Using Nuclear Materials To Prevent Nuclear Use and Proliferation

G.P.Gilfoyle and J.A.Parmentola
ASCO, Defense Threat Reduction Agency

While the end of the Cold War greatly reduced the threat of an all-out nuclear war between the United States and the Russian Federation, it created a new set of challenging national security concerns. The political and economic volatility in Russia has resulted in growing fears about the lack of fissile material security there and raised the specter of this material falling into the hands of `rogue' nations, terrorists, and other opportunists. While a nuclear blast would have dire consequences even acquisition of weapons-grade, nuclear material by such groups would damage US interests. In this note we describe a way of significantly reducing these threats by making it easier to detect smuggled fissile material and creating a nuclear fingerprint to aid law enforcement in identifying the source of a `leak'.

We propose uniformly mixing specific substances into fissile materials to act as intrinsic tags. The tags work in two ways. First, they brighten the radioactive signature of highly-enriched uranium (HEU) making it easier to detect. HEU emits far less radiation than plutonium and is more difficult to detect. The HEU tag emits a high-energy, penetrating gamma ray that would set off passive, non-intrusive monitors located at nuclear facilities, border stations, and other choke points; making theft of the fissile material much more difficult. There is no need to intensify the plutonium signature because it is already bright. Second, the tags provide the opportunity to perform attribution on stolen plutonium or HEU. A storage-site-specific amount of the tag is added to the fissile material during chemical processing which associates the tagged material with the site; different amounts label different sites. If material is stolen and later recovered, analysis of it with readily available techniques would identify the source (the nuclear fingerprint) and enable law enforcement to cut off the leak at its source.

The best choices for the intrinsic tags are a mixture of ²³²U and ²³³U for HEU and ²⁴⁴Pu for plutonium. For the HEU, the ²³²U produces a high-energy gamma ray that brightens the signature. The ²³³U tags the material and enables attribution to be performed. For plutonium the addition of the ²⁴⁴Pu identifies the material. The tags are difficult to defeat. The amount of each tag added to the fissile material is far above any background contamination and the tags cannot be readily removed since they are the same chemical element as the tagged material. They are safe and don't disrupt later use of the nuclear material as reactor fuel because they are added in small amounts.

This proposal exploits a unique confluence of opportunities to make fissile materials more secure at a small incremental cost. First, the US and Russia have already embarked on several efforts to enhance fissile material security. Two of these are development of the Fissile Material Storage Facility (FMSF) in Russia (at a US cost of $1.3 billion) and the US purchase of Russian highly-enriched uranium for $20 billion. Nuclear weapons components will be dismantled and the plutonium (and possibly HEU) stored in the FMSF. The HEU purchase agreement will involve 500 metric tons of HEU through the year 2013 for use as reactor fuel. Much of the HEU will remain in storage for some length of time before final processing. Both programs will process fissile material; opening a pathway to introduce the intrinsic tags. Second, adequate supplies of the tagging materials already exist in US stockpiles. Plans are being developed at DOE for the final disposition of this excess radioactive material. We propose re-directing some of it to tags that would significantly enhance fissile material security at a cost of several tens of millions of dollars for the additional processing. Third, the US and Russia have already begun installation of detectors at nuclear facilities, border stations, etc. The tags will make this existing program more effective at intercepting smuggled nuclear materials.