ML20027B060
| ML20027B060 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 09/13/1982 |
| From: | Vandewalle D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| TASK-03-04.C, TASK-3-4.C, TASK-RR NUDOCS 8209160306 | |
| Download: ML20027B060 (10) | |
Text
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d Consumers Power
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l Nudtar Licensing Administrator General Offscos: 1945 West Pernell Road, Jackson, MI 492(,1 + (517) 788-1636 September 13, 1982 Dennis M Crutchfield, Chief Operating Reactors Branch No 5 Nuclear Reacto:: Regulation US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-155 - LICENSE DPR BIG ROCK POINT PLANT - SEP TOPIC III h.C - INTERNALLY GENERATED MISSILES The enclosure to this letter responds to a recent NRC request for additional,
information regarding Consuners Power Ce=pany submittals of May h,1982 and June 31, 1982 which provided our evaluation of SEP Topic III h.C for the Big Rock Point Plant.
The attached Consumers Power Company response to the six (6) questions were discussed with the NRC during a plant tour of Big Rock Point on September 8 and 9,1982 and the staff concluded that we have adequately addressed these questions.
Dv ande al e Nuclear Licensing Administrator CC Administrator, Region III, USNRC NRC Resident Inspector - Big Rock Point ATTACHMENT - 9 Pages l
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8209160306 820913 DR ADOCK 05000
BIG ROCK POINT SEP REVIEW OF TOPIC III-4.C INTERNALLY GENERATED MISSILES REQUEST FOR ADDITIONAL INFORMATION 1.
Describe applicable valve design aspects which reduce probability of missile generation of valve stems, bonnets, and unrestrained valve operators in high energy lines such as isolation valves in main loop, auxiliary systems, and main steam.
If it cannot be shown that missile generation is a low probability event, then discuss the protection provided to safety-related equipment from the missiles, by being out-side of the flight path of the missiles, by the use of intervening shields, or other means.
Answer At Big Rock Point, most valves have bolted bonnets, with the bolting systems conservatively designed in accordance with standard industry practices when the plant was built.
Even if such bolts were subject to chronic failure, multiple simultaneous failures would be required s
in order for a significant missile to be generated.
Threaded valve bonnets have multiple restraining threads that prevent ejection of the bonnet, so that leaks would call attention to the
2 impending failure well before the occurrence of complete severance.
Pressure seal valve bonnets contain a retaining ring that would have-to fail dramatically in shear to permit missile generation.
Valve stems are retained by threads or other locking devices, as well -
as by the bonnet, so that leakage would be a precursor to any severance failure. Motor operators and air actuators are typically retained by multiple bolts, which would have to fail simultaneously to cause ejection.
Additionally, their mass is sufficient to prevent a significant trajectory if ejection were possible.
Single bolts used to retain valve bonnets or operators do not contain sufficient energy to become significant missiles.
Therefore, valve bonnets, stems, and operators are not credible sources of high energy missiles. Support for this position is contained in a report by E.R.
Kilsby, Jr.
(" Reactor Primary Piping System Rupture Studies," Nuclear Safety, Volume 7, Winter 1965-1966) on severance type failures in piping systems.
He concludes that only gross design errors s
could cause such f ailures and the data presented supports an aciditional conclusion that such errors would normally lead to short-tenn failure.
s It is significant to note that this report investigates piping systems of similar vintage and state-of-the-art to Bic
.k ?oint.
Further,
the 20-year " burn-in" time at Big Rock F.. '
- l., -ly exceeds the time
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during which the vast majority of dramat;, sevez e;ce-type f ailures have occurred.
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Even though valves are not credible source of high-energy missiles, a plant walkdown was performed by experienced engineers who observed I
. valve' orientations and potential trajectories.
Discussions in the Safety Evaluation Report were presented to show that additional damage j
would be absent or minimal even if missile ejection were possible.
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Additional discussion is presented in the response to Question 6, j
relative to RDS valves and liquid poison valves.
