ML17299A425
| ML17299A425 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 06/26/1985 |
| From: | Ley M Office of Nuclear Reactor Regulation |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| TAC-57419, NUDOCS 8507120258 | |
| Download: ML17299A425 (36) | |
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~0 UNITEDSTATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 JUN 86 )985 Docket Nos.:
50-528, 50-529 and 50-530 LICENSEE:
Arizona Public Service FACILITY:
Palo. Verde Nuclear Generating Station, Units 1, 2 and 3
SUBJECT:
SUMMARY
OF SPRAY POND PIPING CORROSION MEETING A meeting was held on May 10, 1985 in Bethesda, Maryland with representatives from the licensee and Bechtel.
Meeting attendees are listed in Enclosure l.
The purpose of the meeting was for the licensee to respond to staff questions concerning an April 3, 1985 submittal on essential spray pond corrosion.
A meeting agenda is provided as Enclosure 2.
In the April 3, 1985 submittal, the licensee concluded that microbiologically influenced corrosion (MIC) is the probable cause for pitting in the welds of the piping in the spray ponds.
Gallionella, an iron bacteria, is believed to 11 were discussed during the meeting, are presented in Enclosure 3.
The spray ponds serve as the ultimate heat sink and by design specifications, must be able to maintain a maximum cooling water temperature of 125F.
The licensee stated that the as-built design for the spray pond system can deliver a flow rate of 18,200 gpm at a nozzle discharge pressure of 8.1 psig, as com-pared to the design requirements of 16,200 gpm at a nozzle discharge pressure of 7.0 psig.
In addition, the licensee had determined by analysis that a flow rate of 15,200 gpm can maintain the cooling water temerature below 125F under postulated accident conditions.
In addition to responding to the staff's questions, the licensee presented the results of a monitoring verification test performed on the spray ponds.
The main objectives of the test were to determine the relationship between pressure and bypass flow (which could result from continued corrosion) and to verify that the spray pond could function within design specifications even at high bypass flow.
The bypass flow was simulated by removing spray nozzles.
The number of spray nozzles removed was varied and the flow rates and nozzle discharge pressures were measured.
A video tape of the test performed was shown at the meeting.
As a result of the test, the licensee determined that it would require a bypass flow equivalent to the removal of 25 nozzles to lower the flow rate to 15,300 gpm (nozzle discharge pressure of 5.5 psig).
Based on the correlation provided in the April 3 submittal, this amount of bypass flow would represent the bypass flow that would result from thousands of through wall leaks of the 1/8 inch size.
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I Currently, there are only three known leakers in the Palo Verde Unit 1 spray ponds which are all less than 1/8 inch in size.
The licensee stated that good chemistry control has now been established for the spray ponds and recirculation of the water will be performed daily.
Per-formance monitoring of the spray ponds will be conducted during plant operation (by measuring nozzle discharge pressure) to assure that the flow rate does not fall below 15,300 gpm.
Reexamination of the Unit 1 piping welds will be per-formed during the first refueling outage.
The licensee stated that a procedure is being prepared to describe the perform-ance monitoring program.
The program will provide for quarterly measurements which will increase to monthly if the nozzle discharge pressure drops to the "alert" level and action will be taken if the pressure drops to a lower level.
The program will also provide for a metal specimen rack to be placed in the pond for observation.
Data compiled from this effort should confirm the mechanism of the weld corrosion, thus ensuring the long term effectiveness of the chemistry control.
The staff stated that the procedure will be incorporated into the technical specifications for the plant and that the scope of the procedure should be provided for staff review.
The licensee stated that it would provide it in a few days.
Enclosures:
As stated cc:
See next page Marilyn Ley, Project Manager Licensing Branch No.
3 Division of Licensing DQ; ]BY33 Ikey/es 6/i9/85 DL:LB83 EALicitra
. 6/
/85 GWKnighton 6/lP/85
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Mr. E.
E.
Van Brunt, Jr.
