a sequence of physical events - Three Mile Island

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the upper head of the reactor vessel. There is alsoa possibility of a dry "hot spot" within the core.][It is now believed that the gas was largely hydrogen.Hydrogen is slightly soluble in water, andits solubility is greater at high pressure. An attemptto depressurize the system would cause some ofthe dissolved hydrogen to effervesce out of the water,thereby increasing the amount of hydrogen inthe bubble. (An analogy is a capped bottle of carbonatedsoft drink. When the cap is firmly seated,the pressure is high and the carbonated gasremains dissolved. If the cap is removed, however,the pressure quickly drops, and gas bubbles out ofthe liquid.) The effervescence of hydrogen out ofthe water would interfere with attempts to depressurize.As the pressure dropped, the bubble wouldgrow in size and could interfere with circulation ofthe reactor coolant.][In addition to growing in size, the bubble and thedissolved gas would make it impossible to depressurizethe RCS completely. The pressure is controlledby the size of the steam bubble in the upperpart of the pressurizer. When this bubble containsonly steam, spraying colder water into the top of thepressurizer shrinks the bubble and reduces thepressure. When the bubble contains a gas like hydrogen,however, spraying does not reduce the sizeof the bubble as much, so there is less control overthe pressure.]Another problem with reduced pressure occurredin the letdown system. As explained, gas comesout of solution when the pressure is reduced. Thegas from the letdown water collected in the bleedtanks and makeup tank, increasing the pressureand making it necessary to vent the tanks often.The gas vented off, though, was not purehydrogen-there were small amounts of radioactivematerials as well. There was a limited space availablefor holding the gas released from the letdownflow. [See Figure II-8 for a schematic drawing ofthe gas venting system.][These two factors would make the reduction ofpressure an extremely slow process that tookseveral days to accomplish.][At 9:25 p.m. on March 28 (17 hours 25 minutesafter turbine trip), it was apparent that the utility believedpressure could soon be reduced to a level atwhich the decay heat system could be used.]Valve DH-V187 from the decay heat pump to the1A cold leg was opened at that time. [The reasonfor opening this valve must have been the utility'sintention to use the decay heat system shortly.]Unfortunately, there was still no bubble in thepressurizer; the pressurizer was reading off scale.The auxiliary building sump was full of contaminatedwater. The auxiliary building neutralizer tank(WDL-T8B) had been filled before the accident. At9:29 p.m. the operators commenced pumping thecontents of this tank to TMI-1, so that the auxiliarybuilding sump contents could later be pumped intoWDL-T8B. The transfer to TMI-1 was completed at12:20 a.m. on March 29.At 10:18 p.m. on March 28, it seemed that a bubblehad been reestablished in the pressurizer.About 30 minutes later, however, the bubble wasagain lost and the pressurizer returned off scale.At 10:34 p.m., letdown flow was lost. [It is believedlikely that the letdown coolers becameclogged with boric acid. Boric acid is more solublein hot water than in cold water. The extensiveboration during the accident might have caused acondition of saturation, so that when letdown waterwas cooled, boric acid precipitated out in the letdowncoolers and filters.]High pressure drop alarms, along with letdownflow alarms, began to come in shortly after midnightand continued through the early morning hours ofMarch 29.During these early morning hours, some radiationalarms also continued to be received. The auxiliarybuilding and fuel handling ventilation was shut offbetween 12:55 a.m. and 2:10 a.m. Shutting downthe ventilation caused radiation levels to increase inthe control room; so from 2:11 a.m. to 3:15 a.m., controlroom personnel were required to wear respirators.March 29,1979-4:35 a.m.At this time, the first of many ventings of themakeup tank MU-T1 was carried out. The wastegas decay tank vent header, to which the tank wasbeing vented, was leaking into the auxiliary building.At 4:43 a.m., the seal water temperature on reactorcoolant pump RC-P2A alarmed high. The operatorthen got a printout of the seal water temperaturesof all reactor coolant pumps. High temperatureswere found on pumps RC-P1B, RC-P2A, andRC-P2B (all nonoperating).Between 8:00 p.m. March 28, and 6:15 a.m.March 29, the pressure slowly decreased from 1300to 945 psig. A pressurizer bubble had been definitelyestablished at 4:00 a.m.; and by 6:15 a.m., thepressurizer level was down to 341 inches. Duringthis period, the cold-leg temperature hoveredbetween 230°F and 280'F.At 6:30 a.m. March 29, the pressurizer wassprayed down. The results were an additional 40-332
FIGURE 11-8. Gas Venting SystemGases vented from the makeup tank are piped to the waste gas vent header in addition togases from several other vents. Gas is pumped from the header to the waste gas decaytanks by the waste gas compressors. The gas is held in the decay tanks to allow decay ofpart of the radioactivity and is finally discharged to the atmosphere through the stationvent (a full chimney) after being filtered in the waste gas filters.
