LOCA experiment med högutbränt bränsle i Haldenprogrammet

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1 LOCA experiment med högutbränt bränsle i Haldenprogrammet Erik Kolstad (erikk@hrp.no) OECD Halden Reactor Project Presented at the: 1 The Halden reactor experimental program The program comprises studies on: Fuel High Burnup Capabilities in Normal Operating Conditions Fuel Response to Transients (LOCA) Cladding Corrosion & Water Chemistry Issues Plant Lifetime Assessment 2 1

2 Phases of loss of coolant accident Clad temperature αphase Power Oxidation Ballooning & rupture Pellet relocation Embrittlement Quench Reflooding time 3 Calculations of Extent of Fuel Rod Failure in LOCAs in LWRs There are basically two types of criteria: empirical failure criterion or probabilistic analyses (rupture temperature vs. clad hoop stress for different heatup rates) (best estimate or conservative limits) mechanistic failure criterion (clad creep properties, clad temperature, rod pressure, time, etc) Corewide calculations are made in some countries Assessment of radiological consequences of a LOCA depends on the calculated extent (number) of fuel clad failures Assumption in USA and in EU: 100% except in Germany and Switzerland where only<10% is allowed 4 2

3 The empirical NUREG0630 Clad Rupture Model T Rup ( O C) vs. Hoop Stress (kpsi) or Rod Overpressure (bar) 5 LOCA testing at Halden (Δp=55bar) High temperature secondary creep of Zircaloy (αphase) ε s = C. S 5. exp(q/rt). T (MATPRO) Strong stress and temperature dependence 6 3

4 LOCA testing at Halden High temperature oxidation t ox = 1400 exp( 9030/T) t (MATPRO) Peak clad temperature (PCT) for: IFA650.4 (PWR) 850 O C IFA650.5 (PWR) 1100 O C IFA650.7 (BWR) 1150 O C IFA650.9 (PWR) 1100 O C Oxide thickness (μm) Time (mins) 7 HRP Loss of coolant studies The Halden reactor test series focuses on inreactor effects that are different from those obtained in outofreactor tests. In particular, the heating from within the fuel rod, in contrast to the external heating of outofpile setups, may affect a number of phenomena. Primary objectives: Measure the extent of fuel (fragment) relocation into the ballooned region and evaluate its possible effect on cladding temperature and oxidation Investigate the extent of secondary transient hydriding of the cladding above and below the burst region 8 4

5 Schematic of Halden LOCA Rig IFA650 Rod Instrumentation: 3 cladding thermocouples 2 upper (TCC2 & TCC3) 1 lower (TCC1) 3 heater thermocouples: 1 upper (TCH3) 1 middle (TCH2) 1 lower (TCH1) Fuel pressure transducer (PF1) Cladding elongation detector (EC2) Activity release monitor (GM) 9 HRP LOCA experiments Design Features ø34 Flask Heater cable Single rod experiment using high burnup fuel Heating provided from within the rod by low level nuclear power simulating decay heat Simulation of the thermal boundary conditions with an insulating channel and heated shroud Spray system for steam supply Possibility for both depressurisation and reflooding PWR/BWR/VVER conditions Heater T/C ø 9.5 rod ø26.5 / ø 20 heater Cross section of fuel pin, flow separator and pressure tube used in HRP LOCA studies 10 5

6 HRP LOCA experiments Some key parameters regarding rod design and test conditions Plenum volume Fill gas pressure Peak cladding temperature (PCT) Duration of temperature transient Slow cooling or quench Spray application at high temperatures 11 Typical axial power profileifa650 TCs TCHs (Heater TCs) 2,

