Swedish officials are downplaying things, but it seems there were very significant systems failures, particularly of the backup generators which were needed to cool the core during shutdown, which led to this being a pretty close call to a nuclear meltdown.
That's disturbing since Sweden is one of the modst advanced nations in terms of nuclear power.
This from DerSpiegel
Sweden's nuclear energy authority, SKI, has largely completed its reconstruction of events in an accident last week that led to the closure of a nuclear power plant in the city of Forsmark and, ultimately, the shutdown of half the country's nuclear plants as a precautionary measure. In the incident, two of the plant's four backup generators malfunctioned when the plant experienced a major power outage on July 25. According to officials, who described the event as "serious," a short-circuit triggered the accident, which caused a cut in power to the nuclear facility. Plant workers told Swedish media that it came close to a meltdown.
In fact, the only thing that appears to have stopped a catastrophe is the fact that two diesel backup generators kicked in, enabling the Forsmark facility to operate at least part of its emergency cooling system. Still, for 20 minutes, workers were unable to obtain information about the condition of the reactor and they were only able to respond after 21 minutes and 41 seconds, according to a report in Germany's Hamburger Abendblatt newspaper.
Swedish media are reporting that a previously unknown technical problem emerged during the emergency that could also be present in all other Swedish nuclear reactors.
for 20 minutes, workers were unable to obtain information about the condition of the reactor 
