EXPERIMENTAL SIMULATION OF THE BEHAVIOUR OF E110 CLADDINGS UNDER ACCIDENT CONDITIONS USING ELECTRICALLY HEATED BUNDLES ZOLTÁN HÓZER, IMRE NAGY, RÓBERT FARKAS, NÓRA VÉR, MÁRTA HORVÁTH, TAMÁS NOVOTNY, ERZSÉBET PEREZ-FERÓ, MÁRTON KIRÁLY, ZOLTÁN KIS, BOGLÁRKA MARÓTI, LÁSZLÓ SZENTMIKLÓSI HUNGARIAN ACADEMY OF SCIENCES CENTRE FOR ENERGY RESEARCH, BUDAPEST, HUNGARY GYÖRGY GÉMES, PÉTER HOLECZ, GYÖRGY AUGUSZT 19 TH INTERNATIONAL SYMPOSIUM ON TÜV RHEINLAND INTERCERT LTD., BUDAPEST, HUNGARY ZIRCONIUM IN THE NUCLEAR INDUSTRY May 20-23, 2019 Manchester, UK The present work was supported by the National Research, Development and Innovation Fund of Hungary (contract number: NVKP_16-1-2016-0014).
Outline • Motivation to perform integral tests • Materials of the experimental bundle • The integral test facility • The CODEX-LOCA test matrix • Methods and results of post-test examinations
Introduction Small scale separate effect tests • important information on the LOCA (loss-of-coolant behaviour of zirconium alloys in accident) high temperature steam • reactor core in high • data for numerical models temperature conditions • changes of Zr Integral tests mechanical properties • demonstration of fuel behaviour under • ballooning and burst 1000 accident conditions with representative 800 • oxidation, H uptake, Temperature ( °C ) scenarios and materials 600 embrittlement 400 • potential loss of 200 integrity 0 0 2000 4000 6000 8000 10000 12000 14000 Time (s)
Materials • Zirconium materials of VVER reactors • traditional E110 tubes produced by electrolytic technology • sponge based E110 tubes (E110G) • spacer grid from fuel factory • E125 (Zr2.5Nb) alloy shroud (2 mm thickness) • Alumina (Al 2 O 3 ) pellets • KÉP TABLETTA
The CODEX (COre Degradation EXperiment) facility • 7 rod bundles • Hexagonal geometry • Hexagonal shroud • Electrical heating • 600 mm heated length • Internal pressurization of rods • Test section inlet: • steam generator • water injection (reflood) • Test section outlet: • cooler
Post-test examination methods • Profilometry (Mitutoyo laser micrometer) • Eddy current tests (with a bobbin-probe) • Position-sensitive prompt gamma-ray neutron activation imaging (PGAI) driven by neutron radiography (NR) at the Budapest Research Reactor • Measurement of hydrogen content by hot extraction (ELEMENTRAC OH-p analyser) • Four-point banding tests (INSTRON 1195 ensile test machine) • Metallography (Reichert optical microscope)
Max. cladding Test Simulated scenarios CODEX-LOCA test matrix temperature CODEX-LOCA- 200% large break LOCA in the cold leg of the 908 °C 200 primary circuit with conservative conditions CODEX-LOCA- 200% large break LOCA in the cold leg of 874 °C 200B primary circuit Shutdown LOCA in the cold leg of primary CODEX-LOCA- circuit with limited availability of emergency 1089 °C E4 cooling water Spent fuel pool LOCA with steam starvation and CODEX-LOCA- with limited availability of emergency cooling 924 °C SFP1 water Spent fuel pool LOCA with unlimited steam and CODEX-LOCA- with limited availability of emergency cooling 896 °C SFP2 water
CODEX-LOCA-E4 1100 1000 CODEX-LOCA-200 CODEX-LOCA-SFP1 CODEX-LOCA-200B 900 Temperature (°C) 800 CODEX-LOCA- SFP2 700 600 scenarios selected on the 500 basis of VVER-440 400 safety analyses 300 200 100 reflood from the bottom 0 -2000 0 2000 4000 6000 8000 10000 12000 14000 16000 Time (s) T>700 ° C 325 s/255 s 737 s 3786 s 4321 s
State of bundles after the experiments CODEX-LOCA-200: • three of the seven rods burst, the degree of oxidation was modest CODEX-LOCA-200B: • none of the rods burst, very little oxidation CODEX-LOCA-E4 • the traditional E110 rods were heavily oxidized and fractured, while the sponge based E110 tubes remained intact CODEX-LOCA-SFP1 • large deformations took place before burst and no oxidation due to steam starving conditions. CODEX-LOCA-SFP2: • considerable ballooning on some of the rods and modest oxidation
Post-test examinations Eddy PGAI Profilo- Four-point Metallo- Hot Test current NR metry bending graphy extraction CODEX-LOCA- + + + + + 200 CODEX-LOCA- + + E4 CODEX-LOCA- 200B CODEX-LOCA- + SFP1 CODEX-LOCA- + SFP2
24 Profilometry 22 Fuel rod internal pressure (bar) 20 The axial distribution of cladding diameter 18 was determined for the CODEX-LOCA- 16 14 200 bundle 12 1 2 3 4 5 6 7 10 16 8 6 15 burst 4 14 2 Max. diamater (mm) 0 13 300 350 400 450 500 550 600 650 700 750 800 Time (s) Significant deformation 12 wihout burst Si burst 11 burst burst 10 9 8 1 2 3 4 5 6 7 Rod No.