Arizona Nuclear Power Project Palo Verde CC:
Arthur C. Gehr, Esq.
Snell 5 Wilmer 3100 Valley Center Phoenix, Arizona 85073 Mr. James'.
- Flenner, Chief Counsel Arizona Corporation Commission 1200 West Washington Phoenix, Arizona 85007 Charles R. Kocher, Esq. Assistant Council James A. Boeletto, Esq.
Southern California Edison Company P. 0.
Box 800
- Rosemead, California 91770 Mr. Mark Ginsberg Energy Director Office of Economic Planning and Development 1700 West Washington - 5th Floor Phoenix, Arizona 85007 Mr. Wayne Shirley Assistant Attorney General Bataan Memorial Building Santa Fe, New Mexico 87503 Mr. Roy Zimmerman U.S. Nuclear Regulatory Commission P. 0.
Box 239 Arlington, Arizona 85322 Ms. Patricia Lee Hourihan 6413 S. 26th Street Phoenix, Arizona 85040 Regional Administrator, Region V
U. S. Nuclear Regulatory Commission 1450 Maria Lane Suite 210 Walnut Creek, Cali fornia 94596 Kenneth Berlin, Esq.
Winston 8 Strawn Suite 500.
2550 M Street, NW Washington, DC 20037 Ms.
Lynne Bernabei Government Accountability Project of the Institute for Policy Studies 1901 Que Street, NW Washington, DC 20009 Ms. Jill Morrison 522 E. Colgate Tempi, Arizona 85238 Mr. Charles B. Brinkman, Manager Washington Nuclear Operations Combustion Engineering, Inc.
7910 Woodmont Avenue Suite 1310
- Bethesda, Maryland 20814 Mr. Ron Rayner P. 0.
Box 1509
- Goodyear, AZ 85338
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Enclosure 1
- NAME PALO VERDE SPRAY POND MEETING MAY 30, 1985 8:30 a.m.
BETHESDA, MARYLAND ORGANIZATION Marilyn Ley Don Katze 0.
D. Parr J.
S. Wermiel Paul Wu Richard A. White Dan Sachs W. G.
Bingham S.
H. Shepherd William quinn Nelson Hallas Victor Benaroya Donald L. Chery, Jr.
C.
D. Sellers Conrad McCracken William J. Collins George W. Knighton Nanny Licitra NRC/DL/LB83 NRC/ASB NRC/ASB NRC/NRR/DS I/ASB NRC/NRR/DE/CMEB Bechtel Group Inc.
ANPP Bechtel Power Corp.
Bechtel ANPP Licensing ANPP NRC/NRR/Df/CMEB NRC/NRR/DE/HES NRC/NRR/DE/MTEB NRR/DE/CMEB IE/EGCB/DEPER NRR/DL/LBP3 NRR/DL/LBA'3
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Enclosure 2
AGENDA DISCUSSION WITH NRC ON PVNGS SPRAY POND MAY 10, 1985 I.
INTRODUCTION o
PURPOSE OF MEETING o
CONFIRMATORY TESTING o
MONITORING PROGRAM II.
BACKGROUND o
APRIL 3, 1985 LETTER CAUSE
-- INSPECTION, ANALYSES, AND TESTS
-- DESIGN MARGIN CORRECTIVE ACTION MONITORING PROGRAM OTHER SAFETY-RELATED SYSTEMS III.
SYSTEM DESCRIPTION AND CRITERIA o
DESIGN CRITERIA o
ASBUILT DESIGN o
DESIGN REQUI REMENTS IV.
MONITORING VERI F I CAT ION TEST o
TEST CRITERI A o
PROCEDURE o
RESULTS o
CONCLUSION W.
QUINN W,
QUINN N;
HALLAS N.
