Study on the thermo-emf of the VR 5/20 thermocouples with different design.


The influence of nuclear radiations on thermo-emf ¦E (transient variations) of thermocouples widely applied for measuring the temperature up to 2000 K in vacuum in inert and carbonaceous media of the VR 5/20 thermocouples, with different design under the pulsed reactor conditions is investigated. The tests have been carried out under the reactor power providing the thermal neutron flux density of about 3.5x10 sub 1 sub 9 neutr./(m sub 2 xs), fast neutron flux density of 6x10 sub 1 sub 7 neutr./(m sub 2 xs) and radiation dose rate of 2x10 sub 6 R/s (1P=2.58x10 sup - sub 4 Kl/kg), pulse duration constituting not more than 10 s. Transient variations have been determined as ¦E=Esub(p)-Esub(0), where Esub(p) and Esub(0) are mean thermo-emf values under nominal and zero reactor power, respectively, ¦E mean square error constituting +-0.6 K. For each thermocouple type ¦E linear dependence on reactor power is obtained. It is shown that if thermal resistance between electric contact of thermoelectrodes and protective coating is negligibly small, transitient variations of thermo-emf of the VR 5/20 thermocouples are negative: from -2.5 to -5.6 K. The VR 5/20 thermocouples with insulated junction and thermocouples with ZrC protection coating have positive transient variations of the thermo-emf (5-10 K). The sign and absolute value of transient variations of the thermo-emf depend not only on radiation conditions but also on the thermocouple structure and the technique of its mounting into the object. Volkov,-E.P.; Nalivaev,-V.I.; Prijmak,-S.V.; Fedik,-I.I.; Tselykovskij,-O.P.; Yakubov,-V.Ya