ML050550240
| ML050550240 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 02/10/2005 |
| From: | Overbeck G Arizona Public Service Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 102-05210-GRO/SAB/JAP IR-04-014 | |
| Download: ML050550240 (37) | |
Text
ENCLOSURE 2 OF THIS LETTER CONTAINS PROPRIETARY INFORMATION AND SHOULD BE HELD FROM PUBLIC DISCLOSURE UNDER 10 CFR 2.390 10 CFR 2.390 Gregg R. Overbeck Mail Station 7602 Palo Verde Nuclear Senior Vice President TEL (623) 393-5148 P.O. Box 52034 Generating Station Nuclear FAX (623) 393-6077 Phoenix, AZ 85072-2034 102-0521 0-GRO/SAB/JAP February 10, 2005 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Dear Sirs:
Subject:
Palo Verde Nuclear Generating Station (PVNGS)
Units 1, 2 and 3 Docket Nos. STN 50-528, 50-529, and 50-530 Response to Information Request in NRC Special Inspection Report 0500052812004014; 0500052912004014; 0500053012004014 In NRC Special Inspection Report 05000528/2004014; 05000529/2004014; 05000530/2004014, dated January 5, 2005, the NRC requested that Arizona Public Service Company (APS) provide additional information regarding APS' assessment of the voided containment sump safety injection suction piping that was corrected on August 4, 2004. The requested information is provided in Enclosure 2 to this letter. APS requests the information in Enclosure 2 be withheld from public disclosure because of its commercial value to APS. The affidavit required by 10 CFR 2.390 is included as . A redacted version of the information is provided in Enclosure 3.
There are no commitments in this letter. Should you have any questions, please contact Mr. Scott A. Bauer (623) 393-5978.
Sincerely, GRO/SAB/JAP A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway
- Comanche Peak
- Diablo Canyon
- Palo Verde
- South Texas Project
- Wolf Creek
ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Response to Information Request in NRC Special Inspection Report 05000528/2004014;.
05000529/2004014; 05000530/2004014 Page 2
Enclosures:
- 1. Affidavit for Information Sought to be Withheld from Public Disclosure
- 2. Response to Information Request in NRC Special Inspection Report 05000528/2004014; 05000529/2004014; 05000530/2004014 (Proprietary Version)
- 3. Redacted Response to Information Request in NRC Special Inspection Report 05000528/2004014; 05000529/2004014; 05000530/2004014 (Non-Proprietary Version) cc: B. S. Mallet NRC Region IV Regional Administrator (all w/enclosures)
A. T. Howell Ill, Director, Division of Reactor Projects, NRC Region IV G. G. Warnick NRC Senior Resident Inspector for PVNGS M. B. Fields NRC NRR Project Manager
ENCLOSURE 1 Affidavit for Information Sought to be Withheld from Public Disclosure
UNITED STATES ON AMERICA NUCLEAR REGULATORY COMMISSION In the matter of ) 10 CFR § 2.390 Palo Verde Nuclear Generating Station ) Docket Nos. 50-528 Units 1, 2 & 3 ) 50-529
) 50-530 AFFIDAVIT I, Gregg R. Overbeck, Senior Vice President, Nuclear, Palo Verde Nuclear Generating Station (PVNGS), do hereby affirm and state:
- 2. APS is providing requested in NRC Special Inspection Report 05000528/2004014; 05000529/2004014; 05000530/2004014 related to the NRC's review of the potential impact of an air void inside a section of piping in systems used to provide emergency cooling in the unlikely event of an accident at PVNGS. APS' response to NRC Special Inspection Report 05000528/2004014; 05000529/2004014; 05000530/2004014 contains data, analysis, methodology and other information that is the proprietary confidential intellectual property of APS. Therefore, APS' response to NRC Special Inspection Report 05000528/2004014; 05000529/2004014; 05000530/2004014 constitutes proprietary commercial information that should be held in confidence from the regulatory agencies of other countries and from the public by the NRC pursuant to the policy reflected in 10 CFR §§ 2.390(a)(4) and 9.17 (a)(4), because:
- i. The information sought to be withheld from public disclosure is owned and has been held in confidence by APS and associated companies who participated in developing this information for APS.
ii. This information is of a type that is customarily held in confidence by APS, and there is a rational basis for doing so because the information contains the proprietary confidential intellectual property of APS.
