40OP-9ZZ10 Mode 3 To 5 Flashcards
What is the preferred RCP pump configuration for 2 pump operation and why?
- RCPs 1A and 1B are the preferred pumps to leave running due to pressurizer spray.
- To minimize RCP bearing damage, the RCP combinations of 1A and 2B or 1B and 2A shall be avoided unless absolutely necessary.
- RCPs 1A/2A or 1B/2B are the preferred pumps to leave running if performing a forced cooldown of the Steam Generators. This will ensure maximum cooling of the Steam Generator metal mass.
Why is it desirable to throttle main spray while cooling down?
The procedure directs the throttling of spray flow to maintain a constant depressurization rate. This is desirable to preclude unnecessary thermal fatigue on the pressurizer spray nozzle. Normally, there is a constant bypass flow through the spray piping and nozzle which keeps the components at a relatively constant temperature. During operation with less than four RCPs, there may be low or no spray bypass flow, which would allow steam from the pressurizer to fill the spray piping and the piping and nozzle to heat up more than normal. Then, when actual spray flow is established, thermal shock occurs. And with auxiliary spray, some amount of thermal shock is always present due to the fact that charging water from downstream of the regenerative heat exchanger is used for that water source, so it is always colder than T-cold loop water.
Main spray flow can be controlled by throttling the spray valves. Auxiliary sprays may be effectively throttled by controlling the number of charging pumps that are running or auxiliary spray valves that are open.
What are the recommended RCS conditions for initiation Shutdown Cooling?
- Shutdown Cooling is normally placed in service at a T-cold of equal to or less than 300°F. However, Shutdown Cooling may be placed inservice when T-cold is less than 350°F. This option is at the discretion of the Shift Manager/CRS based on current plant conditions.
- To minimize SDC pump mechanical seal degradation, operation of SDC with the RCS temperature greater than 300°F should be minimized.
- For maximum SDC pump seal life, long term SDC system operation with the RCS temperature greater than 180°F should be avoided.
- To maximize SDC pump seal life when extended Shutdown Cooling operation (greater than four days) is anticipated, the RCS should be cooled down to less than 135°F to maximize SDC pump seal life.
- If the plant is to be maintained in Mode 4, and cooldown to Mode 5 is NOT intended, Shutdown Cooling should NOT be placed in service. RCS heat removal should be maintained by the steam generators.
Why is it desirable to maintain an RCP in operation while in SDC?
When SDC has been placed in service, the RCPs may be stopped; however, it is preferred to keep them operating to:
• Facilitate cooldown of the steam generators.
• Facilitate cooldown of the reactor vessel head to aid in preventing steam bubble formation in the head when RCS pressure is lowered.
• Allow operation of pressurizer main sprays.
Why is it important to maintain RCS pressure above the shutoff head of the RWMPs?
Decreasing RCS pressure below that of the shutoff head of the Reactor Makeup Water pump may allow an uncontrolled dilution of the RCS.
Why are HPSI breakers placed in an inoperable status in Mode 5?
The purpose of disabling the HPSI breakers is to prevent a possible low temperature overpressure condition which could be caused by an inadvertent or accidental start of the high head HPSI pumps pressurizing the cold primary system.
What is the time limitation for re-closing the Main Generator Output Breakers and why?
The Main Generator 525KV breakers should NOT be opened and remain energized in excess of two hours. To do so will reduce the life or cause premature break down of the surge capacitors which are shunted to the breaker contacts.
How will RCS boron concentration change when SDC is placed in service?
Shutdown Cooling loops typically have a higher boron concentration than the rest of the RCS. Initiating shutdown cooling will result in an increased boron concentration in the RCS. This increase may be greater than boron concentration needed to meet the shutdown margin required by LCO 3.1.1 or LCO 3.1.2.
What is the RCS boration strategy that is used to achieve desired SDM during cooldown?
Cold shutdown boron concentration will be achieved in two bulk additions:
• The first addition occurs prior to commencing cooldown. This addition will borate the RCS to the required shutdown margin at 270°F. (or whatever temperature shutdown cooling will be initiated) All makeup for contraction during the cooldown will be at the blend necessary to maintain this concentration.
• The second addition is the result of placing Shutdown Cooling in service.
Describe why 40OP-9ZZ10 directs the operator to refer to a table which includes RCS temperatures (greater than or equal to 485°F) and RCS pressures PRIOR to lowering the Low Pressurizer Pressure Trip setpoint.
If pressure were originally TOO low for the existing temperature, and a LOCA (or other event) were to occur, saturation conditions could exist in the RCS before the new, lower setpoint is reached. When saturation conditions occur, the pressure drop due to the LOCA is greatly reduced as water flashes to steam and holds the pressure up. This could prevent (or delay) the SIAS actuation and HPSI injection. Following the directions of the table will ensure that the SIAS actuates and HPSI injects at a pressure corresponding to at least 140 psia greater than saturation pressure.
Describe the response by BDAS if the Flux/setpoint switch is depressed several times rapidly.
CAUTION - Pressing the “FLUX/SETPOINT” pushbutton more than two times within 3 seconds will place the channel in test impacting channel operability until the test is complete.
