Transient analysis of the 1970 Windscale nuclear criticality incident

• Published in: Progress in nuclear energy (New series) Vol. 170; p. 105095
• Main Authors: Daniels, J.R., Williams, M.M.R., Eaton, M.D.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.05.2024
• Subjects: Criticality transient; Neutron kinetics; Neutron transport; Phenomenological modelling; Plutonium nitrate; Neutron kinetics; Phenomenological modelling; Plutonium nitrate; Criticality transient; Neutron transport
• ISSN: 0149-1970
• DOI: 10.1016/j.pnucene.2024.105095

This paper describes a novel methodology for the analysis of transient nuclear criticality in layered aqueous-emulsion-organic plutonium nitrate systems. The presented methodology includes point neutron kinetics equations coupled with phenomenological one-dimensional nuclear thermal hydraulics models, which describe the variation in mass, power, reactivity, temperature and voidage within the system. Equations to describe the mean neutron generation time and changes in reactivity due to changes in the system’s temperature and void fraction are formulated from fits of the results predicted by the criticality transient multiphysics model. Using these developed models, the nuclear criticality incident that occurred at the Windscale Works in 1970 is analysed and presented. In this criticality transient, two immiscible fissile liquids (an aqueous solution and an organic solvent) were disturbed such that an emulsion layer formed between them, inducing a transient nuclear criticality excursion and yielding around 1015 fissions. It was determined that parameters such as emulsion globule size and vessel outlet pipe radius had negligible impact on the total fission yield of the corresponding transient when compared to variations in organic solvent volume and emulsion band thickness. Several possible configurations were identified which could result in a transient similar to that of the Windscale Works in 1970. Notably, a system containing 39.75 L of organic solvent which underwent a transient with the formation of an emulsion band that was a maximum of 5.4 cm thick and 54% aqueous solution by volume yielded 9×1014 fissions, and thus is expected to closely resemble the 1970 Windscale nuclear criticality incident. However, the uncertainties associated with the original transient and the system parameters (e.g. thermophysical properties of the three layers) are such that the configuration is likely to vary from these exact quantities. •Models to simulate transient nuclear criticality in layered liquids are developed.•Material properties of plutonium nitrate phases are determined.•Kinetics and reactivity feedback data are determined.•The nuclear criticality incident at the Windscale Works in 1970 is investigated.•Transient variations, e.g. in power and thermal hydraulics, are investigated.