The crisis that radioactive water is leaking into the groundwater is not anything new. But the amount of contamination is hard to comprehend.
"Asahi Shimbun: A liter of the water was also found to contain 750 million becquerels of radioactive substances that emit beta rays, such as Strontium."
"EXSKF: 5,000 cubic meters, or 5,000 tonnes of this water is in the trench.
Note: 5,000 cubic meters of water is equal to 5 million liters.
One liter was found to contain 2.35 Billion Becquerels of Cesium.
If this concentration is consistent, the total amount would be nearly 12 Quadrillion Becquerels of cesium in this one trench."
Now when we have heavily contaminated groundwater there is for a certain fact the reactor core is exposed to this water. And considering the amount of contamination found in the water there is a high probability that the reactor core or should we say molten reactor corium is the cause for the steam seen here.