Making the Essential Ingredients of Nuclear Weapons. Matthew Bunn IGA-232, Controlling the World s Most Dangerous Weapons September 12, 2013

Transcription

1 Making the Essential Ingredients of Nuclear Weapons Matthew Bunn IGA-232, Controlling the World s Most Dangerous Weapons September 12, 2013

2 Two paths to the bomb The plutonium route Reactor: uranium fuel absorbs neutrons, makes plutonium Reprocessing plant: chemically separates plutonium from rest of spent fuel The highly enriched uranium (HEU) route Enrichment plant: separates nearly identical U-235 and U-238 isotopes Several techniques (gaseous diffusion, centrifuges, laser ) A few other isotopes could support explosive nuclear chain reactions, are not used in any stockpiled weapons None of these materials occur in nature; all are extraordinarily difficult to produce REPROCESSING ENRICHMENT

3 Two paths to bomb material: enrichment and reprocessing Enrichment 90% U-235, 10% U-238 (product) 0.2% U-235, 99.8% U-238 (tails) Natural Uranium: 0.7% U % U-238 Reactor Spent Fuel: 1% Pu, 99% U + FPs Pu (product) U Reprocessing HLW (FPs) Both routes start from mining uranium; both end with converting products to metal and making bomb components

4 Steps on the two paths Conversion to UF6 Mining Enrichment Milling Conversion to metal or UO2, fuel fabrication Conversion to metal and fabrication Reactor Reprocessing

5 Nuclear reactors a complicated way to boil water Source: Source:

6 Enrichment cascades Source: Alexander Glaser, Princeton University

7 A cascade for HEU (90%) Source: International Panel on Fissile Materials

8 A cascade for LEU (3-5%) Source: International Panel on Fissile Materials

9 Gaseous diffusion enrichment Originally dominated world enrichment Huge, readily observable facilities required Immense energy requirements United States, France still operating large diffusion plants but both planning to replace them with centrifuges Sources: USEC, Atomic Archive

10 Centrifuge enrichment Now dominates world uranium enrichment Far more efficient than gaseous diffusion: small, readily hidden facilities, modest energy requirements Technologically demanding A.Q. Khan network marketed technology to many countries including North Korea Key question: is North Korea making HEU? Sources: URENCO, Reuters

11 How centrifuges work Source: Alexander Glaser, Princeton University

12 P-1 (Ir-1) centrifuges at Natanz Source:

13 Enrichment: large cascades, accelerating success Need to hook up centrifuges in cascades of hundreds or thousands to get substantial enrichment of kilograms or tons Very non-linear process once enriched from 0.7% U-235 to 4.5%, ~ ¾ of the work of going to 90% U-235 is already done Hence, having stock of LEU could allow a country to enrich to HEU more quickly, or with a smaller, easier-to-hide facility Source: DOE

14 How difficult is enrichment? Differing evidence Iran: had complete centrifuges designs in ~ 20 years to operating cascade Building IR-1 centrifuges requires hard-to-get specialty materials, exquisite balancing, a very difficult-to-make bottom bearing Iran, Libya, N. Korea all pursued variants on this Source:

15 How difficult is enrichment? Differing evidence (II) But, United States, U.K., Australia, many other countries developed and built simple, good enough centrifuges in a few years with a few people Source:

16 Centrifuge plants: easy to hide Centrifuges take up little space, little power Plant to make enough HEU for 1 bomb per year could fit in this building, use less power than typical supermarket Uranium leakage is modest How to find them? North Korean centrifuge plant only identified when Siegried Hecker visited it North Korean centrifuge plant at Yongbyon Source: ISIS, image from Digital Globe

17 Producing plutonium Step 1: Irradiate uranium in a nuclear reactor, so that U-238 atoms absorb neutrons, become plutonium Step 2: Reprocess the irradiated uranium ( spent fuel ) dissolve it in boiling nitric acid, use series of solvent extraction steps to separate plutonium from uranium and radioactive fission products Typically (but not always) large, detectable facilities North Korean reactor at Yongbyon Source: Keith Luse, U.S. Senate staff

