ML20236H435
| ML20236H435 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 07/31/1987 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| IEIN-86-049, IEIN-86-49, NUDOCS 8708050188 | |
| Download: ML20236H435 (18) | |
Text
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~. TENNESSEE VALLEY AUTHORITY CH ATTANOOGA. TENNESSEE 37401 SN 1578 Lookout Place JUL 811987 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C.
20555 Gentlemen:
In the Matter of
)
Docket Nos. 50-327 Tennessee Valley Authortty
)
50-328 SEQUOYAH NUCLEAR PLANT (SQN) UNITS 1 AND 2 - REVISED CABLE TEST PROGRAM
References:
1.
Letter from B. J. Youngblood to S. A. White dated January 15, 1987 2.
Letter from B. J. Youngblood to S. A. White dated March 9, 1987
- 3.. Letter from R. L. Gridlcy to NRC dated April 8, 1987 The purpose of this letter is to provide a revised program to resolve the NRC's concerns relative to cable pullbys, jamming, and the. lack of support of vertical cable runs with 90-degree condulets at the top of the run. This revised program supersedes the original cable test program as submitted in reference 3.
Following submittal of the proposed program on April 8, 1987, TVA began the investigations and analyses to determine the " worst-case" conduits to test for the issues of cable pullbys and jamming.
The results of.this
-review indicated that a large portion of'these conduits terminated at, and/or ran above, electrical equipment, which is-part of the' Reactor Protection System (RPS) or Emergency Safety Features Actuation System (ESFAS). Because of the conduits' configurations and their orientation with respect to this essential safety-related equipment, it was determined by TVA that the introduction of water to these conduits, as stipulated in the original proposal, could jeopardize the overall safety of'an operating plant. TVA reevaluated the necessity, and on a case-by-case basis,:the prudence of attempting to introduce water into each conduit.
.In parallel with the above reviert for cable pullbys and jamming, TVA proceeded with implementing the test program for the issue of vertical cables supported by 90-degree condulets.
The testing was conducted in accordance with the program outlined in attachment 4 of reference 3.
As has been widely discussed, several anomalies were noted during this testing. A detailed presentation of the test results and the further investigations to determine the cause of the anomalies were presented at 8708050188 870731 g.
DR ADOCK 05 g7 An Equal opportunity Employer
- j
. <JUL 311987 U.S. Nuclear Regulatory Commirsion the July 13, 1987 meeting between TVA and NRC in Bethesda, Maryland.
)
Additional testing will yet be performed in the field on silicone rubber insulated cables.
The purpose of this testing is to confirm the nature of the damage noted during the previous test.
The complete test results, as well as the documented additional investigations and analyses performed by TVA and the University of Connecticut's Electrical Insulation Research Center, will be forwarded via a separate letter to NRC.
Preliminary conclusions from this investigation, which were subsequently l
substantiated, also raised the concerns on the validity and applicability of the original test parameters.
In particular, it was apparent that the test voltages utilized were higher than necessary to verify the integrity of the cable.
In addition, this testing, which was performed without the introduction of water, was able to detect damage that was insignificant when compared with the type of damage postulated in the technical evaluation report (TER) for pullbys and jamming. Previously, it had been inferred that such damage could be detected by de high potential testing only in the presence of water.
As a result of the above, TVA concluded that continued testing, conducted at the original parameters, could potentially impact plant safety and, furthermore, could result in the replacement of acceptable cable with no increase in plant safety.
The revised test program maintains the goals of the original proposal and consists of condecting in-situ nondestructive tests on representative worst-case cables.
In evaluating this cable test program, TVA requests that NRC consider those bases for it that are listed in enclosure 1.
This program will support the adequacy of SQN's installation practices and will verify the performance capabilities of the cable system in view of the concerns.
The proposed criteria for cable selection, testing, inspection, and acceptance for cable pullbys, jamming, and cables support by 90-degree condulets are provided in enclosures 2, 3, and 4 respectively.
In addition to the program described herein, a cable test program will be l
established that will be consistent with Inspection and Enforcement (IE) i Notice 86-49.
The program will also address low-voltage cables.
The I
purpose will be to demonstrate margins above the system design basis.
l This program will be described to NRC within six months after restart of SQN unit 2 and will be implemented by the end of the SQN unit 2 cycle 4 refueling outage.
