A late April Tepco underwater image, taken by a robotic camera, showing the debris-clogged Unit 3 storage pool for high-level radioactive wasteNHK World reports that Tokyo Electric Power Company is adding boric acid to the water of the Unit 3 pool for high-level radioactive waste in order to counteract the corrosive effects of alkaline chemical attack on irradiated nuclear fuel aluminum storage racks. A massive hydrogen explosion in mid-March sent large chunks of concrete debris into the pool, which have likely since leaked alkaline chemicals into the water. If the racks were to fail, nuclear fuel could reconfigure into a critical mass, sparking a chain reaction in the pool.