**1. NAME AND TITLE**

HASSAN**: **Time-Dependent Temperature
Distribution and Stress and Strain in HTR Fuel Pins.

**2. CONTRIBUTOR**

Imperial
College, London, United Kingdom through the OECD Nuclear Energy Agency Data
Bank, Issy-les-Moulineaux, France.

**3. CODING LANGUAGE
AND COMPUTER**

Fortran IV; IBM 370 Series (P00593I037000).

**4. NATURE OF
PROBLEM SOLVED**

The HASSAN programme calculates simultaneously, stepwise in time, the temperature, stress and strain distributions in high temperature reactor (HTR) fuel pins of tubular and hollow rod types. Any sequence of ramp and step changes of power may be followed. At each time step, the programme computes the operating stresses, also the residual stresses which develop if, at that point in time, the reactor is shut down and the fuel pin cools to a uniform temperature. Variations of material properties with temperature and neutron dose may be taken into account. In the structural analysis, axial symmetry and plane strain conditions are assumed. The programme cannot therefore give the stresses with sufficient accuracy in the region of pin ends or in regions of cross-pin flux or temperature tilt. In the thermal analysis, the fuel is assumed to be distributed uniformly along the fuelled length of the channel. The calculated temperature distributions are therefore not accurate for the pin end regions.

**5. METHOD OF
SOLUTION**

At each time step, the energy equation is integrated numerically along the channel to obtain the coolant axial temperature distribution(s). In the case of a tubular fuel pin, the radius of the adiabatic surface, which determines the heat fluxes to the inner and outer channels, is found by iteration. Radiation and convection heat transfer mechanisms are assumed, using appropriate empirical convective heat transfer correlations. The one-dimensional Fourier equation is used to determine the fuel pin internal temperature distribution. Heat transfer across internal (helium filled) gaps is assumed to be by conduction and radiation. The neutron-irradiation-induced dimensional changes (Wigner strains) are determined from sets of polynominals fitted to experimental data. Incremental creep strains are calculated iteratively assuming a Maxwell model with dose and temperature dependent parameters. Total creep strains are obtained by summation of the incremental creep strains and the stresses are calculated using closed-form expressions. Radial displacements are calculated and checked for interaction between components. In the case of interaction, the interface pressure is found by iteration.

**6. RESTRICTIONS OR
LIMITATIONS**

The present version of HASSAN is restricted to the following maximum dimensions:

number of axial positions for stress/strain analysis = 10

number of axial positions for temperature calculation = 21

number of radial mesh points in each component (tube) = 20

**7. TYPICAL RUNNING
TIME**

The programme running time, on a CDC 6600 computer, for a typical case requiring thirty time steps, is about 15 min.

**8. COMPUTER
HARDWARE REQUIREMENTS**

IBM 360 or IBM 370 mainframe.

**9. COMPUTER
SOFTWARE REQUIREMENTS**

MVT.

**10. REFERENCES**

**a) Included Documentation:**

A. Alujevic, J.L. Head and J.C. Uhry: “Hassan - A Computer Programme for Thermal and Structural Analysis of Prismatic HTR Fuel Elements,” DP Report 826 (June 1974).

**b)
Background Documentation:**

A. Jezernik, J.L.Head: “Stresses in the Graphite Fuel Tubes of a High Temperature Gas Cooled Reactor,” D.P. Report 662 (January 1970).

U. Weicht, W. Mueller: “TAPIR-COCO-DELTAP, Three Computer Programmes for the Thermal Analysis of a Reactor Core Containing Internally and/or Externally Gas Cooled Prismatic Fuel Elements,” D.P. Report 748 (March 1971).

**11. CONTENTS OF CODE
PACKAGE**

The package is distributed on a CD with a compressed zip file including source files, sample problem data, output, and documentation.

**12. DATE OF ABSTRACT**

November 2013.

**KEYWORDS: **FOURIER
TRANSFORMATION, HTR REACTORS, FUEL ELEMENTS, GRAPHITE MODERATED REACTORS, HEAT
TRANSFER, STRAINS, STRESS ANALYSIS