An anti-nuclear activist crashed through a locked gate at the second Fukushima power plant today after being thwarted from driving into the radiation-leaking Dai-ichi complex a few miles away, the plants' operator reports.

Both plants are guarded. But Japan's nuclear safety agency questioned the level of security in the wake of the disaster and ordered Tokyo Electric Power Co. (TEPCO), which operates both plants, to "take all measures to ensure security especially from the viewpoint of nuclear material protection," Kyodo News writes.

The driver, identified as 25-year-old Hikaru Watanabe of Tokyo, drove through the western gate of the Daini plant around 1:10 p.m. Thursday, Kyodo News says, adding, "The purpose of the intrusion remains unknown."

In its daily status update on conditions at Daini, however, TEPCO characterized Watanabe as "a campaigner" -- meaning anti-nuclear -- who drove a "sound truck" around the complex for 12 minutes before driving out the gate he crashed. The company alerted Fukushima Prefecture police, who stopped Watanabe.

"We have shut the gate with our own vehicles after the campaigner's vehicle left," TEPCO said.

Watanabe and his vehicle were decontaminated before both were taken to a police facility.

About 50 minutes earlier, Watanabe allegedly tried to crash the front gate of the Dai-ichi complex, about 6 miles north of Daini, but TEPCO workers blocked him.

The four reactors at Daini achieved ''cold shutdown'' after the March 11 quake and are, as Kyodo News writes, "basically in a stable situation." The day after the quake, Daini lost backup power, the cooling systems for three reactors failed and an emergency was declared. But TEPCO regained off-site power and has kept the reactors under control.

Here's how it's reporting the status of each reactor: