ML040770261
| ML040770261 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 01/15/2004 |
| From: | Millar D Entergy Operations |
| To: | Alexion T Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML040820923 | List: |
| References | |
| Download: ML040770261 (10) | |
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fThomas Alexion - Draft resp-onses to Materials & Chemn Branch Pane 1 1 From:
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' mMILLAR, DANA.<DMILLAR @entergy~comn>
"'twa~nrc.gov"' <'twa~nrc.gov>
1/1 5/04 2:13 PM Draft responses to Materials & Chem Branch
- Tom, Attached are Entergy's draft responses to the Materials and Chemical Branch RAls related to ANO-11 Metamic.
Dana
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Draft responses to Materials & Chem Branch 1/15/04 2:10PM "MILLAR, DANA" <DMILLAR@enterav.comn>
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DMILLAR@cntergv.com Recipients nrc.gov owf4_po.OWFNDO TWA (Thomas Alexion)
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I i Thomas Alexion! - NRC Chemn Draft.doc Page I1 Thomas Alexion - NRC Chem Draft.doc Page 1 Page 1 of 6 Response to Request for Additional Information Materials and Chemical Engineering Branch Question 1:
In its review of the topical reports submitted on August 8, 2002, supporting the use of MetamicO in the SFP, the staff conditioned the use of this material on the implementation of a coupon sampling program to ensure consistent material performance with that described in the reports. The condition is based on the first-time use of this material in the SFP environment and the limited operating experience supporting its performance. In addition, the staff requested that the details of this program be provided in applications referencing the topical reports.
The licensee, in its license amendment request dated April 2, 2003, referenced the topical reports and committed to establishing this program to monitor the physical and chemical properties of the material over time.
The staff requests, upon approval of the license amendment request, the licensee to implement the Metamic!6 coupon sampling program as a license condition requiring prior notification and approval by the staff for any changes to the approved program.
The basis for this request is found in Section 4.0 of the staff's safety evaluation report of the topical reports dated June 17, 2003.
Response 1:
Need more discussion with NRC Question 2:
The licensee responded that preliminary tests with post-extrusion glass beading showed absence of any significant pitting corrosion after an extended period of soaking in heated water. In addition, the licensee indicates that a test report will be finalized after the neutron attenuation test data can be fully analyzed.
The staff requests the licensee to describe the pitting corrosion observed and if such pitting occurred preferentially.
In addition, the staff requests the licensee to provide details on the results and conclusions of the test report referenced in its response.
Response 2:
Corrosion tests on Metamic are still underway and we believe it would be premature to prepare a report at the present time. So far we have not seen any difference between the EPRI report and the testing performed to date. The testing which has been performed is discussed below:
Preliminary tests - These tests used eight Metamic coupons with 31% B4C, in a 45-day soak test in demineralized water at 170 "F.
The following tests have been completed or are underway:
- l. Thomnas Aiexion' - N-RC dhe-n Draft.doc Page' 2-1 I.
Thomas Alexion - NRC Chem Draft.doc Page 2j Page 2 of 6
- 1) 45-day soak test in demineralized water at 170 'F has been made with 4 large (10"x5") coupons of 25% B4C content. These coupons also showed no evidence pf swelling, pitting or other corrosion mechanisms. These tests were intended primarily to confirm the absence of any blistering or swelling (as has been observed in Boral absorbers).
- 2)
Special Test - Two coupons were exposed to a water solution of sodium chloride at 170 'F in an effort to intentionally induce pitting. Some pitting was created in this manner. Comparison of pre-and post-exposure neutron attenuation measurements showed no loss of neutron absorption capability. These measurements suggest that there is no significant loss of neutron absorption capability, even if pitting were to occur.
- 3) 30-Day soak test in demineralized water at 200 'F were made on 32 coupons of 25% B4C Metamic. The first test period of 30 days has recently been completed and the coupons will be replaced and exposed for an additional 30-day period. Initial examination of the coupons after the first 30 days of exposure showed no evidence of pitting or other corrosion mechanisms.
Items 1 and 3 used coupons from MetamicS panels manufactured with the extruded
'bloom" stock cleaned by glass beading.
Neutron attenuation measurements were made on several coupons from the test cited above and showed no loss in B10, the important neutron absorbing nuclide. To date, with "cleaned" Metamic samples, no corrosion, pitting or loss in B10 content has occurred.
The corrosion test program is on going to assure a complete investigation supplementing the EPRI work. The 30-day soak test will be returned for an additional 30-day test at 200 OF. In addition, a 30-day soak test in a boric acid solution (2500 ppm) at 200 'F will be started soon.
The tests already performed and those still underway are intended to simulate long-term exposure by using high temperature water (or boric acid solution) to accelerate any corrosion behavior.
Question 3:
The licensee indicates that after the rolling and sheering processes, on an as needed basis, the Metamicd panels will be cleaned by an appropriate process (glass beading, aluminum powder blasting, or cleaning with a dilute nitric acid rinse).
The staff requests the licensee to discuss the criteria by which, the panels will be cleaned by one or more of the processes listed.
Response 3:
Glass beading of the extruded "bloom" stock has removed the ferritic inclusions on the surface of the work piece. These inclusions were the primary source of the surface
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- age3, Page 3 of 6 impurities that caused pitting in some of the final hot-rolled Metamics panels in the EPRI tests. Scanning electron microscope (SEM) examination of samples of the as-manufactured Metamic panels showed very few ferritic impurities remaining on the surface. However, current procedures call for cleaning (wiping down) with a solution of nitric acid at a pH of 0
- 8 - 1.2. This procedure has been effective as evidenced by the initial corrosion tests discussed in response 2 above.
