2　Terms，Symbols，and Codes

2.1　Terms

2.1.1　Nuclear power station

A power station in which electricity is generated utilizing the nuclear power released in fission，generally consisting of primary circuit and secondary circuit.

2.1.2　Restricted area

An area with defined boundaries，operated under the effective control of the management personnel of nuclear power station.

2.1.3　Original point of surveying area

Reference point transferred from national or regional horizontal and vertical datum points，serving as the starting point for survey of whole nuclear power station area.Generally it is required where the national or regional datum points are remote from surveying area or inconvenient to use directly.

2.1.4　Primary control network

A set of control networks of required accuracy ratings throughout the nuclear power station site，established based on the original point of surveying area or the national or regional datum points to provide reference for positioning and setting out the buildings or structures and associated components during the early stage of civil construction and establishment of the secondary control network.

2.1.5　Secondary control network

Horizontal and vertical control networks consisting of a number of observation piers around the main power buildings including nuclear island and conventional island，established based on the primary control network to provide reference for positioning and setting out the main buildings or structures in the station，establishing micro-grid control network，monitoring deformations and partially densifying control points after the site ground is leveled.

2.1.6　Micro-grid control network

A small-sized survey control network of high accuracy consisting of a number of survey marks made on the concrete foundation slabs or platforms and the inter-visible penetrations reserved on floor slabs and walls in power buildings including nuclear island and conventional island，established based on the secondary control network to provide reference for determining and checking the positions of buildings or structures and installations，monitoring deformations，and partially densifying control points within power buildings.

2.1.7　Antenna phase center

Electrical center of microwave antenna，theoretically designed to coincide with the antenna's geometric center.

2.1.8　differential global position system

A navigation system which provides improved position accuracy for users by broadcasting DGPS differential corrections via radio beacons，mainly consisting of reference station，broadcast station，monitoring station，and monitor center.