ML20236L888
| ML20236L888 | |
| Person / Time | |
|---|---|
| Site: | Palisades, Point Beach, Arkansas Nuclear, 07201007  |
| Issue date: | 03/06/1998 |
| From: | Howe A NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Haughney C, Shankman S, Sturz F NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| Shared Package | |
| ML20236J176 | List: |
| References | |
| FOIA-98-164 NUDOCS 9807130219 | |
| Download: ML20236L888 (4) | |
Text
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Allen Howe, A> /"JJ To:
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Date:.
3/6/9812:17pm u
Subjecf.:
Latest VSC-24 UT issues Yesterday, SFPO had two telephone calls with the VSC-24 Owners Group - VSCOG (ANO/
Palisades / Point Beach, SNC). In the calls, the VSCOG updated us on the status of the UT i
l development process using the P-scan system. This method involves a partial (-5') lift of the l
MSB in the MTC to gain access to the MSB shell side. The weld team described two issues, (1) i l
UT 'near field" effects and (2) accuracy of flaw sizing using the transducer selected, to the licensee so they could be prepared to address them during the inspection.
The VSCOG Indicated their dose assessment for the P SCAN UT inspection estimated a dose increase of -2 rem for each cask loaded. By comparison, the dose for the entire 1
loading process of the last VSC-24 cask loaded at ANO was 500 mrem. High gamma dose rates of ~10.7 rem /hr, unshielded, and ~1.8 rem /hr, shielded, were estimated on contact in the MSB/MTC. As stated above, access to the MSB shell from the side the requires the MSB to be lifted - 5 inches. The VSCOG was not satisfied with this significant increase in dose and they are looking at altematives. These dose estimates have given the VSCOG pause and as a j
l result the March 16,1998 inspection may be delayed.
One altemative yields an estimated per cask load dose increase of ~200 mrem. This method involves UT examination from the top, without a MSB lift, and without grinding the weld crown.
l This method is the TestPro ultrasenic inspection system from Structural Integrity Associates, Inc. So far, initial examinations had been encouraging. Testing at elevated temperatures is pending.
I plan to call the VSCOG spokesperson at 3:30 pm 3/6/98 for an update. I will advise you of the results.
CC:
LEK, CKB1, SCO, ENK, RWP i
e i
e Mall Envelope info:
(35002F90.A46 : 17 : 42080)
Subject:
Latest VSC-24 UT issues Creation Date:
3/6/9812:17pm j
From:
Allen Howe l
Created By:
WND1.WNP7:AGH1 Recipients Action Date & Time Post Office WND1.WNP7 CJH (Charles Haughney)
CKB1 CC (Charles (Ken) Battige)
EJL (Eric Leeds)
ENK CC (Elaine Keegan)
FCS (Frederick Sturz)
LEK CC (Lawrence Kokajko)
SCO CC (Stephen O'Connor)
SFS (Susan Shankman)
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f Call Summary: 3/5/98,10:30 AM EST, SFPO/ANO/ Palisades / Point Beach l.
ANO described the latest developments in the use of the P-scan system. Although examination performance was acceptable at temperatures ranging from room temperature up to about 175*F, accuracy was affected when scanning was done at 200*F. A-Scan data is shown during data acquisition, but not currently saved. It is possible to save A-scans, but it is not currently done.
THE VSC OG is considering use of the TestPro ultrasonic inspection system from Structural Integrity Associates, Inc. So far, initial examinations had been encouraging. The TestPro system a
uses th: Time of Flight Diffraction (TOFD) techniques with two transducers mounted on the top i
of the weld (P-scan uses a side mounted transducer). This method results in very accurate sizing of flaws, but alone cannot locate the flaw precisely in the radial direction (distance from outside of shell towards center of cask). Additional scans, using another technique, could pinpoint the flaw (s). No high temperature tests have been done with TestPro. No cask lift is necessary with TestPro since scans are done from the top of the weld, and no crown grinding is necessary.
TestPro records A-scans during acquisition for later analysis.
The UT procedure is in a final draft format; the majority is generic, but certain parts are tailored to the P-Scan /ANO site-specific items. It discusses process, qualifications, and so-called essential variables.
IMPORTANT POINT:
ANO indicated their dose assessment for the P-SCAN UT inspection estimated a 2 REM dose to personnel. (By comparison, the dose for the entire loading process of the last VSC-24 cask loaded at ANO was 500 millirem..NRC was surprised by this value, and asked for a call at 3PM on 3/5/98 to discuss this point further. The high dose rates, up to 10 R/hr, are a result of streaming when the afSB is lifted approximately 6 inches up from the MTC to allow access for inspection.
The following questions were brought up to the licensee so they could be ready to respond during the inspection, currently planned for the week of March 16,1998:
- 1. UT "near field" effects The structural-lid weld examination technique, as currently described (a 10MHz,0.5 in. diameter transducer) would result in exammation of the weld volume that was well within the near-field range. It is known in the UT industry that the characteristics of sound waves in the near field range are not well-behaved and that it is more difficult to obtain reliable and repeatable results from near-field examinations. From ASNT NDT Handbook on UT Volume 7, page 831, Second Edition "Within the nea field, the test information may not be reliable and the operator may w1mt to avoid testing with that range." Examinations within this range will need a high level of control on equipment and process to produm a reliable test. While UT examination in the near field is possible, it is not clear what measures have been taken to address UT examination in the near-field regime to assure reliable and repeatable examination results. The owners group should be prepared to address concerns with the near-field effects during the inspection.
ANSWER: They are aware of this, and it does not present a problem as 20 scans have shown repeatable results, and many nuclear UT inspections are done in the near field. Will discuss during inspection.
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- 2. Transducer size The size of the transducer and the resultant sound beam cross sectional area is much greater than most of the flaws that are being sized. It is known that better accuracy in flaw sizing is obtained with Ur equipment that produces a sound beam cross sectional area at the flaw location that is the minimum practicable. The owners group should be prepared to address concerns with the flaw sizing accuracy of the equipment selected for this UT examination technique.
Also, it might be a good idea for us to point out that any sizing errors (reported earlier to be minus 0.050, plus 0.100),
for better or worse, may be an artifact of the near field effects, as well as the beam diameter problem (s). At any rate, they should probably give this some thought and be ready to respond to any questions we raise pertaining to these issues during our inspection.
I ANSWER: Similar to above, aware of the situation, and will discuss response during inspection. The technique they are using is approved through EPRI/PDI and they can get information from signals ringing at the tip of the flaw.
- 3. Is the owners group adopting one examination method that will be uniformly implemented at the three sites or are l
licensee specific techniques planned? ANSWER: YES t
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