not restrict water withdrawal at the Krümmel plant. For the nuclear
power plants in the Rhine basin all three restrictions for electricity
generation come into operation (shown in Fig. 5 for Biblis A&B
only), whereby the maximum discharge water temperature is the
main cause of restrictions. Occasionally, the maximum mixing
water temperature of 28 C is already reached at the point of
intake, i.e. the withdrawal water temperature restricts electricity
generation.
In summary it can be stated that the upper temperature limit of
the discharge water is the main restriction on electricity generation.
This also means that an increase of water availability is not a
solution to this problem. Only in those cases where the maximum
mixing water temperature in the river causes the restriction, the
situation can be improve by increased runoff at the location of the
power plant.
The sum of mean daily electricity generation and the mean
minimum daily electricity generation by all nuclear power plants
are displayed in Fig. 6. The sum of mean daily electricity generation
is the mean value of all days per time period and 100 realisations.
The mean minimum daily electricity generation is the mean of the
lowest value of each year for each time period. This means that
from each year and realisation the lowest value is extracted for each
power plant and from these values the mean value is calculated.
Using these numbers not only the effects on utilisation rates of
power plants for one year or realisation can be estimated but the
overall effect of climate change.
Using the data given in Deutsches Atomforum [12] for the
extremely hot and dry year 2003, a minimum daily utilisation rate
of all nuclear power plants of 82% can be calculated. For the scenario
without an increase in air temperature (0 K scenario) the
simulated absolute minimum daily utilisation rate of all nuclear
power plants is 80%, which fits quite well with the observed value
for the year 2003. The small difference of 2% may be due to an
optimisation ofwater use not taken into consideration in the power
plant simulation. In the þ1 K scenario the absolute minimum daily
utilisation rate of all nuclear power plants is 77%, in the þ2 K scenario
72%, and in the þ3 K scenario 64%. These very low values are
reached on days where in some rivers or parts of them, e.g. in the
Rhine basin, a water temperature of 28 C is reached. In such cases,
the respective power plants must be shut down completely This can also be seen in Fig. 7 where the results of one selected
year and climate realisation are shown as an example. For instance,
on day 209 the nuclear power plants located on the Rhine, i.e.
Philippsburg 1&2 and Biblis A&B (see Fig. 7), are shut down
completely due to water temperatures exceeding the 28 Cthreshold.
At other power plants, e.g. Unterweser or Krümmel, the
electricity generation is reduced significantly. Of the 17 nuclear power
plants only 6, comprising approximately 37% of the installed
capacity, continue generation without or with negligible restrictions.
Table 3 gives the sum of electricity generation and deficits, and
mean value of utilisation rate, broken down according to
different cooling systems and for all nuclear power plants. Presented
results are simulated for 2010 and for the climate scenarios
in 2050. Especially for the nuclear power plants with
once-through cooling a strong reduction of electricity generation
and an increase in deficits is simulated. Although a mean
utilisation rate of all nuclear power plants of 99.5% in the þ3 K
scenario in 2050 seems very high, the effects can be very strong
because the deficit is restricted to a few days in summer. Under