2, You stated in your write-up that the reactor cleanup system can be l
l isolated.
Please confirm that an isolation valve exists in the reactor f
cleanup system on 3" line between the reactor vessel and cleanup pump lf _
suction for the system to be isolated.
Big Rock Drawing M-107 does not l'
show any isola *, ion valves between reactor vessel, heat exchangers, de-l mineralizer and cleanup pump suction.
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Answer i
Please refer to Big Rock Point Drawing M-121 (Coordinate R-9 ) showing two valves VCU-2 and VCU-3 which isolate the cleanup system from the 4
i reactor for both system inlet and outlet linos.
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Since the walkdown inspection for this topic evaluation, (1 ) an addition-i.
al valve VCU-61 was installed near the suction of the cleanup pump which i
' allows for the isolation of the pump if needed, without valving out the entire cleanup system and, (2 ) Drawing M-107 (ref. Coordinate M-3 ) was t
' changed to show this modification.
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4 3.
In your evaluation of the reactor depressurization system (RDS) you stated that missiles generated due to failure of the RDS isolation valves can damage safety-related NSSS panels. Assuming damage to the NSSS panels, it is not clear what systems are still operable to safely shutdown the plant.
Please provide this information.
Answer As stated in the response to Question 1, the ejection of missiles from valves is consideSed to be an event of acceptably low probability.
'Ihe RDS valvct.: werc, only identified as a potential source of missiles based on the trajectory possibilities.
Furthermore, it is not conclusive that i
damage would be significant to the NSSS panels even in the unlikely e
event of a missile ejection from an RDS valve combined with the low prob-ability of the missile striking a panel.
Assuming damage to the NSSS panels in question, the following components /
systems would be available for safe plant shutdown (not all inclusive):
Dnergency Condenser CRD System (Scram)
RDS s
C-30 Panel / Steam Drum Wall Instrumentation (Sa f ety-Related )
C-20 Panel (not Safety-Related )
j MCC-2D 480 Volt System (not Safety-Related)
A failed RDS valve, being a missile generator, will cause a LOCA and would depressurize the NSSS, however, the other RDS valves would provide their intended function and depressurize the NSSS as required.
Even if the Safety-Related NSSS Panel / Steam Drum Wall Instrumentation were damaged by the missile from the RDS valve, causing an additional LOCA, the RDS would still provide its function of depressurization.
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5 Fire Suppression Water System /ECCS/Por,c Incident (Sprays)
Containment Isolation Equipment Instrument Air System Electrical System (s ) (include Station Batteries) 1 4.
Please provide information on the modification which shows that instru-ment and service air systems will not be required for safe plant shut-down as per your letters dated May 4 and June 3,1982.
In your evaluation of SEP Tbpic III-4.C. you stated that this system is required for vacuum relief system and reactor depressurization system.
Please clarify.
Answer An electrical solenoid valve (SV4947) was added to the fire water supply line (redundant supply) providing make-up water to the emergency condenser.
This valve was installed between valves VEC-2 and VEC-1 under modifica-tion FC 538 (DCN 20-82).
The modification now allows the plant operator personnel to open and close this valvo (using DC power ) remotoly by hand switch from the control room or manually in the containment (sphere ).
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Normally, air operated valve CV4028 controls the demin water supply line i
(primary supply) providing make-up water to the emergency condenser.
If for some reason, the instrument air system fails to Cv4028 closing the valve, the redundant fire water supply line is available for opera-tion of the emergency condenser.
Consequently, instrument air is not required during a postulated event.
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6 a.
CLARIFICATION OF INSTRUMENT AIR REQUIREMENTS FOR THE VACUUM RELIEF SYSTEM The vacuum relief system for the sphere depends on operation of the sphere inlet and outlet ventilation valves during a postulated in-cident. The ventilation valves are normally open during plant opera-tions but are required to close when the incident requires sphere isolation.
If sphere vacuum becomes a problem during the incident, the ventilation valves are required to open to allow for pressure equalization between the sphere and atmosphere.
