Blog Post - Nuclear Security Matters

What Kind of Material Needs What Level of Security?

| Apr. 15, 2014

In August of 2002, the United States – assisted by a gift from the Nuclear Threat Initiative, when it turned out no U.S. agency had money that was not blocked from doing what was needed – helped airlift 48 kilograms of 80% enriched highly enriched uranium out of the Vinca nuclear research institute in Serbia.  A force of 1,200 armed troops guarded the shipment as it moved from the lab to the airport.  Under international rules, this was dangerous “Category I” material requiring the highest level of security. But under Department of Energy (DOE) rules for categorizing nuclear material, if the same material had been at a DOE site, it would have been considered “Category III” material requiring hardly any security.

Clearly there are serious disputes about what material terrorists could most easily make a bomb from, and therefore which material requires the most security.  Unless the world gets this right, nuclear security resources will be focused on the wrong places.  In a recent talk, I outlined an approach – described in more detail in a forthcoming book – for adjusting the security required for different kinds of material based on how much chance terrorists would have of making a bomb if they got that particular type of material.  Factors that should be considered include isotopics, chemical form, weight and mass, and level of radioactivity.

HEU awaiting secure transport
by rail (NNSA photo)

One important piece of progress on this front in recent years has to do with how much radiation is enough to scare terrorists off from stealing nuclear material.  Both U.S. and international rules used to say that if someone a meter away from the material would get a dose from it of one Sievert per hour, the material was “self protecting” from theft, and could have much less security.  But careful time-and-motion studies suggest that level of radiation would not be remotely enough to stop thieves who did not care about their own health from carrying out a theft.  To actually disable someone while the theft was taking place would require a dose rate of many tens of Sieverts (thousands of rads) per hour.  Hence, the latest DOE rules say you cannot reduce the level of security for nuclear material based on its radiation level unless it is radioactive enough to ensure “a high probability of failure of task(s) by an adversary” – that is, they will be disabled by the radiation while the theft is still under way. And the latest IAEA recommendations suggest that states should “carefully consider” not reducing the level of security based on material’s radiation if their design basis threat includes adversaries “willing to commit a malicious act.”

The Nuclear Regulatory Commission (NRC) is also working on rules that would get rid of the ineffective “self-protecting” criteria of the past.  But in the same revision the NRC staff are also proposing to reduce security requirements substantially for HEU or plutonium that is mixed with other material so that it is less than 20 percent of the total weight.  In my talk I argue against this approach, pointing out that the amount of material that would have to stolen is still well within adversaries’ likely capabilities, and any state or group able to do the difficult job of making a nuclear bomb from pure plutonium or HEU is likely to have a good chance of doing the easier job of getting pure plutonium or HEU out of, for example, fabricated HEU research reactor fuel or fabricated plutonium-uranium mixed oxide (MOX) fuel.  In the 1970s, the NRC concluded (correctly, in my view) that separating plutonium from MOX fuel not yet used in a reactor would require “relatively modest facilities and effort” and hence “lowering the concentration of plutonium through blending should not be used as a basis for reducing the level of safeguards protection.”  This rule revision is still in development, so where it will end up remains to be seen.

For another perspective on nuclear security and MOX, read Ed Lyman’s “The Nuclear Security Summit Communiqué Statement on Separated Plutonium Is a Step Backward.”

For more information on this publication: Please contact the Belfer Communications Office
For Academic Citation: Bunn, Matthew.What Kind of Material Needs What Level of Security?.” Nuclear Security Matters, April 15, 2014,

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