Nuclear Heating Measurements Research Articles

Nuclear heating measurements for fusion and fission relevant materials in the JSI TRIGA reactor

The knowledge of nuclear heating inside nuclear (fission or fusion) reactor is essential for safe reactor operation, to know and meet limits expressed in terms of cooling requirements, and it represents critical input information for the design of any experimental irradiation device. In the framework of a research collaboration project between the Atomic and Alternative Energy Commission (CEA) in France, and the Jožef Stefan Institute (JSI) in Slovenia, a new project was launched in 2018 with the objective to measure the total heating rates in different materials of interest inside the JSI TRIGA Mark II reactor using the calorimetry technique. Three standard materials, graphite, aluminum and tungsten, and a fusion-relevant material, Eurofer-97, have been selected. The design of the calorimeters to host the four selected material samples is based on the CALMOS and CARMEN differential calorimeters, previously developed at the CEA, which were used to perform nuclear heating measurements in the OSIRIS material testing reactor (MTR) at the Saclay research center.The design of these specific calorimeters, and the dimensioning of the material samples located within, necessitated preliminary particle transport calculations using the MCNP V6.1 Monte Carlo code in order to estimate the expected heating levels in the experimental Central Channel of the core, and to avoid excessive perturbation of the measured radiation field. On the other hand, a parametric study was carried out using the COMSOL multiphysics code, to evaluate the expected temperature differences that could be measured using calorimeters designed specifically for low heating rates in the JSI TRIGA reactor core. A dedicated measurement campaign took place in July 2021 in which heating measurements were carried out at 100 kW reactor power and at nominal reactor power - 250 kW. This paper presents the design and preparation of the calorimeters, their preliminary calibration, the measurements carried out and the analysis of the obtained experimental results.

Measuring gamma doses over the mGy-kGy range with a single type of TLD detector

Thermo-luminescent detectors are currently used to measure gamma doses in the medical and environmental surveillance fields. During the past few years, the CEA Reactor Studies Division tested and validated the use of these detectors for gamma flux characterization and nuclear heating measurements in mixed neutron/gamma fields of low power reactors. Doses were comprised between a few mGy and a few Gy for dose rates up to a few Gy.h-1. However, in MTR or TRIGA reactors, the gamma flux level is much higher (> 1012 n/cm2/s) and the TLD currently in use (CaF2:Mn and 7LiF:Mg,Ti) and their readout protocols were no longer suitable for the resulting doses. In order to extend the applicable dose range up to ∼1 MGy (dose rate of a few kGy.h-1), several options were explored. On one side, some adjustments were made to the readout protocols of CaF2:Mn and 7LiF:Mg,Ti, notably by testing the use of filters to reduce the amount of light received by the reader PMT to avoid saturation. On the other side, a new type of TLD (LiF:Mg,Cu,P) with different Li enrichments (natural or enriched in 7Li) was tested. This paper presents the calibration measurements results performed in pure gamma fields, at the irradiation platform of the CEA Cadarache Radioprotection Division, between 250 mGy and 3 Gy for all detector types. In addition to the calibration, these measurements also studied the Mg,Cu,P-doped detectors response: reproducibility, dose rate dependence, incoming photon energy dependence, high temperature effect when reading TLD, etc. Results show that at low doses Mg,Cu,P-doped TLDs are slightly less stable than CaF2:Mn and 7LiF:Mg,Ti. The sensitivity modification after a high dose exposure seems to indicate that a new protocol readout should be defined for Mg,Cu,P-doped sensors (high temperature peak).

