ML12340A540
| ML12340A540 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 12/06/2012 |
| From: | Xcel Energy |
| To: | Office of Nuclear Reactor Regulation |
| Wengert T | |
| References | |
| Download: ML12340A540 (40) | |
Text
1 Prairie Island Nuclear Generating Plant Reactor Core Cooling & Heat Removal FLEX Strategy -Phase 1 Prairie Island Nuclear Generating Plant Reactor Core Cooling & Heat Removal FLEX Strategy -Phase 1
2 Purpose
Describe the Prairie Island baseline capability to provide reactor core cooling and heat removal per NEI 12-06, Diverse and Flexible Coping Strategies (FLEX)
Implementation Guide
This presentation will present our strategy for Phase 1:
Cope relying on installed plant equipment
This strategy relies on the turbine driven auxiliary feedwater pump, as supplied by the diesel driven cooling water pumps
3 Following Discussion
Review NEI 12-06 language
Auxiliary Feedwater System Design
Cooling Water System Design
Emergency Intake Structure Design
Screenhouse Design
FLEX Phase 1 strategy for core cooling
4 NEI 12-06, Coping Phases
Phase 1: Cope relying on installed plant equipment.
Phase 2: Transition from installed plant equipment to on-site FLEX equipment.
Phase 3: Obtain additional capability and redundancy from off-site equipment until power, water, and coolant injection systems are restored or commissioned.
5 NEI 12-06, Section 3.2.1.1
Procedures and equipment relied upon should ensure that satisfactory performance of necessary fuel cooling and containment functions are maintained. A simultaneous ELAP and LUHS challenges both core cooling and spent fuel pool cooling due to interruption of normal ac powered system operations. (emphasis added)
6 NEI 12-06, Table 3-2 Use of installed equipment for initial coping Connection of portable pump to feed required SGs Use of alternate water source to support core heat removal AFW/EFW Depressurize SG for makeup with Portable Injection Source Sustained Source of Water Reactor Core Cooling & Heat Removal (steam generators available)
Baseline Capability Method Safety Function
7 NEI 12-06, 3.2.1.3 (4) Normal access to the ultimate heat sink is lost, but the water inventory in the UHS remains available and robust piping connecting the UHS to plant systems remains intact. The motive force for UHS flow, i.e.,
pumps, is assumed to be lost with no prospect for recovery. (emphasis added)
(6) Permanent plant equipment that is contained in structures with designs that are robust with respect to seismic events, floods, and high winds, and associated missiles, are available.
8 NEI 12-06, Section 3.2.2 (5)
Plant procedures/guidance should ensure that a flow path is promptly established for makeup flow to the steam generator/nuclear boiler and identify backup water sources in order of intended use. Additionally, plant procedures/guidance should specify clear criteria for transferring to the next preferred source of water.
Alternate water delivery systems can be considered available on a case-by-case basis
Finally, when all other preferred water sources have been depleted, lower water quality sources may be pumped as makeup flow using available equipment (e.g., a diesel driven fire pump or a portable pump drawing from a raw water source).
9 Normal Access to the UHS
For Prairie Island, normal access to the ultimate heat sink is provided by the 11 and 21 Motor-Driven Cooling Water pumps via the intake traveling screens.
These non-safeguard pumps are located in the 670 elevation of the plant screenhouse
Normal access is lost as a result of the ELAP event (i.e., motor driven pumps are unavailable)
10 Phase 1 Core Cooling - Overview
Turbine Driven AFW pumps will provide feedwater supply to the steam generators
Condensate Storage Tanks (CST) provide water source to AFW pumps, if available
Diesel Driven Cooling Water (i.e. Service Water) pumps provide backup source to AFW pumps
This strategy provides a highly reliable source of feedwater to the steam generators
11 Prairie Island Auxiliary Feedwater Design
Auxiliary Feedwater System (AFW) consists of (per unit)
(System diagram on slide 13)
One steam turbine-driven pump
One motor-driven pump
Each is capable of delivering 100 % of required feedwater to both steam generators
Turbine-driven AFW pump:
Independent of plant AC power sources
Supplied steam from both main steam lines of associated unit.
12 Prairie Island Auxiliary Feedwater Design
Auxiliary Feedwater System (AFW) water sources are redundant and diverse.
Normal source: gravity feed from three cross-connected 150,000 gallon condensate storage tanks (CST).
Safety related water supply: Class I Cooling Water System (CL)
On postulated loss of normal coolant source (CST),
existing procedures direct aligning AFW suction to Cooling Water System
13 AFW System
14 Prairie Island Cooling Water System
Cooling Water System provides the following functions:
(System diagram on Slide 18)
Suction Source Water Supply
AFW pumps
Cooling
Unit 1 diesel generators
Air compressors
Component Cooling Water heat exchangers
Containment fan-coil units
Auxiliary Building unit coolers
15 Prairie Island Cooling Water System (cont)
Cooling Water System is a Safety Related system with five pumps feeding a dual-unit shared ring header
Normal supply is from the Circulating Water (CW) pump bays in the plant screenhouse
Two horizontal, motor-driven, CL pumps
Located at 670 elevation of screenhouse
Take a suction on the CW pump bays
Provide normal access to the ultimate heat sink
16 Prairie Island Cooling Water System (cont)
Three Safety-Related vertical pumps (one motor-driven and two diesel-driven)
Housed in a robust structure (695 elevation of screenhouse)
Take a suction on the Emergency Bay
Provide the emergency (safeguard) access to the ultimate heat sink.
