Reprocessing Enriched Material Through The MAGNOX Reprocessing Click to add text Plant At Sellafield
Duncan Ellis, Criticality Technical Lead (Magnox Reprocessing) The Problem:
Dounreay • Significant quantity of metallic material.
• Unusual isotopics.
Sellafield • Requirement to make safe.
• Solution - Reprocessing?
29/09/13 2 How did we solve the problem?
• Magnox reprocessing at Sellafield
• Differences between Dounreay material and Magnox
• How the case was made:
– Pond storage – Dissolution – Isotopics – Consequences
29/09/13 3 Magnox Reprocessing at Sellafield
Fuel Fuel rods receipt* and storage Uranium Dissolution* processing Irradiated Chemical natural separation* uranium Raffinate treatment Pu Evaporation & storage
29/09/13 4 Pond Storage
29/09/13 5 Dissolver
Optimised Safe Mass Magnox > 10, 000 kg Remaining plant lifetime issues Optimised Safe Mass DFR < 100 kg
29/09/13 6 Modelling Strategy
• Optimised pessimistic background array of worst case theoretical Magnox fuel. • RANDROD hole in the code MONK used to place a random accumulation of Dounreay slugs at the centre of the lattice. Constrained within H=D cylinder.
29/09/1329 September 2013 77 Mass Controls
• Modelling demonstrated sufficiently conservative (but not deterministic) safe mass.
• Taking into account: – Safe mass and – Dissolution half life,
a safe regime of blending of Dounreay magazines with Magnox feed was established.
29/09/13 8 Isotopics
• Neutron monitors assume certain isotopics. Dounreay isotpoics very different to Magnox.
• Blending regime ensures overall isotopics largely unchanged.
29/09/13 9 Consequences
•Shielding calculation performed for worst placed operator. Assuming 2x1019 fissions (MCBEND):
Table 1: Shielding calculation operator dose results
Source of radiation Coefficient Dose (μSv) of variance (%) Fission neutrons ±5.4 4.634 x 104
Secondary gamma ±3.7 2.061x104
Prompt fission gamma ±10.0 9.127 and fission product gamma 67 ± 2.6 Total Dose* mSv
29/09/13 1 0 Summary
• Case made to process Dounreay through Magnox Reprocessing plant.
• Case approved by all stakeholders – overall ALARP context important.
• Reprocessing underway.
29/09/13 1 1