Rx Startup / ECC / ACP

Question 1

State the major limits and precautions associated with the Rx startup procedure 40OP-9ZZ03

Answer 1

Precautions / Limitations:

• Below the POAH (< 1x10^-1%), only one method of +δk additions allowed at a time (except LPPT)
  
  • ± 0.5°F temperature change is allowed to be considered zero.
• Criticality is prohibited with CEAs below the PDILs OR below the ECRP (-500/-750) pcm position
• 1 dpm: Max sustained SUR (insert CEAs to lower SUR if needed)
• Suspension of CEA withdrawals to facilitate maintenance will require that CEAs are positioned such that there is a reactivity margin of at least 200 pcm to the most recent Anticipated Critical Position (ACP).
• If RG CEA insertion is not possible due to CEDMCS issues when Supercritical/Critical, stabilize power using PSCEAs.
• If power level/count rate doubles during a dilution, stop the dilution and investigate.
• 550°F Tcold (Min temp for DNBR LCO)
• 545°F Tcold (Min temp for criticality LCO)

Question 2

State the criteria that, if met during startup, would necessitate a reactor trip.

Answer 2

Reactor Trip Criteria:

• Startup termination required when withdrawing Shutdown and PSCEAs
• Reactor goes critical while withdrawing Shutdown or PSCEAs (emergency boration required)
• Count rate doubles during withdrawal of RG3 before the first two hold points (PDIL)
• Critical below PDILs (emergency boration required)
• Critical -500 pcm below ECRP (emergency boration required) (-750 pcm initial S/U)
• Reactor unexpectedly goes subcritical after criticality has been achieved
• Reactor power reaches 1%
• Two consecutive ACPs using the same power channel are below the PDIL position or ECRP (-500/-750) pcm position AND most recently performed ACP predicts criticality to occur below the PDILs

Question 3

State the initial conditions that must be met to perform a Rx startup.

Answer 3

Initial Conditions for Start-up (Section 5.0/6.1)

• SBCS in Local-Auto (setpoint maintaining Tcold at 565 ± 0.5°F)
  
  • Controlling SBCV in Auto with a Manual Permissive
• Tcold ≥ 545°F (MTC)
• BDAS operable and audible CR
• ECRP (Estimated Critical Rod Position) -500 pcm CEA position is above PDILs
• Establish boron for start-up (within the larger band)
  
  • Cb within ± 1% or ± 10 ppm of ECC value
• Close RTBs

Question 4

How are the Shutdown and PSCEA groups withdrawn on a startup?

Answer 4

• Withdrawal CEAs in MG (A, B, P) to UGS, then to UEL in MI
• Reset pulse counters to 150”

Question 5

What major action occurs when Log power is approx.

1E-6% to 1E-5% power?

Answer 5

• 1x10^-6% - 1x10^-5%: Remove CPCs from bypass (LOG 2)

Question 6

How is withdrawal of RG3 performed?

Answer 6

• Withdrawal RG3 to 60” (PDIL) using 4 hold points
  
  • Each hold point adds 500 pcm
  • 4^th hold point is 60” on RG3
  • Monitor CR for doublings
  • Monitor overlap at 95”
  • W/D RG3 in MS to hold points OR doubling
  • Reactor Engineer performs 1/M at each hold point. STA IV’s the plot.

Question 7

What method of CEA withdrawal is used following the 4th CR doubling and why?

Answer 7

• After the 4th doubling, each withdrawal is limited to add ≤ 100 pcm, to ensure SUR does NOT exceed 1 dpm.
• When RG3 is at 60”, withdrawal RG1/RG2 to UELs in MI

Question 8

What actions are required if criticality will be achieved at all rods out and < +500 pcm from ECRP?

Answer 8

• Stop withdrawal and dilute if criticality will be achieved ARO and less than +500 pcm from ECRP

Question 9

What occurs on the HI CPS alarm at ~10000 cps?

Answer 9

• High CPS alarm (10,000 cps)
  
  • Complete CEA withdrawal to stopping point
  • Check NI overlap (1 decade) and turn off SU channels

Question 10

When is mode 2 entered?

Answer 10

• Mode 2 entry (CEAs above -500 pcm position) (-750 pcm for initial start-up)

Question 11

When should criticality be anticipated?

Answer 11

At any time positive reactivity is being added.

especially when CEAP position is within 2 withdrawal sequences.

~ 0.3 dpm SUR

Question 12

Is withdrawing RG 5 beyond 135” allowed during rx startup?

What actions must be performed?

Answer 12

• Withdrawing RG5 past 135” is not allowed (rod insertion to below 135” and dilution will be required)

Question 13

Describe the major actions required immediately following criticality.

Answer 13

Post Criticality Actions (Section 6.5)

• Insert RG CEAs to stabilize power
• Record critical data (time, log power, Tcold, C_b, CEA position)
• LOG 1 lit (> 1x10^-4%): bypass Hi Log power trip
• Withdrawal CEAs (< 1 dpm SUR) to raise power and stabilize at 1x10^-4% - 1x10^-3%
• Perform LPPT if required

Question 14

How is power raised to the POAH following a rx startup?

