1 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France FP release from VERCORS tests: semi-volatile, low-volatile FP and actinides Classification by volatility degree  Semi-volatile FP: Mo, Ba, Rh, Pd, Tc  Low-volatile FP: Ru, Nb, Sr, Y, La, Ce, Eu  Non volatile FP: Zr, Nd, Pr  Actinides: U, Np, Pu, Am, Cm Analysis of the main parameters affecting their release  Temperature  Oxidising/Reducing conditions  Material interactions  Fuel burn-up  Fuel nature  UO 2 /MOX  steady state fuel/debris bed/molten pool

2 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Semi-volatile: Molybdenum, main characteristics Only one significant radioactive isotope: 99 Mo …  2,7 days of half life  acting in the short term  Low radiological effects, as well as low impact on residual power … but several stable isotopes  High mass inventory and ability to be chemically associated with other FP (Cs to form Cs 2 MoO 4 ) and to modify their volatility Essentially under metallic precipitate within the fuel  Associated with Ru, Rh, Pd

3 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Mo release: impact of oxidising conditions Test number Fuel and conditions Test atmosphere Mo release Ba release Rh release Vercors 4UO 2 3 cycles 2570 K Reducing47%80%45% Vercors 5UO 2 3 cycles 2570 K Oxidising (pure steam) 92%55%20% Vercors 6UO 2 5 cycles 2620 K (collapse) Oxidising (H 2 O-H 2 ) 79%28%4% HT3UO 2 4 cycles 2680 K (collapse) Reducing33%85% HT2UO 2 4 cycles 2420 K (collapse) Oxidising (pure steam) 100%38% RT7MOX 3 cycles 2890 K (collapse) Reducing7% Mox effect ? 64% RT2MOX 3 cycles 2440 K (collapse) Oxidising (H 2 O-H 2 ) ~ 50% RT6UO 2 6 cycles 2470 K (collapse) Oxidising (H 2 O-H 2 ) BU effect ?

4 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Mo release: interaction with Cs (from VERCORS 6) Same location of deposit on the upper part of the sleeve Same location in the fuel-corium zone  And different from 95 Zr distribution, representative of the fuel-corium location Upper sample (extracted from the crucible) Lower sample (remained within the crucible) Downstream deposit along the sleeve

5 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Mo retention in the fuel: large metallic precipitates associated with Ru (from RT3)

6 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Semi-volatile: Barium, main characteristics Main radioactive isotope: 140 Ba, parent of 140 La  12,7 days of half life  acting in the middle term Important radiological effect  Released fraction High impact on residual power  "Corium" fraction, but also deposit within the upper part of the RPV  140 Ba/ 140 La holds 15-20% of the total residual power between 1 day and 1 month

7 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Ba release: impact of reducing conditions Test number Fuel and conditions Test atmosphere Mo release Ba releaseRh release Vercors 4UO 2 3 cycles 2570 K Reducing47%80%45% Vercors 5UO 2 3 cycles 2570 K Oxidising (pure steam) 92%55%20% Vercors 6UO 2 5 cycles 2620 K (collapse) Oxidising (H 2 O-H 2 ) 79%28% Lower release after melting 4% HT3UO 2 4 cycles 2680 K (collapse) Reducing33%85% HT2UO 2 4 cycles 2420 K (collapse) Oxidising (pure steam) 100%38% RT7MOX 3 cycles 2890 K (collapse) Reducing7%64% RT2MOX 3 cycles 2440 K (collapse) Oxidising (H 2 O-H 2 ) ~ 50% RT6UO 2 6 cycles 2470 K (collapse) Oxidising (H 2 O-H 2 ) BU effect ?

8 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Ba release: interaction with the cladding (trapping by Zr) – From VERCORS 5  int clad  ext clad 15% of initial Inventory inside the cladding

9 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Ba release: high upstream retention (from VERCORS 5)

10 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Ba release without cladding – Debris bed configuration from RT3 Higher kinetics than Mo (the only time) Nearly total release at the end of the test (60% at the beginning of debris melting)

11 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Semi-volatile FP: Rh, Pd, Tc - main characteristics Very low radiological impact Rh: only 105 Rh  1,5 days  acting in the short term Pd, Tc: no radioactive isotopes Essentially under metallic precipitate within the fuel  Associated with Ru and Mo

12 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Rh release: similar behaviour than Ba Test number Fuel and conditions Test atmosphere Mo release Ba release Rh release Vercors 4UO 2 3 cycles 2570 K Reducing47%80%45% Higher release in reducing cond. Vercors 5UO 2 3 cycles 2570 K Oxidising (pure steam) 92%55%20% Vercors 6UO 2 5 cycles 2620 K (collapse) Oxidising (H 2 O-H 2 ) 79%28%4% Lower release after melting HT3UO 2 4 cycles 2680 K (collapse) Reducing33%85% HT2UO 2 4 cycles 2420 K (collapse) Oxidising (pure steam) 100%38% RT7MOX 3 cycles 2890 K (collapse) Reducing7%64% RT2MOX 3 cycles 2440 K (collapse) Oxidising (H 2 O-H 2 ) ~ 50% RT6UO 2 6 cycles 2470 K (collapse) Oxidising (H 2 O-H 2 ) BU effect ?

