C GRANDJEANIRSN CadaracheNRC IRSN Meeting Bethesda January 24 - PDF document

1 C. GRANDJEANIRSN, CadaracheNRC / IRSN Me
C. GRANDJEANIRSN, CadaracheNRC / IRSN Meeting, Bethesda, January 24-26, 2007Considerations and Questions C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 2/30 In 1967, the Ergen Task Force concluded :“The analysis of a LOCA requires that the core be maintained in place and essentially intact to preserve the heat-transfer area and coolant-flow geometry.”In 1971, the USAEC promulgated the Interim Acceptance Criteria (IAC) for ECCS, in which Criterion 3 states that:“The clad temperature transient is terminated at a time when thecore geometry is still amenable to cooling, and before the cladd

2 ing is so embrittled as to fail during o
ing is so embrittled as to fail during or after quenching.”ªECCS Rule-Making Hearing (1972-1973)Current ECCS acceptance criteria (10 CFR50.46)Opinion of the Commission, Docket RM-50-1, December 28,1973:“In view of the fundamental and historical importance ofmaintaining core coolabilitywe retainthis criterion as a basic objectivein a more general form than it appeared in the IAC. C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 3/30 In France, within current considerations for a future revision of the LOCA acceptance criteria, the original objective of maintaining core coolabilityand possib

3 ly complemented with additional concerns
ly complemented with additional concernsdispersal of fuel particles in the reactor primary circuit,radiological release,structural material integrity,New Basis for a Revision of the Acceptance Criteria ? C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 4/30 In LOCAs there are two modes in which the coolabilityof the core may be Ductile mode :clad ballooning leading to partial blockage of the FA channels)adressedin 10CFR50.46 by: Coolablegeometry: Calculated changes in core geometry shall be such that the core remains amenable to cooling.Brittle mode :Loss of cladding integrity upon quench a

4 nd post-quench loadsadressedin 10CFR50.4
nd post-quench loadsadressedin 10CFR50.46 by the well-known embrittlementlimits:Peak cladding temperature : PCT 2200°F (1204°C)Maximum cladding oxidation : ECR 17%.Maintaining the Core Coolability C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 5/30 Coolabilityof Partially Blocked Assemblies under LOCA Conditions Current ECCS acceptance criteria (10 CFR50.46) requires§50.46 (b)(4). Coolable geometry +(b)(5) Long-term coolingCalculated changes in core geometry shall be such that the core remains amenable to cooling.Although a quantitative limit is not associated to the above criteria, the r

5 equirement is generally considered as me
equirement is generally considered as met in consideration of :the results of FEBA/SEFLEX experiments (coolabilityof blocked arrays) showing that a 90% blockage keepscoolablethe maximum flow blockage ratio, inferred from NUREG-630 review (~71%)value deduced from NUREG-630 burst strain curves, recognized later as non conservative (see next slide) C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 6/30 Coolabilityof Partially Blocked Assemblies under LOCA Conditions Slow-ramp burst strain correlation from NUREG-630 and data reported after NUREG-630 was published(R. Meyer, ANS Meeting, Sun Valle

6 y, 1981) C. GrandjeanNRC / IRSN Meeting,
y, 1981) C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 7/30 COOLABILITY OF BLOCKED REGIONS. Main findings from SOAR Experiments with longer blockages (THETIS)have shown that the maximum tested ratio of 90% may not necessarily be the most penalizing case for axially extended balloons.Experimental results of flooding experiments with partially blocked rod arrays FEBA/SEFLEX, THETIS, ACHILLES, CEGB, SCTF, FLECHT-SEASET)have shown that blockages, even of high ratio (90%) but of moderate length (10 cm), do not impair the bundle coolability under LOCA reflood.Analytical simulations confirm tha

7 tsignificant increases in blockage wall
tsignificant increases in blockage wall temperatures, that may threaten blockage coolability,require a high blockage ratio &#x-3.9;( 80%) and a long extension &#x-3.9;( 15 cm) of the blockage.The coolabilityof blocked bundleswith fuel relocated in clad balloonsremains an open question, particularly for long balloons and low refloodrate, for which the blockage ratio still coolablemight be less than the widely admitted value of 90% derived from FEBA/SEFLEX tests results. C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 8/30 Pending questions : 1.What is the maximum flow blockage ratio in a b

8 locked assembly that can still be amenab
locked assembly that can still be amenable to cooling, with taking account of a relocation of fragmented fuel in the ballooned claddings ?2.What is the maximum flow blockage that can be obtained in an assembly and what is the available margin with respect to Q1The lack of current quantitative criteria rises questions on:How to characterize a coolablesituation in specific experiments ? Which quantitative (revised) criteria would be appropriate to specify the ECCS calculated performance with respect to the coolabilityof blocked assemblies under LOCA scenarios ?Maintaining Core Coolability -Duct