Question 4:
The first bullet indicates that the coupons will be mounted in stainless steeljackets simulating actual insert design.
The staff requests the licensee to discuss the fabrication materials of the coupon tree to ensure that it does not adversely affect the coupons.
Response 4:
The Metamic insert frame material, which is in contact with the Metamic panels, is made of 26 gauge 304 stainless steel. The coupon tree materials that will be in contact with the Metamic coupons is 26 gauge 304 stainless steel. The coupon tree frame is also made of 304 stainless steel.
Question 5:
The first bullet indicates that the coupon tree will be located in the Region 2 racks.
The staff requests the licensee to discuss the criteria for selecting Region 2 racks for coupon placement in light of the April 2, 2003 cover letter which states that a portion of the current SFP Region 2 (which has no poison material) will be converted into a Region 3 with MetamicO inserts.
Response 5:
The ANO-1 current Region 2 consists of 6 spent fuel storage racks that have full length uncovered flux traps. These racks do not have any poison material. Two of these racks will be converted to Region 3 racks by the insertion of Metamic panels into every flux trap in these racks. The Region 1 racks currently contain Boraflex as a poison material and the flux traps in these racks sealed. The only racks left that can accept a coupon tree in a flux trap region is the Region 2 racks.
Question 6:
The second bullet describes the techniques for measuring boron carbide content of the MetamicO panels and coupons.
The staff requests the licensee to clarify that the procedures governing these tests are completed under a QA program.
'[ Thma exion - NRC cie~m br'aft".doc s
A o NC Ce Page 4 1 Page 4 of 6 Response 6:
The testing for initial B4C content in the Metamic panels and the Metamic test coupons is performed under a QA program and the testing is performed using written procedures.
Question 7:
The third bullet describes the means by which scratches will be simulated on the coupons.
The staff requests the licensee to describe the materials of the tool used to simulate the scratches to ensure that trace materials left behind do not adversely impact the coupons and accurately represent the scratching which may occur in the panels.
Response 7:
The scratches on the coupons will be formed using hardened materials. The tools will be made out of carbon steel, stainless steel, and Metamic. The scratches will not be cleaned after being applied because the corrosion affects of leaving the trace material in a scratch is what will be investigated.
Question 8:
The fourth bullet indicates that the panels will be examined on a two year basis for the first three intervals and increasing intervals over the service life of the inserts.
The staff requests the licensee to provide the length of each interval and a discussion on the rationale and criteria by which increasing intervals are determined. In addition, the staff requests the licensee to indicate the maximum length of time for the interval Response 8:
All the testing performed to date was performed under very harsh conditions that are more sever than the operating conditions that will be observed within the spent fuel racks. The Metamic coupon surveillance program will be used to monitor the effects pool chemistry in conjunction with irradiation has on the Metamic panels. Based on the accelerated corrosion testing performed at 195 0F, Metamic coupons did not exhibit any detectable signs of corrosion effects until 4,124 or more hours transpired. For the operating condition in the spent fuel pool (SFP) this would equate to a little over 2 years of operation. This is why a two year operating scheme was chosen for the first set of coupons. A time duration of 2 years will also assure freshly discharged assemblies would be placed next to the coupon in order to capture the irradiation affects on the Metamic during an outage. Pulling of the first 3 coupons in 2 year intervals will supply a sufficient base line to determine if there are any adverse corrosion affects occurring.
After the first 3 coupons are tested the sampling period will be increased to 4 years and then finally to 5 years. The 5 year is the maximum sampling period that will be used.
I Thomas Alexion - NRC Chem Draft.doc Pa
'I.Thomas Alex-ion - NRC Chem Draf t.doc Page 5 I Page 5 of 6 Five years is the maximum because it equates to the maximum time tested in the acceleration corrosion testing which was 9,020 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br /> based off the SFP operating conditions. Provide below, Table R8.1 summarizes the sampling period for the Metamic coupon program. The number of coupons was based on the testing the Metamic for at least 40 years which bounds the current operating license for ANO-1.
In general the Metamic coupon testing program is very similar to testing programs used on Boral surveillance coupon testing programs.
Table R8.1 Sample coupon Measurement Schedule Coupon Duration in SFP Sampling Period Years Years 12 2
2 4
2 3
6 2
4 10 4
5 15 5
6 20 5
7 25 5
8 30 5
9 35 5
10 40 5
11*
Spare At Any Time 12*
Spare At Any Time
- The last two coupons are not required. These coupons will be pulled only if additional testing is desired.
Question 9:
The fifth bullet indicates that thickness measurements will be monitored for bulging and swelling.
The staff requests the licensee to describe over what area and/or sections on the coupons this measurement will be completed.
Response 9:
Prior to placing the coupons in the ANO-1 spent fuel racks, thickness measurements will be made in five procedurally defined locations. Once removed thickness measurements
Thotas Alexion-NRC Chem Draft.doc Pageg 61 Page 6 of 6 will be performed in the same locations as the original measurements.
Question 10:
The fifth bullet indicates that neutron attenuation or destructive chemical testing is an option to determine boron content.
To ensure a sufficient number of coupons for the service life of the inserts, the staff requests the licensee to clarify if any coupons are replaced after the surveillance and, if not, to indicate the number of coupons used in light of the surveillance frequency discussed in the fourth bullet and Question 7.
Response 10:
Placing coupons back on the coupon tree will be at the discretion of the reviewing engineer. If the integrity of the coupons is compromised or if the contamination levels are extremely high, the coupons will not be placed back on the coupon tree. As discussed in response to question 7 there are a sufficient number of coupons to last the existing operating life of the plant even if the coupons are not reinserted back into the SFP.