ML093510115
| ML093510115 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 12/30/2009 |
| From: | Vaaler M Plant Licensing Branch II |
| To: | Burton C Carolina Power & Light Co |
| vaaler m | |
| References | |
| TAC MC4688 | |
| Download: ML093510115 (10) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 December 30, 2009 Chris L. Burton, Vice President Shearon Harris Nuclear Power Plant Carolina Power & Light Company Post Office Box 165, Mail Zone 1 New Hill, North Carolina 27562-0165
SUBJECT:
SHEARON HARRIS NUCLEAR POWER PLANT, UNIT 1 - REQUEST FOR ADDITIONAL INFORMATION REGARDING SUPPLEMENTAL RESPONSES TO GENERIC LETTER 2004-02, "POTENTIAL IMPACT OF DEBRIS BLOCKAGE ON EMERGENCY RECIRCULATION DURING DESIGN BASIS ACCIDENTS AT PRESSURIZED WATER REACTORS" (TAC NO. MC4688)
Dear Mr. Burton:
By letters dated February 28,2008, March 28, 2008, and January 27, 2009, Carolina Power & Light Company (the licensee), now doing business as Progress Energy Carolinas, Inc.,
submitted supplemental responses to Generic Letter (GL) 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized Water Reactors," for the Shearon Harris Nuclear Power Plant, Unit 1 (HNP).
The U.S. Nuclear Regulatory Commission staff has reviewed the licensee's submittals and determined that it needs additional information in order to conclude there is reasonable assurance that GL 2004-02 has been satisfactorily addressed for HNP. Please respond to the enclosed requests by the date that will be established after a subsequent public meeting to discuss these items.
Please contact me at 301-415-3178 if you have any questions on this issue, would like to participate in a conference call, or if you require additional time to submit your responses.
Marlayna Vaaler, Project Manager Plant Licensing Branch 11-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-400
Enclosure:
Request for Additional Information cc w/enclosure: Distribution via ListServ
REQUEST FOR ADDITIONAL INFORMATION SHEARON HARRIS NUCLEAR POWER PLANT, UNIT 1 SUPPLEMENTAL RESPONSES TO GENERIC LETTER 2004-02:
"POTENTIAL IMPACT OF DEBRIS BLOCKAGE ON EMERGENCY RECIRCULATION DURING DESIGN BASIS ACCIDENTS AT PRESSURIZED WATER REACTORS" DOCKET NO. 50-400 By letters dated February 28, 2008 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML080670099), March 28,2008 (ADAMS Accession No. ML080940495), and January 27, 2009 (ADAMS Accession No. ML090300267), Carolina Power & Light Company (the licensee), now doing business as Progress Energy Carolinas, Inc.,
submitted supplemental responses to Generic Letter (GL) 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized Water Reactors," for the Shearon Harris Nuclear Power Plant, Unit 1 (HNP).
The U.S. Nuclear Requlatory Commission (NRC) staff has determined that it needs responses to the followinq questions, which relate to the January 27,2009, supplemental submittal, in order to continue its review of the HNP response to GL 2004-02:
Break Selection
RAI 4
The RAI noted that a zone of influence (ZOI) reduction for encapsulated Min-K from 28.6D to 4D was used based on Continuum Dynamics, Inc. testing of Diamond Power reflective metal insulation. The RAI requested the details of the testing conducted to justify the ZOI reductions.
The response provided additional information regarding the construction of the insulation system installed in the plant and the testing conducted on the Diamond Power reflective metal insulation. The staff reviewed the additional information as well as the test reports that were cited. The staff could not verify that the seams in the test cassettes were riveted similarly to the plant cassettes.
The response claimed that the Min-K insulation is less likely to deform than the aluminum foils within the cassettes that were tested. The staff considers that the assertion that a less deformable fill material would result in less damage does not have a technical basis because less deformation may cause increased stresses in other components of the insulation system. In addition, the licensee reduced the destruction pressure from that measured in testing for conservatism.
Enclosure
- 2 The assertion that the cassettes would not be damaged outside a 40 lOI rests on a comparative analysis between the tested and installed insulation systems.
However, the comparative analysis did not show that the tested and installed cassettes were constructed similarly enough to ensure that the 40 lOI is sufficiently conservative.