HALLAS lQ Fg S/io/eS
V,
RESPONSE
TO NRC QUESTIONS o
CHEMISTRY o
AUXILIARYSYSTEMS o
HYDROLOGIC VI, CONCLUSIONS o
SLOW RATE OF CORROSION o
LARGE DESIGN MARGIN o
GOOD CHEMISTRY AND ADMINISTRATIVE CONTROL o
ADEQUATE BASELINE o
INCYCLE VERIFICATION o
POSTCYCLE REVIEW AND EVALUATION D,
SACHS N.
HALLAS N.
HALLAS
'l0, QUINN s/> o/g 5
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-OO Enclosure 3
PALO VERDE SPRAY POND CORROSION 8 drolo ic En ineerin uestions Question 1:
You state that a cross sectional bypass flow area of 11.5 in is equivalent to a bypass flow'of approximately 800 gpm.
How was this relationship between area and flow reduction determined?
Response
The cross sectional bypass flow area of 11.5 in equivalent to 2
a bypass flow of 800 gpm was determined by calculating the leakage flow through a single i)8-inch diameter hole in the submerged supply header, and then multiplying the area of the single hole by the ratio of 800 gpm to the calculated flow rate. through the single hole (0 85 gpm).
.The ratio of the total leakage flow rate to the single hole flow rate defined the number of 1/8-inch diameter holes that should leak 800 gpm.
The actual calculation of the leakage flow through a 1/8-inch diameter hole was based on flow through a square-edged circu" lar orifice.
The pressure drop across the leakage path was taken as the nominal nozzle pressure drop plus the net static head of water in the header relative to the pond surface.
A flow coefficient of 0.6, consistent with the Reynolds'umber and relative hole to pipe diameter, was used.
The number of smaller diameter holes yielding 800 gpm leakage was simply determined from the flow area of the smaller holes relative to the area of the 1/8-inch diameter hole.
Question 2:
How was the pressure drop of 0.1 psig per nozzle used in your analysis?
How does this relate to a five percent flow reduc-tion of 800 gpm?
Response
The observed pressure drop was not used in the calculation analysis.
It was an observation of the initial testing performed to determine if pressure drop was a viable method to monitor spray system performance.
The removal of each nozzle increased bypass flow by about 1.93 square inches.
h total of six nozzles were removed to approximate 11.5 square inches of flow area described in the response to Question 1.
The pressure drop per nozzle was approximately 0.1 psig.
Question 3:
You state that removing nozzles one-at-a-time and measuring pressure drop established a relationship between the pressure drop and an increase in bypass flow area.
@hat is this relationship?
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Respease:
Based upon testing, the relationship is P ~ 8.1 - 0 05A Where P ~ nozzle pressure and A
bypass area Question 4:
What is the relationship between water flowing out of a nozzle arm (with the nozzle removed) and water flowing out of a small hole in a submerged pipe?
'sResponse:
The flow through a nozzle main is greater than the flow through numerous small holes in ~ater of an equivalent flow area due to friction factors.
Question 5:
You state that " -.testing successfully established that system pressure drop can be used to detect and quantify an increase in through-wall pitting (i.e., increased bypass flow area)."
That this can be done is not evident from the information you pro-vided.
Discuss how pressure drop can be used to detect and quantify an increase in bypass flow area.
Response
The pond spray nozzles themselves function as flow metering devices.
The supplier of the nozzles, Spray Engineering
- Company, has provided a curve relating nozzle pressure drop to nozzle flow.
Since the downstream pressure is always atmo-
- spheric, an accurate measurement of pressure in the header supplying the spray network (corrected for the elevation difference between the gage and the nozzles) should provide a
reliable indication of average spray nozzle flow.
The header pressure is actually the sum of the average nozzle pressure drop and the head loss between the pressure gage and the nozzles.
Assuming all reductions in header pressure represent a reduction in nozzle+P will conservatively overestimate the reduction in nozzle flow and the resultant bypass leakage.
The vendor's nozzle pressure drop curve is very close to linear over a range of plus and minus 4
gpm about the nominal 53 gpm/
nozzle design point.
