Abstract
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.
Highlights
THE accurate determination of nuclear heating remains a key point in the design studies of power and research reactors
The experimental validation of neutron and photon propagation calculation schemes related to nuclear heating prediction requires the implementation of nuclear heating measurements usually performed in zero-power reactors (ZPRs)
The use of thermoluminescent dosimeters (TLDs) is remarkably well suited to gamma heating. They are highly sensitive to gamma radiation, TLDs are to a lesser extent, sensitive to neutrons. Since the latter currently relies on literature data with relatively high uncertainties, a promising approach to experimentally determine this neutron contribution is based on the use of two types of doped lithium fluoride TLDs pre-calibrated both in gamma and neutron fields
Summary
Nuclear heating is assessed by using dosimetry techniques rather than calorimetry techniques which are usually used in power reactors like MTRs. They are highly sensitive to gamma radiation, TLDs are to a lesser extent, sensitive to neutrons Since the latter currently relies on literature data with relatively high uncertainties (up to 50100%), a promising approach to experimentally determine this neutron contribution is based on the use of two types of doped lithium fluoride TLDs pre-calibrated both in gamma and neutron fields. Such approach has been recently developed for medical purposes at the national institute for nuclear physics (INFN, Milan, Italy) [1]. In the following two sections are described the implementation and the results of the test irradiations carried out at LPSC, and a preliminary assessment of the neutron contributions to the total doses measured by LiF TLDs in the EOLE reactor
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