ML20141J481
| ML20141J481 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 01/14/1986 |
| From: | Sanders G SANDIA NATIONAL LABORATORIES |
| To: | Sells D Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20141J487 | List: |
| References | |
| REF-GTECI-A-45, REF-GTECI-DC, TASK-A-45, TASK-OR NUDOCS 8601210282 | |
| Download: ML20141J481 (5) | |
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A-t);4uerque.' New Men to 8718$
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e January 14, 1986 supplement to January,6 Letter l
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Donald E. Sells t
j Division of Licensing i
Nuclear Regulatory Commission j
Washington, DC 20555 j
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Dear Don,
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r As described in my letter of January 6, the Task Action plan i
i A-45 program is at a point where it would be beneficial to 4
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discuss our initial analysis insights with st. Lucie plant l
3 personnel.
The purpose of this visit would be to show the plant l
1 personnel our initial findings and discuss the feasibility and I
timing of operator recovery actions.
In addition, three 1
engineers from United Engineers and Constructors would be i
included on the visit for three reasons:
- 1) External event I
analysts have requested additional engineering assessments and j
pictures regarding the seismic supports of 4 EV switchgear and the missile protection for several components located outdoors.
- 2) If plant personnel provide no recovery actions for a i
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" vulnerability,' then the AE will be'available to discuss the i
design and location of a modification.
- 3) The A-45 effort has been tasked to design and cost an alternative add-on decay heat l
1 removal system for all plant sites.
Realistic costs are very j
j plant specific and need first hand assessments of locations, j
accessibility, etc.
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I Enclosed you will find a short detailing of possible i
8 modifications being reviewed for st. Lucia depending upon i
possible operator recovery actions.
These modifications are very preliminary and are agi being required for backfit.
We j
have no results on St. Lucie as yet.
1 There have been five internal event failure modes and three i
external event failure modes identified which' dominate our I
initial analysis.
Removing or reducing these failure modes (by I
j recovery action, diverse system success or modification) can provide reductions in the estimated core melt frequency.
Each of these failure modes will be described individually along with any potential modifications.. In addition to the modifications i
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addressing the dominant failure sequences, a dedicated decay i
)I heat removal system add-on is being considered for all plants.
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I Nr. Sella Page 2
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Internal Event Failure Modes i
'1.
Failure of the connonent coolina water isolation valves for l
the nonessential header.
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Failure of these valves to close would fail sufficient cooling for the high pressure injection pumps, low pressure injection I
pumps, containment spray injection pumps, and shutdown cooling j
heat exchangers.
Combinations of these valve failures in j
i conjunction with failure of the sump recirculation valves r
constitute a core melt scenario by failing the emergency high i
j and low pressure recirculation modes.
These recirculation
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scenarios contribute 5E-5 to the core melt probability before recovery credit is given.
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s The failure of these CCW isolation valves will also cause l
j overheating of the high pressure pumps in the injection mode.
1 Loss of high pressure injection scenarios contribute 1E-4 to the "
core melt probability before recovery actions are taken.
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If no operator recovery actions are available should the CCW valves stick open, the proposed modification is tne addition of j
a valve downstream of valve HCV 14-8A to act in series as a redundant isolation valve.
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2.
Common mode failure of actor onorated auxiliary feedwater l
1 valves.
Notor operated valves 1-NV-09-9 and 1-MV-09-10 are notaally in a f
closed position and receive an SI signal to open.
A common mode i
j failure of these valves for any reason will fail all actor driven AFW.
A simultaneous failure of the steam driven AFW pump i
or its valving could lead to a core melt scenario.
Recovery actions may include manual operators on the valves, or a enange t
to leave them normally open.
Loss of feedwater sequences currently contribute 6.7E-4 to the core melt probability before I
recovery.
The vast majority of the failure modes, however, are considered to be recoverable.
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3.
Failure of the turbine driven auxiliary feedwater system
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valves.
The FSAR indicates that the motor operated valves in the turbine driven AFW line receive 125 VDC power from bus 1AR.
In addition, valve 1-NV-08-3 presents a single failure mode for i
this line.
Verification of this configuration is requised.
Modifications would include leaving valve 1-MV-08-3 open and i
transferring power to 1-MV-04-14 to a redundant DC bus.
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Mr. Sells Page 3 I
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Bleed and Feed.
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'It has been noted that Unit 1 has no written emergency operating procedures for a bleed and feed mode of operation, but that such procedures do exist for Unit 2.
A proposed modification to reduce total plant core melt probability would be the addition i
of procedures at Unit 1.
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S.
Manual override of electrical separation interlocks.
The FSAR states that the AC and DC electrical buses denoted as d
AB are normally aligned to the A side.
Interlocks prevent simultaneous alignment to both the A and B sides, however, there may be instances where a 4 KV bus is unavailable.
In such a b*
j circumstance, the ability to align the 480 volt A buses to the B side via the AB bus may allow a-Sditional capability for decay heat removal.
Such scenarios contribute 1E-5 to the core melt
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probability.
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External Event Failure Modes 1.
Seismic failure of 4.16 KV switchaear cabinets.
On first inspection, it appeared that the 4.16 KV switchgear 1
j cabinets were bolted at the tops only.
Such an arrangement, if confirmed, would lead to loss of electrical AC power in the event of a severe earthquake.
The proposed modification would j
entail the addition of bolts along the base of the cabinets.
2.
. Flood vulnerability of safety related eauinment.
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An external flood in excess of 22 ft MSL would be capable of l
damaging the AFW, CCW, SW, diesel generators, switchyard, and 3
other components.
The probability of such an event is estimated l
to be.,op the order of 10-5/yr.
The proposed modification would j
increase the height of the existing flood wall and stop gates.
3.
Missile vulnerability of diesel fuel and storace tank.
The diesel fuel oil storage tank appears to be exposed to high i
winds and wind generated missiles.
A modification to be j
explored would be some sort of missile-proof grating or shield i
to protect the tank.
Application of an Add-on Train j
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i In order to address the full spectrum of potential modifications i
for decay heat removal vulnerabilities, an add-on train of j
auxiliary feedwater and primary makeup must be examined.
It is proposed that the system described in NUREG/CR-2483, Study of the 1
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1 Mr. Sells Page 4
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Valve and Impact of Alternative Decay Removal Concept for Licht 1 Water Reactors be used for this purpose.
The design would be adapted as required to meet the specific site conditions at St.
Lucie and costing will be revised to be consistent with that for other proposed solutions.
j The proposed add-on will examine both single and dual trains of feedwater and primary makeup, designed with both a bunkered building as well as a seismic Category 1 structure compatible with existing containment.
The structure should have a minimum number of access points.
The ad,d-on train can use existing spare penetrations to containment to provide as much separation i
i and independence as possible.
The analysis has not yet been requantified with recovery actions to produce a true measure of core melt probability.
Such a requantification~will be performed shortly after the St. Lucie l **
visit when plant personnel input is received.
Therefore, it is impossible at this stage to determine the true value of any i
i modifications.
If there are ang questions, please call me.
Sincerely, Gary Sanders i
Reactor Systems Studies j
Division 6414 l
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i A-45 Attendees t.
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t NRC FP&L l
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- D. Sager D. Sells J. Mazetis W. Pierce s-A. Pell NRC Contractors-N. Roos R. Gritz G. Sanders'
--Sandia L. McLaughlin f
F. Cook
- UE&C J. Lyman
- UE&C J. Sosnowsky
- UE&C k
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