Santa Susana Field Laboratory y Energy Technology Engineering Center Sodium Reactor Experiment Accident Sodium Reactor Experiment Accident Sodium Reactor Experiment Accident Sodium Reactor Experiment Accident July 1959 July 1959 August 29, 2009 Dr. Paul S. Pickard Sandia National Laboratories Sandia Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, National Laboratories for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. 1
SANDIA NATIONAL LABORATORIES Livermore, Sandia's Primary Mission Areas: Sandia's Primary Mission Ar eas: Albuquerque, California New Mexico • Energy, Resources and Nonproliferation • Defense Systems & Assessments • Homeland Security & Defense H l d S it & D f • Nuclear Weapons Sandia Labs Other Locations Kauai (HI), Carlsbad (NM), Tonopah (NV) Space Systems Renewable Energy Research Radiation Effects Research Basic Sciences Nuclear Energy Inertial Confinement Fusion Large-Scale Tests Safety Research 2
Presentation Purpose and Approach Presentation Purpose and Approach • Purpose: Purpose: – Overview of nuclear reactor technology relevant to the Sodium Reactor Experiment (SRE) – Description of the cause and D i ti f th d progression of the accident and fuel damage that occurred in July 1959 SRE Facility (1957) • Approach: – Reviewed available information on SRE design and July 1959 reactor accident – Review focused on accident causes and resulting fuel damage Review focused on accident causes and resulting fuel damage – Review covered only 2 weeks of operations at the site and did not include subsequent recovery activities or other Area IV operations 3
Presentation Outline Presentation Outline • Background – early nuclear reactor technology • Description of SRE reactor • July 1959 sequence of • July 1959 sequence of events • Reactor fuel damage • Fission products* release mechanisms • Comments and observations S SRE Facility (1958) ( ) * Fission products are the atomic fragments left after a large nucleus fissions 4
Early Nuclear Power Reactor Development Water and Sodium Cooled Systems • Early nuclear power reactor development focused Early nuclear power reactor development focused primarily on Light Water cooled Reactors (LWR) - Water cooled reactors were selected for Naval applications - Water cooled reactors were already being Water cooled reactors were already being commercialized - LWRs have limited efficiency (~33%) due to low temperature operation (~350 º C, 660 º F) - LWRs operate at high pressures (~2200 psi) • Sodium (liquid metal) cooled reactors with Shippingport Pressure Vessel graphite moderators were considered promising Operational – 1957 p ETEC 1985 ETEC 1985 options for achieving higher efficiencies ti f hi i hi h ffi i i (60 megawatt-electric) • Sodium cooled reactors could operate at - Higher temperatures, higher efficiencies - But still operate at lower pressures B t till t t l 5
Overview of Area IV Reactor Operations Overview of Area IV Reactor Operations Reactors Operated within Area IV (1956 – 1980) p ( ) Power, Operating Facility Name • Area IV – research focused on kW t Period development of new types of Kinetics Experiment Water Boiler 1 07/56 -11/66 nuclear power reactors L-85 Nuclear Experiment Reactor 3 11/56 - 02/80 Sodium Reactor Experiment Sodium Reactor Experiment 20 000 20,000 04/57 - 02/64 04/57 02/64 • SRE was the largest of the 10 S8ER Test Facility 50 09/59 - 12/60 reactors operated in Area IV SNAP Environmental Test Facility 65 04/61 - 12/62 Shield Test Irradiation Facility 50 12/61 - 07/64 S8ER Test Facility 600 05/63 - 04/65 Shield Test Irradiation Facility 1 08/64 - 06/73 SNAP Environmental Test Facility SNAP Environmental Test Facility 37 37 01/65 01/65 - 03/66 03/66 SNAP Ground Prototype Test Facility 619 05/68 - 12/69 kW t = kilowatt-thermal SNAP = Systems Nuclear Auxiliary Power Sodium as a Coolant ETEC 1985 ETEC 1985 - Low pressure operation (boiling point of 883º C, 1621º F ) - Excellent heat removal - Flammable in air - Can become radioactive - Melting point of 98º C, 208º F 6
Experiment Description Sodium Reactor 7
