fukushima daiichi unit 1 (melcor 1.8.6) · fukushima daiichi unit 1– braun matthias, dtipp7-g –...
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FUKUSHIMA DAIICHI UNIT 1(MELCOR 1.8.6)
BRAUN Matthias, DTIPP7-G
Zagreb, 04/26/2018
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Not part of the BSAF OECD Benchmark Project Did not receive undisclosed information from TEPCO / JAEA Relying only on publically available input data No legal restrains for usage & publication (project and export control)
Why Test of simulation capabilities (code and user) and as MELCOR 1.8.6 to 2.x conversion test base Support for training courses (accident awareness trainings for crisis team members and sometimes operators ) Improvement of Severe Accident Management Guidelines (SAMG) Optimization of usage of severe accident hardware
(Passive autocatalytic recombiners, Filtered containment venting systems) Contribution to the international MELCOR community
Model description report containing all input data (FGF_D02-ARV-01-111-828) revision B (hardcopy) on EMUG2018 revision C (electronically) and the MELCOR input model at CSARP/MCAP 2018. (planned)
p.2
Introduction
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RPV & Core Typical GE BWR RPV geometries (well standardized) Generic 7x7 fuel assemblies
Experimental (non-recommended) features RPV leakage before failure via TIP dry tubes More CVH volumes in lower plenum Separating lower plenum in channel & bypass,
representing the control rod guide tubes Fuel assembly skeleton as supporting structure Maximizing the COR detail depth to
7 rings and 35 levels (more leads to crash) Additional core collapse criteria
(collapse of fully oxidized assemblies without lateral support)
Maximum void 0.4 -► 0.7 (RPV water inventory) Time-dependent oxidized rod collapse model
(Critical thickness of unoxidised Zr -► 0.0)
p.3
Overview of the MELCOR model for 1F1
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Nuclear systems Operational systems like main steam,
feedwater (steady state initiation) Safety systems like Isolation Condenser,
core spray, External water injection (fire engines) RPV liquid level measurement system
(failure of the measurement)
Noticeable from core spray system Spray package can malfunction at high pressure
Noticeable from IC modelling: MELCOR overestimates departure
from nucleate boiling at low pressures IC operation did not work until secondary side pressure
was increased from 1 bar-abs to 2 bar-abs
p.4
Overview of the MELCOR model for 1F1
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Containment Wet-well / suppression pool sub-divided
to allow for thermal stratification(-► spool scrubbing issue)
Dry-well sub-divided to address over-temperature failure of hatches(-► too fast convection in lumped parameter codes)
p.5
Overview of the MELCOR model for 1F1
CV750
CV745
CV721CV723
CV7
80
CV790
HS721.01 HS750.01 HS723.01
751.11
HS
761.
11H
S741
.21
771.12
HS771.13
HS7
70.1
4
HS
763.
11H
S743
.21
773.12
HS773.13
HS7
83.1
1
CV760
FL750 FL755
HS721.11
HS721.12
HS731.11
HS731.12
HS731.13
HS731.15
HS731.16
FL753
CV7
41
CV7
43
HS790.15
HS741.11
HS741.12
HS741.13
HS791.11
HS7
81.1
1
HS
783.
12
HS
781.
