ESD Flashcards
Describe the operator actions assumed in the Increased Heat Removal safety analysis.
Operator action is not credited in the MSLB safety analyses until 30 minutes following event initiation.
Plant operators are credited to take actions to initiate a controlled plant cooldown to SDC entry conditions(300F/385#) by establishing AFW flow and steaming path through ADVs on unaffected SG.
State the single failure assumed for the Increased Heat Removal analysis and explain the basis.
The single failure for an ESD is:
Failure of 1 HPSI pump to start.
This is based on reduced capacity of the SI system to provide boron to the core region of the RCS, which raises the potential for a RETURN TO POWER. Other single failures such as MSIV failure were less limiting than single HPSI failure.
State the analysis conclusions of the Increased Heat Removal analyses.
10CFR100 site boundary limits are not exceeded.
CR dose limits will not be exceeded.
RCS pressure remains below 110% of design value(2750psia)
Main steam pressure will remain below 110% of design value(1397psia).
State the entry conditions associated with an ESD.
Following SPTAs, an ESD was diagnosed.
ESD in mode 3 or 4 AND LTOP not inservice AND any or all of the following:
- Loud noise associated with high energy break or stuck MSSV
- Lowering RCS temperature and pressure
- Rising RCS temperature due to reduction in FWLB(tricky)
- Rise in FW flow until MSIS occurs.
- Possible CMNT humidity, temperature and pressure.
State the distinguishing characterists between an ESD and a LOCA.
ESD is distinguished from a LOCA by the following:
- Rising Rx power and steam flow with lowering MWe.
- Lowering Tc AND Ppzr.
- Rising CMNT temperature, pressure and humidity with NO RU-1 alarms.
- Increasing SCM. For a LOCA SCM will get worse.
- Lowering Ps/g in both until MSIS then one will deviate, if unisolable. If isolable, both Ps/g will stabilize.
- For a FWLB, RCS temperature will rise as a SG heat removal is impacted. Once the SG water level has emptied, it becomes a conventional ESD.
Describe the major steps associated with the mitigation strategy for an ESD.
- Isolate the most affected SG: Feed, steam and BD paths are all isolated.
- Stabilize RCS temperature: Utilize ADVs to steam unaffected SG when cooldown on the faulted SG ends. Prevents overpressurization of the RCS.
- Throttle HPSI: Prompt HPSI throttling when criteria met helps prevent PTS concerns.
- Control RCS heat removal withunaffected SG: Once RCS temp stabilized, prepare for plant CD(SDM, boron, etc)
- Cooldown the RCS to SDC entry conditions
Discuss how to use SG parameters to determine presence and relative severity of an ESD.
Pay particular attention to RCS Subcooling, CMNT T/P/Hum and steam plant/CMNT activity alarms.
ESD will have high SCM, CMNT T/P/H with NO RU alarms.
Most affected SG should be determined by the following:
- SG pressures
- SG levels
- RCS Tcold
If the ESD is isolated, the SG with the lowest of these parameters will be the most affected SG.
Discuss how to determine when rebound occurs and actions required.
Tcold should be monitored for ‘rebound’, a condition where the RCS heat removal stops(due to the faulted SG drying out) and Tcold(and Thot) trend back up.
This condition, with the inventory added by SI flow and CHPs can result in a water solid condition and cause a rapid and egregious RCS pressure increase which could result in PTS.
Once the unaffected SG is stabilized by heat removal, the affected Tc is allowed to rise. This represents evidence that cooling has been established.
How is RCS temperature stabilized following rebound during an ESD?
SBCS is preferred, but if nonfunctional or isolated by MSIS, ADVs will be used.
Target pressure(determined by the LOWEST Tc Psat +/- 50spia) for the UNAFFECTED SG is used to stabilize the RCS. Get there rapidly and stay within that band.
How can a water solid condition be determined?
Lpzr indicating < 100% shows that a saturated steam-water interface exists.
RVLMS may be used to identify or corroborate a bubble in the vessel head.
RCS subcooling at saturation conditions show that steam bubbles exist inthe RCS.
Exaggerated or severe pressure responses show that the RCS may be water solid. 1F temp change will cause 100psia pressure change.
Discuss how changing RCS conditions can affect RCS pressure in water solid conditions.
Any changes is SG feeding, steaming rate should be slow and deliberate.
Changes to HPSI flow, CHP ops, RCP bleedoff, sampling, LD flow etc., should be done with anticipation of an exaggerated pressure response and minimized. Simultaneous or multiple changes should be avoided.
When drawing a bubble following an ESD, why should the SG pressures be less than the highest RCS pressure, or have an RCP running?
To avoid drawing a bubble in the SG utubes. If the SG pressures are below the RCS pressure corresponding to the highest RCS temperature, then the SG steam space cannot be the hottest part of the RCS and a steam bubble cannot form at the top of the u tubes. This is not possible at any condition in forced flow conditions.
How do we determine if the RCS is over subcooled and what actions are required?
RCS is oversubcooled if the 100F/hr line on APP 2 has been crossed or if the 200F SCM line has been crossed AND one of the following:
Plant experienced a > 100F/hr cooldown
Plant cooled down uncontrollably < 500F.
If the RCS is over subcooled, the cooldown should be stopped and plant depressurized with main, aux spray or throttling HPSI/CHPs.
If the cooldown rate has been exceeded, the operator must stop the cooldown and soak(stable P/T) until the cooldown rate is once again within limits then recommence the cooldown.
State SFSCs for Rx control as they pertain to ESD
- Power lowering or <2x10^-4% and stable or lowering
- All FSCEAs are inserted OR > 40gpm boration OR SDM verified
State the SFSCs for MVA as they pertain to ESD
- At least 1 vital 4.16kv bus energized
- At least one of the following(must be on same train as above):
- PKA-M41, PKC-M43, and PNA-D25
- PKB-M42, PKD-M44, and PNA-D26
- No jeapordized safety functions require restoration of electrical power to avital AC or DC bus. Not met if recovery of equipment is dependant on restoration of power.
