Chair of Physical Problems of Material Science, National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow, Russia:

A. A. Shmakov, Professor, e-mail: shm-mephi@rambler.ru
B. A. Kalin, Head of a Chair
V. M. Ananin, Leading Engineer
E. A. Smirnov, Assistant Professor

Dilute zirconium alloys are the major materials for pressure and fuel cladding tubes in water-cooled nuclear reactors. A part of hydrogen, produced by corrosion reaction Zr + 2H₂O  ZrO₂ + 4H, is absorbed by zirconium alloys. This hydrogen diffuses towards the colder regions of the tubes, precipitates as zirconium hydrides and leads to their local embrittlement and cracking. This paper shows the analysis of literature data about the heat of hydrogen transport (Q^*) in zirconium materials. Experimental values for Q^* from 18.8 to 35.6 kJ/mol were found by various investigators. At the same time, the most reliable data for Q^* conformed to the value of 24±2 kJ/mol. Measurement of the Q^* value in Russian zirconium materials required the use of E110 (Э110) (Zr — 1 % Nb) alloy plates and axial fragments from WWER fuel cladding tubes of E110M (Э110М) (Zr – 1% Nb – 0,12% O – 0,075% (wt.) Fe) and E635 (Э635) (Zr – 1% Nb – 1,2% Sn – 0,3% Fe – 0,08% (wt.) O) alloys. Concentration of initial uniform hydrogen in 20 mm length prepared specimens varied from 0,0084 to 0,0150% (wt.). The prepared specimens were annealed for 160 hours in air under the constant temperature gradient. The hot and cold ends of the specimens were held at the temperature of 773 К and 673 К, respectively. Optimum duration of annealing was calculated as sufficient time to the steady-state hydrogen distribution. After annealing, the specimens were sectioned along their length into slices and analyzed for hydrogen concentration, using LECO RH-402 hydrogen determinator. The treatment of obtained experimental points allowed to define the value Q^* = 231 kJ/mol for all tested specimens. The obtained results can be used for analysis and forecast of the processes of hydrogen redistribution in real zirconium-based fuel cladding tubes.

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