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Fabrication of E110 Alloy Fuel Rod Claddings on Electrolytic Zirconium Base with Removing Fluorine Impurity for Providing Resistance to Breakaway Oxidation in High-Temperature Steam

• V. Markelov1, A. Malgin1, N. Filatova1, V. Novikov1, A. Shevyakov1,
• A. Gusev1, I. Shelepov1, A. Golovin1, A. Ugryumov2, A. Dolgov2, A. Ziganshin3,
• V. Donnikov4, V. Latunin4

A.A. BOCHVAR HIGH-TECHNOLOGY RESEARCH INSTITUTE OF INORGANIC MATERIALS (JSC «VNIINM») 19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK

«ROSATOM» STATE ATOMIC ENERGY CORPORATION

1) 2) 3) 4)

• Introduction. Problem essence.

2

The E110 alloy is used as the fuel rod claddings of VVER reactors. Electrolytic zirconium powder with additives of iodide zirconium and remains of zirconium production from these materials is used as a charge basis for the standard version of alloy. The ingots are smelted by double vacuum arc melting (VAM). Fuel rods with E110 alloy cladding satisfy the design parameters of operation. At the same time the E110 alloy under certain high-temperature conditions of the LOCA design basis accident is characterized by appearance of breakaway

• xidation.

In [9] on the basis of phenomenological ideas about the mechanism of influence

• n oxidation of various impurities it was stated that the breakaway effect of E110

alloy was caused by the presence of residual fluorine (F) impurity, which accompanied the fluoride technology for producing of electrolytic powder.

[9] Chung Hee M., «Fuel behavior under loss-coolant accident situations» // Nuclear Engineering and Technology, vol.37, №4, August, 2005, p. 327-362.

19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK

3

Breakaway oxidation does not appear on the E110 alloy with a charge based on sponge zirconium, in which F impurity is practically absent. In [8] the negative effect of F was confirmed experimentally by comparative studies of resistance to breakaway oxidation of fuel rod claddings made of ingots from electrolytic zirconium based alloy after two, three and four melts. It is shown that the key factor of a pronounced early breakaway effect of the standard E110 alloy after 400-500 s of steam oxidation at 1000ºС is the residual content of F in the amount of 4-5 ppm. The content of F decreased to less than 1 ppm after four melts of the ingot and breakaway effect at 1000°C does not appear at least during oxidation up to 5,000 s which corresponds to 20% ECRC-P.

• Introduction. Ways to solve the problem.

19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK

[8] Markelov, V.A., Malgin, A.G., Novikov, V.V. “Providing durability in a LOCA design basis accident of fuel rod cladding made of electrolytic zirconium E110 alloy”, Presented at the 2017 WRFPM, Jeju Island, Korea, September 10-14, 2017, Paper No F-162

• Introduction. Aim and tasks of the work.

4

At the same time melts regimes were not specifically worked out but corresponded to the current technological documentation for the melting of E110 alloy ingots. The aim of this work was to develop a new technological process for manufacturing of industrial ingots of the electrolytic zirconium based E110 alloy to ensure a guaranteed and maximally uniform content of residual F impurity in the ingot volume less than 1 ppm. At the same time the tasks were to optimize the regimes and methods of melting and to achieve the result using the least number of ingot melts. Fuel rod claddings made of ingots manufactured by the new technology were tested to breakaway oxidation resistance and as shown by the results satisfy criterion of the material safety in conditions of LOCA design basis accident with margin.

19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK

Scheme of standard manufacturing technology of E110 alloy ingots and cladding tubes

5

19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK

Dynamics of reduction of F content in the manufacture of E110 alloy ingots based on electrolytic zirconium

6

[8] Markelov, V.A., Malgin, A.G., Novikov, V.V. “Providing durability in a LOCA design basis accident of fuel rod cladding made of electrolytic zirconium E110 alloy”, Presented at the 2017 WRFPM, Jeju Island, Korea, September 10-14, 2017, Paper No F-162

Ion chromatography (Dionex ICS-2100 unit) was used to determine the F content quantitatively, which has the detection limit of 0.5 ppm and the error of 15-44% in the range of F concentrations of 0.5-100.0 ppm (the smaller F content the higher error value). Three samples per point were analyzed and the mean values were determined. EBM – Electron Beam Melting Using of EBM makes possible to remove F more efficiently compared to the VAM. This feature of EBM is due to the high vacuum in the chamber

• f the electron-beam facility,

the fully open surface of the melt in the ingot mold and the possibility to widely vary the power and rate of melting

19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK

New technology manufacturing of E110 ingots

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𝐷0 𝐷 = 𝑔(𝑄

𝑡, 𝑊)

where: C0 – initial F concentration in the consumable billet, mole/m3; C – F concentration in the ingot after EBM, mole/m3; Ps – specific melting power of EBM, kW/cm2; V – melting rate, kg/h.

19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK

F F

Billet

Vacuum System

Electron Beam

F

Ingot Bath with liquid metal Crystallizer Drops

Dependence of E110 alloy fluorine refinement coefficient

• n EBM parameters

8

Optimized EBM parameters compared to the fourfold melting scheme (VAM-VAM- EBM-VAM) in [8] were applied to melt for the ingot in the new technical process based on the

• btained dependence:
• specific melting power (Pspec)

is increased by ~ 20%;

• melting rate (V) is reduced

by ~ 80%.

