Modelling of fission chambers in current mode—Analytical approach

Assessment of fissionable material behaviour in fission chambers

“…The saturation plateau will gradually disappear and the transition between the recombination and the avalanche modes will be less visible [9] as the fission rates increase with the total fluence.…”

“…However, the addition of contaminants with low ionization potential (e.g. xenón) involves a shift of avalanche towards lower voltages, having catastrophic consequences on the size of saturation plateau [9]. It has been experimentally observed that in standard FC with Argón at a pressure of 1 bar, the contamination of 0.1% in Xe shifts the voltage at the beginning of avalanche by 20 V.…”

“…Although the geometrical characteristics of the CFUR43 are not totally known, we have taken its geometrical and physical features from [9,12]: Ar as internal gas, pressure at 1 bar, interelectrode gap of 0.25 mm (the suggested valué is between 0.2 and 0.3 mm [12]) and length of 17.55cm (z max : 0.71 cm; z min : -1.045cm [9]). These valúes lead, considering a cylindrical volume, to an Ar mass of about 4.2 x 10~8 kg; i.e.…”

Fission Chambers Designer Based On Monte Carlo Techniques Working in Current Mode And Operated in Saturation Regime

“…MCFCD computes the distance covered by each fission product giving an average figure at the end of the simulation process. Table 3 compares MCFCD electron-ion pairs production data with those reported in [87], as well as those recommended in [88]. Electron-ion pairs simulated by MCFCD are 4.8% higher than those reported by [88], and 14% than [87].…”

“…This is supported by Figure 94, where the thermal U235 ENDF B-VII.1 independent fission yields (blue circles) with MCFCD simulations (black cross) are confronted, showing that simulated data correctly match with ENDF B-VII.1 library. Gaseous fission products are of outstanding importance, since the mixture of small quantities of alien products with the filling gas can strongly slope up or down pair formation, alter the size of the saturation plateau [87] and influence the drift velocity of electrical carriers. MCFCD uses Monte Carlo and fission yield libraries to provide fission products inventory.…”