Instrument air is required to open the ventilation valves for normal plant operations or for reopening the valves during an incident, a
spring operator closes the valves in both cases.
If for some_ reason, the instrument air supply fails to the ventilation valves, nitrogen pressure is available (for approximately 50 operations) as backup to allow for functioning of the ventilation valves.
Consequently, the vacuum relief system is fail-safe if instrument air fails.
b.
CLARIFICATION OF INSTRUMENT AIR REQUIREMENTS FOR THE RDS Normally, instrument air is supplied to the RDS valves to keep them closed during operations.
However, if for some reason the instrument 7
I air supply fails to these valves, the supply lines are equipped with i
check valves to allow the air to be contained in the supply lines l
holding the RDS valves closed.
Consequently, the valves would remain l
closed until opening them is necessary thus, making. the RDS fail-safe.
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7 Only if the check valve (s) above fail af ter a loss of the instrument air supply would the RDS isolation valve (s ) open.
An electrically operated depressurizing valve (located down stream of the RDS isola-tion valve (s)) would remain closed until it is actuated / opened by a safety actuation system signal or other means thus, preventing an anomalous (LOCA) and PCS depressurization.
Again, this system has sufficient redundancy to be fail-safe.
5.
You stated in your write-up that failure of motor generator set flywheel will result in damage to safety-related equipment.
If damage will re-sult, describe the capability of surviving equipment to safely shut down the plant.
Answer In clarification of the Safety Evaluation, analysis based on Regulatory Guide 1.14 demonstrated that the flywheel guard may not retain the missiles generated by flywheel failure.
This analysis, however, assumed a flywheel overspeed of 20) above synchronous speed of the motor.
While this is a reasonable assumption for pumps, which can overspeed due to a pipe break releasing fluid energy, no mechanism has been identified that could lead to overspeed of the subject motor generators.
Con -
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sequently, consideration of 20% overspeed may be excessively conservative.
I If flywheel failure were to occur at the rated speed of 1,800 rpm, the flywheel cover would reduce the missile energy sufficiently to make
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significant damage to safety-related equipment unlikely, even though the cover may be penetrated.
If damage were to occur, it should be possible 4
to safely shut down the plant, based on the abundance of shutdown systems.
For example, even if a motor generator set flywheel should fail and some-i how a missile would strike the 1 A, 2A and 2B panels, the emergency con-I j
denser and the fire suppression system (via the diesel driven fire pump) are available for safe shutdown.
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However, given that no flywheel overspeed is possible, there is no reason B
to further consider the potential for flywheel failure. The flywheels t
have operated at rated speed without failure for the operating history f
of the Big Pock Point plant; therefore, they are not considered subject I
to failure caused by flaws in the flywheel material.
The flywheel covers i
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are adequate protection against damage by casual objects (such as work-4 4
men's wrenches, etc), and there are no other sources of high energy l
missiles that would affect the flywheels.
Therefore, the probability of flywheel failure is deemed sufficiently low as to be negligible.
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6.
Please confirm that postulated missiles due to nearby components (reactor e
I depressurization system valves and liquid poison system valves ) will is i
not damage the emergency condenser or its ",at pipe, whose failure may 1
result in loss of containment integrity and release of radioactivity to i
the atmosphere.
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Answer As stated in the response to Question 1, valve stems and bonnets are not considered a credible source of high-energy missiles.
- However, even if the stated valves were to generate missiles, the missiles would not have sufficient energy to perforate the 14-inch Schedule 40 (0.438-inch wall) vent pipe or the 1/2-inch shell of the emergency condenser.
This is true even if a direct trajectory were available from the RDS valves, which in actuality would have to be deflected from the spherical containment shell to reach either the condenser or its vent pipe.
Missiles generated by the squib valves would be smaller and have less penetrating power than the RDS valve stems or bonnets.
Therefore, missiles generated by these unlikely sources could not damage the emergency condenser or its associated vent pipe.
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