Main Steam Flashcards
What is the purpose of Main Steam System?
- Conduct Steam from Rx to Turbine Generator
- Prevent uncontrolled release of primary steam
- Limit pressure transient on RPV during abnormal conditions
What is the normal flowpath for the Main Steam Line?
-4 20-in steam lines (each with 2 safety valves) tap off RPV through drywell through an inboard and outboard MSIV (x-area) into the Steam Equalizing Header. This header supplies the House Loads, Turbine Stop and Control Valves, and the Bypass Valves.
- Also, Rx Head Vent removes non-condensable gases from top of RPV to B steam line
Inboard and outboard steam line drains combine and route to RBEDT
What provides steam flow indication? does this device have any other purpose?
Flow Restrictor (Venturi). Also restricts flow on main steam line rupture
What is the main steam rated steam flow total? per line?
11.71x10^6 lbm/hr; 2.92x10^6lbm/hr/line
Where are teh MSIVs?
North side of drywell for Inboard, outboard are in x-area
What is another name for the equalizing header?
Turbine Throttle
How many major house loads are there and waht are they?
- 125# SJAE Steam; 250# Preheater; 4# Gland Seal Steam; 125# Recharge SJAE
Where do the Steam Line Drains route to?
Condenser or RBEDT
Where does the Reactor Head Vent route to (Normally at power)?
B MSL
Where does the Reactor Head Vent route to when not at Normal Operating Conditions?
DWEDS until Rx Water Temp reaches >=190F
How many Main Steam Safety Valves are there and where to they exhaust to?
8 (2 per line), exhaust to DW atmosphere
How many Main Steam Relief Valves are there and where do they exhaust to? Are they all the same?
- They all conduct steam from Main Steam Line to Below Torus Water Line. The A MS Relief Valve is the Target Rock. THe other 4 are Electromatic Relief Valves.
There are 5 relief valves and 4 Main Steam lines. Which Main Steam Line has 2 Relief Valves
B MSL has both the B and E ERV
What is used to pressurize the downstream main steam line follosing a shutdown and allow for the MSIV to open?
Drain valves
What interrelation does Main Steam have with the Isolation Condenser?
THe Iso Condenser vent retun line routes to the A MSL and maintains the ISCO steam line free of non condensable gases
During NOC, what is the position of the Main Steam System Valves?
All 8 MSIVs open, Safety/Relief valves closed, all drain valves closed, bypass valves closed, head vent valve to B MSL open, Iso Condenser vent lines open
What are the design functions of the Main Steam Lines?
Permit testing of the turbine stop valve and MSIV without severely limiting load
LImit DP on RPV internals during main steam line break
Limit inventory loss on steam line break
Permit High Power operation with one line isolated
What are the set points for the Main Steam Safety Valves?
2 lift at 1240psig; 2 lift at 1250psig; 4 lift at 1260psig
All close 100psig below setpoint
What is the design basis for the Main steam safety valves?
Prevent overpressurizing RPV during MSIV closure with failure of ERVs.
They limit dome pressure to below 1345psig due to limiting pressure being at the bottom head due to steam + water pressure (~30psi)
What is the limiting design pressure for the RPV and it’s basis?
Limiting design pressure is ASME classified 1250psig + 10% transient overpressure = 1375psig
What is used to detect leakage or lifting of Safety Valve?
Temperature element and Accoustic monitors
What is used to prevent overpressure during a turbine trip with:
failure of ERV
failure of Turbine Bypass Valve
Failure of Turbine Trip Scram
Safety Valves
How many Electromatic Relief Valves does Main Steam have?
4 - B, C, D, E
What are the lift setpoints for the ERVs?
B&C have lift set at 1110.5psig
D&E have lift set at 1133.5psig
Where do the ERVs relief to?
Below Torus Water Level
What safety (ECCS) function doe the ERV’s perform?
