Text

Response to Concerns Use of a Certain Type Cable Manufactured by the Continental Wire and Cable Company
	ML19093B112
Person / Time
Site:	Surry
Issue date:	07/14/1978
From:	Stallings C; Virginia Electric & Power Co (VEPCO)
To:	Harold Denton, Schwencer A; Office of Nuclear Reactor Regulation
References
	Download: ML19093B112 (28)
	v • d • e

e VIRGINIA ELECTRIC AND POWER COMPANY RXCHMOND,VIRGXNIA 23261 Julv 14".,1978:

}fr. Harold.R. Denton; Director:

Office of Nuclear.Reactor.Regulation Attn:. Albert. Schweilcer

. U. S.. Nuclear. Regulatory. Commission Washington~ D. C. 20555

Dear Sir:

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This in response to concerns expressed by members of.your staff.regarding the use of a.certain type cable manufactured by the Continental Wire and Cable Company at Surry. Power Station Unit Nos> 1 and 2.

This letter summarizes our investigation of this matter and presents.. our conclusio11s.

Background On June 29, 1978',, Anaconda Cable, who now* own Continental Wire and Cable, notified.Vepco that their.records indicated that.certain cable which had failed environmental.testing at another utility ~ight also.be in use at Surry Power Statiqn.

In.response to this notification~ an invest_igation was initiated immediate'-

ly to determine if this type.of cable was in use in safety systems, inside con-tainment, at Surry.Power Station.

Concurrently, Anaconda Cable was.to.determine

. the exact specifications of the cable which had failed. as compared to cable pur-chased. for use at Surry Power Station. The.utility which had.conducted the cable test was also contacted to determine the conditions under which the cable had failed as compared to our LOCA.performance criteria..Our findings are summarized below.

Throughout this letter the other utilities Continental cable which failed will.be ref~rred toas the "failed cable".

The Continental cable in use at Surry will. be referred. to.. as. the "Surry cable".

cable Specifications A.review of the.records of Continental Wire and Cable has determined that the failed cable. is different in. several. respects. from the Surry cable.. The failed cable. is described in. test. reports. which you now have~ *. The. Surry cable specifications are briefly.as.follows (additional information is provided in the attachments):

conductor:* :16: gage,: 7 'strand, copper insulation: :25 mils** cross-linked fire-,-resistant polyethylene,*

.(compound number CC-'2210)

Shield:

100.percerit coverage aluminum mylar tape, withl8 gage 7 strand copper* drain wire.

jacket:.; AS: mils hypalon *

7:32() 1 ():3:22

e VIRGil'!IA ELECTRIC AND POWER COMPANY TO Mr. Harold R. Denton Page 2 The major differences between the failed cable and Surry cable are in in-sulation compound number and in insulation and jacket thicknesses.

Test Results - Failed Cable The test in which Continental Cable failed was performed recently for another utility.

Since you now have the detailed results of this test, only a brief description will be provided here.

The test performed was a comgination LOCA/steam break test including a prior radiation exposure of 1.5 X 10 rads.

The test sequence was as follows.

irradiation of cable sample to 1.5 X 108 rads increase temperature and pressure to 340° and 110 psia.

T0 was es-tablished when these conditions were reached 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months at 340° and 110 psia After 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months , temperature was dropped to 250° and maintained for a total test duration of 120 hours0.00139 days 0.0333 hours 1.984127e-4 weeks 4.566e-5 months This was an extremely conservative test which combined the worst effects of both the LOCA and steam break.

This combination of conditions would never occur 0 under any accident conditions.

For example, irradiations on the order of 10° would occur only during a LOCA during which temperature and pressure would be considerably less than 340° and 110°F.

Sirailarly, the temperature and pressure in this test are cgaracteristic of a steat~ break wherein irradia-tion levels of approximately 10 rads would occur.

This test was apparently intended to emcompass all conceivable test require~ents in order to reduce the number of tests required.

For this reason, the test did not establish that the cable would perform unsatisfactorily in either a LOCA or* a steam break.

Discussions with personnel involved in this testing indicated that the failed cable was replaced with another make of cable following this test.

Our impression from these discussions was that the cable was replaced not so much due to any concern over its performance, but because replacement of the small number of circuits affected was easier and faster than the running of additional, less conservative tests.

In summary, these test results indicate that certain instrument cable which is similar to cable in use at Surry, will not perform satisfactorily when exposed to test conditions which were far more severe than would occur in the event of a LOCA.

There is no evidence that the Surry cable would not perform satisfactorily under more realistic test conditions or under actual LOCA conditions.

However, to resolve concerns over this issue we have con-ducted a review of the specifications of Surry' s cable and of the test data available relative to its performance during a LOCA.

Use of Continental Cable at Surry A complete review of all cable runs has not been completed. It has been determined that Continental Cable is extensively used in safety related applica-tions at Surry.

The cable is used only as instrument cable.

The 1naximum vol-tage used in these applications is 50 volts.

Note that the voltage applied in

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VIRGINIA ELECTRIC AND POWER COMPANY TO Mr. Harold :R... Denton

~age 3 the failed cable*. test* was 300. volts.

The.Surry cable.is in.the pressurizer pressure and.level and the.steam generator.level. instrumentation ori: Unit: 1.

Sirice.. the. exact extent of its. use on bothunitshas not.been.determined, wehave.assumed for purpose of this evaluation that the cable has been.used in every possible instrument application~

*Acceptance criteria. and :Test :Results..:. *sutry Cable All safety.related electrical equipment for Surry Power.Station was pur-chased to meet the.LOCA.performance.requirementsspecifiedin Sectiori8 of.the FSAR.

Sectiori*s.,requires operability* in an environment of 280°F.and 40: psig for a period of 30 minutes.

Purch~se specifications for instrumen,t cable

require the capability.ofwithstand1:ng a total radiation dose*of108 rads with-out a significant ch~nge _in physical and. electrical properties,* a value well in excess of:. the 2 X 107 rads exposure estimated for a Surry LOCA.

All Surry cable purchased from Continental Wire and Cable, was subjected to.extensive.test1:ng and inspection.to ensure quality ahd.performanGe.

A representative.test.report for one cable sample is included in Attachment 1.

Test reports for all Continental Cable are.available if desired.

These* tests included the verification-of-mechanical design parameters and of basic electri-cal properties of.the conductor and insulatiqn~.Tests were.performed to moni-

. tor the performance of the cable and insulation under a variety of severe en-vironmental.condition.s.

These included measurements of the effect on.tensile strength*and elongation 0£*7 days in an air oven at.1so0c~

The cable was tested for heat *distortion at.150°Cand accelerated water.absorption at.75Pc.

In all cases, cable.performance was satisfactory *. Additional information in-cludi:ng acceptance.criteria is shown on the.test.report form (attachment :1) *

. The suitability of this cable for operation under ~igh irradiation has been confirmed.both in tests.performed by theinanufacturer and by.other test.performed independently~

The following article, included.as attachment 2, provides a concises~ary of the effects of radiation on the electrical properties of various insulation materials.

"Insulation and Jackets for Control and Power Cables in Thermal

.Reactor:Nuclear.Generati:ng.Stations" by Robert B. Blo_dgett and Robert G. Fisher IEEE*Transactions onPowet Apparatus and Systems; VqL PAS-88, No.*. 5 May 1969 This article,*in additiontodiscussing radiation effects on the standard

.measures of. insulation performance, : Le.* tensile. strength and el~ngation~ also directly addresses the effects of* irradiation* on other electrical properties.*

Note that on page 2 of: the article, the types of: cable coverings tested are listed~

Covering type.No. 4, CB CLPE i~ of the same general.type.as the Con-tinental Cable *used.at Surry.

As shown.*in Table XI. of.the article, under*

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VIRGINIA ELECTRIC AND POWER COMPANY TO Hr. Harold R. Denton Page 4 column 4 for CB CLPE, elongation begins to show deterioration prior to other parameters and identifies the theshold of irradiation damage.

This confirms the validity of the accepted practice of relying on measurement of elongation and tensile strength to check for insulation deterioration for this type of insulation.

In reviewing this article, please note the following.

1)

In Table XI under column 4, 5 X 107 rads is identified as the theshold of d~age for the type of cable used at Surry.

A dose of 1 X 10 rads represents the end of serviceability.

2)

Under nconclusions 11

cross-linked polyethylene is identified as among the most suitable insulation materials for nuclear plant service.

We will now discuss test results for the specific type of Continental cable used at Surry.

This test was performed by the manufacturer in 1971, on insulated conductor only, with no jacket.

Test information is included as attachment 3.

The test sequence and results are listed on page 2 of the attachment.

The test sequence was as follows:

120 hours0.00139 days 0.0333 hours 1.984127e-4 weeks 4.566e-5 months , 50 PSIG steam, followed by 120 hours0.00139 days 0.0333 hours 1.984127e-4 weeks 4.566e-5 months innnersion in 0.5% Boric acid solution at 160°F Sequence repeated at radiation exposures of O, 1 X 10 7, 5 X 10 7, and 1 X 108 The test results are listed below as Table 1 with the addition of estimated tensile and elongation values for an exposure of 2 X 10 7 rads.

This has been added because 2 X 107 rads is the maximum calculated irradiation under LOCA conditions at Surry.

CONDITIONING NONE STEAM/BORIC ACID RADIATION ONLY 1 X 107 RADS (GAMMA)

,;~2 X 107 RADS (GAMMA) 5 X 107 RADS (GAMMA) 1 x 108 RADS (GAMMA)

TABLE 1 LOCA TEST RESULTS CLPE -

COMPOUND f/2210 TENSILE PSI 2440 (100) 2390 (98) 2640. (106)

~~2538 (104) 2230 (92) 1710 (70)

ELONGATION 550 (100) 450 (82)

. 425 (77)

'1~378*

(69) 238 (43) 100 (18)

e Vrnorn1A ELECTRIC AND PowER CoMPANY To Mr. Harold :R.. Denton RADIATION AFTER: STEAM BORIC.-ACID 1 X 107 AADS (GAMMA)

2 X 107 RADS * (GAMMA) 5 X to7 RADS* (GAMMA) 1 X *108 RADS (GAMMA)

2580 (105)

, *:*2385 * *: (98)

. :2200

(90)

(% RETENTION VS ORIGINAL VALUE)

ESTIMATED BY LINEAR INTERPOLATION P_age 5 393 * (72) 200'. (36) 69.(13)

Based on IPCEA standards,*an acceptable value for.tensile strt:ngth and elo_ngation following.this.test is 50.percent of the or:iginal value of each.

The.test sequence which.most closely approximates the.Surry.LOCA condition.is the 2 X 107 tads exposure follow~ng the steam and boric acid exposure *. Based on a linear interpolation* of actual test data the. tensile strength and elo_nga-tion following a LOCA would be'.95% and 63% (results underlined) of.. the or:iginal values.. This. is acceptab:I..e.

These. test.results indicate* that, under. the highest possible irradiation~ and in.temperature, moisture.and pressure.conditions of greater severityand duration than.Surry LOCA.conditions, the cable will per:...

form satisfactorily.

The.results also confirm the theshold of irradiation damage at 5 X 107 rads.

Note also that irradiation. is the major:. contributor. to deterioration*

of cable properties and is far more s_ignificant than the. steam and water ex:...

posure.

