Steam Generator Tube Rupture EOP

Question 1

SGTR: What are the methods to lower SG level following a tube rupture?

Answer 1

1. Lower RCS pressure to that of the ruptured SG and allow backflow from the SG
2. Drain the bad SG to the condenser using SA 33/34 via the Blowdown system
3. Steam the ruptured SG via a MSIV bypass valve to the condenser (must assess the release to the environment using the offsite dose coordinator)

Question 2

SGTR: Why do we lower Th to < 540F prior to isolating the ruptured SG

Answer 2

To prevent the SG safeties

Question 3

SGTR: While you are depressurizing the RCS for a SGTR, which requirement takes precedence:

RCP NPSH and RCS Subcooling
OR
Lowering RCS pressure to equal the ruptured SG?

Answer 3

Maintaining RCP NPSH and RCS Subcooling
1. Ensures the adverse effects of a dilution are minimized when backflow is established
2. You are not allowed to backflow if you have no RCPs in service

Question 4

SGTR Inventory Control

Answer 4

Condition 1

1. Pressurizer Level > 10%
2. RCS > 24F subcooled
3. Upper Head > 16%

Condition 2

1. SI flow is adequate
2. Outlet plenum > 21%

Question 5

SGTR Core Heat Removal

Answer 5

a. Th < 650F
B. Max quadrant CET < 650F

Question 6

SGTR RCS Heat Removal

Answer 6

CONDITION 1
A. Good SG 45-60% NR, or being restored

CONDITION 2
A. SDC in service

Question 7

SGTR Containment Isolation

Answer 7

A. Containment Pressure < 2.5 psig
B. No containment radiation alarms
C. No abnormal rise in containment sump levels
D. Bad SG < 1135 psia

Question 8

SGTR CTPC

Answer 8

A. Containment Temperature < 117F or 125F (with a LOOP)
b. Containment pressure < 2.5 psig

Question 9

SGTR Rad Monitors

Answer 9

RU-141, Condenser off-gas
RU-4/5, SG Blowdown
RU-139/140, Main Steam Line monitors
RU-142, Main Steam Line N16 monitor

Question 10

SGTR: What is the order of preference to cooldown the RCS?

Answer 10

1. SBCVs to the condenser
2. ADVs (less desirable due to unmonitored release of activity)
3. SA 116, Operation of SBCVs 1007/1008, to steam with SBCV 1007 and 1008 via the MSIV or MSIV bypass
4. SA 18, Local ADV operation

Question 11

SGTR: If an MSIS has actuated, why do we open the steam trap isolation valves if there is level in the indicating range on the Condenser Reheat Trays?

Answer 11

Step 19
These steam supply line drains to the AF turbine are required to ensure AFA is operable if needed.

Question 12

SGTR: State the reason and the requirements for HPSI throttle criteria.

Answer 12

When RCS inventory, pressure and heat removal control are regained, the additional inventory added by HPSI could expand and fill up the pressurizer and further complicate recovery.
- RCS > 24F subcooled
- PZR level > 10% and not lowering
- Good SG 45-60% NR, or being restored to..
- RVUH > 16%

Question 13

SGTR: What is the LPSI stop criteria?

Answer 13

Step 22: If PZR pressure is > 220 psia, stop LPSI pumps and close injection valves

Question 14

SGTR: Describe how adequate shutdown margin is maintained during the cooldown.

Answer 14

1. If letdown is available, borate to the cold shutdown RCS boron concentration prior to the cooldown
2. If letdown is not available, borate to the minimum SDM corresponding to Tc (tech specs).
   A. During the cooldown, RCS shrinkage will provide more space in the PZR.
   B. In the initial stages of the cooldown, a 75F/hr CDR will lower level faster than 3 CHPs can makeup
3. If all that still doesn’t work, just borate as much as you can

Question 15

SGTR: What limitations are in place if you are performing a cooldown with no RCPs?

Answer 15

Step 30: 30F/hr cooldown rate, to ensure the two SGs remain thermodynamically coupled and are cooled together

If the cooldown is too aggressive, the temperature of the isolated SG will lag and the SGs will uncouple. Ultimately RCS flow in that loop will lower and eventually stop. If this were to happen, the adverse consequences of boron dilution due to backflow (when the SG eventually cools down and depressurizes) is more serious because there is no mixing.