The slope of the curve at 53 gpm is 0.26 psig/gpm.
On this basis, a reduction in header pressure of 0.1 psig would be equivalent to a nozzle flow reduction of 0.38 gpm, or about 122 gpm for the entire 320-nozzle array.
From the analysis tha) relates leakage flow area to leakage flow (800 gpm/11.5 in ), an O.l psig2header pressure reduction would be indicative of about 1.75 in of leakage area.
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Spray flov rate can decrease for reasons other than leakage due to pond piping corrosion-Heat exchanger fouling or
- plugging, a leaking spray header bypass block valve or pump performance degradation could all contribute to reduced spray flow.
Sensitive pressure instrumentation located elsevhere in the spray pond circuit, such as at the pump discharge and at the ECWS heat exchanger inlet and outlet, would provide information on the probable cause of any indicated reduction on spray flow.
Question 6
Since a portion of the 16,000 gpm flowing through the system vould leak out through the pitted pipes, a smaller flov at a
lover pressure would be available to be sprayed through the 320 nozzles.
Thus the cooling efficiency would be affected.
Also, the hot crater leaking out into the pond would result in higher temperatures in. the water being pumped from the spray pond to the heat exchangers.
Discuss hov reduced nozzle efficiency and higher vater temperatures vere considered in your analysis since you used prior computer runs to evaluate the impact of flov reduction on cooling pond temperature.
Response
It is true that the header pressure and nozzle flov rate are reduced by the leakage bypass flov.
hn expected result of reduced nozzle flov vould be reductions in spray pattern dimensions (height and diameter) and an increase in the average sprayed vater droplet size.
Theoretically, these changes should reduce the spray nozzle heat transfer effi-ciency used to predict pond cooling performance Given the small changes in flov and pressure at issue, the changes in nozzle efficiency are expected toy similarly, be small.
As defined in the PVNGS FSAR (Equation 9.2-2 on Page 9.2-85),
the spray efficiency is.the fraction of the maximum spray cooling range that is actually realized.
The maximum cooling range is the difference between the sprayed ~ster temperature exiting the nozzle and the. vet bulb temperature.
Since a
reduction in spray flov elevates the pond and sprayed water temperatures, the maximum cooling range, or driving force for spray cooling is increased.
To a first order approximation, it has been assumed that any reduction in spray heat transfer efficiency is at least counter balanced by the increased dri.ving force for spray heat transfer.
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The effect of hot ~ster leaking directly into the pond is reflected in the analysis through conservation of energy.
The base case computer analysis provides an integral of the energy leaving the pond through spray heat transfer to the atmosphere out to any point in time throughout the analysis.
The net effect of reduced spray heat transfer is to increase the energy inventory of the spray pond.
hs described in the response to Question 8, spray heat transfer is essentially directly proportional to spray flow.
- Thus, a five percent reduction in spray flow would equate to a five percent reduction in integrated energy leaving the pond out to the time of occurrence of maximum ECWS temperature and a corre-sponding increase in pond energy inventory.
Based on the pond mass, a pond temperature increase equivalent to the accumulated reduced spray heat transfer can be calculated to define the pond temperature with a leakage flow condition.
The pond temperature, of course, is the temperature of the
~ster cooling the diesel generators and the ECWS heat exchangers-Question 7:
What is the relationship between loss of flow and increase in pond ~ster temperature?
Response
Please refer, to the response to Question 6.
Question 8:
You assumed that spray pond heat transfer is directly propor tional to spray flow rate.
Provide the basis for this assumption.
It is not clear to the staff that this is a valid assumption.
Response
To a first approximation, given the small changes in spray flow rates involved, spray pond heat, re3ection should be directly proportional to spray flow rate.
Equation 9.2-3 on Page 9.2-85 of the PVHGS PSAR describes the calculation of the sprayed ~ater evaporation loss.
In the water loss
- equation, the terms (T
- T
) LC represent the spray heat transfer rate where (T T
) is the temperature change of in out the sprayed water, C is the water specific heat and L is the in out spray flow rate.
Clearly, the assumption of direct propor" tionality to spray flow neglects, for small changes in flow, any change to the sprayed water+ t.
hs discussed in the response to Question 6, the sprayed water t is a function of the spray heat transfer efficiency and the overall driving
- force, one of which decreases and one of which increases with spray flow reduction.
The assumption of no overall effect on t is reasonable for small flow changes-Question 9:
Can the design pressure be maintained in the system even with leaking pipes?
What is the design pressure of the system~
Response
Yes-Seven psig at the spray nozzles.
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Auxilia 5 stems Branch uestions Question 1:
A limiting criteria for the ultimate heat sink (essential spray pond) is the essential spray pond system flow.
An indirect test method was developed by ANPP in their letter dated April 3, 1985.
It's purpose was to determine when the bypass area (pipe leakage) has increased to the point (5X bypass flow) where system performance will not meet design requirements.
FSAR Figure 9.2-1 for the essential spray pond system indi-cates two instruments for measuring flow in each essential spray pump train.
They are FI-5 (FIT-7) and FI-6 (FIT<<8).
The licensee should elaborate on why these instruments are not used to determine bypass flow-The licensee's response should include a discussion of the accuracy of the existing flow indicators (FI-5 and FIT-7) as opposed to that for the instru-mentation utilized in their proposed indirect monitoring method per the licensee's letter of April 3, 1985.
Response
The existing flow indicators, FI-5 and FI-6 are 0-20,000 gpm
- range, graduated in 200 gpm increments, with an accuracy of
+ 2X.
Their primary purpose is to sense differential flow between the discharge and return legs of the spray system piping.
High differential flow, as alarmed in the control room, could be indicative of a break in the piping.
An increase in bypass 'flow does not represent a-one-for-one increase in total flow since it is compensated for by some loss in flow to the spray nozzles.
These instruments are not sensitive enough for the bypass flow monitoring.
These
, instruments are not sensitive enough for the bypass flow monitoring.
The pressure drop monitoring uses 0-15 psig
- range, graduated in one tenth of a pound increment gages with + 0.5X accuracy.
Question 2:
With increased bypass flow, the essential spray pond system flow resistance will decrease.
Depending upon the essential spray pond pump head/flow characteristics, system total flow may increase.
We are concerned that proper pump performance at this increased flow can be maintained with regard to adequate available net positive suction head (NPSH) and/or pump submergence.
Confirm that bypass flow up to the maximum allowable (5X) will not affect essential spray pond pump performance.
Response
The spray pond pump. curves, Bingham-Willamete Curve Nos.
37649 and 37650 have been reviewed.
Curve No. 37650 specifically tested with the minimum six feet NPSH and established a flow of 16,000 gpm.
With more than the minimum NPSH, flow rates up to approximately 21,000 gpm were achieved.
With the spray pond water level at Technical Specification limits, there is 16-1/2 feet of NPSH.
Pump performance will not be affected by the maximum five percent bypass flow.
This has been confirmed by testing.
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Question 3:
Given that the licensee has identified no corrective action for the currently identified leakage in the spray pond piping, and that the licensee is relying on the proposed leakage monitoring program to assure ultimate heat sink performance (safety function) ~ithln design limits, it is our position that the licensee propose technical specification revisions Mith appro-priate surveillance, limiting conditions for oper'ation, and action statements to assuie spray pond operability.
These technical specifications should be in place prior to receipt of a full power license for Palo Verde Unit l-
Response
The licensee wi11 submit, for staff approval and incorpor-ation into the technical specifications, a copy of the administrative procedures assuring spray pond operability.
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Chemical En ineerin
()uestions What is the chemistry of the water in the pond?
