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Ensuring tritium fuel self-sufficiency while maintaining continuous and high-specification fuel flow to the tokamak via a low tritium inventory and controllable fuel cycle is a significant challenge to the STEP plant design. Effective and high-quality fuelling and exhaust design is required to sustain and control a stable plasma, whereas fuel sufficiency is required to prevent depletion of available tritium supply. Concerns regarding the lack of tritium availability preventing continuous tritium import are countered by breeding, where highly energetic neutrons from the core fusion reactions interact with lithium atoms suspended in the surrounding breeder blanket to produce tritium. The compact nature of STEP prohibits the integration of inboard breeder blankets posing a significant challenge for the design team looking to ensure more tritium is bred and made available than consumed within the core plasma. This paper outlines how purposeful technology selection and system architecting has converged on the outline of a conceivable and tritium-capable fuel cycle and breeder blanket design. Before introducing the STEP fuel cycle design outline and summarizing the approach undertaken to address the challenges facing plasma fuelling, key aspects of fuel self-sufficiency are discussed. This includes discussing a proposed helium-cooled liquid lithium breeder blanket and possible technology options for tritium extraction from lithium. Lastly, there is a brief process modelling overview, which emphasizes the central contribution of various employed modelling methods. Reflections on the presented fuel cycle design outline conclude that substantial development work is still required to realize a continuous tritium fuel cycle design and overcome the major challenges posed by tritium and lithium handling. Reflections on the presented breeder blanket design proposal conclude that while many substantial risks and blockers remain to achieve fuel self-sufficiency, high breeding ratios are expected to be achievable with a compact spherical tokamak configuration. Nonetheless, it is recognized that further consideration is required to ensure that the selection of liquid lithium as a breeder medium provides the overall simplest route to a self-sufficient and realizable design.This article is part of the theme issue 'Delivering Fusion Energy - The Spherical Tokamak for Energy Production (STEP)' .

Prevailing philosophies about parental and other caregiver responsibilities toward children tend to be protectionist, grounded in informed benevolence in a way that countenances rather than circumvents intrusive paternalism. And among the kinds of children an adult might be called upon to parent or otherwise care for, children with disabilities figure among those for whom the strongest and snuggest shielding is supposed be deployed. In this article, we examine whether this equation of securing well-being with sheltering by protective parents and other care-givers should unreflectively be adopted for disabled children. We also consider why healthcare providers might reasonably be reluctant to yield to this principle, even if parents instinctively suppose that protectionism is the parenting policy that best serves their disabled child's interest. We contend that caregivers owe children with disabilities at least as much, and possibly more, respect for self-governance than other children need. In spite of disabled children's vulnerability and even in view of it, we argue that they should be accorded not only welfare rights to well-being but at least a modified version of liberty rights as well. Healthcare providers are especially favorably positioned to facilitate the latter response. The main components of respectful caregiving can come into conflict with one another, but we present some priorities that advise against adopting a protectionist account of parenting rights, or at least against accepting protectionist views that focus parenting narrowly on shaping ideas about the child's welfare. In sum, caring for a disabled child, we argue, involves more than creating conditions that will afford her contentment and comfort over the course of life.

Fertility specialists, adoption agents, judges and others sometimes take themselves to have a responsibility to fairly adjudicate conflicts that may arise between the procreative and parenting interests of people with disabilities and the interests that their children or potential children have to be nurtured, cared for and protected. An underlying assumption is that having a disability significantly diminishes a person's parenting abilities. My aim is to challenge the claim that having a disability tends to make someone a bad parent by arguing that the interests of prospective parents with disabilities and the interests of their children or potential children are often aligned and mutually supporting., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/)