Embrittlement trend curve

M. Kirk, Revision of AT30 embrittlement trend curves, EPRIMRP/NRC PTS Re-Evaluation Meeting, RockviUe, MD, 30 August, 2000. 

There are three important databases that have been developed by (or for) the NRC PR-EDB, RVID and the so-called Eason database used for research and development of improved embrittlement correlations and trend curves. 

Abstract This chapter describes the embrittlement processes in WWER reactor pressure vessel (RPV) materials during operation - radiation embrittlement and thermal ageing. Current trend curves for both types of WWER RPV materials are given and explained. Surveillance specimen programmes are shown, as their results are used for RPV integrity and lifetime evaluation. Finally, anneahng of the RPV is proposed as the most efficient mitigation measure. 

Original trend curves given in the Russian Code were constructed on the basis of test results obtained after irradiation within the material qualification programmes in experimental reactors. Thus, their lead factor (relation between neutron flux in the experiment and in the RPV) was more than 100, and such a large factor is not allowed by current standards. Moreover, the database of results was relatively small at that time and irradiation embrittlement of 15Kh2NMFA-type steel was studied only on steePwelds with nickel content lower than 1.5 mass %, as this was the original intention for this type of steel. 

For calculation of 50 % (median) curves of AT i(F, t) according to Eq. 5.5, the value a = 0 should be taken, both for base and weld metal. This type of dependence is used for direct determination of radiation embrittlement parameters based on results of RPV-specilic surveillance specimen tests. Typical trend curves calculated according to the Eq. 5.4 for base metal and weld metal are shown in Figs 5.2 and 5.3. It can be seen that mean curves provide a good description of the distribution of test results from surveillance specimen programmes. 

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