Implementation of three gamma measuring stations on the Colentec loop in Cadarache for the on line observation of the clogging phenomena in Steam Generator

The Tube Support Plate blockage, also named clogging, is a complex phenomenon that can occur in the steam generator of Pressurized Water Reactors. This deposit of iron oxides, that can reduce the coolant flux and constraint the primary tubes, could have significant consequences on heat exchanges and the integrity of the primary tubes. Since 2014, an experimental program carried out jointly by CEA-EDF, has been performed on a representative dedicated equipment, the COLENTEC loop at Cadarache. The physico-chemical properties of the deposit formed (chemical composition, thickness...) were determined at the end of each experimental campaign lead at thermohydraulic and chemical stable conditions. ... In order to determine the influence on clogging of parameters such as the chemistry, the temperature, the pressure in an on line process and without performing separate experimental campaigns, a method of measurement on radioactive tracer, the gamma emitter 59Fe, has been studied by our laboratory. First, a modelization with a monte carlo code, MCNP, has been carried out with the geometrical configuration of the Tube Support Plate zone of COLENTEC in order to determine the most adapted measuring station. These calculations had shown that a 30% efficiency, high purity, germanium detector, with a specific collimation would be able to detect the accumulation of 59Fe in the Tube Support Plate of COLENTEC. Then, in order to improve and ensure those important online measurements, our laboratory has proposed the installation of two additional measuring stations. One will be dedicated to a second on-line measurement, with a gamma detector of the same type, but positioned on a section of the loop remote from the previous area, to verify that there is no significant secondary deposit evolution elsewhere on the circuit. The last additional gamma measurement station will consist of a low background system able to carry out 59Fe concentration measurements of liquid samples taken from the loop during the test. This paper presents the context of this experiment and then focuses on the spectrometry measuring stations, modelizations and tests

Implementation of three gamma measuring stations on the Colentec loop in Cadarache for the on line observation of the clogging phenomena in Steam Generator

The Tube Support Plate blockage, also named clogging, is a complex phenomenon that can occur in the steam generator of Pressurized Water Reactors. This deposit of iron oxides, that can reduce the coolant flux and constraint the primary tubes, could have significant consequences on heat exchanges and the integrity of the primary tubes. Since 2014, an experimental program carried out jointly by CEA-EDF, has been performed on a representative dedicated equipment, the COLENTEC loop at Cadarache. The physico-chemical properties of the deposit formed (chemical composition, thickness...) were determined at the end of each experimental campaign lead at thermohydraulic and chemical stable conditions. ... In order to determine the influence on clogging of parameters such as the chemistry, the temperature, the pressure in an on line process and without performing separate experimental campaigns, a method of measurement on radioactive tracer, the gamma emitter 59Fe, has been studied by our laboratory. First, a modelization with a monte carlo code, MCNP, has been carried out with the geometrical configuration of the Tube Support Plate zone of COLENTEC in order to determine the most adapted measuring station. These calculations had shown that a 30% efficiency, high purity, germanium detector, with a specific collimation would be able to detect the accumulation of 59Fe in the Tube Support Plate of COLENTEC. Then, in order to improve and ensure those important online measurements, our laboratory has proposed the installation of two additional measuring stations. One will be dedicated to a second on-line measurement, with a gamma detector of the same type, but positioned on a section of the loop remote from the previous area, to verify that there is no significant secondary deposit evolution elsewhere on the circuit. The last additional gamma measurement station will consist of a low background system able to carry out 59Fe concentration measurements of liquid samples taken from the loop during the test. This paper presents the context of this experiment and then focuses on the spectrometry measuring stations, modelizations and tests