Although some conservatism was added to the evaluation, the staff is not able to conclude that the 40 lOI assumption is conservative because of the large variability in cassette construction, test results, and questions regarding the scaling of jet impingement tests. Therefore, please provide additional information to demonstrate that the 40 lOI is justified.
Debris Transport
RAI 6
The RAI requested further justification for crediting the settlement of fine debris assuming that the analyses used Stokes' Law as the basis. The staff deduced that more than 15 percent inactive pool volume was likely credited for holdup of fine debris (a value which the safety evaluation recommended as a limit).
Latent fibrous debris is a significant contributor to the limiting strainer head loss based on existing testing. Therefore, please clarify whether more than 15 percent of latent debris was credited with being held up in inactive volumes (including non-operating sumps). If so, provide a basis for this assumption considering Section 3.6.3 of the associated safety evaluation.
RAI 6
The RAI requested further justification for crediting the settlement of fine debris assuming that Stokes' Law was used as the basis. The staff understood the following main points based on the supplemental responses: (1) the case where the Stokes' Law approach is credited is not considered to be the limiting break based on existing strainer testing, and (2) the quantity of fine fiber assumed to settle during recirculation is fairly limited (about 5.1 cubic feet, which is approximately 7.6 percent of the fine fiber quantity at the strainer).
The staff did not consider that the response adequately justified the settlement, however, because (1) it was not clear that the crossover leg testing was performed in a prototypical manner, and (2) given the uncertainties with the Stokes' Law settling approach, when combined with uncertainties associated with latent debris being held up in inactive pool volumes and with the estimation of debris erosion, it was not clear that the limiting quantity of fine fibrous debris was considered in the licensee's evaluation.
As SUCh, it was not clear to the staff that the fine fibrous debris credited with settling during recirculation can be considered insignificant. Therefore, please provide a technical basis to justify the current Stokes' Law approach used to credit the settlement of fine debris, or else demonstrate that a bounding quantity of fine fibrous debris was included in the strainer head loss tests.
- 3
RAI 8
The RAI requested further justification for the crediting of debris retention on gratings in upper containment. The staff did not consider the response to have fully addressed the question for the following reasons:
- a. It appears the analysis may have assumed a 50 percent capture percentage for each level in a series of gratings. The staff would expect downstream gratings to have reduced capture percentages, since the less transportable debris pieces would be preferentially filtered out on upstream gratings.
- b. Part of the response was based on data for 6-inch x 4-inch debris pieces, which, although grouped with small pieces in the HNP analysis, would be considered large pieces, per Nuclear Energy Institute (NEI) 04-07, "Pressurized Water Reactor Sump Performance Evaluation Methodology,"
guidance, rather than small pieces.
Furthermore, per the blowdown data in NUREG/CR-6369, "Drywell Debris Transport Study," these 6-inch x 4-inch pieces would seemingly tend not to pass through gratings to the extent the analyses assumed during the blowdown phase (which would impact the credit taken for such pieces subsequently being retained on the upper side of gratings during washdown).
- c. Although the uniform spray flow areal densities in pressurized water reactors are typically significantly lower than the spray flow rate tested in NUREG/CR-6369, a substantial fraction of the debris interdicted by gratings would likely be exposed to more concentrated streams of drainage.
- d. It is not clear to the staff why a significant amount of debris blown to upper containment would be capable of gravitationally settling in sheltered areas of containment where spray cannot reach.
Please address these remaining points related to the credit taken for retention of debris pieces on gratings in upper containment, or demonstrate that the total fiber used in the strainer testing was prototypical or conservative.
RAI10 This RAI requested further justification to demonstrate the adequacy of the testing credited to support an erosion percentage of 10 percent for small and large pieces of unjacketed low-density fiberglass. Based on the information provided in the supplemental response, the staff considers it possible that the erosion testing being credited could be the generic testing performed by Alion as reported in the February 23, 2009, RAI response from the San Onofre Nuclear Generating Station (ADAMS Accession No. I\\IIL090580024).
The staff is concerned that these test results may be spurious, because the longer-duration tests showed a significantly lower cumulative erosion percentage than the shorter-duration tests. Therefore, please identify the vendor that performed the debris erosion testing credited by HNP and provide a graph of the percent of eroded debris as a function of time for the erosion tests that were
-4 performed. In addition, please provide justification that the tests are valid if anomalous behavior is apparent in the test results.