Page 3 of attachment 3 is a graph oftensil strength*and elongation versus irradiation. for the polyethylene compound number 2210 as. used in.*the Surry cable.

This data provides additional confirmation:of-theonsetof deterioration at approximately 5 X io7 rads, accelerating rapidly.as irradiation.approaches 108.

This graph also.demonstrates thevalidityof linear interpolation between 1 X *107 )3.nd 5 X 107tvhich was used in Table i.

. While.weare confident that our.Continental.instrument cable.will.perform satisfactorily throughout a LOCAand thereafter, it.is.pertinent.to.note that the safety ~elated.*instrumentation located inside. the containment. is only.needed for a short time following a LOCA.

The instrumentation.and coincidence logic required for. the function of: engineered saf_eguards dur~ng a LOCA are disC:ussed

in Section 7 of the.Surry FSAR.

Pressurizer pressureand.level are the only instruments inside containment which are.necessary. for the initiation of: saf_eguards during a LOCA.

Except

e VrnornrA ELECTRIC AND PowER CoMPANY To * * };[r. Harold : R *. Denton P_age 6 for very small breaks, :Le.. less than 1 inch~ the initiating function: would be completed withiri 5 minut~s.

The. containment pressure* transmitters which** are.. the. most** important. instru-

. ments. for sat:eguards. initiation*. are located outside the containment.

The follow~ilg instruments, located in containment, while riot:.required to initiated safeguards, are of value in.establishirig.the*natureof the*accident and for confirmi:ng the proper initiation: of safety* functioIJ.s.

containment sump.level containment temperature safety. injection flow accumulator:. levels steam line pressure steam.flow wide r~nge reactor coolant.temperature.

wide range.reactor coolant pressure In. response to a. LOCA, these instruments are.. used. by. the operator:. to. veri..-

fy system conditions and safeguards operatiqn~

A loss of one or*more of these.

instruments would not affect the operation* of saf_eguarcls.

These instruments

are. ot: *greatest* value for:. the first half*. hour following an accident.

In summary, instrumentation located inside containment is needed.only for*

a short time follow~rig a LOCA for saf_eguards initiation and. for -.verification of*

system.conditions.

Within 30" minutes following a LOCA, this.instrumentation is no l~nger.essential; its failure.would pose no problem to safe post accident operatiqn~

Thus these instruments*haveservedtheir function.long before signi-ficant* irradiation has occurr~d.

Thirty minutes after the worst* LOCA,

irradia-tion. is still lessthari 106 rads, far below the threshold of damage.

StiI1IDJ.ary*and*cortcltision The.objective of this evaluation has.been to determine if certain instru-ment cable in use at Surry Power Station~is suitable for.its intended purpose~

.This concern developed following.the.failure by similar cable of a LOCA/steam break environmental test at another* utility* *

. We have reviewed the failed cable.test results.to.determine if any.new cable.performance information was.developed which would cast doubt on the bases upon.which our o:i::iginal cable. selection* was macle..We found no. such evidence.

In fact, iri many.respects, the failed cable.test*confirmed the.test data deve-loped for.our cable iri 19.71'.:.. The failed cable.test has demonstrated once again that cross linked.polyethylene insulation~ wheri irradiated.beyond 108 rads, will not. perfo'1;1n.

The unrealistic and abusive cable test*which initiated this concerned.is in no way an indication that such cable would not.perform its intended function*.under accident conditions.

Indeed,. test.results performed by. the manufacturer and con.:..

firmed byother.s indicates* satisfactory performance under.severe.accident condi-tioI).s.

e VIRGINIA ELECTRIC AND POWER COMPANY TO Hr. Harold R. Denton Page 7 The data presented herein demonstrates that for cross linked polyethylene insulation, irradiation is the major contributor.to cable deterioration under LOCA conditions.

The data also established 5 x 107 tads as the.theshold for irradiation damage.

This is far above the irradiation which would occur under Surry LOCA conditions.

We are confident that the Surry cable will perform its intended function under LOCA conditions.

No further investigation or corrective action is con-sidered necessary.

cc:

Hr. James P. O'Reilly Very truly yours,

~~

C. M. Stallings r

Vice President -

Power Supply Production Operations I

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Insulatio11s and Jackets for Control a11d Po\\ver Cables in Thermal Reactor Nuclear Generating Statjons p, BI ODGI,,TT IEEE AND ROBERT G. FISHER ROBERT ~.

'... *, SF-'.ton ME!'>IBEn, Abstrar.t-The permanent change in the physical strengths, rate*

of oxidation, dielectric loss, and electrical stability in 40~psig (142°C) steam and dielectric strength arc reported for 13 elastomer-based

,. insul:i.tion-jacket combinations after irradiation up to 10" rad in air at S X 105 rad/h from a cobait 60 source. Threshold of damage for each property, overall threshold of damage, :iud highest dose rate still serviceable for the combinations are sumr:urized. On the basis of these dat?, suggestions are made for IEEE nuclear environ-ment classification of cable coverings rate for continuous 90°C

.and higher.

INTRODUCTION I

N A RECENT survet, Grecm~ald pointed out that by 19_85 new nucle:i.r gencrntmg capacity was expected to be twice tliat for hydro and fo!-i:::il-fueled additions in the United States

[l]. Up to now, thermal reactors have been employed, but high-gain breeder reactors, reiern.-d. to :i.:, "fa.st breede:;;," a.:e expected to come into u..c in the next decade [2]. ThJS rapid increase in the use of nuclear reactors by elcctric!i.l. utilities has focused attention on the need for electrical power and control cables that,.-ii! withstand gamma s.nd neutron radiation o\\*er the projected life of the ger.erating :,tation.

Coosidor fi.r:;t the situation near the reactor core within the primary *shiclcl. Klein :mo Manrui.l concluded that only an es..

sentially inorganic insulation structure would function in this area where P.xposures up to 101: rad/h occur [3]. Elastomer-based insulations and jackets are not suitable for use within the primary reactor shield because the covalent bonds of the organic elas-tomers are e2.Sily di~rupted by the high gamma. and neutron fiux near the reactor cores. Similarly, only essentially inorganic insulations will be suitable.,,,;thin the containment vessel of fast breeder reactc-1'5 where the normal flux is expected t~ be as high as 105 rad/h.

Next, consider the situation out.~ide the primary shield but within the containment vessel of thermal reactors. In this area gamma dose rates ranging from 0.5 up to 160 rad/hand temper-atures up to 70°C arc to be expected during normal operation.

Should :ibnormal bur.sts of energy develop as a r~ult of a nuclear or primary coolant incident, radiation, levels may increase to

. 108 rad/h, while the temperature in the area may rise rapidly to 150°C with steam build in~ up to 50 psig.

If we assume a 40-ycar life for a thermal nuclear generator, the tolal radi:::.t.ion dose o.hsorbcd by a cable within the contain-ment n.rea. may approach 5 X 107 rad if there are no abnormal..

Paper 68 TP 651-PWR, r.ccommr.ndcd ~~d; approv:~ by the lrt<iUllllcd Conductor:3 Comrmtte<! nf the U.l*,E ~ ower <;Jroup for presentation nt the IEEE ~umml'r _Power. :\\lceL111g,. Cl11c;1~_0, Ill.,

Jun., 2:1-28, l!Hi8. ::-.tnn*1scnr,t ~ul,m1Ltcct h:bruary 12, H.168, ma<le n.v11ilable for printin~.\\prii :n, 1%8.

lt. B. Blo<lgr:tt i~ w!th 1:hc Okon\\te C'.omp:m:;, 1,'ass8:1C, ~- J.

lt. U. Fi~hcr was wit.I, 1 he Oko111te Company, l ll.'!.'>:uc, N. J. Hc IS..

11"' 11*ith Amcrscc-1!:.~nn, Butler, N. J.

bursts of energy. If such an incident does occur and it is brought back under control within four houn;, the additional close ab-sorbed might be 0.4 X 107 rad.

The exposure of cable.-.; to radiation in the auxiliary strnctures, e.g., the rc:;iduai-h~t-r~moval compartments, outside_ the con-tainment vessel is less severe, since the maximum dose rates are expected to be two order:; of magnitude lower, i.e.'. 0.0~ time:s those in the containment vessel. However, cables m Hus area must operate even during an abnormal burst of energy, becau:;e they supply power to pumps, fans, and other safeguard systelll.5 needed to prevent a disastrous increase in energy output.

The main question to which this papzr is addrc,.se<l is whether cables insulated and jacketed with elastomer- (polymer-) re~e,i material can be expected to perform satisfactorily in lhe cont~in-ment and lower radiation areas outl;iue the containment v~el oi thermal reactors. Other investigator;; have established. the effect of radiation on the physical prcperties of various org:inic materials. In fact, AST.!\\1 has held se\\*eral symposia on radiation effect.s on materials [4}-[7]. However, the effect of radiaticu on electrical and heat s.ging properties of cable covP.rings has received less attention and is less well cs~b!ishcd.

DA.MAGE 1\\fECHAN1Sll1S For the most part, radiations of primary intere:1t from the standpoint of damage to elastomer-ba.'i*~d insulations and jac1:et.s have energies of the order of 1 MeV, gamma photon3, a.ad fas.;

neutrons, for example. Most radiation damage to elastomer;; i3 caused by internal electron bombardment from the elastic col-lision between gamma photons and electrons [SJ, [9].

Since bond energies and ionizatio11 potential are as much as six orders of magnitude lower than that for high-energ:,* radi-ations and the resultant collision-produced ener~*, both tl-mµo-rary and permanent changes result when ela;;tomer-based insu-lations and jackets are irradiated. First, consider the tempor:uy changes produced by incident radiation. These are thermo-"

luminescence, increased de conducth*ity, and gas evolution [3],

[8], [9]. Thermoluminescence *i:; of no concern for cables.. \\n increase in de conductivity would be of concern only if dr:.1-,tic increases occurred. We will see later that this L-; nut the ca.,e.

Evolution of gases can be tolerated where adequate ventihticm exists, but remains a problem where hermetic *euclosure:s are required. Reed discussed this problem [14].

Now consider permanent damage. ?\\lost elll.Stori,e~ ultimatel::,-

become brittle on prolonged irradiation, depcufiing on their sensitivity. This emhrittlcmcnt is cati:;cd by racliation.:indu:1 u cross-links between the polymer molecules extending the three-dimensional networks to the degree seen in hard rubber and

phenolic resins. A fow polymers, e.g., *butyi n:bbe.r, drgnde rather than cross-link when irradiatcJ. In su<,h ca:;e;, the scis.-ion of the main chain bO!:ds r!.':<ults in the formatiou of !ow-mo!..-ci1br-weight chairi fragments which resemble soft tar-lik~_sub:;ts.11<:e-!.

