Shutdown Margin

Question 1

Define Shutdown Margin

Answer 1

Amount of Reactivity by which Reactor is Subcritical or would be subcritical from present conditions assuming ALL full strength CEA’s fully insert with exception of highest worth CEA (fully withdrawn)

Question 2

What do SDM requirements provide?

Answer 2

Sufficient reactivity margin to ensure that acceptable fuel design limits will NOT be exceeded for a normal shutdown and AOO’s

Question 3

During power ops, SDM is assured by what 2 things?

Answer 3

Shutdown CEA’s fully withdrawn
Regulating CEA’s above PDIL’s (3.1.7)

NOTE: SDM met by adjusting boron during refuel and shutdown

Question 4

What is the MOST limiting condition for SDM requirements?

Answer 4

> or Equal to 350F, MSLB at EOL. Resulting cooldown adds a lot of positive reactivity

< 350F, limiting accident is Dilution

Question 5

What is the required boron concentration during a Refuel?

Answer 5

> or Equal to 3000 PPM

Question 6

In Modes 3,4 and 5, SDM requirements protect against what 4 things?

Answer 6

Inadvertent Dilution
Uncontrolled CEA withdrawal in source range
Startup of idle RCP cold water accident
CEA ejection