Eddy current measurements of intact and failed rods • Examination of cladding tubes in as-received conditions – no defects, measurement of geometric data • Examination of cladding tubes after experiment (CODEX-LOCA-200): • direct correlation between the expansions and the eddy current signals
1600 Neutron radiography No. 1 Sponge based E110 No. 2 Traditional E110 1400 No. 3 Sponge based E110 No. 4 Traditional E110 No. 5. Sponge based E110 H/Zr mass ratio (ppm) 1200 No. 6 Traditional E110 • hydrogen distribution along the No. 7. Sponge based E110 1000 longitudinal axis of fuel cladding tubes 800 600 CODEX-LOCA-200 400 • Cladding tubes without opening 80 – 100 ppm and no clear peaks 200 • Traditional E110 cladding tubes with burst 0 the hydrogen 1100 and 1500 ppm 340 360 380 400 420 440 460 480 500 520 540 Distance from the bottom (mm) • Sponge based cladding tube with opening 250 ppm
Neutron radiography CODEX-LOCA-E4 • sponge based E110 cladding tubes, small opening 500 – 700 ppm peaks • traditional cladding tubes, large visible burst and fracture, 6000 – 7000 ppm • sponge based E110 cladding tubes larger opening,1600 – 1800 ppm
Hydrogen content by hot extraction • The individual measurements showed large scatter. Neutron radiography Hot extraction • Several hundreds ppm variations between different circumferential positions
Four-point bending tests 1400 CODEX-LOCA-200 1200 • only one rod, showed brittle behaviour 1000 (bending moment 11.5 Nm, traditional Load (N) E110 alloy with burst) 800 Rod No. 1. Rod No. 2. 600 Rod No. 3. Rod No. 4. 400 Rod No. 5. Rod No. 6. 200 Rod No. 7. 0 0 1 2 3 4 5 6 7 8 9 10 Displacement (mm)
Metallography CODEX-LOCA-SFP1 • Large deformations before burst • No oxidation due to the limited steam supply
Metallography CODEX-LOCA-SFP2 • formed oxide layer was compact on the sponge based E110 cladding tubes • layered structure and spalling on the traditional E110 tubes • both oxide and α -layer thicknesses 10 µm on the external surface, no oxide layer detected inside 540 Distance from the bottom (mm) 510 480 Rod No. 1. 450 Rod No. 2. Rod No. 3. 420 Rod No. 4. Rod No. 5. Rod No. 6. 390 Rod No. 7. 4 6 8 10 12 14 16 18 20 Oxide layer ( m m)
Conclusions 1/2 • The behaviour of traditional and sponge based E110 cladding tubes was compared in integral LOCA experiments. • Design basis cold leg break 200% LOCA scenario for a VVER-440 reactor: • the representative pressure and temperature conditions would not result in cladding burst for this scenario for both traditional and sponge based E110 alloys. • LOCA events with limited availability of emergency core cooling water injection in the shut-down reactor and in the spent fuel pool: • the long oxidation times at high temperatures resulted in the formation of oxide scale on the zirconium surfaces. The spalling oxide scale and high hydrogen pick-up of the traditional E110 cladding resulted in brittle fracture of fuel rods with long oxidation scenarios.
Conclusions 2/2 • Profilometry examinations pointed out that large deformations may take place even in those rods under high internal pressure, which did not burst during the high temperature experiment. • Using the eddy current technique direct correlation was established between the expansions and the eddy current signals. • The hydrogen content in ballooned region showed the typical two peaks distribution only in case of long oxidation times. In several cladding tubes with short oxidation times only one peak was observed. • According to the four point bending tests the fuel rods after high temperature LOCA test still had significant load bearing capability and ductility in design basis accident scenarios.
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