They were visiting Richland, which is next to Hanford nuclear reservation.
Activist Helen Caldicott said protesters wanted to visit "the belly of the beast."
But the Tri-City Herald reported that the protest also brought children, dogs, good food and the music of Portland bands to the sunny Sunday protest.
Along George Washington Way, demonstrators in anti-contamination suits waved signs at passing traffic.
A woman in a flowing cape and gas mask waved a rubber salmon and other people blew bubbles because, as their sign said, radiation travels through the air.
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