Investigation of the Performance of D₂O-Cooled High-Conversion Reactors for Fuel Cycle Calculations

Abstract

SUMMARYThis report presents FY13 activities for the analysis of D 2 O cooled tight-pitch High-Conversion PWRs (HCPWRs) with U-Pu and Th-U fueled cores aiming at break-even or near breeder conditions while retaining the negative void reactivity. The analyses are carried out from several aspects which could not be covered in FY12 activities. SCALE 6.1 code system is utilized, and a series of simple 3D fuel pincell models are developed in order to perform Monte Carlo based criticality and burnup calculations.The performance of U-Pu fueled cores with axial and internal blankets is analyzed in terms of their impact on the relative fissile Pu mass balance, initial Pu enrichment, and void coefficient. In FY12, Pu conversion performances of D 2 O-cooled HCPWRs fueled with MOX were evaluated with small sized axial/internal DU blankets (~4cm of axial length) in order to ensure the negative void reactivity, which evidently limits the conversion performance of HCPWRs. In this fiscal year report, the axial sizes of DU blankets are extended up to 30 cm in order to evaluate the amount of DU necessary to reach break-even and/or breeding conditions. Several attempts are made in order to attain the milestone of the HCPWR designs (i.e., break-even condition and negative void reactivity) by modeling of HCPWRs under different conditions such as boiling of D 2 O coolant, MOX with different 235 U enrichment, and different target burnups.A similar set of analyses are performed for Th-U fueled cores. Several promising characteristics of 233 U over other fissile like 239 Pu and 235 U, most notably its higher fission neutrons per absorption, , in thermal and epithermal ranges combined with lower in the fast range than 239 Pu allows Th-U cores to be taller than MOX ones. Such an advantage results in 4% higher relative fissile mass balance than that of UPu fueled cores while retaining the negative void reactivity until the target burnup of 51 GWd/t. Several other distinctions between U-Pu and Th-U fueled cores are identified by evaluating the sensitivity coefficients of k eff , mass balance, and void coefficient.The effect of advanced iron alloy cladding (i.e., FeCrAl) on the performance of Pu conversion in MOX fueled cores is studied instead of using standard stainless-steel cladding. Variations in clad thickness and coolant-to-fuel volume ratio are also exercised. The use of FeCrAl instead of SS as a cladding alloy reduces the required Pu enrichment and improves the Pu conversion rate primarily due to the absence of nickel in the cladding alloy that results in the reduction of the neutron absorption. Also the difference in void coefficients between SS and FeCrAl alloys is nearly 500 pcm over the entire burnup range.The report also shows sensitivity and uncertainty analyses in order to characterize D 2 O cooled HCPWRs from different aspects. The uncertainties of integral parameters (k eff and void coefficient) for selected reactor cores are evaluated at different burnup points in order to find similarities and trends respect to D 2 O...

Conceptual design of an innovative reduced moderation thorium‐fueled small modular reactor with heavy‐water coolant

“…As a result, extreme care is required in handling elemental/metallic liquid sodium to avoid leakage of this coolant from the reactor. [14][15][16] Using MOX fuel loaded in hexagonalshaped assemblies, a series of important mechanisms were revealed, such as effects of MFRs to the spectrum hardening and influences of blankets to the breeding behavior and the coolant VC. In a nuclear reactor, lead and LBE are intrinsically suitable for radiation shielding and fission product (FP) retention and are amenable to the acquisition of hard neutron spectra.…”

“…Elaborate work was conducted by Hiruta and Youinou at Idaho National Laboratory on the analysis of D 2 O-cooled tight-pitch high-conversion PWRs, aiming at break-even or near-breeder conditions while retaining negative void reactivity. [14][15][16] Using MOX fuel loaded in hexagonalshaped assemblies, a series of important mechanisms were revealed, such as effects of MFRs to the spectrum hardening and influences of blankets to the breeding behavior and the coolant VC. However, the work was confined to simple models such as 3D pin-cells and 3D fuel assemblies.…”