Julien de Troullioud de Lanversin

Hong Kong University of Science and Technology

Zoom link: https://mit.zoom.us/j/98115087408

Abstract:

While the Comprehensive Nuclear Test Ban treaty (CTBT) bans nuclear weapon test explosions, it does not define what a nuclear explosion is. The U.S. interpretation of the treaty is that any test involving a supercritical chain reaction is prohibited; this is the “zero-yield” standard. Very low-yield nuclear tests release million times less energy than full-scale nuclear test explosions and are conducted in metallic containment vessels. Subcritical very low-yield tests that the U.S. regularly conducts for its stockpile stewardship are allowed according to the “zero-yield” standard.

In the past, however, countries have conducted very low-yield tests involving supercritical chain reactions, such as the hydronuclear tests conducted by the U.S. and the U.S.S.R. The U.S. has recently accused Russia and China of violating the “zero-yield” standard by conducting such tests.

There is currently no technical method to verify whether a very low-yield test was subcritical or supercritical. This seminar presents ongoing work on a new technical method where gamma rays are used to deduce whether a test conducted in the past was supercritical or subcritical. This method relies on on-site measurements of gamma rays emitted by the fission and activation products that are generated during a test and that remain in the containment vessels. Preliminary results have been obtained through computer simulations using open-source neutronics and isotopic software. This work also discusses possible verification protocols based on this method and policy measures that could facilitate onsite inspections of very low-yield tests. Such a verification method could contribute to strengthening adherence to the CTBT and reducing the risks of a resumption of full-scale nuclear tests.

BIO:

Julien is an Assistant Professor at the Division of Public Policy at the Hong Kong University of Science and Technology (HKUST). His research focuses on understanding and addressing the risks that technologies can generate for national and international security, such as nuclear technologies, specifically in the Asia Pacific region and in the context of the U.S-China rivalry. With a background in physics engineering, Julien develops technological solutions to help address global security issues. As the project lead for the nuclear reactor physics code ONIX, Julien also develops open-source software to promote the use of open and transparent scientific tools in academic research and education.

Before joining HKUST, Julien was a fellow at the Project on Managing the Atom at Harvard’s Belfer Center from 2021 to 2022 and a nuclear security postdoctoral fellow at Stanford's Center for International Security and Cooperation (CISAC) from 2019 to 2021. He was also part of the Science and Global Security research team at Princeton University from 2014 to 2019. Julien holds a Ph.D. in Applied Physics from Princeton University, an M.Sc. in Nuclear Science and Technology from Tsinghua University Beijing, and a Diplôme d'Ingénieur (M.Sc. and B.Sc.Eng.) from Ecole Centrale de Marseille.