1. Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
2. Union of Concerned Scientists, Washington, DC, USA.
3. Nuclear Science and Engineering Program, Department of Mechanical Engineering, Colorado School of Mines, Golden, CO, USA.
4. IBM Thomas J. Watson Research Center, Yorktown Heights, NY, USA.
5. Program on Science and Global Security, Princeton University, Princeton, NJ, USA.