Power supply knocked out by earthquake. Backup diesel generators knocked out by tsunami. These are old reactors but still an order of magnitude safer than Chernobyl Modern, ultrasafe Gen 3+ designs use gravity operated emergency cooling together with power independent emergency activation systems. The damaged reactor appears to have been an early generation 2. pressurised light water design.
It is still a disaster but not the unmitigated disaster of Chernobyl. Latest info suggests one fuel rod may have been exposed when its cladding partially melted. However it is still early in this disaster and most of the facts are yet to unfold. I watched a video of the explosion and there was a distinct pressure wave. I thought it could have been a steam explosion caused by superheated water fracturing its containment, flashing to steam then rapidly expanding. This of itself may not have released radiation. However venting of the primary coolant would have released some radiation if one of the fuel rods had been damaged.
