Reactor Thermomechanics
Code  Completion  Credits  Range 

17TER  Z,ZK  3  2+2 
 Lecturer:
 Tutor:
 Supervisor:
 Department of Nuclear Reactors
 Synopsis:

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

17ZAF, 17JARE, 17THN1,2
 Syllabus of lectures:

1. Heat generation in reactors
Scope: 4 lectures
Energy released by fission
Role of the course within studyprogram, 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. Onegroup 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 radiusdependent heat generation, central gap effect, heat conduction in hollow rod with double sided heat removal.
Heat transfer in fuelcladding gap
Heat transfer coefficient in fuelcladding 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, burnedup fuel. Calculation models for fuelcladding gap heat transfer.
Heat transfer in core
Theory of similarity, dimensionless numbers. Singlephase flow: convective and conductive heat transfer. Forced convection, natural convection. Spacer grid effect on heat transfer coefficient. Heat transfer coefficient of VVER reactors.
Twophase 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. Steadystate 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.
Steadystate 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 steadystate 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 fuelcladding gap
Scope: 4 tutorials
3. Steadystate temperature distribution in fuel channel
Heat transfer in fuel channels, steadystate 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: 0894480383
 Note:
 Further information:
 No timetable has been prepared for this course
 The course is a part of the following study plans: