Radioactive Materials from U.S. Nuclear Plants

Transcription

1 Routine Releases of Radioactive Materials from U.S. Nuclear Plants Dave Lochbaum Union of Concerned Scientists August 2014 Revision i 1 1

2 The idea for this material came during a November 2013 workshop on radiation monitoring conducted by the Bellefonte Efficiency & Sustainability Team (BEST) and the Mothers Against Tennessee River Radiation at (MATRR) in Chattanooga, TN (check out Thanks to Garry Morgan and Gretel Johnston of BEST/MATRR for reviewing drafts and providing very helpful feedback. 2

3 Background Boiling Water Reactors Pressurized Water Reactors Browns Ferry and Sequoyah (click on link to jump to topic or hit the space bar to advance to the next slide or the ESC button to exit the slideshow) 3

4 Parts of an Atom 4

5 Sources of Radioactive Materials FISSION BYPRODUCTS atoms split into two smaller atoms, and not always the same two smaller atoms; many of these fission byproduct atoms are unstable and seek stability ty by emitting radiation in the form of particles or energy waves FUEL CLADDING INTEGRITY fission byproducts are retained within fuel rod cladding, but only when cladding remains free of cracks and holes TRAMP URANIUM dust and flakes from uranium fuel pellets can adhere to the outside surface of fuel rod cladding and/or the fuel bundle hardware as tramp uranium 5

6 Sources of Radioactive Materials ACTIVATION PRODUCTS non-radioactive material can become activated t by interactions ti with radiation (e.g., get hit by neutrons or gamma rays) while flowing through the reactor core CHEMICAL INJECTION many plants inject chemicals into the feedwater that coat pipes to retard rusting and corrosion; some of these chemicals get activated RADIOLYTIC DISASSOCIATION water molecules flowing through the reactor core can get broken apart into hydrogen and oxygen molecules; subsequent interactions involving oxygen and nitrogen molecules l can form Carbon-14 RUST AND OTHER PARTICLES debris in the water can get activated flowing through the reactor core 6

7 Types of Radioactive Emissions ALPHA PARTICLES are the nuclei of helium atoms stripped of their electrons. Their large size allows the skin to stop them, but their size and energy level can severely damage whatever they hit. BETA PARTICLES are electrons. Their small size enables them to travel farther than alpha particles, but their relatively low energy levels allows aluminum foil, paper, and plastic lens to stop them. 7

8 Types of Radioactive Emissions GAMMA RAYS are photons emitted during nuclear transformations. Although having the same energy levels as beta particles, these energy waves require denser materials, like lead, to stop them. NEUTRONS are neutral subatomic particles. Possessing up to four times the energy levels of beta particles and gamma rays, it takes larger amounts of dense materials, like concrete, to stop them. 8

9 Timing of Radioactive Emissions HALF-LIFE is the time required for half an inventory of unstable atoms to emit radioactivity en route to stability. Half-lives range from small fractions of a second to many tens of thousands of years. Atom A Atom B Example: Half Life, years Atoms at 0 years Atoms after years Atoms after 0.50 years Atoms after 1.0 year ATOMS A AND B have 0.25 and 1.0 year half-lives, respectively. If they decay via emissions of the same type and energy level, which is more hazardous? It depends on the time context. Within a year, Atom A will have emitted 87.5% more radioactive bullets than Atom B. But Atom B will have 8 times more radioactive bullets to fire in its future than Atom A. 9

10 Types of Radioactive Waste HIGH-LEVEL WASTES from nuclear power plants are essentially the spent fuel. High-level wastes remain onsite in wet pools and/or in dry storage pending the opening of a federal repository for them. LOW-LEVEL WASTES from nuclear power plants are primarily the materials contaminated through contact with radioactively contaminated water. These materials include the fibrous filter elements and demineralizer resins used to process water and consumables (such as mop heads, shoe covers, wipes, etc.) used to protect against and cleanup water. Low-level wastes fall into three categories - Class A, B and C depending on the concentrations of radioactivity with Class C containing the highestlevels. Low-level wastes can be shipped to government licensed burial facilities for disposal. 10

11 Types of Radioactive Releases BATCH deliberate and planned (usually) discharges of radioactive material to the air (e.g., from the waste gas decay tank of a pressurized water reactor) or to the nearby lake, river, or ocean (e.g., from the floor drain sample tank of a boiling water reactor) BATCH PROCESS - tank to be discharged is mixed first to allow for more homogeneous blending of its contents, workers sample and analyze the contents to check against release limits, and contents are then discharged 11

