CORVALLIS, Ore. — Jose N. Reyes has a surefire way to make certain that in case of accident, his nuclear reactor is surrounded by plenty of cold water: install it at the bottom of a giant swimming pool.

After the triple meltdown of the Fukushima nuclear plant in Japan in March 2011, a swarm of new ideas about nuclear power drew attention. One of those is the brainchild of Mr. Reyes, who came up with a scheme to make a reactor small enough so that if there is a loss of electric power, as happened at Fukushima, its tiny core will cool on its own, and quickly, the way a small cup of coffee chills faster than a big pot.

His reactor, which so far exists only in computer designs, sits inside a containment vessel that looks like a steel thermos bottle and measures 82 feet in height and 15 feet in diameter — a mini version of reactor containments some 200 feet in height and 120 feet in diameter at American nuclear plants now under construction.

Although Mr. Reyes’s reactor delivers only one-twentieth the power of conventional reactors, his design is such that more reactors can be added as more power is needed.