12
HS723.12
HS733.11
HS733.12
HS733.13
HS731.14 HS733.14
HS733.16
HS733.17
HS791.12
HS741.14
HS743.11
HS743.12
HS743.13
HS793.11
HS743.14
HS793.12
HS799.14
FL721 FL723
FL733FL731
FL743FL741
FL78
0
FL78
0
FL909
FL763
FL760 FL765
CV770
FL781
FL786
FL783
FL788
Sector 1 (315° - 45°) Sector 3 (135° - 225°)
HS711/8.16
HS711/8.14
HS711/8
.13HS711/8.15
CV711/8
CV661/8
CV621/8CV600
FL701/8
FL611/8
HS711/8.11
HS711/8.12
CV641/8FL631/8
HS600.01HS600.02
HS621/8.01
HS641/8.01
HS641/8.02
HS641/8.03
HS661/8.01
HS661/8.02
HS661/8.03
HS661/8.04
HS661/8.05
HS661/8.06
HS661/8.07HS661/8.08
HS661/8.09
HS661/8.10
HS723.11
Access door (1.9m x 0.77m)
HS71 .144/5
HS71.13
4/5
HS71 .154/5
CV714/5HS714/5.16
FL704/5
CV624/5
CV644/5
HS600.01
HS600.02
HS62 .014/5
HS64 .014/5
HS64 .024/5
HS64 .034/5
HS66 .014/5
HS66 .024/5
HS66 .034/5
HS66 .044/5
HS66 .054/5
HS66 .064/5
HS66 .074/5HS66 .084/5
HS66 .094/5
HS66 .104/5
CV664/5
CV600
FL614/5
HS71 .114/5
HS71 .124/5
FL634/5
CV731CV733
HS733.91Inner HS10t steel5mm thick
HS731.91Inner HS10t steel5mm thick
HS741.91Inner HS5t steel5mm thick
HS743.91Inner HS5t steel5mm thick
HS760.91Floor grating
753.11
780.01
HS7
90.1
4H
S790
.13
+2.055 - Torus 05/16 heightth
+2.560 - Torus 06/16 heightth
+3.065 - Torus 07/16 heightth
+4.075 - Torus 09/16 heightth
+4.650 - Header center
+4.580 - Torus 10/16 heightth
+3.570 - Torus center elevation
+7.609 - Torus inner top
+7.624 - Torus outer top
+1.046 - Torus 03/16 heightth
+1.551 - Torus 04/16 heightth
+1.461 - Downcomer end
+0.541 - Torus 02/16 heightth
+0.036 - Torus 01/16 heightth
+0.000 - RB zero
-4.000 - Soil
-1.230 - Torus room floor
-0.484 - Torus outer bottom
-0.469 - Torus inner bottom
+7.104 - Torus 15/16 heightth
+6.599 - Torus 14/16 heightth
+12.200 - Sphere equator
+15.100 - RPV outer bottom
+27.800 - Shield wall top
+19.572 - Sphere - Cylinder
+25.000 - 2nd floor ceiling
+25.900 - 3rd floor
+18.700 - 2nd floor
+11.700 - 1st floor ceiling
+30.400 - 3rd floor ceiling
+30.700 - Reactor well floor
+35.536 - PCV head outer top+35.500 - PCV inner top
+38.900 - Service floor(5th)
+31.000 - 4th floor
+33.000 - PCV cylinder top
+9.550 - Torus room ceiling
+10.200 - 1st floor
+38.500 - 4th floor ceiling
+27.100 - SFP Floor
+31.300 - Storage pit floor
2.565 - RPV outer
2.870 - Shielding wall inner
3.370 - Shielding wall outer
5.500 - Reactor well inner
7.100 - Reactor well outer
3.111 - RPV stud ring outer
+8.173 - Vent pipe top
+6.527 - Vent bottom
+6.180 - D/W floor
+6.777 - Vent bottom + 25cm
+9.708 - Floor grating top
+13.340 - CRD hydraulic openings
+14.660 - Lower pedestal top
+33.412 - Stud ring top
+30.888 - Stud ring bottom
+31.650 - RPV seal surface
+34.290 - RPV outer top
2.500 - Lower pedestal inner
3.500 - Lower pedestal outer
1.877 - Skirt inner radius
4.877 - PVC cylinder inner
14.785 - Torus major radius
8.858 - PCV shpere outer
8.850 - PCV shpere inner
10.100 - PVC basemat outer
10.600 - PVC walls (ground floor)
7.000 - PCV walls (1st & 2nd floor)6.472 - PCV floor radius
1.800 - RPV support ring inner
1.917 - Skirt outer radius
4.913 - PVC cylinder outer
CV721
HS72HS721.11
HS721.12
HS731.11
HS731.12
FL721
HS711/8.16
HS711/8.14
HS711/8
.13HS711/8.15
CV711/8
CV661/8
CV621/8CV600
FL701/8
FL611/8
HS711/8.11
HS711/8.12
CV641/8FL631/8
HS600.01HS600.02
HS621/8.01
HS641/8.01
HS641/8.02
HS641/8.03
HS661/8.01
HS661/8.02
HS661/8.03
HS661/8.04
HS661/8.05
HS661/8.06
HS661/8.07HS661/8.08
HS661/8.09
HS661/8.10
+8.173 - Vent pipe top
+6.527 - Vent bottom
+6.180 - D/W floor
+6.777 - Vent bottom + 25cm
+9.708 - Floor grating top
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Surroundings Reactor Building (-► CF-based add-on to calculate dose rate in building) HVAC, SGTS & stack (deposition and release of radionuclides) Filtered Containment Venting System (fictional, for “what-if” studies) Spent fuel pool (heat-up, boil-off, RN deposition)
p.6
Overview of the MELCOR model for 1F1
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14:46:23 - Tohoku earthquake about 150 km from Fukushima Daiichi Based on seismic readings of the KNET Station FKS005(1) relative distance to the Fukushima site and wave
propagating speed ~4 km/s, seismic trip threshold reached in Fukushima Daiichi at 14:47:32 ±1s 1F1 alarm recorder(2) states first
seismic scram signals 14:46:46 Correction of the alarm recorder clock by 46 s