They serve as the ADS depressurization point. ERVs relieve pressure in sufficient time to allow LPCI and CS to function and supply coolant from the torus
What are the flow rates for the Safety valves and ERVs?
640000lbm/hr and 540000lbm/hr
What is installed in the ERV discharge lines from impacting Torus via water slug?
Pair of Vacuum breakers prevents drawing water up into line after blowdown
What is leakage and flow through ERV detected by?
Temperature element and acoustic monitor
What is the reseat pressure for teh ERVs?
70psig below initiation setpoint
How is the actuation of the ERV performed?
Normally a “balanced valve”. Actuated via a pilot valve to “unbalance” the valve for opening
During overpressure, solenoid valve will energize and open the pilot valve
Pressure is released from chambers at a faster rate than supplied through space between main disc and guide - opening the valve
What position does the pilot valve provide indication of?
Open and closed by position switch
What gives the ERV discharge line vacuum breakers enough time to function?
THere is a time delay on the B&C ERVs that inhibits reopening on a demand signal from ADS within 10 seconds of any previous closure (Not inhibited on manual activation)
At what setpoint will all ERV’s and Target Rock be fully Open?
1135psig
What is are the normal and alternat feeds for the ERV Solenoid Assembly Power?
Two 125vdc power supplies with normal seeking transfer circuit: U2 Normal: 125vdc TB Main Bus 2A-1 U2 Alt: 125vdc TB Main Bus 2B-1 U3 Norm: 125vdc RB Dist. Panel U3 Alt: 125vdc TB Main Bus 3B-1
Where are teh Control Power Fuses for the ERV Solenoid Assembly?
U2 AEER
U3 RB 545 near 5 rack
What type of MCR control is provided for the ERV/Target Rock?
3 position switch:
Manual - solenoid assembly always energized and valve open;
Off - Solenoid only energized from auto blowdown and not from a relief signal
Auto - Solenoid is energized from auto blowdown signal and relief signal from controller
What type of relief valve is installed in the A MSL?
Target Rock
What is special about the Target Rock?
Acts as a safety and/or relief valve
What is the flow through Target Rock?
622,000lbm/hr
What are teh set points and where does the target rock discharge?
Relief set at 1133.5psig; Safety set at 1135psig; Torus below water
Describe the relief actuation of the target rock.
DC solenoid valve energize sending DW nitrogen 85psig to remote air actuator, stroking air plunger and opening the valve
closed by spring force when pressure vented
What provides normal actuating nitrogent for target Rock?
DW Pneumatic system
What is the backup actuator for Target Rock Relief function?
Accumulator and check valve arrangement in loss of DW Pneumatics
FOr the DW Pneumatic supply to Target rock actuator, how is the position of the pneumatic operator determined?
Pressure switches - Below 40psig - closed
Above 50psig - open
What is the Target Rock DC solenoid energized by?
Same as ERV: U2 Normal: 125vdc TB Main Bus 2A-1 U2 Alt: 125vdc TB Main Bus 2B-1 U3 Norm: 125vdc RB Dist. Panel U3 Alt: 125vdc TB Main Bus 3B-1
What actuation signal for Target Rock Relief Function?
Pressure >=1133.5psig
Manual position on keylock switch
ADS Autoblowdown
What actuates Target Rock Safety Function for Target Rock?
Bellows expand from RPV pressure and lifts against spring
What is Target Rock Safety Setpoint?
lift at 1135psig, reseats at 50psig below lift
What happens if the Target Rock bellows ruptures?
pressure switch MCR alarm at 25psig rendering Target Rock INOP for Safety actuation; Relief Mode Still Operable.
What are teh Accoustic monitors powered by?
ESS Bus
What provides indication ov ERVs and Safety Valves Opening?
Accoustic Monitors
What MCR indications exist for ERVs and Safety Valves?
Green Light - Closed
Red light open
amber light indicated cycled open
(If vavle is open, both amber and red will be lit)
What is the powersource for the ERV tailpipe temperature elements?