Head loss and Vortexing RAI13 This RAI requested the basis for (1) attributing the lower head loss associated with the test without debris bypass eliminators (DBEs) installed solely to the removal of this mesh and (2) the position that the expected variation associated with a repeat test performed for the HNP strainer design without DBEs could not exceed the small demonstrated margin (0.12 ft) available for the residual heat removal pumps.
The supplemental response provided additional information regarding the tests conducted with (test 3) and without (test 4) the DBE mesh. The RAI response states that the tests were conducted identically with the exception of the installation of the DBE. Graphs of the test results were provided; however, the graphs were too compressed along the time scale to allow the staff to compare behavior of the head loss during the addition of the various debris types.
In addition, the difference in bed formation was attributed to the DBE. The supplemental response stated that a bed forms across the DBE and also that the DBE affects the bed formation on the strainer surface, resulting in a more uniform bed. However, the staff has not observed or been made aware of other cases in which an Enercon strainer DBE has formed a debris bed. In addition, the assertion that the DBE results in a more uniform debris bed on the top hat surface is contrary to observations made by Alion during most similar tests.
The response also stated that during non-chemical testing, two Microtherm tests were performed with relatively similar results, thereby showing test repeatability.
In addition, the response stated that Min-K is fabricated from the same constituents as Microtherm and therefore should behave similarly. However, the staff noted that the response to RAI 14 pointed out significant differences between the percentages of each constituent making up the two types of insulation; therefore, the staff believes that the chemical effects tests conducted with the two different materials should not be compared.
The staff concludes that there is not enough information to justify that the full difference between test 3 and test 4 was due solely to the absence of the DBE in test 4. Further information may be available to assist in this justification, and is requested in order for the staff to complete its review. For example, the licensee could provide higher resolution test traces of head loss during debris addition to provide additional insight. The licensee could also provide details of industry experience for other problematic debris tests both with and without the DBE installed in Enercon strainers.
RAI14 The RAI raised questions regarding the repeatability of the Alion testing based on the results of HNP test cases using Min-K and Microtherm [microporous insulation]. Specifically, given that Min-K and Microtherm are composed
- 5 essentially of the same base materials (silicon dioxide and titanium dioxide), and given that the amounts of Min-K and Microtherm in the material-specific testing were close to the same (11.6 cubic feet (fe) and 12.1 fe, respectively), the staff asked for the basis for why these two similar materials had significantly different head loss results in the tests with the DBE mesh installed. Although the final HNP strainer configuration does not contain a DBE mesh, this observation demonstrates the potential for a lack of repeatability in the head loss test results.
The supplemental response stated that although the materials are composed of the same constituents, the percentage of each constituent is sufficiently different, such that the head loss from tests of the two materials would be expected to be different. The staff understands that there are differences in the amount of each constituent in the insulation. However, the information provided does not remove doubt about the consistency of test results attained during the strainer testing.
The staff noted the following during its review: 1) the fibrous portion of the microporous debris should not be a large contributor to any differences due to the other fibrous debris (latent) included in the test; 2) the amount of fumed silica in each test was approximately the same; 3) the titanium dioxide was significantly higher in the Microtherm test, yet this test had lower head loss; and 4) unless the titanium dioxide is a contributor to reduced head loss, or the fibrous debris added to the test(s) for latent debris was not prepared properly as fines, it is difficult to understand how the test results are consistent. Therefore, please address the above stated staff concerns regarding test repeatability.
RAI15 The RAJ requested the fibrous debris size distribution used for testing, as well as a comparison to the size distribution predicted by the transport evaluation.
The supplemental response provided additional information on the fibrous debris sizing. The test debris was stated to be within size classes 1-4 as defined by NUREG/CR-6808, "Knowledge Base for the Effect of Debris on Pressurized Water Reactor Emergency Core Cooling Sump Performance," and deemed to be readily transportable. However, the response provided neither a predicted size distribution for the debris at the strainer nor a comparison to the size distribution used during the testing.
Based on the percentage of fiber calculated to be available for the crossover leg break, the use of size class 1-4 fibers is likely conservative for the test corresponding to that break. However, this size distribution is not representative of typical latent debris. For the hot-leg and pressurizer cubicle break, all fiber should have been size class 1-3, with a relatively low percentage of size 3 fibers because almost all fibers for these breaks are latent (treated as individual fibers).