MAGIX, a new software for the analysis of complex gamma spectra

International audienceThe MAGIX code (a French acronym standing for Automatic Gamma and X-ray Measurement) is a software developed to analyze γ/X spectra on the topic of severe accident diagnosis. Indeed, the gamma spectra obtained after a severe reactor core accident are complex because they are composed of hundreds of lines of short-lived fission products and Fukushima accident demonstrated a lack in robustness of data interpretation during a crisis. MAGIX allows a complete and entirely automatic analysis of the spectra, with identification of radionuclides and calculation of activities. It can analyze spectra measured by detectors with excellent resolution such as HPGe detectors as well as detectors with medium resolution (e.g. CZT and LaBr3). For most detectors, the analysis of the spectra can be done without a detection efficiency curve because its process can include the calculation of a relative detection efficiency. MAGIX accepts spectra corresponding to any experimental setup (energy slope, energy range, resolution, absorber, etc.). However, these experimental conditions can have an impact on the quality of the results. Results on spectra simulated in different configurations showed that the analysis of the HPGe spectrum with the user defined efficiency and with the MAGIX detection efficiency were close. Furthermore, they also showed that the accuracy of activities was similar with increasing energy slopes but decreased with resolution degradation, with fewer correctly identified radionuclides in this case

Study of gamma-ray background noise for radioactive waste drum characterization with plastic scintillators

In the framework of the radioactive waste drum characterization using neutron coincidence counting, the Nuclear Measurement Laboratory of CEA Cadarache is studying plastic scintillators as an alternative to ideal but costly 3He gas proportional counters. Plastic scintillators are at least 5 times cheaper for the same detection efficiency, and in addition, they detect fast neutrons about three orders of magnitude faster than 3He detectors. However, they are sensitive to gamma rays, which implies the necessity to identify precisely gamma background sources that may affect the useful signal. This paper presents a detailed analysis of the gamma-ray spectrum of a radioactive waste drum containing glove box filters contaminated by plutonium dioxide. Gamma emissions accompanying inelastic scattering (n,n’) and (α,n) reactions that can lead to neutron-gamma coincidences parasitizing useful coincidences from plutonium spontaneous fissions are identified. Some of these parasitic gamma rays having energies up to several MeV, we plan to reject high-energy scintillator pulses with an electronics rejection threshold above 1 MeV, which should preserve the major part of useful fission neutron pulses

Study of gamma-ray background noise for radioactive waste drum characterization with plastic scintillators

In the framework of the radioactive waste drum characterization using neutron coincidence counting, the Nuclear Measurement Laboratory of CEA Cadarache is studying plastic scintillators as an alternative to ideal but costly 3He gas proportional counters. Plastic scintillators are at least 5 times cheaper for the same detection efficiency, and in addition, they detect fast neutrons about three orders of magnitude faster than 3He detectors. However, they are sensitive to gamma rays, which implies the necessity to identify precisely gamma background sources that may affect the useful signal. This paper presents a detailed analysis of the gamma-ray spectrum of a radioactive waste drum containing glove box filters contaminated by plutonium dioxide. Gamma emissions accompanying inelastic scattering (n,n’) and (α,n) reactions that can lead to neutron-gamma coincidences parasitizing useful coincidences from plutonium spontaneous fissions are identified. Some of these parasitic gamma rays having energies up to several MeV, we plan to reject high-energy scintillator pulses with an electronics rejection threshold above 1 MeV, which should preserve the major part of useful fission neutron pulses

Measurement of cumulative photofission yields of 235^{235}U and 238^{238}U with a 16 MeV Bremsstrahlung photon beam

International audienceIn the frame of a long-term research program on the characterization of large radioactive waste packages by photofission, the Nuclear Measurement Laboratory of CEA IRESNE, France, has measured cumulative photofission yields of $^{235}$U and $^{238}$U short-lived and long-lived fission products by using a Bremsstrahlung photon beam produced by a 16 MeV electron linear accelerator (LINAC). To this aim, a characterization of the Bremsstrahlung photon beam has been carried out by photon activation analysis with different samples of gold, nickel, uranium and zirconium. The residual neutron flux exiting the LINAC head (lead collimator, borated polyethylene and cadmium shield) has also been characterized by neutron activation analysis with indium samples to estimate the contribution of photoneutron fissions in the uranium samples used to assess the photofission yields. Finally 49 fission product yields are reported for $^{238}$U and 26 for $^{235}$U, with half-lives ranging from 64 s to more than 3 days, some of them not recorded so far in the literature Some photofission products cumulative yields show significant differences between $^{235}$U and $^{238}$U, which confirms the possibility of an isotopic discrimination method based on delayed gamma-ray ratios analysis for radioactive waste characterizatio