I e

It follows th:it the clcrnc,n~l cornpositio11, molecular structure, and* volume of matr.rial invoh*e<l arc important considerations in "radiation c11viro11mc11L,;. IJo,;c rate and ki11d of radiation arc also important factors. Generally, the damage to a polymer by mdiation is dependent on the total dose absorbed regardless of the type of radiation. Kill!!; et al. [OJ and Collins and Calkins (10] rcportrd reasonable agreement for the changes that oc-curred in polymers when expo!-ed to alpha, be~. gamma, and neutron radiation fields. The main factor :;cems to be the total energy to which the material is exposed; this is known as the equal-energy equal-damage concept. It as.,;umcs independent

action of heat, water, and radiation, EXPERIMENT.AL GAMMA IRRADIATION OF THIN-WALLED CABLE CovERI!'.GS The following 13 insulation-jacket combinations on nos. 12 and* 14 A WG copper wires were exposed in two configurations to gamma radiation. Both configurations used cobalt 60, gamma= 1.17 to 1.332 MeV, and beta= 0.31 MeV, at a. dose rate of 5 X lOS rad/h. Bausch and Lomb cobalt. gla.,;.,; chip dosimetry was used to confirm dose rate to le:;s than-+/-5 percent.

Si.'C sets of the insulation-jacket combinations were exposed to Southwest Research Institute':; cobalt 60 source. The wire samples, each 10 feet long, were coiled in a cardboard drum with a diameter of 2 feet. Each coil was one wire t.hick and several wires tall. The drum rotated at 3 r/min in a.ir. Air temperature ranged from 3Q-40°C. Total integrated dosages of 5 X lOS, 5 X 106, and 5 X 107 were thus obtained. Two ad-ditional sets of wires were wrapped around a. 5.25-X 11.25-inch long b~ke;; and exposed in Esso Research and Engineering Company's radiation core in air and water at the same dose rate as that above to a total dose of 108 rad.

1) PVC: Pclyvinylchloride per IPCEA S-61-402, section 3.8, and UL types THW and MT. No. 4-AWG (7X) copper, 0.047-inch wall.

2) HD Poly-PVC: High-density polyethylene, type III, class B, grade 3 per AST.M D1248-63T and polyvinylchloride per IPCEA S-61-402, section 3.7, and IPCEA S-19-81, section 4.13.5.

No. 12 A WG (7X) copper, 0.030-inch insulation, and 0.015-inch jacket.

3) SBR-Ne-0prene: Styrene-butadiene synthetic rubber-ba.sed insulation per IPCEA S-19-81, section 3.13, and polychloroprene-based jacket per AST).! D-752 and IPCEA S-19-81, section 3.13.3, a.nd UL type RHW. No. 14 AWG (7X) copper, 0.047-inch insulation, and 0.0156-inch jacket.

4) CB CLP E: Low-voltage carbon black-filled chemically cross-linked polyethylene per IPCEA S-66-524, Interim Standard 2, and UL type RHW-RHH. No. 14 AWG (7X) copper, 0.047-inch wall.

5) CF EPDM-Neoprene:

Ozone-resisting, mineral-filled EPD:\\-f-bascd, low-voltage insulation exceeding the requirements of IPCE.A S-19-81, sections 3.15 and 3.16,* and polychloroprene-ba.scd jacket per AST~! D-752 and IPCEA S-19-81, section 4.13, UL type RHH. No. H AWG (7X) coppcr,0.047-inch insulation,

.and 0.0156-inch jacket.

6) Butyl-Neoprene: Ozone-resisting butyl-based insulation per Il'QEA S-19-31; sections 3.15 and 3.16, a1id polychloroprene-ba.,;eci jacket per AST.M D-752 and IPCEA S-19-81, section 4.13.3, and UL type RHW-RIIII. No. 14 AWG (7X) copix*r;.

0.0-17-inch insulation, and 0.0156-inch jacket.

7) Oil-lliue CSPB: Ozonc-rcsu;ting 90°C oil-base, high-volt~

age insulation meeting the requirements of IPCEA S-Hl-81 t.ection8 3.1-1 and 3.15, UL type RHH, and chlorosulfonatcd

+ ;'**, t >.IQ!~-~'!+.:wz_¥,:Zdi'::'.2. u.s. ;;;.u,::s..-

Jt:t:*: TRAN/IACTIOS~ OX l'le APl'AIIATl:ll AXD KYllTt:ml. lfAT HJ(j[)

polycthylP11c- (('Sl'J,;) li:L'-t'f l jarkct sic AST:\\1 D-752 a.ncl I PCEA 8-10-81,,;l'ction 4.13.3, li L Lype l{! !H. No. 14 A WG (7X) copper, 0.047-inch i11s11l:iti1111, and 0.0156-inch jacket.

8) NFC LI'/~: llil-\\h-n,ltaµ;c, nonfillcd chemically cross-linked polyethyl!!m* (no11>>t.ai11i11;.: :mtioxidant) per I l'CEA S-66-524, Interim Sta11dard I. i'\\o. 14,\\ \\\\"G solid copper, 0.04i-incl{ wall.

9) CF BP.11-C I' H: Ozm1c,-rcsisti11g, clay-filled EP.:\\I-based, high-volta~e insulation per IPCK\\ S-19-81, section 3.16, and UL type RI I\\Y-Rll! I, and chlorinated polyethylene-based jacket SIC AST.:\\I D-752 and IPCEA S-10-81, section 4.13.3. Xo. 14 AWG i-oli<.l copper, 0.0*17-ii,ch insulation [15], and 0.0156-inch jacket.

10) Silicone: Ozone-resisting silicone rubber insulation per IPCEA S-l!J-Sl, section 3.17, UL type SA. No. 14 A'\\VG (7X) copper, 0.047-iuch i11sulatio11, and 0.010-inch glas.s braid.

11) Neoprene: l'olychloroprene-based jacket per AST.:\\! D-752 and IPCEA 8 10-81, section 4._13.3, UL type RlIH. No. 14 A WG solid copper, 0.047-inch wall.

12) CSPE: Chloro:-ulfonated polyethylene-based jacket SIC AST1'{ D-752 and Il'CK\\ S-Hl-81, section 4.13.3, UL type RHII. No. 14 AWG solid copper, 0.047-inch wall.

13) C PE: Chlorinated polyethylene-based jacket SIC AST).!

D-752 and IPCEA. S-19-8!, section 4.13.3. No. 14 A WG solid copper, 0.047-inch wall..

I_t should be emphasized that rndi::.tiou conditions in a nucle:::r generating station will be less ideal and more con,µlex. Changes in the gamma and neutron flux caIL~ed by interactions *,vith surrounding structures may occur. The mass of the c.:i.ble as-sembly, cable design, and the number of cables racked in tr:iys may also affect the degree of radiation. Compounding techni°ques and combinations of ingredients may also influence the resistance to radiation of any polymer-based cable covering. Even so, we feel that the data. in the foliowing sections provide a meaningful basis for estimating the wscful life of cable insulations and jackets intended for use in nuclear generating stations.

PERMA..>iENT CHANGES IN PHYSICAL AND AGING PROPERTIES OF CABLE COVERINGS Physical Strength The datn. in Table I show that the permanent changes in 23°C tensile strength for cable co\\*erings based on polyethykne, EPDM, polymerized oil, SI3R, PVC, neoprene, chlorosulfcnatcd polyethylene, a.nd chlorinated polyethylene were not large enough to affect their useful liie when exposed to gamm."'!. radi-ation between 5 X lOS up to 108 rad. Silicone became brittie between 107 and 108 rad, And butyl was deiroded to a. tar-like liquid between 5 X 106 and 107 rad. Stress at 200-percent strain (modulus) followed a similar pattern. l!'or all materials, elon-gation decrca:;ed, undoubtedly due to radiation cross-linking.

Elongation datn. for butyl and silicone were not obtainable after exposure to 5 X 107 rad.

Rate of Oxidation To &S.5eSS the permanent effect of g:1mmu radiation a.nd the rate of oxidation for insulating materials, the conductors and jackets were removed from the irradiated :,.!lmples, and the resulting tubular insulations were aged at !75, 150, 136, 121, 100, a.nd 75°C in forced-air-circulation ovens. For each of the*

coverings the time to a 40- or SO-percent loss in elongation w::i.s determined before and after e.-ich radiation dose, For insulations

'n'.e used time to 40-perccnt loss in elongations. For jackets wa used time to 80-pcrccnt loss in elongation, beca1u;e jacket com-

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EPM Silicone PVC pa*eno C8PE CPJ~

~

JI

i.

~

Tensile strength

=

Origina:l (psi) 2114 2213 1520 2045 1455 708 804 2:.!72 872 1101 21l01 2544.

ma

mo

=

~

Percent.retention after irradi-ation

0 5 x-101

110 06 08 122 104 06 121 102 101 76 80

10.a 100 112 6 X 101 104 98 100 112 07 58 103 07 106 100 88 08 113

!18 ie 5 X 101 79 123

82 101 03 98 70 110 100 61 77 124 13/j I

1 X 10' 83 118 40 05 79 71 50 00 t

200-perceut modulus*

=

0 Original (p.:si) 2260 2000 588 1767 1oa3 1120 335 1200 730 85U 2-115 030 884 620 Percent retention niter lrradi*

0 ation

~

6 X 10' 94 95 106 125 100 103 121 06 116 76 81 107 116 108

~

0 5 X 10*

00 98 121 115 94 69 126 102

. 127 112

*95 103 156 152

t, 5 X 101 i

i 150 *.

i 120 121 108 t

98 '

t 160

. 203..

i

-~

c 1 X lOt t

t t

i i

103 t

i t

.(

'JI Elongation Original (percent) 260 640 460 550 Percent retention 'alter irradl-270 470 450 870 480 300 290 250 560 670 ation

5 X 101 115 103 03 104 111 93

97.

00 96 107 100 06 80 O\\J 5 X 101 115 103 96 96 102 87 00 06 81 90 80 03 86 63 e

5XW 31 70 48 47 71 58 41 34 40 46 59 18 1 X 105 19 2

33 37 32 53 25 26 t

Degraded (scission).

t Brittle.

t Elougated <200 percent.

TABLE II PERMANENT EFFECT OP GAMMA RADIATION ON RESISTANCE TO OXIDATION 01' CADLl!I COVERINGS

CB 40-Percent Loss Elongation c1~

oo*o NF CF SO-Percent Loss Elongation Neo,,

PVC SBR CLPE EPDM Butyl*

Oil BllBe CLPE EPM Silicone

~;yo prene CSPE CPE Estimated years at 70°0 Nonirradiated (rad)

>115 0 36

>115

>115 25*

64

>115

>115 115 1.9 62 115 Ratio: Irradiated to non*

irradiated 5 X 101 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 5 X 101 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 10-*

5 X 10' 5 X 10-*

J.00 1.00 1.00 t

1.00 3 X 10-1 1.00 10-1

~00 1.00 1.00 1.00 1.,00 1.00 1.00 1.00 llr' 0.50 1.00 10-,

Activation energy K1&, kcal/mole Nonirradiated (rad) 47.5 18.0 35.0 33.0 32.0*.

25.4 34.3 34.3 45.5 Ratio: Irradiated to non.

irradiated 40.2 20.5 38.3 40.2 e 5 X 101 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 LOO 1.00 0.00 1.00 1.00 5 X 101 1.00 1.00 1.00 1.00 1.00 1:00 1.00 1.00 0.40 1.00 0.00 1.00 1.00 5 X 107 0.34 1.00 1.00 1.00 t

i.oo 0.40 1.00 0.23 0.28 0.90 1.00 *.

0.89

Based on loss of tensile strength.

t Degraded (scission).

