nuclear power and public health measures in nuclear plant emergencies
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Nuclear Power and Public Health Measures in Nuclear Plant EmergenciesR. E. Toohey, Ph.D., CHP
Lesson ObjectivesFamiliarize students with the basic characteristics of nuclear power plant accidentsDescribe planning guidelines and considerations for accident responseApply considerations to the accidents at Three Mile Island and Chornobyl
The Fission ProcessFissile nuclideneutronneutronsFission products
Fission Product Yield by Mass
Approximate Distribution of Fission EnergyMeVKinetic energy of fission fragments 165Instantaneous gamma-ray energy 7Kinetic energy of fission neutrons 5Beta particles form fission products 7Gamma rays from fission products 6Neutrinos 10Total fission energy 200
Neutron BalanceNeutrons released in fission may be lost by escaping the container, or by being absorbed by non-fissile materialsIf more neutrons are lost than are produced, the reaction is subcritical and dies out (safe)If the number lost equals the number produced, the reaction is critical (steady state, e.g., a reactor)If the fewer neutrons are lost than are produced, the reaction is supercritical and energy release increases exponentially (e.g., a nuclear weapon)
Nuclear Reactor SchematicsPressurized Water Nuclear Reactor
Nuclear Reactor SchematicsBoiling Water Nuclear Reactor
Reactor AccidentsLoss of Coolant Accident (LOCA)Pipe breaks in the primary loop remove cooling water from the core, leading to an increase in core temperatureFuel rods fail, releasing volatile radionuclides (iodine, cesium, etc.)Core meltdownall the way to China?
What Really HappensFuel expands, reducing reaction rateReactor scrams with gravity-induced lowering of control rodsEmergency core cooling system activates and floods coreEven if core does melt, containment systems works, as at TMI
Reactor AccidentsMost likely route of exposure to the public would be a release to the air.Plume materials could consist of particulates, vapors, mists, or gases.Plume could be short duration (puff) or continuous.Particulates will tend to settle to the ground as the plume drifts from the plant.
Atmospheric ReleasesVolatile radionuclides may be released from containmentPrincipal radionuclide of concern is 131IReleases are monitored by sensors placed around plantPlume dispersal is mathematically modeled, taking local terrain into account
Airborne RadioactivitySource term - source of the exposureexamples - stack effluent, burning aircraft, etc.complex function of the material (quantity and type), flow rate,distribution,etc.units - activity/unit of time (e.g., Ci/sec; Bq/sec)Population/personnel exposureairborne (radioactivity) concentration [Ci/ml; Bq/m3]resuspended (ground/surface) contamination [Ci/ft2; Bq/m2 Ci/ml; Bq/m3]
Exposure PathwaysExternal dose from plume overhead (cloud shine) or material on ground (ground shine).Internal dose due to inhaling materials directly from plume or from stirred dust.Ingestion of contaminated materials in the form of food or water.
Emergency Planning ZoneAreas for which planning is needed to assure that prompt and effective actions can be taken to protect the publicPlume EPZ: radius of approximately 10 milesIngestion EPZ: radius of approximately 50 miles
Exclusion AreaAn area surrounding the plant such that an individual located at any point on its boundary will not receive a dose to the whole body exceeding 250 mSv (25 rem) nor a dose to the thyroid exceeding 3 Sv (300 rem) within 2 hours of the postulated incident
Classification of EmergenciesUnusual Event: a potential degradation of the level of safety of the plantAlert: readiness of on-site and off-site response organizations increased.Site Area Emergency: event resulting in major decrease in protection of public or on-site personnel.General Emergency: event resulting in risk requiring implementation of urgent off-site actions.
Who is Responsible for Actions?Staff at the facility at the time of the accident.Local officials.National and regional officials.