Instrument Bus
What is the Design fucntion for the MSL Flow Restrictors?
Venturi restrictor to limit steam flow to <175% total steam flow during MSL rupture.
Limits loss of coolant inentory
provides steam flow input to MCR and FWLC & PCIS
What is primary function of the MSIVs?
- with steam line break outside containment; prevent exceeding radiation release rates by 10CFR100 guides
- Maintain Cladding Integrity
How to MSIVs Operate?
Air to Open, air/spring to close
What is maximum set for MSIV to open?
200psid
How is redundant power supplied to MSIVs?
Each MSIV has one AC and one DC solenoid operated valve to control air supply
What are the power supplies to the MSIV solenoid valves?
AC: IB and OB from Instrument Bus
DC: I/B from 125VDC Turbine Bldg Main Bus 2A-1 (RPS A)
O/B from 125vdc TB Reserve Bus 2B-1 (RPS B)
What is the closing time for the MSIVs?
3 - 5 seconds
3 seconds: slow enoug to minimize severity of pressure transient
5 seconds: fast enough to prevent gross release of fission products
What supplies air to the MSIVs?
I/B : DW Pneumatics
O/B : Instrument Air
What causes a loss of MSIV Pilot solenoid valves?
Group I Isolation
close valve via control switch
test pushbutton
Loss of both AC and DC power supply
What are the Group I Isolations?
REQUIRED VALUES FOR OPERATION LISTED
Low Low Rx Water Level : >= 56.34in (-59in)
Steam Tunnel High Temp : <=200F
High Steam Flow in any MSL (U2 125%, U3 140%)
Main Steam Line Low Pressure : >=791psig (<820psig) (bypassed when not in RUN)
What happens when you manipulate the MSIV Test Switch?
Energizes control relay and test valve solenoid,
Both AC AND DC solenoid valves de-energize
slow closure of MSIV until 90% open
at 90% open, solenoid valves re-energize and MSIV opens
What happens if MSIV Test switch is held in test?
90% limit switch is bypassed and valve will go full closed
What happens with 1 MSIV full closure at full power?
High steam flow in other three lines, and will be necessary to reduce power below 50% rated power. (likely scram if not addressed immediately).
What Opens the MSIV and is the motive force supplied or removed for opening?
Air (DW Pneumatics & IA) to open
WHat is the motive force to close the MSIVs?
Air to close (unless air lost, then spring to close)
How many Turbine Bypass valves are there and what is their capacity?
9 mounted on equalizing header, with a total flow of 33.5% rated flow.
How much steam flow goes to house loads?
~5%
What maintains the air temperature in the steam tunnel?
X-Area Coolers
What is the air temperature maintained at in the X-Area?
<150F
How many X-Area Coolers does each Unit have?
U2 - 8 - 4 way reversing valve;
U3 - 6 coolers - 4 individual SW valves for reversing
What provides cooling to X-Area Coolers?
Service Water
What is performed to clear High DP on X-Area Coolers?
Flow reversal
What is limit to leakage from X-Area coolers?
5 to 10gpm
What are the power sources to the X-Area coolers?
MCC 28-2, 38-2
What is impact to Main Steam System if RB Vent isolates?
Steam Tunnel Temperatures Increase
What is TS Limit for X-Area Temperature?
200F (normally kept below 180F)
What is the steam flow limit on any MSL?
U2 125%; U3 140%
If ERV use is done manually, what pattern of opening the ERV’s should be performed and why?
A-C-E-D-B (ACE DOG BONE) to prevent overheating Torus
What happens to MSIV’s on Group 1 Isolation?
Auto close and limit swithc on MSIV’s at 90% open will cause reactor scram
TS: How manySafety function valves and how many relief function valves need to be OPERABLE, and in what modes do they need to be operable?
9 safety; 5 Relief; Modes 1, 2, & 3