18 Plutonium production: Schematic of North Korean reactor Source: Sandia

19 North Korean reprocessing plant Source: Digital Globe

20 Civilian nuclear power and the bomb: How close a connection? Enrichment and reprocessing are the key technologies that pose serious proliferation risks Any country with either of these types of plants can decide to make nuclear bomb material at any time Having a civilian light-water reactor by itself does not get a country very close to the bomb Reactors under IAEA safeguards diversion would be detected Fresh fuel: low-enriched, can t be used in nuclear weapons Spent fuel: contains plutonium, would take reprocessing to get the plutonium out from the spent fuel But, civilian reactors provide: Base of personnel trained in nuclear matters and extensive contacts with other countries (which may lead to more sensitive transfers) Justification for pursuing enrichment, reprocessing Bureaucratic power base for nuclear advocates

21 Civilian nuclear power and the bomb: How close a connection? (II) These issues are the origins of several current controversies: Iran: says its enrichment is for peaceful purposes, and legitimate S. Korea: wants U.S. consent for pyroprocessing and enrichment Gold standard : UAE agreed to civilian nuclear cooperation agreement with United States that explicitly barred enrichment and reprocessing Vietnam, Jordan, Saudi Arabia resisting similar terms Nuclear Suppliers Group has just agreed on new criteria that should be met before any exports of enrichment and reprocessing technologies to countries that do not have them would be considered More on proliferation-resistance of civilian nuclear energy later in the course

22 Some (sometimes misleading) terms to remember Highly enriched uranium (HEU) Uranium with at least 20% U-235 As opposed to natural uranium (0.7% U-235), low-enriched uranium (LEU, typically 4-5% U-235), or depleted uranium (<0.7% U-235) Weapons-grade uranium Uranium with ~90% U-235 But bombs can be made with material far below weapons-grade Weapons-grade plutonium Plutonium with ~ 90% Pu-239 As opposed to reactor-grade plutonium (much less Pu-239) contained in spent fuel from typical nuclear power reactors Weapons-makers prefer weapons-grade plutonium, but reliable, effective weapons can also be made with reactor-grade plutonium (once reprocessed from spent fuel)

23 Backup slides if needed.

24 History of North Korean plutonium production first phase 1980 construction begins on 5 MWe reactor 1985 DPRK accedes to NPT under Soviet pressure (but does not complete safeguards agreement) 1986 reactor starts operation 1989 long shut-down how much fuel unloaded? 1991 U.S. unilaterally announces removal of all nuclear weapons from South Korea 12/1991 North-South Denuclearization agreement no enrichment or reprocessing facilities 1/1992 North Korea-IAEA safeguards agreement 9/1992 IAEA confirms discrepancies in North Korean declaration plutonium separated at times not declared

25 History of North Korean plutonium production first phase (II) 2/93 IAEA demands special inspections at DPRK waste sites 3/93 DPRK announces intention to withdraw from NPT, kicks out IAEA inspectors 6/93 DPRK suspends NPT withdrawal after U.S. talks 2/1994 DPRK agrees to resume IAEA inspections, averting Security Council sanctions 3/94 DPRK refuses inspectors access to reprocessing plant, Board of Governors demands it comply 5/94 DPRK begins removing plutonium-bearing fuel from its reactor, preparing to reprocess with no safeguards

26 Other enrichment technologies Calutrons grossly inefficient, energy hogging, but technology comparatively easy to get (used by Iraq) Lasers selectively ionize atoms or molecules of one isotope, then bend charged ones with magnetic field difficult technology, potentially small, efficient Many others chemical, aerodynamic Sources: DOE, UNSCOM

27 Nuclear reactors a complicated way to boil water Source:

28 Fuel assemblies fresh and spent NEI NEI

29 Some important reactor types Reactor type Fuel Moderator Coolant Pu production Light-water 4-5% U235 Light water Light-water R-Pu Graphite % Graphite Gas or water W-Pu or R-Pu CANDU % Heavy water Heavy water R-Pu or W-Pu Fast neutron 20-30%, or Pu None Liquid sodium, other W-Pu

30 Nuclear energy and proliferation Most nuclear weapons programs since civilian nuclear energy became widely established have had crucial contributions from the civilian sector Most programs: dedicated military production facilities for Pu or HEU, but civilian sector provided: source for open or covert technology acquisition cover for purchases actually intended for weapons program buildup of infrastructure and expertise A few programs: Pu or HEU directly from ostensibly civilian facilities -- or consideration of purchase of stolen fissile material