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iii. This information is being transmitted to the NRC in confidence.
iv. The information is not available in public sources or available information has not been previously employed in the same original manner or method to the best of my knowledge and belief.
- v. Public disclosure of this information would create substantial harm to the competitive position of APS by disclosure of APS' proprietary confidential intellectual property. Disclosure of this information to regulatory agencies in other countries would also create substantial harm to the competitive position of APS by disclosing information to governments with ownership and interest in competitors.
Greg Overbeck STATE OF ARIZONA )
) ss.
COUNTY OF MARICOPA )
Subscribed and sworn to before me, a Notary Public, this /O A,*Day of 2 - ,2005, in and for the State of Arizona, by Gregg R. Overbeck.
My Commission Expires:
i ~OFMCItA1SA S _ ~LINDA G. REOA NOARYPBICUACNT Mi VMy ComKUH UUrsFb.820 2
ENCLOSURE 3 Redacted Response to Information Request in NRC Special Inspection Report 05000528/2004014; 0500052912004014; 05000530/2004014 (Non-Proprietary Version)
Response to Information Request in NRC Special Inspection Report 0500052812004014; 0500052912004014; 05000530/2004014 (Non-Proprietary Version)
In NRC Special Inspection Report 05000528/2004014; 05000529/2004014; 05000530/2004014, dated January 5, 2005, the NRC requested additional information regarding the preliminary results of pump testing, associated analyses, and preliminary assessment of the safety significance of the Emergency Core Cooling System (ECCS) voided suction piping condition as submitted to the NRC in letter dated December 27, 2004. The additional information is provided below. Arizona Public Service Company (APS) will submit a comprehensive final report containing a description of the final results of the tests and analyses performed, and our final assessment of the safety significance prior to the Pre-decisional and Regulatory Enforcement Conference scheduled for February 17, 2005.
NRC Question I
{Provide} a comprehensive account of the differences between the as-found configuration of the affected systems and the test configurations, including but not limited to the differences in components, process parameters, system operation and control, power usage, indications and environmental conditions.
APS Response In order to determine the safety significance of this condition, the air volume fraction that could be ingested by the high pressure safety injection (HPSI) and containment spray (CS) pumps, needed to be determined. Once the air volume fraction was determined, each pump's tolerance for the projected air ingestion was assessed and ultimately the impact on the ECCS safety functions.
A comprehensive scale model testing program was employed to develop a full understanding of the system response to the void and the resulting air/fluid conditions that would be delivered to the pumps' suction inlets. The impact on pump performance was then assessed via full-scale testing, given the projected air/fluid conditions.
The scale model tests were performed at Fauske and Associates (FAI), and simulated the system response during and following a Recirculation Actuation Signal (RAS) with the affected section of piping initially voided. The scale tests were conducted in three phases. The first phase modeled the reactor water tank (RWT) and associated piping, and the sump and associated piping down through and including the long vertical run of pipe. The purpose of the first phase was to demonstrate the ability to simulate the transient and measure the important parameters such as void fraction, pressure, and flow rate. A series of tests were performed to test important scaling parameters to ensure the results of the test could be confidently applied to the full scale Palo Verde units. A series of phenomenological tests (the second phase) using a larger scale Enclosure 3- Response to Information Request (Non-Proprietary Version)
model was incorporated into the test plan to verify that the flow regime in the vertical section of the scaled piping configuration was representative of large pipe behavior.
The second phase extended the scale model to include the individual pump suction piping up to each pump inlet. An extensive series of tests under varying flow and pressure conditions were performed.
] These results established the inlet conditions for the subsequent full-scale pump performance tests.
