Hot-Water Layer, Heat-Loss Characteristics of an Open-Pool-Type Research Reactor for Reducing the Pool Top Radiation Level

Abstract

During an open-pool-type research reactor operation, it is necessary to access the pool top area for un/loading irradiation test pieces by a required irradiation period. However, when the reactor pool top radiation level exceeds the limit of radiation level by the rising of reactor chimney water contaminated by radioactivity due to a natural convection of the pool water, access the reactor pool top area is denied due to the high radiation level. In the case of HANARO, a hot-water layer (HWL, hereinafter) is maintained below a depth of 1.2 m from the top of the reactor pool in order to reduce the radiation level of the reactor pool top area. After a normal operation of the HWL, the pool top radiation level is safely maintained below the limit of the pool top radiation level. For studying more the characteristics of the HWL under a reactor coolant downward flow condition, The HWL heat loss is calculated based on the HANARO HWL calculation model. The HWL heat loss characteristics were reviewed by variations of the HWL temperature, reactor core coolant flow direction, and reactor power. It was confirmed through the results that the HWL heat loss under a reactor coolant downward flow condition was increased by about 20% to 60% over that under a reactor coolant upward flow condition, as per the HWL temperature variation. It was the reason that the HWL bottom convection heat loss was increased by the higher flow rate under a reactor coolant downward flow condition than that under a reactor coolant in an upward flow condition.