Nuclear Heating Measurements by Gamma and Neutron Thermometers

A gamma thermometer (GT) suitable for very high gamma heating levels (up to 20 W/g) has been designed and modeled by means of detailed finite element calculations. Based on a sensitivity analysis, the predicted accuracy of this GT is better than 5%. Experimental verification of the time constants has been performed, showing excellent agreement. A novel miniaturized GT in which a single thermocouple is used as the gamma absorption element, allowing a reduction of the sensor diameter down to 3 mm, is proposed. The sensitivities of the GTs with stainless steel, W, Mo, and Rh as the heated materials have been modeled by finite element calculations. It is found that both the Mo- and the Rh-based sensors have a very linear response up to a nuclear heating of 20 W/g. Monte Carlo calculations [by Monte Carlo N-Particle (MCNP)] have been performed to assess the relative contribution of neutrons to the nuclear heating in a GT. Calculations have been performed for GTs with an inner body made of various materials, such as stainless steel, tungsten, molybdenum, and rhodium. By using GTs made of different materials, it will be possible to deduce the nuclear heating rates in these materials and also to separate out the neutron and gamma heating contributions. The Monte Carlo calculations show that nuclear heating of rhodium is mainly due to neutrons, converting the rhodium GT effectively in a neutron thermometer.

Nuclear heating measurements by gamma and neutron thermometers

A gamma thermometer suitable for very high gamma heating levels (up to 20 W/g) has been designed and modelled by means of detailed finite element calculations. Based on a sensitivity analysis, the predicted accuracy of this gamma thermometer is better than 5 %. A novel miniaturized gamma thermometer is proposed in which a single thermocouple is used as the gamma absorption element, allowing a reduction of the sensor diameter down to 3 mm. Monte Carlo calculations (by MCNP) have been performed to assess the relative contribution of neutrons to the nuclear heating in a gamma thermometer. Calculations have been performed for gamma thermometers with an inner body made of various materials, such as stainless steel, tungsten, molybdenum and rhodium. By using gamma thermometers made of different materials, it will be possible to deduce the nuclear heating rates in these materials and also to separate out the neutron and gamma heating contributions. The Monte Carlo calculations show that nuclear heating of rhodium is mainly due to neutrons, converting the rhodium gamma thermometer effectively in a neutron thermometer. The sensitivities of the gamma thermometers with W, Mo or Rh as heated materials have been modelled by finite element calculations. It is found that both the Mo and the Rh based sensor have a very linear response up to a nuclear heating of 20 W/g.

Recent developments in nuclear heating measurement methods inside the OSIRIS reactor

Nuclear heating inside a Material Testing Reactor (MTR) needs to be known in order to design and to run irradiation experiments that have to fulfill target temperature constraints. To improve the incore nuclear heating knowledge of the French OSIRIS reactor operated by CEA, an innovative calorimetric system CALMOS (French acronym for CALorimètre Mobile OSiris) has been studied, manufactured and tested. This device can be inserted in any in-core experimental location. It is based on a mobile probe moving axially along the core height. First tests of this new probe, offering several ways for the heating evaluation, were performed in the reactor periphery. Then, two complete prototypes dedicated to incore measurements (calorimeter and the associated displacement system) were designed and tested during several reactor cycles. This paper presents a comprehensive analysis of all the results collected during the measurement campaigns carried out between 2013 and 2015 with these new prototypes in various reactor conditions. A comparison is made with previous calorimeters and obtained advantages are emphasized. This new calorimeter has been designed as a real operational measurement system, well suited to characterize the radiation field inside an MTR reactor.