9 ile Mode C. GrandjeanNRC / IRSN Meeting,
ile Mode C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 9/30 RATIONALE FOR EMBRITTLEMENT CRITERIA in 10 CRF50.46Maintain coolable geometryKeep fuel pellets inside the claddingion or break in several piecesRetain some in the claddingLimit cladding oxidation and temperaturePCT and ECR limits (2200°F, 17%) derived from Hobson’s ring compression tests on oxidized and quenched samples of unirradiated Zy claddingNo effects of BU were consideredMaintaining Core Coolability -Brittle ModeBasic requirement is to preclude clad failure upon quench and post quench loads at any location, including th

10 e ballooned and bursted region C. Grandj
e ballooned and bursted region C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 10/30 Total oxidation As originally formulated in 50.46, the embrittlementcriteria applied implicitly to an initially non oxidized cladding, thus to a fresh fuel rod.means the total thickness of cladding metal that would be locally converted to oxide if all the oxygen absorbed by and reacted with the cladding locally were converted to stochiometric zirconium dioxide.”In NRC Information Notice 98-29, as an interim measure to account for the pre-corrosion effect, “total oxidation” was considered differently:“ The

11 acceptance criterion in 10CFR50.46(b)(2)
acceptance criterion in 10CFR50.46(b)(2) requires that thecalculated maximum total oxidation of the cladding not exceed 0.17 times the total thickness of the cladding before oxidation. includes both pre-accident oxidation and oxidation occurring during a Maintaining Core Coolability -Brittle ModeModifications to embrittlement criteriaRevision of the criteria in 1988 (based on “Compendium of ECCS Research for Realistic LOCA Analysis : NUREG-1230)Allows to use, alternatively to Appendix K evaluation models, best-estimate evaluation models together with an assessment of calculational uncertaintie

12 sKeep unchanged the previous limits in 1
sKeep unchanged the previous limits in 10CFR50.46(b) C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 11/30 Main Findings from a State-of-the-Art Review of LOCA Research (I)Maintaining Core Coolability -Brittle ModeThermal shock quench tests after 1973 (ANL, JAERI, EdF/IRSN) (1)Significant margin with respect to ECR limit in tests with quench at oxidation temperature 90011001300150017001900 Equivalent Cladding Reacted (%) 17% limitChung & KassnerHessonScatenaGrandjean & Lebuffe 1204°C limit C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 12/30 Main Findings from a State

13 -of-the-Art Review of LOCA Research (I)M
-of-the-Art Review of LOCA Research (I)Maintaining Core Coolability -Brittle ModeThermal shock quench tests after 1973 (ANL, JAERI, EdF/IRSN) (2)Influence of quench temperature and cooling rate prior quenchSlow cooling in domain increases the quench bearing limit C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 13/30 Main Findings from a State-of-the-Art Review of LOCA Research (I) Maintaining Core Coolability -Brittle ModeThermal shock quench tests after 1973 (ANL, JAERI, EdF/IRSN) (3)Influence of an initial corrosion, H pre-charging or prior irradiationLow or no influence on quen

14 ch bearing limit under unrestrained cond
ch bearing limit under unrestrained conditions Failure map under no restrained condition for as-received and pre-hydridedcladdings (JAEA)(ECR from B-J equation , 2 sided oxidation on ballooned cladding) C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 14/30 Main Findings from a State-of-the-Art Review of LOCA Research (I)Maintaining Core Coolability -Brittle ModeThermal shock quench tests after 1973 (ANL, JAERI, EdF/IRSN) (4)Influence of an initial H content under axial restrained conditions (A) Failure map under fully restrained condition for as-received and pre-hydridedcladdings (JAEA)

15 C. GrandjeanNRC / IRSN Meeting, Januar
C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 15/30 Main Findings from a State-of-the-Art Review of LOCA Research (I) Maintaining Core Coolability -Brittle ModeThermal shock quench tests after 1973 (ANL, JAERI, EdF/IRSN) (4)Influence of an initial H content under axial restrained conditions (B))Conservatism of the 17% ECR criterion for quench of as-received or irradiated cladding under “realistic” axial loading conditions Failure map under controlled load conditions for two hydrogen concentration levels (JAEA) C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 16/30 Main Findings