7 LOCA testing at Halden Tests carried out: IFA650.1 (Fresh PWR) May 2003 IFA650.2 (Fresh PWR) May 2004 IFA650.3 (PWR, 82 MWd/kg) April 2005 IFA650.4 (PWR, 92 MWd/kg) April 2006 IFA650.5 (PWR, 83 MWd/kg) Oct IFA650.6 (VVER, 55 MWd/kg) April 2007 IFA650.7 (BWR, 40 MWd/kg) April 2008 IFA650.8 (Fresh PWR) Dec.2008, Feb.2009 IFA650.9 (PWR, 90 MWd/kg) April 2009 Planned: IFA (PWR, 60 MWd/kg) May 2010 IFA (VVER, 55 MWd/kg) Sept Fuel rod data Items 3rd test 4th test 5th test 6th test 7th test 8th test 9th test Fuel type Rod id. Span no. Length, cm Cycles Burnup (MWd/kgU) Oxide, (μm) Hydrogen (ppm) Enrichment, (w/o U 235 ) Grain size, (μm) Cladding Diameter, (mm) Thickness, (mm) Liner, (μm) Heat treatment Target PCT, O C PWR V1515/ Zr SRA 800 PWR 14D/ Zr SRA 800 PWR V1515/ Zr SRA 1100 VVER J ~5 3.6 E No Standard 850 BWR AEBO70E ~40 < LK3/L Yes Standard 1150 PWR 50 Fresh Zr SRA PWR 14D/ Zr SRA ~

8 LOCA Testing at Halden Selected results (inpile & PIE) from PWR test IFA650.4 (92 MWd/kg) PWR test IFA650.5 (83 MWd/kg) BWR test IFA (40 MWd/kg) 15 Test scheme IFA650.4 (PWR) Fill gas 95% Ar/5% He, pressure 40 bar (RT) Rod power ~10 W/cm, heater power ~15 W/cm Heater for simulating heat from surrounding rods Power levels from code calculations & previous experience PCT 800 O C, hold time ~5 min Application of spray after clad failure Termination by scram Gamma scanning at Halden To verify cladding deformation and fuel relocation Rig filled with epoxy To keep fuel intact for PIE PIE at Kjeller (completed) 16 8

9 IFA650.4 temperatures 17 IFA650.4 Cladding ballooning burst indications 18 9

10 Axial γscan, diameter profile (2 orientations), and sampling locations Topp Bottom IFA Balloon zone Ballooning&burst with fuel fragmentation. Fuel fragments inside and outside the clad. Fuel fragment diameters vary from <6mm to <0.1mm. Fuel fragments were stabilised by epoxy impregnation. Epoxy penetration through burst / open crack. Crosssections reveal balloon size and maximum deformation. M6 235m m M4 275 mm M6n 232 mm M5 255m m M3/4r 305m m 20 10

11 Summary IFA650.4 Target PCT, 800 C, achieved Rod power ~10 W/cm, heater power ~15 W/cm Cladding burst at ~785 C Internal pressure 51 bar Burst indication by pressure drop, elongation and cladding thermocouple responses Fuel relocation indicated by lower heater thermocouple and neutron detector signals Hold time ~5 min (from burst to scram) Application of spray at end of test Test terminated by scram Gamma scanning revealed ballooning and fuel relocation Rig filled with epoxy for PIE 21 Test scheme IFA650.5 (PWR) Fill gas 95 % Ar / 5 % He, pressure 40 bar (RT) Rod power ~25 W/cm, heater power ~17 W/cm (estimated to reach 1100 C) Clad failure at 750 C (TCC1, lower part) (corresponds with previous experience) Application of spray after clad failure PCT 1100 C Termination by scram 22 11

12 IFA650.5 Cladding deformation and burst Clad ballooning deformation by rod pressure measurement (maximum at 171 s) Cladding failure at 178 s (rod pressure drop, slow compared with previous tests) 23 1 s) Gamma scanning results IFA650.5 Two scans from different angles Some small deformations at the lower part of the rod Fuel detected at the bottom of the flask Fallen through the narrow opening in cladding 24 12

13 Failure appearance in IFA650.5 Diameter increase about 1 med mer (original diameter indicated with red arrow) Failure location in the lower end of fuel stack Clear crack opening. Slow pressure drop probably result of impeded gas communication at upper unballooned end 25 IFA650.5 cracking pattern 13 12, , , Pellet cracking is influenced by the constraint exerted by the cladding at the moment of failure. At the upper half (strong contact), the cracking from normal operation prevails. Where the cladding distended (lower half), the sudden drop of pressure caused additional pellet cracking