Full-scale pump tests were performed at Wyle Labs utilizing a spare Palo Verde HPSI pump and a representative CS pump to determine the impact on pump performance under the projected air ingestion conditions. [
Differences between Plant and Phase I and 11Scale Model Tests The purpose of the first phase was to demonstrate the ability to simulate the transient and measure the important parameters such as [ I For the purpose of this response to NRC Question 1, the first phase of testing need not be considered since it was a prelude to and is encompassed by the second phase of testing.
The Phase 2 test facility was composed of two tanks with water inventories (the simulated containment sump and RWT), -centrifugal pumps, piping, valves, a gas separator for the HPSI suction line and associated instrumentation as indicated in the following figure.
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I The piping and valves from the upstream isolation valve, the downcomer piping as well as the pump suction header were all 4 inch in diameter and fabricated from clear plastic to facilitate observation of the initial air inventory and its behavior during the opening of the MOVs. The major differences between the plant and the Phase 2 test loop can be categorized into five areas:
- 1. Differences in size (geometric scaling affects)
- 2. Differences in geometrical scaling in different sections of the loop
- 3. Differences in process parameters
- 4. Differences in components
- 5. Differences in operation and control Differences in Size (geometric scaling affects)
The use of 4 inch diameter (Schedule 40) pipe to represent the 24 inch diameter (Schedule 20 and 30) pipe in the plant defined a linear scale ratio of approximately 1/6.
Thus, the balance of the suction line pipe lengths and valve locations also used a 1/6th scale unless there were other considerations that took precedence [
] (Schedule 40). As a result, linear segments in the horizontal and vertical test elements were dimensioned to be approximately 1/6th of those dimensions that apply for the plant (see Table 1). Thus, the scaled test configuration simulates the sump suction lines in all three Palo Verde units. The affect and implications of differences in geometrical difference between the plant and the test loop (i.e., scaling affects) are covered in detail in the response to NRC Question 4.
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Differences in Geometrical Scalinq in Different Sections of the Loon, Previous Phase 1 and Phenomenological Tests showed that it was important for the vertical downcomer to have a downward velocity like that of the plant [
] The basis and implications of these differences are also discussed in the response to NRC Question 4.
There were also some minor differences in geometrical scaling due to the fact that it was not possible to procure the PVC pipe used in the test loop in the exact relative proportions as existed in the plant. The use of 4 inch diameter (Schedule 40) pipe to represent the 24 inch diameter (Schedule 20 and 30) pipe in the plant defined a linear scale ratio of approximately 1/6. In the plants, the HPSI pump suction lines are 10 inch diameter pipes so the 1/6 scale branch line used 1.5 inch diameter (Schedule 40) pipe.
Similarly, the CS pump suction branch is 18 inch diameter so the 1/6 scale branch line used 3 inch diameter (Schedule 40) pipe. Table 1 shows the actual plant pipe inside diameters, the Phase 2 test pipe inside diameters, and the ratio between the test and plant.
Table I Comparison of Plant and Phase 2 Pipe Diameters Plant Phase 2 Ratio Sump Common Supply Line 22.876 Inch 4.026 inch 0.176 CS Pump Suction 17.376 inch 3.068 inch 0.177 HPSI Pump Suction 10.25 inch 1.61 inch 0.157 The minor difference in ratio for the HPSI pump suction relative to the Sump common supply and the CS pump supply could not be avoided and did not affect the results of the Phase 2 test. [
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In addition, there were differences in fluid temperature between the plant and Phase 2 loop. Since the Phase 2 test model was constructed primarily of clear plastic piping, the Phase 2 testing was performed under cold conditions whereas the postulated post-accident conditions include some high temperature cases. The affect of this difference in process parameter is discussed in detail in the response to NRC Question 2.
Differences in Components ComDrising the System There were some differences in the components comprising the plant system versus the Phase 2 test. The pumps used in the Phase 2 test were single stage horizontal pumps as compared with the multi-stage horizontal HPSI pump and the single stage vertical CS pump used in the plant. However, the purpose of the Phase 2 test was to maintain the properly scaled parameter [ ] in the loop. The Phase 2 testing did not investigate pump operability. Therefore, the differences in pumps between the test and plant are of no consequence.
