Are Japanese and US reactors the same?

Yes and No. In the US we have both Boiling Water Reactors (BWR) and Pressurized Water Reactors (PWR). The reactors in Japan where the releases have occurred are US designed BWR's.

BWR's (as the name implies) boil water IN the reactor and send the radioactive steam into a turbine building where the steam turns turbines to create electrical power. These reactors are more efficient than PWR's but have some (now) obvious inherent flaws. I was never comfortable with the idea being an ex-Navy guy where all of the reactors are of the PWR variety.

PWR's use a closed-loop system. All of the radioactive stuff stays in the containment. Sort of like your car's cooling system where the coolant is separated from the oil. The "hot" loop (very hot and radioactive water) is circulated through heat exchangers which heat non-radioactive water which is then turned to steam and turns a turbine in another building to create electricity.

In Louisiana we have both types of reactors. Waterford III near New Orleans is a PWR while Riverbend near St. Francisville is a BWR.