Page 2: COVER:A heat-sensitive DOE photogra
Page 5 and 6: 15. Public Announcements16. Board N
Page 7 and 8: 4. Estimates of Doses and Potential
Page 9 and 10: 7. Effects on Aquatic Biota and Fis
Page 11 and 12: IV.Safety Management Factors German
Page 13 and 14: A SEQUENCE OFPHYSICAL EVENTSThe fol
Page 15 and 16: polisher system are discussed in Se
Page 17 and 18: FIGURE 11-3. The Makeup and Letdown
Page 19 and 20: pumps 6 into the RCS. At TMI-2, the
Page 21 and 22: FIGURE II-5. The Once-Through Steam
Page 23 and 24: March 28,1979-4:30 a.m.At approxima
Page 25 and 26: still having trouble stabilizing th
Page 27 and 28: [The low steam pressure in steam ge
Page 29 and 30: [Leakage through the PORV had now b
Page 31 and 32: shut. Closing this valve, with pump
Page 33 and 34: Each of the two core flood tanks ho
Page 35: March 28,1979-3:10 p.m.At 11 hours
Page 39 and 40: perature in the loop A cold leg was
Page 41 and 42: Up to this time, degassing of the R
Page 43 and 44: oxygen in the presence of radiation
Page 45 and 46: B RADIOLOGICALRELEASES AND THEIREFF
Page 47 and 48: either trapped or chemically bound.
Page 49 and 50: FIGURE 11-9. Ventilation and Waste
Page 51 and 52: a representative sample of carbon r
Page 53 and 54: FIGURE II-10. Liquid Radioactive Wa
Page 55 and 56: cess radioactive material. The IWTS
Page 57 and 58: FIGURE 11-12. Release PathwaysConti
Page 59 and 60: tective efforts did not provide any
Page 61 and 62: TABLE 11-3. 1-131 releases-Continue
Page 63 and 64: TABLE 11-4. Calculated 1311 release
Page 65 and 66: The cleanup components installed in
Page 67 and 68: was made prior to the large influx
Page 69 and 70: TABLE 11-7. Analysis of TMI-2 conta
Page 71 and 72: TABLE 11-9. Inventories of radioact
Page 73 and 74: a. Offsite Radiological Environment
Page 75 and 76: COLOR PLATE I. LOCATION OF OOSIMETR
Page 77 and 78: These samples were later counted wi
Page 79 and 80: TABLE 11-12. NRC TLD locations-Cont
Page 81 and 82: TABLE II-13. Raw milk sample progra
Page 83 and 84: TABLE 11-14. Source locations for H
Page 85 and 86: TABLE 11-14. Source locations for H
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TABLE 11-14. Source locations for H
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TABLE 11-16. EPA milk sampling loca
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0331 3:28 a.m. GE-4; Fence, east Gr
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0331 9:03 p.m. '/4 east ofObservati
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April 6, 1979-By April 6, offsite e
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TABLE 11-20. Met Ed Teledyne and RM
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TABLE 11-21. Net exposures, attribu
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Table 11-22 contains daily data fro
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SW-1 0.9±0.1 0.8 1.2 ±0.3 1.1 ±0
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Other Collective Dose Estimate-Usin
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not have any discernible effect. Th
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em and dose rates on the order of r
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dose will, according to BEIR III es
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cancer, which corresponds to 175.8
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The technical specifications for TM
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that facility did not provide suffi
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FIGURE 11-17. Actual Organization o
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FIGURE II-18. "Normal" Emergency Or
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monitoring activities and Dubiel wo
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FIGURE 11-21. Emergency Radiation P
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clothing was exchanged for paper co
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As part of the training conducted b
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equipped with Geiger-Muller (G-M) t
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TABLE 11-37. Atmospheric monitoring
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SAM-2 in another kit was issued eve
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Preaccident Personnel Dosimetry-The
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ecommendations for correcting them.
