Experimental study of the processes at the corium melt retention in the reactor pressure vessel (Invecor)

(1)

ISTC project K-1265:

Experimental study of core melt in-vessel retention

IN-VEssel COrium Retention (INVECOR)

Presented by Vladimir Zhdanov

IAE NNC RK

5

thth

Eurasian conference “Nuclear science and its application”,

_{Eurasian conference “Nuclear science and its application”,}

October, 14 – 17, 2008

Ankara, Turkey

(2)

Presentation contents

• Background

Background

• Main directions of work and results

Main directions of work and results



Design of experimental section for INVECOR test

_{Design of experimental section for INVECOR test}



Major directions of LAVA-B facility modernization

_{Major directions of LAVA-B facility modernization}



Testing of Zr-coating technique on graphite

_{Testing of Zr-coating technique on graphite}

surface



Creation of INVECOR test conditions

_{Creation of INVECOR test conditions}



Test with one plasmatrons

_{Test with one plasmatrons}



Test section design (RPV model)

_{Test section design (RPV model)}

(3)

INVECOR project general information

Project participants and coordination

FZR,

Germany

FZR,

Germany

ISTC,

Moscow

ISTC,

Moscow

FZK,

Germany

FZK,

Germany

IRSN,

France

IRSN,

France

ITU-JRC,

EU

ITU-JRC,

EU

CEA,

France

CEA

,

France

Collaborators

Steering

committee

Steering

committee

Operation Agent: IAE NNC RK, Kazakhstan

Coordinator

Pisa

University,

Italy

Pisa

University,

Italy

Project duration

36 months

Financial party

(4)

Background

In vessel core degradation during the severe accident

Metal/oxide stratification

in the molten pool

Schematic diagram of reactor

core following TMI-2 accident

“

Classical” representation

MASCA observation

In-vessel configuration

with inverted metal

stratification

(5)

Test scenario using LAVA-B facility

• Corium composition:

Corium composition:

UO2+ZrO2+Zr

• Corium mass:

Corium mass:

up to 60 kg

• Corium temperature:

Corium temperature:

up to 3000 deg. C

• Heating technique:

Heating technique:

induction heating in the

“hot crucible”

• Height of melt dropping:

Height of melt dropping:

1,7 m

(6)

Design of experimental section

for INVECOR test

Gained power of single plasmatrons

• Up to 16 kW with argon-gas

Up to 16 kW with argon-gas

• Up to 19 kW with nitrogen

Up to 19 kW with nitrogen

• Total power approx. 90 kW

Total power approx. 90 kW

Maximum time of plasma burning -

Up to 2,5 hours

Directing cone for

corium discharge

Coaxial

plasmatrons

(5 units)

Graphite

Plasmatrons

nozzles

Corium pool

RPV model (1:8)

Wall thickness 50 mm

Thermal screen

Design of coaxial plasmatrons

nozzles

External electrode

Internal electrode

Lower part of external

electrode (protected

with Zr)

Zone of electric arc

burning

(7)

Major directions of LAVA-B facility

modernization

Graphite crucible coating

DAS improvement

Electric melting furnace

Facility pressure vessel

Experimental section

Electrode nozzles design, testing and coating Copper electrode design

RPV model design and calculation

(8)

Testing of protective coating

on graphite surfaces (1)

Main objective of coating – to prevent

the interaction between graphite

and corium component at high

temperature

Technique of coating consists in

spreading of molten zirconium

along the protected graphite

surface with subsequent zirconium

carbiding

Surfaces to be protected are:

• inner surface of the melting

inner surface of the melting

crucible

• Outer surface of the external

Outer surface of the external

nozzle of the coaxial plasmatrons

_{Graphite crucibles of different}

dimensions with protective

coating on internal surface

(9)

Testing of protective coating

on graphite surfaces (2)

Results of protective coating testing against molten corium attack

2600 deg. C

Time 30 minutes

2600 deg. C

Time 40 minutes

2800 deg. C

Time 60 minutes

2600 deg. C

Time 90 minutes

Corium C-30

Re-melting

(10)

Creation of INVECOR test conditions (1)

Temperature of corium/steel interface should be higher than 950 deg. C

to creation of conditions for physico-chemical interaction between corium and RPV steel

