## Abstract

The aim of the present work, performed in the scope of the Belgian plutonium recycling programme, is to develop a reliable and practical measurement method for determining the reactivity and the prompt neutron decay constant. A practical and reliable method in this field implies: a straightforward interpretation of the measured quantities, the possibility of checking the validity of the results, and no or small calculated corrections.

First, the various approximations involved in the methods using the pulsed neutron technique, more especially in Sjöstrand's method, must be analysed. Next, methods must be found to eliminate the influence of these approximations during the measurements itself rather than by sophisticated interpretations or calculated corrections the third step consists in elaborating the experimental determination of the error margin related to the measured values.

The main problem arising in the measurements is the elimination of both the space and energy harmonics induced by the outer source. it can be solved by the adequate location of the source and the detectors and the adequate choice of the detector type. The interest of measuring the reactivity is closely related to the improvement of calculation methods. Therefore the knowledge of the error margin of the measured values is necessary.

A useful application of the prompt neutron decay constant consists in the extrapolation of the critical mass, on the basis of measurements performed on loadings representing only one half to one third of this critical mass.

First, the various approximations involved in the methods using the pulsed neutron technique, more especially in Sjöstrand's method, must be analysed. Next, methods must be found to eliminate the influence of these approximations during the measurements itself rather than by sophisticated interpretations or calculated corrections the third step consists in elaborating the experimental determination of the error margin related to the measured values.

The main problem arising in the measurements is the elimination of both the space and energy harmonics induced by the outer source. it can be solved by the adequate location of the source and the detectors and the adequate choice of the detector type. The interest of measuring the reactivity is closely related to the improvement of calculation methods. Therefore the knowledge of the error margin of the measured values is necessary.

A useful application of the prompt neutron decay constant consists in the extrapolation of the critical mass, on the basis of measurements performed on loadings representing only one half to one third of this critical mass.

Original language | English |
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Publisher | SCK CEN |

Number of pages | 73 |

State | Published - Dec 1973 |

### Publication series

Name | SCK CEN Reports |
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Publisher | SCK CEN |

No. | BLG-498 |