I J
Very truly yours, TEN E EE Y AUTHORITY I
L R. G idley, Dir>ctor i
Nuclear Safety and Licensing Enclosure; cc:
see page 3
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p.
w e
U.S. Nuclear Regulatory Commission hk $1 %[
cc (Enclosures):
Mr. G. G. Zech Assistant Director 4
for Inspection Programs Office of Special Projects U.S.. Nuclear Regulatory Commission 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia.30323 Mr..J. A. Zwolinski, Assistant Director
(
for Projects' Division of TVA Projects Office of.Special Projects U.S. Nuclear. Regulatory Commission 4350 East West Highway EWW 322 Bethesda, Maryland 20814 Sequoyah Resident Inspector a
.Sequoyah Nuclear Plant 2600 Igou' Ferry Road Soddy Daisy,. Tennessee 37379 1
t
/
li t-
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4 ENCLOSURE I SEQUOYAH NUCLEAR PLANT BASIS OF THE REVISED TVA CABLE TEST PROGRAM
- 1.
The SQN conduit and cable configuration does not significantly differ from other plants of its vintage.
In many respects the installations reflect conservatism such as the use of numerous pull points and short conduit runs.
The walkdowns performed by TVA confirmed these SQN installation practices..This should be considered when determining the extent of testing required for resolution of issues on SQN.
2.
Recent interviews of electricians who had actually performed the cable installation at Sequoyah, conducted by the NRC/ Consultants, indicated a thorough understanding of the cable installation process and the relevant concerns.
These interviews substantiated conformance to proper construction practices used throughout the industry and utilization of the engineering approved installation procedures and specification and confirmed the presence of a Quality Control Inspector on all Class 1E cable pulls.
In addition, the close working relationship between construction and engineering was outlined including the evaluation made before each Class IE pull to determine the best method of installation, which included determining-the direction of the pull and the need for manual assistance at pull points to reduce tensions.
The testimony in these interviews was contrary to Watts Bar Nuclear Plant employee concerns in this area.
3.
The test voltage stress proposed by TVA (240 V dc/ mil) is in accordance with the recognized industry standard test (IEEE 383-1974 Section 2.3.3.4) for determining that cables are adequate to perform their intended Class lE function. The actual test voltage is based on the SQN specific minimum environmentally qualified insulation thickness for the i
voltage rating and insulation type and manufacturer.
This takes into i
consideration the fact that any greater thickness of insulation on these l
low-voltage cables is provided for mechanical purposes only.
This test therefore accounts for the known and accepted reduction in cable dielectric strength because of the normal rigors of shipping, handling, installation, and operation, while confirming the level of integrity previously demonstrated as sufficient for electrical and qualification purposes during the equipment qualification testing.
This test voltage was selected over the Insulated Cable Engineers Association (ICEA) factory i
voltage since testing of installed cables at the factory voltage levels 1
exceed! manufacturers' recommendations for installation and maintenance l
proof-testing. As such, use of the factory test voltage at this stage in the life of SQN cables may damage cables that are otherwise acceptable and l
inhibit a toot cause determination of any test failures.
1 4.
The in situ dc high-potential test proposed by TVA does not degrade or i
damage the cables in question and therefore allows for determination of the true cause of any test failures.
IEEE 400-1980 recommends this type of testing not only for determining the present operating condition of the cable but also for detecting cables that are approaching failure.
This test method was previously utilized at Grand Gulf and' accepted by the NRC as a method to determine the existence and extent of cable pullby damage.
5.
SQN has completed tests following the original installation on its cable system that are consistent with current day industry practices and I
establish the adequacy of the installation.
I i
i ENCLOSURE 2 SEQUOYAH NUCLEAR PLANT CABLE PULLBYS Cable Selection Criteria The total population of conduits containing safety-related circuits at SQN through which one or more cable pulls subsequent to the_. initial installation have' occurred will be identified and screened using the criteria outlined below.
The purpose of the screening process is to identify a. population of conduits that have some credible chance of.
having sustained conductor insulation damage because of pullbys.
Within this bounded population, a further screening will be performed to create additional subpopulations consisting of 20 conduits each.
The first H
group of 20' conduits will represent the " worst" (i.e., highest pullby damage potential) conduits in the screened population; the second group of 20 conduits will represent the second worst group of conduits and so forth.
For the purposes of this evaluation, the representative worst-case conduits and' cables will be considered to be any that meet, or come closest to meeting, the following:
1.
