Coupled point neutron kinetics and thermal-hydraulic models of transient nuclear criticality excursions within systems containing plutonium nitrate
File(s)
Author(s)
Daniels, Jasmin
Type
Thesis
Abstract
This PhD thesis describes phenomenologically based mathematical and computational methodology for the simulation of transient nuclear criticality excursions in multi-layered plutonium nitrate systems. Transient nuclear criticality excursions are more likely to occur in fissile liquid systems over dry or powder systems. Aqueous and organic phases of plutonium nitrate are most prevalent in nuclear fuel reprocessing facilities, where plutonium generated in a nuclear reactor is recovered for reuse or disposal.
To understand the behaviour and characteristics of multi-layered plutonium nitrate systems, steady-state analysis of the 1970 nuclear criticality incident at the Windscale Works is presented. The development and verification of a collision probability-based neutron transport code is presented, which provides a lower-fidelity, yet sufficiently accurate, description of neutron transport in the multi-layered systems under investigation.
Two transient models are presented, which couple the point neutron kinetics equations with one-dimensional models describing the thermal hydraulics and radiolytic gas generation and propagation within the system.
The first model describes transient nuclear criticality in multi-layered (aqueous-emulsion-organic) systems of plutonium nitrate, using phenomenological models describing emulsion formation and separation. The collision probability code is coupled to the point neutron kinetics and phenomenological equations, enabling the computation of the system's reactivity during the simulation. This model is used to simulate possible configurations of the 1970 Windscale nuclear criticality incident.
The second model describes transient nuclear criticality excursions within homogeneous, dilute, aqueous systems of plutonium nitrate. Such systems can have positive temperature coefficients of reactivity and may lead to highly energetic power excursions. The simpler phenomenology of a single-liquid system enabled the inclusion of more detailed radiolytic gas models, describing aqueous and gaseous concentrations of radiolysis products, alongside bubble nucleation radii and advection speeds. This model was used to analyse the effects that positive coefficients of reactivity have on the subsequent transient nuclear criticality excursions.
To understand the behaviour and characteristics of multi-layered plutonium nitrate systems, steady-state analysis of the 1970 nuclear criticality incident at the Windscale Works is presented. The development and verification of a collision probability-based neutron transport code is presented, which provides a lower-fidelity, yet sufficiently accurate, description of neutron transport in the multi-layered systems under investigation.
Two transient models are presented, which couple the point neutron kinetics equations with one-dimensional models describing the thermal hydraulics and radiolytic gas generation and propagation within the system.
The first model describes transient nuclear criticality in multi-layered (aqueous-emulsion-organic) systems of plutonium nitrate, using phenomenological models describing emulsion formation and separation. The collision probability code is coupled to the point neutron kinetics and phenomenological equations, enabling the computation of the system's reactivity during the simulation. This model is used to simulate possible configurations of the 1970 Windscale nuclear criticality incident.
The second model describes transient nuclear criticality excursions within homogeneous, dilute, aqueous systems of plutonium nitrate. Such systems can have positive temperature coefficients of reactivity and may lead to highly energetic power excursions. The simpler phenomenology of a single-liquid system enabled the inclusion of more detailed radiolytic gas models, describing aqueous and gaseous concentrations of radiolysis products, alongside bubble nucleation radii and advection speeds. This model was used to analyse the effects that positive coefficients of reactivity have on the subsequent transient nuclear criticality excursions.
Version
Open Access
Date Issued
2024-02-28
Date Awarded
01/12/2024
Advisor
Eaton, Matthew
Bluck, Mike
Sponsor
Engineering and Physical Sciences Research Council
Atomic Weapons Establishment (Great Britain)
Grant Number
EP/T517690/1
Publisher Department
Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)