16 from a State-of-the-Art Review of LOCA R
from a State-of-the-Art Review of LOCA Research (II)Maintaining Core Coolability -Brittle ModeResistance to 0.3 J impact tests (ANL) Ballooned cladding Still adequacy of the 17% ECR criterionUnballoonedcladding Conservatism of the 17% ECR criterion(impact on opposite side of burst opening) 900100011001200130014001500 failed Equivalent Cladding Reacted (%) C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 17/30 Main Findings from a State-of-the-Art Review of LOCA Research (III)Maintaining Core Coolability -Brittle ModePost oxidation and post quench ductility tests (ANL, JAERI, CEA,UJP,…)Pos

17 t-oxidation ductility of undeformedZy4 c
t-oxidation ductility of undeformedZy4 cladding tubes 04812162024283236Total Deflection (mm) ANL tests 1980, unirradiated(H wppm), no quenchDuctility retained (deflect&#x 130;&#x-9.3;ion 2 mm)for ECR (measured) 17% and T 1315°C Recent ANL tests, irradiated HBR samplesDuctility retained ( offset stra�in 3%)for ECR-CP 8% without quenchthreshold unclear with 800°C quench C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 18/30 Main Findings from a State-of-the-Art Review of LOCA Research (III)Maintaining Core Coolability -Brittle ModePost oxidation and post quench ductility testsPost

18 -oxidation ductility of ballooned and bu
-oxidation ductility of ballooned and burstANLDiametralCompression Tests (0.043 mm/s at 300 K) on Ruptured Zircaloy-4 Cladding That Survived Thermal Shock and Impact Loads. Total Deflection to Maximum Load as function of ECR parameter (from NUREG/CR-1344 data) 05101520253035404550ECR (%)Total Deflection to Maximum Load (mm) brittle C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 19/30 Main Findings from a State-of-the-Art Review of LOCA Research (III)Maintaining Core Coolability -Brittle ModePost oxidation and post quench ductility testsInfluence of transient H pickup from inner side of

19 a burst cladding Distribution of H conte
a burst cladding Distribution of H content, ID oxide layer thickness and total deflection at 100°Cof Zy4 rings sectioned from burst region (JAEA, 1981))Lowest ductility at the top and bottom necks with highest concentration of H C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 20/30 Main Findings from a State-of-the-Art Review of LOCA Research (III)Maintaining Core Coolability -Brittle ModePost oxidation and post quench ductility testsInfluence of quench temperature and cooling rate prior quench (ANL, CEA) Cooling rate influences ’transformation, microstructure and hydride precipitation N.

20 Waeckel, ANL LOCA Meeting, June2006, Co
Waeckel, ANL LOCA Meeting, June2006, Copyright EDF/CEA C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 21/30 Main Findings from a State-of-the-Art Review of LOCA Research (III)Maintaining Core Coolability -Brittle ModePost oxidation and post quench ductility testsInfluence of quench temperature and cooling rate prior quench (ANL, CEA) Cooling rate influences ’transformation, microstructure and hydride precipitation V. Maillot, J.C. Brachet, ANL LOCA Meeting, June2006, Copyright CEA C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 22/30 Main Findings from a State-of-the-Art Review of

21 LOCA Research (III)Maintaining Core Cool
LOCA Research (III)Maintaining Core Coolability -Brittle ModePost oxidation and post quench ductility testsOxygen diffusion from an initial corrosion layer at T(UJP) Pre-oxidised standard ASTM Zircaloy-4 (950°C0510152025ECRCath-Paw [%]Residual ductility at RT [ % ] 0 µm 2 µm 10 µm 50 µm Residual ductility at RT after steam oxidation at on samples pre-corroded at 425 °C in steam up to 50 (V. Vrtilkova, SEGFSM Meeting, Paris, April 2005)ECR cannot account for the partial dissolution of the pre-oxide layer in the underlying prior (influenced by T and H content near the oxide/metal interface

22 ) C. GrandjeanNRC / IRSN Meeting, Janua
) C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 23/30 Main Findings from a State-of-the-Art Review of LOCA Research (IV)Maintaining Core Coolability -Brittle ModeIntegral tests (CEA, ANL, JAEA)(1)PhebusLOCA Test 219 (CEA), 25 rods bundle, fresh fuel Rod 18, exposed to Tmax~1330°C, was found fragmented despite ECR 16%Likely due to a deleterious bundle effect : assembly constraints due to bending of rods and possibly rod-to-rod impact duringreflooding. C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 24/30 Main Findings from a State-of-the-Art Review of LOCA Research (IV)Maintaining

