VGB POWERTECH 5 (2021) - International Journal for Generation and Storage of Electricity and Heat

Safety-related residual heat removal chains for pressure water reactors VGB PowerTech 5 l 2021
a few safety-relevant additions – became
the standard and has since been used for all
following PLWR plants [5, 6]. The number
of RHR lines usually, but not necessarily,
corresponds to the number of reactor cooling
loops. For this size of units (and also for
the EPR concept (≥ 1,600 MWel) four
Steam Generators and thus four reactor
cooling loops are required for heat transfer
to the water/steam cycle in power operation.
Accordingly, the RHRC also consists of
four independent RHR lines with a heat
transfer capacity of 50 % each, based on the
design case. (Note: Even for plants with
only three reactor cooling loops, this “one
to one” assignment of loop and line number
can be obtained without violating the safety
philosophy (repair and simultaneously
single-failure) when the heat transfer capacity
of each line is increased to 100 %.) In
F i g u r e 5 , the two inner Component Cooling
Circuits are designed for the alternating
supply of operational component points.
For this purpose, in addition to the regular
Component Cooling Pump, a second pump
is connected in parallel, operated in case of
a very high cooling water demand.
NPPs of DWR 1300 MW class
The increasing safety-related requirements,
set down e.g. in the “RSK Guidelines
for Pressurized Water Reactors” [7]
and in “Safety Regulations of the KTA”
[8, 9], in particular
––
elevated awareness of the fuel pool inventory
as a source of activity, and
––
the inclusion of “civilization-related external
impacts” (aircraft crash, explosion
pressure waves, third part influences) as
cases to be managed,
led to important extensions for the system
technology of the steam generator feed as
well as for the RHRC [10] (F i g u r e 6 ).
With the Emergency Feed Water System, a
possibility of short and medium-term heat
removal from the Reactor Coolant System
via the Steam Generators was created, independent
of the Feed Water Tank and the
regular Emergency Power Supply. For the
subsequent long-term cooling via the socalled
Emergency RHR Chain in this two of
the four RHR lines, whose residual heat
removal circuits contain a Fuel Pool Cooling
Pump,
* With introduction of the new “Power Plant Labeling
System (KKS)” in 1976 the Component
Cooling System was, without any technical impact,
split into “Safety Component Cooling
System” and “Operation Component Cooling
System”. The former includes the Component
Cooling Pumps, the Component Cooling Heat
Exchangers as well as the supply of all cooling
points that are relevant for operation of the
RHRC. The latter only consists of the connected
pipe network, which distributes and collects
the cooling water flows to consumers of nuclear
operating systems inside Reactor- and
Reactor Auxiliary Building.
SG
RCP
SG
1 Residual Heat Removal Pumps
1a Fuel Pool Cooling Pumps
2 Residual Heat Exchangers
3 Component Cooling Pumps
3a Emergency Component
Cooling Pumps
RCP
Reactor
RCP
4 Component Cooling
Heat Exchangers
5 Secured Service
Cooling Water Pumps
5a Emergency Secured Service
Cooling Water Pumps
SG
RCP
SG
6 Safety-related Cooling Points
7 Secured Intermediate Coolers
8 Emergency Feed Water Pumps
9 Emergency Generators
10 Emergency Diesel Engines
Fig. 6. DWR 1,300 MW, Reactor Coolant System and RHR Chain.
SG
From
Condenser
Cooling
Tower
RCP
3
5
Reactor
SG
RCP
Feedwater
System
Fig. 7. MZFR, Reactor Coolant System and RHR Chain.
4
1
2
7
Main Steam System
Reactor Coolant System
Residual Heat
Removal System
Safety Component
Cooling System
Operation Component
Cooling System
Secured Service
Cooling Water System
SG Steam Generator
RCP Reactor Coolant Pump
11 Demineralized
Water Pool
––
an Emergency Component Cooling
Pump within the Safety Component
Cooling System*, and
––
an Emergency Secured Service Cooling
Water Pump in the Secured Service Cooling
Water System.
are installed in parallel to the existing
pumps.
The Fuel Pool Cooling Pumps themselves
act as “Emergency Residual Heat Removal
Pumps” as part of the Residual Heat Removal
System in this case. If required, all
this pumps are supplied with power via the
Emergency Generators, which – after the
Emergency Feed Water Pumps have been
disconnected – are driven by the Emergency
Diesel Engines.
For the fuel pool cooling, in addition to the
two RHR lines that include the Fuel Pool
Cooling Pumps, there is also another fuel
pool cooling circuit whose Fuel Pool Cooler
is supplied by the Operation Component
6
SG
RCP
1
2
3
4
5
6
7
Main Steam System
Reactor Coolant System
Moderator System
Component Cooling
System
Secured Service
Cooling Water System
Steam Generator
Reactor Coolant Pump
Moderator Pumps
Moderator Coolers
Component Cooling Pump(s)
Component Cooling
Heat Exchanger
Secured Service
Cooling Water Pumps
Further Component Cooling
Water Consumers
Further Secured Service
Cooling Water Consumers
52