MAIN STEAM SYSTEM

Diagram
- Main Steam System P&ID YJE M VVP FD221
1 FUNCTION
The main steam system provides routing of the NSSS steam from downstream the steam generator MSIVs located in the valve compartments to the main turbine and to the following components :
- MSRs 2nd-stage reheater (normal supply) (GSS),
- turbine bypass (GCT),
- turbine gland seal (CET),
- feedwater storage tank (steam backup) (ADG),
- steam transformer (STR) (if any) and,
- vacuum ejectors (CVI).
2 DESIGN BASES
The main steam pipes material and dimensions are calculated according to ASME Standard.
Design pressure : 100 bar abs Design temperature : 311 °C
3 DESCRIPTION
The main steam piping system comprises four main steam lines (one for each steam generator), pressure equalizing and auxiliary supply connecting pipes, drain pipes and drain tanks.
The main steam pipes are connected together for pressure equalizing and supply the steam turbine HP casing through the four main stop and control valve assemblies.
Pipe connections are provided on the main steam supply system for :
- heating steam supply to the 2nd-stage reheater of the MSRs (GSS),
- turbine bypass to the condenser (GCT),
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Appendix 5.2.11 Main Steam System
- HP steam supply to the turbine gland seal system (CET), feedwater storage tank main steam backup (ADG),
- steam transformer (STR) (if any) and,
- condenser vacuum ejectors (CVI),
The following drains are recovered in drain tanks, as follows :
- from upstream each steam generator isolation valve to the turbine hall drain system or to the turbine condenser during hot shutdown, hot standby and pipe warmup.
- from the main steam supply pipes and the turbine bypass pipes via a drain tank to
the turbine condenser during pipe warmup and normal operation.
Startup drains are evacuated via the drain tank through an automatic drain valve.
During normal operation, the drains from the main steam pipes are continuously evacuated via the drain tank through a drain trap bypassing the drain valve.
Each main steam pipe is fitted with pressure taps, thermowells and sampling taps. Metal temperature transmitters allow the temperature increase rate to be monitored from the main control room during the pipe warmup phase.
Pressure measurement transmitters are also provided on the main steam supply for the turbine bypass.
4 EQUIPMENT LOCATION
The main steam pipes come in the axis of the steam turbine and cross the turbine hall wall at a level of approximately 13.900 m.
They spread out to the turbine into expansion loops and come up towards the main stop valves located on the turbine floor.
The drain tanks are located in the turbine hall at an elevation that allows proper drainage by gravity flow from the drain extraction points. Drain discharge valves and drain traps are located in the vicinity of the condenser HP flash compartment.
#- A

Appendix 5.2.11 Main Steam System

TABLE 21

MAIN STEAM SYSTEM DESIGN DATA



Main steam pipes within turbine plant
- number of pipes
- design pressure
- design temperature
- material
- outside diameter
- thickness
- mass flow, each
- main steam velocity in pipes
- moisture content at NI/CI interface

100 bar a
311 °C
A672B60CL22
813 mm
39 mm
652.4 kg/s
39 m/s
0,4 %



APPENDIX 5.2.12
TURBINE BYPASS SYSTEM






Appendix 5.2.12 Turbine Bypass System
Diagram
- Turbine Bypass System P&ID YJE M GCT FD411
1 FUNCTION
The turbine bypass system provides an artificial load for the NSSS during turbine transient operations which exceed normal NSSS capability by discharging HP steam directly to the turbine condenser.
It expands and desuperheats steam before its admission into the condensation zone of the condenser.
2 DESIGN BASES
The turbine bypass system is designed for a capacity of 60 % of the rated steam flow at the rated steam pressure. It allows turbine sudden load reduction from full load to house load, without actuation of the steam generator overpressure protection devices and opening of the pressurizer relief valves.
The six pressure reducing valves are capable, when combined, to handle the total bypass flow.
3 DESCRIPTION
The turbine bypass performs the following functions:
- allow turbine trip without incurring a reactor trip, or reactor trip without actuation of the main steam relief control valves or lifting of the steam generator safety valves,
- remove stored energy and residual heat from the reactor coolant system to bring coolant average temperature (TAVG) to no load temperature,
- maintain the reactor coolant temperature at the no load con-ditions, during hot shutdown,
- allow reactor coolant system controlled cooldown from hot shutdown conditions until startup of the residual heat removal system,
- at startup, allow heat up of the main steam pipes and turbine run up and loading up over the manual rod control range.
The turbine bypass system is composed of one steam manifold connected to the main steam piping system and six pressure reducing valves. These valves discharge steam into the condenser. Valve flow characteristics are linear. The valves are arranged in
#~

Appendix 5.2.12 Turbine Bypass System
parallel, so that when combined the required bypass flow is produced. All valves are interlocked and controlled to prevent operating modes which may have adverse consequences on plant safety and to protect the condenser against overpressure.
The steam is discharged into the condenser through expansion compartments integral with the condenser. These expansion compartments are supplied with desuperheating water taken at the condensate extraction pump discharge through on-off pneumatically-operated valves.
OPERATION
Detailed description of the turbine bypass control system is given by the nuclear island designer.
EQUIPMENT LOCATION
The turbine bypass manifold runs alongside the condenser at a level of approximately 9,600 m. The pressure reducing valves spread out from this manifold in front of the condenser wall.

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4t~

Appendix 5.2.12 Turbine Bypass System

TABLE 23

TURBINE BYPASS SYSTEM DATA



TURBINE BYPASS TO THE CONDENSER
Bypass pipes (upstream bypass control valves)
- number
- design pressure
- design temperature
- material
- outside diameter
- thickness
- mass flow, max each

6 100 bar a
311°C
A106GrB
406.4 mm
26.19 mm
286 kg/s



Pressure reducing control valves
- number