12 Types of Radioactive Releases CONTINUOUS steady, routine discharge of radioactive material to the air (e.g., via offgas system of a boiling water reactor) or to the nearby lake, river, or ocean (e.g., from the cooling tower blowdown system of a boiling water reactor or pressurized water reactor) CONTINUOUS PROCESS radiation detectors monitor continuous flow pathways to sound alarm and perhaps p even automatically terminate the discharge when high radiation levels are discovered 12

13 What Causes Releases to Increase? Failed Fuel! Source: Areva presentation (ML12194A373) 13

14 Links to Applicable Regulations 10 CFR DOSE LIMITS FOR INDIVIDUAL MEMBERS OF THE PUBLIC APPENDIX A TO 10 CFR 50 GENERAL DESIGN CRITERIA FOR NUCLEAR POWER PLANTS (ESPECIALLY CRITERIA 60, 63, AND CFR 61 LICENSING REQUIREMENTS FOR LAND DISPOSAL OF RADIOACTIVE WASTE 14

15 Links to Other References REG GUIDE 4.1 RADIOLOGICAL ENVIRONMENTAL MONITORING FOR NUCLEAR POWER PLANTS STANDARD REVIEW PLAN (SRP) 11.2 LIQUID WASTE MANAGEMENT SYSTEM STANDARD REVIEW PLAN (SRP) 11.3 GASEOUS WASTE MANAGEMENT SYSTEM STANDARD REVIEW PLAN (SRP) 11.5 PROCESS AND EFFLUENT RADIOLOGICAL MONITORING INSTRUMENTATION AND SAMPLING SYSTEM Return to Main Menu 15

16 Routine Releases of Radioactive Materials: Boiling Water Reactors Liquid releases Gaseous releases Solid releases 16

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18 Browns Ferry Fuel Performance Intact fuel rods preserve a barrier against discharge of fission byproducts to the environment. The Reactor Coolant System Activity performance indicator reflects fuel integrity the value increases when holes and cracks form in the metal walls of the fuel rods. 18

19 Browns Ferry Fuel Performance Results dating back to the year 2000 are online. 19

20 1.264 curies (1.42% of total liquid release) curies (98.58% of total liquid release) curies (0% of total liquid release) 44,043,000 liters (or 11,635,280 gallons) (i.e., scads of water) Source: TVA annual report 20 to NRC (ML14122A344)

21 Legend: Rarely radioactive Sometimes mildly radioactive Nearly always radioactive Drawing Source: TVA Browns Ferry Offsite Dose Calculation Manual, Rev. 21 (ML12123A018) 21

22 Browns Ferry Liquid Radwaste System Water leaked or spilled onto the floors as well as water used to clean components and areas is collected in the floor drain collector tanks. Water leaking from gaskets and seals that is collected in piping/tubing and carried to equipment drain sumps gets pumped to the waste collector tank. Water is treated, sometimes multiple times, before results from sample tanks show it is clean enough to be re-used or discharged to the river via the piping monitored by radiation monitor RM and volume recorded by flow indicator FI-77-60). 22

23 Browns Ferry Liquid Radwaste System Filters and resins are replaced when differential pressure across components or downstream chemistry indicates they have reached end of life. They are disposed of as solid waste. Drawing Source: TVA Browns Ferry Offsite Dose Calculation 23 Manual, Rev. 21 (ML12123A018)

24 Browns Ferry Reactor Building Equipment Drain Sump (right) 24

25 Browns Ferry Radwaste Tanks 25

26 Browns Ferry Liquid Radwaste System Water gets treated via filtration and demineralization to remove unwanted materials. Filteration uses fibrous cartridges to remove debris (e.g., rust flakes, cigarette butts, etc.) from the water. Used cartridges are disposed of as solid waste. Demineralizers use resin beads to remove dissolved materials (copper, salts, etc.) from the water. Used resin beads are either regenerated or disposed of as solid waste. 26

27 Browns Ferry Radwaste Resin Bags About the size and shape of sand, but way more expensive. Return to BWR Menu 27

28 curies (0.0015% of total gaseous release) curies (0.0135% of total gaseous release) curies (88.53% of total gaseous release) curies (11.45% of total gaseous release) Source: TVA annual report to NRC (ML14122A344) 28