[8] Markelov, V.A., Malgin, A.G., Novikov, V.V. “Providing durability in a LOCA design basis accident of fuel rod cladding made of electrolytic zirconium E110 alloy”, Presented at the 2017 WRFPM, Jeju Island, Korea, September 10-14, 2017, Paper No F-162

9 ingots

19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK

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Sampling scheme of fluorine content distribution analysis in longitudinal (c) and in radial (d) directions in ingot Ingot appearance after first EBM melting (a) and after second EBM-VAM melting (b)

Ingots and sampling scheme of fluorine analysis

(c) (d)

19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK

Fluorine content distribution in the ingot after each melting

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19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK

EBM-VAM EBM-VAM-VAM EBM-VAM-VAM-VAM EBM

2.7 2.3

Average fluorine content in semi-finished products and cladding tubes

11

The total of 465 samples taken from ingots melted three and four times semi-finished and finished tubes were analyzed for F content. All data showed that the concentration of F in the metal is below 1 ppm. This result indicates that the new technology of melting the electrolytic zirconium based E110 alloy ensures sufficiently uniform distribution of F throughout the ingot and the required quantity.

Melting scheme Average fluorine content, ppm Billet (2 pc.) Billet after mechanical treatment (18 pc.) Hot extrusion sleeve (18 pc.) Tube after 1-st pillgering (10 pc.) Tube after 2-nd pillgering (10 pc.) Cladding tube (10 pc.)

EBM-VAM-VAM 0,75±0,05 0,70±0,05 0,79±0,06 0,83±0,06 0,86±0,06 0,89±0,06 EBM-VAM-VAM-VAM 0,72±0,05 0,65±0,05 0,62±0,05 0,72±0,05 0,77±0,06 0,85±0,06

19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK

Impurity elements content in ingots of investigated materials

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Melting scheme Alloy marking Impurity element, ppm

Fe O Ni N С Si Al Cr F

EBM-VAM-VAM

E110-3m

100 400 20 30 65 30 20 15 0.8

EBM-VAM-VAM-VAM

E110-4m

100 390 20 30 70 30 20 15 0.7

VAM-VAM

E110-2m (lot1)

100 600 30 25 100 25 20 20 4-5

VAM-VAM

E110-2m (lot2)

160 520 40 20 55 30 20 30 2-3

VAM-VAM-VAM

E110opt Sponge based

510 820 30 30 60 30 25 40 <1.0

The most pronounced breakaway effect at high temperature steam oxidation for fuel claddings made from the E110 alloy appears at the temperature of 1000 ºС. Therefore, the oxidation tests for evaluating E110 alloy breakaway resistance were conducted at that temperature.

Resistance to breakaway oxidation in high-temperature steam

19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK

Reference material

Oxidation procedure and examination of tube samples

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VTI experimental setup Oxidation Kinetics Appearance analysis RCT at 135°C Microstructure analysis Hydrogen measurements

Full length cladding tube / sampling scheme (E110-2m/lot2; E110-3m; E110-4m)

High-temperature

• xidation scheme

Max oxidation time for E110-2m - 4000 s for E110-3m, E110-4m, E110opt – 10,000 s

19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK

Results of steam oxidation tests at 1000°C

14

19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK ↑ thermocouple spot #1

600s

E110-2m(lot1)

4,000s 700s 4,000s 5,000s 10,000s 5,000s 10,000s 10,000s 5,000s 10,000s 10,000s

E110-2m(lot2) E110opt (Sponge based) E110-3m E110-4m

nodule nodule nodules

• xide spallation

Appearance

Ring compression tests results at 135°C

15

The lowest degree of residual ductility at 135ºC is observed in E110-2m samples made of ingot with two melting. The residual ductility degree of oxidized samples from E110-3m and E110-4m alloys was the same and comparable with the residual ductility of E110opt alloy on sponge base.

19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK

Conclusions

16 ■ Removal of F impurity to the level below 1 ppm by means of the new technology for manufacturing of E110 alloy ingots on electrolytic zirconium based using optimized electron beam melting as the first melt and then at least two optimized vacuum arc melting provides fuel claddings resistance to breakaway oxidation in high- temperature steam. ■ The breakaway effect in water steam at 1000°C for 5,000 s up to

• xidation state 20% ECRC-P is not observed on the fuel rod

claddings from the electrolytic zirconium based E110 alloy ingots with the F content less than 1 ppm. This is similar to the behavior of the fuel rod claddings from E110 alloy based on zirconium sponge and meets the relevant safety criterion in the conditions of LOCA design basis accident.

19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK

Thank you for attention!

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19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK

Hydrogen content in oxidized tube samples

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Alloy Oxidation Time, s Hydrogen Content, ppm E110-2m 700 10-15 4000 650-810 E110-3m 5000 10-20 10000 (10-20) / 150* E110-4m 5000 10-20 10000 (10-20) / 250* E110opt 5000 10-20 10000 20 * - the hydrogen level in nodules area on some samples

19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK

nodule area

(a) (b)

Microstructure analysis

19

E110-2m E110opt E110-3m E110-4m

τ = 4,000 s τ = 10,000 s τ = 10,000 s τ = 10,000 s

19TH INTERNATIONAL SYMPOSIUM ON ZIRCONIUM IN THE NUCLEAR INDUSTRY MAY 20-23, 2019, Manchester, UK