TABLE III r

PERMANENT ErFECT OF GAMMA RADIATION ON DIELECTRIC CoNBTA.NT o~ CABLE CoWRINOS R

l'l "

MeMured after Two

-~

z Dose Hours CB CF 90°0 NF CF (rad) c*c>

PVC HD Poly BBR CLPE EPDM

Butyl Oil Base CLPE.

EPM Silicone en >

!:I 0

k'(SIC), 40 V /mil, 60 Hz None 23 4.90 2.58 3.32 3.58 3.37 4.35 3.44 2.25 3.47 3.11 z

en 0

2 75 6.82 2.52 3.84 3.44.

3.19 4.21 3.27 2.30 3.49

2.06

!JO 7.32 2.51 a.o4 3.18 4.14 a.oo 2.30

. 3.44 2.08 Percent change.

5 X 101 23

+3

-1

+5

-1

-4

-2*

+5

+1

+s 0

0 e 75

-4

-2

+10

-2

-4

-2 0

+a 0

-1 00

+52

+1

+4

+5

-2

+2

-4

.+3.

-1 5 X 101 23

+4

+3o

+o

+3

-9

-20

+10

+3

+8

+29 75

+6

+42

+6

-7

-6 0

-4

-7

+a

-8

~

c::

en

!)0

+132

+4

+5 0

+a

+4

+a

-8 z

C 6 X 10' 23

+21

+a6

+1

+a

-7

-20

+o

+a

+10

+2 Ill

'4 75

+41

+ao

-9

-1

. -8.

t

+1

-1

+o

+1

!JO

+104

+o

+2*

t

+JO

+o

+o 0

.1 X 101 2:3

+uo

-6

+1

+2

+1 t

+7

+2

+1

+o Tho hiKh diclccl.ric constnnl.~ or the neoprono,., CSPE-, and CPE-hllBed Jacket mo.terial9.wurn not eigniflco.ntly o.lTcctcd.

J.om1 hii:hcr tlum limit of bridge.

t No tc11t, 11nmplo d1igrmlr.d.

f!i l'I ffi

~

'4...

L'.) s

... -.. *~-...,.,.~"°".. l"-C-.~~.,.:-..,....,,.**

None Dose (rad)

Percent change 6 X 10' 5 X 101 6 X 10' 1* X 10' T.

E IV, PERMANENT EFPECT OJ' GAMMA RADIATiON ON TAN a (POWEil FACTOR) OF CABLl'l INBULATioN!I Mea.,ured after Tw.o

)

Dose llnnr.i en CF 90°c NF CF (rad)

("C)

PVC HD Poly SDR CLPE EPDM Butyl Oil Base CLPE EP:\\[

D - tan 6 X 10',... 100 percent PF, 40 V /mil, 60 Hz None 23 540 143 231 65 217 110 118 J.l 75 1424 80 1s:14 106 254 5:14 200 2-l

!10 2085 140

>3000 380 540 1040 44:3 27 Percent change 5 X'l01 23

+1

-20

+1

+11

-41

+6 l

-33 75

+21

+375

-14

-16

-12 1

+aso

\\:

00

+34

+750

-24

-36

-13

-18

+519 5 X 101 23

+34

-22

+16

+48

-25

+11

-22

+29 75

+oo

+235

-14

+as

-4

-13

-7

+10s 00

+5!13

-;50

-20

-1

-30

+100 5 X 107 23

+50

-20

-22

. +20

-23

+02

-20

- +-li 75

+11

+oa

-38

-6

.:...37 t

-5

+or OD

+29

-60

-20 t

-48

+rn>

1 X 101.

23

+111

. -2:

-30

+2

+ao t

-11

+:m Tan a of the neoprene-, CSPE-, and CPE-bn.sed jacket materials we1"e not significantly affected.

Lo~s higher than limit of bridge.

i No teHt, sample <legrac.lec.l.

TABLE V Pt:R&IANt:NT EFFECT OP GAMMA RADIATION ON DC RESISTIVITY OF CABLE COVERINGS Meaeurec.l after Two Hours CF oo*c NF 86 150

?i'O

+2

-2

-13

+2!)

+*>-_,

-'i

+as

+au

-:m

+:ss*

("C)

PVC HD Poly SDR CB OLPE EPDM Butyl Oil BllSe CLPE CF EP:\\-1 Silicone De resistivity, 100 teraohm-em, 500 V de 23 0.15 240 2.3 70 12 76 15 141 il 0.2 75 10-,

25

10-1 40 0.3 0.2 1.2 68 1.3 10-1 00

\\ 10-*

20 10-*

37 0.3 0.1 0.1 60 1.0 10-*

\\

23

-28

-43

+60

+33

-20 0

-1

-4

+u

+67 75

..-00

-32

+48 00 t23

-oo

-6 23 48

-70

+13 75

+10

-00

+40

+50

+32

-14

+100

-3

+10 0

-33

-29

-61

+100

-3 0

+s2

-59 *

-4 0

-1

-4

+as 0

+11

-8

-84

+oo

.:...3

-0

+25 90

-47

-!l2 0

-43

. -61

;;..93

+oo

-3 0

+1s 23

-67

-81

+48

-68

.+53

-82

-5

-4

+25

+oo 75

. +100

-80

+250

-52

-34

+aa

-4

-7

+20 00

+21

-!)I}

+100

--75

-7!)

+2s

-3

-40

+O*l 23

.. +120

-70

+68

-7

+oo

+as

-8 0

+oo

N° 0 iciit,.. ~rnpld dogrliillid.

1

~

~....,,.'If',~ ::**:

Silirone 110 a,o

-li'II

-li

-a

+:!O

-1!)

-1

+:?4

. + Ill

-1!1.

+u

+**-_,

Neoprene 10-~

io-,

10-*

-:n l

-85

+1s

+4

+415 0

+11

+:mo

~

CRPF.

CPJ*:

o. :!

111-*

10-*

111-,

10-,

m-*

-1,I

-*111

-:1:?

-55 l

+ms

-5 0

-ti 0

-8:!

+rn 0 l

-Ii

-!I:!

-iii

-RS

~ s

~

A >

~

l:l

~

~ >

> 4 -,

==

C:

~

==

~

C

?4

~

i e

~

?:!

....,..........,......"1"~1*,~~....,,,,~~

/

I pouuds, in genrral, nre le,.,-1 n-sisw.nt to oxidalion than most insulatiom1 in u:-e today. The log of that time WIL'i then )>lotted versus the reciprocal of nh,;olute temperature in cll'grecs Kelvin (1/ T) to 1':ilirnatc the time to the :,mne cl11111µ;c in propct-ty at 70°C [11]. The data in Table I I show dccl"<'ascs as larµ;c as i-ix orders of magnitude for the oxidation rc.... istance of PVC:, silicrmc, and nonfillcd, non,;taining CLl'E. The oxidation rcsistanc!.) for CPE anci PVC cleerca,,cd by a."' much a_,; tlm.*c orders of 111aµ;11itm1c after exposure to 5 X 107 rad. The others were not affcctccl..

Data on the oxidation rc:;istance of II D polyethylene Wl're not.**

included in Table II bcr~'luse the samplN di1l 11ot yidd \\llliformly after aging. Irradiated :samplN aµ;cd ahovc the melting point of the polyethylene did not flo,v, indicating that the polymer was cross-linked; the u:se or radiatio11 to cro,:.-.-Jink polyethylene, or course, is well known. We speculate that agi111,!; characteristics:

o( irradia"tcd IID polyethylene would be similar to those for chemically cross-linked nonfillcd polycthyleues. In rcµ;:l.l'd to the activation energies calculated from the Arrheuius plots of our aging data, the higher the value, the more temperature dependent the 14,*ing *mcchanlsm. However, different aging mechanisms can have :similar activation energies. For example, the 47.5 kcal/mole value for non irradiated PVC i:s clo:;e to the 45.5 value for silicone.

(This level is equivalent to 2 eV.) However, the PVC.had a useful lire of 200 hours0.00231 days 0.0556 hours 3.306878e-4 weeks 7.61e-5 months at 13G°C, while silicone retainer! mol"C than 65 percent of its unaged propcrtie:; after 1440 hours0.0167 days 0.4 hours 0.00238 weeks 5.4792e-4 months . This difference, we feel, was due to rapid loss of pla:;ticizer in the case of the PVC and normal oxidation for the silicone. The predicted values.;how that both PVC and silicone should have a long service at 70°C where both plasticizer volatility rate for the PVC.. 1.11d the oxidation or silicone would proceed at a f.,'Teatly reduced r:i.te.

CH.\\NGES IN ELECI'IUCAL PROPERTIES OF CABLE COVERINGS Dielectric Constanl (SIC), Tangent of Dielectric Lo88 Angle(PF),

and DC Remtiuity These parameters were monitored during irradiation at 5 X 105 rad/h in 30°C air. or 40°C water in the Esso laboratory. Any.

changes were small and relatively unimportant;. they were es-sentially the same whether the irradiation occurred in air or water. Dielectric constant did not change noticeably. Tan o in-creased by factors of 2-4. A tenfold decrease in resistivity was noted for butyl, nonfilled CLPE, EPD.M, and EP:\\1 while the 90°C oil-base material, carbon black-filled CLPE, and HD poly-ethylene showed no change. A tenfold increase was seen with PVC.

The data iii Tahlc Vi.how that de resisliuily of thr c*ry:-talli11e polyclhyle11e-liasl'rl nmterials generally decreased while the re-sistivity of the amorphous _ruhhcr-hased materials inct'ca.*,cd.

Further, the dr r<':-istivity of fl D polyethylene a11ci 11011fill,..-I cros,;-linkcd polyc*tliy[ene became more sensitive to tcrnpcratu:*e

'with incre:L-<e<I irradiation a.-; c\\*iclcnc<'rl by the 2.r incrc!L"iC in actirntion energy K. from 23 to 00°C shown in Table \\"I.

Carbon hlack-fillcd cross-linked polyethylene and c:ay-fillcd El'D:\\I wc1*c le.-;,; :;ensitivc to temperature with increased radi-ation. Other:-, were 11ot affected.

It wa."i not part of our work to e,;tablish the cau:;e o

the challl,!;C!l in cable covcring.i after irradiation. Howc,*cr, some

speculation on the cau.-;e of the marked change:; in the product

of dielectric con,;tant and tangent delta. (dielectric lo::-s index) observed for the nonfilled polyethylene is in order. Consider the ca.~e of polycthylcue in,mlations with or without a PVC jacket.

Since the chanr:cs arc about the same, chlorine from the PVC jacket is probably not reacting with the polyethylene. It is more likely that electrons trapped in the cry.;tallinc portions of the polyethylene during radiation were released after radiation when temperature was inc!'eased during electrical measurements.

This will also ~xplain the fact that tangent delta for the non-filled cross-linked polyethylene (SP= 110°C) wires _was at its usual low level when measured at 90°C after conditioning ior 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months in steam at 40 psig (142°C).

Specific Surjace Resistivity The following data show that this parameter (measured after four weeks' immersion in water) was not significantly affected by radiation. PVC was an exception, since the radiation c:i.uscd it to deform during water immersion (see Table VII).

