Large-scale containment experiments

Knowledge about the chemical reactions of the fission products as discussed in the preceding sections and about their resulting behavior in the course of a severe reactor accident is mainly based on the results of laboratory experiments. These 

The experiments demonstrated that the condensation of water droplets in the originally transparent saturated steam atmosphere started a few minutes after the introduction of the simulant fission products. Simultaneously, a rapid decrease in the concentration of airborne fission products started, as can be seen from the results of a typical experiment shown in Fig. 7.43. From the data obtained in the measurements, an initial halftime of the iodine concentration in the gas phase of about 15 minutes was calculated after having reached values below 1% of the initial concentration, further reduction of the gas-phase iodine concentration proceeded more slowly, with a halftime of about 2 hours. Typical values for the distribution of iodine and cesium in the experimental system at the end of a test (about 24 hours after the introduction of the simulant fission products) are shown in Table 7.16. A considerable fraction of iodine as well as of cesium was retained in the feed line, CS2O by condensation in the lower temperature region of the line, I2 probably 

After termination of the experiment, the containment atmosphere contained only a comparatively small fraction of the fission products iodine and cesium. From these data, iodine partition coefficients between sump water and gas phase in the range 10 to 10 were calculated, which are comparatively high values when one considers that the sump water consisted solely of condensed steam and, consequently, had a pH of about 7. Obviously, a large fraction of the initial h was 

Regarding the initial rate of fission product plate-out from the atmosphere, the results of the CSE tests can be assumed to be conservative, since the radionuclides were fed into a preheated containment. Thus, the extent of initial steam condensation in these experiments was considerably smaller than is to be expected in an actual reactor accident when the gas-steam mixture escaping from the primary circuit will enter a containment which is nearly at ambient temperature there is no doubt that stronger steam condensation favors fission product plate-out in the early stages of a severe accident. Moreover, the aerosol concentrations applied in these CSE tests were significantly lower than those to be expected in a real accident, resulting in a lower aerosol deposition rate. 

The washout of gas-phase iodine by containment sprays (alkaline borate solutions) was also studied in the CSE tests. As was mentioned in Section 6.2.1.2., the action of the spray in the initial period of a test greatly exceeded the natural removal processes. However, in the later stage of the test, when recirculated sump water was used as a spray solution, the effect on the now low gas-phase iodine concentration was weak. 

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When the results of the large-scale containment experiments are to be applied to the conditions of a real reactor accident, one cannot ignore the absence of ionizing radiation in these experiments, an effect which is able to influence significantly iodine chemistry and behavior, as was discussed in detail in Section 7.3.3.4.4. 

Most entrainment functions contain many adjustable parameters, and unfortunately there is not much turbulence data from large-scale field experiments. Model developers have therefore been forced to look for alternative reference cases. One strategy is to fit the entrainment function to certain limits, e.g., the four scenarios listed in Table 18.6. 

Ritzman, R. L., McCormack, J. D., Dickinson, D. R., Alleman, R. T. The ACE large-scale iodine experiment at the Containment Systems Test Facility (CSTF). Proc. 3. CSNI Workshop on Iodine Chemistry in Reactor Safety, Tokai-mura, Japan, 1991 Report JAERI-M 92-012 (1992), p. 264-278... 

The Interim Report of the People s League of Health in England on Nutrition of Expectant and Nursing Mothers (153) contains data of a large scale nutritional experiment. The investigation which lasted from March 1938 to the end of 1939 was planned to show whether additions of vitamins and minerals would benefit the course of pregnancy and labor and the newborn child. An inquiry into the diet of 6022 expectant mothers... 

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