Fukushima Daiichi Nuclear Plant Weekly Review

Tokyo Electric Power Co. has identified a water leak from the containment vessel of unit 3 at its Fukushima Daiichi nuclear plant, and elsewhere at the site a worker was exposed to a small internal dose of radiation.

Recent developments related to the reactors severely damaged following Japan's 2011 earthquake and tsunami include:

Water leak in Fukushima unit 3. Source: TEPCORobot Reveals Leaking Water from Unit 3 PCV

On Saturday, TEPCO found water inside unit 3 believed to be leaking from its primary containment vessel. According to a TEPCO release Monday, a remote camera showed the water flowing into a drainage ditch in an area on the unit's first floor near the main steam isolation valve. (View a video of the leak on TEPCO's site.) The water is flowing into the basement. TEPCO did not find evidence that it is flowing out of the building, and monitors have not shown an uptick in radiation since its discovery. Kyodo news quoted the company as saying a sample of the water showed 700,000 becquerels per liter of cesium-134 and 1.7 million becquerels per liter of cesium-137.

For months, TEPCO has used robots to search for leaks where water used to cool damaged reactors at Fukushima escapes into plant basements. The current system used to cool units 1-3 pumps up water from the reactors' basements, runs it through treatment equipment to remove radionuclides and salt, then feeds it back into the reactor pressure vessels to restart the process. The leaks must be identified and sealed before work can begin on removing damaged fuel.

Worker Receives Internal Dose

On Monday, TEPCO reported that a man in his 50s received a small internal dose of radiation while working at the site. The Mainichi Daily News reported that he had loosened his face mask to wipe away condensation inside. Testing indicated his internal exposure from the incident would amount to 0.38 millisieverts over 50 years. By comparison, the United Nations Scientific Committee on the Effects of Atomic Radiation estimates the average yearly dose from all natural sources is 2.4 millisieverts, with 0.29 millisieverts from ingestion and 1.26 millisieverts from inhalation.

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