(consistent with TEPCO timing) Correction of the 1F1 transient recorder(3)
by additional 33 s Timing of the paper strip
recorders manually corrected
p.7
First hour of the Incident in 1F1
Epicenter
F. Daiichi
FKS005
(1) http://www.strongmotioncenter.org/cgi-bin/CESMD/iqrStationMap.pl?ID=Japan_11Mar2011_usc0001xgp(2) http://www.tepco.co.jp/en/nu/fukushima-np/index10-e.html#anchor02(3) http://www.tepco.co.jp/en/nu/fukushima-np/index10-e.html#anchor05
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14:47:32 - First seismic trip signals T + 12 s - 2 out of 2 signals causes SCRAM, terminating nuclear fission
p.8
First hour of the Incident in 1F1
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After SCRAM steam generation stalls, but turbine still draws steam T + 15 s - RPV pressure drops
p.9
First hour of the Incident in 1F1
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Turbine control valves automatically close to stabilize PRV pressure T + 30 s - Steam flow to turbine stops and RPV pressure stabilizes
p.10
First hour of the Incident in 1F1
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T + 30 s - Void in the RPV core collapses, seemingly decreasing the RPV liquid level Measurement malfunctioning between loss of offsite power and start diesel generators
p.11
First hour of the Incident in 1F1
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T + 30 s - Lower RPV level causes automatic ramp-up of the feedwater injection
p.12
First hour of the Incident in 1F1
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T + 40 s - Increased feedwater injection causes RPV pressure transient
p.13
First hour of the Incident in 1F1
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T + 20 s – RPV recirculation system runs down to 30% after SCRAM T + 63 s – Recirculation pumps stops at LOOP
p.14
First hour of the Incident in 1F1
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14:53:05 (T +333 s) – RPV pressure exceeds 72.2 bar, automatic activation of the Isolation Condenser (IC) train A & B
p.15
First hour of the Incident in 1F1
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Plant situation prior the arrival of the Tsunami Plant is in a stable hot-shutdown state, decay heat controlled by operating the IC RPV is filled with water (significantly more than during power operation) Small water injection into RCS by pump seal / CRD purge water (supplied by diesel generators) Slight PCV heat-up / pressure rise by stop of dry-well cooling system (not supplied by diesel)
Analytical aspects of initial transient Transient timing and bottom lying physics is well understood The MELCOR thermohydraulics corresponds well to the time-corrected plant data Based on deviations between simulation and recorded measurements
a timing error of ±15 min can be expected for predictions of the start of core damage
Fit parameters within the MELCOR model Closure time of the turbine control valves (direct fit to measurements) Run-down of the primary loop recirculation pumps (direct fit to measurements) Feedwater flow dependence on RPV liquid level (simplified modelling) Flow/Void within and outside the RPV steam separator tubes (no detailed design knowledge)
p.16
First hour of the Incident in 1F1
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Escalation into an Accident
15:37 to 15:38 Tsunami flooding of the plant site
Loss of instrumentation and control Loss of all core cooling functions IC currently inactive, and if it would have been active, fail-safe tube rupture signal would have shut it down
Further accident progression
Decay heat ~10 MW vaporizes coolant PRV pressure rises until a SRV opens Coolant is discharged into the wet-well RPV liquid level drops
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Escalation into an Accident 17:45 (T+2.5h) Top of active fuel (TAF) is reached
Quake Tsunami
TAF
BAF
18:18 - IC on18:25 - IC off
21:30 - IC on
0
2
4
6
8
10
12
14
12:00 14:00 16:00 18:00 20:00 22:00 0:00 2:00 4:00 6:00
Rea
ctor
wat
er le
vel [
mR
PV0]
Local time [3/11/2011 hh:mm]
W/R A (transient recorder 1min)
W/R B (transient recorder 1min)
MELCOR (CF49504)
Liquid level visible in MCR
MELCOR (Core swell level)
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Escalation into an Accident Core oxidation releases large amounts of hydrogen
