With diversity in the heat transport system, the ECC system and the moderator system, the core melt frequency reduces to a simple product of the failure frequency of the heat transport
CONDENSERS AND PASSIVE PRESSURE PULSE TRANSMITTERS C. PALAVECINO
Power Generation Group (KWU) of Siemens AG, Offenbach am Mein, Germany
Abstract
The Power Generation Group (KWU) of Siemens AG and the German electrical power utilities - particularly those operating boiling water reactor plants - are together de-veloping a new reactor type which is characterized in particular by its passive safety systems.
These passive safety systems are the emergency condensers, the containment cooling condensers, the passive pressure pulse transmitters, the gravity-driven core flooding lines, the rupture disks arranged in parallel to the safety-relief valves, and the scram systems.
This presentation constitutes a report on the emergency condensers and the passive pressure pulse transmitters.
The most important reasons for introducing passive safety systems are to increase the safety of future nuclear power plants, to simplify reactor safety systems and to re-duce capital costs.
The emergency condensers are heat exchangers consisting of a parallel arrangement of horizontal U-tubes between two common heads. The top header is connected via piping to the reactor vessel steam space, while the lower header is connected to the reactor vessel below the reactor vessel water level. The heat exchangers are located in a pool filled with cold water. The emergency condensers and the reactor vessel thus form a system of communicating pipes. At normal reactor water level, the emer-gency condensers are flooded with cold, non-flowing water. No heat transfer takes place in this condition. If there is a drop in the reactor water level, the heat exchang-ing surfaces are gradually uncovered and the incomexchang-ing steam condenses on the cold surfaces. The cold condensate is returned to the reactor vessel.
The design of the emergency condensers must meet the requirements dictated by the given thermal and hydraulic conditions.
The effects of the thermal condition parameters are relatively well known to us from the evaluation of emergency condenser testing conducted at Gundremmingen
Nu-clear Power Station. As we have altered the elevation conditions in the radial direc-tion in comparison to Gundremmingen Unit A, new sizing calculadirec-tions have been performed. An emergency condenser test rig was constructed at the Julich nuclear research center in order to provide experimental verification of our calculations.
Taking into consideration a redundancy degree of N + 2, a specific thermal rating of 63 MW per emergency condenser results for a reactor with an output of 2778 MW.
The total performance of the emergency condenser system is thus 252 MW, or 9.1 % of reactor output.
Given this emergency condenser rating, accident control of some transients becomes very interesting:
The heat removal capacity in the lower pressure range corresponds to that of 2 to 3 relief valves.
In the event of a stuck-open relief valve with simultaneous failure of all reac-tor vessel injection possibilities, the core will not become uncovered until some 24 hours after the onset of accident conditions.
The following can be said of this component:
a) It is more reliable than components designed for comparable functions.
The probability of failure of the emergency condenser of Siemens' BWR 1000 is approximately 10-4 per demand, while that of older emergency condenser signs such as at Gundremmingen Unit A is approximately 2 to 3 x 10-3 per de-mand, and that of the active residual heat removal systems of Siemens ad-vanced boiling water concept about 2 to 3 x 10-2 per demand.
b) It is considerably less expensive than the residual heat removal systems imple-mented to date, which comprise a primary circuit, a component cooling system and a final cooling system, each equipped with pumps, valves and heat ex-changers, etc. These latter systems are provided with a diesel generator as a re-dundant power supply system. The cost of one train (without considering in-frastructure elements such as the building, etc.) can be assumed to amount to some DM 100 million. In contrast to this, the cost for an emergency condenser system (comprising four emergency condensers) is estimated to cost between somewhere between DM 10 and 20 million.
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The reliability of the electrically-operated reactor protection system represents a limitation to achieving a higher degree of safety. It was therefore necessary to du-plicate the functions of the reactor protection system in a different way. These ef-forts successfully culminated in the development of the passive pressure pulse
trans-mitter.
Passive pressure pulse transmitters function in the same manner as the emergency condensers. The pressure generated in a heat-exchanger secondary circuit is used to actuate pilot or main valves. These passive pressure pulse transmitters allow the scope of reactor protection systems requiring electric power to be reduced consider-ably, while plant safety and reliability are increased through the combination of electrically-operated reactor protection systems with passive safety equipment.
No Quantity
1 Emergency condenser 4 2 Safely- relief valve 8 3 Spring- loaded pilot valve 8 4 Diaphragm pilot valve 8 5 Passive pressure pulse transmitter 4 6 Rupture disk 8 7 Flooding line 4 8 Containment cooling condenser 4 9 Core flooding pool
10 Pressure suppression pool
11 Honzontal discharge vent 42 12 Vertical discharge shaft 12 13 Scram system 4
Fig. 1. SWR 1000 Passive Safety Systems
28,7 m
Fig. 2. SWR 1000 - Containment
Orywell 22.258
17430
9.000
4394
Water level at lull cooling capability of me condenser
Fig. 3.
SWR 1000 - Isolation condenser (schematic) (Height in m above ± 0.0 elevation in RPV) 140
Containmentwall
Emergency or Isolation Condenser
Fig. 4.
KRB - A Emergency condenser diagram
70
60
50
40
30
20
10
cold water (30 *C)
boiling wal
\
er {116 °C) Design capabilityO Measuring point
10 20 30 40 50 60 Pressure [bar]
70
Fig. 5.
KRB-A
Cooling capability of the emergency condenser Measurement on May 10,1975
100
SWR 1000 - Emergency condenser.
Cooling capability as a function of the pressure in the RPV
QH = Cooling capability at lower RPV water leval Qo = Maximum cooling capability
/
SWR 1000 - Emergency condenser.
Cooling capability as a function of loss of water level in the RPV. (AH in m)
142
400
-300
200
100
20 40 60
pressure in RPV [bar]
80
Fig. 8.
SWR 1000 - Comparison between the cooling capability of the isolation condenser and those of the safety relief
valves
Steam Line to
r-Emergency Condenser
Pressure Pulse Line
to Pilot Valve
Condensate from Emergency Condenser
Fig. 9.
SWR 1000 - Passive Pressure Pulse Transmitter
ou
Fig. 10. SWR 1000 - Reaction Time of PPPT
Table 1: Principal Data of Emergency Condenser System
Number of emergency condensers 4
Design
Performance of each emergency condenser
Heat transfer area per condenser
Design conditions:
Size (diameter) of connected piping
1 tube bundle comprising a four-pass U-tube configuration, with connection to two
com-mon headers
63 MW given a primary system pressure of 70 bar, a core flood-ing pool temperature of 40 °C, and a reactor vessel water level drop of 8.20m
138m2, comprising 104 tubes;
tube diameter: 44.5;
- Supply steam line: 400 mm - Condensate discharge line:
200mm - Headers
o steam side: 500mm o condensate side: 300 mm
144
Table 2: Comparison of Magnitude of Failure Probabilities per demand of Various Residual Heat Removal Systems
Table 3: Principal Data of Passive Pressure Pulse Transmitter
Type 200 400 600 800 1000 1200 1400
BWR - Degression of Specific Plant Costs as Fuction of Output and Technical Design
DESIGN, FABRICATION AND TESTING OF FULL SCALE