The conduit contains a minimum of seven cables.
2.
There were at least two separate pullbys in the conduit.
3.
At least three polyvinyl chloride (PVC)-jacketed cables were present in the conduit before the final pullby.
4.
The initial pull and at least two pullbys were made before Polywater J was used as a lubricant (August 1984).
5.
The total length and number of bends between a set of adjacent pull points exceed or come closest to exceeding the requirements of G-38 Appendix F.
For the purposes of this evaluation, straight through.
condulets ("C" type) will not be considered as pull points.
6.
The conduit.contains at least two conduiets.
7.
Preference shall be given to those conduits that meet all of the above and any or all of the following:
4 a.
At least two of the pullbys made before August 1984 contained a minimum of two cables with hypalon or chlorinated polyethylene 1
(CPE) jackets.
b.
If it is determined through analysis that any of the cable pulls j
required mechanical assistance.
c.
The length of the conduit between potential lubrication points exceeds the requirements of G-38 Appendix F.
. d.
If the direction of pull of any of the pullbys is determined and the conduit bends were near the pull point (i.e., end of pull).
e.
If the direction of pull of any of the pullbys is determined and the first portion of the conduit was an upward or horizontal section such that lubricant could not be poured into the condult.
Implementation of the above criteria will be documented in a calculation.
Cable Test and Inspection Criteria As stated by NRC in reference 1 identified in the letter, the predominant I
concerns during cable pullbys are for saw-through and mashing of the jacket and insulation.
In all cases, any potential damage would occur to the jacket first and to the insulation only if the protective jacket had been totally compromised in the area of concern.
The postulated failure mode is the degradation of dielectric properties because of reduction in insulation wall thickness, perhaps influenced by the presence of moisture.
The following test program is specifically designed to identify if such a potential condition exists.
Sampling will begin by selecting a random sample of 15 conduits from the worst of the subpopulations of 20 conduits.
This sample size is sufficiently large to provide 95-percent confidence that no greater than 5 percent of the conduits in the first group contain cable damage discernable by the test method being employe<., provided that no damaged circuits are detected in the sample.
1.
After having randomly selected the 15 conduits from the worst of the subpopulations of 20 conduits, the installed configuration of the conduits shall be reviewed on a case-by-case basis to determine the feasibility of introducing water into, and removing it from, the conduit system without compromising equipment integrity or personnel safety.
It is preferred that all sections of all conduits be subjected to the water injection.
However, water will not be introduced into any conduit segment that could result in jeopardizing plant safety by compromising equipment integrity or personnel safety.
In addition, water will not be introduced into any conduit segment from which it cannot readily be removed.
The justification for not introducing water into all sections of all conduits shall be documented.
2.
All sections of each cond/it, except those for which wetting has been documented as a plant safety concern, or from which water cannot readily be removed, shall be subjected to the introduction of ordinary tap water. As a minimum, portions of three conduits shall be tested in a fully wetted condition.
The purpose is to ensure, as a minimum, that sufficient water is introduced so that moisture is present along the entire surface of the installed cables in that conduit segment. A fully wetted condition shall be considered to have been achieved when water injection is accomplished in one of the following manners:
i
. a.
Water is injected slowly into the conduit segment at a rate faster than it is lost through conduit openings or connections untti the cables in that segment are initially submersed.
It is not intended or expected that the cables will remain submersed throughout the test.
b.
Water is sprayed into the conduit segment under pressure at all conduit segment openings such that the water spray cascades down over the installed cables.
The water spray shall be maintained at each injection point for a minimum period of 2 minutes.
3.
Each conductor shall be subjected to a 5-minute dc high-voltage test at 240 V/ mil of insulation (per IEEE 383-1974, Section 2.3.3.4).
For the purposes of this test, the voltage may be based on the minimum SQN environmentally qualified insulation thickncss for the voltage rating and insulation type and manufacturer.
These voltage values are shown in enclosure 5.
Testing on the first of those cables, in conduits which will be wetted, will commence within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of completion of the water injection.
The test will be performed between each conductor and the remaining conductors in the conduit and the conduit tied together and grounded.
For shielded cables, the test will be performed between each conductor and the remaining conductors in the conduit, the shield (s) and the conduit tied together and grounded.
In addition, for shielded cables a 5-minute test shall be performed between all shields bundled together and the conduit at 500 V dc.
