Replacing Highly Enriched Uranium in Naval Reactors

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Replacing Highly Enriched Uranium in Naval Reactors Currently, the United States and Russian Federation, and perhaps China and others, have the capability of using HEU-fueled reactors in space. The amount of HEU used by these reactors is typically much less than the amount used in submarine reactors but is more similar to the quantities used in research reactors. Where submarine reactors typically produce between 50 and 200 MW, space reactors are two orders of magnitude less, typically producing 1 MW or less. Although space reactors are typically not discussed in plans to convert from HEU to LEU, they do represent a system that has historically, albeit infrequently, consumed HEU. More importantly, in contrast to ships and submarines, the weight penalty for using LEU in space reactors is extremely significant, a factor that would make replacement with LEU very difficult. A number of nations have acquired and used HEU for valid scientific research efforts. Typically the quantities used are rather small and many of the states satisfy their NPT obligations under the Small Quantities Protocol. Russia is the only nation that operates non-military maritime propulsion reactors that use HEU. Its fleet of nuclear-powered icebreakers/Arctic resupply vessels is used to clear the “northern-route shipping lane from the Atlantic to the Pacific across Russia’s northern arctic coast. 37 Its commercial nuclear fleet includes five currently operating icebreakers and two that are out of commission while being repaired. All five of the vessels are currently powered using HEU fuel enriched from 30–90 percent U-235. 38 It has not always been that way; the first Soviet Russia is the only nation that operates non-military maritime propulsion reactors that use HEU. icebreaker, the Lenin, was initially powered with LEU. However, following an accident that required replacement of the core, it was subsequently fueled with HEU. 39 Although there is discussion that the next generation of Russian icebreakers and Arctic resupply ships may be fueled with LEU, 40 a great deal of concern surrounds both these reactors and Russia’s floating nuclear power plants, particularly because Russia has begun more actively seeking buyers to purchase or lease the vessels, a possibility that is certain to present further challenges to international safeguards. In the limited history of commercial nuclear-powered ships, the Soviet Union/Russian Federation’s HEU powered icebreakers/Arctic supply ships are unique in their use of HEU. Other nations have designed commercial nuclear-powered ships that use LEU fuel. The first was the Savannah, the sole U.S.-built commercial cargo ship that was built for demonstration purposes only. Following that came the Otto Hahn, a German built nuclear-powered cargo vessel that operated from 1968–1979. 41 Finally, the Japanese designed Mutsu was the last nuclear-powered commercial vessel, which was decommissioned in 1992 following a tumultuous 23-year history plagued by technical and public opinion problems and never commercially operated on the high seas. 42 Although all three of these vessels were initially designed to demonstrate the possibilities of peaceful nuclear energy, they were not economical and the countries that built them chose not to build any more nuclear-powered commercial vessels. Finally, HEU has been used extensively in the preparation of medical isotopes. Molybdenum (Mo) 99 is a fission fragment that decays to technetium (Tc) 99m. 43 Tc 99m is one of the most commonly used radionuclides for medical diagnostic purposes. To prepare Mo 99, HEU is exposed to a neutron flux (typically in a small research-size reactor) and the Mo 99 is then chemically separated from the other fission fragments. The Mo 99 is then loaded onto a chemical ion exchange column and shipped to a hospital or distribution point near to where the daughter Tc 99m is to be used. When needed, the shorter- 37 Christine Egnatuk, “Chapter 5—Russia: Icebreaker Ships and Floating Reactors.” In Nuclear Terrorism and Global Security the Challenge of Phasing Out Highly Enriched Uranium, ed. Alan J. Kuperman (New York: Routledge, 2013), 66–81. 38 The wide range exists because there are conflicting reports in this matter. Specifically, the Murmansk Shipping companies, which produces the icebreakers, reports 30–40 percent U-235. However, a report to the Norwegian Port Authority prior to an icebreaker arrival claimed 90 percent U-235 at one point, creating dome doubt among experts. Ibid., 74. 39 Ole Reistad and Povl L. Ølgaard, “Russian Nuclear Power Plants for Marine Applications,” Nordic Nuclear Safety Research (NKS) Report, NKS-138 (April 2006), 15. 40 Egnatuk, “Russia: Icebreaker Ships and Floating Reactors,” 78. 41 Peter von Dobschuetz, “Dismantlement of NS Otto Hahn,” International Atomic Energy Agency, Vienna. 42 Ronald E. Yates, “Setbacks Submerge Japan’s Nuclear Ship,” Chicago Tribune (September 2, 1990), available at http://articles.chicagotribune.com/1990- 09-02/news/9003130692_1_reactor-radiation-ship. 43 The small “m” is a reference to the fact that the principal decay comes from a “metastable” energy level in the technetium 99. The metastable state is at a higher level than the ground state of the isotope. NTI Paper 14 www.nti.org
Replacing Highly Enriched Uranium in Naval Reactors lived Tc 99m is eluted off the column in a process that is known as “milking,” giving rise to the distribution column unit being called a “Moly Cow.” Inroads have been made in replacing HEU with LEU in a number of these applications. Research reactor cores have been successfully redesigned to use LEU without too significant a loss of neutron flux levels and a worldwide replacement program has been converting research reactors to LEU use. However, more than 120 HEU-based research reactors and critical assemblies still are in use with approximately half of the total in the Russian Federation. 44 LEU, although less efficient and producing more radioactive waste, has been successful as an HEU replacement in the production of medical isotopes. 45 For better or for worse, many of the older ideas about the use of HEU-based reactors for aircraft and smaller vehicle propulsion are no longer considered viable options. In the area of FBRs there are options of using plutonium to replace HEU, but this replacement itself has a number of unattractive features from nonproliferation and terrorism perspectives. In summary HEU can be replaced, albeit with difficulty, in all of the non-weapons applications. Replacing HEU in space reactors is probability the most challenging due to the enormous penalties paid to launch the increased weight of an equivalent power output LEU-fueled space reactor. 44 International Panel on Fissile Materials, “Facilities: Research and Isotope Production Reactors,” available at http://fissilematerials.org/facilities/ research_and_isotope_production_reactors.html. 45 However, the importation of LEU produced medical molybdenum 99/technetium 99m has encountered some tariff opposition and regulatory prohibitions on its use in various states for what appear to be protectionist and unfounded non-technical reasons. NTI Paper 15 www.nti.org
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Replacing Highly Enriched Uranium in Naval Reactors

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