The CANDELLE Experiment for Characterization of Neutron Sensitivity of LiF TLDs

As part of the design studies of future power and research nuclear reactors, the validation of neutron and photon calculation schemes requires the implementation of nuclear heating measurements. Such measurements are usually performed in very low-power reactors, whose core dimensions are accurately known and where irradiation conditions are entirely controlled. The use of thermoluminescent dosimeters is particularly well suited to gamma heating measurements, although the TLDs are also sensitive to neutrons depending on their composition. Hence, for gamma heating assessment in a mixed gamma–neutron field, the neutron sensitivity correction factors of TLDs has to be accurately determined to ensure a better interpretation of doses measured in a reactor with reduced uncertainties. This paper presents the CANDELLE experiment, which is dedicated to the implementation of a pure neutron field calibration of lithium-enriched TLDs, by using the Platform for Studies and Research on Nuclear Energy platform of LPSC. This calibration step is part of a promising approach that has been recently developed at INFN for medical purposes, aiming at determining the gamma and neutron contributions to the doses measured by LiF TLDs in the mixed field, from the peak height ratios of the gamma and neutron calibration glow curves of this type of TLDs. The test irradiations conducted at LPSC within the first phase of the CANDELLE project allowed retrieving the peak height of LiF TLDs in fast neutron field, hence providing an early assessment of the neutron components of doses measured in the EOLE reactor at CEA Cadarache with around 10% uncertainty at $1\sigma$ . From these preliminary results, the second phase of the project will be devoted, on the one hand, to the use of moderator screens aiming at achieving a thermal neutron field while avoiding a too strong attenuation of the flux, and on the other hand, to the determination of the neutron spectrum at different locations within the irradiation area.

Last Improvements of the CALMOS Calorimeter Dedicated to Thermal Neutron Flux and Nuclear Heating Measurements inside the OSIRIS Reactor

Nuclear heating inside an MTR reactor needs to be known in order to design and to run irradiation experiments which have to fulfill target temperature constraints. To improve the nuclear heating knowledge, an innovative calorimetric system CALMOS has been studied, manufactured and tested for the 70MWth OSIRIS reactor operated by CEA. This device is based on a mobile calorimetric probe which can be inserted in any in-core experimental location and can be moved axially from the bottom of the core to 1000 mm above the core mid-plane. Obtained results and advantages brought by the first CALMOS-1 equipment have been already presented. However, some difficulties appeared with this first version. A thermal limitation in cells did not allow to monitor nuclear heating up to the 70 MW nominal power, and some significant discrepancies were observed at high heating rates between results deduced from the calibration and those obtained by the “zero method”. Taking this feedback into account, the new CALMOS-2 calorimeter has been designed both for extending the heating range up to 13W.g-1 and for improving the “zero method” measurement thanks to the implementation of a 4-wires technique. In addition, the new calorimeter has been designed as a real operational measurement system, well suited to characterize and to follow the radiation field evolution throughout the reactor cycle. To meet this requirement, a programmable system associated with a specific software allows automatic complete cell mobility in the core, the data acquisition and the measurements processing. This paper presents the analysis of results collected during the 2015 comprehensive measurement campaign. The 4-wires technique was tested up to around a 4 W.g-1 heating level and allowed to quantify discrepancies between “zero” and calibration methods. Thermal neutron flux and nuclear heating measurements from CALMOS-1 and CALMOS-2 are compared. Thermal neutron flux distributions, obtained with the Self-Power Neutron Detector suited to the CALMOS-2 calorimetric probe, are compared with those obtained with current devices. This campaign allowed to highlight advantages brought by the human machine interface automation, which deeply refined the profiles definition. Finally, the decay of the reactor residual power after shutdown could be performed after shutdown, demonstrating the ability of such type of calorimeter to follow the heating level whatever the thermohydraulic conditions, forced or natural convection regimes.

The CANDELLE experiment for characterization of neutron sensitivity of LiF TLDs

As part of the design studies conducted at CEA for future power and research nuclear reactors, the validation of neutron and photon calculation schemes related to nuclear heating prediction are strongly dependent on the implementation of nuclear heating measurements. Such measurements are usually performed in low-power reactors, whose core dimensions are accurately known and where irradiation conditions (power, flux and temperature) are entirely controlled. Due to the very low operating power of such reactors (of the order of 100 W), nuclear heating is assessed by using dosimetry techniques such as thermoluminescent dosimeters (TLDs). However, although they are highly sensitive to gamma radiation, such dosimeters are also, to a lesser extent, sensitive to neutrons. The neutron dose depends strongly on the TLD composition, typically contributing to 10-30% of the total measured dose in a mixed neutron/gamma field. The experimental determination of the neutron correction appears therefore to be crucial to a better interpretation of doses measured in reactor with reduced uncertainties. A promising approach based on the use of two types of LiF TLDs respectively enriched with lithium-6 and lithium-7, precalibrated both in photon and neutron fields, has been recently developed at INFN (Milan, Italy) for medical purposes. The CANDELLE experiment is dedicated to the implementation of a pure neutron field “calibration” of TLDs by using the GENEPI-2 neutron source of LPSC (Grenoble, France). Those irradiation conditions allowed providing an early assessment of the neutron components of doses measured in EOLE reactor at CEA Cadarache with 10% uncertainty at 1σ.

