Federal State Unitary Enterprise MAYAK Production Association

1. Federal State Unitary Enterprise MAYAK Production Association ROSATOM State Atomic Energy Corporation Quality control procedure for welded joints of fuel elements designed for the BN-800 reactor with mixed oxide uranium-plutonium fuel Presented by Marina Litvinova Process Engineer- Corrosion Researcher Mayak Production Association, Central Plant Laboratory May 27-31, 2019 Dimitrovgrad, JSC “SSC RIAR”

2. Approval of measurement procedure I.TsZL.MI-343-2018 was carried out according to GOST R 8.563

3. Analyzer of fragments of solid bodies microstructure (AFSBM) • AFSBMconsists of an inverted metallurgical microscope OLYMPUS GX-51, a digital colour camera SIMAGIS XS-6CU and dedicated software SIAMS 800. • The hardware-software complex performs the following functions: • it measures linear dimensions of fragments of microstructure of solid bodiesprepared in a form of thin sections and polished thin sections with the surface treated as required in the corresponding standard; • using special programs, it automatically converts measurements into analysis results; • it carries out a statistical analysis, draws a report based on the research resultsand prints the data out. • 3. The primary measurement instrument of the complex is a gaged stage micrometer. • 4. Range of length measurements is from 0.5 tо 2000 μm. • 5. Absolute value of the root mean square deviation of length measurements does not exceed 1 μm;fundamental relative error does not exceed 0.75 % over the entire range of measurements.

4. Fuel element of bn-800 fuel assembly with pelleted mox fuel311.335.000TU

5. PARAMETERS OF WELDED JOINTS OF BN-800 FUEL ELEMENTS WHICH ARE MONITORED IN ACCORDANCE WITH ОSТ 95 503-2016 • Wall thickness of the fuel element (WT) is about 400 μm. • Depth of penetration of a welded joint of the fuel element (DP) must be not less than an actual thickness of the thinnest wall (WT). • 3. Average conventional grain diameter in the heat-affected zonealong weld-fusion line of a fuel element (ACGD) must not exceed 4 points/ numbersaccording to GOST 5639-82.

6. Measurement of wall thickness (LW, μm) of a fuel element Figure 1 – Example of measuring fuel element wall thickness

7. Measurement of depth of penetration for a fuel element welded joint (LDP, μm) Figure 2 – Example of a microphotograph of a thin section of a fuel element welded joint with an identified depth of penetration Figure 3 – Measurement of depth of penetration of a fuel element welded joint

8. Heat affected zone of a fuel element welded joint (haz) Figure 4 – Formation of heat affected zone in a fuel element welded joint (HAZ width is up to 150 μm)

9. Monitoring of average conventional grain diameter within heat affected zone along weld-fusion line of a fuel element welded joint (dconv, μm) Figure 5 – Plotting auxiliary straight lines within heat affected zone Figure 6 – Plotting two cut lines (line segments) to count grains within heat affected zone

10. Processing of measurement results and quality control of the fuel element welded joint • Measurement results for the depth of penetration and for the wall thickness of the controlled sample of a fuel element welded joint (FEWJ) -LDP, μm, andLW, μm, correspondingly -are understood as the least numerical value of LDP, μm, fromthose obtained in the course of control procedure for both sides of the welded joint and the corresponding to it value of LW, μm, for the same section. • For each of the two sides of the welded joint, average conventional grain diameter dconv,μm, is to be determined using the following formula: • whereLis the total length of the two drawn line segments, μm; • Nis the number of grains transversed by these line segments, pcs.

11. Thank you all for attention!