Time dependent heat transfer of proliferation resistant plutonium

Abstract

Increasing proliferation resistance of plutonium by way of increased 238Pu content is of interest to the nuclear nonproliferation and international safeguards community. Considering the high alpha decay heat of 238Pu, increasing the isotopic fraction leads to a noticeably higher amount of heat generation within the plutonium. High heat generation is especially unattractive in the scenario of weaponization. Upon weaponization of the plutonium, the plutonium may generate enough heat to elevate the temperature in the high explosives to above its self-explosion temperature, rendering the weapon useless. In addition, elevated temperatures will cause thermal expansion in the components of a nuclear explosive device that may produce thermal stresses high enough to produce failure in the materials, reducing the effectiveness of the weapon. Understanding the technical limit of 238Pu required to reduce the possibility of weaponization is key to reducing the current limit on safeguarded plutonium (greater than 80 at. % 238Pu). The plutonium vector evaluated in this study was found by simulating public information on Lightbridge’s fuel design for pressurized water reactors. This study explores the temperature profile and maximum stress within a simple (first generation design) hypothetical nuclear explosive device of four unique scenarios over time. Analyzing the transient development of both the temperature profile and maximum stress not only establishes a technical limit on the 238Pu content, but also establishes a time limit for which each scenario would be useable. Keywords: Proliferation resistance, Plutonium, Heat transfer, Thermal stress