Review of Nuclear Heating Measurement by Calorimetry in France and USA

This paper gives a short review of sensors dedicated to measuring nuclear heating rate inside fission reactors in France and USA and especially inside Material Testing Reactors. These sensors correspond to heat flow calorimeters composed of a single calorimetric cell or of two calorimetric cells at least with a reference cell to obtain a differential calorimeter. The aim of this paper is to present the common running principle of these sensors and their own special characteristics through their design, calibration methods, and in-pile measurement techniques, and to describe multi-sensor probes including calorimeters.

State of the art on nuclear heating measurement methods and expected improvements in zero power research reactors

The paper focuses on the recent methodological advances suitable for nuclear heating measurements in zero power research reactors. This bibliographical work is part of an experimental approach currently in progress at CEA Cadarache, aiming at optimizing photon heating measurements in low-power research reactors. It provides an overview of the application fields of the most widely used detectors, namely thermoluminescent dosimeters (TLDs) and optically stimulated luminescent dosimeters. Starting from the methodology currently implemented at CEA, the expected improvements relate to the experimental determination of the neutron component, which is a key point conditioning the accuracy of photon heating measurements in mixed n –γ field. A recently developed methodology based on the use of 7 Li and 6 Li-enriched TLDs, precalibrated both in photon and neutron fields, is a promising approach to deconvolute the two components of nuclear heating. We also investigate the different methods of optical fiber dosimetry, with a view to assess the feasibility of online photon heating measurements, whose primary benefit is to overcome constraints related to the withdrawal of dosimeters from the reactor immediately after irradiation. Moreover, a fibered setup could allow measuring the instantaneous dose rate during irradiation, as well as the delayed photon dose after reactor shutdown. Some insights from potential further developments are given. Obviously, any improvement of the technique has to lead to a measurement uncertainty at least equal to that of the currently used methodology (∼5% at 1σ).

First In-Core Simultaneous Measurements of Nuclear Heating and Thermal Neutron Flux Obtained With the Innovative Mobile Calorimeter CALMOS Inside the OSIRIS Reactor

Nuclear heating inside a MTR reactor has to be known in order to design and run irradiation experiments which have to fulfill target temperature constraints. This measurement is usually carried out by calorimetry. The innovative calorimetric system, CALMOS, has been studied and built in 2011 for the 70MWth OSIRIS reactor operated by CEA. Thanks to a new type of calorimetric probe, associated to a specific displacement system, it provides measurements along the fissile height and above the core. Calorimeter working modes, measurement procedures, main modeling and experimental results and expected advantages of this new technique have been already presented in previous papers. However, these first in-core measurements were not performed beyond $6~\mathrm {W} \cdot \mathrm {g} ^{-1}$ , due to an inside temperature limitation imposed by a safety authority requirement. In this paper, we present the first in-core simultaneous measurements of nuclear heating and conventional thermal neutron flux obtained by the CALMOS device at 70 MW nominal reactor power. For the first time, this experimental system was operated in nominal in-core conditions, with nominal neutron flux up to 2.7 $10 ^{14} ~\mathrm {n}\cdot \mathrm {cm}^{-2} \cdot \mathrm {s} ^{-1}$ and nuclear heating up to $12~\mathrm {W} \cdot \mathrm {g} ^{-1}$ . After a brief reminder of the calorimetric cell configuration and displacement system specificities, first nuclear heating distributions at nominal power are presented and discussed. In order to reinforce the heating evaluation, a comparison is made between results obtained by the probe calibration coefficient and the zero methods. Thermal neutron flux evaluation from SPND signal processing required a specific TRIPOLI-4 Monte Carlo calculation which has been performed with the precise CALMOS cell geometry. In addition, the Finite Element model for temperatures map prediction inside the calorimetric cell has been upgraded with recent experimental data obtained up to $12~\mathrm {W} \cdot \mathrm {g} ^{-1}$ . Finally, the experience feedback led us to improvement perspectives. A second device is currently under manufacturing and main technical options are presented.

