RQ-C-4923, LOCA Analysis

Question 1

During a LOCA, why is a CL break worse than a HL break?

Answer 1

• Void in Rx Head is needed to push through loop seal which results in lower vessel level

Question 2

During a LOCA, why is the goal to get steam through the break location

Answer 2

• More steam out the break means more energy (and less mass) out of the system

Question 3

Why is downcomer boiling during the reflood phase of a LOCA problematic?

Answer 3

• Because if the downcomer (CL) is boiling, then there is not enough pressure built up to overcome steam void in the head and cover fuel

Question 4

How is downcomer (CL) boiling minimized during the reflood phase of a LOCA?

Answer 4

• Initiation of CTS is delayed to raise pressure on the CL to minimize boiling.

Question 5

What is the basis for the RCS pressure criterion used to trip RCPs during a SBLOCA?

A. Maintain forced circulation for larger small break LOCAs to improve core cooling.
B. Ensure peak clad temperatures do not exceed ECCS acceptance criterion limit.
C. Minimize reactor vessel downcomer level to delay core reflood.
D. Maximize energy removed from the break before securing RCPs.

Answer 5

B. Ensure peak clad temperatures do not exceed ECCS acceptance criterion limit.