allegro gas cooled reactor severe accident … · 2020-01-09 · allegro gas cooled reactor severe...
TRANSCRIPT
ALLEGRO GAS COOLED REACTOR SEVERE ACCIDENT PROCESSES
USING MELCOR 2.2Dr. Gábor L. Horváth
EMUG‐2019Brugg‐Windisch, Switzerland 3‐5 April 2019
Contents
• ALLEGRO 75 MW reactor• MELCOR model• 10 inch LOCA Severe Accident• Thermal Hydraulics• Radioactivity release mechanisms• Extent of radioactivity release• Conclusions
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Background ‐ Scope• ALLEGRO 75MW is under development in the frame of V4 countries (Cz,SL,HU,PL)
• NUBIKI Share: Severe accident calculations
• MELCOR selection has been based on:• Capability to calculate with gas only• Experiment post‐test recalculations (HeFus)• Compare to Cathare (steady‐state and DBC)• ALLEGRO DBC and BDBC calculations
• Main goals – study processes in ALLEGRO gas cooled reactors:• Severe accident thermal hydraulics• Fission product transport• Establish accident management procedures
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75 MW ALLEGRO Modelling Scope
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Containment+GVPrimary+DHR
GV–Guard Vessel
L5
Slide 4
L5 nagyon zsúfolt nekem
mi a DHR HXLG; 01.04.2019
ALLEGRO 75 MW – model parts
• CORE+2 loop primary circuit + pony motor• SCRAM• Secondary circuit• DHR heat exchangers + DHR gas blowers• Nitrogen accumulators• Guard Vessel and an assumed containment
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Allegro 75 MW – Primary + Core model
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Allegro 75 MW – Severe Accident
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• 10 inch LOCA SA accident with N2 accu and DHR connected but with loss of water in DHR(loss of heat sink)
• Insulated surfaces:• Reactor vessel wall• DHR system downcomer• Guard Vessel wall and cap• Core boundary HS
• Primary circuit disconnected after LOCA onset
Allegro 75 MW – SA accidents10 inch Coldleg LOCA initial conditions
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Accident N2 accum.
PonyMotor+ Sec. Circ.
DHR‐ HX DHR‐blower
DHR waterreserve
LOCA ON No Natural circ. No 0 m3
GV leak GV init. pressure
0.1 vol%/d 1 bar
Allegro 75 MW – 10inch LOCA SA events
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Events TimeCold leg LOCAd=0.254 m 0.0
SCRAM 0.25 s
DHR – HX valve ON 20 s
Gap release ring 1 288 s
Fuel cladding temperature >1700 K 4218 s
Core Support plate fails by over‐temperature in R1 3.2 d
Core Support plate fails by mass loss in R1 31.9 d
Vessel failure 32dGuard Vessel failureContainment cavity core‐concrete interaction is ON
33d34.5d
Allegro 75 MW – Severe Accident –Very long time until LH failure
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ALLEGRO 75 MW 10 inch Cold leg LOCA Main processes
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ContainmentGravitation: 150x 11.5d
DHR HX– thermophoresis:36x 1000s
GV–Gravitation + thermophoresis12x 2.3d
Allegro 75 MW – BDBA accidentsSevere Accidents – conclusions
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• Main reasons of very delayed LH failure:• Low power of the reactor• Relatively small core and a lot of surrounding metal• Reflector and shielding above the core provide steel to
be heated up stabilizing the core nodes temperature for a long time
ALLEGRO SA: 10” CLeg LOCAwith Loss of HSRadioactivity distribution after 1 day
2019.04.05. 13
ALLEGRO SA: 10” CLeg LOCAwith Loss of HSRadioactivity distribution after 3 days
2019.04.05. 14
Only Xe increase aft 3 days
ALLEGRO SA: 10” CLeg LOCAwith Loss of HSRadioactivity distribution after 34 days
2019.04.05. 15
Cont: Xe appearsGuard Vessel incr.Xe, Te, Ba, Cs
Allegro 75 MW – Severe Accidents – Vessel failure
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• All aerosols remain deposited in Prim.circ+GV+DHR Hx
• however
• After vessel failurea surge of airborneaerosols (like: Cs)to GV appears
• Reason forsurge is atemperature surge
Allegro 75 MW –MELCOR Experience
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• MELCOR 2.2 managed to calculate ALLEGRO cooled rector SA
• Code often crashed after RPV failure at start of core-concrete interaction
• Typical user error was a small T/H mass with heat source resulting in over 10000 K temperature
• How is the Cs modeled if no water is available in the system?
Allegro 75 MW
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Thank you for your attention
The work has been supported by theHungarian National Research and Development Fond
Under VKSZ_14-1-2015-0021