Moore, George M., Cervando A. Banuelos, and Thomas T. Gray

Abstract
Minimization or elimination of globally held stockpiles of highly enriched uranium (HEU) has been a long-standing U.S. policy goal since the Carter administration in the late 1970s. Most states recognize that elimination or minimization of HEU would have significant benefits for global nonproliferation and counterterrorism efforts. These concerns have driven several efforts to eliminate or minimize HEU use in several applications.
Significant progress has been made in reducing the use of HEU in civilian research reactors, in the preparation of isotopes used for medical purposes, and even in the elimination of weapons stockpile HEU by programs involving blending down the weapons grade HEU to low enriched uranium (LEU) fuel for civilian power reactors. The largest remaining non-weapons use of HEU is as fuel for naval propulsion reactors. In contrast to the attention given to other HEU minimization efforts, there has been relatively little international effort to eliminate or minimize the naval propulsion use. The topic has been addressed in some studies, particularly in the period shortly after the 9/11 attacks, and there has been some focus on the issue in the international arena, such as discussions at the two International Symposia on HEU Minimization.
One of the major reasons for lack of progress in reducing HEU use in naval propulsion is that these are – except for the Russian ice breaker program – military programs, and the use of HEU, particularly for submarines, has historically be perceived to have a number of significant advantages. In addition, the non-weapons uses of HEU, such as for submarine propulsion, present a unique set of problems for the nonproliferation regime because, as is discussed in the body of this paper, there is a “loophole” in the Treaty on the Non-Proliferation of Nuclear Weapons (NPT).
The Russian Federation and the United States are the world’s largest holders of HEU, each of which has well over 500 metric tons (MT) of HEU. By comparison the next largest stock of HEU is the approximately 18 MT held by China. The sum total of HEU in all other states is on the order of 70 MT, a small fraction of the U.S./Russian total.
The United States holds the largest declared reserve of HEU designated for naval reactors, approximately 140 MT. In addition, the U.S. Navy and United Kingdom’s Royal Navy almost exclusively use an HEU enrichment that is as high as or higher than that used in nuclear weapons. Other navies, such as the Russian Federation and the Indian Navy, typically use HEU that is enriched in the 40 percent to 50 percent range, approximately one half that of the typical enrichment for nuclear weapons. Finally, the remaining navies (France and China) that have nuclear-powered vessels use LEU fuel, most of which is enriched to a level of less than 10 percent.
Currently, all marine propulsion reactors are military with the exception of the Soviet/Russian fleet of icebreakers/Arctic supply shits. Although the Soviet Union built its first icebreaker initially using an LEU core, it later retrofitted that vessel with HEU as well as all icebreakers that followed. These vessels are still operated by the Russian Federation. Except for the Soviet Union, early attempts at nuclear-powered commercial vessels elsewhere proved to be uneconomical; Japan, Germany, and the United States at one time built nuclear-powered commercial vessels fueled by LEU. These vessels are no longer in service.
The nuclear-powered vessels of the French Navy are of particular note. Although the earliest French submarines were powered by LEU fueled reactors, a few vessels were fueled using HEU before the French Navy ultimately decided to return to the use of LEU in its modern naval reactors. Currently, all of France’s submarines and nuclear-powered aircraft carrier use LEU fuel.
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