The Tri-City Herald reports that more unknown material has been found in a third place between the two shells of Tank AY-102, which went into use in 1971. A photo taken of the same spot in 2006 shows that the area was clean then.
The finding this week of a third spot increases concerns that the tank, one of Hanford's 28 double shell tanks, has a leak from its inner shell.
The tanks are needed to hold high level radioactive waste for up to 40 more years until the last of the waste can be treated for disposal.
Tank AY-102 has a capacity of about 1 million gallons but currently stores about 707,000 gallons of liquid waste and 151,00 gallons of waste sludge.