For the leakage currents all tests, it the final test voltage will be recorded at 1-minute intervals.
Cable Acceptance Criteria 1.
The cables must pass the in-conduit de high-voltage test.
The acceptance criteria for this test is that specified in ANSI /IEEE 141-1986, section 11.11.4.
Any conductor with a polarization index less than 1.0 will be considered a failure unless it can be demonstrated, by engineering evaluation or by retest, that the conductor is acceptable.
The polarization index is the ratio of the current after 1 minute to the current after 5 minutes of maximum voltage test.
2.
If the cables fail the high-voltage test, the NRC will be notified promptly.
The location of the failure will be determined, and the cables will be removed from that conduit segment and inspected to determine the cause.
If the cause is determined to be the result of other than cable pullbys, the section(s) of cable (s) containing the failure (s) will be electrically isolated.
The test will then be repeated, provided that the method of isolation does not alter or disturb the portion of cables in the remaining conduit segments.
If this test then passes, it will be considered a successful test for tne purpose it was performed.
The section(s) of the cable (s) containing tne failtre(s) will be removed from the conduit segment and inspected to determine the cause.
TVA will take the necessary actions, which may include further testing and analysis, to identify ana bound the problem.
Appropriate corrective action will then be implemented.
. The possible findings from the initial sample and the subsequent actions to be taken as a result of failures which are due to cable pullbys are as follows:
' a.
If two or more conduits containing failed conductors are observed in the initial sample, the five reinaining conduits in
-the group will also be tested.
Corrective action will be taken to replace all failed conductors.
The second worst group of 20 conduits will then be sampled using the same procedure as for the first group of conduits.
A finding of two or more conduits l
with failed conductors in the second group would also lead to a 100-percent examination of the remaining circuits in that group, implementation of appropriate corrective action, and sampling l
examination of the third group of 20 conduits.
b.
If, in the worst group of 20 conduits, only one conduit in the random sample of 15 conduits is found to have failed conductor 1, the_ remaining five conduits in this group will also ce examined.
A finding of one or more additional conduits in this group of five'.will result in corrective action and require 'the sampling inspection of the second worst group of 20 conduits, etc...as described for item A.
c.
If, in the first (worst) group of 20 conduits, either no conduits with failed conductors are found in the random sample of 15 conduits, or if one conduit with failed conductors is found in the random sample of 15 conduits but no similar conditions occur in the remaining five conduits of this group, it may be concluded with 95-percent confidence (100-percent confidence if all 20 conduits in the group are examined) that no greater than five percent of the conduits in that group have damage to conductors exceeding the test criterion.
d.
Because the groups of 20 conduits each are to be sampled in the order of the highest to lowest potential for conductor damage due to pullbys, and if for any group it can be demonstrated with at least 95-percent confidence that at least 95 percent of the conduits are free of conductor damage exceeding the test criteria, it can be inferred with greater than 95-percent confidence that any conduit groups ranked lower than the group
]
also meet the 95-percent reliability criterion.
On that basis i
the sampling will be terminated at the point where the first 95/95 demonstration can be made; lower ranked groups are inferred also to meet the acceptance criterion.
Failed conductors discovered during sampling will be repaired or replaced.
Those cables in each group which pass the test will be considered acceptable.
If damage to the conductor insulation which is determined to be due to pullbys is inadvertently discovered during the test program by means other than the in i
situ high-voltage t' sting, this cable will be subjected to the high voltage test.
If the cable passes the test, the damage will be evaluated and repaired or replaced as necessary.
However, this cable will then not be considered a failure for the purposes of this test.
If the test fails, subsequent actions shall be as described above.
]
-1
. TECHNICAL BASIS:.The. sample size chosen for the c9nduit pullby sampling l
plan was determined using the hypergeometric likelihood density function method described by Goodman (1984).
The applicable equation is:
k-x\\
j-Pr(x<m.)k,n,N,)-
- m. i k )1 -
N-x 7x 4
)
-[n+1}
Equation 1
.~
N+1 x-k g
j Where j-x 100 - the target confidence level (as a percent) k '- the number of conduits with damaged.
~
conductors observed in.the sample the maximum number of conduits containing' m.
=
damaged conductors that occur.in the population from which the sample is drawn and still^ meet the target reliability-criterion n-the size of the random sample N-the size.of the. population from which the sample-is drawn, and fa-a!
b b!(a-b)!
gj For random sampling from a population of size N = 20 conduits, with k - o conduits in the sample exhibiting conductor damage because of the potential concern (pullbys or jamming), and m.
1 the maximum number of conduits in the total population that can have conductor damage and still meet the target reliability criterion (95 percent 19 of 20 conduits having no conductors with damage exceeding the measurement criterion), solution of Equation 1 for incrementally increasing n yields first exceeding 0.95 (i.e., 95-percent confidence) for n 15 conduits as the minimum required sample size.
REFERENCES:
- Goodman, J., 1984, " Sampling Inspection of Nuclear Power Plants."
Proceeding of the 1984 Statistical. Symposium on Nation Energy Issues, Seattle, Washington, October 16-18, 1984.
]
)
ENCLOSURE 3 SEQUOYAH NUCLEAR PLANT CABLE JAMMING Cable Selection Criteria The total population of conduits containing safety-related circuits at SQN will be identified and screened using the criteria outlined below.
The purpose of the screening process is to identify a population of conduits that have some credible chance of having sustained conductor insulation damage because of cable jamming.
Within this bounded population, a further screening will be performed to create additional subpopulations consisting of 20 conduits each.
The first group of 20 conduits will represent the " worst" (i.e., highest potential for cable jamming damage) conduits in the screened population; the second group of 20 conduits will represent the second worst group of conduits and so forth.
For the purposes of this evaluation, the representative worst-case conduits and cables will be considered to be any that meet, or come closest to meeting, the following:
l.
The conduit contains three single conductor cables (larger than No. 10 American Wire Gage [AWG]) of the same conductor size.
2.
The cables are routed in a conduit such that the ratio of the inside diameter of the conduit divided by the average diameter of one of the cables is in the range of 2.8-3.1.
This is in accordance with IEEE 690-1984, Section A9.2.4.4, and as stated accounts "for tolerances in cable and conduit sizes, and for ovality in the conduit at a bend..."
(An initial review indicates that SQN units 1 and 2 have approximately 46 conduits that meet the above criteria and all contain low-voltage unshielded power cable with cross-linked polyethylene insulation.)
3.
The conduit contains field-or factory-fabricated bends.
4.
The total length and number of bends between a set of adjacent pull points exceed or come closest to exceeding the requirements of G-38 Appendix F.
For the purposes of this evaluation, straight-through condulets ("C" type) will not be considered as pull points.
l S.
There were at least two potential pulling points before the segment of conduit of highest interest (i.e., the segment that would have experienced the highest pull tension).
For the purposes of this evaluation, straight-through condulets ("C" type) will not be considered as pull points.
6.
Preference shall be given to those conduits that meet all of the above and any or all of the following:
a.
If it is determined that the conduit bends were made in the field as opposed to the factory; b.
If it is determined through analysis that the cable pull required mechanical assistance.
Implementation of the above criteria will be documented in a calculation.
___________-_ a
- , Cable Test and Inspection Criteria Jamming is a consideration when three single conductor' cables of like diameter are being pulled into a condult. As described in IEEE Standard 690-1984, section A9.2.4.4, ".... Up to a ratio of 2.5 the cables are constrained into a triangular configuration.
However, as the value approaches 3.0, jamming of-the cables could occur and the cables would freeze in the duct causing serious cable damage...."
Once jamming occurs, it can only be overcome by " brute force."
Either the pulling rope or conductors break or the insulation and jacket are deformed by crushing ~to relieve the wedging action.
In either case the damage extends over a considerable length of the cable and is severe.
The following test program is specifically designed to determine whether or not such damage has occurred.
Sampling will begin by selecting a random sample of 15. conduits from the worst of the subpopulations of 20 conduits.
This sample size is sufficiently large to provide 95-percent confidence that no greater than 5 percent of the conduits in the first group contain cable damage discernable by the test method being employed, provided that no damaged circuits are detected in the sample.
1.
After having randomly selected the 15 conduits from the worst of the subpopulations of 20 conduits, a field measurement of the actual cable diameter shall be made to verify that the selected cable does, in fact, fall within the range specified in Cable Selection Criteria No. 2.
If it does not, another conduit from the subpopulation will be selected.
2.
After having determined that the selected conduits and cables do fall within the specified range, the installed configuration of the conduits shall be reviewed on a case-by-case basis to determine the feasibility of introducing water into, and removing it from, the conduit system without compromising equipment integrity or personnel safety.
