THE NUCLEAR COMMUNICATIONS NETWORK News in Brief/ No. 77 / 23 March 2011
· IAEA on radiation measurements at Fukushima
23 Mar (NucNet): Tokyo Electric Power Company (Tepco) is continuing its efforts to restore external AC power to all six units at Fukushima-Daiichi nuclear power plant, with external power now available at units 2, 4, 5 and 6, the Japan Atomic Industrial Forum (JAIF) said.
JAIF said “integrity checks” of electrical equipment are being carried out in each unit and these must be completed before energising them.
In unit 3, the lights have been turned on in the control room area and backup batteries for essential instrumentation and control systems are operational. Tepco technicians are testing the pump integrity of the residual heat removal system for the reactor and spent fuel pool (SFP) cooling. JAIF said this was “encouraging news”.
JAIF also said the residual heat removal system was being energised with external power in unit 5.
According to Japan’s Nuclear and Industrial Safety Agency (NISA) unit 6 has had AC power for the residual heat removal system since 19:17 Japan time on 22 March 2011 (11:17 central European time) and lights were turned on in unit 3 at 22:43 Japan time.
Without electrical power, cooling systems at Fukushima-Daiichi’s six reactors cannot operate. Many of the problems facing the nuclear power plant stem from the 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.
The International Atomic Energy Agency (IAEA) said restoring external power to the plant does not mean the reactors will immediately resume normal safety function. The earthquake and tsunami may have inflicted considerable damage in addition to knocking out electricity supplies, the agency said. “Because the extent of this damage is unknown, it is not possible to accurately estimate a work schedule.”
JAIF also said today that pressure and temperature in the reactor pressure vessel (RPV) of unit 1 has increased to a very high level and more seawater injection was necessary. NISA said the injection rate was increased at 02:33 Japan time on 23 March from 2 cubic metres per hour to 18 cubic metres per hour.
NISA said about 180 tonnes of seawater was sprayed onto the SFP of unit 3 yesterday by the Tokyo Fire Department, and about 150 tonnes of seawater was sprayed onto the SFP of unit 4 yesterday evening.
On 21 March, work had resumed on pumping seawater into the RPV and primary containment vessels (PCVs) at units 2 and 3 after it was suspended on 20 March when smoke was detected and it was decided to evacuate personnel from the reactor buildings.
Defence minister Toshimi Kitazawa said that because of the smoke from units 2 and 3 a helicopter would continue to take daily measurements of the surface temperature at these units.
Seawater spraying onto the SFPs of units 2, 3 and 4 is continuing.
According to NISA and Tepco, radioactivity readings from monitoring posts on the Fukushima-Daiichi site and at the site boundary have been more or less constant since yesterday afternoon until today at 08:30. At the main gate at 11:10 today (Japan time) the reading was 226.8 microsieverts per hour (microSv/hr) and to the north of the service building on 21 March at 16:30 it was 2015 microSv/hr.
Tepco has published the results of environmental analysis of seawater from a sample taken next to the plant yesterday (22 March) at 06:30 local time. The results are as follows:
- cobalt-58: 17,000 becquerel per cubic-metre (0.02 times the regulatory limit);
- iodine-131: 1,200,000 becquerel per cubic-metre (30 times the regulatory limit; yesterday 127 times);
- iodine-132: 1,400,000 becquerel per cubic-metre (0.5 times the regulatory limit);
- cesium-134: 150,000 becquerel per cubic-metre (2.5 times the regulatory limit; yesterday 25 times);
- cesium-136: 24,000 becquerel per cubic-metre (0.1 times the regulatory limit);
- cesium-137: 150,000 becquerel per cubic-metre (1.7 times the regulatory limit; yesterday 17 times).
The IAEA has confirmed that Tepco’s monitoring will be checked using independent samples taken by the Japan Agency for Marine-Earth Science and Technology (Jamstec) and the Japan Atomic Energy Agency (JAEA).
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IAEA Briefing On Lack Of Data And Radiation Monitoring Results
23 Mar (NucNet): The International Atomic Energy Agency (IAEA) has said essential data on water levels and temperatures are lacking from units 1, 2, 3 and 4 of Fukushima-Daiichi and further measurements are needed to assess contamination.
The IAEA said in a technical briefing on 21 March 2011 that following the restoration of cooling at units 5 and 6, temperatures in those spent fuel pools continue to decline. The agency said it was seeing some steady improvements, but the overall situation at the Fukushima-Daiichi nuclear power plant remains “very serious”.
High levels of contamination have been measured in the locality of the plant, the briefing said.
The IAEA said restoration of electrical power to unit 2, which was reported on 20 March 2011, is good news. “AC power is available and an electrical load check to pumps etc. is currently on-going,” the briefing said.
Seawater is still being injected into the reactor pressure vessels of units 1, 2 and 3. Pressure in the reactor pressure vessel and the containment-vessel drywell at unit 3, which had been rising on 21 March, has fallen.
Radiation Monitoring
The IAEA also said its radiation monitoring team had taken measurements at distances from 56 to 200 km from the Fukushima nuclear power plant. At two locations in Fukushima Prefecture, gamma dose rate and beta-gamma contamination measurements have been repeated. These measurements showed high beta-gamma contamination levels, the IAEA said.
Measurements by the IAEA and the Japanese authorities were taken at the same time and locations. And both sets of measurements gave comparable results. Measurements of gamma dose rate and beta-gamma contamination were taken on 20 March at more locations.
The dose-rate results ranged from 2 to160 microsieverts per hour (microSv/hr), which compares to a typical natural background level of around 0.1 microSv/hr. High levels of beta-gamma contamination have been measured between 16 and 58 km from the plant. Results show contamination ranging from 0.2-0.9 megabecquerels (MBq) per square metre.
The agency said: “Further measurements are needed to assess possible contamination beyond the area currently monitored – both closer to the facility and further away.”
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