Reactor Thermomechanics

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Code Completion Credits Range Language
17TERR Z,ZK 4 2+2 Czech
Garant předmětu:
Department of Nuclear Reactors

Heat generation in nuclear reactors - distribution and time evolution, residual heat generation. Steady-state and transient heat conduction in fuel elements, heat conduction in cladding, heat transfer in fuel-cladding gap. Convection heat transfer in nuclear reactors and boiling crisis of the first kind. Temperature distribution in fuel channel in steady-state and transient conditions. Core hydrodynamics. Hot channel theory. Steady state thermohydraulic calculation of nuclear reactor.


17ZAF, 17JARE, 17THN1,2

Syllabus of lectures:

1. Heat generation in reactors

Scope: 4 lectures

Energy released by fission

Role of the course within study-program, relationship to other courses, goals of the course. Energy released in fission process and recoverable energy. Heat generation in core. Power peaking factors. Heat generation function. Linear heat generation.

Heat generation in cylindrical reactor

Uniform grid. One-group equation of the reactor. Heat generation in bare cylindrical reactor. Effect of reflector on spatial distribution of heat generation. Equivalent reactor. Influence of control rods. Influence of voids and gaps. Radial distribution of heat generation in campaign refueling strategy.

Xenon effect and chemical reactions

Xenon effect on spatial power distribution. Initial equation, heat generation distribution at a change of reactor operation regime, xenon oscillations, oscillations in VVER reactors. Chemical reaction of cladding with steam: chemical reaction kinetics, reaction energy, time evolution of cladding oxidation.

Residual heat generation in reactors

Fission reaction after shut down, radioactive fission products decay, radioactive decay of transuranic elements. Importance of residual heat generation for safety of nuclear reactors. Calculation code ORIGEN.

2. Heat transfer in fuel elements

Scope: 4 lectures

Heat conduction in fuel elements

Heat conduction equation for cylindrical geometry. Integral thermal conductivity. Thermophysical properties of the fuel. MATPRO code. Heat conduction in cylindrical fuel rod: simplified approach, effect of radius-dependent heat generation, central gap effect, heat conduction in hollow rod with double sided heat removal.

Heat transfer in fuel-cladding gap

Heat transfer coefficient in fuel-cladding gap: heat conduction in gas filling, contact thermal conductivity, radiation heat transfer. Thermophysical parameters affecting state of the gap. Schlykov similarity approach. Heat transfer coefficient of the VVER fuel - fresh fuel, burned-up fuel. Calculation models for fuel-cladding gap heat transfer.

Heat transfer in core

Theory of similarity, dimensionless numbers. Single-phase flow: convective and conductive heat transfer. Forced convection, natural convection. Spacer grid effect on heat transfer coefficient. Heat transfer coefficient of VVER reactors.

Two-phase flow and boiling crisis

Nucleate boiling regime. Nucleate boiling, film boiling. Boiling crisis of the first kind: physical principle, calculation correlations. Transition boiling, stable film boiling. Fuel performance under extreme conditions, results of PCM tests.

3. Steady-state temperature distribution in fuel channel

Scope: 2 lectures

Heat transfer in fuel channels

Energy equation of coolant flow. Temperature distribution in coolant, cladding, and fuel pellet. Homogenous model of fuel rod. Theory of similarity - dimensionless temperatures.

Steady-state temperature distribution in fuel channel

Axial temperature distribution of the coolant in the fuel channel with sine heat generation. Temperatures at fuel pin surface. Temperatures in fuel rod axes. Maximal temperatures at fuel rod surface and in fuel rod axis. Ring fuel rod. Similarity of temperature fields. Boiling in fuel channel.

4. Reactor hydrodynamics

Scope: 1 lecture

Pressure drop: Bernoulli formula, friction of coolant, local hydraulic resistances, acceleration pressure drop, gravity pressure drop. Total pressure drop and coolant distribution in the core. VVER reactors hydrodynamics. Hydraulics characteristics of core, reactor and primary loop. Pumps characteristics.

5.Thermohydraulic reactor analysis

Scope: 1 lecture

Hot channel theory: principle, hot channel factors, temperatures in hot channel. Deterministic and statistic approach. Thermohydraulic analysis of the reactor in steady-state conditions. Limiting criteria on maximal allowable thermal power of the reactor. Maximal allowable power (Operational limits and conditions). Integral computational codes (RELAP, ATHLET)

Syllabus of tutorials:

Content of exercises supports lectures with concrete calculations.

1. Heat generation in reactors

Energy released by fission, heat generation in cylindrical reactor, chemical reaction of cladding with steam

Scope: 6 tutorials

2. Heat transfer in fuel elements

heat conduction in fuel elements, heat transfer in fuel-cladding gap

Scope: 4 tutorials

3. Steady-state temperature distribution in fuel channel

Heat transfer in fuel channels, steady-state temperature distribution in fuel channel

Scope: 3 tutorials

Study Objective:

Detailed knowledge of physical aspects affecting spatial heat distribution in nuclear reactors. Orientation in basic laws of heat transfer in reactor core. Conception of nuclear reactor thermohydraulic analysis issues.

Application of basic courses (17ZAF, 17THN1, 17THN2) on nuclear power reactors. Orientation in given issues, use of obtained knowledge in further courses (17DYR, 17JBEZ).

Study materials:

Key references:

Heřmanský B.: „Thermomechanics of nuclear reactors“, Academia, Praha 1986, (in Czech)

Recommended references:

Tong, L.S., Weisman, J.: Thermal Analysis of Pressurized Water Reactors, American Nuclear Society, Illinois USA, 1996, ISBN: 0-89448-038-3

Further information:
No time-table has been prepared for this course
The course is a part of the following study plans:
Data valid to 2023-08-30
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