Monte Carlo Simulation Study of a Differential Calorimeter Measuring the Nuclear Heating in Material Testing Reactors

The nuclear heating measurements in Material Testing Reactors (MTRs) are crucial for the study of nuclear materials and fuels under irradiation. The reference measurements of this nuclear heating are especially performed by a differential calorimeter including a graphite sample material. Then these measurements are used for other materials, other geometries, or other experimental conditions in order to predict the nuclear heating and thermal conditions induced in the irradiation devices. This paper will present new simulations with MCNP Monte-Carlo transport code to determine the gamma heating profile inside the calorimeter. The whole complex geometry of the sensor has been considered. We use as an input source in the model, the photon spectra calculated in various positions of CARMEN-1 irradiation program in OSIRIS reactor. After a description of the differential calorimeter device, the MCNP modeling used for the calculations of radial profile of nuclear heating inside the calorimeter elements will be introduced. The obtained results of different simulations will be detailed and discussed in this paper. The charged particle equilibrium inside the calorimeter elements will be studied. Then we will focus on parametric studies of the various components of the calorimeter. The influence of source type will be also took into account. Moreover the influence of the material used for the sample will be described.

Parametric study of the energy deposition inside the calorimeter measuring the nuclear heating in Material Testing Reactors

The nuclear heating measurements in Material Testing Reactors (MTRs) are crucial for the study of nuclear materials and fuels under irradiation. The reference measurements of this nuclear heating are especially performed by a differential calorimeter including a graphite sample material and two calorimetric cells. Then these measurements are used for other experimental conditions in order to predict the nuclear heating and thermal conditions induced in the irradiation devices.This paper will present simulations with MCNP5 Monte-Carlo transport code (using ENDF/B-VI nuclear data library) to evaluate the nuclear heating inside the calorimeter during irradiation campaigns of the CARMEN-1P mock-up inside OSIRIS reactor periphery (MTR based on Saclay, France). The whole complete geometry of the sensor has been considered. The calculation method corresponds to a calculation in two steps. Consequently, we used as an input source in the model, the neutron and photon spectra calculated in various experimental locations tested during the irradiation campaign (H9, H10, H11, D9). After a description of the differential calorimeter sensor, the MCNP5 model used for the calculations of nuclear heating inside the calorimeter elements is introduced by two quantities: KERMA and energy deposition rate per mass unit. The Charged Particle Equilibrium (CPE) inside the calorimeter elements is studied. The contribution of prompt gamma and neutron is determined. A comparison between this total nuclear heating calculation and the experimental results in a graphite sample will be made. Then parametric studies performed on the influence of the various calorimeter components on the nuclear heating are presented and discussed. The studies of the influence of the nature of materials, the sensor jacket, the source type and the comparison of the results obtained for the two calorimetric cells leads to some proposals for the sensor improvement.

Simulation and Comparison of the Calorimeters Measuring the Nuclear Heating in the OSIRIS Reactor, with the TRIPOLI-4 Monte-Carlo Code

Two calorimeter devices are used in the OSIRIS Material Testing Reactor (CEA-Saclay center) for the nuclear heating measurements. The first one is a fixed five-stage calorimeter device. The second one is an innovative mobile probe called “CALMOS”. The design of these devices is different (in particular their geometry), implying modifications on the local neutron and photon fluxes and hence on nuclear heating measured values. The measurements performed by the two calorimeter devices cannot directly be compared; this requires perfect irradiation conditions in the reactor core, especially for the core loading and the control element positions. Simulation is here a good help to perform a fully relevant comparison. In this paper, differences between calorimeter devices in terms of nuclear heating and particle fluxes are evaluated using the TRIPOLI-4 Monte-Carlo code. After a description of the OSIRIS reactor and the design of the two calorimeter devices, the nuclear heating calculation scheme used for simulation will be introduced. Different simulations and results will be detailed and analyzed to determine the calorimeter geometry impact on the measured nuclear heating.