The Phase 2 test modeled the RWT and Sump but did not model the reactor coolant system.
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Differences in Operation and Control There were some minor differences in operation and control of the Phase 2 test loop resulting from the differences in components between the plant and test loop. The Phase 2 test loop did not model the reactor coolant system. When the pumps were operating with suction from the RWT their discharge was also routed to the RWT. This simplified inventory control and allowed the chosen initial conditions for each test to be maintained indefinitely. In the plant the RAS is generated by low level in the RWT. In the Phase 2 test, the initial conditions of the test included the pumps discharging back to the RWT. Therefore, RWT inventory was maintained and the RAS was manually initiated by the test operator in the Phase 2 loop.
The following test procedure was used during the Phase 2 test.
I. Pre-Conditions and Safety Checks A. Confirm initial conditions have been established, i.e. pressure and water levels in each tank, pump running on recirculation to RWr tank, horizontal segment voided, and vertical segment water filled.
B. Assure data collection system is ready, instrumentation is operating, and power for three motor operated valves is available.
C. Assure safety precautions are in place. All test personnel and observers should have proper eye protection.
II. Testing A. Establish applicable initial and test conditions per test matrix.
B. Assure sump recirculation isolation valve (FAI-1) is open and the check valve (FAI-2) is closed.
C. Start digital movie cameras.
D. Start data collection.
E. Start butterfly valves opening (initiate RAS).
F. Confirm closure of check valve in pump supply line from RWT.
G. [
H. Collect data and observe flow behavior.
I. Stop data collection.
Step l.A of the above procedure starts the test with the pumps running on recirculation to the RWT. Step ll.B of the above procedure ensures that the sump recirculation valve (FAI-1) is open and the check valve (FAI-2) is closed. Therefore, the pump discharge is aligned to both the RWT and sump. However, the initial pressure in the sump prevents the pump from discharging into the sump. The RAS is initiated in step I.E of the procedure. This causes the check valve in the pump supply from the RWT to automatically close as confirmed in step II.F.
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Differences between Plant and Phase 3 Test The Phase 2 testing identified the air volume fraction to the suction of the CS and HPSI pumps as a function of time for each case included in the test matrix. Therefore, since the purpose of the Phase 2 testing was to predict the rate of air transfer to the pump suction, it was necessary to model the physical layout of the plant, system process parameters, and system operation during the test. The Phase 2 test results were then used to define the full scale Phase 3 pump tests to determine the affect of the voided pump suction conditions on pump performance and the ability of the pump to withstand the voided conditions. As such, the Phase 3 tests were component level tests instead of system level tests. [
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The Phase 3 tests were not intended to replicate the plant system operations following a RAS. The objective of the test was to determine the impact of the fluid air volume fraction on pump performance.
The actual plant pipe diameter and layout were duplicated in the Phase 3 test from the air injection point to the suction of the HPSI and CS pumps.
] Based on the results and evaluations of the Phase 2 testing, no attempt was made to perform testing with elevated water temperatures which may exist during the initiation of post-accident operation following a RAS; the Phase 3 testing utilized water at ambient temperature. Although the Phase 3 testing facility had the capability to allow testing at an elevated temperature, this would have introduced a disconnect between the Phase 2 and Phase 3 test conditions. [
These affects were all accounted for in the Phase 2 tests and therefore it was important to maintain consistency between the two sets of tests. The implications of increased sump temperature are discussed in more detail in the response to NRC Question 2.
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The Phase 3 testing used a storage tank to supply water to the pumps. In order to facilitate inventory control during the test, the pumped fluid was recirculated to the tank.
] The purpose of the test was to quantify the pump performance under various voided conditions. The results of the Phase 3 testing were then used to analytical predict the ability of the pump to inject water into the reactor coolant system at conditions calculated to exist following post-accident operation. This is discussed further in the response to NRC Question 4.
NRC Question 2 An assessment of these differences, including the bases, relative to any final conclusions that you may reach regarding system operability and the risk significance of the voided conditions that actually existed.
