ML20125C777
| ML20125C777 | |
| Person / Time | |
|---|---|
| Issue date: | 12/09/1992 |
| From: | Hopenfeld J NRC |
| To: | Burdick G NRC |
| References | |
| NUDOCS 9212140072 | |
| Download: ML20125C777 (4) | |
Text
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Nowl fot NOTE TO: G. Burdick FROM :
J. Hopenfeld
SUBJECT:
Reply to your request for comments on Draft "RES POSITION ON STEAM GENERATO;l TUBE IffTEGRITY" by LC. Shao Based on certain data, discussed in items 1-8, the document concludes that 'it is reasonable to corunue operation for one fuel cycle with flaws greater than 40% through-wall at TSP intersections.' The document further suggests that " subsequent operation will require additional review after completion of one cycle and willinclude consideration of information developed at that time'.
GENERAL COMMENT
The information provided in items 1-8, of the subjec: document does not address the main issue concoming steam ganerator tube integrity which arose from recent operating experience with ODSCO. The issue is as follows:
Is it safe to operate plants where an accident such cs steam or feed line break may open existing but previously undetected cracks wh8ch will result in a significant primary-to-secondary leakage. Whether the leakage is signaicant or not would depend on whether the operator can stop the ieak before the RWST is depleted.
Degraded tubes also may cause a significant invease on risk from severe accidents.
The fact that cracks within the TSP can withstand the MSLB pressure and that their length will not become critical during one fuel cycle is not an indicat'on that they also will not leak. The Trojan burst test results show that three out of the L test specimen developed leaks at pressures, of 3300 psi, 7500 psi, and 550Gpse,. with an average depth of penetrations of 38%,58% and 72% respectively.
I Item (7) points out that the above specimens "have shown no leakage under normal operating or MSLB pressure conditions'. IT FAILS TO POINT OUT, HOWEVER, THAT THERE IS NO DATA WHICH WOULD ALLOW ONE TO RELATE THE ABOVE LEAKAGE WITH THE OBSERVED DEGREE OF DEGMDATION. In other words, if these specimen had undergone a more severe wall penetration would these specimens have leaked at 2600 psi.7. Considenng that the 21 specimen represent a sample of a population of R.000, the conclusions in (7) above are questionable.
The document ignores two other tubes which were pulled out of two US plants and developed leaks at PLB pressures. The leakage was at least an order of magnitude higher than under normai delta ps'. A third tube from a Belgian plant indicates a factor of eight increase iri lec.kage under SLB conditions, (see Mar. 23 memo). Theoretical
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considerations also indicate a factor of 1000 increase in Mkage under SLB conditions.
In conclusion, the absence of a deterministic and empirical models for these newly observed cracks precludes the conclusions reached in the subject document. The claim that the conclusions in item 9 are supported by items 18 could be considered valid only if one ignores the available data which indicate that higher than normal leakage will-occcur at SLB pressures even if the tubes do not rupturs Finally the justificaticns for any plant operation should not be based on staff opinions or published data on SCO.
SCC is a semi empirical art, in the absence of applicable database eher routes of approaching the problem should be considered.
The justification for operating with cracked tubes should be based on what procedures would this operator follow given certain primary to secondary leak and a MSLB between the containment and the MSIV.
These justifications should clearly demor$ strate compliance with 10CFR100.
I beleive that the staff can more property judge operator action than predict localized corrosion behavior.
SPECIFIC COMMENTS Item 1.
7,e EDM irtiated grooves studies provide some measure of the ability of the tube to resist rupture given certain kncwn wall imperfections. It bears lide relation to how ODSCC forrt, propagate and leak in steam generator environments.
9 Item 4 l-This definition of "significant' is questionable. It makes no difference whet..er the cracks -
extend beyond the TSP if they leak at the gap. -lt appears that operators rely on such
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leakage because they lowered the leakage requirements during normal operations.
l Unless one can show that the TSP will cause cracks to plug and they will remain plugged L
under MSLB pressures the above definition may lead to confusion.
l l.
The statement that " upper bound laboratory ODSCC....
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would not oe. expected to' occur during one fuel cycle " is not' supported _ by data. The -
3 document should compare and present plant and laboratory data with regard to stress R
. intensities and environments before making such claims.
1 Item 5 The high frcquency quoted,6.8x 10-4/RY contradicts the statement that " it is reasonable"
, item 9, because this frequency would result in a core nelt probability of 6.8x 10-3/RY -
with containment bypass as discussed in the March 27 Memo. The above number is considerahly higher than present safety goals.
.l The statement that the key initiating event for SGTR is MSLB is incorrect when taken in -
the context of the entire document. Item 6 contradicts this statement.
Item 7 i
Although this item is conact, as stated, it presents only-part of the data. As already discussed, three tubes leaked at Trojan. Three tubes from other plants' also leaked at MSLB pressures. Rudimentary consideration dictate that leakage increases when delta j
p across the wall is increased.
H
- l Item 8 The lengthy discussion of uniform thinning only confuses-the main issue. There are several ways that the reduction load bearing capabilities of _ a component due to-cortosion can be accounted for there is nothing special about these equations. The ASME L
-code takes this into account. The main problem here is LOCAUZED corrosion with an U.NKNOWN ATTACK RATE.
item 9 L
A discussion should be added of the type of new information which is required for the
" additional review" to justify subsequent operations.
l i-ATTACHMENT 1 n
Second item : Dr. Instead of Mr. or just Hopenfeld The following is missing:
On Sep? 11,'1992 J. Hopenfeld filed an addendum to the March 27,1992 concluding:
that " strong coupling exists between hot leg mass flow, SG tube leakage and crack-w
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~d On Sept 11,.1992 J. Hopenfeld filed an addendum to ths March 27,1992 concluding that
- strong coupling exists between hot leg mass w, SG tube leakage and crack propagation. If confirmod, such a relation between system behavior and undetected tube defects may cause small leaks to quickly enlarge and results in a MULTIPLE TUBE RUPTURE BEFORE THE RCS IS DEPRESSURIZED BY FAILURE OF THE SURGE LINE.
THE RESULTANT CONTAINMENT BYPASS WILL INCREASE T E S URCE TERM."
J. H e
CC; P. Norian, Gm. Mazetis, W. Minner,. Beckjor e
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