13 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Pd, Tc: similar behaviour than Mo ? Data obtained by chemical analysis at TUI Test number Fuel and conditions Test atmosphere Mo release Pd release Tc release RT1UO 2 3 cycles 2440 K Oxidising (H 2 O-H 2 ) 70%34%21% RT2MOX cycles 2440 K Oxidising (H 2 O-H 2 ) 53%42%11% RT3UO 2 Debris bed Reducing (H 2 O-H 2 ) 26%16%0% ? RT4UO 2 -ZrO 2 Débris bed Oxidising (H 2 O-H 2 ) 100%45%42% Slightly lower release than Mo Slightly lower release in reducing conditions

14 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Semi-volatile FP release: conclusion Significant released fraction  Can be as high as for volatile FP, but … High sensitivity to oxidizing/reducing conditions  Mo more volatile in oxidizing conditions  And probably also Pd, Tc  Ba, Rh more volatile in reducing conditions Materials interactions, affecting their release  Ba trapped by Zr of the cladding  Potential chemical interaction of Mo with Cs, limiting Cs release Additional Burn-Up effect  Seems to increase Ba release in oxidising conditions

15 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Low volatile: ruthenium, main characteristics 2 important radioactive isotopes  103 Ru: 39 days  acting in the middle term  106 Ru: 1 year  acting in the long term  High inventory in MOX fuel  Metallic precipitate within the fuel Potentially very high radiological impact Volatile oxide forms can be produced in very oxidising environment, particularly under air ingress  Among them, RuO 4 may stay gaseous at low temperature within the containment

16 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Ru release: impact of oxidising conditions VERCORS 4 and VERCORS 5 comparison (UO 2 38 GWj/t)  Low Ru release in both tests: 6%  Deposit mainly located at high temperature, but …  For Vercors 5 (pure steam conditions), 10% of the released fraction reaches the impactor heated at 870K Vercors HT3 and HT2 comparison (UO 2 50 GWj/t)  Same low release (6%) for HT3 as for VERCORS 4, both performed in reducing conditions, with total deposit at high temperature  HT2 (pure steam conditions) exhibits a large release (65%), with 20% of the released fraction recovered at low temperature (400 K) Significant release may also occur in steam (even mixed steam and hydrogen) conditions Significant impact of burn-up is also evidenced

17 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Ru release in HT2 test 53% of Ru deposited in a hot zone (12% downstream in a colder zone)

18 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Ru release kinetics for HT2 and RT6 tests Same kinetics up to fuel delocation: Burn-up effect for RT6 More oxidising conditions for HT2

19 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Low volatile: Niobium, main characteristics Refractory element, with 2 radioactive isotopes, both daughter of a radioactive Zr isotope  97 Zr/ 97 Nb (16,9/1,2 hours)  acting in the short term  95 Zr/ 95 Nb (64/35 days)  acting in the middle term No stable FP isotope  very low mass inventory Under oxide forms within the fuel (dissolved and precipitates)  Nb is less refractory than Zr, with several oxides, one of them (Nb 2 O 5 ) having a relatively low melting point (~ 1500°C)

20 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Nb release: only detected in HT/RT grid at very high temperature Test number Fuel and conditions Test atmosphere Nb release Comment HT1 UO 2 4 cycles 2900 K (collapse) Reducing 9%Lower release in oxidising condition ? But earlier fuel collapse HT3 UO 2 4 cycles 2680 K (collapse) Reducing 18% HT2 UO 2 4 cycles 2420 K (collapse) Oxidising (pure steam) 10% RT3 UO 2 Debris bed Reducing (H 2 O-H 2 ) 40%Large release in debris bed configuration RT6 UO 2 6 cycles 2470 K (collapse) Oxidising (H 2 O-H 2 ) High release Significant BU effect

21 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Large Nb release in debris bed configuration (RT3)

22 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Nb release: main parameters Firstly high temperature Burn-up effect  No release measured below 50 GWj/t  Significant increase of the release at 70 GWj/t (RT6) Debris bed configuration  Seems to be an important factor for Nb (RT3 test, highest release of all the Vercors grid) Impact of oxidising conditions ?  Seems to be less important than expected  The comparison between HT2/HT3 highlights a potential compensation effect of a long duration time at high temperature before fuel collapse

