Question: What tributary enters the Clinch near the former site which goes by the codename given it by the Manhattan Project during World War II for the project to produce enriched uranium for atomic bombs using the gaseous diffusion method?

Context paragraphs:
Poplar Creek (Tennessee): Poplar Creek is a tributary of the Clinch River in Anderson and Roane counties in East Tennessee.  Draining a watershed area of more than 82 mi2 , it enters the Clinch near the former K-25 site, a short distance downstream from the confluence of East Fork Poplar Creek, its largest tributary.

Kellex Corporation: The Kellex Corporation was a wholly owned subsidiary of M. W. Kellogg Company.  Kellex was formed in 1942 so that Kellogg's operations relating to the Manhattan Project could be kept separate and secret.  "Kell" stood for "Kellogg" and "X" for secret.  The new company's goal was to design a facility for the production of enriched uranium through gaseous diffusion.  In gaseous diffusion, isotopes of Uranium-235 could be separated from Uranium-238 by turning uranium metal into uranium hexafluoride gas and straining it through a barrier material.

Paducah Gaseous Diffusion Plant: The Paducah Gaseous Diffusion Plant (PGDP) is a facility located in McCracken County, Kentucky, near Paducah, Kentucky that produced enriched uranium 1952–2013.  It is owned by the U.S. Department of Energy (DOE).  The PGDP was the only operating uranium enrichment facility in the United States in the period 2001–2010.  The Paducah plant produced low-enriched uranium, originally as feedstock for military reactors, weapons and later for nuclear power fuel.

John R. Dunning: John Ray Dunning (September 24, 1907 – August 25, 1975) was an American physicist who played key roles in the Manhattan Project that developed the first atomic bombs.  He specialized in neutron physics, and did pioneering work in gaseous diffusion for isotope separation.  He was Dean of the School of Engineering and Applied Science at Columbia University from 1950 to 1969.

Timeline of the Manhattan Project: The Manhattan Project was a research and development project that produced the first atomic bombs during World War II.  It was led by the United States with the support of the United Kingdom and Canada.  From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army Corps of Engineers.  The Army component of the project was designated the Manhattan District; "Manhattan" gradually became the codename for the entire project.  Along the way, the project absorbed its earlier British counterpart, Tube Alloys.  The Manhattan Project began modestly in 1939, but grew to employ more than 130,000 people and cost nearly US$2 billion (about $ in 2016 dollars).  Over 90% of the cost was for building factories and producing the fissionable materials, with less than 10% for development and production of the weapons.

Gaseous diffusion: Gaseous diffusion is a technology used to produce enriched uranium by forcing gaseous uranium hexafluoride (UF) through semipermeable membranes.  This produces a slight separation between the molecules containing uranium-235 (U) and uranium-238 (U).  By use of a large cascade of many stages, high separations can be achieved.  It was the first process to be developed that was capable of producing enriched uranium in industrially useful quantities.

K-25: K-25 was the codename given by the Manhattan Project during World War II for the project to produce enriched uranium for atomic bombs using the gaseous diffusion method.  Originally the codename for the product, over time it came to refer to the project, the production facility located at the Clinton Engineer Works in Oak Ridge, Tennessee, the main gaseous diffusion building, and ultimately the site.  When it was built in 1944, the four-story K-25 gaseous diffusion plant was the world's largest building, with over 1640000 sqft of floor space and a volume of 97500000 cuft .

S-50 (Manhattan Project): The S-50 Project was the Manhattan Project's effort to produce enriched uranium by liquid thermal diffusion during World War II.  It was one of three technologies for uranium enrichment pursued by the Manhattan Project.

Portsmouth Gaseous Diffusion Plant: The Portsmouth Gaseous Diffusion Plant is a facility located in Scioto Township, Pike County, Ohio, just south of Piketon, Ohio that previously produced enriched uranium, including weapons-grade uranium, for the United States Atomic Energy program and U.S. nuclear weapons program.  The plant is in shutdown status and is in preparation for decontamination and decommissioning (D&D), with some facilities overseen by the United States Enrichment Corporation, a subsidiary of USEC Incorporated, a publicly traded corporation (NYSE: USU).  The D&D work on the older facilities to prepare the site for future use is expected to continue through 2024 and is being conducted by Fluor-B&W Portsmouth LLC.

Ames Project: The Ames Project was a research and development project that was part of the larger Manhattan Project to build the first atomic bombs during World War II.  It was founded by Frank Spedding from Iowa State College in Ames, Iowa as an offshoot of the Metallurgical Laboratory at the University of Chicago devoted to chemistry and metallurgy, but became a separate project in its own right.  The Ames Project developed the Ames Process, a method for preparing pure uranium metal that the Manhattan Project needed for its atomic bombs and nuclear reactors. Between 1942 and 1945, it produced over 1000 ST of uranium metal.  It also developed methods of preparing and casting thorium, cerium and beryllium.  In October 1945 Iowa State College received the Army-Navy "E" Award for Excellence in Production, an award usually only given to industrial organizations.  In 1947 it became the Ames Laboratory, a national laboratory under the Atomic Energy Commission.

Supporting paragraphs: Poplar Creek (Tennessee) K-25
Answer: Poplar Creek