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nel, reflect the continued inadequa
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that have evolved comprehensively a
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REFERENCES AND NOTES1 Met Ed, "Fina
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term Environmental Radiation Monito
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United Nations Scientific Committee
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302NRC, "Investigation into the Mar
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the emergency feedwater system, amo
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FIGURE 11-22. Pressurizer Surge Lin
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k)ss of heat removal from the prima
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main feedwater pumps and turbine ar
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Recommendations-The categorization
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through the break will not result i
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Findings-Under normal circumstances
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psig, 66although some reactor build
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A thorough evaluation should be per
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Shortly after their start the diese
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thereby providing high level coolin
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the service-instrument air cross-se
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Following recovery of hotwell level
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TABLE 11-44. Accident monitoring in
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TABLE 11-47. Information readouts a
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TABLE 11-47. Information readouts a
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2TABLE 11-47. Information readouts
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TABLE 11-49. Errors at most recent
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TABLE 11-51. Estimated data reliabi
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expected to survive environments mo
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TABLE 11-52. Sources of data about
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FIGURE 11-23. TMI-2 Isometric Schem
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FIGURE 11-25. The Pressurizer492
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COLOR PLATE IV. HOT AND COLD LEG TE
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egan to heat up. When the hottest p
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FIGURE 11-26. System Parameters for
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Steaming to Condenser.SRM-count rat
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emained open for more than 1 1 /2 h
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FIGURE II 2'1. Hydrogen Burn at 9.9
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PZR Vent and Spray Valves-closed.De
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
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of time, to determine a heat balanc
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locked to steam flow by hydrogen th
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two-phase mixture of water and stea
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e made for two reasons: (1) the act
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FIGURE 11-31. Fuel Temperature Hist
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Additionally, it is estimated that
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15 minutes (3 hours 21 minutes to 3
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system if all of the water removed
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FIGURE 11-32. Reactor Primary Syste
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eleased before melting. In general,
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the decay calculation. Table 11-57
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RadiolysisRadiation absorbed in wat
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principle-the compliance of a liqui
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Error AnalysisAn error analysis of
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Explosive Hazard in Reactor VesselA
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gression was such that a substantia
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TABLE 11-58. Timing of a meltdown a
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vessel steel are matters of conside
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Reactor Building Base Mat Penetrati
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1 Met Ed, "Final Safety Analysis Re
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Injection Signal Reset Following a
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175Id. at 18-21.176Electrical Power
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D ALTERNATIVEACCIDENT SEQUENCESIn t
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• failure of operators to recogni
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Two variations in the flow rates fr
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gression than alternative sequences
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TABLE 11-59. Description of alterna
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FIGURE II-39. Comparison of Base Ca
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lack of emergency feedwater after a
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FIGURE 11-42. Effect of Pump Trips
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egions occurring as the reactor coo
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TABLE 11-61. Typical containment de
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E HUMAN FACTORS1. INTRODUCTIONFrom
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FIGURE 11-44. PORV Indicator Light
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cable to this written procedure and
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FIGURE 11-46. EFW Control Station S
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accident; and (2) these errors resu
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guidance on the use of some very im
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TABLE 11-62. TMI-2 control room key
