Application of Serpan's damage function to heavy-water moderated power reactors and its control with surveillance data of the Karlsruhe power reactor, MZFR

For calculating ΔNDT, the irradiation-induced shift of the nil-ductility transition temperature, for the design of pressurized water reactor vessels, literature data envelope curves are used. In the case of light-water moderated reactors no correction of different spectra influence is considered. Calculations with the damage functions, published by Serpan et al., demonstrate that neglecting spectrum influence yields conservative design data. For heavy-water moderated reactors an adjusting factor is calculated from Serpan's damage function. The ΔNDT measured with samples of the ASTM reference steel A302-B irradiated in the heavy-water reactor, MZFR, is compared to irradiation results of samples from the same steel irradiated in the Oak Ridge low intensity test reactor (LITR) which are published by NRL. From this comparison an experimental adjusting factor is derived. Both calculated damage function and experimental factors agree very well. This result demonstrates that Serpan's damage function is applicable also to MZFR surveillance samples. The neutron spectrum in the MZFR surveillance location is extremely soft. Thermal neutron population is 900 times the fast flux (e>0.9MeV). Its damage contribution, calculated with damage function, amounts to 73%. (Auth.)