The potential use of Am as proliferation resistant burnable poison in PWRs

This paper discusses the use of ²⁴¹Am as proliferation resistant burnable poison for light water reactors. Homogeneous addition of small (as little as 0.12%) amounts of ²⁴¹Am to the conventional light water reactor fuel results in significant increase in ²³⁸Pu/Pu ratio in the discharged fuel improving its proliferation resistance. Moreover, ²⁴¹Am, admixed to the fuel, acts as burnable absorber allowing for substantial reduction in conventional reactivity control means without a notable fuel cycle length penalty. This is possible due to favorable characteristics of ²⁴¹Am transmutation chain. The fuel cycle length penalty of introducing ²⁴¹Am into the core is evaluated and discussed, as well as the impact of He production in the fuel pins and degradation of reactivity feedback coefficients. Proliferation resistance and reactivity control features related to the use of ²⁴¹Am are compared to those of using ²³⁷Np, which has also been suggested as an additive to the conventional fuel in order to improve its proliferation resistance. It was found that ²⁴¹Am admixture is more favorable than ²³⁷Np admixture because of the smaller fuel cycle length penalty and higher burnable poison savings. Addition of either ²³⁷Np or ²⁴¹Am would provide substantial but not ultimate protection from misuse of Pu originating in the spent fuel from the commercial power reactors. Therefore, the benefits from application of the concept would have to be carefully evaluated against the additional costs and proliferation risks associated with manufacturing of ²³⁷Np or ²⁴¹Am doped fuel. Although this work concerns specifically with PWRs, the conclusions could also be applied to BWRs and, to some extent, to other thermal spectrum reactor types.     

Transboundary atmospheric lead pollution

A high-temporal resolution collection technique was applied to refine aerosol sampling in Jerusalem, Israel. Using stable lead isotopes, lead concentrations, synoptic data, and atmospheric modeling, we demonstrate that lead detected in the atmosphere of Jerusalem is not only anthropogenic lead of local origin but also lead emitted in other countries. Fifty-seven percent of the collected samples contained a nontrivial fraction of foreign atmospheric lead and had 206Pb/207Pb values which deviated from the local petrol-lead value (206Pb/207Pb = 1.113) by more than two standard deviations (0.016). Foreign 206Pb/207Pb values were recorded in Jerusalem on several occasions. The synoptic conditions on these dates and reported values of the isotopic composition of lead emitted in various countries around Israel suggest that the foreign lead was transported to Jerusalem from Egypt, Turkey, and East Europe. The average concentration of foreign atmospheric lead in Jerusalem was 23 +/- 17 ng/m3, similar to the average concentration of local atmospheric lead, 21 +/- 18 ng/ m3. Hence, the load of foreign atmospheric lead is similar to the load of local atmospheric lead in Jerusalem.     

The effects of ionisation density on the thermoluminescence response (efficiency) of LiF:Mg,Ti and LiF:Mg,Cu,P

In this paper, the various models dealing with the effects of ionisation density on the thermoluminescence (TL) response (efficiency) of TL LiF dosemeters are discussed. These include (i) the Unified Interaction Model (UNIM), which models photon/electron linear/supralinear dose response; (ii) the Extended Track Interaction Model (ETIM), which models heavy charged particle (HCP) TL fluence response; (iii) Modified Track Structure Theory (MTST), which models relative HCP TL efficiencies; and (iv) Microdosimetric Target Theory (MTT), which models both relative HCP efficiencies and photon energy response.     

Periodic Review Production Models With Variable Yield And Uncertain Demand

A periodic-review production model with variable yield (uncertain supply) and uncertain demand is formulated and investigated. First, we provide a complete analysis of the final (single) period problem. The order point turns out to be unaffected by the yield distribution, but the expected yield corresponding to optimal lot size generally does not equal the difference between the order point and initial stock. We then explore properties of the two-period problem, the solution of which is generally non-myopic. Finally, the solution structure of the n-period problem is reported.     

Chemical and microbiological changes occurring in wheat silage maintained under modified atmospheres

In wheat silage maintained for 21 days at 26°C and 9-9 kPa water vapour pressure under a continuous flow of modified atmospheres (MAs) containing 20% v/v O₂ and different concentrations of CO₂ (from 20 % v/v to 80 % v/v) there was a significant increase in pH and in the colony-forming units (CFU) of aerobic bacteria, yeasts and moulds. In addition, water-soluble carbohydrates (WSC) and acetic and lactic acids decreased considerably. Similar results were obtained with a continuous flow of 90 %, 95 % and 99 % v/v CO₂ (supplemented to 100 % v/v with O2) and with 100 % v/v pure O₂ Only with silage kept in an atmosphere of 100 % v/v CO₂ or of 100 % v/v N₂ were no changes observed.     

European atmospheric pollution imported by cooler air masses to the Eastern Mediterranean during the summer

In this study we combine Pb isotopes, Pb, Ni, Cu, Zn, and several major metal concentrations, identification of the aerosol particles, and synoptic and back trajectory analyses to obtain direct evidence for the extent and nature of mixing between Middle Eastern and European sources emissions of metals and aerosols. During the summer months aerosols collected in Israel are highly polluted by metals (EF(Ni) = 120, EF(Cu) = 320, EF(Zn) = 30, EF(Pb) = 540; average values). The fraction of European Pb of mostly industrial sources is 61 +/- 21% in Jerusalem, and the fraction of European Cu, Zn, Ni, and aerosols should be on the same order. Whenever a steep pressure gradient is built between the barometric trough originating from the Persian Gulf and the subtropical ridge along the African coast, stronger westerly winds and cooler temperatures (deep Persian Trough) prevail overthe Middle East, and higher amounts of European pollution are observed in the atmosphere (74 +/- 13%). On the other hand, when the Persian Trough is in its shallow mode, the proportion of European pollution is lower (45 +/- 18%, based on Pb isotopes). This study demonstrates that atmospheric pollution over the East Mediterranean region during the summer is influenced not only by local atmospheric dispersion conditions but also by the ability of the atmosphere to inherit a significant proportion of pollutants from European sources.