Overview of S di Sodium Reactor Experiment (SRE) R t E i t (SRE) Design Rendition of • The SRE was a 20 megawatt-thermal (MW t ), low g ( t ) SRE Facility (1957) pressure sodium cooled nuclear reactor • Purpose of the SRE was to investigate different nuclear fuel materials and the use of sodium as a coolant a coolant • SRE was operational from 1957 to 1964 • SRE did not operate on a continuous basis - each experiment (or run) lasted up to a few each experiment (or run) lasted up to a few weeks • Experiments were conducted under varying operating conditions in order to test designs and components, which required frequent Below Ground startups and shutdowns, and refueling operations • During Core I operations involving uranium During Core I operations involving uranium metal fuel; 14 experimental runs were conducted between 1957 and July 1959 SRE Core and Vessel 8
SRE Core and Vessels SRE Core and Vessels Control Rod Drive Below Ground Concrete Plug Concrete Main Auxiliary Sodium Sodium Cover Gas Outlet Outlet Sodium Tank Main 6 ft Sodium Inlet Handling of Upper Concrete Plug Handling of Upper Concrete Plug Auxiliary Sodium Inlet Core Tank 6 ft 19 ft Fuel Bundle Thermal Shield Thermal Shield C Concrete t Graphite (5.5 inches steel) Moderator Stainless Grid Plate Steel 11 ft SRE Upper Concrete Plug Vertical Section of SRE Reactor 9
SRE Fuel Bundle and Moderator Can 11 11 inches inches Vent Tube Hanger Cross-section of moderator can containing fuel bundle comprised of 7 ft. f fuel rods l d Approx. 6 Other Nonfuel Tubes Control Rod Safety Rod Zirconium Fuel Bundle (Metal) Neutron Source Can Graphite Moderator Hexagonal Moderator Cans Moderator Can Containing Fuel Bundles (Top View) Fuel Bundle Assembly 10
SRE Fuel Bundle SRE Fuel Bundle 0.75 inch Diameter Fuel Slugs 0 090 inch 0.090 inch Hanger Rod • Uranium metal fuel 0.010 inch Stainless Steel Tube • 2.7% U-235 enrichment Helium Filled (natural uranium is 0.7% (natural uranium is 0 7% 0.010 in NaK Bond Expansion Space U-235) Fuel Rod Jacket (NaK filled) prox. 6 ft. • Fuel slugs are 0.75 inch 6 inch Fuel Slugs diameter and 6 inches in length length App 6 inches Stainless Steel • Clad in stainless steel tubes cladding • Sodium-potassium (NaK) NaK Bond 6 inches bonding between fuel and bonding between fuel and cladding Fuel Slugs 6 inches (12 total • Wire wrap around fuel per rod) bundles 0.75” Fuel Rod 7-Rod Fuel Bundle 11
SRE Fuel Bundle Cooling SRE Fuel Bundle Cooling Control Rod Drive Below Ground Concrete Plug Stainless Concrete Steel Cladding Main Auxiliary Sodium Sodium Sodium NaK Bond Cover Gas Coolant Outlet Outlet Flow Sodium Tank 6 ft 6 inch 6-inch Fuel Slugs Auxiliary (12 per rod, Sodium Inlet 84 per bundle) Core Tank 6 ft 19 ft Fuel Bundle 0.75” Thermal Shield (5.5 inches steel) Graphite Moderator Grid Plate 11 ft 12
SRE Cover Gas and Venting S System Under Normal Operations t U d N l O ti • Gaseous activation products* Gaseous activation products produced during normal operations would collect in the cover gas • Cover gas was pumped to storage tanks to allow activation products to decay • After decay to acceptable release levels, storage tanks were vented to atmosphere t d t t h through a HEPA filter and stack • Stack was monitored with radiation alarms and radiation alarms and automatic shut-off valves to prevent release of activation products exceeding acceptable levels * Activation products are materials made radioactive by neutron activation 13
SRE Cooling Systems SRE Cooling Systems SRE Cooling System Features SRE Cooling System Features • SRE core could produce up to 20 MW t of power • Primary sodium cooling loop P i di li l removed heat to an intermediate heat exchanger • Secondary sodium loop isolated Secondary sodium loop isolated core and radioactive coolant from power generation system • Numerous other pumps and valves • Numerous other pumps and valves existed to startup and control system operations 14
Barriers to Release of Fission Products under Accident Conditions d A id t C diti • Multiple barriers were used to M lti l b i d t minimize release of radioactive Cover Gas materials - fuel SODIUM SO SOLID FUEL – retains most fission U products in matrix unless melted - cladding or vaporized - coolant METAL CLADDING – fission SOLID products release if cladding is FUEL - vessels breached • Physical and chemical SODIUM – reacts with some fission products characteristics of different fission products affected the probability of release from fuel or coolant in an accident 15
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