It is preferred -
that all sections of all conduits be subjected to the water injection.
However, water will not be introduced into any conduit segment that could result in jeopardizing plant safety by compromising equipment integrity or personnel safety.
In addition, water will not be introduced into any conduit segment from which it cannot readily be removed.
The justification for not introducing water into all sections of all conduits shall be documented.
3.
All sections of each conduit, except those for which wetting has been documented as a plant safety concern, or from which water cannot readily be removed, shall be subjected to the introduction of ordinary tap water.
As a minimum, portions of five conduits shall be tested in a fully wetted
' condition.
The purpose is to ensure, as a minimum, that sufficient water is introduced so that moisture is present along the entire surface of the installed cables.in that conduit segment.
A fully wetted condition shall be considered to be achieved when water injection is accomplished in one of the following manners:
A
. a.
Water is injected slowly into the conduit !<jnent at a rate faster than it is'.. lost. through conduit openings or connections until the cables in that segment are initially submersed.
It is not intended or expected that the cables'will remain submersed throughout the test.
b.
Water is. sprayed into the conduit segment under pressure at all conduit segment openings such that the water spray cascades down over the installed cables.
The water spray shall be maintained at each.
Injection point for a minimum period of two minutes.
- 4. -Each ' conductor - shall be subjected to a 5-minute dc high voltage test at
'240 volts / mil of insulation (per IEEE 383-1974, section 2.3.3.4).
For;the purposes Lof this test, the voltage may be based on the minimum SQN environmentally qualified insulation thickness for the voltage rating and insulation type and manufacturer.
These voltage values are shown in.. Testing on the first of those cables, in conduits which will be wetted, will commence within four hours of completion of the water injection.
The test will be performed between each conductor and the remaining conductors in the conduit and the conduit tied together and a
grounded. ' The leakage currents at the final test voltage will be recorded 1
at one-minute intervals.
-Cable Acceptance Criteria 1.
The cables must pass the in-conduit dc high voltage test.
The acceptance criteria for this test is that specified in ANSI /IEEE 141-1986, section 11.11.4.
Any conductor ' with a polarization index less than 1.0 will be considered a failure unless~ lt can be demonstrated, by engineering evaluation or by
- retest, that the conductor is acceptable.
The polarization index is the ratio'of the current after one minute to the current after five minutes of maximum voltage test.
2.
If' the cables fall the high voltage test, the NRC will be notified promptly. The location of the failure will be determined, and the cables shall be removed from that conduit segment and inspected to determine the cause.
If the cause is determined to= be.the result of other than cable jamming, the section(s) of cable (s) containing the failure (s) will be electrically isolated.
The test will then be repeated, provided that the method of isolation does not alter or disturb the portion of cables in the q
remaining conduit segments.
If this test then passes, it will be-considered a successful test for the purpose it was performed.
The section(s) of the cable (s) containing the failure (s) will be removed from the conduit segment and inspected to determine the cause.
TVA will take the necessary actions, which may include further testing and analysis, to l
identify and bound the problem.
Appropriate corrective action will then be implemented.
The possible-findings from the initial sample and the subsequent actions
)
to be taken as a result of failures which are due to cable jamming are as follows:
l l
l
~
O,
_a_
a.
If two or more conduits containing failed conductors.are observed in the initial sample, the 5 remaining conduits in the group will also be tested.
Corrective action will be taken to replace all failed conductors.
The 2nd worst group of 20 conduits will then be sampled using the same procedure as for the first group of ccnduits.
A finding of 2 or. more conduits with failed conductors in the 2nd group would also lead to a 100 percent examination. of the remaining circuits in that group, implementation of appropriate corrective action, and sampling examination of de third group of 20 conduits, b..
random sample of 15 conduits is found to have failed. conductors, the If, in the worst group of 20 conduits, only one conduit in the' remaining five conduit: in this group will also be exarxined.
A finding of 1 or more additional conduits in this group of 5 will result in corrective action and require the sampling inspection of the 2nd worst group of 20 conduits, etc., as described for item A.
c.
If, in the first (worst) group of 20 conduits, either no conduits.
with failed conductors are found in the random sample of 15 conduits, or if one conduit with failed conductors is found in the random sample of 15 conduits but no similar conditions occur in the remaining 5 conduits of this group, it may be concluded with 95 percent confidence (100 percent confidence if all 20 conduits in the-group are examined) that no greater than.5 percent of the conduits in that group have damage to conductors exceeding the test criterion.
d.
