What are the two types of reactors commonly used in the U.S.?

The Boiling Water Reactor (BWR) and Pressurized Water Reactor (PWR) are indeed the two most commonly used types of reactors in the United States. BWRs generate steam directly in the reactor core, which then drives the turbine for electricity generation. This design allows for a simpler system since the same water serves to both cool the reactor and convert to steam.

PWRs, on the other hand, use pressurized water to keep the water in a liquid state even at high temperatures. The pressurized water transfers heat to a secondary coolant system, which then turns to steam to drive the turbines. This two-loop system adds complexity but increases safety by ensuring that radioactive water is contained within the primary loop.

These two reactor designs account for the vast majority of nuclear power generation in the U.S., illustrating their importance and widespread adoption in the industry. The other options listed represent reactor types that are either less common or used in specific contexts, hence their lower prevalence compared to BWRs and PWRs.