Използване на смесени окисни горива при експлоатацията на ядрени съоръжения
Creators: name: Naydenov, Ivaylo
Publisher: name: Zenodo
Year: 2017
Subjects: nuclear fuel cycle, mixed oxide fuel, proliferation resistance, plutonium management

description: Summary

<strong>PhD Thesis Title:  Mixed Oxide Fuels’ Utilisation in Nuclear Facilites’ Operation</strong>

It is anticipated that the worldwide primary energy consumption would rise with 30% by 2040 in comparison with 2016. That would lead to sharp growth of greenhouse gases’ emissions, unless a change in the power generating mix is carried out. Currently, power generation contributes to 68% of the global anthropogenic emissions of CO<sub>2</sub>. One of the power generating technologies that could have impactful contribution to reducing CO<sub>2</sub> emissions is nuclear power. It has four main advantages – high reliability, guaranteed security of energy supply, forseeable operational cost, and no direct emissions of CO<sub>2</sub>, SO<sub>x</sub>, NO<sub>x</sub>, and particulate matter. Moreover, the forecasts show that nuclear power’s average growth rate until 2040 would be 1.4% per annum, second only to the growth rate of renewables. In addition, there are several conditions that nuclear power should comply with in order its future development to be guaranteed: diminishing the mass and volume of spent nuclear fuel and radioactive wastes, and their efficient management; guaranteeing nuclear safety; guaranteeing nuclear security and non-proliferation; resource and economic efficiency.

In that context the goal of the PhD thesis is to investigate the possibilities for partial or complete closure of the nuclear fuel cycle, so that fissile isotopes be more efficiently utilized. That is accomplished by achieving four objectives: analysis of plutonium recycling impact on the fuel cycle’s resource efficiency; determining the concentrations and isotopic compositions of minor actinides in various types of spent nuclear fuel (uranium, mixed uranium-plutonium (MOX), REMIX); determining spent fuels’ decay heat; assessing the influence of the fuel type, burn-up, and cooling time on the quality of plutonium’s material barrier to proliferation.

The operation of MOX fuels leads to increased resource utilization – up to 18%, alongside decreasing the stockpiles of depleted uranium and plutonium. By plutonium recycling a 15-fold decrease of the disposable material’s mass can be achieved. In the case of linked WWER-1000 and AP1000 fuel cycles the mass of the disposable material could be diminished between 1.8 and 8-fold, depending on the chosen spent fuel reprocessing option, in comparison with once-through cycle.

REMIX fuel utilization leads to lower minor actinides’ inventory compared to uranium-plutonium MOX which makes it more attractive option for fissile materials’ recycling.

Increased PWR fuel burn-up affects positively the quality of the material proliferation barrier, especially when UOX fuel is considered. MOX fuel operation increases material’s proliferation resistance by improving isotopic barriers’ quality, albeit leading to increased plutonium inventory.

The form of the material is of paramount importance to its proliferation resistance properties, the unseparated plutonium having 50% better proliferation resistance than refined plutonium metal. On the other hand, short term spent fuel cooling (up to 30 yrs. after discharge) does not impact significantly the quality of the material barrier. Proliferation resistance analysis has been carried out using three independent methodologies, the results showing similar trends.