Radiological environmental assessment of the recycle of LMFBR advanced fuels

The environmental impact resulting from the release of radioactive material during reprocessing and refabrication of spent LMFBR advanced fuels was compared with that from similar treatment of reference oxide fuel. Candidate advanced fuels include carbide ((U,Pu)C) in addition to nitride ((U,Pu)N) with selected concentrations of /sup 15/N. Several techniques for preparing enriched /sup 15/N were reviewed and estimates were made of the cost of preparing nitrogen enriched to greater than 99 percent by each method. Core neutronics, fuel management, and designs appropriate for each fuel were used with the ORIGEN code to calculate the compositions of spent core and blanket fuel. The mass of fuel recycled annually was that providing 50 GW(e)-years of energy at the burnup attained by each fuel. Confinement factors for each isotope were identified for reprocessing and refabrication operations and were used to calculate source terms describing isotopic release rates. These source terms were used in the AIRDOS-II code to estimate the 50-year dose to the maximally exposed individual and to both the local and world populations. Total body dose commitments to the maximally exposed individual for oxide and carbide fuels are about 2.8 millirem, while nitride fuel would result in a range of 59 to 3.4 millirem as the /sup 14/N content in fresh fuel is varied from 99.64 percent to zero

A TRACER STUDY OF THE TRANSPORT OF CHROMIUM IN FLUORIDE FUEL SYSTEMS

An experimental study was made of the mass transport of chromium in poly- thermal Inconel-fluoride fuel systems. The transport of chromium was followed by toe technique of adding radioactive Cr/sup 51/ to the system as either CrF/sub 2/ , in the salt or as elemental chromium in the solid phase. The rates of diffusion of chromium in Inconel at 600, 700, 800, and 900 deg C were determined by an electropolishing technique. Polythermal studies were carried out by three methods, tilting capsules, thermal-convection loops, and pumping loops. Tilting- capsule experiments indicated that the preferred location for chromium deposition on the wall was in the region of maximum temperature but the conclusions were not clear cut. Thermal convection loops operated for 125 and 288 hr showed radioactivity profile which could be attributed to simple exchange, with some distortion in the 288 hr case. The duration of these experiments was evidently insufficient io allow equilibrium to be reached in the salt. A thermal- convection loop operated for 400 hr showed distortion in the exchange radioactivity profile which indicated a favorable position for chromium deposition at a point about 100 deg F below the maximum wall temperature, and on the upstream side of the flow. A pumping loop of Inconel and salt mix gave an activity profile which was very similar to that of the 400-hr thermalconvection loop, indicating a favorable deposition point 100 deg F below maximuim temperature on the upstream side. One hypothesis advanced is that the long-term corrosion rate of chromium in the Inconel-salt system is controlled by the rate of diffusion of chromium into the wall at a temperature about 100 deg F below the maximum temperature on the upstream side. (auth

Research on injury compensation and health outcomes : ignoring the problem of reverse causality led to a biased conclusion

Objective\ud \ud This study highlights the serious consequences of ignoring reverse causality bias in studies on compensation-related factors and health outcomes and demonstrates a technique for resolving this problem of observational data.\ud \ud Study Design and Setting\ud \ud Data from an English longitudinal study on factors, including claims for compensation, associated with recovery from neck pain (whiplash) after rear-end collisions are used to demonstrate the potential for reverse causality bias. Although it is commonly believed that claiming compensation leads to worse recovery, it is also possible that poor recovery may lead to compensation claims—a point that is seldom considered and never addressed empirically. This pedagogical study compares the association between compensation claiming and recovery when reverse causality bias is ignored and when it is addressed, controlling for the same observable factors.\ud \ud Results\ud \ud When reverse causality is ignored, claimants appear to have a worse recovery than nonclaimants; however, when reverse causality bias is addressed, claiming compensation appears to have a beneficial effect on recovery, ceteris paribus.\ud \ud Conclusion\ud \ud To avert biased policy and judicial decisions that might inadvertently disadvantage people with compensable injuries, there is an urgent need for researchers to address reverse causality bias in studies on compensation-related factors and health