Patent Number: 040240177
Section: summary

The present invention relates to a method of, and apparatus for, measuring burn-up of nuclear fuel in a nuclear reactor. Safety as well as economic conditions make it imperative to have accurate knowledge of the local burn-up in nuclear power reactors and thus to be able dependably to avoid power density peaks, on the one hand, and to adjust the operating conditions to optimum fuel utilization, on the other hand, when the local burn-up of the nuclear fuel in the reactor core is known. Furthermore, the inherent stability of the reactor depends on the form of the neutron flux distribution and, therefore, on the burn-up condition. In essence, conventional on-line methods for determining the burn-up in a nuclear reactor are based on a time integral of the neutron flux or on a time integral of the power density, which requires the continuous measurement of the neutron flux in the core and storing the measured data. This is disadvantageous not only because of the possible loss of data but this method is also inaccurate if large control rod movements of long duration were necessary between the individual measurements, for instance at irregular cycles or peak power cycling. It is the primary object of this invention to provide a method and apparatus avoiding these disadvantages of conventional nuclear fuel burn-up measurements. The above and other objects are accomplished in accordance with the invention by producing two measuring signals, each measuring signal being the function of the flux density of a different neutron group or energy, and computing the burn-up by comparing the two signals.