Based on the response to RAI 15, the staff could not determine that the fibrous debris used for the pressurizer and hot-leg breaks was representative of latent debris which would provide a conservative test condition for these breaks.
Further information may be available to assist in this determination, and is requested in order for the staff to complete its review.
- 6 RAI16 This RAI requested details of the debris addition procedures used.
The supplemental response stated that the debris was mixed with water into a homogeneous slurry using 5 gallon buckets prior to introduction into the test flume. About 1-3 pounds of debris was added to each bucket for mixing with water. Stirring was used as necessary to ensure that a majority of the debris was transported to the strainer. The response stated that the addition methods resulted in thorough mixing and dispersion of the debris and lack of agglomeration while allowing the debris to transport to the strainer.
The description provided by the response indicates that the debris introduction was conducted in a manner that would prevent agglomeration. Additionally, the response indicated that stirring prevented excessive debris settlement and that mixing of the debris typically occurred just prior to addition to the test tank.
However, during a trip to Alion to observe testing, the staff identified issues regarding debris preparation and introduction that could affect head loss and transport during testing (refer to the trip report located at ADAMS Accession No. ML071230203). The staff noted that these issues were likely more important for tests with low fibrous loads.
Therefore, for HNP the debris preparation and introduction issues would have the most impact on the Min-K and Microtherm tests. The staff considers it likely that the debris addition practices for the HNP testing were similar to those used during the testing that the staff observed. Based these observations of similar testing, the HNP testing may not have used a conservative debris introduction process.
Accordingly, please address the above staff concerns and demonstrate that the HNP testing led to prototypical or conservative results for the strainer head loss.
RAI19 This RAI requested information to show that a valid thin bed test was conducted such that: (1) fibrous debris preparation and introduction would result in prototypical transport and bed formation (note that the staff considers that the most transportable debris will reach the strainer first); (2) flow conditions, including any stirring used during testing, would allow prototypical bed formation; (3) the installation of the DBE would not change the prototypicality of bed formation on the strainer, or verification that testing was conducted with the same top hat arrangement (i.e., no DBE) installed in the plant; and (4) various incremental amounts of fiber were used in conjunction with limiting particulate debris loads during thin bed testing.
The supplemental response provided additional information on how head loss testing was conducted with respect to acceptable thin bed test practices. The information provided answered some areas adequately. The response regarding flow conditions (item 2) was acceptable overall. However, the other items were not addressed satisfactorily.
- 7 The response regarding item 1 stated that fibrous debris was prepared such that a range of individual fibers through inch tufts was represented in the testing.
For the Nukon case, which was the only case for which a thin bed test needed to be conducted, the fibrous debris should have been added such that the fine fibrous debris was introduced before the small fibrous debris, and the particulate debris should have been added prior to any fibrous debris. This position is documented in the "NRC Staff Review Guidance Regarding Generic Letter 2004 02 Closure in the Area of Strainer Head Loss and Vortexing" (ADAMS Accession No. ML080230038). However, this was not the case for the HNP testing, as all the debris was mixed together.
The response to item 3 indicated that the installation of the DBE results in a more uniform debris bed, and would therefore result in a higher likelihood of thin bed formation. However, this statement is in conflict with information that has been provided to the staff during discussions with Alion. According to Alion, the installation of the DBE is likely to result in a less uniform bed. Testing with the DBE installed appears, therefore, to be non-conservative for thin bed considerations when compared to the strainer installed in the plant (i.e., no DBE).
With respect to item 4, the response stated that for the Min-K and Microtherm tests, batching of fiber is not required due to the low amounts of fibrous debris created by the break. The staff considers this acceptable. However, for the Nukon break, the two amounts of fiber tested would result in 1/8-inch and
-3/4-inch theoretical bed thicknesses. These two test points do not include the likely limiting thin bed thickness for the strainers used during Alion testing. The NRC staff guidance document cited above recommends that debris be batched in small increments to determine the limiting thin bed.
Based on the above, the staff concludes that a valid thin bed test may not have been conducted. Therefore, please address the above concerns regarding the adequacy of thin bed testing for HNP.
