ISO 16117:2013 pdf download.Nuclear criticality safety一Estimation of the num ber of fissions of a postulated criticality accident.
ISO 16117 provides a methodology to estimate a reasonably maximal value of the number of fissions of a postulated criticality accident.
The fission number estimate, associated with its postulated criticality accident, impacts the accident emergency planning and response because it is used for the estimation of radiation doses and of radioactive materials release.
ISO 16117 does not provide a methodology and guidance to determine bounding accident scenarios.
ISO 16117 does not cover criticality accident detection which is dealt with by ISO 7753.
ISO 16117 does apply to nuclear facilities, plants, laboratories, storage, and transportation of fissile material (but not to nuclear power reactor cores) where a credible criticality accident may occur.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
postulated criticality accident
postulated association of one accident scenario and one accident evolution
Note Ito entry: One postulated criticality accident is associated with one estimated number of fissions.
2.2
accident scenario
set of credible, postulated conditions under which a fissile material-containing facility/process develops one or more fault conditions such that it is likely to exceed the critical state and thus to result in a criticality accident
Note 1 to entry: This definition is drawn from ISO 27467.
2.3
accident evolution
progress of the criticality accident (after the critical state is exceeded), taking into account physical phenomena (for example, temperature and void effects) and possible human interventions to stop it
2.4
area of applicability
set of parameters (for example, environment, geometrical characteristics, tissue material, accident duration) within which a tool/model is intended to be used
Note 1 to entry: In Annex D. the last columns of the tables summarize the area of applicability of some simplified formulae.
3 General principles
PREREQUISITES Once the objectives of the criticality accident analysis (analysis based, for example, on Iso 27467) are defined, one or several criticality accident(s) may be postulated. The assumptions of the postulated criticality accident, and therefore the potential consequences, are to be related with the objectives of the criticality accident analysis (for example, design of evacuation routes, dose mapping, assembly station(s) choice).
EXAMPLE 1 Because bounding assumptions may be different for radiation dose estimates and for radioactive materials release estimates, it is possible to choose a set of assumptions adapted for each estimate.
EXAMPLE 2 The design of evacuation routes maybe performed with an arbitrary number of fissions; the goal is to optimize the operators’ evacuation routes, whatever the value of the dose is. In this case, the location of the postulated criticality accident is the most important parameter.
31 For the estimation of the number of fissions, the following assumptions, as well as their variations,
should be considered:
— description of the equipment (geometric configuration, reflector, etc.);
— degree of confinement and environment (vessel open or closed, pressure, cooling, etc.);
— fissile material (quantity, enrichment, media, physical shape, chemical form, etc.);
— total reactivity addition;
— rate of reactivity addition;
— time delay before the first persistent chain reaction (function of the initial neutron source, i.e. spontaneous fissions, (alpha, n)-reactions, etc.);
— duration of the criticality accident (calculated/estimated with and without intervention, where applicable).ISO 16117 pdf download.