High levels of radioactivity have been discovered in water in trenches outside units 1 and 2, and a trench behind unit 3 is also likely to be contaminated, according to Japanese news network NHK.
The findings come after radioactive water was found in the basements of the turbine halls of units 1-3. TEPCO reported levels of 1000 mSv/hour in a trench behind unit 2, 0.4 mSv/hr in the trench behind unit 2. The trench behind unit 3 was not measured because of debris, according to NHK. The concrete trenches carry cables and pipes, and are in the plants but outside the radiation control area. They do not drain into the sea. The unit 1 trench is nearly full of water, and its drain has been blocked with sandbags and concrete to prevent it from overflowing. The unit 2 and 3 trenches are both about a metre from overflowing. TEPCO said that it is trying to find the source of the contaminated water, and is preparing to dispose of it.
The radionuclides appear to have leaked out of the reactors. As a result, Japanese safety regulator NISA directed electricity utility TEPCO to balance the needs of cooling the reactors with preventing radioactivity leaks.
In other news, concrete pumps have injected seawater into the unit 3 and unit 4 spent fuel pools of the Fukushima-Daiichi nuclear power plant; 100 tons and 125 tons of water was injected into each on 27 March. No water pumping was scheduled for Monday 28 March. For the other spent fuel pools, fresh water pumping is due to start at unit 2 on 29 March, and a concrete pump is due to arrive and be set up at unit 1 on 30 March.
Pumping of fresh water into the reactor pressure vessels of units 1 and 3, as of Monday 28 March, is being performed by fire engine pumps. Staff are planning to switch pumping functions to temporary electric pumps.
Electric equipment continues to be tested in all six units. Units 1-4 have been energised on a 480V line; units 5-6 have been energised on a 6900V line.
TEPCO engineers have found two samples of plutonium in five site soil tests on 28 March. It said that the concentrations are too low to cause no major impact to human health. It said it will expand sampling points in the site and surrounding areas.
Plutonium makes up from 3-10% of MOX fuel, some of which has been loaded into unit 3, according to an American Nuclear Society technical report from 25 March. However, there were only 32 MOX fuel assemblies in a core of 548. And these were loaded into the core only five months before the incident, compared with a typical 36-48 month burn, so had relatively little time to build up dangerous fission products and minor actinides.