Accident responseIndependent of the type of accident:determine and control hazards to responders & victims assess, treat, evacuate victimsimplement further control proceduresassess personnel exposuresmonitor clean-upverify clean-up effectiveness
Exposure Guidance for RespondersAll activities:5 rem TEDE, 15 rem eye, 50 rem organProtecting major/valuable property:10 rem TEDE, 30 rem eye, 100 rem organLife saving or protecting large populations:25 rem TEDE, 75 rem eye, 250 rem organExceed latter only on a voluntary basis by persons fully aware of risks involved
Additional Guidance for RespondersRisk of injury in rescue and recovery operations shall be minimizedRisks to responders shall be weighed against benefits to be gainedRescue actions involving substantial personal risk shall be performed by volunteersEach individual subjected to emergency dose limits shall be thoroughly briefed
Some More Guidance for RespondersVolunteers above age of 45 preferredTEDE shall not exceed 1 Sv (100 rem)Internal exposure should be minimizedExposure under such conditions should be limited to once in a lifetimePersons receiving exposures above 250 mSv (25 rem) should avoid procreation for several months
Guidance for Population Protection: 1st PrincipleIntervention to avoid serious prompt health effects should be carried out as a first priorityserious prompt health effects may be expected in susceptible populations at doses > 1 Gy (100 rad), and in all at doses > 2 Gy (200 rad) (whole-body)evacuation is usually the only effective intervention measure in high dose situations
Guidance for Population Protection: 2nd PrincipleProtective actions to avoid delayed health effects should be initiated when they will produce more good than harm in the affected populationiodine prophylaxis in case of radioiodine releasessheltering in place, evacuation, or temporary relocation
Guidance for Population Protection: 3rd PrincipleThese actions should be introduced and withdrawn at levels that produce a maximum net benefit to the populationguidelines available from USEPA, IAEA, and IRPAmay well be driven primarily by logistical considerations (e.g., availability of transport, availability of temporary shelters, etc.)
Protective Actions Available to the PublicShelteringEvacuationStable Iodine ProphylaxisOther actions to reduce dose
Guidelines for Protective ActionsEarly phase: initiation of release to about 4 daysEvacuate to avoid TEDE of 1 - 5 remShelter in place if equal or greater protection afforded by doing soAdminister KI to prevent thyroid dose of 25 rem
Logistical Requirements for Early Protective ActionsSheltering:Normal emergency services; additional policeEvacuation:TransportationTemporary housing (schools, tentage, etc.)Food and waterSanitationIodine prophylaxis:KI tablets (or tincture of iodine on skin)
Intermediate Phase PAGsIntermediate phase: source or release is under control, and additional protective actions are being implemented; weeks to monthsRelocate to avoid 2 rem TEDE or 100 rem to skin in first yearApply dose reduction techniques (e.g., decontamination, hot spot removal) if less than 2 rem TEDE anticipated in 1st year
Late Phase PAGsLate phase: recovery phase; site remediation and long-term mitigation; months to yearsTEDE not to exceed 0.5 rem in any year after the firstCumulative dose (TEDE) from all years not to exceed 5 rem
Logistical Requirements forLater Protective ActionsTemporary relocation:TransportationHousing & furnishingsSecurityDecontamination equipment & waste disposalPermanent resettlement:TransportationHousing & furnishingsSecurity
Food Chain ConsiderationsEarly times: radioiodine pathway is air to soil to vegetation to cow to milk to manLate times: cesium and strontium pathways includeair to soil to food plants to manair to soil to forage plants to food animals to manair to water to aquatic vegetation to fish to man
Action Levels for Foodstuffs for General Consumption
RadionuclideAction Level89Sr103Ru, 106Ru134Cs,137Cs131I1 kBq/kg(30 pCi/g)90S0.1 kBq/kg(3 pCi/g)238Pu, 239Pu 241Am0.01 kBq/kg(0.3 pCi/g)
Action Levels for Milk, Infant Foods and Drinking Water
RadionuclideAction Level89Sr103Ru, 106Ru134Cs,137Cs1 kBq/kg(30 pCi/g)90S 131I0.1 kBq/kg(3 pCi/g)238Pu, 239Pu 241Am0.001 kBq/kg(0.03 pCi/g)
Logistical Requirements for Control of Food and WaterMonitoring capabilityCentralized distributionAlternate (distant) sourcesIn case of food shortages, alternate (higher) action levels should be instituted
Three Mile Island
Three Mile IslandUnit 2 feedwater pump tripped at 4:00 a.m. on March 28, 1979Reactor scrammed 8 seconds laterPressure relief valve stuck open, so ECCS water lostPressurizer (only way of controlling water level and pressure in primary loop) filling up, so high pressure injection pumps shut down
TMI, contCore partially uncovered by 6:15 a.m.Site emergency declared at 7:00 a.m.General emergency declared at 7:24 a.m.Radiation levels indicated fuel damage around 8:00 a.m.Core covered with water by 10:30 a.m.
TMI, contState route 441 closed at 12:45 p.m.Everything fairly calm the next dayBecause of confusion and concern over the hydrogen bubble, evacuation advised for pregnant women and preschool children with 5 miles at 12:30 on March 30Schools closed a