ALLEGRO GAS COOLED REACTOR SEVERE ACCIDENT … · 2020-01-09 · ALLEGRO GAS COOLED REACTOR SEVERE...

ALLEGRO GAS COOLED REACTOR SEVERE ACCIDENT PROCESSES 

USING MELCOR 2.2Dr. Gábor L. Horváth

EMUG‐2019Brugg‐Windisch, Switzerland 3‐5 April 2019

horvathlg@nubiki.hu

Contents

• ALLEGRO 75 MW reactor• MELCOR model• 10 inch LOCA Severe Accident• Thermal Hydraulics• Radioactivity release mechanisms• Extent of radioactivity release• Conclusions

2

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

3

75 MW ALLEGRO Modelling Scope

4

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

5

Allegro 75 MW – Primary + Core model 

6

Allegro 75 MW – Severe Accident

7

• 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

8

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

9

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

10

ALLEGRO 75 MW 10 inch Cold leg LOCA Main processes

11

ContainmentGravitation: 150x 11.5d

DHR HX– thermophoresis:36x 1000s

GV–Gravitation + thermophoresis12x 2.3d

Allegro 75 MW – BDBA accidentsSevere Accidents – conclusions

12

• 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

16

• 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

17

• 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

18

Thank you for your attention

The work has been supported by theHungarian National Research and Development Fond

Under VKSZ_14-1-2015-0021