The BTRS is a subsystem of the CVCS and is shown diagrammatically in Fig 1.65. Its function in support of the RCS chemistry is to remove and store boron on anion resin at low temperature (10°C), and subse­quently release it on demand from the resin at higher temperature (60°C). By this means the required control of the boron concentration in the RCS is achieved in an economic way.

The boron capacity of the resin is proportional to the boron concentration in solution and inversely pro-

(2) Solids concentration determined by filtration through a filter having 0.45 micron pore size.

(3) Excluding boric acid.

portional to the water temperature. Low temperature operation is achieved by the use of chiller units and higher temperature operation by the use of modulated process heat.

It should be noted that although the BTRS was included in most PWR reference designs prior to 1980, it was not always operated. It can be argued that the operational advantages which led to the original con­ception of the BTRS, can be outweighed by a com­bination of safety related plant layout requirements, operational considerations and economics. It is possi­ble therefore that not all PWR designs will feature a BTRS type system, and may quite justifiably achieve an acceptable level of boron recovery by other means such as evaporation.