ML20195F794
| ML20195F794 | |
| Person / Time | |
|---|---|
| Issue date: | 11/17/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20195F782 | List: |
| References | |
| NUDOCS 9811200086 | |
| Download: ML20195F794 (7) | |
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_U.S. NUCLEAR REGULATORY COMMISSION
_ OFFICE OF NUCLEAR REACTOR REGULATION S IBWRVIP VESSEL AND INTERNALS PROJECT. IN _
AND SPARGER REPLACEMENT DESIGN CnlTERIA (B -
EPRI REPORT TR-106708, MARCH 1997. AND IBWRVIP VESSEL AND INTERNALS PROJECT. INT AND SPARGER REPAIR DESIGN CRITERIA (BWRV EPRI REPORT TR-106893. SEPTEMBER 1996
1.0 INTRODUCTION
1.1 Background (BWRVIP) submitted the Electric asPower roject r e ary Report TR-Research i 106708, "BWR Vessel and intemals Project, Intemal Core Spray Piping a n parger Replacement Design Criteria (BWRVIP-16)"(Ref.1). - The BWRVIP 16 re design acceptance criteria for full and/or partial portreplacement provides general of 300 series s a n ess steelinternal replacements which will maintain the nstructurat ng integr operation as well as under postulated transient ands.design basis accident c under normal By letter dated September 16,1996, as supplemented by letter dated Feb BWRVIP submitted the EPRI proprietary Report ,
ruaryTR 106893 24,1997, the "BWR Vessel and Internals The BWRVIP 19 report provides porary general P-19)" (Ref. 2).design acce and permanent repair of 300 series stainless steelinternal core spray piping rs. In dated January 22 1 response to the staff's request for additionalinformation provided supplemental information in a letter dated February ,
24 1997 e WRVIP 1.2 Purpose guidances will provide acceptable levels of qualitThe staff revie er their respective related internal core spray piping and spargers. y for replacement and/or repair of the safety-1.3 Organization of this Report Because the BWRVIP-16 and -19 repoits are proprietary, this SE was writt proprietary information contained in the reports. The en so as not io repeat staff does not disc provisions of the guidelines nor the parts of the eguidelines a the it finds acce reports were virtually identical, except for one beingerfor .
replacement and the oth e wo staff has combined its review into a single SE which addresses both reports.
for repair, the ENCLOSURE 9811200086 981117 PDR C TOPRP EXIEPRI PM
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2.0 STAFF EVALUATION
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2.1 Section 3, intemal Core Spray Piping and Sparger Characteristics and Safety Function 3
Section 3 of the BWRVIP-16 and -19 reports, " Internal Core Spray Piping and Sparger j Characteristics and Safety Function," discusses the safety design bases and event analyses of '
- the core spray system. The BWRVIP stated that the safety function of the core spray piping and j spargers is to deliver emergency core cooling system (ECCS) water to the reactor core, and to 4
distribute this flow over the core. Each BWR has two separate and independent core spray
- systems (i.e<, two trains of core spray). These two core spray systems will maintain their original
- Independence in the replacement configuration.
f i The BWRVIP-16 and -19 reports discuss the general load cases that should be considered in i the design of the proposed replacement. These loads include normal operation, anticipated operational occurrences (upset conditions), design basis accidents (emergency / faulted
, conditions), and combined loads. When considering design basis loads, the BWRVIP stated i that the licensee shall specify whether or not core spray integrity is a required design j
requirement for the core spray replacement, following a steam line break, based on existing j design basis requirements. Since the discussion of core spray distribution following a steam line a
' break refers to some BWR/3 - BWR/6s and includes statements that instruct licensees to follow their licensing basis, the staff finds the description of design basis load requirements acceptable.
2.2 Section 8, System Evaluation Section 8 of the BWRVIP-16 and -19 reports," System Evaluation," discusses how the core spray repairs and repla:ements impact system leakage, core spray piping pressure drop, core spray flow and sparger distributions, emergency operating procedures (EOPs) calculations and power uprate. The staff notes that leakage paths may have resulted from previously repaired or replaced reactor intemais. The impact of this leakage should be evaluated for normal operations and accident conditions. The BWRVIP-16 and -19 reports states that the leakage evaluation should be based on system temperature, pressure, and system flow that is consistent with those values used in the 10 CFR Part 50, Appendix K, licensing basis LOCA analysis.
