Kyodo News reports that the company analyzed the water in the spent fuel pool of reactor No. 4. The water had iodine-131 and cesium-137 at much higher than expected levels. TEPCO said it measured 220 becquerels per cubic centimeter of iodine-131, 88 becquerels per cubic centimeter of cesium-134 and 93 becquerels of cesium-137. Such levels are up to 100,000 times normal, according to the Japanese Nuclear and Industrial Safety Agency.
Many outside experts had already said that it was likely the fuel rods were damaged because of the presence of iodine and cesium isotopes in the areas around the plant. A tell-tale sign that rods are damaged is the presence of iodine-131, because its half-life is only about eight days. Cesium-134 has a half-life of about two years and cesium-137's half-life is about 30 years.