Short.Term Reactivity Change: Xenon Effects

Most fission products absorb neutrons to some extent and they accumulate slowly as the fuel burnup increases, hence decrease the long-term reactivity. The neutron-absorbing fission-product xenon-135 has particular operational importance. Its concentrations can change quickly in a power maneuvre, producing major changes in neutron absorption on a relatively short-time scale (minutes).

Short.Term Reactivity Change: Local.Parameter Reactivity Feedback

A change in power for an operating reactor generally alters local parameters in the reactor such as the temperatures of the fuel, moderator, and coolant. A change in any of these local parameters causes a change in reactivity that, in turn, affects reactor operation (a feedback effect). Local parameters help to understand the feedback reactivity components related to the core evolution. For the CANDU reactor, the most important local parameters are the following:

BURNUP CALCULATIONS OF THE JSI TRIGA REACTOR FUEL AND COMPARISON WITH MEASUREMENTS

Fuel burnup of the JSI TRIGA was calculated by simulating complete operational history consisting of 240 different core configurations from 1966 to 2020. At the moment we are unable to perform burnup measurements, e.g. gamma spectroscopy on burned fuel elements, hence we used weekly measured excess reactivity as a reference point of different core configurations to verify the calculated core reactivity. Changes in reactivity due to burnup were assumed to be linear and this assumption was verified for burnup intervals smaller than 3 MWd/kg(HM). The comparison was performed on 46 different core configurations with different type of fuel elements. The Serpent-2 calculations decently predict the rate of reactivity change on different cases, as 52 % of calculations are withing 1σ and 86.9 % within 2σ of the measurements for total number of 46 cases. Additional analysis was performed by comparing unit cell calculations of different fuel types. Four different types of TRIGA fuel were used to analyse burnup changes in LEU and HEU fuel, where positive reactivity feedback on burnup was observed for HEU fuel due to burnable absorbers. Serpent-2 and WIMSD-5B were compared on unit-cell basis where good agreement within 200 pcm of reactivity change for large burnup was observed. In addition neutron spectrum changes due to burnup were investigated using unit-cell calculations where 4 % increase of the thermal peak and 1 % decrease of fast peak of the spectrum was observed for typical fuel burnups of 20 MWd/kg(HM), which approximately represents JSI TRIGA burnup at this moment.

INTRODUCTION TO NANOTECHNOLOGY AND MOLECULAR SELF-ASSEMBLY

What is nanoscience? What is nanotechnology? What is so special about nanoscale? These questions are only a few important to discuss, in order to understand the nanoworld. We describe nanoscience and nanotechnology introducing the basic ideas of the new technology that can significantly change our lives. Nanoworld is invisible to the naked eye, and with many unusual properties of material. It has been observed that nanoscale numerous properties such as melting point, electrical conductivity, or chemical reactivity, change as a function of the size of the sample, and many nanomaterials have been produced. Special attention in this paper is focused on the formation of self-assembled monolayers. This process is described as the creation of organic thin films of nanometer thickness and it is an emerging area of materials chemistry, utilized in many applications.