Page 295 and 296:
FIGURE 11-49. Visual Scan Necessary
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FIGURE 11-51. Relationship of Makeu
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FIGURE 11-53. Typical TMI-2 Alarm P
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than the other two, having only one
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• too many exceptions to the go-n
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tion or production facility," which
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5. classroom training course on TMI
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applicants for CRO licenses for nuc
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6. It took an archaic approach to l
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may be compared to nuclear powerpla
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evaluating the need for operator tr
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• misleading labeling due to viol
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encourage an increased rate of inco
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REFERENCES AND NOTES1 NRC, Investig
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' * Letter from Miller, Met Ed, to
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F ENVIRONMENTAL ANDSOCIOECONOMICIMP
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FIGURE 11-55. Map of Area621
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FIGURE 11-58. Initial Sources of In
Page 331 and 332:
FIGURE 11-59. Percent of Persons Sa
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FIGURE 11-62. Percent of Individual
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FIGURE 11-64. Respondents' Reasons
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FIGURE 11-66. Respondents' Evaluati
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considered changing jobs more frequ
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FIGURE 11-70. Respondent's Concern
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FIGURE II-71. Costs Per Evacuating
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three-tenths of 1% of annual person
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posed by the municipality and appro
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achieved with volunteer labor, addi
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eady done so. Within 15 miles, an e
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APPENDIX 11.1I NTRODUCTION TOSEQUEN
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EventNumberDateTimeafterinitiationE
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EventNumberDateTimeafterinitiationI
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EventNumberDateTimeafterinitiationI
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APPENDIX 11.2CARBON PERFORMANCEWITH
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presented in App. Table 11-2. The g
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APP. TABLE 11-4. Physical propertie
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APPENDIX 11.3RADIOLOGICAL ENVIRONME
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Sampling locations are shown in Fig
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APPENDIX 11.4OFFSITE RADIOLOGICALMO
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APP. TABLE 11-7. Field Ge(Li) and H
Page 425 and 426:
APP. FIGURE 11-2. EML Measurement S
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APPENDIX 11.5ATMOSPHERIC RELEASE AD
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they did not have enough familiarit
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APPENDIX 11.6RADIOLOGICAL CHRONOLOG
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ITEM DATE AND TIME EVENT DESCRIPTIO
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Page 437 and 438:
Page 439 and 440:
Page 441 and 442:
REFERENCES AND NOTES1 NRC, "Investi
Page 443 and 444:
The apparent surface area isFor Apr
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APPENDIX 11.8TMIBOIL CODE CALCULATI
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APP. TABLE 11-8.TMIBOIL calculation
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APP. FIGURE II-3. Fuel Temperature
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APP. FIGURE 11-7. Fuel Temperature
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APP. FIGURE II-11. Fuel Temperature
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Page 457 and 458:
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Memorandum from G. P. Marino and J.
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This equation (which contains no ap
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We have not included the effects of
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APP. FIGURE 11-22. Bubble Volume at
Page 467 and 468:
a) The fugacity coefficient of hydr
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TABLE 1. Hydrogen solubility dataTe
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APP. FIGURE 11-24. Hydrogen Solubil
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APP. FIGURE 11-26. B&W Test #5-Prop
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APP. FIGURE 11-28. B&W Test #7-Prop
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APP. FIGURE 11-30. Reactor Coolant
Page 479 and 480:
2. EXCERPTS FROM TMI-2 SENSITIVITYS
Page 481 and 482:
APP. FIGURE 11-32. Relative SRM Res
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tegration over time dependent varia
Page 485 and 486:
A99 FIGURE D-33 Plots of Input Data
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APP. FIGURE 11-35. Postulated Core
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APP. FIGURE 11-37. Postulated Core
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APP. FIGURE 11-39.SRM Reading Versu
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4. ALTERNATE INTERPRETATION OFTHE A
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etween about 740 and 775 minutes (1
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APP. FIGURE II-43. Hydrogen Pressur
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APP. FIGURE 11-45. Hydrogen Pressur
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APP. FIGURE II-47. Water Flow Rates
Page 503 and 504:
APP. FIGURE 11-49. Water Height in
Page 505 and 506:
APP. FIGURE 11-51. Temperature Leve
Page 507 and 508:
ing fuel (G. W. Parker et al. ORNL-
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a sequence of physical events - Three Mile Island

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