ML20064L340
| ML20064L340 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Crane |
| Issue date: | 05/19/1982 |
| From: | Johnston W Office of Nuclear Reactor Regulation |
| To: | Novak T Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML082180535 | List:
|
| References | |
| FOIA-82-261 NUDOCS 8205280533 | |
| Download: ML20064L340 (5) | |
Text
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n,4 3-pg.c l ;c e ' ;.g C, 'T MEMORANDUM FOR:
Thomas Novak, Assistant Director R^u
" A,y g g N... for Operating Reactors ~
__a.. m a., Divjsion of Licensing 1;
' _ 7. gy FROM: itT '-
William V. Johnston, Assistant Director
.,J-Materials & Qualifications Engineering Div,ision of Engineering n
SUBJECT:
STAkFEVALUATIONOFTMI#1 STEAM GENERATOR CORROSION PROBLEM
'We have determined that the subject problem constitutes an unreviewed a
safety question and recommend that formal staff review be required.
a Our determination is based on four primary factors, as follows; 6
1.
Uniqueness and extent of the S.G. corrosion damage.
2.
Potential for this type of corrosion to affect other primary pressure boundary materials.
3.
Uniqueness of the repair method which is proposed by GPUNC.
4.
Unpredictability of ECT in detecting and quantifying this type of corrosion.
In all likelihood, the GPUNC program will answer the questions which are necessary to ensure that a significant safety hazard does not exist.
Enclosed is a more detailed discussion of our rationale in support of this recommendation.
W.A$ w +
A William V. Johnston, Assistant Director Materials & Qualifications Engineering Division of Engineering
Contact:
C. McCracken Ext. 28595 0
cc:
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zwe:v _ _. The potential for TMI No.1 S.G.
ATE _. 4 ire,Mif;,~;,'Unreviewed' Safety Question
' Corrosion Problems to Constitute an 9 -
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' The'pEoposed.Yepair b/ THI-1. ' to' resol' e their'st'cani generator problems v
appears to be rea 1.'yl@g7syM, sonable.
Basically,.they are'in the process of identifying:
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The, extent"of degradation in the S.G. 's.
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'[~ThEextdn'"oi ilegradation, if any, in the remainder of the reactor 2
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yleanup techniques to remove the causative agent (s) and
- 5. ' Optiinum S.G. repair techniques.
However, we bel'ieve there are a number of issues regarding the program which should be formally reviewed by. the staff.
Our reasoning in deciding that fonnal staff review is r6 quired is based on three major factors.
A.) To the extent that we have not experienced this type of behavior before, the corrosion mechanism is unique, thus the staff has not rev.iewed the potential consequences of additional operations sub-sequent to repair of knom. defects. Particularly, the potential for this type of corrosion to rapidly progress upon restart and adversely affect the S.G. primary pressure boundary.
B) The potential for this type of corrosion to adversely affect other primary pressure boundary materials.
C) The proposed S.G. tube repair technique, although having a similarity to some past repair techniques is in itself unique.
We consider the existance of a type of corrosion which has extensively degraded the steam generators, to also have the potential to degarde other reactor coolant system materials.
In addition, the licensee proposes to employ a unique repair technique.
We believe that the combination of all these becomes an unreviewed safety question.
As stated at the beginning, the program which GPUNC is conducting' appears reasonable.
In all liklihood, the GPUNC prcgram will answer the questions which are necessary to ensure that a significant safety hazard does not i
f exist.
Based on our knowledge to date, we have the following comments and/or concerns:
)
1.
Eddy current test requirements in the plant technical specifications a
and in the ASME code are by themselves inadequate to assure that (U
a meaningful inspection will be perfoTmed, given the nature of the
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c6rrosion'inechSnism'which exists at TMI-1.
The licensee's inspection
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2.'. Licensee, which,is the required tube repair method and specified inis" proposk plugging the pl. ant Technical Specification.
Thus, some modification of the plant Tech. Specs. would be necessary.
3.
The proposed repair technique involves a leak limiting rather than j
a leak free seal against primary to secondary leakage.
Because the expansion joint seal will function as the primary pressure boundary for as many as 20,000 tubes, leakage characteristics under normal and postulated accident conditions should be established by test.
Testing should include expansion into dirty crevices.
4.
The staff has some questions pertaining to the proposed repair.
e For example, will pre-existing cracks on the repair process itself t
result in a significant relaxation of tube preload?,1f so,
- s excessive compressive loading may result upon heatup of the plant which could lead to bowing or local buckling which could f;
cau'se new corrosion initiation sites.
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The corrosion mechanism is unique, apparently very fast acting, I
and not well understood.
The licensee's recovery program should l
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be closely reviewed by the staff to establish that there is adequate assurance against rapid failures occuring upon plant y
restart.
In addition, some licensing actions may be necessary, such as (a) more restrictive limits on primary to. secondary leak.
(Note the current 1 gpm limit is the most liberal in the PWR industry) and (b) frequent shutdowns for inspection as part of the restart program.
Considering the above listed concerns, we believe that specific staff review and concurrence is required at least in the following areas:
j 1.
Review of ECT data and scope of the inspections performed to determine that indications outside the tubesheet have been adequately characterized and addressed in the repair program.
2.
Review of ECT data and basis for rolling / plugging various tubes.
Including an assessment of tube relaxation due to cracking or the repair technique (if tubes have been relaxed from tension due to cracking, excessive compressive loads may exist on restart).,
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analytical and test yerification program,
4.. Review of.,the, basis for and materials. selected for primary side r -Q
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a examination to detect the presence on corrosion on other pressure boundry inaterials.. Also, an evaluation of the examination techniques to determina the presence of corrosion in these materials.
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{uj The staff should be present during examination of some pre-selected primary system materials.
!h Review of test data which supports the method selected for sulfur d
5.
removal froin system surfaces or conversely, the data which demonstrate
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that removal is not necessary.
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a Review of the current Tech. Spec. limit (1.0 gpm) for primary 6.
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to> secondary leakage to determine the impact of operation with t
up to that volume of leakage and whether it adequately supports j
the leak before break objective.
Review of the restart program to ensure that' sufficient check points
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e are included to detennine that excessive primary pressure boundary 1
At least degradation does not occur during subsequent operations.
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the following general type of program would seem to be prudent.
i a) Perform a series of leak checks utilizing nitrogen, helium i
etc. prior to pressurization.
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b) Conduct a hydrostatic test b
1 c) Perform a full temp. and press, hot functional for two to three weeks. Then, shutdown and ECT a selected number of tubes to ensure that excessive degradation is not occurring.
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d) Operate for 30 to 60 days.
Then, shutdown and ECT to assess the progression of degradation.
e c) Assuming no excessive degradation in "d" above, operate for j
150 to 210 days.
Then ECT again.
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f) During refueling, ECT and examine additional primary system materials for evidence of corrosion.
If no new or excessive corrosion is found, return to normal reg. guide test frequencies.
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