Question

Which of the following statements regarding the heat transfer in a PWR are true?

The single phase coolant enters the core with fixed temperature and high pressure (15.5 MPa) and it is heated up by fission heat by about 33 K

As the heated-up coolant leaves the core, it is passed into the turbine.

The water in the secondary side of the steam generator is heated up by the coolant in the primary loop until boiling

Answer 1

Correct Statements: First and Third

Incorrect Statement: Second

Explanation

· In a PWR, the primary coolant (water) is pumped under high pressure to the reactor core where it is heated by the energy released by the fission of atoms. The heated water then flows to a steam generator where it transfers its thermal energy to a secondary system where steam is generated and flows to turbines which, in turn, spin an electric generator. In contrast to a boiling water reactor, pressure in the primary coolant loop prevents the water from boiling within the reactor.

· Light water is used as the primary coolant in a PWR. Water enters through the bottom of the reactor's core at about 548 K (275 °C; 527 °F) and is heated as it flows upwards through the reactor core to a temperature of about 588 K (315 °C; 599 °F). The water remains liquid despite the high temperature due to the high pressure in the primary coolant loop, usually around 155 bar (15.5 MPa ,153 atm, 2,250 psi). In water, the critical point occurs at around 647 K (374 °C; 705 °F) and 22.064 MPa (3200 psi or 218 atm).

This implies first statement is correct

· After picking up heat as it passes through the reactor core, the primary coolant transfers heat in a steam generator to water in a lower pressure secondary circuit, evaporating the secondary coolant to saturated steam — in most designs 6.2 MPa, 275 °C (530 °F) — for use in the steam turbine. The cooled primary coolant is then returned to the reactor vessel to be heated again.

This implies second statement is wrong and third statement is correct.