Dielectric Strength i1& Water and Steam The data in Table VIII show that the dielectric strength (measured immediately after imrneNion in water) of insulating materials, with two exceptio:is, was not significantly changed by exposure up to 108 rad. PVC retained i3 percent of its brcakdcnm value up to 5 X 107 rad, but retained only 41 percent after 108 rad. Dielectric strength for butyl did not change up to 5 X 106 rad, but was 80 percent lower after 5 X 107 rad when it became very soft. The dielectric strength for jackets decrea.."'<!d nearly fivefold for neoprene and twofold for" CSPE and CPE.

Similar effects were seen when irradiat-0d samples were sub-jected to conditions simulating the steam environment C.\\.--pected within the containment vessel during abnormal bursts of energy.

Water-filled jars containing the samples (except for the therino-plastic materials) were maintained in a steam autoclave at 40 psig (142°C) for a. maximum period of 32 days. Periodically, the ~amples were removed from the autoclave a,id pl::.ccd in 90°C wat~r for two hours, after which electrical measurements at 40 a11d 80 V /mil were ma.de. The thermoplastic HD poly-ethylene and PVC wires were kept continually in the oocc water; thr.y did not go in the autoclave. The data. in Table IX show that the ability of the carbon. black-and nonfiHed

cr~s-Permanent changes in*these three parameters also were rela-th-ely unimportant. Table III shows that, with one exception, the dielectric conslant was not affected by irradiation. The ex-ception was the high-density polyethylene/PVC covered wire for which k.' increa:;ed 132 pcr~ent after 5 X 10-' rad. The room temperature dielectric con.;;tants of the neoprene-, CSPE-, and CPE-based materials (23, 6.5, and 10) were not affected sig-nificantly by radiation. We were unable to study the effect of radiation in the high-temperature values of dielectric constant; we wer~ unable to balance the Schering bridge when these materials were at 75 and 90°C.

Table IV shows that with two exceptions, tangent delta (tan o) was not pcrmancn tly affectei:1 hr irrodiatio*n. The exceptions we~ the high-<lcnsity and nonfilled cross-linked polyethylene whose tan c5 incrcasec.l as much as 750 percent. The room temper-ature tan c5 X 10-1 values of neoprene-, CSPE-, and CPE-bn."ied material!! (1157, 93i, 2i7) were not affcctec.l significantly. by radiation. Bridge balances were not ~iblc at 75 and 00°C.:

. linked polyethylene, clay-filled EPD:\\I and EP:'II, high-temper-

_*ature oil-bas~ and silicone materials to withstand so* Y/mil was not seriously affectr<l by gamma* radiation up to 5 X 107 rad.

SBR was less stable after irradiation, but independent of dosage.

Butyl wo.s unstable above 5 X 106 rad. Silicone had the poore:;t

. rcsisw.nce to steam;* the nonirradiatcd control lasted only four days. The silicone had hydrolyzed to a powdery residue. HD*

polyethylene did not* fail in !)0°C water rcgardicss or do;;age; D (tan o"X 10~) was higher than expected, near 1000 for *irradi-

/*..

111,0ll<:t:Tl' Mill Fl!;.Ht:R: CAB!.>~ l::i Tllt:Rll.\\l, Rt:.\\C"'\\9-.1*c~t:.\\R m:::it:R.\\Tl:'<i(I STATIOSK e

535 TADLE YI Acr,;,.ATIO::i ENERGY K. KCAL/MOLE FOR 23 TO oo*c J)C HF-';ISTl\\"lTY OF INSUl.,ATIOSS Dot<e CB CF HT NF CF (rad)

PYC Ill> Poly snu.

CLPE.*

EPmI*

Butyl Oil Ba:se CLPE EPli Silicone None 17.5 10.5 2G.6

'Zl.i 10.5 17.G 10.9 1.4 15.1 15.5 5 X 101 11.s*

22.4 2G.6

'Z1.1 7.9 17.6 10.9 1.4 15.1 15.5 s x101 17.5 2'2.4 26.6 9.0 1.9 17.6

.10.9 2.8 15.1 15.5 5 X 101 17.5 22.4 26.6 9.0 7.9 10.9 2.8 15.l 15.5

Not tested, sample degraded.

TABLE VII SP.tietnc ScRFACE REslSTIVITY AnER Foua WEEKS

. bilMERSION IN w A"rER (l\\h:oomts)

PVC

Neoprene CSPE CP~

z2°c 00°c 22*c oo*c 22*c oo*c 22°C oo*c None

. 3.5 3.5 210.0 8.0 21.0 21.0 0.6 21.0 5 X 10*

I.I

210.0 0.1 21.0 21.0 0.6 21.0 5 X 101 0.3..

2.1 0.2 21.0 0.6*

180.0. 10.5 5 X 107 2.5

8.4 0.4 4.2* 0.6 180.0 21.0

No reading, badly deformed, and irregular.

-(

TABLE VIII PElwANENT EFFECTS OF G.utMA RADIATIOY ON DIELECTRIC STRENGTH OF CABLE CoVERISGS Dose HD CB CF oo*c NF CF Neo-(rad)

PVC Poly SBR CLPE EPDM

.Butyl Oil Base CLPE EPM Silicone prene CSPE CPE Rapid rise 60 Hz, Smaa V /mil at 23°C None 1000 1176 960 1000 865 564 625 2028 811 1192

1304 13~

1242 5 X 105 862 1130 952 928 653 618 794 1300 871 1130 204 612 sso 5 X 101 863 1220 843 1030 915 542 968 1430 870 1560 170 595 715 5 X 107 725 805 925 1060 842 129 817 1300 788 1490 289 510 648 I

1 X IO' 414 670 612 828 838 744 1360 788 1045

No test, sample degraded.

TABLE IX Pl:ms:ANENT Eie"FECTS OF 0AY:llA RADIATION ON DIELECTRIC 8-rRF.~GTH OF C..i.BLE COVERINGS CF 00°c CF Dose SBR/

en EPD:\\1/

Butyl/

Oil Base/*

NF EP;\\1/ Silicone/ HD Polveth-(rad)

Neoprene CLPE Neoprene Neoprene CSPE CLPE CPE Glass ylene/i.>YC PVC Days in steam 40 psig {142°0) to failure at 80 V /mil at 90°C Weeks in oo*c water to failure at.SO V/mil

None 11

>32

>32 11 32

>32

.18 4

>9

>9 5 X 101 4

>32

>32 11 32 4

18 3

>9

>lJ 5 X 10' 4

>32

>32 11 32

>32 18 4

>9 2

5 X 107 4

>32 25 1

25

>32 18 3

>9 1

\\,

r

/

\\

(.\\

\\ \\..

530 TABLE X Pt:RMANENT ]~FFECT OF GAllMA UADIATION ON FLA!tlE HESISTANCE OF THIN WALL,vim,:.,; IN UL FL.Un: Ti,::;T CF EPDM/

!J0°C CF HJ> Poly/

SBR/

en Neo-Butyl/

Oil Ilw;e NF EPM/

Silicone/

PVC PVC

Neoprene CLP.I!:.

prene Neoprene

-CSPE CLPE CPE.

Gla.s:5 Dose (rad) 0 10' 0 !QI

-0 10' 0

1011-0 10' 0

103 0 101 0

109 0

10*

0 103

Results p

P F

p F

F F

F p

p F

F p

p F

F p

p pp Percent flng 0

0 100 0

100 100 100 100 0

0 100 20 0

0 100 100 0

0 0 0 destroyed o* - *. i80 After burn 0

0 180 0

52 60 180 100 o* 0 50 80 0

180 0

0 0 0 (seconds) l>-pa&1; F-Cailure.

TABLE XI THRESHOLD OF G.u!MA. RADIATION DAMAGE (RAD) FOR ELASTO.\\IER-BASED CABLE INSULATIONS HD Poly SBR CB Property PVC CLPE Tensile strength 109 108 5 X 107

!QI Elongation 5 X 107 5 X 101 5 X 107 5 X 107

Rate of oxidation 5 X 101

>5 X 107 >5 X 107 Dielectric loss 5 X 107 5 X 101 108 lQI Electrical stability 5 X 105 s X 101 5 X 101 >5 x 107 Dielectric strength 5 X 107 >5 X 107 5 X 107 lQI Overall threshold of 5 X 101 5 X 101 s xio*. 5 X 107 damage Highest dose still 5.X 10' serviceabl~

,~5 X 10'

..... ____ *****, 5 X 107 lQI TABLE XII

1'1mzsaoLD OF GAMMA. R.U>IA.TION DAMAGl!l (BAD)

FOR ELASTOMER-BASED CABLE J AC:S:ETS Property Neoprene CSPE CPE Tensile strength 5 X 107 s*x 101 5 X 107 "Elongation 5 X 107 5 X 107 5 X 101 Rate of oxidntion 5 X 101

. 5 X 107

5 X 101 Overall.threshold or damage 5 X 101 5 X 107

5 X 101 Highest dose still serviceable 5 X 107 5 X 107 5 X 107 CF 90°0 Oil NF CF EPDM Butyl

.Base CLPE EP~I Silicone p,*c

!QI 5 X 101 109 5 X 107 10~

5 X 107 5 X 107 5 X 107 5 X 10s 109 5 X 107 5 X 107 5 X-107 5 X 107

>5 X 107 5 X 10* >5 X 107 5 X 101 5 X 107 5 X 101 5 X 10s lQI 5 X 101 103 5 X 101

103 108-5 X 107 5 X 107 5 X 101 5 X 107 5 X 107 >5 X 107 >5 X 107 5 X 101

>IQI 5 X 101 10'

>lQI

>109

>103 5 X 10*

_5 X 107 5 X 101.

5 X 107 5 X 104 5 X 107 5 X 105 5 X 10' lQI 5 X 101 103 1()1 108 5 X 107 5 X 10' TABLE XIII

. SUGGESTED IEEE NUCLEAR EYVIR0:0.3.IENT CL.-\\SSIFICATIOY FOR ELASTOMER-BASED CABLE J:,;;;CL.-\\.T!OYS Radiation Class 2

3 4

5

See Conclui;ions.

Class 0 (90°C)

Silicone*

Butyl EPDM EPM

-Oil base NF CLPE CB CLPE None None Temperature Cln.'>S A Cla,;:s B (105°0)

(130°C)

Silicone*

Silicone None EPD.M None CB CLPE EPl[

None None None

None

,I

., J r

-l ;_. ~"~'"' "" "'" "",,......, '" """'""* *~" ""'"*"-'~ """""'"' '~"""".. *.

. (_

atcd :<arnplC'S v1*n-11s 12-l for Liu: control. l'VC wire,; WC'rn 1111stahle ouly up to 1*las... 2 railiat11111 IC'Wl:<. "r r-.i.te. thl':<e i<y:<IC'lll:< i,11!:,-

and fail rel at. 80 V / mil in 90°C water ~Ctr.r r.xposurc to 5 X 10~

for 1*la,,-<e,;_ 0 I aucl 02.

rad.

