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Remarks to the President’s Council of Advisors on Science and Technology (PCAST) on Defense Nuclear Nonproliferation Research and Development by Deputy Administrator Anne M. Harrington

March 08, 2011

Introductory Comments

We are fortunate to have an Energy Secretary who is a Nobel laureate and reminds us every day that science and technology are at the heart of everything we do.  Secretary Chu understands the need to invest in science, technology and engineering to support our missions.  With support from the President, the Department and NNSA are making major investments in the people, the infrastructure, the facilities, and the ST&E base to support nuclear security efforts around the world. 

NNSA’s Defense Nuclear Nonproliferation programs play a central role in implementing the President’s nuclear security agenda.  Our programs to secure nuclear and radiological materials often are in the spotlight, but our efforts to pre-empt the diversion of material through our material protection, control and accounting (MPC&A) and Second Line of Defense are no less critical.  Programs that promote the adoption of nuclear security standards, develop and implement export controls, and address the proliferation of weapons-relevant knowledge are also an important part of our portfolio of activities, as are our efforts to meet the U.S. commitment to dispose of excess weapon-useable material through disposition programs.

Radiation Detection Equipment (RDE) and New Start

The New START Treaty is different from START agreements in that actual numbers of deployed warheads are verified during inspections.   Counting rules existed under START, but there existed counting rules that attributed warhead numbers based on delivery vehicle type.  The parties were not permitted to deploy more reentry vehicles (RVs) on a given missile type than the number of warheads attributed.   Verification essentially came down to counting shrouded bumps on a missile front section to confirm that the number of RVs present did not exceed the number permitted. 

Under New START each party will verify that the number of RVs on a specific system match the number of warheads declared.  Objects deployed on the front section of a missile will be counted as nuclear RVs unless demonstrated to be non-nuclear, which can be accomplished using radiation detection equipment (RDE) designed to detect neutrons that would be emitted from the plutonium in a nuclear weapon.  Fast neutrons are uncommon in the background and their detection is a strong indicator of the presence of plutonium.  

The U.S. detector consists of a 3He-filled tube surrounded by polyethylene and encased in cadmium.  The cadmium layer stops thermal neutrons that are more common in the background while allowing fast neutrons to pass.  Fast neutrons are slowed down by the polyethylene layer and counted with good efficiency by the helium 3 tube.  The output is a neutron count rate, which in the case of New START must remain below a threshold close to background to confirm that the object presented as non-nuclear is in fact non-nuclear.  

Technology Beyond New START

While the New START treaty requires the ability to determine that an object is not a nuclear warhead, for a future regime that limits total stockpiles of warheads, including non-deployed warheads, it will be necessary to confirm that an item is a nuclear warhead, particularly for items in storage or otherwise not directly associated with a deployed delivery system.  In addition, the ability to count deployed weapons in situ with high confidence may be highly desirable from an operational point of view. 

NNSA has pursued the technical means to verify warhead presence for several years, and technologies are currently being developed within the NNSA Complex that are likely to be able to count warheads in situ with minimal operational impact.  One example would be coded- aperture thermal neutron imaging.  Neutrons cannot be focused with lenses like light, but it is possible to form an image without a lens using a variation of the child’s pin-hole optical camera.  Instead of a pin-hole, the neutron camera uses a mask with an irregular grid of neutron blocking areas and open areas, a so called coded-aperture.  This approach allows approximately one-half of the neutrons to be counted and so is much more sensitive than a pin-hole where most of signal is lost.  The neutrons that reach the backplane, where the film would be in a pin-hole camera, can then be used to construct an image using a simple computer program.  There are several advantages to this technique including the fact that thermal neutrons can travel many meters through a variety of intervening material, neutrons from the background do not point back to the source and thus do not contribute to the image, and the data reveals little or no design information and can be shared by the two parties.  The result is an image that represents a warhead as a bright spot on a dark background without the need for any a priori knowledge of the weapon, and without the need for any type of information barrier.

A number of other technologies are also under development to address warhead counting including gamma imaging, fast neutron imaging, and template matching techniques using both gamma and neutron signals.  Many of these techniques have the possibility of revealing classified information, so the scope of potential information release will need to be assessed, and appropriate information barriers will needed to be considered, such as those used in an experiment on warhead dismantlement that was concluded last year by the UK-Norway.  We are confident that the vast experience and tremendous scientific talent within the NNSA Complex can provide the technical solutions to future arms control agreements, although it will be necessary to conduct the early research far in advance of any formal requirements.  We also hope to strengthen our approach by finding appropriate ways to work with international partners, who ultimately must be involved.

Dismantlement and Disposition

As the numbers of warheads in stockpiles shrink, the need for high confidence in the declared numbers becomes more urgent.  In order to increase confidence that declarations are correct, more intrusive measurements and procedures will be required. At the same time, certain types of sensitive information must not be revealed. Technologies designed specifically to make highly intrusive measurements to provide high confidence while not revealing sensitive information -- “information barriers”  --  generally rely on a computer to make automated measurements and execute analysis algorithms to determine the truth of the declaration.  The actual sensitive data are not stored, and a simple result of the measurement is displayed, such as a pass/fail indicator. The problem of trusting the declaration is then transferred into a new problem of trusting the computer and its sensors and programs.

Moreover, the computer can be designed to be entirely non-sensitive in every detail, including every line of code. In fact, the computer might ideally be developed jointly by experts from both host and inspecting parties. Considerable study has already gone into describing this type of technology, and the associated procedures for its use, but there are still many issues to be resolved, many of which evolve with time because of the increasing complexity of electronics components and software.

Depending on the specifics of future regimes that require warhead dismantlement verification or transparent processes for fissile material disposition, new technologies will be needed to uniquely identify a weapon removed from active status, transport and store it securely, disassemble that weapon, store its fissile material, and then dispose of the fissile material with monitoring and attribution along each step of the process.  The technology is under development and could incorporate an information barrier to prevent revealing sensitive information, such as certain design information.  The detector would give a yes or no answer on the attributes of the weapon, or on its match against a pre-established template.  The weapon could then be transported and stored under appropriate secure tags and seals until dismantlement. 

At the dismantlement facility, the weapon would be dismantled by the host country and inspected by the verifying party without the verifying party actually seeing the disassembled weapon.  We anticipate that at one or more points during the dismantlement process, the weapon would be placed in a container to hide design data and measured using radiation detection equipment to determine that the fissile material is still consistent with what should be in the weapon being dismantled. Again, this will likely require some form of an information barrier to protect sensitive information. New technology using ultra-fast detection and timing to measure correlated gamma and neutron signals of fissile material, are being developed to provide high accuracy and high confidence measurements of nuclear material throughout dismantlement. 


NNSA’s Defense Nuclear Nonproliferation Programs meet daily challenges by drawing on the scientific, technical and engineering across the nuclear security complex and by engaging the best talents in our universities and research centers, and with industry to bring new technology to the market.  These investments not only address the nonproliferation and arms control challenges we face today, but helps foster and challenge a new generation of expertise that will respond to our challenges in the future.  Maintaining and exercising this expertise is essential to supporting our work in defense of the nation and the President’s nuclear security agenda.