SPECTRON, a neutron noise measurement system in frequency domain.

This paper is dedicated to the presentation and validation of SPECTRON, a novel neutron noise measurement system developed at CEA Cadarache. The device is designed for the measurement of the ß(eff) parameter (effective fraction of delayed neutrons) of experimental nuclear reactors using the Cohn-α method. An integrated electronic system is used to record the current from fission chambers. Spectra computed from measurement data are processed by a dedicated software in order to estimate the reactor transfer function and then the effective fraction of delayed neutrons as well as the prompt neutron generation time. After a review of the pile noise measurement method in current mode, the SPECTRON architecture is presented. Then, the validation procedure is described and experimental results are shown, supporting the proper functioning of this new measurement system. It is shown that every technical requirement needed for correct measurement of neutron noise is fulfilled. Measurements performed at MINERVE and EOLE, two experimental nuclear reactors at CEA Cadarache, in real conditions allowed us to validate SPECTRON.

New measurement system for on line in core high-energy neutron flux monitoring in materials testing reactor conditions.

Flux monitoring is of great interest for experimental studies in material testing reactors. Nowadays, only the thermal neutron flux can be monitored on line, e.g., using fission chambers or self-powered neutron detectors. In the framework of the Joint Instrumentation Laboratory between SCK-CEN and CEA, we have developed a fast neutron detector system (FNDS) capable of measuring on line the local high-energy neutron flux in fission reactor core and reflector locations. FNDS is based on fission chambers measurements in Campbelling mode. The system consists of two detectors, one detector being mainly sensitive to fast neutrons and the other one to thermal neutrons. On line data processing uses the CEA depletion code DARWIN in order to disentangle fast and thermal neutrons components, taking into account the isotopic evolution of the fissile deposit. The first results of FNDS experimental test in the BR2 reactor are presented in this paper. Several fission chambers have been irradiated up to a fluence of about 7 × 10(20) n∕cm(2). A good agreement (less than 10% discrepancy) was observed between FNDS fast flux estimation and reference flux measurement.

EMG changes in thigh and calf muscles in fin swimming exercise.

Because previous researchers have reported a reduced lactic acid production that accompanies a delayed or an absent ventilatory threshold (VTh) in water-based exercise, we hypothesized that the metaboreflex, activated by muscle acidosis, might be absent in fin swimming. This motor response, delaying the occurrence of fatigue, is characterized by a decreased median frequency (MF) of electromyographic (EMG) power spectrum. Seven healthy subjects performed a maximal fin swimming exercise protocol with simultaneous recordings of surface EMGs in VASTUS MEDIALIS (VM), TIBIALIS ANTERIOR (TA) and GASTROCNEMIUS MEDIALIS (GM). We computed the root mean square (RMS) and MF and recorded the compound evoked muscle potential (M-wave) in VM. We also measured the propulsive force and oxygen uptake (VO (2)), and determined VTh. VTh was absent in 4/7 subjects and measured at 70-90% of VO (2max) in the other three. In the three studied muscles, the global EMG activity (RMS) increased while the MF decreased in proportion of VO (2), the MF changes being significantly higher in VM (-29%) and GM (-39%) than in TA (-19%). Because no M-wave changes were noted, the MF decline was attributed to the recruitment of low-frequency, fatigue-resistant motor units. Our most important finding is the persistence of the metaboreflex even in a situation of reduced muscle acidosis.

Fin swimming improves respiratory gas exchange.

Data in the literature suggest that compared to dry-land exercise fin swimming might delay the activation of the anaerobic metabolism. To verify this hypothesis, we explored indirect indices such as the oxygen pulse (VO(2)/HR), carbon dioxide production (VCO(2)), and ventilatory threshold, comparing fin swimming exercise to dry-land cycling. Thirteen participants, experienced or inexperienced in fin swimming, completed an incremental fin swimming exercise and a maximal exercise on a cycloergometer with breath-by-breath measurements of heart rate (HR), ventilation (VE), tidal volume (VT), VO(2), VCO(2), and VO(2)/HR and determination of the ventilatory threshold and maximal oxygen uptake (VO(2)max). Compared to dry-land cycling exercise, fin swimming resulted in elevated or absent ventilatory threshold. Although VO(2)max did not differ in either condition, in fin swimming the maximal HR value was lower (-18%, p=0.0072), maximal VO(2)/HR higher (+20%, p=0.0325), and maximal VCO(2) lower (-17%, p=0.0071). We also measured significant reduction of VE, VT, and HR variations for the same VO(2) increase. This study suggests that the anaerobic muscle metabolism might be delayed in fin swimming. An attenuated chemoreflex drive to the heart and respiratory centres exerted by muscle metabolites might explain the depressed cardiopulmonary response to fin swimming.