18:18 - IC on
18:25 - IC off
21:30 - IC onQuake Tsunami
0
100
200
300
400
500
600
700
800
0
500
1000
1500
2000
2500
12:00 14:00 16:00 18:00 20:00 22:00 0:00
Hyd
roge
n in
RPV
[kg]
Cla
ddin
g m
ax. t
empe
ratu
res
[ K ]
Local time [3/11/2011 hh:mm]
max. Cladding (CF200728)
hydrogen release (COR-DMH2-TOT)
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Escalation into an Accident Hydrogen causes strong pressure buildup in BWR containments
Quake Tsunami
0
1
2
3
4
5
6
7
8
9
10
12:00 14:00 16:00 18:00 20:00 22:00 0:00 2:00 4:00 6:00 8:00 10:00 12:00
Con
tain
men
t pre
ssur
e [b
ar]
Local time [3/11/2011 hh:mm]
D/W (paper strip record) W/W (paper strip record) MELCOR (CVH-P.795) MELCOR (CVH-P.661) Dry-well presssure recorded data Wet-well presssure recorded data
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Escalation into an Accident Observed vs. calculated dose rates in RB due to containment design leakage
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Escalation into an Accident Failure of water level measurement only achievable by early RCS leakage,
not by bare heat-up of containment through intact RCS walls
QuakeTsunami
TAF
BAF
0
2
4
6
8
10
12
14
12:00 14:00 16:00 18:00 20:00 22:00 0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00
Rea
ctor
wat
er le
vel [
m]
Local time [3/11/2011 hh:mm]
Fuel range A (CF480.04) Fuel range B (CF480.04) Wide range (CF495.04) F/R A (parameter data) F/R B (parameter data)
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Fukushima Daiichi Unit 1– BRAUN Matthias, DTIPP7-G – Zagreb, 04/26/2018 p.23
2. SCIENTIFIC CONDUCT
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Example BSAF – RPV pressure Unit 3
What do we see here:Fit of the simulations to measured pressure values
What is NOT-necessarily seen:Numerical simulated accident progression in U3 with a high degree of accuracy
Every model (good or bad) can be forced onto plant data
Such pictures can suggest a higher accuracy than one really have
Over-confidence in simulationscan result in “negative training”
p.24
Scientific Conduct
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Fitting is not worthless! With fitting one can access unknown information Fitting allows to assume a certain situation, and then one can evaluate derivative quantities
Example BSAF - PCV pressure of U3 as result of the fitted RPV pressure
Good practices when Fitting Disclose the fit Do not state a fit / boundary condition
as simulation result Evaluate the invasion strength
on the simulation Choose a reasonable fit parameter
(e.g. not an opening/closing containment leakage area to fit PCV pressure)
p.25
Scientific Conduct
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Fukushima Daiichi Unit 1– BRAUN Matthias, DTIPP7-G – Zagreb, 04/26/2018 p.26
3. EXAMINATION OF THE NUCLEAR FALLOUT
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Database for Radioactive Substance Monitoring Data by of the Japan Atomic Energy Agency
http://emdb.jaea.go.jp/emdb/en/
Deduction of the core release fraction from the fallout isotope composition
Insights into the core degradation ~ 2400 K to release silver << 2800 K to not release americium Sub-stoichiometric melts, and probably no
large-scale liquefaction of oxides No ruthenium release due to lack of oxygen
(RuO2 boils at 1200°C, but Ru can not be oxidized by steam)
Low niobium but high molybdenum release,but in MELCOR both are the same class-►Cs2MoO4 class definition
Exchange on FKH activities in IB & DTI – BRAUN Matthias, DTIPP7-G – Telecom, 03/16/2018 p.27
Examination of the Nuclear Fallout
ElementRelease fraction
from CoreIodine, Cesium, Tellurium, Technetium, Molybdenum up to 100 %
Silver up to 100 %
Antimony ~ 5 %
Barium ~ 1 %
Niobium, Barium, Strontium ~ 0.1 %
Ruthenium < 0.1 %
Americium < 5E-4
Uranium, Plutonium Not measurable
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Plutonium release of high public interest Numerous papers claim to have
observed reactor plutonium
Plutonium background from surface nuclear weapon test
Separation of reactor plutoniumfrom weapon plutonium by different isotope composition
Signal vanishes with increasing signal strength -► measurement errors?
p.28
Examination of the Nuclear Fallout
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p.29