APS Response Assessment of the impact of minor differences between actual plant configuration and conditions and those utilized in the scale model and full scale pump tests are contained within the response to NRC Question 1. For these minor differences, APS has concluded that the differences have either no impact on our final conclusions, or that the differences result in conservative test results.- Therefore, APS response will be provided in the context of the following aspects of the testing and analysis program:
- 1. The influence of sump temperature on over-all conclusions,
- 2. An overall assessment of conservatism within the testing and analysis program, and
- 3. An overall assessment of APS' conclusions regarding system operability and risk significance.
The Influence of Sump Temperature As discussed in the response to NRC Question 1, it was not possible to perform the scale model tests at high temperatures such as could be encountered during actual accident conditions. Furthermore, it was determined that performance of the Phase 3 pump performance tests at high temperatures could not be performed in a manner that, when combined with air injection near the pump inlet (the primary purpose of the Phase 3 pump tests), would produce prototypical plant conditions. It was also judged that high temperature testing would also introduce a disconnect between the scale model tests and the full scale pump performance tests. Instead, an engineering approach was utilized to evaluate the influence of high sump temperatures.
During an actual plant accident involving a RAS, the sump water temperature entering the air volume is a function of the accident conditions. [ ]
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[
I Overall Assessment of Conservatism within the Testing and Analysis Program Other conservative aspects of the scale model and full-scale pump testing program j more than compensate for any potentially non-conservative prediction of peak air volume fraction delivered to the pump inlets that may result from the inability to perform the scale model tests at high temperatures. Some of the major conservatism, and the impact on test results, are discussed below:
- 1. [
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[
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- 2. Use of smaller f 1:
As discussed in detail in the response to NRC Question 4, a [
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- 3. Use I 1and air injection:
For most of the scale model tests, a [ ] was installed in the HPSI suction line upstream of the HPSI pump. It behaved as intended and [
] The important results from the scaled experiments are the extent of gas intrusion into the HPSI and CS pump suction lines immediately following the opening of the two butterfly valves.
The results from these scaled experiments were used to develop the gas intrusion histories used in the full scale evaluations of the HPSI and CS pump performances.
While this information can be characterized in a number of different ways, such as void fraction, flow regime, gas mass flow rate, etc., the most meaningful representation for full scale systems was to develop (1) a conservative characterization of [ ] and (2) the flow regime existing in the suction line as this occurs.
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[
[ ] For the plant system under accident conditions, air transported through the HPSI line could degrade the pump performance and cause a decrease in the flow rate being pumped, which decreases the HPSI suction flow rate thereby reducing the rate of air intrusion. With these considerations, it is clear that the air mass flow rate deduced from these scaled experiments with [ ] provides a conservative representation of the plant response for an accident condition.
]
- 4. Prolonged exposure to peak r 1:
In the Phase 2 scale model tests, the [
], as illustrated in the following figures (figures are for a series of tests for a 1310 gpm equivalent HPSI flowrate. All tests results are similar in this regard).
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[
] Again, the resulting test of the pump's tolerance for air ingestion is judged to be much more severe than would have been experienced in the actual plant.
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Overall Assessment on APS Conclusions Regarding System Operabilitv and Risk Significance As described in the preliminary report dated December 27, 2004, it is concluded that for all reactor coolant system (RCS) break sizes equivalent to [ ], the HPSI pump would have experienced a temporary reduction in developed head and flow but would have continued to operate without failure or air binding. At some break size From the discussion in the preceding sections of the response to NRC Question 2, Palo Verde's assessment is that the sum total of the differences between the test conditions and configurations and the corresponding plant conditions and configurations results in an overall conservative prediction of the conditions that would have been experienced at the plant, specifically with respect to the air ingestion rates that would have been experienced by the ECCS pumps. Accordingly, the conclusion that the HPSI pumps would have continued to function though-out the course of the accident following receipt of the RAS, for break sizes corresponding to [ ] is a conservative conclusion.