Answer 14

• Withdraw CEAs to raise Reactor power to just < 1x10^-1% (POAH)
  
  • Reaching the POAH with SBCS in automatic will cause reactor power to rise and stabilize above the POAH.
  • If SBCS is in manual, RCS and Fuel Temperature will rise until the Isothermal Temperature Defect inserts enough – δk to make net core reactivity zero. Reactor power will stabilize at the POAH and RCS temperature will be off program high.
• Insert CEAs to stabilize power at the POAH
• Go to 40OP-9ZZ04 to continue the startup

Question 15

State the mid cycle ECC equation and who performs and approves the ECC.

Answer 15

• Performed by Reactor Engineering. Approved by the SM.

Mid-cycle ECC

Δρ (Xenon) + Δρ (Tcold) + Δρ (Power) + Δρ (Boron) + Δρ (CEA) + Δρ (FP) = 0

Question 16

Summarize the effects of Xe concentration on the Rx and include how ECC may change during its duration of effects.

Answer 16

• Adds – δk during first 8-10 hours post trip from 100%, then begins to decay away which adds + δk.
• 96 hours post trip: Xe is considered to be completely gone from the core, for the purpose of ECC calculations
• 24 hours post trip: Xe concentration drops to its pre-trip level and continues to decay for another 72 hours (total of 96 hours).
• If the reactor is started up before 24 hours the Xenon reactivity contribution will be negative compared to the previous critical condition and after 24 hours, it will be a positive contributor.

Question 17

What is the effect of boron on the ECC

Answer 17

Boron (ppm)

• Calculated – δk insertion due to soluble boron must be corrected for Boron-10 depletion and refreshment.

Question 18

How are transient FPs accounted for inthe ECC?

Answer 18

Transient Fission Products (similar to Xenon)

• Time dependent factor accounts for the build in of fission products (Samarium which produces – δk and Pu-239 which adds + δk).
• The net difference between the fission product reactivity is determined.

Question 19

How does power history affect the ECC?

Answer 19

Power:

• When the reactor is shutdown the ECC will account for the + δk added back into the core as negative power defect is recovered.
• This contributor will always be positive compared to the previous critical condition power contribution.

Question 20

How does Tcold affect the ECC?

Answer 20

Tcold

• If Tc was on program in the previous critical condition and will be on program when the reactor is returned to criticality this contributor will be 0 as the ECC assumes those temperatures.
• If Tc deviates from those temperatures, Isothermal Temperature coefficient will be used to account for the difference.

Question 21

What time requirements exist with regard to the ECC?

Answer 21

ECC calculation must be performed for a time that is within:

• 1 hour of the estimated time of criticality (ETOC) if the ETOC is within 96 hours of the reactor shutdown
• 24 hours of the ETOC, if the ETOC is > 96 hours after the reactor shutdown

Question 22

What are the ECC limits and why do they exist?

Answer 22

ECC Limits:

• Upper and lower CEA limits (500/750 pcm) ensure that the reactor goes critical where it is expected to.
  
  • CEA positions for critical rod worth ± 500 pcm will be found in the Core Data book and become the upper and lower CEA limits. (± 750 pcm used for initial start-up.)
  • Lower limit must be above PDIL.

Question 23

Describe why we have CEA hold points and any requirements on where they should be.

Answer 23

CEA Hold Points

Calculate the CEA Worth from All Regulating CEAs fully inserted (ARI) to RG3 at 60” then divide the value by 4.

Then convert the δk values to CEA positions.

Hold Points shall not be below the CEA Lower Group Stop (LGS).

Hold Points should be CEA positions consistent with indications of the pulse counter and RSPTs and divisible by 1.5.

Question 24

Describe the method of calculating the ACP.

Answer 24

Purpose:

• Method of calculating the Anticipated Critical CEA Positions (ACP) during a Reactor Startup to preclude an early criticality.
• Limits the supercritical SUR to < 1 DPM.
• Reactor Engineering performs the calculations, STA performs the IV.
• Reactivity Manager will use the ACP provided after each CEA withdrawal to determine the magnitude of the next pull.

Question 25

Describe how a 1/M plot is generated.

Answer 25

* 1/M calculation is based on the initial count rate * CR₁(1-K₁) = CR₂(1-K₂)

Question 26

How are ACPs determined and why?

Answer 26

* ACPs are determined using the last two 1/Ms. * This utilizes the higher, more accurate neutron flux signals. * This renormalizes the plots at each step. * Precludes the need to renormalize at any particular CEA position or count rate level, except when necessitated by a swap from Startup channels to Log channels.

Question 27

What parameters are used by the CRIT8 program to calculate 1/M and ACP?

Answer 27

* CRIT8 calculation uses C_B, CEA worth, CEA differential worth, stabilized SR counts, stabilized Log Channel power level and CEA positions from the highest numbered group moving or about to move per the CEA overlap plan. * Use S/U NIs and Log Channel NIs (once S/U NIs de-energized, only use log NIs) * ERFDADS count rate is the most accurate

Question 28

State the target CEA withdrawal when the core is estimated to be within 150 pcm of being critical.

Answer 28

* When it is estimated that the core is within 150 pcm of the anticipated critical position, the CEA withdrawal shall target ~ 75-100 pcm OR an amount determined by the Reactivity Manager.