fukushima daiichi unit 1 (melcor 1.8.6) · fukushima daiichi unit 1– braun matthias, dtipp7-g –...

Restricted

FUKUSHIMA DAIICHI UNIT 1(MELCOR 1.8.6)

BRAUN Matthias, DTIPP7-G

Zagreb, 04/26/2018

Restricted - Framatome

Property of Framatome - © FramatomeAll rights reserved

Fukushima Daiichi Unit 1– BRAUN Matthias, DTIPP7-G – Zagreb, 04/26/2018

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




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




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





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


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




HS760.91Floor grating

753.11

780.01

HS7

90.1

4H

S790

.13

+2.055 - Torus 05/16 heightth




+4.650 - Header center


+3.570 - Torus center elevation

+7.609 - Torus inner top

+7.624 - Torus outer top



+1.461 - Downcomer end



+0.000 - RB zero

-4.000 - Soil

-1.230 - Torus room floor

-0.484 - Torus outer bottom

-0.469 - Torus inner bottom



+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




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





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




14:47:32 - First seismic trip signals T + 12 s - 2 out of 2 signals causes SCRAM, terminating nuclear fission

p.8





After SCRAM steam generation stalls, but turbine still draws steam T + 15 s - RPV pressure drops

p.9





Turbine control valves automatically close to stabilize PRV pressure T + 30 s - Steam flow to turbine stops and RPV pressure stabilizes

p.10





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





T + 30 s - Lower RPV level causes automatic ramp-up of the feedwater injection

p.12





T + 40 s - Increased feedwater injection causes RPV pressure transient

p.13





T + 20 s – RPV recirculation system runs down to 30% after SCRAM T + 63 s – Recirculation pumps stops at LOOP

p.14





14:53:05 (T +333 s) – RPV pressure exceeds 72.2 bar, automatic activation of the Isolation Condenser (IC) train A & B

p.15





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





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




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)




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 ]


max. Cladding (CF200728)

hydrogen release (COR-DMH2-TOT)




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]


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




Escalation into an Accident Observed vs. calculated dose rates in RB due to containment design leakage




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]


Fuel range A (CF480.04) Fuel range B (CF480.04) Wide range (CF495.04) F/R A (parameter data) F/R B (parameter data)



Fukushima Daiichi Unit 1– BRAUN Matthias, DTIPP7-G – Zagreb, 04/26/2018 p.23

2. SCIENTIFIC CONDUCT




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




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



Fukushima Daiichi Unit 1– BRAUN Matthias, DTIPP7-G – Zagreb, 04/26/2018 p.26

3. EXAMINATION OF THE NUCLEAR FALLOUT




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




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




Any reproduction, alteration, transmission to any third party orpublication in whole or in part of this document and/or its content isprohibited unless Framatome has provided its prior and writtenconsent.

This document and any information it contains shall not be used forany other purpose than the one for which they were provided. Legalaction may be taken against any infringer and/or any personbreaching the aforementioned obligations.

EPR is a registered trademark of Framatome or its affiliates, in the United States or othercountries

p.29

fukushima daiichi unit 1 (melcor 1.8.6) · fukushima daiichi unit 1– braun matthias, dtipp7-g –...

Documents