14 IFA650.5 Hydraulic Diameter The concept of hydraulic diameter has been used in various Halden reactor experiments to assess the permeability of fuel columns High burnup fuel is known to exhibit quite impeded axial gas communication In a LOCA test, as long as general cladding distension has not opened the fuelclad gap, (parts of) the fuel stack will hinder gas flow In this situation, ballooning will be driven by the locally available gas pressure IFA650.5 can be evaluated with respect to gas flow 27 Test scheme IFA650.7 (BWR) PCT 1150 C Rod power ~35 W/cm, heater power 20 W/cm Fill gas 95 % Ar / 5 % He, pressure 6 bar (RT) Clad failure predicted around 1050 C Application of spray above 900 C Termination by scram after exceeding 1204 C, or ~300 seconds after blowdown 28 14

15 Cladding deformation and burst Start of ballooning: cladding deformation detected by rod pressure measurement Pressure maximum (~110 bar) reached at 190 s, hoop stress 5.5 MPa Cladding failure 247 s after blowdown at ~1100 C Rod pressure drops suddenly Gamma monitor response in blowdown line ~10 s later 29 IFA650.7 Gamma Scanning (Halden) 30 15

16 IFA650.7 Post test diameter measurements 31 Summary IFA650.7 (BWR) PCT ~1150 C (Reached) Rod power ~35 W/cm, heater power ~1520 W/cm Application of spray above 900 C Rod burst at ~1102 C (247 s) (βphase) Internal pressure ~10.5 bar, hoop stress ~5.0 MPa Burst indication by pressure decrease and cladding thermocouple response Hold time ~64s (from burst to scram) ~310s after start of blowdown Evidence of fuel relocation heater and fuel TCs Gamma scanning in Halden PIE in progress at Kjeller hot cells 32 16

17 : Inpile Halden data (Irradiated cladding) Zr2 (BWR) Zr4 (PWR) D.L. Chapin et al. Top Fuel 2009 (Paris) E110 (VVER) 33 SUMMARY The Halden LOCA program has investigated the behaviour of high burnup fuel (4092 MWd/kg) Cladding failure mode is depending on fill gas pressure, cladding conditions (ductility)and fuel burnup Axial fuel relocation/dispersal was indicated in one test (IFA650.4) with fully developed ballooning Another test resulted in brittle failure without ballooning (IFA650.5) The evaluation of the pressure drop (hydraulic diameter) indicates impeded axial gas flow and consequently less driving force for the ballooning in the latter case The first VVER and BWR tests have been performed (VVER test not dealt with here) PIE in support of the inpile measurements is ongoing The series will continue with further PWR, VVER and BWR fuel behaviour studies under simulated LOCA conditions 34 17

18 References E. Kolstad, W. Wiesenack, B. Oberländer, A comparison of fuel fragmentation & relocation behaviour in Halden reactor LOCA experiment Fuel Safety Research meeting, Japan. May 2009 W. Wiesenack, L. Kekkonen, B. Oberländer, Axial gas transport and loss of pressure after ballooning rupture of high burnup fuel rods subjected to LOCA conditions Physor 2008 conference, Switzerland. September E. Kolstad, W. Wiesenack, L. Kekkonen, B. Oberländer, LOCA testing at Halden, recent tests and plans LOCA workshop meeting at Argonne. October 2007 W. Wiesenack, L. Kekkonen, Overview of recent and planned Halden Reactor Project LOCA experiments Fuel Safety Research meeting. Japan. May 2007 E. Kolstad, LOCA testing at Halden, Status and Plans LOCA workshop meeting at Argonne. June 2006 E. Kolstad, W. Wiesenack, V. Grismanovs, B. Oberländer, LOCA testing at Halden; second inpile test in IFA650 and preliminary PIE Fuel Safety Research meeting Tokyo March 2005 E. Kolstad, V. Lestinen, W. Wiesenack, LOCA testing at Halden, trial runs in IFA650 at Nuclear Safety Research conference. Washington October Thank you for your attention 36 18