Because the groups of 20 conduits each are to be sampled in the order of highest to lowesi potential for conductor damage due to cable jamming and if for any group it can be demonstrated with at least 95 percent confidence that at least 95 percent of the conduits are free of conductor damage exceeding the test criteria, it can be inferred with greater than 95 percent confidence that any conduit groups ranked -lower than the group also meet the 95 percent reliability. criterion.
On that basis the sampling will be terminated at the point where the first 95/95 demonstration can be made; lower ranked groups are inferred also to meet the acceptance criterion.
Failed conductors discovered during sampling will be repaired or replaced.
Those cables in each group which pass the test will be considered acceptable.
If damage to the conductor insulation which is determined to be due to jamming is inadvertently discovered during the test program by means other than the in situ high-voltage
- testing, this cable will be subjected to the high-voltage test.
If the cable passes the test, the damage will be evaluated and repaired or replaced as necessary.
However, this cable will then not be considered a failure for the purposes of this test.
If the test fails, subsequent ' actions shall be as described above.
i TECHNICAL BASIS:
See Enclosure 2, " Cable Pullbys" l
i
____-_-___________________-O
ENCLOSURE 4 SEQUOYAH NUCLEAR PLANT CABLES SUPPORTED BY 90-DEGREE CONDULETS Cable Selection Criteria The following criteria will be utilized to select a worst-case conduit and cables for evaluation of potential damage that could have resulted from supporting cables by 90-degree condulets. The test quantity is in accordance with NRC recommendations in references 1 and 2 identified in the letter.
During the selection process, if a single worst case is not obviously apparent, several representative worst-case conduits may be examined.
Selection of the worst case will then be based upon examination of the cables in the 90-degree condulets to determine the cable with the highest force being exerted by the condulet corner.
For the purposes of this evaluation, a representative worst-case conduit and cables will be considered to.be any that meet the following:
1.
The conduit will contain only cables with silicone rubber insulation.
(An initial review indicates that SQN unit 2 has approximately 340 conduits that contain only 10 CFR 50.49 cables with silicone rubber insulation.)
2.
The conduit shall have a minimu.n of five cables and a minimum fill of 20 percent.
(An initial review indicates that approximately 180 of the above 340 conduits contain five or more cables. After applying the minimum fill requirement to these 180, it is expected that a sufficient population will exist to select a representative worst case.
The intent of the minimum fill and number of cables requirement is to obtain a conduit in which the cables lie on top of one another, thereby exerting more force on the lower cables.)
3.
The cables will be supported by a 90-degree condulet at the top of the run.
4.
The cables will have a vertical drop immediately below the 90-degree condulet that exceeds the requirements of National Electrical Code (NEC) Article 300-19. Preference should be given to a conduit that exceeds the NEC Article 300-19 requirements by the greatest amount when compared with other similar installations.
Implementation of the above criteria will be documented in a calculation.
1 Cable Test and Inspection Criteria As stated by NRC in reference 1 above, the predominant concern from supporting cables by 90-degree condulets is the potential for cutting the insulation by the corner of the condulet.
The following test program is specifically designed to identify if such a potential condition exists:
. With the cables in the conduit, perform a 5-minute de high-voltage test at 240 V/ mil of insulation (per IEEE 383-1974, section i
2.3.3.4).
For the purposes of this test, the voltage may be based on the minimum SQN environmentally qualified insulation thickness for the voltage rating and insulation type and manufacturer.
These i
voltage values are shown in enclosure 5.
The test will be performed between each conductor and the remaining conductors in the conduit and the conduit tied together and grounded.
The leakage currents at the final test voltage will be recorded at 1-minute intervals.
Cable Acceptance Criteria The cables must pass the in-conduit dc high-voltage test.
The acceptance criteria for this test is that specified in ANSI /IEEE 141-1986, section 11.11.4.
Any conductor with a polarization index less than 1.0 will be considered a failure unless it can be demonstrated, by engineering evaluation or by retest, that the conductor is acceptable.
The' k
polarization index is the ratio of the current after one minute to the current after 5 minutes of maximum voltage test.
If the cables fail the high-voltage test, the NRC will be notified promptly.
The location of the failure will be determined.
If the failure is due to supporting the cable by 90-degree condulets, the extent of the problem will be evaluated and the need for further corrective action determined.