Emergency Bay is supplied from:
CW pump bays through 2 normally open, gated tunnels or
36-inch emergency cooling water intake line from the ultimate heat sink
17 Diesel-Driven Cooling Water Pumps
Diesel driven pumps take suction from the Emergency Bay and discharge to the common discharge header.
17,500 gpm each (400 gpm total needed for AFW)
Independent of plant AC power sources
Two Auto-Start Signals - 1) Safety Injection, 2) low discharge header pressure
Can be manually started in Control Room or locally
18 Cooling Water System
20 12 and 22 Safeguard DD CL Pumps
21 121 MD CL Pump
22 Emergency Cooling Water Intake
Design Basis
Provide cooling water for reactor shutdown cooling after a DBE
Assumes
CW intake canal is blocked or
Dam break at Lock and Dam #3 downstream of the plant
Source
Independent of the normal access to the ultimate heat sink.
Connects to a submerged crib in the branch channel of the Mississippi River
Consists of a 36 pipe buried approximately 40 below the circ water intake canal level in a nonliquifiable soil.
23 Emergency Cooling Water Intake (cont)
Intake
Class I structure, as is the approach canal which supplies its intake crib.
Designed to exclude trash and means are provided for back flushing.
24 Emergency Intake Pipe Emergency Intake Pipe
25 Emergency Pipe Profile
26
27
28 Screenhouse Structure
Screenhouse areas (housing the Cooling Water facilities, equipment and piping) are a Class I structure.
Structures are analyzed for each of the following conditions;
- 1. Normal Operating Conditions
- 2. Operational Basis Earthquake Conditions
- 3. Design Basis Earthquake Conditions
- 4. Tornado Condition
Screenhouse structure housing the CL equipment is flood protected to the PMF level.
29
30
31 Emergency Intake Maintenance/Testing
Monthly Backflush of Emergency Bay Intake Pipe
Approach, Intake, and Discharge Canal Hydrographic Survey
Diver inspection of emergency intake crib every five (5) years
32 CL-AFW Flow Path Testing
The Flow Path, including pumps, valves, and diesel engines, are tested per Prairie Island ASME IST Program
33 Relationship to FLEX Strategy (NEI 12-06)
Relationship to FLEX Strategy (NEI 12-06)
C28.1, AOP3 Auxiliary Feedwater System Operation when AC Power is Lost (existing)
If/when CSTs inventory is depleted the Cooling Water system is manually aligned to supply AFW
Includes step to locally align the Cooling Water Supply to the AFW system
Valves needed to perform switchover are located in robust structure (AFW pump room, ground floor of turbine building)
35 1[2]ECA 0.0, Loss of all Safeguards Power (Step 2) Verify AFW Flow - GREATER THAN 200 GPM (RNO) Perform the following:
IF pump can NOT be started, THEN dispatch personnel to locally start pump per C28.1 AOP3, AUX FEEDWATER SYSTEM OPERATION WHEN AC POWER IS LOST.
36 AFW Operation per C28.1 AOP3
Local operation of Motor Valves to transfer source from CST to Cool Water Supply CL Supply CST Supply
37 AFW Operation per C28.1 AOP3
Dedicated ladders pre-staged in AFW room
38 C28.1, AOP3 Training
Non Licensed Operators
Perform local actions
Initial classroom and OJT/TPE, as well as continuing training
Licensed Operators
Monitor system, direct local actions in CR
Initial classroom and OJT/TPE, as well as continuing training
39 Core Cooling Strategy - Compliance with NEI 12-06
Normal access to the ultimate heat sink is lost
Motor driven cooling water pumps lost as a result of the ELAP event
Permanent plant equipment that is contained in robust structures are available
Screenhouse structure housing the diesel driven cooling water pumps is robust relative to seismic, flooding, high winds, tornados
40 Core Cooling Strategy - Compliance with NEI 12-06 (cont)
A simultaneous ELAP and LUHS challenges both core cooling and spent fuel pool cooling due to interruption of normal AC powered system operations
Turbine driven AFW and diesel driven cooling water systems operate independent of AC power
Plant procedures/guidance should ensure that a flow path is promptly established for makeup to the steam generators.
This strategy exists in current plant procedures and within the Operations training curriculum.
41 Phase 1 Core Cooling Strategy -
Summary
Rely on TD AFW pumps.
Credit Diesel Driven CL Pumps as water source if/when CSTs are depleted or lost
This strategy is consistent with Order EA-12-049 and NEI guidance.