THERMAL-HYDRAULIC IN
NUCLEAR REACTOR
GS. Tr n Đ i Phúcầ ạ
THERMAL-HYDRAULIC IN
NUCLEAR REACTOR
Summary
1.Introduction
2.Energy from fission
3.Fission yield
4.Decay heat
5.Spatial distribution of heat sources
6.Coolant flow & heat transfer in fuel rod assembly
7.Enthalpy distribution in heated channel
8.Temperature distribution in channel in single phase
9.Heat conduction in fuel assembly
10.Axial temperature distribution in fuel rod
11.Void fraction in fuel rod channel
12.Heat transfer to coolant
THERMAL-HYDRAULIC IN
NUCLEAR REACTOR
I. Introduction
I. Introduction
An important aspect of nuclear reactor core analysis involves the
An important aspect of nuclear reactor core analysis involves the
determination of the optimal coolant flow distribution and pressure
determination of the optimal coolant flow distribution and pressure
drop across the reactor core. On the one hand, higher coolant flow
drop across the reactor core. On the one hand, higher coolant flow
rates will lead to better heat transfer coefficients and higher Critical
rates will lead to better heat transfer coefficients and higher Critical
Heat Flux (CHF) limits. On the other hand, higher flows rates will also
Heat Flux (CHF) limits. On the other hand, higher flows rates will also
in large pressure drops across the reactor core, hence larger required
in large pressure drops across the reactor core, hence larger required
pumping powers and larger dynamic loads on the core components.
pumping powers and larger dynamic loads on the core components.
Thus, the role of the hydrodynamic and thermal-hydraulic analysis is
Thus, the role of the hydrodynamic and thermal-hydraulic analysis is
to find proper operating conditions that assure both safe and
to find proper operating conditions that assure both safe and
economical operation of the nuclear power plant.
economical operation of the nuclear power plant.
THERMAL-HYDRAULIC IN
NUCLEAR REACTOR
This chapter presents methods to determine the distribution of heat
This chapter presents methods to determine the distribution of heat
sources and temperatures in various components of nuclear reactor. In
sources and temperatures in various components of nuclear reactor. In
safety analyses of nuclear power plants the amount of heat generated in
safety analyses of nuclear power plants the amount of heat generated in
the reactor core must be known in order to be able to calculate the
the reactor core must be known in order to be able to calculate the
temperature distributions and thus, to determine the safety margins.
temperature distributions and thus, to determine the safety margins.
Such analyses have to be performed for all imaginable conditions,
Such analyses have to be performed for all imaginable conditions,
including operation conditions, reactor startup and shutdown, as well as
including operation conditions, reactor startup and shutdown, as well as
for removal of the decay heat after reactor shutdown. The first section
for removal of the decay heat after reactor shutdown. The first section
presents the methods to predict the heat sources in nuclear reactors at
presents the methods to predict the heat sources in nuclear reactors at
various conditions. The following sections discuss the prediction of such
various conditions. The following sections discuss the prediction of such
parameters as coolant enthalpy, fuel element temperature, void fraction,
parameters as coolant enthalpy, fuel element temperature, void fraction,
pressure drop and the occurrence of the Critical Heat Flux (CHF) in
pressure drop and the occurrence of the Critical Heat Flux (CHF) in
nuclear fuel assemblies
nuclear fuel assemblies
THERMAL-HYDRAULIC IN
NUCLEAR REACTOR
I.1. Safety Functions & Requirements
I.1. Safety Functions & Requirements
The safety functions guaranteed by the thermal-hydraulic design are
The safety functions guaranteed by the thermal-hydraulic design are
following:
following:
Evacuation via coolant fluid the heat generated by the nuclear fuel;
Evacuation via coolant fluid the heat generated by the nuclear fuel;
Containment of radioactive products (actinides and fission products)
Containment of radioactive products (actinides and fission products)
inside the containment barrier.
inside the containment barrier.
Control of the reactivity of the reactor core: no effect on the thermal-
Control of the reactivity of the reactor core: no effect on the thermal-
hydraulic design.
hydraulic design.
Evacuation of the heat generated by the nuclear fuel: The aim of
Evacuation of the heat generated by the nuclear fuel: The aim of
thermal-hydraulic design is to guarantee the evacuation of the heat
thermal-hydraulic design is to guarantee the evacuation of the heat
generated in the reactor core by the energy transfer between the fuel
generated in the reactor core by the energy transfer between the fuel