RICHLAND — Internet signup for tours this year of Hanford’s historic B Reactor opens at noon Saturday.

The tours are separate from the Hanford-wide tours, which include a shorter look inside B Reactor and a wider tour of the nuclear reservation. Signup for those tours starts at 6 p.m. Monday.

To signup for either tour, go to www5.hanford.gov/publictours.

B Reactor tours will be offered on 41 days from April 1 to Sept. 21, including some Saturdays.

Participants must be at least 12 years old to tour B Reactor. Last year, the age requirement was 18.

More than 35,000 visitors have toured B Reactor since 2009 from all 50 states and more than 60 countries.

Participants will ride a bus to the reactor from north Richland.

B Reactor, the world’s first full-scale nuclear reactor, was built in 11 months during World War II.

It produced plutonium for the world’s first nuclear explosion and the atomic bomb dropped on Nagasaki, Japan, helping end the war.

Supporters are working to make the reactor part of a proposed new national park telling the story of the Manhattan Project, the race to create an atomic bomb during World War II.