trailNuclear probabilistic risk assessments predicted core-damage frequencies well below the observed historical accident rate
Complex risk analyses historically exhibit error rates exceeding their claimed risk bounds
Actuarial comparison· for
Published probabilistic risk assessments for nuclear power plants typically estimated core-damage frequencies of about one in 10,000 to one in 100,000 reactor-years or lower
atomic
Core-damage accidents in commercial nuclear reactors have occurred historically at a rate on the order of one per few thousand reactor-years
At least five commercial nuclear power reactor units have experienced core-damage accidents
Worldwide commercial nuclear power reactors have accumulated roughly 20,000 reactor-years of operating experience
Reference-class mismatch· against
The historical core-damage record is dominated by early-generation and Soviet reactor designs outside the scope of most probabilistic risk assessments
Core-damage events before 1980 occurred almost entirely in experimental or first-generation reactor designs
The Chernobyl RBMK reactor design had no probabilistic risk assessment before the 1986 accident
The Fukushima Daiichi reactors had plant-specific probabilistic risk assessments predicting core-damage frequencies around one in a million reactor-years before the 2011 accident
Japanese nuclear plant probabilistic safety assessments before 2011 addressed internal events only, excluding tsunami hazards
claim · empirical · derivedA factual claim that rests on inference from other evidence rather than direct observation.constitution →claim page ↗︎
Nuclear probabilistic risk assessments predicted core-damage frequencies well below the observed historical accident rate
↑SupportedEvidence favors the claim, but the chain is incomplete or the sources are secondary.constitution →credence 0.85Credence, from 0 to 1: the Steward's probability that the claim, as stated, is true. Stated only where a single number is an honest summary; normative and evaluative claims usually carry none.constitution →
1depended on by
this rests on ↓
claimA box is a claim: a single proposition the graph assesses, with its own page and map. Click any claim to centre the map on it.constitution →argumentA pill is an argument: one line of reasoning stating how the claims beneath it combine to bear on the claim above it, for or against. Arguments are not destinations; click their claims to explore.constitution →✓verifiedThe claim traces to reliable primary sources through a clear chain of evidence.constitution →↑supportedEvidence favors the claim, but the chain is incomplete or the sources are secondary.constitution →⇄contestedCredible evidence or argument exists on multiple sides.constitution →○unsupportedNo credible evidence found, though the claim is not contradicted.constitution →✕contradictedAvailable evidence weighs against the claim.constitution →?unknownInsufficient information to assess.constitution →◌unassessedNo current assessment. Attention goes where its expected value is highest and someone funds it; nothing has funded an assessment of this claim yet, and anyone can.constitution →verified factopen questionvalue premisesupportsthis provides evidence for the parentsteward instructions →contradictsthis argues against the parentsteward instructions →assumesbackground the parent's framing takes as givensteward instructions →requiresa load-bearing premise: the parent is false without itsteward instructions →Fig. Detail falls off with distance; every claim is an address.