Comparison of methods for determination of boron in heavy water moderator

Abstract

. Can. J. Chem. 62, 1452Chem. 62, (1984. Five analysis methods were compared for the determination of boron in heavy water moderator: isotope dilution mass spectrometry, spectrophotometry, neutron activation, inductively coupled plasma -atomic emission spectrometry, and ion selective electrode potentiometry. Ten samples were analysed by each method; the results showed close agreement between all of the methods. Only mass spectrometry achieved the required precision (< 1% rsd) for samples taken during initial reactor operation, but all of the methods achieved sufficient precision (<lo% rsd) for samples taken during normal operation. For samples for which the "' B concentration must be determined, only mass spectrometry and neutron activation are applicable.L. W. GREEN, E. C . DAVEY, J. GULENS, T . H. LONCHURST et J. P. MISLAN. Can. J. Chem. 62, 1452 (1984. On a compark cinq mtthodes d'analyse pour la ditermination du bore dans des modkrateurs a l'eau lourde: la spectromktrie de masse par dilution isotopique, la spectrophotomCtrie, l'activation neutronique, la spectromCtrie d'Cmission atomique par plasmas induits par radiofr6quence et la potentiomktrie a I'aide d'tlectrodes spkcifiques a certains ions. On a analyst dix Cchantillons par chacune des mCthodes. Seule la spectromttrie de masse a permis d'obtenir la prtcision requise (coefficient de variation plus petit que 1%) pour des Cchantillons prklevCs au cours de I'optration initiale du rkacteur, mais toutes les mCthodes donnent une prCcision suffisante (coefficient de variation plus petit que 10%) pour des Cchantillons obtenus durant le cours normal des opCrations. Si on doit dtterminer les concentrations en "' B dans les Cchantillons, seules la spectromitrie de masse et I'activation neutronique peuvent Etre utiliskes.[Traduit par le journal] Introduction Boron, in the form of boric acid, is added to the heavy water moderator of CANDU~" power reactors to compensate for excess reactivity that exists during initial operation conditions and to serve as a readily removable reactivity shim during long term operation (1). It is also used during reactor commissioning to calibrate the reactivity worth of control devices such as the liquid zone control system, mechanical control absorbers, and adjuster rod adsorbers. The mass 10 isotope of boron is well suited for these purposes because its thermal neutron capture cross section is large (3.81 x lo-" cm2) and varies linearly with the inverse of neutron velocity over a wide velocity range.For calibration of the reactivity devices and for many of the reactivity assessments during normal operation, an uncertainty of less than 1 part in 1000 in the neutron balance (uncertainty : I mk) is required. This corresponds to a precision of k0.03 pg/g (2 s) for ' OB or, in the case of isotopically natural boron, LO. 12 p,g/g for total boron. The ' OB concentration is -1.5 p,g/g during initial operation and decreases to -0.15 p,g/g during normal operation, thus relative uncertainties of 5 2 % (2 s) for the initial operation samples a...