23 Core Coolability -Brittle ModeIntegral
Core Coolability -Brittle ModeIntegral tests (ANL, JAEA, CEA)(2)ANL : ICL Tests on high BU Limerick BWR single rods (56-57 GWd/MTU)From the 4 in-cell tests on irradiated rods, two (ICL#3, #4) were conducted with a 300 s hold at 1204°C, cooling at 3°C/s to 800°C and quench (unconstrained). Burst occurred at 730 and 790°C respectivelyMaximum calculated ECR was ~ 21% and 20%)Both LOCA integral samples remained intact during and following the quenchSamples were not subjected to post-quench ductility tests (bend test) C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 25/30 Main Findings from a S

24 tate-of-the-Art Review of LOCA Research
tate-of-the-Art Review of LOCA Research (IV)Maintaining Core Coolability -Brittle ModeIntegral tests (ANL, JAEA, CEA)(3)JAEA : Tests on irradiated PWR single rods (39-44 GWd/MTU)with 540 N axial constraint Initial hydrogen concentration (ppm) 540N 050010001500 ECR (%)Initial hydrogen concentration (ppm) 540N 050010001500 ECR (%) Irradiated claddingSurvivedFracturedUnirradiated claddingSurvivedFractured Irradiated claddingSurvivedFracturedUnirradiated claddingSurvivedFractured failure boundary is not significantly reduced by PWR irradiation at the examined moderate BU level( 15-25 µm oxide, 1

25 20-210 ppm H ) C. GrandjeanNRC / IRSN Me
20-210 ppm H ) C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 26/30 Summary of Main Results of LOCA Researchwith Respect to Embrittlement Limits (1)Maintaining Core Coolability -Brittle ModeResistance to quench thermal shock)Conservatism of the 17% ECR criterion for quench of as-received or irradiated cladding under unconstrained and “realistic” axial loading conditionsResistance to 0.3 J impactConservatism of the 17% ECR criterion forunirradiated unballoonedcladding and still adequacy for ballooned cladding C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 27/30 Summary of Main Res

26 ults of LOCA Researchwith Respect to Emb
ults of LOCA Researchwith Respect to Embrittlement Limits (1)Maintaining Core Coolability -Brittle ModeRetention of a residual post-quench ductility Ductile-brittle transition ECR-CP threshold� 17% for unirradiated unballoonedcladding Low ECR threshold for high BU Zircaloy undeformed cladding due to hydrogen influence (ECR threshold % for the HBR quenched sample) Very low ECR threshold for irradiated cladding after oxidation at T due to O diffusion from initial oxide layer into metal sublayer(to be confirmed !) No practical limit can be derived to ensure ductility retention in balloons

27 due to the very large H content absorb
due to the very large H content absorbed on ID upon secondary hydriding C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 28/30 Is it necessary to preclude clad fragmentation upon quench and post quench loads at any location , including the ballooned and burstedregion?Maintaining Core Coolability -Brittle ModePendingQuestionsIf no, it will be needed :to define new requirements on the extent of acceptable fragmentation,to evaluate its impact on radiological release and integrity ofstructuresIf yes,it appears that a ductility retention in ballooned regions cannot be ensuredWhich requirement

28 to be applied to ballooned regions ?Can
to be applied to ballooned regions ?Can the requirements be different in ballooned and unballoonedparts of the cladding ? Upon which physical justification ? C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 29/30 ation cannot be precluded in ballooned regions, which requirement should be chosen for the other regions :Which representative loads to be considered for a reasonably conservative prevention of clad fragmentation : quench thermal-shock under “realistic” restraint, orpost-quench mechanical loads ?Which physical requirement :Quench resistance under which restraint (axial / radial lo

29 ad) ?Resistance to PQ loads, at which T
ad) ?Resistance to PQ loads, at which T ?(RT, 135°C…) : ductility : brittle-ductile transition in compression or bending test toughness : impact teststrength : tensile testIs there an impact of the LOCA scenario ?Is a unique criteria appropriate for both LB and SB LOCAs ?Is the existing data base sufficient or not ?Maintaining Core Coolability -Brittle ModePendingQuestions (cont.) C. GrandjeanNRC / IRSN Meeting, January 24-25, 2007 30/30 Selection of an adequate parameter to quantify an embrittlement limit ECR (any combination of tranRelates essentially to the amount of brittle phases (oxide,

30 alpha layers)Oxygen content in tandem w
alpha layers)Oxygen content in tandem with thickness in (ex. Chung/Kassner handling limit : % ox�.7 ;&#xwt-7;&#x.500;ygen in 0.3 mm layer)Relates to the properties of the remaining ductile phaseMaintaining Core Coolability -Brittle ModePendingQuestions (cont.)safety analysis to calculate the selectedembrittlementcriteriaModeling of oxygen diffusion in moving-boundary systems makes it possible to correctly evaluate the oxygen distribution in layerImprovements to include the recent findings for the effects of Handpretransientcorrosion layer are under development at IRSN in an advanced diffu