2850C

2690C

2600C

2400C

1975

C

1850

C

1760

C

1450C

1420C

1300C

1200

C

940C

Melting of UO

2

Melting of ZrO

₂

Formation of ceramic U-Zr-O melt

Formation of

-Zr(O)-UO

₂

and U-UO

₂

monotectics

Melting of

-Zr(O)

Start of UO

₂

dissolution by

molten Zircaloy – formation of

metallic (U-Zr-O) melt



Melting of zirconium (by different authors)

Melting SS+Zr eutectic

Melting of stainless steel and Inconel

Eutectics Fe–Zr formation

Eutectics Ni–Zr, formation

Start of rapid Zircaloy oxidation by

H

2

O – uncontrolled temperature

escalation

First eutectics Ni–Zr, Fe–Zr formation

(11)

Creation of INVECOR test conditions (2)

Design of RPV model

Corium pool pre-calculation using

profile thermal insulation

_{profile thermal insulation}

on the outer RPV model surface

(12)

Test with one plasmatrons (1)

Main objectives

• Testing of thermal insulation efficiency

Testing of thermal insulation efficiency

• Testing of protective coating reliability against prototypic

Testing of protective coating reliability against prototypic

corium attack at high temperature

• Finding the ways of coaxial plasmatrons power increase

Finding the ways of coaxial plasmatrons power increase

• Testing of electrode nozzles life-time to estimate the

Testing of electrode nozzles life-time to estimate the

duration of integral INVECOR test

(13)

Test with one plasmatrons (2)

Scheme of experimental cell

Result on pre-calculation at

plasmatrons power 18 kW

(14)

Test with one plasmatrons (3)

Temperature of the inner vessel wall

Assembled plasmatrons

(lower part of graphite

nozzle is covered with Zr)

(15)

Test with one plasmatrons (4)

Cross section of the experimental cell

and results of phase analysis

(16)

Test with one plasmatrons (5)

State of protective coating on the graphite surface after test

Coated electrode nozzle before

test

(17)

Test with one plasmatrons (6)

Relative erosion rate of internal electrode depending on current in the arc

0 2 4 6 8 10 12 14 16 0,215 0,235 0,255 0,275 0,295 0,315 0,335 Erosion rate/energy input, g/(GJmin)

ARV-1

Electric current in the arc, kA

(18)

Test with one plasmatrons (7)

Parameter TOP-1 TOP-2 TOP-3 TOP-4 TOP-5 TOP-6 TOP-7 Time of operation, hh:mm 1 : 00 2 : 00 2 : 00 1 : 53 2 : 30 2 : 20 2 : 32 : 34 4

Gas composition in the inter-electrode space N₂ N₂ N₂ N₂; 36%N₂+64%Ar N₂ 15%N₂+85%Ar N₂+Ar Gas pressure in the inter-electrode space, atm n.d. n.d. n.d. 1,5-1,8 1,35 2,6 1,5 Average pressure of gas in facility vessel, atm. 1,3 1,2 1,4 1,1-1,0 1,2 2,4 1,2 Average voltage value of electric arc, V 62 60 75 60,5 65 52 59 Average current value of electric arc, A 270 272 220 312 290,6 318 307 Average plasmatrons power, kW 16,8 16,3 16,5 18,3 18,7 15,9 18,1 Power input, MJ 60,7 119,2 119,0 125,3 170,7 138,4 167,0 Maximum temperature of outer electrode nozzle

(148 mm from the bottom end face) 387 594 511 767 828 590 656 Max. temperature of gas exhausted from the melt,

deg.C 352 483 381 818 859 683 547

Maximum temperature of inner vessel wall, deg.C ‑ 2 mm from the bottom

‑ 30 mm from the bottom ‑ 60 mm from the bottom ‑ 90 mm from the bottom - on the bottom 673 1107 1149 880 n.d. 623 693 980 951 287 527 764 846 844 235 413 856 929 861 345 605 777 936 842 625 384 869 964 774 229 471 755 877 742 203 Maximum temperature of corium, deg.C

‑ 30 mm from the bottom ‑ 55 mm from the bottom ‑ 80 mm from the bottom ‑ 105 mm from the bottom

1319* 2133* 2230* 1429 2002* 1985* 2190 2034 1843* 2215 1949 1576 1920* 1997* 2176* 2264 1921* 2245* 2469* 2113 1970* 2402* 2573 1979 2418 2090 2682 1975 Rate of graphite erosion, g/min 0,26 0,23 0,464 1,89 1,16 0,29 0,607