results of first stage of vver rod simulator quench tests

Results of First Stage of VVER Rod Simulator Quench Tests

11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27, 2005

Presented by I. Kuzmin RIAR, Dimitrovgrad, Russia

11th International QUENCH Workshop Forschungszentrum Karlsruhe October 25-27, 2005 2

Stage A : “Study of the irradiated fuel rod segments behavior under reflood conditions”

1648.2 Project ISTC “Examination of the VVER fuel behavior under the severe accidents. Reflooding stage”

Simulator cladding and fuel characteristics, preoxidized cladding failure character on the quench stage

Hydrogen generation

Fission products release

The purpose of the tests:

Expansion of an experimental database for the irradiated fuel

rod characteristics after reflooding


Study of the spent fuel rod segments behavior

under reflood conditions.

Stages of work

Designing and manufacturing the test rig

Experiments with unirradiated fuel rod simulators Working out the experimental technique Comparison with results of the similar tests carried out in FZK Expansion of an experimental database for the unirradiated

VVER fuel rod characteristics after reflooding

Executing the tests with the irradiated fuel rod simulators.


Unirradiated fuel rod simulator

cladding material E110 alloy cladding length 150 mmfuel pellets UO2 VVER-1000 type

Pre-oxidation parameterstemperature 1200 °C environment Ar-O2 mixtureoxidation time 100 soxide thickness 15 - 20 m

Instrumentation3 Pt/Rh thermocouples were fixed at the elevationof 27, 77 and 127mm on the cladding outer surfaceby a Pt/Rh wire

1 W/Re thermocouple was located in the fuel pellets hole at the elevation 75mm


Heating module

1 – sample2 – operating channel 3 – vapor-argon-hydrogen mixture outlet 4 – sample movement drive 5 – sample suspension6 – thermocouples 7 – argon inlet of sample suspension8 – current supply of heater 9 – thermal protection 10 – molybdenum screens11 – split tubular molybdenum heater12 – water sampling 13 – argon (vapor-argon mixture) inlet 14 – water inlet15 – heated quench tank

1

2

15

9

10

11

4

65

3

14 13

12

8

Based on the resistive heatingSpecimen is flooded by means of its movement into the quench tank filled with water at the set speed

7


steam flow rate 10 mg/(s·sm2)the steam generator is switched off before heating up to quenching temperature, but some steam still supplies from the quench tank specimen is dropped at water level in the quench tank with a speed of 245 m/sspecimen is immersed into water heated up to 90C with a speed of 15 mm/s

0

400

800

1200

1600

2000

0 600 1200 1800 2400 3000

Time, s

Tem

pera

ture

, °С

Ar+steamAr Ar

0.5 °С/с

1.5 °С/с

1.5 °С/с

Design test regime


Experimental results

# of sample 1 2 3

Oxidation time at 1400°С, s 800 240 240

Flooding temperature, °С 1400 1600 1600

Hydrogen release per whole experiment, mg 320 276 270

Hydrogen release at flooding, mg 25 35 38

ECR, % 32 30 -

Thickness of ZrO2 outer

layer along the sample height*, m

top 202 183 -

center 201 216 -

bottom 167 165 -

Cladding metal thickness along the sample height

*, m

top 581 591 -

center 574 571 -

bottom 591 602 -

* - the section coordinate is calculated from the sample lower end Sample No1: upper cross-section 114mm, central cross-section – 57, lower cross-section – 27mm. Sample No2: upper cross-section –127mm, central cross-section –77mm, lower cross-section 27mm


600

800

1000

1200

1400

1600

1800

1500 2000 2500 3000 3500Time, s

Tem

pera

ture

, °С

0

4

8

12

16

20

24

28

32

36

40

Hyd

roge

n co

ncen

trat

ion,

%

T fuel, 77 mm T cladding, 127 mmT cladding, 77 mm T cladding, 27 mmhydrogen

Experimental resultsTemperature and hydrogen concentration. Simulator #2


Experimental resultsTemperature and hydrogen release rate at the flooding of simulator #2

0

200

400

600

800

1000

1200

1400

1600

1800

2780 2800 2820 2840 2860 2880Time, s

Tem

pera

ture

, °С

0

0.2

0.4

0.6

0.8

1

1.2

Hyd

roge

n re

leas

e ra

te, m

g/s

T fuel, 77 mm T cladding, 127 mmT cladding, 77 mm T cladding, 27 mmhydrogen


Experimental resultsTotal hydrogen production

0

50

100

150

200

250

300

350

400

2500 3000 3500 4000 4500Time, s

Hyd

roge

n re

leas

e, m

g

sample #1sample #2sample #3


Experimental results Sample claddings appearance after tests

crack visualization

crack visualization

Sample #1

oxidation 800 s, quenching 1400°C Sample #2 Sample #3

oxidation 240 s, quenching 1600°C


Experimental results Fuel pellet state

Sample #1 crossection appearance (57 mm) after test (oxidation 800 s, quenching 1400°C)

Pellets after the tests are in the stable state

There are narrow crakes in the pellets

The interaction between cladding and fuel

was observed (samples #1 and #3)

The cracks in the cladding are observed

in the areas of its tight contact with fuel


Experimental results Sample #1 cladding state

(oxidation time 800 s, flooding temperature 1400°С)

upper cross-sections(114 mm)

center cross-sections(57 mm)

bottom cross-sections(27 mm)


Experimental results Sample #2 cladding state

(oxidation time 240 s, flooding temperature 1600°С)

upper cross-sections(127 mm)

center cross-sections(77 mm)

bottom cross-sections(27 mm)


Experimental results

Cladding state

The monolithic oxide film without any tangential cracks

is observed on the samples.

In the cladding of both samples there are radial cracks

spreading from the inner surface to the outer oxide film.

The majority of cracks ends in the oxide layer.

There are no any oxide films on the crack surfaces.

The distribution of the thickness of oxide films and metal part

of the cladding confirms that the center of samples

was placed lower maximum temperature.


Conclusion

The facility to study the release of hydrogen and fission products from single fuel rods under the conditions typical for the VVER core flooding during the LOCA accident was developed. The facility operation is based on the indirect resistive heating of the specimen.

The experiments with unirradiated VVER fuel rod simulators were performed under the reflooding conditions in the frame of the first testing stage.

The hydrogen release into the gas phase is measured both at the stage of preliminary oxidation of the simulator claddings and at the flooding stage.

The experiments with unirradiated simulators will be continued to expanse the database for the irradiated fuel rod characteristics after reflooding. At present, the facility is being prepared for the experiments with simulators fabricated from spent VVER fuel rods at a burn up of 45-50MW*day/kgU.

results of first stage of vver rod simulator quench tests

Documents

fuel characteristics

heated quench tank

quench tank specimen

vver fuel behavior

lower crosssection

fuel pellets hole

water inlet

sample no2