Nuclear Archeology in a Bottle: Evidence of Pre-Trinity U.S. Weapons Activities from a Waste Burial Site

Abstract

During World War II, the Hanford Site in Washington became the location for U.S. plutonium production. In 2004, a bottle containing a sample of plutonium was recovered from a Hanford waste trench. Here, state-of-the-art instrumental analyses, reactor model simulations, and investigative science techniques were used to provide insights as to the origin of this unknown sample, a process collectively termed as nuclear archeology. Isotopic age dating conducted on the sample in 2007 indicated the sample was separated from the spent fuel 61.6 +/- 4.5 years earlier. The isotope (22)Na, a detectable product of a secondary nuclear reaction, proved useful as a powerful tool for nuclear forensic analysis as (1) an easily detectable signifier of the presence of alpha emitting actinides, (2) an indicator of sample splitting, and (3) a measure of the time since sample splitting. Analytical results of minor actinide isotopes and reactor model simulations confirmed the material originated from the X-10 reactor in Oak Ridge, TN. Corroborated by historical documents, we concluded this sample was part of the first batch of Pu separated at T-Plant, Hanford, the world's first industrial-scale reprocessing facility, on December 9, 1944. This sample represents the oldest known collection of man-made (239)Pu in the world.

Nuclear Forensic Science: Analysis of Nuclear Material Out of Regulatory Control

“…An analogous approach was used in an investigation of Manhattan Project-era plutonium discovered buried in a glass jug in a waste trench at the Hanford site in Washington State (Schwantes et al 2009). The jug contained hundreds of milligrams of Pu, and radiochronometry analyses were made, among other analyses, in the attempt to identify the origin and history of this material.…”

“…There are three potential sources for the U present in this sample: (a) U produced by radioactive decay of Pu, (b) U derived from irradiated reactor fuel that was not completely separated from Pu during reprocessing, and (c) natural U derived from the local environment. Historical records indicated that US plutonium production reactors operating at the time were using natural uranium fuel, and reactor modeling indicated that reactor operations would not have substantially modified the isotopic composition of the uranium fuel (Schwantes et al 2009). Therefore, any uranium present that was not produced by radioactive decay is expected to have a near-natural uranium isotopic composition.…”

“…Thus, all 238 U present in this material was derived from either the U fuel or the local environment. In contrast, because 236 U is generally undetectable in natural U, it can be confidently assumed that all 236 -240 Pu isotope systems were used together to determine a production date of 1946 ± 4.5 years (Schwantes et al 2009). The absence of detectable 241 Pu in this sample is consistent with this age.…”

“…Because of its short half-life (∼14 years), any 241 Pu originally present in the sample in ∼1946 would have nearly completely decayed in the intervening ∼60 years. The model age determined for this Pu material, together with its isotopic composition at that time, was compared to historical records of US reactor operations between 1944 and 1950 to conclude that this plutonium was produced in 1944 at the X-10 reactor in Oak Ridge, Tennessee (Schwantes et al 2009). …”

“…Researchers at Pacific Northwest National Laboratory (PNNL) applied nuclear forensic techniques in an interesting study of Pu-containing material (determined to be trace Pu in a LaF 3 solid phase in a dilute HNO 3 solution) in an old glass jug found in an abandoned safe at the Hanford site in Washington State (Schwantes et al 2009). The PNNL researchers applied nuclear counting methods (gamma and alpha spectrometry), inductively coupled plasma optical emission spectrometry, ICP-MS, ion chromatography, and radiochronometry to the residual Pu material.…”