核反应堆工程核反应堆工程 (5).ppt
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1、Nuclear Engineering ReactorBWR and Fukushima NPP Accident 1.The accident process(after the earthquake)2.The accident process(after the tsunami)3.The accident process(Unit 1)4.The accident process(Unit 3)5.The accident process(Unit 2)6.DiscussionOverviewThe accident process(after the earthquake)March
2、 11,2011,about 14:46:magnitude 6-strong earthquake hitsUnits 1 through 3 were in normal operation,and 4 through 6 were in scheduled shutdown.Units 1 through 3 automatically SCRAMed,operators switched the electric power to the site to an external power sourceAt the same time of the switching,external
3、 power was lost and the emergency D/Gs kicked in automatically.Steel TowerEmergency D/GThe accident process(after the earthquake)March 11,about 14:50:Unit 2 RCIC started manuallythe operator manually started the RCIC with remote operation.RCIC automatically stopped because of high water level.Eleven
4、 minutes later,the operator restarted the RCIC.March 11,2011,14:52:Unit 1 IC started automaticallythe operator started and stopped the IC three times,controlling the reactor pressure at 6-7 MPa.March 11,15:05:Unit 3 RCIC started manuallyAt about 15:25,on detecting high reactor water level,the RCIC s
5、topped automatically.Conceptual sketch of the IC.Proceeded normally!March 11,about 15:27:first tsunami waveIt was low enough to not cause damage that led to the SBO.March 11,about 15:35:second tsunami waveThis wave caused the loss of almost all electric power sources.The plant response headquarters
6、were set inside the seismic isolation building in a room with no windows and no cameras to look outside.loss of AC power with all units and even DC power with Units 1,2,and 4.The accident process(after the tsunami)the starting point of this severe accident Elevations of Elevations of Fukushima-1Fuku
7、shima-1The accident process(after the tsunami)This picture shows the areas affected by the tsunami at the fukushima daiichi nuclear power plant(Blue:flooded area)Almost all of the plant were submerged福岛第一核电厂受海啸影响的情况福岛第一核电厂受海啸影响的情况Assumed highest tsunami water level O.P.+5.7mInundation heightapx.O.P.
8、+14-15mFukushima The accident process(after the tsunami)March 11,about 15:35:second tsunami waveThe states of water submergence were about the same for Units 1 through 3.Seawater entered the turbine buildings from the equipment hatch and ventilation holes to flood the basement and the concourse floo
9、r between the basement and first floor of the turbine,control,and reactor buildings.The basement of the turbine buildings contained the emergency generators and the regular and emergency switchboards.The control building basements contained the DC power systems(Units 1,2,and 4)The reactor building b
10、asements contained the pumps and other equipment for RCIC and HPCIThe accident process(after the tsunami)the sea water pumps fails,the nuclear rectors loses its heat sink to the oceanAll units that were up and running at the time of the accident had lost their ultimate heat sinks Locations of emerge
11、ncy D/Gs and their Locations of emergency D/Gs and their switchboardsswitchboardsThe accident process(after the tsunami)March 11,15:37-42:loss of all AC powerExcept for the Unit 6 air-cooled emergency D/G(6B),all AC power sources for Units 1 through 6 were lost.Units 1 and 2 lost their DC power as w
12、ell.Unit 3 had its DC power on the concourse level between the basement and first floor.The unit was covered with water,but managed to retain its function;Unit 3 allowed operation of its RCIC and HPCI for a few days.All M/C switchboards and most of the P/C switchboards were submerged and had lost th
13、eir functions.The description“the earthquake destroyed the external power source,and then the tsunami submerged the emergency D/G to cause the total loss of AC power”is wrong!The accident process(after the tsunami)SwitchboardsUnits 1-4,all the M/C switchboards and most P/C switchboards were sub merg
14、ed and had lost their functions.Even if the external power had reached,the state of loss of all AC power during initial stage of accident would have been the same.Unit 6,one D/G and its M/C were functional.Units 5 and 6 did not have to face SBO The description“the earthquake destroyed the external p
15、ower source,and then the tsunami submerged the emergency D/G to cause the total loss of AC power”is wrong!March 11,about 15:37:IC isolation valves closed with fail-safe functionUnit 1 lost all its electrical power including DC.The central control room was pitch dark.The most critical reactor water l
16、evel and pressure became unknown.IC was in normal operation with the operator turning it on and off.The loss of DC power,however,caused the fail-safe logic to send“close”signals to all four valves.The cooling function of the IC was almost completely lost.This design philosophy contradicts the requir
17、ement to“keep the valves open”on a severe accident.The accident process(Unit 1)The Unit 1 IC was designed that on failure(an abnormal condition),all flows were stopped to prevent possible radioactivity leakage IC in operationIC in operationMarch 11,about 15:37:IC isolation valves closed with fail-sa
18、fe functionNo one had ever experienced the IC in operation.Lack of education and training for the hypothetical situation of loss of DC power.The staff were not aware of the Unit 1 IC stoppage with the fail-safe function Unit 1 was in an abnormal situation with no water injected into the core until w
19、ater injection from a fire engine started at 4:00 the next morning.The accident process(Unit 1)Pig snoutPig snoutThe accident process(Unit 1)March 12,about 02:30:sudden rise of D/W pressureThe D/W pressure was reported to be at 0.84 MPaMarch 12,02:45:sudden RPV pressure dropthe RPV pressure was meas
20、ured at 0.8 MPa.That was a large drop from 6.9 MPa,there was a large leakage from the pressure vesselRPV pressure and D/W pressureRPV pressure and D/W pressureThe accident process(Unit 1)March 12,15:36:hydrogen explosionThe accident process(Unit 3)March 11,about 15:38:Unit 3,SBORCIC had started at 1
21、5:05 and stopped automatically with the“reactor water level high”signal at 15:25 before the loss of AC power.March 11,16:03:RCIC manually startedDC power had survived in Unit3,the central control room was able to operate the RCIC and other equipment as well as read parameters off the indicators.Marc
22、h,12,11:36:RCIC automatically stoppedThe RCIC stopped for some reason(still unknown)The operators looked for the cause and tried to restart it from the central control room,but did not succeed.The RCIC had two sources of water,the condensate storage tank(2500 tons)and S/C(3000 tons).The accident pro
23、cess(Unit 3)The accident process(Unit 3)March 12,12:35:HPCI automatically startedHPCI automatically started on detecting the lower water level in reactor.HPCI is driven by steam from the reactor and thus does not require AC power for running its pump.HPCI is the last resort of emergency core cooling
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