An apparatus for the study of high temperature water radiolysis in a nuclear reactor: Calibration of dose in a mixed neutron/gamma radiation field

Abstract

The cooling water of nuclear reactors undergoes radiolytic decomposition induced by gamma, fast electron, and neutron radiation in the core. To model the process, recombination reaction rates and radiolytic yields for the water radical fragments need to be measured at high temperature and pressure. Yields for the action of neutron radiation are particularly hard to determine independently because of the beta/gamma field also present in any reactor. In this paper we report the design of an apparatus intended to measure neutron radiolysis yields as a function of temperature and pressure. A new methodology for separation of neutron and beta/gamma radiolysis yields in a mixed radiation field is proposed and demonstrated.

Neutron and β/γ Radiolysis of Water up to Supercritical Conditions. 2. SF6 as a Scavenger for Hydrated Electron

“…In part 1, hydrated electron yields were determined by the reaction of hydrated electrons (e − ) aq with the scavenger N 2 O, which gives the easily measured stable product N 2 : ( e − ) aq + normalN 2 normalO → N 2 + OH • + OH − Phenol was added to the water to scavenge • H atoms, some of which could otherwise convert to solvated electrons (equilibrium reaction ) and contribute to the observed N 2 yield. PhOH + H • → HPhOH • H • + OH − ⇔ ( e − ) aq + normalH 2 normalO It was found that N 2 O decomposes to some extent on the hot metal walls of the flow system at 380 and 400 °C, but it was possible to subtract this thermal component from the radiolytic yield because the dwell time is quite shorton the order of 1 s. This is not the case for the reactor flow loop, and the much longer dwell time poses a serious problem for the use of N 2 O in that system at supercritical temperatures.…”