4) Nonfillrrl cr11:s."-li11ked polycthylcnC'S and oil-lJa,-e in,-u-To a.-.."<'S.'- the flar;1c-rl'sist::mt propcrtic:,; of the thin wall wirei in this study, we used the Undcrwritcr.i' Lahoratoric.-; vertical flame tc---t. The data in Tahlc X show that. the flamc-n*tarrlant propcrtici<, cxcrpt for the I-ID polyethylene/ PVC were not changrd after exposure to 101 rad. The improvement in HD polyethylene/PVC cxpo;;cd to 108 rad was due, we feel, to radi-ation cre$.~linking which prevented

the polyethylene from.

melting and flowing into the flame, but one should not depend on rodint-ion effrcts to make the wire fume resii;tant. The ri;;ks or sprr!Lding a fire also appear to be great. with the cros,;-linked polyethylenes, butyl/neoprci1e, and Sl3R/ncoprene combina-tions. Of course, 'the flume re.-;ist.ance of carbon black-an<l non-filled cro!'..<;-:.linked polyethylenes can be markedly improved by the application of a suitable flame-retardant jacket [12]. PVC,

silicone/gla...,'> braid, D0°C oil-ba.-;c/CSPE, El'D}.I/neoprene, and EPl\\I/CPE combination,- should offer greater a.'IBurance against the spread of fires.

THRESHOLD OF DAl1AGE OR RADIATION LIMITS 'FOR CABLE COVERINGS From the data in the previous tables, we have selected the ma~;mum total intc:i;mtrd dose that a covering can withstand

\\\\;t.hout a :significant change in each of the properties studied in this work. These doses are given in Table XI and XII in terms of a. -threshold of radiation damage. Table XI covers the insu-lation and Table XII the jackets. The results are given in two tabl~ because the effect of radfation of electrical properties is not perti~1cnt for jackets.

Ne.xt we took the lowest maximum dose which affected a significant property and combined them with the IEEE temper..:

ature designations, classes 0, A, and B into the following sug-g<?Sted IEEE nuclear environmental classification [13]..Maxi-mum gamma radiation vs.lues in Table XIII arc those from Table I in [13] eon,*erted to radians using the factors 1 roent-gen= 87.7 erg g-1 (c) and 1 rad= 100 erg g-1* RAdiation class 1

is equivalent to 0.9 X 105 rad; class 2-9 X 105 rad; class 3-8800 X 105 rad; class 4-88 000 X 105 ~d; class 5--greater than 1010 rad.

CONCLUSION'S We believe* the data given above justify the following con..

clusions:

1) Dimethyl-;ilicone-bascd insulations (IPCEA S-19-81, par..

3.17) arc suitable at their usual 130°C temperature rating only in low-radiation environments, because of its sc*nsitivity to steam and its poor resistance to oxidation after radiation. We rate it only in clas:;es 01, Al, and Bl.

2) Carbon black-filled (and probably clay-filled) crosl1-linked polyethylenes and clay-filled EP~1 or EPD:\\[-bascd insul::i.tions are suitable at 105°C up to da.ss 3 radiation le\\*els, when pro-tected with suitable flame-resistant braids-such as the glass construction in this study or flame and water resistant asbestos

.constructions. We rate the:;e two materials for cl~es 01, 02, 03 and Al, A2, A:l.

3) Butyl and high-density polyethylenes* when properly jackrlccl are suitable at their usual 90°C tcm11crature rnti11~

latio11, whr11 properly jarkrtrd, arc suitable at their \\L~ual H/JcC:

tcmp<'rature rat.inµ: up to cla.,,; 03. \\\\'e rate thc:'e systrm,. f11r ela-;sc.~ 0 I, 02, :i.11rl 03. *

5) 8BH-am! l'VC-ha.-;cd co\\*crings arc suitable only at. rc::'.l-tivcly low tr.mp1*raturcs and radiation levt>b. In partiC'Ul:ir, IPC'EA 8-61-402, par. 3.7 and 3.8 PVCs are scn~itive to !J!)t

\\\\'atcr and steam when t>xpo~rd to more tlum 5 X 105 r:1ci.

6) Neoprene, CSJ>E, m; CPE jackets are. suitable at thc:r U!lual 70°C temperature rating up to 107 rad. The rat1i'.!.t?Gil limit is ba,,cd on oxidation effects; flame resistance is not af.",*cteJ by radiation.

Finally, we belie\\*e that the mo:-t attractive combination of materials for thermal nuclear generating plants will be CSPE-or Cl'E-jaekcted insulations based on nonfilled CLPE, CI3 (c:

clay-) filled CLPE, 90°C oil-base, EPDJI, or EP:\\I. Such cia.5i!

03 cable; should lai;t at least 40 year.:; when* exposed to a total radiation dosage up to 5 X 107 rad and will,:till be sen*ic~

able after exposure up to 108 rad.

Acx.-..owLEDG:\\tENT The authors wish to emphasize that many of their associat~,,-;

throughout the company and in LTV Research Center partici-pated in and contributed to this study. Further, we gratefa!J}*

acknowledge the assistance received from Dr. Forster and E;::;;o Research and Engineeri.ng Company.

. *.. R.EFERENO:S (11 D. Greenwald, "U. S. economy moves ahead aiter a brief slowdown," Elec. World, vol. 168, pp. 128-lco, Sepvm:ber 18, 1!)67.

[2] J. C. R. Kelley, Jr., and P. G. DeHaff, "Prototype to i,b,1.e

\\

trail t-0 fa.st-breeder reactors," Elec. World,...-ol. 169, pp. 30-3:!,

January 8, 1968.

[31 P.H. Klein and C. ~fauna!, "The effects of high-energy ga;u;,:;:i radiation on dielectric solids," AIEE Trans. (Co1:wmniC'r.(.-,.,

and Elecl.ronics), vol. 74, pp. 723-,29, 195.5 (January l[J:iG (4] ~dia.tion efiects*on. materials,." vol. 1, ASTII Special Tecb:.:-

csl Publication-208,' 1957.

(5) "Radiation effects 011 materials," vol. 2, ASTII Special Ttci.n:-

cal Publication-2"20, 1958.

[6] "Radiation effect.'! on materials," vol. 3, ASTII Special Technl-cal Publication-233, l!l59.

[7] "?1Iateriais in nuclear applications," AST::\\'1 Special Technic.:J Publication-276, 19GO.

[SJ "lrradiatioa. of polymers," in Advances in ChemistT"J (65 s~r.\\

R. F. Gould, Ed. Washington, D. C.: American Chemk.;.l Society, 1967, pp. 1-21.

(9) R. W. King, N. J. Broadway, R. A. ?.layer, and S. Palin.::b!.

"Polymers," in Effects of Radiation on Mate rials a n.J Component~,

J. F. Kircher and P... Bowman, Eds. ~ew York: TI.ci1,l,oi<l.

1964, PR* 84-1G6.

(10] C. G. Collins and V. P. Calkins, "lladiation damage to cl:,:;-

tomers, organic liquids, and pla..,tics," Office oi Tech. Sr-rv.,

U.S. Dept. of Commerre,_.APE..\\:-261, September 1956.

(11} L. C. Whitman, "Simplified methods of calculating insulali0a.

life characteristics," A I EE Tra11.. 1. (Pou:er Apparatus an,:/

Systems), vol. SU, pp. 683-685, October HJ61.

Il2J R. n. *mod!!;ett and ll G. Fisher, "Insulations and jackf:t; for cross-linked polyethylene cables," IEEE Trans. P,,,rrr Apparatus a11d Systems, vol. 82, pp. 9if-9SO, Dt:reml,cr }!_1,.;;;,

[13l L. Horn, "New nuclear standard approve<! by IEEE stanJ:iru.;

committee," IEI::E Trans. Sue/ear Science, vol. !l."S-l-l, r*P*

67-i'l, Augu!1t 1967.

[HJ IL}'. Heed, "Coping with radiation in nuclear rcactio!I pbnt..;,"

pre,;cnled at IEEE Summer Power ::'lleet.ing, PurtlanJ, Orr.,

Juh-9-14, 1967.

(15] R. B. Blodgett and R G. Fisher, "Present slatt;s of the cor.1na*

and heat-resista11t cable insulation base<l on ctln*lrn1..~propykn*~

ruhbrr," IEEE 'l'ra11s. Pou*er Apparatus a11il Systems, vcii.

P.-\\:--S,, pp. 11:!9-,-1 H:I, April HlG8.

e..

--,-s.,.,.. -....er Discussion J.B. Gardner (Tim Kcrilc Compnny, ~cy111011r, Conn.): The nulhn,_,.

ue to he 1:,,111,;rnt.11lutc1l on the cm1ccplin11 n11cJ cnrryi11g nut or 11 :;ignilicaut. program to develop sl111rl-li11m pcrformn11cc data on a wide 5pcctr11m of mntcrinls that. mighL he c:onsidcrctl for w,c in

. nnclenr power plant cnhle<. The paper L'I i11lere;t.i11g and most cerfniuly t.imcly.

The pnrposc i<ccrns clcnrly i;tatcd in the paper; namely, "The main qne.-;tion to which this paper i.'I addre:ssc<l is whet.her cables immlntcd and jacketed with clastmner-(polymcr)-lm.-;ecl material can b<: expected to perform satisfactorily in the containment area.

and in f.he lower radiation area 011!.,,;ide t.hc cont.ninment vessel of thermal rcal*lors." However, the conl'hL,;inns listed are more con-cerned with material or system'! cla.-.-;ificat iom,; than they are with the suitability to perform in nuclear power plant...;. The Kcrite Company has been active in nuclear power plant oriented tcst.ing for many yea!'1'l. A serie"I of radiation te:<t.'I were made in 1958, and 0U1e1~ more recently, to dosages np to 6 X 101 rad mat-eriaL-; being exposed under wet. and dry conditions. The objectives of the testing, however, 'were nowhere near as broad S.'1 those in this paper. In onr case we wi.shed to evaluate only tho.<<e materials (mostly proprietary compound~) which had already proven successfnl or very promising for genera.ting plant application, to det.ermine if they would meet the :c1pecific radiation in tensitie.'I stated a.'I required of ca.hies in the

. new nuclear plants.

None of the data reported from the authors' inve,;tigation contra-dicts the prior findings of onr more limited investigations, but the conclusions we have drawn and would dr:i.w from either our or their experimental data. are at some variance with those of the authors.

Before addres.~in!; several specific quc:;tions to the authors, it seems appropriate to comment on two aspects of overall testing which should be kept in mind by all cable users and cable designers.

The first point is one which the authors themselves have made strongly in prior published papers, but seems overlooked in the present work; namely, that very significant differences in per-(

ormance can be expected from various commercial compound'! all

~-ontainiug a polymer (or polymer blends) in common. *Notwith-standing this fact, the common polymer mny tag the materials with identical names. If name classification of mate~ia!::i has to be, then we all should be warned of the pitfall:! that may occur when we ignore major differences among materials of a given name. It may be easier to organize one's thinking, tabulnt-e data, or specify rnnterial.s by reference to polymer name tags, but it also is likely to be completely erroneous in its implie!.tions.

Secondly, with regard to radiation level cla.*,si.fications, I believe it is rather unfortunate that the IEEE classes 1, 2, and 3 differ by factor::s of 100 in radi::i.tion exposures. For instance, the total radiat.ion requirements that have been stated for a number of nuclear in-stallations extend over 101 rad of cla,;s 2 but do not approach the 10' rad of "class 3. Therefore, materials which would not apparently qualify -within the broad range of class 3 might well be applicable in installations requiring only radiation up to the low end of the range.