The BWRVIP-16 and -19 reports proposed leakage acceptance criteria for internal core spray piping and core spray sparger replacements and repairs, respectively. For core spray piping repair and replacements, postulated leakage from the core spray piping could potentially bypass the core and reduce the available core cooling during an event when core spray operation is required. Additionally, any reduction in the core spray flow delivered inside the core shroud could result in an increase in the fuel peak cladding temperature (PCT) as calculated in the plant specific LOCA analysis. The BWRVIP 16 and 19 reports suggests two ways to show that the postulated leakage is acceptable. These include showing that the potential increase in PCT is insignificant with regards to the overall LOCA analysis, or showing that the total post-replacement leakage is bounded by the original or newly established core spray system capacity in excess of that assumed in the limiting accident analysis. The staff finds the suggestions to be acceptable with respect to potential leakage from core spray piping replacements.
For core spray spargers, the BWRVIP stated that any leakage from the core spray spargers would not prevent injection of coolant inside the core shroud. However, a less effective core spray distribution may result in the loss of localized cooling of some fuel assemblies. The
3 BWRVIP does not believe that this is a concern for non-geometry critical (also known as geometry tolerant) plants. For geometry critical plants, the BWRVIP stated that geometry critical plants rely upon core spray distribution as part of their LOCA analyses. Therefore, any leakage from the core spray spargers should be shown to meet the minimum ECCS long-term flow per fuel bundle per the original design or perform a plant-specific analysis to show compliance with NRC regulations. The staff has not accepted the concepts of geometry critical and geometry tolerant plants, as discussed below. The staff concluded in its SE on the BWRVIP-18 report that licensees should evaluate the amount of leakage and its effect on localized cooling of the fuel and establish that leakage from core spray spargers is not a concern on a plant-specific basis.
i The BWRVlP-16 and -19 reports states that for core spray sparger replacements on non- l geometry critical plants, the design of the repair shall retain the number, type and aiming of the spray nozzles in the origir.a! design, but it is acceptable to partially block spray nozzles as required by the replacement design. However, an evaluation of the acceptability of the partial l blockage on the overall system function shall be performed. The report further states that, for l geometry critical plants, the core spray distribction over the core after the sparger replacement shall be at least as good as the original design unless plant-specific accident analysis justifies otherwise. The staff has concluded that core spray sparger replacement and spray distribution for all BWR types should be consistent with the original design basis. Plant-specific analyses should be used if the original design basis cannot be maintained. ,
The BWRVIP-18 report, "BWR Core Spray Internals inspection and Flaw Evaluation j Guldelines,"(Reference 4), defines geometry critical and geometry tolerant (non-geometry critical) plants as follows: ,1 Geometry Critical: These are plants where post-LOCA steaming is not sufficient, so maintaining sparger geometry is critical to assure that the analyzed minimum spray flowrate into any given fuel bundle is accomplished accnrding to the design.
Geometry Tolerant: These are plants where it has been staown thatpost-LOCA steaming of the waterat two-thirds core heightis sufficient to meet fuelsafetylimits, so spray distribution per the design is not essential. For such plants, it is only necessary to deliver core spray waterinside the shroud to maintain two-thirds core coverage.
In the ctaff's SE on the BWRVIP-18 report (Reference 5), the staff concluded that it is not appropriate to use the concept of geometry tolerant and geometry critical for the purposes of reducing the inspections of the core spray sparger or nozzle welds. The staff discussed this conclusion with the BWRVIP during a public meeting on August 20,1998, and the BWRVIP has agreed with the staff's position on the concept of geometry tolerant and geometry critical, and has informally informed the staff that future revisions to the BWRVIP-16, -18, and -19 reports will treat all BWRs as geometry critical.
As stated above, the BWRVIP-16 and -19 reports also incorporates the concepts of geometry tolerant (non-geometry critical) and geometry critical plants for core spray sparger replacement and core spray flow distributions. Basert on the conclusions of the staff's SER on BWRVIP-18, the staff does not believe the use of the concepts of geometry critical and tolerant is appropriate for core spray sparger replacement and core spray flow distribution. The staff believes that licensees should design replacements for the core spray piping and spargers that are consistent with their original licensing basis and design.
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2.3 Section 9.1, Materials This section provides acceptance criteria pertaining to the selection, procurement and manufacturing of materials to be used in the design of the intemal core spray piping an replacement. Specific requirements regarding the use of nuclear grade stainless stee 750, Type XM 19 or austenitic stainless steel materials are provided is this section.
