Preliminary neutronic study of D2O-Cooled high conversion PWRs

This paper presents a preliminary neutronics analysis of tight-pitch D2O-cooled high-conversion pressurised water reactors (HPWR) loaded with MOX fuel aiming at high Pu conversion and negative void coefficient. SCALE6.1 code has been exclusively utilized for this study. The analyses are performed in two separate parts. The first part of this paper investigates the performance of axial and internal blankets and seeks break-even or near-breeder core even without the presence of radial blankets. The analyses showed that the relative Pu mass balance was effectively increased by the addition of the axial blanket. The addition of only 4 cm of blanket resulted in the 4000 pcm increase in the void coefficient. Thus, the presence of the axial blanket made the void coefficient hardly negative. The second part of this paper performs sensitivity and uncertainty analyses of integral parameters (keff and void coefficient) for selected systems in order to analyze the characters of this high-conversion PWR from different aspects. The uncertainty analysis of keff showed that its breakup contributions for D2O-HPWR were very similar to other fast systems (SFR and H2O-HPWR) such that the key contributors were 238U inelastic and 239Pu ν-bar. However, breakup uncertainties of void coefficients showed that while those of D2O-HPWR resembled to H2O-HPWR, Na elastic became the significant contributor of the void coefficient uncertainty of SFR. Also sensitivity profiles of 238U inelastic and 239Pu ν-bar to the void coefficient revealed that those of SFR were quite dissimilar to both HPWRs. The study also found that while the absolute values of void coefficient uncertainty for D2O-HPWR were invariant through the burnup, its percentage uncertainty was significantly increased