If seems that many of the organic materials considered for wire npplication show rnq.jor changes in su.:;ceptibility within the 107 to lQt rad range. Just how useful the IEEE classifiC!l.tion system is going to be for detcrmin;ng s11itability of *materials for cable in-stallation in nuclear plants i,;, therefore, very que,itionable.

Specific qne:stioru; stemming largely from the above considerations are a-; follows:

1) In the authors' first conclu:sion, the limitations of classifica-tion or silicone appear to Le related to the steam sensitivity of this material. Is steam sensitivity a factor properly used in the IEEE cln.,,;;;ification? Or, i::! stC'am sensitivity more properly related to the applicability of *a cable in certain circuits which have to operate after a loss of fluid accident within a containment vessel? We also note a typical ambiguity in thoughlll in the first conchL-;ion having to do with the whole cln.~sification problem; namely, in the first

-:1entence of the concllL'sion, silicone immlntions

are referred to, "nt at the end they arc lumped together anJ unfort11nately referred

\\

, as "i~".

\\la11w,cript recch*ed July 11, HJGS.

. ' I u:,:,: TRA:',SACTICJSH o:S l'CJ\\n:R rARATt"M ANU sn,-n:At:<, ll.\\\\" l!}(r.)

2) llcfcrri111t to their se1*1111d conclusion, how can mat.edal,1 never leitc<l hy t.hc nut.hors hcyoucJ to* rad he properly placed in a cla-1.~i-ficnlion which implie< suitability for up to 101 ra<l?

3) Noling that some materials arc being cla.'l.'U.fied by the nut hors.

for 10.'>°C operation in nuclear pl::mts, we wmild a.~k; "\\\\'hy pi1.--k**

nuclear plants as an appropriate location for proposing a higher*

temperature cla.-,,,ificntion of a given cable than ha.i been done elsewhere in in<lrn,;try.standards?"

4) The prcscuce of flame resisting coverings appears* to be in-volved in the IEEE cln.,,,;ification suggested in the second con-cl11sion.,vc would qncstion t.hat this is an appropriate eon:;ideration in using the IEEE cJ1L...,.ificatio11s for materials, and would appreciate the authors' comment.-;.

5)" In their third concln.siou, the antho~ have progrc,;,;ed from material *cla-;.<;ifications to S\\'slcm-; ela.-.-sifications. In thi.i conchL~ion flammability L'! quite evidc"ntly not considered. However, it would seem much more appropriate for one to consider fire a.~ a relevant factor of system'! than individual materials. \\Ve. wonder why there is thi:-i apparent di.~crepancy and v.*het.her fire resistance shcnld affect IEEE cla.,-sifications at all. *

6) In their fourth conehL-;ion, is it proper to cla.-;;;ify a.sy;;tem cla.-;s 3 for radiation when one of the components of that sy.stem (neo-prene) is only rat.ed at cla.,,,; 2?

7) Have the tested PVCs been omitted from the cla.."'<lificatiou intentionally or by oven;ighl.?

8) The anthor,;' technique of using cnble sample. in jar:; of ;,;ater at 140°C to invesligat-e susceptibility of materials to "steam atrnc.:;-

phere" is very intere.~ting. Knowing the susceptibiiity of certain material"l to the combination of ste2.m and air from D!l.5t test.:! in our laboratories, we would ask, "Do the author,; have* a firm b~.,-i.s for accepting water immersion tests as indicative of re~i.,tance to the steam-air atmosphere expected in containment.-s?"

9) Are the ~pecific compound!l used throughou~ the im,estign.tion those with a. service record and commercinlly available toda)", or were they selected to represent typical materials that* meet the various cited IPCEA, UL, or ASTM: specifications?

E. M. Davis (Gilbert Associates, Inc.* Reading, Po.. 19G03}: Thi, paper presents some very import:mt information for thv.Se wh9 are concerned with the selection and applic::i.tion of c:i.bie to be installe...i

within the containment vessel for nuclear reactors.

In the design of nuclear generating stntioll3 we feel thst the r:ihle insulations materials should, if not e.xposed ~ conditions out:;ide the limits for which the cable was intended to oper:at-e, om]a.-;t the life of the station. The installation and operati.n!,: proofoms as well as the shutdown time involved, if found that the emire cable,,y:;tem IDlL~t be replaced, dictate that the cable should certainly have aa expected life well. beyond the time when the station is finally de-commissioned for the usual reasons of economy and operation. The authors have suggested a 40-yenr life and a to.till r!l.diation do~e of 5 X 107 rad during this time, and these numbers appear to be a rea.~onablc basis for the aclive life oi the present generation of thermal nuclear reactors. In order to ailow for a co;nfortable margin of safety and also for a short-time high-exposure conditiou daring an incident, it appears that the cnble in the containment ye:;;,el should be capable of at least a total radiation do~e oi 5 X 108 rad.

It is encouraging to note that the authors' findings show that such a requirement does not prohibit the use of ela.stomer-b:i.-;ed.compounds, since these compounds are so much ea.~ier to handle than inorganic types of insulation systems.

From an application point of view, a vah:aLle a.~pect of thi:! paper is the consideration given to those other fnctoni of environment which affect the life of the cable. ~Iuch of the prcviou.:;ly publi,hed rc,;ea.rch wa;s directed at finding out what the effect,; oi rr.diation

-were upon certain bn.:!ic materials used for electrical in,mlation.

In thi.~ connection, we* would like to lmow if the test sample:! u~ed arc representative of the actual compounds that would be supplied by the author,;' compa11y.

Manuscript =ived July 8, 19GS *.

-~

(,

\\

e

'fABLE XIV T11t:RllAL lh:co~IPOSITIO.S 01' CAl.11,t: Con:rm,as CB CF Oil Base NF CF Neo-CLPE EPJHI Butyl

!J0°C CLP!!:

EP)l

~ilirone PVC prene CJ>E CSPE Onset temperature or 245

2QQ '

2!l0 250 250

mo

>300 120 200 150 200 volatilc:s not con-densnhlc at 25°C

. Weight lo.,s* (percent) 3 1

11 4

2 I

2 35 20 33 8

cm1 ga,o 1icr itrnm of 5

4 20 3

5 3

<2 40 20 50 6

compoundt

After onc-miuute heati1111: at :i:m*c.

t Volume of noncondensable (:.!5°C) gn.~es in milliliters at STP after compound wns heated for one minute at 330°C.

Anyone who is nov; involved in the del<ign of a nnclcnr generating statio~ is acutely aware of the va:;tly increased cor,cern over the subject of flamm:ibility in the cable system. The authors have touched on this subject, but I believe that much more emphasis i'l needed. Flame-resi.-;t:mce charnctcri:,tics can no longer be COIL"idered

as merely de:;irable, but must now be given top priority as an ab-solute necessity. It is far better to use matctit.J.s which.,..;u prevent the spread of fire in a cable system than to rely on water spray systems, for example, to control a fire after it ho.'> occurred. \\Yill the autho:s offer further comment on this subject? Also, do the authors feel that the jacket can be relied upon to provide the necessary flame protection w!,E:;re the insulation material is of a type that will con-tribute to the spre!!.d of fire? I am rcfcrriug to their statement that "The risks of spreading of fire also appear to be great with the cross-linked polyethylenes, butyl-neoprenes, and SER-neoprene combinations, but foe flame re;;istance of carbon black-filled and nonfilled, cross-iinked polyethylenes can be markedly improved by the application.of a suitable flame retardant jacket." For example, it appears that the aging characterist.ics of PVC after radiation e.'C!)OSure would make it a poor candidate to provide flame pro,.

tection as a. jacket, e..-en though Table XIV showll no permanent effect of gamma radiation on flame resistance.

We are pleased to sec that attention was given to conditions simuhting irradiated cable subjected to a high-humidity high-*

tempet*atu.re environment. This kind of data is necessary* during the discussions with the A~C licensing authorities.

One final comment is in regard to the short-time ability of an irradiated cable to simultaneously witru;tand temperatures of liiO~C and &team pressures of 50 psig. Certain cables must continue to supply power to vital equipment for many hours after an incident.

There are some who believe that only a solid lead sheath or copper tube can a.d('quately protect a *c.'lble ir.sulntio11 system against such.

conditions. Will the authors plea:;c comment on this?

The author.; are indeed to be commended for their contribution to the available knowledge pn this very* important aspect of cable covering:s. We hope experiments of this type wiU continue in order to keep abrea.<;t of the rapidly changing technology of nuclear designs and applicatiom1.

M. G. Noble (General Electric Compnny, Waterford, N. Y. 12188):

would like to make the following comments.

Sream Resislanre of Silicoue Rubber: While silicones in general have excellent hot water rc,;i.~tnnce, it is recognized that high-pres.-;urc steam cnn induce degradation of the silicone polymer.

Ilowever, it should be pointed out that silicone rubber cables have had an excellent service record in a number of nuclear plant installations (Indian Point, Yankee Atomic Power, etc.).

Specificl\\tions involved hnve c.*lilcd out the need for resi.,;t.ance to 100-percent relative humidity at 100°C, spl:LShing wa!A!r at boiling temperatures, and similar environmental conditions.

Manuse_ript.received July 15, 1968.

T11i.o; performance would indicate that the high-pressure steam conditions described in the paper nre rarely encountered in a.etus.l

. service. Furthermore, if they should be introduced, the U5e of

.proper cable dc,;ign will prevent a malfunction. By incorporating a resin-~atnrated glu.*,;s braid over the insulation, a protecth*e barrier will exi~t which will preserve circuit integrity even in a. ca...-se of severe polymer degradation.

Radiation Resisla11re of Silicone Rubber: The compound :;elected b~-

l\\lr. Blodgett and )[r. Fisher i:, designated a.,; a dimethyl :;ilico:ie.

In (16J the author reports that "dimethyl silicones are generally less resbtant to radiation than the other silicone type,. )[ethyl*

pher.yl silicones: show in general the best resistance to radiation of all the silicone types."

Whereas the componr.d used in this evaluation became brittle at 5 X 107 rnd, it is predictable that a rnethylphenyl or ruethylpheny!-

vinyl silicone compound would be flexible up to 1 X 104 rad. Thi5 factor emphasizes the need to consider silicone rubber as :i. fair.:!:,*

oi compounds rather than a specific composition 0£ matter. Pro?er compound tielection is essential to achieve optimum resiotance to radiation and many other environmental conditions.

Resistance to Ozidatio11.A/I.er Radiation: \\'\\ie ha~*e never seen any

indication that the oxidative stability oi silic~me rubber w~ in-fluenced by exposure to gamma radiation.

Obviously, the combined effect of radiation and high-temperat'.1.'"C exposure will accelerate hardening and ultimate embrinlement.

However, ottr interpretation ha.s been that the radiation e:1.-po;;*.1re merely advanced the point at which the silicone rubber,tood on the hcs.t aging curve. Subsequent aging would continue at the ~=e rata as would normally be observed from that specific point with a nonirradiated sample.

It should be further noted that the r:i.tio in Table II indicating relative service life at i0°C for irradiated versus nonirradiated silicone rubber obscures an important point: even after an initial radiation doseagc of 5 X 105 rad, the silicone rubber b.3d an c:::ti-mated exposu.re time at 70°C, t-0 sustain a 40-percent 1055 in elon-gation, of about eight years-an extremely long period of ti!'..:e.