ESPS WATER QUALITY SPECIFICATIONS Parameter Maintained Normally Maximum Following 30 Days W/0 Makeup pH at 77F Conductivity, (pmhos/cm)
TDS (ppm)
Chlorides, as CaCO (ppm) 3 Fluorides, as CaCO (ppm) 3 7.8 1220 670 t
344 7.5 8715 4800 2458 17 Provide more detail on the scenario and the mechanism for the corrosion process.
Postulating the mechanism of microbiologically influenced corrosion requires combining two disciplines: microbiology and metallurgy.
Previously there has been little to no common interest,
- hence, investigators in these two diverse fields rarely even communicated with each other.
It is, therefore, not surprising that the mechanism of microbiological corrosion is not well understood.
This was reaffirmed by the leading experts in the field during a panel discussion at the March 85 NACE Conference.
There is, however, general agreement that the role of the bacteria is one of stimulating the corrosion process on the surface of the metal.
Gallionella, an iron bacteria which has, been identified on the pitted pipe removed from the spray
- pond,
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is reported to consume iron ions and exude metal hydrate as waste products.
Gallionella is also reported to concentrate chloride ions.
It is well known that all metals will release some ions into solution forming an ionic layer.
This process establishes the electro chemical potential that can be measured, with reference to a standard half cell, in a solution.
One can therefore, envision the following scenario:
When iron ions are released into solution the Gallionella immediately consumes them.
This causes more ions to be immediately released in the same area.
As iron ions are released rapidly in this area, it becomes an anode with respect to the surrounding metal surface.
The chloride ions are then further concentrated by the Gallionella.
Ir is well known that high concentrations of chloride ions break down passivity of stainless steels and create low pH environments in pits.
The low pH is cr~ated as the iron ions rear t with the hydroxvl ion
) eavinp the hydrogen ion from dissociated water.
The low pH further accelerates local corrosion, putting more iron ions into solution which the rapidly multiplying Call ionella quickly consume and the cycle is begun all over again.
If sulfate reducing bacteria are also present (some investigators believe they always are) they are reported to produce oxygen and sulfide ions from the sulfate ion at cathodic sites.
The oxygen then reacts with the hydrogen produced at the cathode ot form water.
This accelerated consumption of hydrogen at the cathodes (depolarization) further accelerates current flow, hence corrosion.
What kind of biocide is being used, what is its chemical composition, and what effect will it have on other materials in the system?
Sodium hypochlorite (NaOCl), which becomes hypochlorous adid in water.
It is a very effective biocide below a
pH of ~ 8, and it does not have a significantly detrimental effect on any material on any materials used in the spray pond systems.
It does have some difficulty in penetrating thick slime layers to reach the surface of the-metal, but the PVNGS piping does not have such layers or tubercules now and none are expected to develop in the future.
Discuss the microstructural characterization of the piping welds.
The microstructure of the spray pond welds is typical of that found in as deposited 308 material.
No unusual characteristics were observed.
In general dendrite sizes are large in 308 welds.
The largest dendrite sizes are normally found in welds made by submerged arc welding processes.
The dendrites contain a network nl'he ferrite phase (in the order of 5-15%)
in an austenite matrix.
When the ferrite content exceeds about 10% the networi becomes continuous.
The chemistry of the 308 is formulated so that some I<'trit('has< wil I i<<rm during s<<l i<li l icaI i<ill.
Ihi -
i l<<n<'
IV>l<l l< <4 cracking and in some cases to avoid intergranular stress corrosion cracking.
~I lp 1
I 1
MEETING
SUMMARY
DISTRIBUTION CDocket-No(.s-)::-
5O 52'/52B/53O Local PDR NSIC PRC System LB3 Reading
- Attorney, OELD GWKnighton Project Manager JLee NRC PARTICIPANTS M. Ley D.
Katze 0.
D. Parr J.
S.
Wermiel P.
Wu V. Benaroya C.
L. Chery, Jr.
D.
D. Sellers C. McCracken G.
W. Knighton E.
A. Licitra bcc:
Applicant 8 Service List
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