As much as 55% of Unit 1’s reactor core at the quake-stricken Fukushima Daiichi nuclear power plant is thought to be damaged; Unit 2’s core is estimated to be 35% damaged, as is 30% of Unit 3’s core, the Tokyo Electric Power Co. (TEPCO) said today. Seven weeks after the crisis began, the utility—which has also admitted damage of the spent fuel rods at Unit 4—continues all efforts to cool the affected reactors.

TEPCO issued the core damage estimates today to correct earlier data published on its website, which said 70% of Unit 1’s core had been damaged.
The data was measured by the Containment Atmospheric Monitoring System (CAMS), which monitored radiation in the containment vessels (both in the dry well and wet well sides) after the reactors lost their cooling systems following the devastating earthquake and tsunami on March 11.

Meanwhile, robots sent into Unit 1 on Tuesday took readings of as high as 1,120 millisieverts of radiation per hour. Water in the basement of Unit 4’s turbine building has also shown abnormally high radioactivity levels, and TEPCO has suggested the leak may be coming from the basement of the adjacent Unit 3. According to Japan’s Nuclear and Industrial Safety Agency (NISA), the basements of Units 1, 2, and 3 had an estimated 70,000 metric tons of stagnant water with high levels of radioactivity. TEPCO is still working out what it will do with these vast amounts of highly contaminated water.

On Tuesday, the utility announced that it would start preparatory work to decide whether it would fill Unit 1’s reactor containment vessel with water—a procedure known as a “water tomb”—to stabilize its reactor core. Industry experts have warned, however, that if this course of action is taken before the source of the high radiation is discovered, the water tomb could result in more radiation.

Workers on Monday managed to quell white smoke that had begun rising from Unit 4 last week. White smoke continues to be emitted from Units 2 and 3. Meanwhile, freshwater continues to be injected into Units 1, 2, and 3 and sprayed over the spent fuel pool of Unit 4. Nitrogen gas injection into the containment vessel in Unit 1 also continues to reduce the chances of hydrogen combustion. The pressure in the reactor pressure vessel is reportedly increasing.

Today, temperature at the feedwater nozzle of the reactor pressure vessel at Unit 1 was 134.7C; at Unit 2, it read 121C; and at Unit 3, it read 67.9C, although the bottom of Unit 3’s reactor pressure vessel read 110.4C.