In the Palo Verde Probabilistic Risk Assessment (PRA) model changes made to incorporate this conclusion and determine the corresponding increase in total risk, it was assumed that the HPSI pump would remain functional for [ ]
break Loss of Coolant Accidents (LOCAs). Since the break size that represents the boundary between [ ] in diameter [
], additional conservatism is introduced. With this assumption, the risk significance as calculated by APS is considered to be very conservative.
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NRC Question 3 (Address) any differences between the predicted test results and the actual tests results.
APS Response APS did not attempt to predict the results of any of the scale model or full scale tests. It was well understood that the phenomenology involved was complex. In general, APS had only three expectations that the tests would demonstrate:
- 1. The air in the originally voided sections of piping would be swept out of this horizontally oriented piping and would not self-vent back into containment. This expectation was based on the initial evaluation of the voided condition performed upon its discovery by the Palo Verde engineering staff. This evaluation concluded that the flow velocity in this section of piping would be sufficient for the pipe to run full and was based on correlations presented in the industry literature in Reference
- 1. [
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- 2. 1 I
- 3. [
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It is noted that this expectation was based on hydraulic performance only. Neither APS nor the pump vendor had data or information regarding the pump's tolerance from a mechanical standpoint. [
I References for Response to NRC Question 3:
- 1. Wallis, G.B. "Conditions for a Pipe to Run Full When Discharging Liquid into a Space Filled With Gas," Transactions for the ASME, Journal of Fluids Engineering, June 1977, pp. 405-413.
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2.
- 3. NUREG/CR-2792. "An Assessment of Residual Heat Removal and Containment Spray Pump Performance Under Air and Debris Ingesting Conditions",
September 1982.
NRC Question 4 A more comprehensive discussion of the scaling factors used to establish the test conditions for the full scale pump tests (e.g., system resistance).
APS Response The following response is provided in three parts:
- 1. Fluid dynamic scaling,
- 2. Geometrical, volumetric, mass and time scaling, and
- 3. System resistance.
THE ENTIRE RESPONSE TO QUESTION 4 IS CONSIDERED PROPRIETARY I
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[
Additional NRC Question 5 Address any potential negative impacts stemming from water hammers APS Response The ECCS voided piping condition did not present any negative impacts stemming from waterhammer. Numerous analyses and experiments have been performed to evaluate the influence of air in a system during a strong hydraulic transient such as a pump start (Chaiko and Brinckman, 2002 (reference 1), Lee and Martin, 1999 (reference 2), and Martin, 1976 (reference 3)). As stated by Martin:
The effect of the presence of entrapped air on transient pressures of a liquid pipeline can either be beneficial or detrimental, depending on the amount of air, the two-phase flow regime of the mixture (whether homogeneous or slug), and the nature and cause of the transient.
Of particular importance are those situations which could be detrimental to the piping system. Generally these are conditions in which a significant coherent gas volume has formed on the discharge side of the pump. Significant means a volume that is comparable to or larger than the integrated volumetric flow discharged from the pump during the time that it comes up to speed. Given these conditions the pump can accelerate to essentially runout flow conditions with the only resistance being the frictional forces generated by the moving water column between the pump discharge and the air pocket. Subsequent to this, the moving water column will begin to compress the air volume and the gas pressure will increase dramatically as volume is reduced.
For example, under these conditions the gas bubble pressure more than doubles when the gas volume is reduced by one half and similarly more than doubles again when it is reduced again by one half, etc. Hence, with a low pressure gas volume on the discharge side of the pump, the compression of the gas bubble will eventually absorb the kinetic energy of the water column. For this to occur the gas volume pressure can increase to values much greater than the maximum pump discharge pressure.
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] Thus, it is concluded there are no negative impacts due to water hammer stemming from the presence of air in this section of the ECCS piping.
References for Response to Question 5:
- 1. Chaiko, M. A. and Brinckman, K. W., 2002, "Model for Analysis of Waterhammer in Piping with Entrapped Air," Transactions of the ASME, Journal of Fluids Engineering, 124, pp. 194-204.
- 2. [
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- 3. [
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- 4. [
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