If the location is found to be at other than the 90-degree condulet of concern, the section(s) of the cable (s) containing the failure (s) will be electrically isolated.
The test will then be repeated, provided that the method of isolation does not alter or disturb the portion of the cables in the 90-degree condulet.
If this test then passes, it will be considered a successful test for the purpose it was performed, that is, to determine whether the insulation has been cut by the corner of the l
The section(s) of the cable (s) containing the failure (s) will be removed t
from the conduit segment and inspected to determine the cause.
TVA will take the necessary actions, which may include further testing and analysis, to identify and bound the problem.
Appropriate corrective action will then be implemented.
If the representative worst-case cable passes the test, it will demonstrate that damage because of supporting cables by a 90-degree condulet has not occurred.
Furthermore, before restart and in accordance with NRC recommendations in references 1 and 2 above, TVA will evaluate all conduits inside containment that contain 10 CFR 50.49 silicone rubber insulated cables. The cables in those conduits, which contain a 90-degree condulet at the top and which have a vertical drop immediately
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below the condulet that exceeds the requirements of NEC Article 300-19, j
will be examined. Only those cables that are exposed to a significant strain will be resupported before restart.
Those cables that cannot l
1
., l easily be lifted off the condulet corners by hand or are found to be severely indented.will.be considered to be under significant strain.
The support. method that will be utilized is. expected to be the insertion of Raychem Corporation heavy wall. nuclear grade heat shrinkable' tubing between the cables and the inner radius of the condulet.
The material was selected since,'in its recovered' state, it has a consistency that.
resists deformation by external force and has a demonstrated ability to withstand the normal and accident environments for the life of the plant.
This tubing,.which will be slit along its axis to allow it to be wrapped around the cables, will be secured to the cable bundle by tie-wraps in addition to treing held by the natural weight of the cables 1
and the confines of the inner condulet configuration.
l This method will. eliminate the failure mode of concern identified by the NRC in reference 1, that is, conductor creep through the insulation to
- the metal condulet corner.
In addition, it will substantially increase 1
the radius of bend, when compared with the relatively small radius of the condulet, thereby substantially reducing the bearing pressure..The radius of curvature of those cables not in contact with the inner radius of the condulet is much greater, resulting in a much lower bearing
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Sequoyah Nuclear Plant Revised Cable Test Program Commitments (1) TVA will perform a 5-minute dc high voltage test in situ dry or with moisture (to be determined on a case-by-case basis) to ascertain the presence of damage caused by cable pullbys on a statistically significant sample.
Cables that fail the tests will be repaired or replaced before restart of the affected unit.
(2) TVA will perform a 5-minute de high-voltage test in situ dry or with moisture (to be determined on a case-by-case basis) to ascertain the presence of damage caused by cable jamming on a statistically significant sample. Cables that fail the tests will be repaired or l
replaced'before restart of the affected unit.
1 (3) TVA will perform a 5-minute de high-voltage test for a worst-case l
conduit to ascertain the presence of damage caused by cables supported by a 90-degree condulet corner at the top of a vertical run that exceeds the r?quirements as outlined in NEC Article j
300-19.
Cables that fall the test will be repaired or replaced J
before restart of the affected unit.
(4) TVA will evaluate all conduits inside containment that contain 10 CFR 50.49 silicone rubber insulated cables that contain a 90-degree condulet at the top and that have a vertical drop immediately below the condulet, which exceeds the requirements of NEC Article 300-19. Only those cables that are exposed to a l
significant strain (cannot be easily lifted off condulet corners by hand or found to be severely indented) will be tupported by a slit piece of Raychem Corporation heavy wall nuclear-grade heat shrinkable tubing tie wrapped around the cables at the point of contact with the condulet corner.
This will be completed before the affected unit restart.
(5) Additional testing of silicone rubber insulated cables will be performed in the field.
The complete test results, as well as the documented additional investigations and analyses performed by TVA and the University of Connecticut's Electrical Insulation Research Center, will be forwarded to NRC by a separate letter.
(6) TVA will establish a cable test program that will be consistent with IE Notice 86-49.
The program will also address low-voltage cables.
I The purpose will be to demonstrate margins above the system design j
basis.
This program will be described to NRC within six months after restart of SQN unit 2 and will be implemented by the end of the SQN unit 2 cycle 4 refueling outage.
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