RAI21 The original submittal stated that the vortexing evaluation was completed using a residual heat removal (RHR) pump runout flow (4500 gallons per minute (gpm>>.
It was not clear to the staff whether containment spray flow was included in the evaluation. It was also not clear whether either testing or the clean strainer head loss calculation included the containment spray flow. The staff requested additional information regarding the pump flows that were used to furnish inputs for head loss scaling, as well as the bases for these flows.
The supplemental response provided additional information that clarified the flow rates used for both the test scaling and clean strainer head loss calculations.
The response for the clean strainer head loss portion of the question is acceptable. However, based on the response, the staff could not determine why the vortexing evaluation was conducted at RHR runout flow (4500 gpm) versus maximum sump flow (5754 gpm).
- 8 The response implies that only the RHR or the containment spray pump can take suction from the sump at any given time, but this is not how the flow through the sump is described in the initial supplemental response (see page A1-31), which indicates that the RHR and containment spray pumps both take suction through the same strainer. In addition, the installation of a vortex suppressor over the strainer, as described in the initial supplemental response, indicates that a vortex from the sump pool surface is of concern.
Accordingly, please provide information to justify that the vortexing evaluation should only consider the RHR flow, and not the containment spray flow, since both pumps take suction through the strainer surface during recirculation.
Net Positive Suction Head RAI26 The RAI requested a description of the methodology used to compute the maximum pump flows for the RHR and containment spray pumps. Although an adequate response was provided regarding the containment spray pumps, the staff considers the response concerning the RHR pumps to be inadequate because: (1) rather than describing the methodology used, the response merely identified the vendor that performed the calculation; and (2) the response indicated that the flow rate used for the sump performance analysis was representative (e.g., as opposed to a bounding or calculated value).
Accordingly, please describe the methodology used to determine the RHR pump maximum flow rate, as well as provide the basis for considering this flow rate to be a conservative or prototypical input to the sump strainer performance analysis.
December 30,2009 Chris L. Burton, Vice President Shearon Harris Nuclear Power Plant Carolina Power & Light Company Post Office Box 165, Mail Zone 1 New Hill, North Carolina 27562-0165
SUBJECT:
SHEARON HARRIS NUCLEAR POWER PLANT, UNIT 1 - REQUEST FOR ADDITIONAL INFORMATION REGARDING SUPPLEMENTAL RESPONSES TO GENERIC LETTER 2004-02, "POTENTIAL IMPACT OF DEBRIS BLOCKAGE ON EMERGENCY RECIRCULATION DURING DESIGN BASIS ACCIDENTS AT PRESSURIZED WATER REACTORS" (TAC NO. MC4688)
Dear Mr. Burton:
By letters dated February 28,2008, March 28, 2008, and January 27,2009, Carolina Power & Light Company (the licensee), now doing business as Progress Energy Carolinas, Inc.,
submitted supplemental responses to Generic Letter (GL) 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized Water Reactors," for the Shearon Harris Nuclear Power Plant, Unit 1 (HNP).
The U.S. Nuclear Regulatory Commission staff has reviewed the licensee's submittals and determined that it needs additional information in order to conclude there is reasonable assurance that GL 2004-02 has been satisfactorily addressed for HNP. Please respond to the enclosed requests by the date that will be established after a subsequent public meeting to discuss these items.
Please contact me at 301-415-3178 if you have any questions on this issue, would like to participate in a conference call, or if you require additional time to submit your responses.
Sincerely,
/raj Marlayna Vaaler, Project Manager Plant Licensing Branch 11-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-400
Enclosure:
Request for Additional Information cc w/enclosure: Distribution via ListServ DISTRIBUTION:
PUBLIC LPL2-2 R/F RidsNrrDorlLpl2-2 RidsNrrPMShearonHarris RidsNrrLACSola RidsOgcRp RidsNrrDssSsib RidsRgn2MailCenter RidsAcrsAcnw_MailCTR ADAMS Accession Number' ML093510115 NRR-088 OFFICE LPL2-2/PM LPL2-2/LA SSIB/BC LPL2-2/BC NAME MVaaler CSoia MScott (RArchitzel)
TBoyce (SLingam for)
DATE 12/18/09 12/18/09 12/30/2009 12/30/09 OFFICIAL RECORD COPY