The U.S. nuclear arsenal is a product of the Cold War. Most of the weapons in the current stockpile are equipped with plutonium pits—the spheres of plutonium that cause the nuclear explosion—that were produced in the 1980s. Because scientists are unsure how plutonium ages over time, and because treaties restrict the testing of nuclear weapons, the U.S. government has undertaken the task of producing new plutonium pits for the existing weapons. Los Alamos National Laboratory (LANL) has been tasked by the Department of Defense and the National Nuclear Security Administration to produce 30 plutonium pits per year by 2026 to replace the aging pits that were originally made in the 1980s. As a student in the Center for Nuclear Security Science and Policy Initiatives (NSSPI), Benjamin Sarawichitr was directly involved in this enterprise. He worked with his advisor, NSSPI Deputy Director Dr. Craig Marianno, on a project to investigate new techniques to track plutonium using its radiation during the production process.
“In order to efficiently produce these pits, the tracking of plutonium throughout the production facility is important. Tracking the plutonium throughout the facility will allow LANL to discover where holdup is occurring,” explained Sarawichitr.
Holdup refers to nuclear material that is deposited in the equipment, such as gloveboxes, used to process the material. Domestic safeguards measures require that all of the material, including the holdup that gets deposited inside the equipment, be accounted for. Improving the methods for locating the holdup will help make the manufacturing of the plutonium pits more efficient. In his thesis work, Sarawichitr developed a localization algorithm to locate holdup within a glovebox using a technique originally used for wifi localization, True-Range Multilateration, or TRM.
“TRM,” Sarawichitr described, “utilizes ‘anchors’ that are stationary and are able to receive a signal from an ‘emitter.’ For wifi localization, the ‘anchors’ are wifi receivers and the ‘emitter’ is a wifi transmitter. Distances are determined between each of the receivers and the transmitter. These distances are then used to determine the position of the transmitter.”
Sarawichitr said he took inspiration from this wifi localization technique and applied the concepts to a radioactive source and radiation detectors.
“The concepts were similar,” he said. “The ‘emitter’ was the radioactive source while the ‘anchors’ were the radiation detectors, and the distances between them could be determined through calibrated detectors utilizing the inverse-square law.”
From there, he was able to determine the position of the radioactive source.
As a NSSPI student, Sarawichitr attended a safeguards workshop organized at Oak Ridge National Laboratory where he learned about the various techniques to detect and measure hold-up. “The skills I learned at this workshop,” he said, “Directly relate to the work I will be doing at LANL since I will use these techniques to measure hold-up for the plutonium processing facility.”
Another unique experience he had as a NSSPI student was doing field measurements at Disaster City in an emergency response exercise for a civil support team from Wyoming. “This exercise allowed me to apply the skills I learned in Dr. Marianno’s emergency response class in practice,” he said.
Prior to joining NSSPI, Sarawichitr earned his Bachelor of Science in nuclear engineering with minors in physics and radiological health engineering from Texas A&M University in 2020. He graduated from Texas A&M University in December 2022 with a Master of Science degree in nuclear engineering with a specialization in nuclear nonproliferation. Since defending his thesis this past fall, he has been working at LANL as an R&D Engineer for NPI-9, the Non-Destructive Assay and Vault Operations Group.