29 Three Categories of Gaseous Releases 1) Elevated releases: discharges through the tall stack that t afford maximum mixing i of the gases being released curies of tritium released in 2013 (5.32% of total tritium gaseous release) 2) Ground-level releases: discharges from building vents that afford minimal mixing of the gases being released curies of tritium released in 2013 (14.42% of total tritium gaseous release) 3) Mixed mode releases: discharges from building vents but propelled upward by exhaust fans to provide moderate mixing of the gases being released curies of tritium released in 2013 (80.26% of total tritium gaseous release) 29

30 Browns Ferry Major Systems 30

31 15.23 curies of tritium released in 2013 (5.32% of total tritium gaseous release) Browns Ferry Gaseous Radwaste System (also called the Offgas System) This text box intentionally blank (until I typed in it) The Steam Jet Air Ejectors (SJAEs) pull air from the main condenser. Hydrogen (H 2 ) and oxygen molecules l are recombined and converted back to water. The remaining i gas and particles takes hours to flow through long, large-diameter piping before passing through charcoal filters and being discharged. Drawing Source: TVA Browns Ferry Offsite Dose Calculation Manual, Rev. 21 (ML12123A018) 31

32 Browns Ferry Offgas System Used during normal reactor operation curies of tritium released in 2013 (5.32% of total tritium gaseous release) Used during shutdowns and when power is no higher than 5 percent. Shutdown and low power p path includes less holdup and no adsorbers/filters. 32

33 229.8 curies of tritium released in 2013 (80.26% of total tritium gaseous release) An accident signal shuts down the normal ventilation systems and closes inlet and outlet dampers. The Standby Gas Treatment System (SGTS) starts to filter releases from the reactor building curies of tritium released at ground level in 2013 (14.42% of total tritium gaseous release) Drawing Source: TVA Browns Ferry Offsite Dose Calculation Manual, Rev. 21 (ML12123A018) 33

34 Turbine buildings with exhaust ducts/fans on roof Offgas exhaust stack Reactor buildings with exhaust ducts/fans on roof Return to BWR Menu 34

35 Return to Main Menu Return to BWR Menu Source: TVA annual report 35 to NRC (ML14122A344)

36 Routine Releases of Radioactive Materials: Pressurized Water Reactors Liquid releases Gaseous releases Solid releases 36

37 Offgas stack (see Alabama) Containment domes Turbine buildings with exhaust ducts/fans on roof 37

38 Sequoyah Fuel Performance Intact fuel rods preserve a barrier against discharge of fission byproducts to the environment. The Reactor Coolant System Activity performance indicator reflects fuel integrity the value increases when holes and cracks form in the metal walls of the fuel rods. 38

39 Sequoyah Fuel Performance Results dating back to the year 2000 are online. 39

40 curies (0% of total liquid release) 1,571 curies (100% of total liquid release) curies (0% of total liquid release) 882,700, liters (or 233,191,686 gallons) (i.e., scads of water) Source: TVA annual report to NRC (ML14118A380) 40

41 Sequoyah Liquid Radwaste System Drawing Source: TVA Sequoyah Offsite Dose Calculation Manual, Rev. 21 (ML13126A173) 41

42 Sequoyah Liquid Release Pathways Continuous release pathways Batch release pathway Continuous release pathway Drawing Source: TVA Sequoyah Offsite Dose Calculation Manual, Rev. 21 (ML13126A173) 42

43 Sequoyah Liquid Radwaste System Water leaked or spilled onto the floors as well as water used to wash down components and areas is collected in the floor drain collector tanks. Water leaking from gaskets and seals that is collected in piping/tubing pp gand carried to equipment drain sumps gets pumped to the waste collector tank. Water is treated, sometimes multiple times, before results from sample tanks show it is clean enough to be re-used (condensate storage tank) or discharged (via line monitored by RM ). Return to PWR Menu 43

44 53.82 curies (23.31% of total gaseous release) 0 curies (0% of total gaseous release) 0 curies (0% of total gaseous release) curies (74.78% of total gaseous release) 4.41 curies (1.91% of total gaseous release) ALL gaseous releases considered ground-level Source: TVA annual report 44 to NRC (ML14118A380)

45 Sequoyah Airborne Release Pathways Drawing Source: TVA Sequoyah Offsite Dose Calculation Manual, Rev. 21 (ML13126A173) Return to PWR Menu 45

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47 Return to Main Menu Return to PWR Menu 47

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49 Nearly one-quarter of a billion gallons of radioactively contaminated water in 2013 Return to Main Menu 49