Week 3: Steam Dumps

Question 1

What is the function of the Steam Dumps?

Answer 1

50% load rejection capacity w/o Rx trip assuming auto rod control
Turbine and Rx trip from 100% without lifting the first SG safety valve at 1185 psig
Maintain steam pressure during plant startup at HZP reference pressure
Remotely control the plant cooldown rate

Question 2

How many Steam Dump valves are there, and how are they connected to the Condenser?

Answer 2

There are 12 steam dump valves in total, connected to the condenser as follows:
7 to LP Condenser
4 to IP Condenser
1 to HP Condenser

Question 3

What interlocks impact the Steam Dump System?

Answer 3

C-7
C-9
P-4
P-12

Question 4

What are the control components associated with a Steam Dump valve?

Answer 4

Steam Dump Controller
I/P Converter
Positioner
4 Solenoid Valves

Question 5

What are the functions of the 4 Steam Dump Control Solenoid valves?

Answer 5

In series:
#1 - Open, closed by P-12 of Train A Protection
#2 - Open, closed by P-12 of Train B Protection
#3 - Arming solenoid, this is opened upon receiving either a C-9 and C-7 or C-9 and P-4 signal combination.
#4 - Trip solenoid, usually closed to force air flow through the Positioner. Opens on trip open signals, bypassing the positioning system and forcing the Steam Dump valve full open.

Question 6

What signals are needed to initiate Steam Dump operation?

Answer 6

Both an arming and demand signal are needed.

Question 7

Describe the conditions needed for a Steam Dump arming signal.

Answer 7

Receiving either a C-9 and C-7 or C-9 and P-4 signal combination.

Question 8

Describe the generation of a Steam Dump demand signal.

Answer 8

Based on a temperature error, Tavg-Tref, where Tref is determined by the mode of Steam Dump operation. Note that PT-505 is used to determine the Tavg input to the controller.

Question 9

What is the significance of PT-506 and PT-505 being from different instrument taps?

Answer 9

This means that an instrument failure can result in either an arming signal or demand signal, not both. This limits inadvertent Steam Dump operation.

Question 10

What are the two modes of automatic Steam Dump control?

Answer 10

Tavg, used during normal operations at powers > 15%
Steam Pressure, used during startups at powers < 15%

Question 11

What are the two sub-modes of Tavg automatic Steam Dump control?

Answer 11

Load Rejection (C-7)
Plant Trip (P-4)

Question 12

Describe the Load Rejection Tavg automatic Steam Dump control program.

Answer 12

Determines positioning based on comparing auctioneered high Tavg to Tref (as established by impulse pressure) to give a mismatch signal, based on the following program:
2F Error - 0% Flow
8.9F - 20%
15.8F - 40%

Question 13

Describe the Plant Trip Tavg automatic Steam Dump control program.

Answer 13

Determines positioning based on comparing auctioneered high Tavg to Thzp (557F) to give a mismatch signal, based on the following program:
0F Error - 0% Flow
15.8F - 20%
31.5F - 40%

Question 14

Describe the Steam Pressure automatic Steam Dump control program.

Answer 14

In this mode, Steam Dumps are controlled based on steam header pressure as compared to a reference pressure (1092 psig, the saturation pressure for 557F). This mode allows the plant to build up as steam load as a function of reactor power before transferring that load to the turbine during plant startup.

Question 15

Describe the Steam Pressure Manual Steam Dump control.

Answer 15

In this mode, P-12 will be bypassed, which allows for the use of the Steam Dump Cooldown valves (Group 1, 3 valves in total) to be manually positioned in order to cool down the plant during shutdowns.