The concerns among activists, experts and politicians focus on Unit 4, which contains most of the plant's spent fuel not stored in dry, hardened storage casks, Stars and Stripes reported Wednesday.
After the 9-magnitude earthquake and tsunami, an investigative report by the Rebuild Japan Initiative Foundation, an independent think tank started to investigate the causes of the plant disaster, cited among risks a loss of cooling water in Unit 4.
If left exposed, the spent fuel could heat and melt, releasing a huge amount of radiation.
The plant's operator, Tokyo Electric Power Co., has said on its Web site Unit 4 is sound and the building could withstand an earthquake of the magnitude of the March 11, 2011, temblor.
But public trust in Tepco remains low, Stars and Stripes said, and calls for more efforts to empty and secure Unit 4 continue in Japan and beyond.
U.S. Sen. Ron Wyden, D-Ore., a member of the Senate Committee on Energy and Natural Resources who visited the plant in April, told MSNBC Tepco "has a 10-year plan for essentially moving the spent fuel rods to dry casks, dry storage. That, in my view, must be sped up because if another earthquake or tsunami hits, it could be very, very damaging and possibly [release] more radiation than earlier."
In letters to Gregory Jaczko, chairman of the U.S. Nuclear Regulatory Commission, Secretary of State Hillary Clinton and Energy Secretary Steven Chu, Wyden asked what support could be offered to the Japanese to secure the plant's spent fuel.
And 72 organizations based in Japan have sent a petition to U.N. Secretary-General Ban Ki-moon requesting the United Nations organize a summit on the future of Unit 4 and set up an independent team to coordinate international assistance.