EXECUTIVE SUMMARYPrevious estimates of environmental impacts associated with the front end of the nuclear fuel cycle (FEFC) have focused primarily on energy consumption and CO 2 emissions. Results have varied widely. This study revises existing empirical correlations and their underlying assumptions to fit to a more complete set of actual data. This study also addresses land transformation, water withdrawals, and occupational and public health impacts associated with the processes of the FEFC. These processes include uranium mining, milling, refining, conversion, enrichment, and fuel fabrication.To allow summing the impacts across processes, all impacts were normalized per tonne of natural uranium mined and then translated into impacts per MWh(e), a more conventional unit for measuring environmental impacts that facilitates comparison with other studies. This conversion was based on mass balances and process efficiencies associated with the current once-through LWR fuel cycle described in Appendix A.Estimates of the environmental impacts of the FEFC are summarized in Table Exec-1. Quantified impacts are limited to those resulting from activities performed within the FEFC process facilities (i.e. within the plant gates). Energy embodied in material inputs such as process chemicals and fuel cladding is identified but not explicitly quantified in this study. Inclusion of indirect energy associated with embodied energy as well as construction and decommissioning of facilities could increase the FEFC energy estimate by a factor of up to ~2. a. Includes mining, milling and refining based on current mix of mining technologies (23% open pit, 41% underground, and 36% in-situ leaching). b. Assumes DU conversion to DU 3 O 8 and shallow land burial. c. Assumes PWR fuel transported by truck a distance of 1000 km between each of the following process facilities: mining/milling, conversion, enrichment, DU disposition, fuel fabrication, and power plant. Measures of the Environmental Footprint of the Front End of the Nuclear Fuel Cycle iv August 23, 2010With the exception of water use, these impacts are very favorable relative to other competing technologies for large-scale energy production. For example, front-end processes have been estimated to account for 38% of the carbon footprint associated with production of electricity from nuclear energy (see Table 2.3). Scaling the above estimate for FEFC emissions accordingly, one estimates 7.4 kg CO 2 /MWh(e) for nuclear electricity production . For comparison, current average U.S. emissions from natural gas and coalfired electricity production are 410 and 979 kg CO 2 /MWh(e), respectively.The estimates given in the foregoing table depend upon a number of parameters that are expected to evolve with time. These include the ratio of ore to overburden and grade of the ore (i.e. % U), the mix and energy efficiency of the technologies used in the FEFC, and the rate of expansion of the nuclear industry. This study considers this time-dependency. Projections intended to bound emissions imp...

The aim of the study was to investigate how patient effective doses vary as a function of X-ray tube projection angle, as well as the patient long axis, and quantify how X-ray tube current modulation affects patient doses in chest CT examinations. Chest examinations were simulated for a gantry CT scanner geometry with projections acquired for a beam width of 4 cm. PCXMC 2.0.1 was used to calculate patient effective doses at 15° intervals around the patient's isocentre, and at nine locations along the patient long axis. Idealised tube current modulation schemes were modelled as a function of the X-ray tube angle and the patient long axis. Tube current modulations were characterised by the modulation amplitude R, which was allowed to vary between 1.5 and 5. Effective dose maxima occur for anteroposterior projections at the location of the (radiosensitive) breasts. The maximum to minimum ratio of effective doses as a function of the patient long axis was 4.9, and as a function of the X-ray tube angle was 2.1. Doubling the value of R reduces effective doses from longitudinal modulation alone by ∼4% and from angular modulation alone by ∼2%. In chest CT, tube current modulation schemes currently have longitudinal R values of ∼2.2, and angular R values that range between 1.5 and 3.4. Current X-ray tube current modulation schemes are expected to reduce patient effective doses in chest CT examinations by ∼10%, with longitudinal modulation accounting for two-thirds and angular modulation for the remaining one-third.

No abstract

There are major differences in organ and effective dose as the x-ray tube rotates around the patient. The results suggest that the use of x-ray tube current modulation could produce substantial reductions in organ and effective dose for body imaging with cone beam CT.

EXECUTIVE SUMMARYPrevious estimates of environmental impacts associated with the front end of the nuclear fuel cycle (FEFC) have focused primarily on energy consumption and CO 2 emissions. Results have varied widely. This study revises existing empirical correlations and their underlying assumptions to fit to a more complete set of actual data. This study also addresses land transformation, water withdrawals, and occupational and public health impacts associated with the processes of the FEFC. These processes include uranium mining, milling, refining, conversion, enrichment, and fuel fabrication.To allow summing the impacts across processes, all impacts were normalized per tonne of natural uranium mined and then translated into impacts per MWh(e), a more conventional unit for measuring environmental impacts that facilitates comparison with other studies. This conversion was based on mass balances and process efficiencies associated with the current once-through LWR fuel cycle described in Appendix A.Estimates of the environmental impacts of the FEFC are summarized in Table Exec-1. Quantified impacts are limited to those resulting from activities performed within the FEFC process facilities (i.e. within the plant gates). Energy embodied in material inputs such as process chemicals and fuel cladding is identified but not explicitly quantified in this study. Inclusion of indirect energy associated with embodied energy as well as construction and decommissioning of facilities could increase the FEFC energy estimate by a factor of up to ~2. a. Includes mining, milling and refining based on current mix of mining technologies (23% open pit, 41% underground, and 36% in-situ leaching). b. Assumes DU conversion to DU 3 O 8 and shallow land burial. c. Assumes PWR fuel transported by truck a distance of 1000 km between each of the following process facilities: mining/milling, conversion, enrichment, DU disposition, fuel fabrication, and power plant. Measures of the Environmental Footprint of the Front End of the Nuclear Fuel Cycle iv August 23, 2010With the exception of water use, these impacts are very favorable relative to other competing technologies for large-scale energy production. For example, front-end processes have been estimated to account for 38% of the carbon footprint associated with production of electricity from nuclear energy (see Table 2.3). Scaling the above estimate for FEFC emissions accordingly, one estimates 7.4 kg CO 2 /MWh(e) for nuclear electricity production . For comparison, current average U.S. emissions from natural gas and coalfired electricity production are 410 and 979 kg CO 2 /MWh(e), respectively.The estimates given in the foregoing table depend upon a number of parameters that are expected to evolve with time. These include the ratio of ore to overburden and grade of the ore (i.e. % U), the mix and energy efficiency of the technologies used in the FEFC, and the rate of expansion of the nuclear industry. This study considers this time-dependency. Projections intended to bound emissions imp...