The leak in a massive underground double-shell nuclear waste tank at the Hanford Site has grown significantly since the leak was first announced to the public last fall, according to sources who have seen new inspection video and photographs.

The tank -- known as AY-102 -- holds 860,000 gallons of radioactive waste generated during decades of plutonium production at the southeastern Washington reservation.

The sources who spoke with KING 5 said the amount of waste that has spilled out of the primary tank into the annulus - the hollow space separating the tank's inner and outer walls -- has grown substantially in recent months. Imagery acquired in the past week showed that the accumulated waste in the annulus had expanded beyond what could be seen in photographs released just two months ago, and was far greater than the leaked amounts first observed in August 2012.

The new video of the waste also shows much more bright green liquid than workers had seen before. The presence of green, wet material means it is new.

A spokesman for Washington River Protection Solutions said only a small amount of liquid has leaked. AY-102 continues to leak small amounts of waste material into its annulus. The current best estimate is that the liquid volume at the leak accumulation site has increased from approximately 0.2 gallons on September 26, 2012, to approximately 0.4 gallons on June 12, 2013. The increase between the last two inspections was approximately 0.1 gallons or about the contents of a 12-ounce can of soda, the spokesman said. WRPS is the private company that manages the Hanford tank farms for the Department of Energy.

AY-102 is the first double-shell tank at Hanford to leak, posing a signficant setback to the federal government's plan to keep the waste secure for decades while a permanent treatment plant is built and put into operation.

In a series of reports, the KING 5 Investigators showed how evidence of the AY-102 leak was ignored for a year after the leak was first detected in October 2011. The private company that manages the Hanford tank farms -- Washington River Protection Solutions -- insists that the leak was not detected until August 2012 and that it worked quickly to assess the situation and announce the news to the Department of Energy and the public.

But documents reviewed by KING 5 and interviews with experienced WRPS employees showed multiple points where the company failed to take appropriate action in response to growing evidence of the leak. Since KING 5's series began, Gov. Jay Inslee has called for a full investigation and the Department of Energy ordered WRPS to conduct a top-to-bottom review of its tank farm operations. In addition WRPS President Mike Johnson abruptly announced his retirement after only 14 months on the job.

The next installment of the series airs Thursday night at 10 p.m. (KONG) and 11 p.m. (KING).

Watch the series: Hanford's Dirty Secrets

KING 5's Russ Walker contributed to this report.

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