[en] Among many factors influencing radiation fields at primary loop of nuclear power plants, two main aspects are the materials of system equipment and the chemical parameters of primary loop water. The effects of dissolution H₂, boron potassium coordination curve control, technology for Zn injection, and reactor shutdown oxidation operation on radiation sources are discussed in this paper. Relevant advices are provided. (authors)

[en] Highlights: • Horizontal and vertical distributions of dissolved oxygen (DO) in the Pearl River estuary. • Low DO phenomenon presented in the sub-layer water column during the summer but not winter period. • Low DO zone with an area of ~ 1500 km² located at the fresh- and saline-water intersection, with high heterotrophic bacteria abundance. - Abstract: Estuarine oxygen depletion is one of the worldwide problems, which is caused by the freshwater-input-derived severe stratification and high nutrients loading. In this study we presented the horizontal and vertical distributions of dissolved oxygen (DO) in the Pearl River estuary, together with temperature, salinity, chlorophyll a concentration and heterotrophic bacteria abundance obtained from two cruises during the summer (wet) and winter (dry) periods of 2015. In surface water, the DO level in the summer period was lower and varied greater, as compared to the winter period. The DO remained unsaturated in the summer period if salinity is 12; while in the winter period it remained saturated throughout the estuary. In subsurface (> 5 m) water, the DO level varied from 0.71 to 6.65 mg L^{− 1} and from 6.58 to 8.20 mg L^{− 1} in the summer and winter periods, respectively. Particularly, we observed an area of ~ 1500 km² low DO zone in the subsurface water with a threshold of 4 mg DO L^{− 1} during this summer period, that located at the fresh- and saline-water intersection where is characterized with severe stratification and high heterotrophic bacteria abundance. In addition, our results indicate that spatial DO variability in surface water was contributed differently by biological and physio-chemical variables in the summer and winter periods, respectively.