STM Dump

Question 1

State the function of the Steam Dump system

Answer 1

Prevents plant trips following a 50% load reduction with auto control rods
Returns plant temperature to a zero load value (557) following a plant trip
Creates an artificial steam load during turbine startup and shutdown to ensure smooth reactor load shifts
Provides a means of cooling down the reactor plant following reactor shutdown

Question 2

State Arming signals for Steam dumps

Answer 2

C-7a, turbine load reduction arming, sensed from PT-506
P-4, A-train reactor trip and bypass breaker opened
Steam Pressure mode
C-9, condenser available

Question 3

State Blocking signals for Steam dumps

Answer 3

C-9, if condensers are not available
P-12, Lo-Lo Tave 550F (2/4)
Manual, place the P-12 bypass switches to off

Question 4

Discuss how and why the steam dump valves are arranged

Answer 4

4 banks open sequentially, this provides a smooth linear response to steam flow increases
Total capacity: 6.4X10^6 lbm/hr
1 valve = 3.33%

Question 5

Discuss how Steam Dumps trip open on Load Reduction

Answer 5

Banks 1 and 2 will open at 8.1F Tave-Tref

Banks 3 and 4 will open at 14.2F Tave-Tref

Question 6

Discuss how Steam Dumps trip open on Reactor Trip

Answer 6

Banks 1 and 2 will open at 15F Tave-Tref

Banks 3 and 4 will open at 30F Tave-Tref

Question 7

State why the load reduction-arming signal (C-7a) is provided with seal-in memory logic

Answer 7

The seal-in memory logic allows the steam dumps to remain armed once the transient has stopped

Question 8

State why two pressure transmitters are required for the load reduction logic

Answer 8

two transmitters are used to prevent inadvertent opening of steam dumps due to a single instrument failure