ML22061A107
| ML22061A107 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 02/15/2022 |
| From: | Brandt T Nextera Energy |
| To: | Thomas Aird NRC/RES/DRA |
| Aird, Thomas - 301 415 2442 | |
| Shared Package | |
| ML22061A095 | List:
|
| References | |
| Download: ML22061A107 (12) | |
Text
Duane Arnold Energy Center (DAEC) Loss of Offsite Power (LOOP) Due to Derecho Terry Brandt Fleet Online Director NEXTera ENERGY
2 DAEC Overview BWR/4 -
An early BWR/4, the B loop of RHR is half of RHR (B+D pumps)
Mark I Containment HPCI (3,100 gpm) & RCIC (425 gpm)
Core Spray and RHR Rated Thermal Power 1,912 MW(t)
Rated Net Electric Power ~615 MW(e) 368 Fuel Bundles in the Core SRVs setpoints:
1 SRV 1,110 psig 2 SRVs 1,130 psig 1 SRV 1,120 psig 2 SRVs 1,140 psig Two safety valves (SVs) discharge directly to the DW airspace at the RPV pressure of 1,240 psig
3 DAEC Plant Status - Monday August 10th, 2020 1.
DAEC was operating at ~80% power due to coasting down to end of cycle (EOC). This power was selected to limit the cycling of a turbine control valve (TCV4) that would have occurred around ~84% power 2.
Diesel Driven Fire Pump (DFP) is inoperable due to maintenance 3.
LPCI B train was inoperable due to testing prior to the event, it was not being tested during the event and was available for use if needed 4.
Two control rods are fully inserted to suppress a fuel leaker 5.
Dry cask storage campaign under way in the spent fuel pool; time to boil is 64 hours7.407407e-4 days <br />0.0178 hours <br />1.058201e-4 weeks <br />2.4352e-5 months <br /> Initial conditions:
Power= 80.2% RTP Gross Electric power = 493.5 MWe RPV water level = +189.5 RPV pressure = 1,009.57 psig SP Temperature = 83.7 °F DW Pressure = 0.5 psig SC Pressure = 0 psig DW Temperature = ~123 °F
4 DAEC Plant Status - Monday August 10th, 2020
11:38 A severe Thunderstorm watch is declared
DAEC entered the Abnormal Operating Procedure (AOP) for Severe Weather and began performing their preparation actions
12:02 The Watch is upgraded to a Severe Thunderstorm Warning
Shift Manager (SM) directed that fuel handling be placed in a safe condition and secured
5 August 10, 2020 Monday 12:30-12:35
12:30 Multiple alarms received due to grid issues
12:35 Grid perturbation occurs which causes the Emergency Diesel Generators (EDGs) to start but not tie on. The EDGs remain running
Wind speeds > 100 mph with onsite peaks between 100 mph & 130 mph
6 August 10, 2020 Monday 12:35-12:49 12:49 Loss of offsite power due to sustained strong winds (> 100 mph) causes:
Generator load reject, tripping the turbine and causing the Reactor to scram EDGs tie onto the safety buses A and B Recirculation pumps trip due to loss of power
7 August 10, 2020 Monday 12:49-12:51
12:49 All control rods fully insert
RPV pressure rises quickly causing 2 SRVs to lift on low-low Set when pressure rose above 1,055 psig and initiation of an SRV on its setpoint (1,110 psig)
12:49 Ops enters EOP-1 on low level (+170 and lowering). RPV pressure 960 psig and steady. RPV Water level +135 and slowly lowering
12:50 Ops directed an initial level control band of 135 to 211
12:51 RPV water level lowers to L2 (+119.5) due to loss of feedwater
8 August 10, 2020 Monday 13:00 - 24:00
Continued Cooldown
Level maintained high to facilitate natural circulation, in accordance with plant procedures.
Restored Systems to facilitate plant reliability:
Reactor Water Cleanup System
Fuel Pool Cooling System
Well Water to keep pressure applied to the Fire System
General Service Water for equipment cooling
Set up DAEC Switchyard for emergent repairs
9 August 11, Tuesday
02:30 Ops established cold shutdown conditions using SDC
11:26 The 161kV Vinton line is restored to the switchyard restoring off-site power
12:15 Startup transformer is reenergized from off-site power
13:12 Safety Bus A is reenergized from off-site power
13:34 Safety Bus B is reenergized from off-site power
16:00 The NOUE is terminated
Storm damage found on roof of the North FLEX building. FLEX function maintained by South FLEX Building equipment
Forced draft Cooling towers severely damaged
10 August 17, 2020 Tuesday 12:49 All six off-site power lines are restored
Interstate Transmission Companys (ITC)
Off Site Heroes 11 Restoration of DAEC Off Site Power
12 DAEC - LOOP Insights ESW Availability following the increase in dP of the strainer:
- The ESW strainer did not start clogging until the Torus Cooling was maximized later in the day with the operation of the HPCI System:
o DAEC procedures required that maximizing of Torus Cooling with the operation of HPCI o This was also done to maintain the Torus under EOP-2 required temperatures
- The ESW system dPs remained low throughout the event
- The high strainer dP came into existence after shutdown cooling was placed in service