Development and Optimization of Nuclear Heating Measurement Techniques in Zero Power Experimental Reactors

The objective of this study is to develop nuclear heating measurement methods in Zero Power experimental reactors. This paper presents the analysis of Thermo-Luminescent Detectors (TLDs) and Optically Stimulated Luminescent Detectors (OSLDs) experiments in the MINERVE research reactors at the French Atomic Energy and Alternative Energies Commission center in Cadarache. The experimental sources of uncertainties on the dose have been reduced by using the optimum conditions of charged particle equilibrium (CPE) of the calibration step and reactor measurement for each detector types; by improving the process of the TLDs/OSLDs reading and calibration processes. The interpretation of these measurements needs to take into account several correction factors related to both the environment of calibration step and the type of detectors used. Similarly, the correction due to the neutrons contributions to the total dose integrated by the detectors is evaluated with Monte Carlo calculation methods. These calculations are based on MCNP simulations of neutron-gamma and gamma-electron transport coupled particles using ENDF/B-VI nuclear data library. TLDs and OSLDs are positioned inside aluminum or hafnium pillboxes. Comparisons between calculated and measured integral gamma-ray absorbed doses by TLDs in these new experiments are carried out in the MINERVE reactor in the surrounding aluminum material. They show that calculations slightly overestimate the measurements by about 8%. By using OSLDs, the calculation slightly overestimates the measurement by about 6%.

Comparison of Thermal Neutron Flux Measured by <formula formulatype="inline"><tex Notation="TeX">$^{235}{\rm U}$</tex> </formula> Fission Chamber and Rhodium Self-Powered Neutron Detector in MTR

Thermal neutron flux is one of the most important nuclear parameter to be measured online in material testing reactors (MTRs). In particular two types of sensors with different physical operating principles are commonly used: self-powered neutron detectors (SPND) and fission chambers with coating. This work aims to compare on one hand the thermal neutron flux evaluation given by these two types of sensors and on the other hand to compare these evaluations with activation dosimeter measurements, which are considered as the reference for absolute neutron flux assessment. This study was conducted in an irradiation experiment, called CARMEN-1, performed during 2012 in OSIRIS reactor (CEA Saclay-France). The CARMEN-1 experiment aims to improve the neutron and photon flux and nuclear heating measurements in MTRs. In this paper we focus on the thermal neutron flux measurements performed in CARMEN-1 experiment. The use of fission chambers to measure the absolute thermal neutron flux in MTRs is not very usual. An innovative calibration method for fission chambers operated in Campbell mode has been developed at the CEA Cadarache (France) and tested for the first time in the CARMEN-1 experiment. The results of these measurements are discussed, with the objective to measure with the best accuracy the thermal neutron flux in the future Jules Horowitz Reactor.

Comparison of the Thermal Response of Two Calorimetric Cells Dedicated to Nuclear Heating Measurements During Calibration

Nuclear heating is a key parameter which contributes to the thermal design and the quality of in-pile experiments performed in Material Testing Reactors (MTRs) for the study of nuclear materials and fuels under irradiation. Nuclear heating is typically measured in MTRs by radiometric calorimeters. However this kind of sensor has to be suited and improved in perspective of the new experimental conditions inside the channels of Jules Horowitz Reactor (JHR). In this paper, we study the responses of two non adiabatic differential calorimeter cells having the same geometric design, but different dimensions. These experimental works are carried out during a preliminary out-of-pile calibration operating procedure of these sensors which consists in simulating the sample heating by Joule effect. The influence of the imposed electrical power and of the forced cooling flow is determined on the sensor calibration curves. A more sensitive sensor leads to a quadratic calibration curve. This behavior difference of the two calorimetric configurations is explained by means of temperature and heat flux measurements performed with a new instrumented jacket.

