Measurement and Modeling of the Hydrogen Distribution in Nuclear Fuel Claddings after Loss of Coolant Accidents

Transcription

1 Measurement and Modeling of the ydrogen Distribution in Nuclear Fuel Claddings after Loss of Coolant Accidents Mirco Grosse, Juri Stuckert, Martin Steinbrueck and Anders Kaestner KIT / / Program NUKLEAR Paul Scherrer Institute Villigen KIT University of the State of Baden-Wuerttemberg and National Research Center of the elmholtz Association

2 Outline Introduction Processes occuring during loss of coolant nuclear accidents QUENC-LOCA tests Neutron radiography investigations ydrogen distribution in QUENC-LOCA claddings Ab-initio modelling to understand the hydrogen distribution Conclusions

3 Processes occurring during LOCA Oidation Zr + O = ZrO + Temperature Burst Balooning time 600 C 135 C Secondary hydrogenation Thermo-shock - Quenching Fragmentation and fuel relocation coolability??? Time dependence of the cladding temperature during a loss of coolant accident

4 Processes occurring during LOCA Influence on mechanical propoerties? M. Billone et al. NUREG/CR-6967/ANL-07/04

5 Introduction In the framework of the KIT QUENC program design basis loss of coolant accidents (LOCA) and severe accidents (accidents beyond LOCA) are simulated eperimentally on fuel rod bundle scale in large scale tests.

6 Neutron radiography investigations Neutron radiography investigations were performed at ICON (PSI Villigen, Switzerland) Spatial resolution ~ 5 µm Illumination time: 300 s L/d: ~ 350 Field of view: 8 mm * 8 mm

7 Neutron radiography investigations Neutron radiography investigations were performed at ICON (PSI Villigen, Switzerland) Spatial resolution ~ 5 µm Illumination time: 300 s L/d: ~ 350 Field of view: 8 mm * 8 mm

8 Calibration I(, y) T (, y) = I0(, y) = ep( Σ Σ total = = i N N σ Zr Zr Nb Nb Σ + N σ i σ i + N N σ O + N cladding material as received + total I B (, y) I B (, y) (, y) s(, y)) σ O σ +... Sn Sn Σ total, cm N /N Zr Calibration of the correlation between total macroscopic neutron cross section and /Zr atomic ratio

9 Quantitative analysis of the neutron radiographs , wt.ppm distance to the burst opening, mm Distribution of absorbed hydrogen in cladding QL0 #03

10 Modeling of the hydrogen distribution ), ( ), ( ) ( * 0), ( ) ( ) ( 0 ) ( r c D r dc c p K r c dt c D t K dc dt t K c D Ma dc m m total S m o o O O δ δ δ δ δ δ = = = + = = Steam transport and consumption in the gap Free hydrogen production and transport ydrogen uptake (amount of hydrogen in the gap has to be taken into account) ydrogen diffusion in the tube wall

11 Modeling of the hydrogen distribution Real time simulation of the development of steam and hydrogen concentration in the gap, oide layer thickness and hydrogen concentration in the cladding

12 Modeling of the hydrogen distribution, wt.ppm D = A*T 3/ distance to the burst opening, mm Influence of the hydrogen diffusion coefficient on position of the hydrogen enriched band and the hydrogen concentration in it

13 Modeling of the hydrogen distribution oide layer thickness, µm D O D O = A * T 3/ distance from burst opening, mm, wt.ppm D O D O = A * T 3/ distance to the burst opening, mm Influence of the steam diffusion coefficient on the position and thickness of the oide layer and on the position of the hydrogen enriched band and the hydrogen concentration in it

14 Modeling of the hydrogen distribution, wt.ppm slit Gap with width offset -1.0 mm -0.5 mm -0.1 mm 0.0 mm 0.1 mm 0.5 mm 1.0 mm distance to the burst opening, mm This is the reason for deviations from radial symmetric hydrogen distributions! Influence of gap width between inner cladding surface and pellets on position of the hydrogen enriched band and the hydrogen concentration in it

15 Summary and conclusions - Secondary hydrogenation of cladding tubes during LOCA was studied by means of neutron imaging and ab-initio modeling. - ydrogen is concentrated in bended bands oriented non-perpendicular to the tube ais. - An ab-initio model was developed to describe hydrogen absorption during LOCA. - The main reason this hydrogen distribution is the obstruction of the hydrogen uptake by the oide layer formed at the inner cladding surface. - Parametric studies show that the position of the hydrogen enriched bands mainly depends on the gap width between inner cladding surface and pellets and on the steam transport rate. The amount of absorbed hydrogen depends on the hydrogen and steam transport rates in the gap and on the gap width.

16 Thanks The QUENC-LOCA tests and pre-test investigations are sponsored by the German Verein der Grosskraftwerksbetreiber VGB KIT: The QUENC team, particularly C. Goulet, J. Moch, C. Roessger PSI: S. artmann

17 Measurement and Modeling of the ydrogen Distribution in Nuclear Fuel Claddings after Loss of Coolant Accidents Mirco Grosse, Juri Stuckert, Martin Steinbrueck and Anders Kaestner KIT / / Program NUKLEAR Paul Scherrer Institute Villigen KIT University of the State of Baden-Wuerttemberg and National Research Center of the elmholtz Association