In a response to the staff's recommendation in an RAI, the BWRVIP proposed a revision of section 9.1.4 by adding an additional reference of NLIREG 0313 Revision 2," Technical Re on Material Selection and Processing Guidelines for BWR Coolant Pressure Boundary Pip NUREG 0313, Revision 2 provides guidelines regarding acceptable measures to increase the IGSCC resistance in the austenitic stainless steel materials. The proposed revision is acceptable.
The requirements specifiad in Section 9.1 are designed to ensure that the materials used for the replacement components possess high resistance to intergranular stress corrosion cracking (IGSCC). These requirements are acceptable with the exception of the items discussed below:
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In Section 9.1.2, it is stated that " Materials shall be manufactured in accordance with ASTM or ASME specifications using ...." The words of " ASTM specification" referenced in this Section should be deleted since only the materials coverea by the scope of ASME Section ill, Material Requirements, are acceptable and, furthermore, not all ASTM materials specifications are covered by equivalent ASME Material Specifications.
However, it is acceptable if the referenced sentence is revised as " Materials shall be t manufactured in accordance with ASME or equivalent ASTM specifications using ...." '
- 2. In the third sentence of Section 9.1.2 regarding the use of attemative materials not covered by the scope of ASME Section ill Material Requirements, the staff recommends that the words "and approved by the governing regulatory authority" should be added to l the end of the sentence so that it would be consistent with the requirements specified in section 9.1.8.
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- 3. The note of Section 9.1 discussed the acceptance by the plant owner of specific l
exceptions to the documents of EPRI NP-7032, ' Material Specification for Alloy X-750 for
! Use in LWR Internal Components, Rev.1," and EPRI #84-MG-18,
- Nuclear Grade l Stainless Steel, Procurement, Manufacturing and Fabrication Guidelines." The staff l
recommends that the words "and the governing regulatory authority" should be added to l the end of the note to indicate that any exceptions to these documents require the l acceptance by NRC as well as the plant owner.
- 4. In Section 9.1.5, the rising-load test is waived and the requirement of cobalt control can be waived by the plant owner when procuring Alloy X-750 in accordance with EPRI NP-l 7032. In a response to the staff's concerns regarding these exceptions as discussed in i
the staff's RAI, the BWRVIP proposed a revision of section 9.1.5 by adding a cautionary note regarding minimizing the cobalt content; however, the appropriate cobalt limits are left to the discretion of the plant owner. The staff has determined that the revised version of Section 9.1.5 is not acceptable, since it still waives the requirement of rising load test and allows the plant owner to set the cobalt limit without anyjustification. The requirement c! rising-load test should be retained since this test is used to confirm that
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the subject materials have been properly heat-treated to the "ClB" condition. The condition is the only condition that is acceptable for use in the BWR environment. T is no other metallurgical test that can be used to confirm the "CIB" condition suc use of the sensitization test to confirm the acceptable metallurgical condition for the 3 series austenitic stainless steel. The requirement to minimize the cobalt conten X-750 is needed for ALARA consideration, because the cobalt content in Alloy X-generate oxidation products with a high level of radiation which is not desirable.
Therefore, the requirement of cobalt control should be retained in procuring Alloy materials. In a BWR report of "BWR Core Shroud Repair Design Criteria" which the NRC has recently approved for use, the requirements of the rising load test and cobalt control are not waived in procuring Alloy X 750 in accordance with EPRI NP-7032. ,
j 2.4 Section 9.2, Crevices This section requires that the crevice condition be minimized in the replacement design. Th requirement is acceptable because crevice condition is known to accelerate stress corrosion cracking and should be avoided in the replacement design.
2.5 - Section 9.3, Welding and Fabrication The requirements provided in this section are acceptable because these requirements are goo welding and fabrication practices and should be implemented to minimize the potential for stress corrosion cracking in the BWR environment.
i in the staffs RAI, the staff raised concems regarding the welding of heavily irradiated materials, because the industry experiences and laboratory testing results have shown that it is difficult to i
! produce a sound weld on such materlats. The staff recommended in the RAI that the 'weldability of such materials shoW "a demonstrated on a mock-up made of materials with similar level of
' radiation damage and helium content and add this requirement and any other available guidelines into section 9.3.7. In a response to the staff's RAI, the BWRVIP recommended that a '
cautionary note be added to Section 9.3.7 and leave the decision of whether to weld the heavily irradiated materials to the plant o mer. The BWRVIP's recommendation is based on the following considerations: (a) comprehensive guidelines cannot be provided at this time because of limited understanding of this issue; (b) there is no s.Jety concern in this issue because an unsound weld can be identified by post weld inspections and the unacceptable weld can be repaired or replaced by other attemative repair; and, (c) the mock up will not duplicate all the parameters that would influence the welding of irradiated materials.
