Assessment of Risk Studies and Severe Nuclear Accidents - The Risks of Nuclear Energy Technology - page 226

equipped fuel cells and batteries. Also underground electrical cables to other power
plants can be applied. It is important that the required connections are prepared at
special locations in advance for all voltage levels and AC or DC current needed in
the reactor plant. The required emergency electrical power for a 1,300 MW(e) plant
is in the range of 700 kW(e) [ 84 ].
10.6.1.2 Securing the Feedwater Supply for the Steam Generators
in PWRs
In the KWU-PWR, as an example, the feedwater tank contains about 300-400 m 3 of
water and after the depressurization of the steam generators about 350 m 3 of water
is available also in the feedwater lines. The preheaters contain about 150 m 3 of
water. In the demineralized water tanks there are about 1,440 m 3 available.
In modern PWRs, e.g. AP1000, US-APWR, EPR the IWRST contains a very
large amount of water (Chap. 3 ).
In addition, water can be supplied—as described above—by independently
powered pumps from deep wells on the site of the reactor plant. Water can also
be taken from a river, a lake or the ocean.
The transfer of the afterheat in a 1,300 MW(e) plant by boiling the coolant water
and steam release needs a supply of about 20 kg/s of water [ 84 ].
10.6.1.3 Securing Core Cooling in PWRs
The most important part of severe accident management measures in PWRs is the
depressurization of the steam generators and of the primary cooling system .
Present PWRs, e.g. in Germany, were equipped with large cross section safety/
relief valves. The safety/relief valves can be opened by the operator staff from the
operation room—if needed. For future reactor designs e.g. AP1000 and EPR the
automatic depressurization system (ADS) were described in Chap. 3 . The electrical
energy supply or the supply of pressurized nitrogen or air for the safety relief valves
must be secured redundantly or even diversely in advance. It is important that the
safety/relief valves can be closed again (see Three Mile Island accident).
10.6.2 Examples for Severe Accident Management Measures
for BWRs
Core melting under high system pressure must be avoided by rapid depressurization
through a number of parallel safety/relief valves into the pressure suppression
chambers (Chap. 3 ) . It is important that the supply of electrical energy and
pressurized nitrogen or air—as described for PWRs Sect. 10.6.1.3 above-is always