SALEM
SALEM STUDY SYSTEM
Systems > Main Steam

Main Steam

⚠️ DRAFT

Main Steam

Function

Transports steam from the four steam generators to the turbine-generator and other auxiliary steam loads. Provides overpressure protection via main steam safety valves and atmospheric dump valves. (UFSAR 10.3)

Main Steam Isolation Valves (MSIVs)

  • One per steam line (4 total)
  • Close on: high steam flow AND (Lo-Lo Tavg OR low steam pressure); Hi-Hi containment pressure (2/4); manual (1/1 per line)
  • Designed to close against full steam flow
  • Flow restrictors (venturi type) in each steam line limit blowdown rate in the event of a steamline break (UFSAR 10.3.2.2, T7.2-1)

Main Steam Safety Valves (MSSVs)

5 valves per loop, 4 loops = 20 MSSVs total.

Valve (per loop)Lift Setting (±3%)Orifice Size
xMS111125 psig16.0 in²
xMS121120 psig16.0 in²
xMS131110 psig16.0 in²
xMS141100 psig16.0 in²
xMS151070 psig16.0 in²

(UFSAR 10.3, TS Table 3.7-4)

Exam — 2019 Q42
MSSVs will start to open when main steam line pressure FIRST exceeds 1070 psig (the lowest lift setting, xMS15). Trap: 1100 psig (xMS14) is the second lowest — the lowest is 1070 psig. LCO 3.7.1.1 purpose: limit secondary system pressure to within 110% of design pressure AND protect against overpressurization of the Reactor Coolant Pressure boundary. It is NOT only for secondary overpressure protection — the MSSVs also protect the RCS pressure boundary.

Atmospheric Relief Valves (MS10s)

  • 4 valves total (one per SG: 21MS10 through 24MS10)
  • Design capacity: 10% of rated steam flow total (all 4 valves combined), 2.5% rated steam flow per individual valve
  • Total flow at no-load steam pressure: 390147 lb/hr at 1005 psig
  • Controllable from the control room; backup nitrogen bottle racks for loss of control air
Exam — 2020 Q43
Each MS10 (SG Atmospheric Relief Valve) has a design capacity of 2.5% rated steam flow (total for all 4 valves is 10% rated steam flow at no-load steam pressure — 390147 lb/hr at 1005 psig). Common trap: 10% is the total design capacity for all 4 valves, not the capacity of a single valve. Per AB.STM-0001, if an MS10 fails open and MSLI does not isolate the leak, a manual SI is required.

Steam Dump System

See Steam Dumps for condenser steam dump valve operation, interlocks (C-9, P-12), and cooldown mode.

Exam — 2022 Q12
MSLI actuation setpoints: High steam flow (>40%) coincident with either Low-Low Tavg (≤543°F on 2/4 loops) OR Low SG Pressure (<600 psig). Also actuates on Containment Pressure >15 psig. SG Pressure differential >100 psig between one SG and the others actuates SI only (not MSLI) — different signals.

Tech Spec LCOs

Exam — 2022 Q77
MS10 atmospheric dump valves during EOP-LOPA-1 (Loss of All AC Power): on loss of all control air, CA330s fail closed isolating air to containment. MS10s remain operable from the control room via DC battery power for controls and nitrogen bottle racks (4 bottles >=2000 psig per MS10) for the air operator. Bottle rack capacity: minimum 72 hours of MS10 operation. Maximum cooldown rate per EOP-LOPA-1 step 17.2 is 100F/hr. 50F/hr is the cooldown rate for EOP-TRIP-6 (Nat Circ without RVLIS above 500F), NOT EOP-LOPA-1.
Scenario — 2022 #3
Main turbine fails to auto trip AND fails to manually trip following reactor trip from AB.RCP-0001. MSLI fails to auto actuate. CT#1 (CT-12): crew manually actuates MSLI using Fast Close pushbuttons on 2CC2 (or Loops 21-24 MSLI on 2CC1 Safeguards bezels). Failure to close MSIVs causes uncontrolled depressurization of all SGs, excessive RCS cooldown, and challenges to Integrity and Subcriticality CSFs. MS10 atmospheric dump valves used in EOP-FRHS-1 to depressurize selected SG to < 575 psig for condensate feed recovery.
JPM — 2020 Sim-g
EOP-SGTR-1 RCS cooldown with steam dumps unavailable (permissive light NOT illuminated on 2RP4): Step 10 directs cooldown using MS10 atmospheric relief valves on intact SGs (21, 22, 23). Table B determines target temperature based on ruptured SG pressure — 1045 psi → 503°F target. Lower MS10 setpoints on intact SGs to fully open for maximum-rate cooldown. When hottest CET reaches 503°F, stop cooldown by matching MS10 setpoints to current SG pressures. Do NOT dump steam from the ruptured 24 SG.
Exam — 2018 Q15
MS10 setpoint adjustment during SG tube leak: IAW AB.SG-0001 Step 3.31, the affected MS10 setpoint is lowered to 1045 psig. Button A on the MS10 controller raises the setpoint. Trap: 1070 psig is the MSSV (MS15) setpoint, not the AB.SG-0001 MS10 adjustment. Button B raises the manual output to open the valve more — it does NOT change the setpoint.
Exam — 2018 Q16
Main Steam warmup (S2.OP-SO.MS-0001): MS7 drain valves are opened BEFORE MSIVs (MS167) to prevent water hammer from pressurized steam forcing residual water in the piping. MSIVs are opened when less than a MAXIMUM of 50 psid across each valve. Trap: 15 psig is used for other MS Header pressure steps in SO.MS-0001, not the MSIV opening delta-P criterion.
Scenario — 2018 #1
During EOP-SGTR-1 for 24 SG tube rupture: PO isolates steam from 24 SG by closing 24MS10 (set at 1045 psig), 24MS167, 24MS18, 24MS7, 24GB4. RCS cooldown initiated using steam dumps at 25% demand in MS Pressure Control or intact MS10s (may have initiated MSLI during TRIP-2 based on uncontrolled RCS temperatures). CT#2: stop cooldown when hottest CETs < 503 F target.
Scenario — 2018 #2
21MS167 drifts from full open position at 40% power. OHA G-34 (21-24 MS167 VALVES NOT FULL OPEN). PO reports CRT and board indication. Recovery: depress open pushbutton to re-open 21MS167 per ARP S2.OP-AR.ZZ-0007.

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