State of the art on nuclear heating in a mixed (n/γ) field in research reactors

This article aims at inventorying the knowledge on nuclear heating measurements in a mixed (n,γ) field in low-power research reactors using ThermoLuminescent Detectors (TLDs), Optically Stimulated Luminescent Detectors (OSLDs) and Ionization Chambers. The difficulty in measuring a mixed (n,γ) field in a reactor configuration lies in quantifying the contribution of the gamma photons and neutrons to the full signal measured by these detectors. The algorithms and experimental protocols developed together with the calculation methods used to assess the contribution of the neutron dose to the total integrated dose as measured by these detectors will be described in this article. This ‘inventory’ will be used to summarize the best methods to be used in relation to the requirements.

Nuclear Heating Measurement in Critical Facilities and Experimental Validation of Code and Libraries – An Application to Prompt and Delayed γ Nuclear Data Needs

Energy from prompt and delayed gammas in actual and future nuclear systems are more and more taken into account into design studies as they play an important role in the assessment of performance and safety concerns. Their incomplete knowledge (both prompt and delayed) require to take conservative design margins on local dimensioning parameters, thus reducing the awaited performances or flexibility of these facilities, with costs that are far from being negligible. The local energy photon deposit must be accurately known for Generation-III (Gen-III), Generation-IV (Gen-IV) or the new MTR Jules Horowitz Reactor (JHR). The last 2 decades has seen the realization, in Zero Power Reactors (ZPR), of several programs partially devoted to γ-heating measurements. Experimental programs were and are still conducted in different Cadarache facilities such as MASURCA (for SFR), and later in MINERVE and EOLE (for JHR and Gen-III reactors). The adequacy of the γ-heating calculation was compared to experimental data using thermo-luminescent (TL) detectors and γ-fission chambers. Inconsistencies in C/E and associated uncertainties led to improvement of both libraries and experimental techniques.For these last one, characterization for TL and optically stimulated (OSL) detectors (calibration, individual response), and Monte Carlo calculation of charge repartition in those detectors and their environment were carefully checked and optimized. This step enabled to reduce the associated experimental uncertainty by a factor of 2 (8% at 2σ). Nevertheless, interpretation of integral experiment with updated calculation schemes and improved experimental techniques still tend to prove that there are some nuclei for which there are missing or erroneous data, mainly in structural and absorbing materials. New integral and differential measurements are needed to guide new evaluation efforts, which could benefit from consolidated theoretical and experimental modeling techniques.

Measurement of photon flux with a miniature gas ionization chamber in a Material Testing Reactor

Nuclear heating measurements in Material Testing Reactors (MTR) are crucial for the design of the experimental devices and the prediction of the temperature of the hosted samples. Nuclear heating in MTR materials (except fuel) is mainly due to the energy deposition by the photon flux. Therefore, the photon flux is a key input parameter for the computer codes which simulate nuclear heating and temperature reached by samples/devices under irradiation. In the Jules Horowitz MTR under construction at the CEA Cadarache, the maximal expected nuclear heating levels will be about 15 to 18Wg−1 and it will be necessary to assess this parameter with the best accuracy. An experiment was performed at the OSIRIS reactor to combine neutron flux, photon flux and nuclear heating measurements to improve the knowledge of the nuclear heating in MTR. There are few appropriate sensors for selective measurement of the photon flux in MTR even if studies and developments are ongoing. An experiment, called CARMEN-1, was conducted at the OSIRIS MTR and we used in particular a gas ionization chamber based on miniature fission chamber design to measure the photon flux. In this paper, we detail Monte-Carlo simulations to analyze the photon fluxes with ionization chamber measurements and we compare the photon flux calculations to the nuclear heating measurements. These results show a good accordance between photon flux measurements and nuclear heating measurement and allow improving the knowledge of these parameters.