is still being checked. Tepco also said that periodical spraying of water onto the spent fuel pools of units 1 to 4 is continuing. Since yesterday Tepco has been spraying fresh water instead of seawater. The pool temperature is known only for unit 2 and was at 46 degrees Celsius this morning (30 March). In unit 4, lighting was re-established in the control room yesterday. This means all control rooms now have light.

 Aktuální zpráva, 29. 03. 2011, 17:00: Plutonium Levels Not A Threat To Human Health’

29 Mar (NucNet): Soil samples at the Fukushima-Daiichi nuclear power plant contain traces of plutonium that probably resulted from the nuclear accident there, the Japan Atomic Industrial Forum (JAIF) has said. JAIF said the level of plutonium detected in the samples, collected on 21 and 22 March 2011, is the same as that found in other parts of Japan and does not pose a threat to human health. Five samples were taken from the site and three contained plutonium, although some of this could have come from atmospheric weapon tests in the late 1940s, 1950s and 1960s. To determine whether these readings are the result of weapons testing the samples must now be compared with samples from outside the site. However, Japan’s Nuclear and Industrial Safety Agency (NISA) said two samples contained plutonium that was probably from nuclear reactor operation, most likely from unit 2 where, along with units 1 and 3, there has been damage to the integrity of the reactor core and the fuel. The two samples contained 1.2 becquerel plutonium-239 and plutonium-240, but no detectable amounts of plutonium-238.

Plutonium is a by-product of the nuclear power generation process. At unit 3 at the Fukushima-Daiichi plant it is an ingredient in mixed oxide, or MOX, fuel. Plutonium is a health risk mainly when it is inhaled because it can remain in the lungs and other organs, causing long-term damage including cancer. NISA said it is waiting for the results of another survey by the Science Ministry using samples taken outside a 20-km radius from the plant, as well as a further survey by plant operator Tokyo Electric Power Company (Tepco) in the plant compound. Tepco also confirmed that highly contaminated water was found in trenches at the plant. The trenches are for cables and are spread over the entire plant site. Tepco said the contaminated water, mainly from unit 2, but also from units 1 and 3, must be cleaned up urgently so it does not spread any further.

Yesterday Tepco detected radiation of more than 1,000 millisieverts per hour (mSv/hr) on the surface of water in unit 2’s turbine building and in a trench outside the building. JAIF said Tepco has blocked the main trench outlet with sandbags and concrete to prevent the water from reaching the ocean. Tepco is also continuing work to remove contaminated water that has accumulated in the turbine building basements. Removal of water from the turbine building basements is an important step before workers can continue efforts to fully restore power to the plant.  One of the next challenges will be a detailed radiological assessment of the entire site, after which decisions will take place on what work will follow, including repairs and cleaning. The amount and composition of isotopes in water that has leaked from the unit 2 primary loop and reactor pressure vessel indicates that fuel damage in this unit is most serious and that fuel might have begun to melt, according to calculations by French Institut de Radioprotection et de Sűreté Nucléaire (IRSN).

Aktuální zpráva, 25. 3. 2011, 17:11: Wenra Releases First Proposal On Definition And Scope Of Stress Tests’

25 Mar (NucNet): A temporary cable for external power has been connected at Fukushima-Daiichi nuclear power plant making electricity available to all six units for the first time since the earthquake and tsunami struck on 11 March 2011, the Japan Atomic Industrial Forum (JAIF) said. Test runs of each item of electrical equipment will now be carried out before vital systems such as instrumentation, and core and spent fuel pool cooling can be turned on. JAIF said that lights were turned back on in the central control room of unit 3 on 22 March and of unit 1 on 24 March. At units 5 and 6 all power has been switched to external sources. JAIF also confirmed that three workers were contaminated when laying cables in the turbine hall of unit 3. The International Atomic Energy Agency (IAEA) said the three were contract workers laying cables in the turbine hall. Two of them were found to have radioactivity on their feet and legs. JAIF said they were exposed to more than 170 millisieverts (mSv). The workers were washed in an attempt to remove radioactivity, but since there was a possibility of beta-ray burning of the skin, the two were taken to the Fukushima University Hospital for examination and then transferred to Japan's National Institute of Radiological Sciences for further examination. They are expected to be monitored for around four days. It is thought that the workers ignored their dosimeters’ alarms believing them to be false and continued working with their feet in contaminated water. According to JAIF, the level of radioactive fission products in the water was about 3.9 million bequerels per cubic centimeter or 10,000 times higher than the reactor water used in the course of normal operations. Japan’s Nuclear and Industrial Safety Agency (NISA) has asked plant operator Tokyo Electric Power Company (Tepco) to review the radiation control system immediately in order to avoid similar incideqnts in the future. As of 24 March at 19:30 Japan time (11:30 central European time), the number of workers at the plant found

Publikace v oboru energetiky, strojírenství a stavebnictví k prodeji
 

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