[en] In order to assess the primary to secondary leakage, radioactive isotopes, formed in the primary coolant as a result of fission or neutron capture, are usually monitored in the pressurized water reactor (PWR) secondary coolant. Some years ago, it appeared necessary to improve both leak rate assessments and the steam generator tube rupture (SGTR) detection. Studies and tests were started with the following goals in mind: (1) to set up a highly sensitive, convenient, and reliable measuring channel to assess the leak rates continuously and accurately; (2) to enable an early detection of an SGTR from the hot shutdown state to full power; and (3) to check the steam volumetric activity. In a first step, French efforts focused on the monitoring of ¹⁶N activity within the secondary coolant, allowing the high-energy gamma rays to be detected through the steam pipe wall and predictability of the rate of ¹⁶N production. The total gamma dose rate due to ¹⁶N at the touch of the steam pipe is rather low. For this reason, EdF has developed and tested a spectrometric method. In a second step, it was decided to analyze the low-energy gamma spectrum with the same apparatus in order to meet the second and third requirements. These gamma rays are emitted by noble gas fission products, which are assumed to be still present in the primary coolant while the reactor is in a hot shutdown state

[en] The method of transit time measurements by cross-correlation of random signals, produced by a physical phenomenon transported by the fluid is described and analysed. Application to primary coolant flow rate of PWR reactors by cross correlation of gamma emission of nitrogen 16 is given, the accuracy is 2 per cent

[en] Two probes are placed inside the reactor containment to measure the concentration of nitrogen 13 in gas which is sampled respectively from the inside space under the casing on the reactor closure head and from free space inside the containment. Each probe consists of a measurement chamber isolated from the ambient radiation by shielding. A signal processing system, outside the containment, indicates the presence of leak and its flow rate. 5 figs

[en] In order to assess the primary to secondary leakage, radioactive isotopes, formed in the primary coolant as a result of fission or neutron capture, are usually monitored in the pressurized water reactor (PWR) secondary coolant. Conventional methods mainly based on the detection of ¹³³Xe, tritium, and ⁴¹Ar are widely used on French Electricite de France (EdF) PWRs. Some years ago, it appeared necessary to improve both leak rate assessments and steam generator tube rupture (SGTR) detection. A volumetric activity measuring channel inside steam (VAMCIS) has been developed for this purpose. The SGTR that occurred at the North Anna PWR has focused the attention of safety authorities on this new measuring channel. It is planned to implement VAMCIS at North Anna in order to check the leak rate variations more accurately

[en] This ionizing radiation particle counter used for measuring the leak rate between primary and secondary circuits of a steam generator has a detector delivering detection pulses, a reference source generating radiation of different energy, an amplitude discriminator counting the number of pulses and a controller adjusting the amplitude ranges and the amplitude of pulses generated by the reference source

[en] Classical methods of flowrate measuring in closed pipes generally make use of indirect principles (for example: the measurements of the pressure loss through an orifice plate). Absolute or fundamental methods of the measurements of volume and time allow the ''in situ'' calibration and control of flowmeters in their nominal conditions of use. The method of transit-time measurements by fast injection of a radioactive tracer is described and analyzed

[en] The circuit which enables the turbine in an electrical power plant to function contains several types of heat exchanges. It is important to detect and trace leaks which may appear since they can have immediate negative effects for the correct operation of the power plant and because the corresponding defects can get worse and lead to ever more important incidents. The most performant methods used to detect leaks are based on the utilization of gaseous (helium) or radioactive (nitrogen 16) tracers, chemical tracers (cesium) and acoustic emission testing

[en] VAMCIS, an on-line steam generator monitoring system which enables very low leak rates (0.1 litre/h) to be continuously recorded is described. It has now been installed at a number of PWRs in France and around the world. (author)

[en] This paper describes a new method of measuring the gamma radiation energy spectrum and the associated dose equivalent rate under the vessel of a 900 MW PWR. The method is based on the use of thermoluminescent detectors (TLDs) placed under iron and neutron-absorbing material screens, overcoming the influence of neutrons. The spectral radiation breakdown is obtained by measuring the response of the TLDs for iron screens of different thicknesses. The thicknesses and types of neutron-absorbing materials have been determined on the bases of transport computations and preliminary tests. The problems posed by the practical implementation of this measurement system under the vessel and inside the pit of the vessel are also described. The measurement results that have become available demonstrate that gamma radiation under the vessel has a high energy level, resulting essentially from phenomena related to the diffusion or capture of neutrons

[en] The VAMCIS system has been jointly developed by Electricite de France (EdF) and the French manufacturer Merlin-Gerin Provence (MGP) for 4 yr. The continuous monitoring of the ¹⁶N activity within steam enables proper assessment of leak rates inside pressurized water reactor (PWR) steam generators (SGs). The VAMCIS system includes three main components: (1) sodium iodine sensor, coupled with its photomultiplier, (2) electrical cabinet, which provides the output signal spectral analysis, and (3) digital rate meters with software to transform the gross count rates into leak rate physical units. The paper discusses the implementation 1E-K3, and operational feedback. VAMCIS is now available in a large number of PWRs all over the world