Title:

Improving Neutron Assays of Dilute Surplus Plutonium Using Gamm-Ray Measurements

Speaker:

Dr. Christopher McGrath

Affiliation:

SRNL Chemical Processing & Characterization

When:

Thursday, November 3, 2022 at 11:00:00 AM   Add to Calendar

Where:

Boggs Building, Room 347

Host:

Steven Biegalski
steven.biegalski@me.gatech.edu

Abstract

Neutron coincidence counting has been chosen as the method for assay of diluted surplus plutonium in Criticality Control Overpacks (CCOs) produced at the Savannah River Site. However, some portion of the material consists of scrap oxide containing low-Z elemental impurities. These impurities interact with Pu and Am alpha particles to create neutrons. In large quantities, these (α,n) neutrons can cause erroneous values with standard neutron analysis techniques and, in fact, can even prevent the analysis from succeeding at all. These large uncertainties and biases can result in measurements falling outside the required bounds for both Material Control & Accountability and Waste Acceptance Criteria. Some of the relevant (α,n) reactions provide an associated gamma ray and, if not, sometimes there is a similar reaction (for example, (α,p)) that produces gamma rays that can be detected. A methodology is under development to allow for the estimation of the quantity and impact of (α,n) neutrons on a Pu neutron assay. This makes it possible to calculate alpha (the ratio of (α,n) to Pu fission neutrons) and utilizing a known-alpha analysis, greatly reduces the associated uncertainty and bias of the measurement. Preliminary implementation has shown positive results and elucidated avenues for further development.

Biography

After receiving a Ph.D. in Chemistry at the University of Kentucky, Dr. McGrath performed two postdoctoral fellowships at LBNL and LANL. Following this, he joined the Idaho National Laboratory and served as a staff scientist for over 13 years. From 2008 to 2013, he served as the radiochemistry lead for the Materials and Fuels Complex at INL. In this role, he led a small team of chemists in performing radioanalytical measurements on samples ranging from environmental levels to fresh nuclear fuel. In 2013, he left the INL to join the staff of Idaho State University where he focused on developing a radiochemistry research and instruction program. In search of greener pastures and milder winters, he came to SRNL in 2019 where he works in the Nuclear Measurement Group and is the team lead for NDA.