NAMIE, Japan — Every month, Hiroko Watabe, 74, returns for a few hours to her abandoned house near the damaged Fukushima nuclear plant to engage in her own small act of defiance against fate. She dons a surgical mask, hangs two radiation-measuring devices around her neck and crouches down to pull weeds.

She is desperate to keep her small yard clean to prove she has not given up on her home, which she and her family evacuated two years ago after a 9.0 earthquake and a tsunami devastated the plant five miles away. Not all her neighbors are willing to take the risk; chest-high weeds now block the doorways of their once-tidy homes.

“In my heart, I know we can never live here again,” said Ms. Watabe, who drove here with her husband from Koriyama, the city an hour away where they have lived since the disaster. “But doing this gives us a purpose. We are saying that this is still our home.”

While the continuing environmental disaster at the Fukushima Daiichi plant has grabbed world headlines — with hundreds of tons of contaminated water flowing into the Pacific Ocean daily — a human crisis has been quietly unfolding. Two and a half years after the plant belched plumes of radioactive materials over northeast Japan, the almost 83,000 nuclear refugees evacuated from the worst-hit areas are still unable to go home. Some have moved on, reluctantly, but tens of thousands remain in a legal and emotional limbo while the government holds out hope that they can one day return.