The staff does not agree that the BWRVIP's recommendation is technically acceptable, because the post-weld inspection is designed to find flaws and is not capable of detecting any potential material property degradation resulting from welding of irradiated materials. However, the BWRVIP is presently cooperating with the staff in confirmatory research on the weldability of l highly irradiated materials. This research is expected to be completed in Fiscal Year (FY) 2000, l which will allow the staff to better determine if non-Irriadiated mock-ups will be acceptable.
i Therefore, umil this research has been completed, the staff's recommendation as stated above j should be added to Section 9.3.7 of the reports.
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2.6 Section 10.2, Pre- and Post Installation inspection The guidelines and requirements provided in the above e sections are acc exception that one additionalitem presented below which should be adde
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The post installation inspections of replacement anchorages, ents repl and new welds should be performed and meet the requirements in the B report, " Core Spray intemals inspection and Flaw Evaluation Guideline "
The BWRVIP 18 report should be referenced in Section n 10.2 to ensure t requirements stated in this section are consistent with 3.0 or .
those require CONCLUSIONS The staff has reviewed the BWRVIP-16 and 19 reports o e and finds that th reports is acceptcble for replacement and/or repair of the subject safe internal components, except where the staff's conclusions guidance, as differ from the discussed above and listed below. Specifically, the staff has not accepted the ncepts of geometry critical and geometry tolerant plants, as discussed in the staff's SER o BWRVIP-18 report (Ref 4.5). Based on the conclusions of the staff's SER IP 18, the core spray sparger replacement and core e for spray flow licensees should design replacements for the core spray piping and sparge with their originallicensing basis and design. This items discussed ab ove, and reiterated below. should a are consistentbe accounted ng the I
I impact of this leakage should be evaluated for nor conditions.
. e Licensees shouM evaluate the amount of core spray zed leakage and its e cooling on of the a plant specific fuel and establish that leakage from core spray sparger basis.
Core spray sparger replacement and spray distribution ould be for all BWR types s original design basis cannot be maintained. consistent e with the orig items 1-4 discussed in section 2.3 above.The materials p on of requireme Until the staff's confirmatory research on the weldability ras s of highlyirrad completed, the staff's recommendation is that the weldability of such m demonstrated on a mock up made of materials with similar level of radiatio amage and helium content. Further, this recommendation and be added into Section 9.3.7 of the BWRVIP reports.
any other available gu nes should Since the discussion of core spray distribution following ection a steam line br follow their licensing basis, the staff requirements is acceptable.
c censees concludes asis load to tha
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For core spray piping replacements (Section 8.1.3), the BWRVIP 16 report suggests two I
' ways to show that the postulated leakage is acceptable. The staff finds the suggestions to be acceptable with respect to potential leakage from core spray piping replacements.
The staff requests that the SWRVIP review and resolve the issues raised above, and incorporate the staff's conclusions into revised BWRVIP-16 and -19 reports. Please inform the
. staff in writing as to this resolution.
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4.0 REFERENCES
4.1 Carl Terry, BWRVIP, to USNRC, "BWR Vessel and Intemals Project, Intemal Core Spray Piping and Sparger Replacement Design Criteria (BWRVIP-16)," EPRI Report TR- i 106708, March 1997, March 18,1997.
4.2 Bruce McLeod, BWRVIP, to C. E. Carpenter, USNRC, "BWRVIP Response to NRC Request for Additional Information on BWRVIP-19," February 24,1997.
l 4.3 C. E. Carpenter, USNRC, to Carl Terry, BWRVIP, " Proprietary Request for Additional Information - Review of BWR Vessel and Internals Project Reports, 'BWR Core Spray inspection and Flaw Evaluation Guidelines (BWRVIP-18),' and ' Core Spray Pip:ng and Sparger Repair Design Criteria (BWRVlP-19),'(TAC Nos. M96219 and M96539),"
January 22,1997.
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1 4.4 J. T. Beckham, BWRVIP, to USNRC, "BWR Vessel and intomals Prohet, BWR Core Spray Intemals inspection and Flaw Evaluation Guidelines (BWRVIP-18)," EPRI Report ,
TR 106740, July 1996.
4.5 USNRC to Carl Terry, BWRVIP, " Safety Evaluation of the BWR Vessel and intamale Project BWRVIP-18 Report (TAC NO. M96219)," June 8,1998.
Principal Contributors: K. A. Kavanagh W. H. Koo J. R. Rajan C. E. Carpenter i
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