Development of Advanced System for Early Detection of Primary Coolant Circuit Piping Leaks
Authors: Hovhannisyan Petros 
Published: February 2010

The critical analysis of existing diagnostics systems of primary circuit piping leaks has revealed, that it’s possible to develop a system allowing to essentially (up to several thousand times more) increase sensitivity of a leak detection. In addition, the location of a leak could be defined, too. The principle for an early leak identification system of the primary circuit piping, of approximately 0,001kg/hr sensitivity and leak detection time no more than one minute is presented. Such sensitivity is far above (several thousands times more), than the level required by LBB concept and that must result in increase of time for response planning and thus to increasing the reliability of selected decision. It will allow revealing a leak at a very early stage of a crack development, thus, increasing not only the safety of NPP equipment operation, but also reducing occupational exposure of the maintenance personnel and additional release into the atmosphere up to a reasonable minimum. Estimating of release reduction into the atmosphere makes up 2.4·107÷4.8·108 Bq/d and estimating of occupational exposure of the maintenance personnel makes up 3÷5 man·mSv per one operation for a crack elimination. Efficiency of application of such system is determined not only by the supposed high sensitivity but also by a correct choice of the pipeline sections for leak monitoring procedure. Therefore, identification of pipeline sections with the greatest probability of leak in operation is an important component of the problem solution. Optimization of the location and number of the inspected pipeline sections may be carried out by identification of the most dangerous pipeline sections in the view of through-crack formation, for that it is purposed: • Calculations of mechanical loadings on the main circulating pipeline and surge lines may be performed within the framework of linear elasticity theory; • Conformity of these calculations with the real situation may be checked by measurements of deformations and displacements of the pipeline elements during normal operation of the nuclear power plant and during reactor transients as well. So, in addition to the system for early detection of the location and the value of leak, you may get the system for on-line remote monitoring of value of deformations and displacements of the primary system pipe elements. As is well known, the value of leak depends on roughness of through-crack. That may lead to miscalculation of through-crack size, which is calculated using the value of leak. Thus if we have enough of sensitivity margin we will be able to guarantee the necessary safety margin without dependence on roughness of through-crack because by detecting the leak much less critical size we will be able to observe the temporal progress of leak value and to confidently control the progress of the crack size. Development of a system of detecting primary piping leaks, which much less critical ones, and identification of their location will allow NPP operators to supervise the crack propagation and to make the best decision. The estimates for topology and technical features of system will be represented in the report; The system will be able to satisfy the requirements for “near-ideal” system of early detection of primary circuit piping leaks. The software of a signal processing from such device at present does not constitute a difficulty and a signal processing may be performed under set-point accuracy and quick response. So, an operator makes a decision, which depends on measured size of leak, which is considered related to certain crack opening and the size of the latter dictate to operator what kind of decision he must accept.