a vapour structures
15
r
20
F 25 30
time / d
Fig.2 Heat flow rates in the containment
35 40
A preliminary analysis of the heat removal capability of the composite containment proposed has been performed using the one-dimensional PASCO computer code [8]. All calculations performed have shown that the contribution of radiant heat transfer to the total heat transfer in the chimneys is considerable. With high emissivities of 0.9 of the walls the heat transferred by radiation equals approximately the amount transferred by convection [9]. Figure 3 illustrates
the removable heat as a function of the steel containment temperature for different emissivities of 0.1 and 0.9, respectively. The calculations have been performed for an inlet temperature of 30°C and no filtering of the cooling air. The following dimensions have been assumed:
diameter of the steel containment 60 m, height of the steel containment 40 m, depth of the annulus 80 cm, thickness of the steel containment 38 mm, thickness of the support ribs 10 cm, circumferential distance of the support ribs 50 cm. It becomes evident from figure 3 that with an emissivity of 0.9 which corresponds approximately to the technical surfaces involved a decay heat of 8 MW can be removed at a steel containment temperature of approx. 150 °C . With the additional pressure increase due to the non-condensable gases released in a core meltdown accident this corresponds to a maximum containment pressure of about 0 8 MPa.
The figure underlines also the significant contribution of the radiant heat transfer which in the past was often neglected in evaluating passive air cooled systems
0)
•a0)
o
0)
100 150
steel containment temperature [°C]
200 250
Fig 3 Heat removal with different emissivities e of the wall
All preliminary evaluations performed show that the composite containment concept with its passive containment cooling by natural air convection is a very promising alternative for future advanced water cooled reactors. However, additional experimental and theoretical research work needs to be done for the given conditions: large channel geometry and strong interaction between convective and radiative heat transfer. To investigate the basic phenomena involved in natural convection coupled with thermal radiation the separate-effects test program PASCO is under way. The MOCKA test facility serves to finally prove the operational performance of the passive cooling system under all conceivable conditions. This integral test facility is presently in the process of a design study.
3. PASCO TEST PROGRAM
The test program PASCO (acronym for passive containment cooling) is presently under way at the Institute of Applied Thermo- and Fluiddynamics (IATF) of the Research Center Karlsruhe 162
(previously Nuclear Research Center Karlsruhe, KfK) The general aim of this separate-effects test program is to investigate passive containment cooling by natural air convection and thermal radiation
crosswise traversing probes (velocity, temperature)
traversing probe
(velocity, temperature)
heated height: 8 m channel cross-section 0 5 x 1 Om (variable)
heated plate
nn i
Fig 4 PASCO test facility
The PASCO test facility shown in fig 4 simulates one cooling channel in the annular gap of the composite containment proposed The test section consists of a vertical rectangular channel of which one wall is electrically heated The other three walls are thermally insulated from the ambient surrounding The maximum channel cross-section is 500 mm x 1000 mm, the heated height is 8000 mm with four individually heatable zones By changing the channel depth and the heated height the effect of the channel geometry on heat transfer will be studied The wall emissivity is varied over a wide range, so that the influence of thermal radiation on the total heat transfer can be investigated To study the methods of enhancing the heat transfer, different internal structures (e g inclined repeated fins) will be used Table I summarizes the test matrix
Table I: Test matrix Heated wall temperature Th, °C Wall emissivity &
The test faciliu is equipped among others with approx 170 thermocouples to measure the distribution of wall temperatures Traversing probes for recording the temperature and velocity of the air are installed at five different elevations Cross-wise traversing probes at the inlet, in the mid-plane and at the outlet measure the temperature- and velocity distributions over each individual channel cross-section Moreover, the pressure at the channel inlet, the air humidity and the heating power are recorded With this comprehensive instrumentation data are generated for the validation and development of multi-dimensional computer codes.
4. EXPERIMENTAL RESULTS
Up to now steady-state experiments have been performed under the following boundary conditions: channel width 500 mm. channel depth 250 - 1000 mm, heated height 8000 mm, wall emissivity 0 9, heated wall temperature 100 - 175 °C
Figure 5 illustrates the wall temperatures measured at the heated plate and the channel walls for the channel cross-section 500 mm x 1000 mm. The boundary conditions of the test (M019) are given in Tab.II. It is evident from the figure that with a nominal temperature of the heated plate of 150 °C the uniformity of temperature can be considered as sufficiently good The temperatures measured at the back wall and the side walls that are heated by radiation underline the great influence of radiative heat transfer
side nil Uorlfc)
Fig 5 PASCO test results. Wall temperatures (channel cross-section 500mm x 1000mm) 164
Figure 6 shows the profiles of the air temperature and of the air velocity measured at the test channel outlet for the channel cross-section 500 mm x 1000 mm. The nominal temperature of the heated plate was 150 °C, the emissivity of the channel walls 0.9. It can be clearly seen in which way the profiles are affected by the side and back wall temperatures induced by thermal radiation.
The experimental data generated by the present PASCO tests represent an important data base for the validation and further development of multi-dimensional computer codes, mainly in respect to a proper modeling of the radiative heat transfer and the mixed convection turbulent flow. Such 3D codes (e.g. FLUTAN, TRIO-EF), if verified, will finally be used to evaluate and design the containment cooling system.