23 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Low volatile FP: Sr, Y, La, Ce, Eu – main characteristics (1/2) The most refractory elements of this group of low volatile FP  Dissolved oxides within the fuel  High melting temperature of the oxides (> 2300°C), but low melting temperature of the metallic form (< 1000°C, except Y)  Like for Ba, we can expect an higher release in reducing conditions (but at higher temperature) Sr: high radiological impact of 90 Sr (30 years)  But also 91 Sr (10 hours), acting in the short term Y: low radiological impact  93 Y (10 hours), acting in the short term  All other isotopes have a behaviour imposed by their parent ( 91 Sr/ 91 Y, 92 Sr/ 92 Y), all acting in the short term

24 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Low volatile FP: Sr, Y, La, Ce, Eu – main characteristics (2/2) La: 140 La (1,7 day), daughter of 140 Ba (12,7 days), which imposes the inventory evolution  Less volatile than Ba  Difficult to quantify precisely  High impact on residual power for 140 Ba/ 140 La Ce: very high impact on residual power (and activity)  144 Ce (285 days)  acting in the long term (20% of the core residual power after one month, 45% after one year)  141 Ce (32 days) and 143 Ce (1,4 day)  acting in the middle and short term Eu: low inventory, low radiological impact  Activity (Pres) always < 1% of total core activity (Pres)  154 Eu (8,8 years), 155 Eu (5 years)  acting in the long term  156 Eu (15 days)  acting in the middle term

25 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Sr, Y, La, Ce, Eu release: main results from VERCORS tests Test number Fuel sample Test atmosphere SrYLaCeEuComment Vercors 3 UO 2 3 cycles Oxidising (H 2 O + H 2 ) 17% Vercors 4 UO 2 3 cycles Reducing   3%Reducing effect Vercors 5 UO 2 3 cycles Oxidising (pure steam) ND HT1 UO 2 4 cycles Reducing 8%5%9%Reducing effect HT3 UO 2 4 cycles Reducing 13%0,8%11% HT2 UO 2 4 cycles Oxidising (pure steam) 5%1% RT6 UO 2 6 cycles Oxidising (H 2 O + H 2 ) ++ % BU effect (La, Ce) RT7 MOX 3 cycles Reducing 14%Additional MOX effect (Ce) ? RT Various ~ 1%~ 1- 2% Chemical analysis

26 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Sr, Y, La, Ce, Eu … Zr, Nd, Pr: main conclusion Sr: very low volatility, nearly non volatile Y: could be measured only one time (VERCORS 3), because of very short half life of 93 Y  Seems to confirm its low-volatile behaviour La:  Higher release in reducing conditions  Higher release for high burn-up fuel Ce:  Same tendency than La, but with lower amplitude of the release  Seems to have an additional effect of higher release in MOX fuel Eu: higher release in reducing conditions Non volatile elements: Zr, Nd, Pr

27 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France Actinide release: U, Np, Pu, Am, Cm Main characteristics  Generally alpha emitters and very long half life isotopes …  High U mass inventory  impact on aerosol transport, even with low release  … Except Np, which has 2 short half life isotopes  239 Np and 238 Np (2 days)  acting in the short term  239 Np loads 20% of the core residual power after 1 day Np release  Very similar to Ce (La) release  Total release up to 10%  Favoured in reducing conditions  Favoured at high burn-up U, Pu release: measured by chemical analyses (RT1 to 4)  U release can reached 10% in oxidising conditions (RT1 – RT4)  Pu release seems to be lesser than U release by a factor 10

28 G. Ducros International VERCORS Seminar, October 15-16th, 2007 – Gréoux les Bains, France General conclusion: FP release classification Volatile FP: (Kr, Xe), Cs, I, but also Te, Sb, Rb, Ag, Cd  Nearly complete release  Kinetics sensitive to oxidising/reducing conditions  Release delay for Te et Sb (trapping in the clad when not fully oxidized) Semi-volatile FP: Mo, Ba, Rh, Pd, Tc  Release can be as high as for volatile FP, but :  High sensitivity to oxygen potential  Sensitivity to material interaction and burn-up (Ba)  Significant retention close to the fuel Low volatile FP: Sr, Y, Nb, Ru, La, Ce, Eu  Release level from some % to 10%, BUT:  Potentially higher release (~30-40%) at high burn-up for some of them  Sensitivity to oxygen potential  Deposit very close to the fuel Non volatile FP: Zr, Nd, Pr  No significant release measured up to now (<1%) Actinides: U, Np similar to low volatile – Pu to non volatile