Qualitative probability

A critical assembly is a split bed on which fissionable material used to mock up up a separated reactor core that is stacked half on each half. One half is on roller guides so that the two halves may be quickly pulled apart if the neutron multiplication gets too high. Use the Preliminary Hazards Analysis method described in section 3,2.1 to identify the possible accidents that may occur and the qualitative probabilities and consequences. List the initiators in a matrix to systematically investigate the whole process. Don t forget human error. 

Figure 18.4.1. Qualitative probability consequence risk analysis...

Allowable qualitative probability No probability requirement Probable Remote Extremely remote Extremely improbable... 

Qualitative probability definition Failure conditions anticipated to occur one or more times during the entire operational life of each aeroplane Failure conditions unlikely to occur to each aeroplane during its total life, but which may occur several times when considering the total operational life of a number of aeroplanes of the type Failure conditions anticipated to occur to each aeroplane during its total life but which may occur a few times when considering the total operational life of all aeroplanes of the type Failure conditions so unlikely that they are not anticipated to occur during the entire operational life of all aeroplanes of one type... 

Use as many Fail Safe Principles [Kritzinger (2006) Chapter 7 para 3] as possible to help provide substantiation of qualitative probability declarations. 

Diffraction of X-rays or neutrons by crystals have provided very rich material on inter-nuclear distances R. If explicit determination of angles is not required, electron diffraction of gaseous molecules, or X-ray and neutron diffraction of vitreous materials, solutions, etc. may many times provide acceptable R values. If one asks for the distribution of distances from a given point in a gas of geometrical points, the density in a shell between R and R -1- dR is jaroportional to 4nR dR = P. This is also valid in actual compounds and alloys for very long R, but not at all for short R. Fig. 1 is a qualitative probability distribution of R values (normalized by division with P) for nuclei of a given element, or for a combination of two definite elements Zj and Zj. Contrary... 

Accident probability (qualitative probability) Occurrence (during operational life considering all instances of the system) Quantitative probability per operating hour ... 

Appropriate qualitative probability terms can then be defined, as per Table 5.2 (based on AMC25.1309) and are commonly accepted as aids to engineering judgement . The International Civil Aviation Organisation advises (ICAO Airworthiness Manual, page IIA-4h-l) that where it is necessary to use numerical assessments, the values given in Table 5.3 may be used in providing a common point of reference. 

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