I guess that 7300 Grays is the dose received by the water which passes only one time in the core. Since the water passes many times in the core we must divided the energy received by the water in one hour by the total inventory of water of the primary circuit ( some water remains in the pressurizer but we can neglect this effect if we want an order of magnitude).

The datas I have is that the volume of primary water for a 3817 MWth 4 loops PWR at full power in steady state is 399 m^3 of liquid water and 25 m^3 of steam (I guess that it is saturated steam in the pressurizer, I don't take it into consideration).

With an approximation of liquid water at 700 kg/m^3 , we have an estimation of roughly 250 tons of water in the primary circuit of your 3400 MWth PWR.

If we assume 4 % of the thermal load generated in the water, that gives us a dose of roughly 2 000 000 Gray/h or 17.5 billions grays per year.

Sorry for the eventual mistakes.

PS : the fraction of power generated in the coolant seems to be 2.6 % in this document ( see page 22 of the PDF ) :

http://www.google.fr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCMQFjAA&url=http%3A%2F%2Focw.mit.edu%2Fcourses%2Fnuclear-engineering%2F22-06-engineering-of-nuclear-systems-fall-2010%2Flectures-and-readings%2FMIT22_06F10_lec06a.pdf&ei=X-y7VIqqHo3saMS-gPgP&usg=AFQjCNFP2AS_9WpFDdytX3APuw1XHBc7fQ&sig2=f5gf7zduRFfoIPa0FTO8VA