We ask whether, particularly in nonflexing application, this siliccne rubber compound could not have been given additional nucl;,,ar environmental cl=ification rs.tings of 02 and.-\\2. It would appe:,r that methyl-phenyl silicones could clearly be gi,en the:;e ratings.

Summation: We wish to comrnend 1Ir. Blodgett and )Ir *.Fi.;;her on an excellent paper. However, we believe that:

"1) Their concern o..-er ste:i.m sen:sitivity of silicone rubber cs11 be di:,pcllcd by proper cable de:;ign. -

2) Proper componud selection will optimize radiation resi:Sta.nce..

3) The retention o! oxidative stability after radiation requires further study.

4) Analysis of the data ii1cluded in thi3 report shows ths.t, e.e11 after a radiation doseage of 5 X 10* rad, silicone rubber ha.; good high-temperature,;ta.bility. It would appear that cla.:,sificatio11 ratings of 02 and A2 might be justifiable, particularly ii a mec~y}.

phenyl silicone rubber compound i,; used as the insulation m!\\terial.

REFERE!iCES

[10) R. Harrington, Rubber Age, December 1957.

~vae1r-tt ltrm-r>> ** r er<<llf:Ot 11 <t d s:

a rtrC.

,: ww--.1t..,..1~"'-"'...,"'"---*----------.- ---ioii*11111

..... a,..,..,.:..;...

e 5:10 M. L. Singer (111\\tficld Wire and Cable Divt~ion, I.indcn, N. J.

Oi036); The authors are to be complime11ted for making available

a on the electrical and hcnt a~cd properties of cnhle coveriugs

.:r exposure to radiation. With the imminent advent or the fast breeder reactors, the study should prove to be of much \\"Rine, combining a.-; it docs, this combination of propertie.-; for the first time.

A,. so often happens when firi<t-rate work L" performed, almo.<t S.'i many qnl)!;tions are raised as are answered. For instance, would diphcnyl-silicone rubbcr-ba.*ed ins11latio11s have done better than the dimcthyl-si icone rubber insulations which were reported? It jg.

true that the dimethvbilicone rubber insulations are the ones most commonly used toda)", but thi-; need not be a permanent situation.

Similarly, I 'll"as surpru;ed at the good performance, after radiation exposure, of the oil-based rubber insulation. Is this really a re-flection of the properties of oil-base mbber, or does it reflect the properties of the ethylene-propylene rubber in the insulation?

Similar studies of t.he older natural rubber and SB-R rubber oil-base insulations could vield the an:;wer. The.<e t'l\\*o questions sug-gest the paths of investigation which can be followed. The effects*

of structure of the polymer, such as the huge poln.r group in PVC, and the effects of fillers in the polymers can be investigated fruitfully.

The authors set out only to find whet her cables which <.".an presently be fabri<."ated can be expected to perform sat.isfactorily. They have achieved their goals successfully. This i'l not the final answer, and

. the authors' data suggest the paths to be followed in future in-vestigations. That the authors achieved this is al,;o to their credit.

Manuscript received July 15, 1968.

(

L McKean (Phelps Dodge Copper Products*Corpora,tion, Yon-

kers, N. Y. 10i02): This pa.per *on nuclear cable insulations is a*

very welcome addition to the technical literature and provides a much needed reference on this particular subject. Anyone who has attempted to search the literature recently for this kind of infor-1IUJ.tion in <."onneetion with insulated cables will appreciate* the availability of this up-to-date study in our particular field.

I thought it would be of interest to describe some interesting

1tudies which we pursued a few years ago in connection with air-

<lielectric or semi-air-spaced coaxial cables such as the Styrofiex aluminum sheathed design employing a polystyrene tape open heli.'< insulation over the conductor.

Such coaxial de;;igns were being sought for applications in con-nection with reactor monit-0ring systems for use in the high-intensity zones within the containment vessel. Hence for a typical test en-vironment, field strengths developed within a. typical reacto_r core and within a reactor shell were considered pertinent.

There was real concern that the presence of "ionizing radiation".

within the dielectric would not only degrade the solid ius*ulation in the course of time, but that it might immediately alter, drastically, the normal high-frequency tran5mission characteri.. tics, thereby developing a. serious impairment in cable efficiency and performance.

Tests were conducted on Styroflex cable samples placed in a. test hole of the reactor core and al:,;o in a test tunnel at the Brookhaven Laboratories. The field strength in the reactor core was rated at 1.5 megara.d.<i per hour-fast neutrons, and* 1.0 megarad per hour-gamma photons. The corresponding field strengths in the test tunnel were approximately two orders of magnitude lower.

In the case of the cable placed in the full reactor field, there wa.'! no measurable change in impedance, velocity, or attenuation at frequencies from 1 :\\Ic to 200 :-.Ic. In addition, pul.,;e transmission was studied but no discernible noise (ionization) was eviden*t on

he wave front of the reflected pulse.

However a decrease in de resistivity of three decades, from 1012 to 10* ohms, was noted immediately upon entering the field, and

~i:!tivity remained essentially at a constant level during the 100-hour exposure period. This effect was duplicated on the.samples*

in the more moderate nuclear field in the teit tunnel. Thus, it appears Manuscript received July 8, 1968.

e IEEE TRASSACTIONS C'S \\*OWEK AFPARATt!S AND SYSTEMS, llAY 100!)

thnt ionizing radi:Lt iou rl1!ffl conlrihute a degree of co11taminatio11 of the air dielectric as mca."nretl on direct current.

The~e test rc,;ults i111E1*nle that HF performance is nut meas11rnbly afTected by ionizing r:u!iatinri of lhe air dielectric d11ri11g its normal opernti11g life. Polrtyrcne, of conr:<e, offern relatively high,;!ability

to radiation, afTurding :i. prncti1:al insulation for app_lications in the intermediate intensity range. For very high field strengths, hc"\\"ever, only inorganic materials will function ::satisfactorily over any sib*nif-icant operating life.

R. B. Blodgett and R. G. Fisher: We thank the discus..<<?rs for their stimulating comments and questions about our finding~. Before we attempt to answer the specific questions raised; we first point out that we concur with Mr. Gardner's comments about the wide

range covered by each of the IEEE radiation classes. We ice! that

. up to 10* rad gamma, divisions of one decade rather than the present two decades wo*.tld be more useful. No doubt change:, along the:::e lines will take pince as more data and e.xpericnce become available.

In another comment, :\\1r. Gardner wa.rned of the pitfalls when major differences between insulation and jacket componnds b:i.-;ed on the same polymer are ignored. We agree that such differences cannot be ignored. However, we have found where compounding techniques have been used a maximize intrinsic polymer strengths and minimize weaknesses, the differences in the response to nonnuclear environ-ments among compound5 based on the same polymer -..,,*ere not*

significant. Our data for different PVC cross-linked polyethylene and ethylene-propylene compounds in Table XI indicate the same situation will hold true for optimized compounds based on the ;5ame polymel'll in the nuclear environments to which our investigation was addressed.

In regard to Mr. Davis and Mr. Gardner's qu~tion abont the compounds used throughout our investigation, all wires except nos. 11, 12, and 13 were obtained on a random ba.sis from onr factory.

stock departments. Items H-13 were fabricated in our laboratory wire line using randomly seleded factory mixed compounds. All compounds are available in commercial products* made at our company..

We want to reemphp_.,ize that our conclusions concen:ing th~

silicone compound investigated may not apply to compounds b:i.;;ed on different elastomers suc.!J. as the methylpheuyl and methyl-phenyl-vinyl silicones referred to by.Mr. Noble. For that very reason we spe~ifically named the type gum employed. Thi.5 should clear up Mr. Ga.rdner.'s question about our first conclusion. Since we did not include several different silicone-based comoounds in our study, we have no data to answer Mr. Singer's question about the relationship of the type and a.mount of organic groups on the main silicone chain to their resistance to gamma radiation. ~Ir.

Noble's comments and our references above should shed some light

on this matter. The important. point here is that some desigr,er:s specify IPCEA S-19-81, par. 3.li silicone for use in thermal nm:lear generating stations. We feel our data are typical for the silicones normally furnished to that IPCEA. specification. Inform:1.tion about the respon.~e oi the other silicones in tests similar to our.s should be required by designers before they set standards for nuclear en-vironments.

The balance of properties reported for the 90°C oil-ba:se insala[iou was primarily due to the elastomer employed as Mr. Singer suggests.

l\\Ir. Gardner asked whether we consider steam, hot ~rnter, fire, and the other factors discus..-1 above ad proper factors to be con-sidered when assigning IEEE chis.sificatiollll to systems or individual

materials. Our ansv,er. is yes. So far as. our autocla-\\*e, *tests are concerned, we feel confident. that it simulates the steam-air atmos-phere expected in containment for two reasons. Fi~t, our test*

periods were long enough to JLllow equilibrium conditions between the water and steam. Second, both the water and st-eam contaiued oxygen.

The class 03 cables di.5cussed in our final conclusion should continue to operate under the incident conditions th:it )lr. Davis ManuscripL received AugusL 2'.?, 1908.

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described. Of course, the a.ddition of a continuous metal sheath over those clasa 03 cables would provide maximum assurance of continued service. l\\fr. Gardner apparently missed the point that our tests, except for air oven agings, were carried out on the insulation-jacket systems dcs~ribed. In addition, the PVC neoprene, CSPE, and CPE coverings were assessed individually. The.,;e data on single materiall:I and combinntiorui of materials nrn the llll,-is for 0111 ruu-

. clusions. The PVCs in our l:ltudy were inte11tio11111"y omi11rd fr11:n

.the IEEE cln.-..~ifications since they were not suitable fur u11'C continuous rnting.

We agree with i\\Ir. Davis that the ffammnhility of l"llhle ~.,*--:l"m"'

reqniro cnrcf11l nttention. The use oC fire-resistant jnckl't.< in **u:n-bination with inorgnnic thermal and fire ban*icr tapt-s,.,,...,,. t!,c cla.~ 03 immllltions, for example, should provide the he-t t~111,i 0i-nation o( all-round properties including rc:<i:<tanre to :ind r_ hc spread o( fires. Ilnt cable design is not the 011ly factor in opl imi,.i1:~

fire resistant cable systems. The m:urner in which fire-re,.ai,t:,11t cables arc installed is aL-;o important. For e:mmple, 1 he pr:iel icr :;i using tieni of cnhles in trays 11eeci'i to be reexamined. ) I ixing puwer and control cables in the same run can be ha1.ardmL-;, if the drra1i1:g factor for the power cables hs.s not been ba..,ed 011 the a1*c11r:ire

&'!SeSSment of the t.hermal circuit in the trays. _Effective prutet:ti,111 of the power circuits to avoid "cooking,;hurt.-;" should al:<o be 1L~1-.J.

When these and other precautions well known to M:?.tion de:-:!:a engineers arc tak.en, a water spray system would pro,*ide n hii.:h degree of assurance *against a major conflagration occnrriug.

In conclusion, we believe the new data in Table XII am! Fig_ 1 in combination with the daLa in the original paper should p1'1,vi,1e designeni of containment ve,;sel penetrations with a 1,,i,;i:; of,;elect :nit insulated cables snitaule for use within sealed cauister,,. l!lsu!:i,i,~n and jacket compounds based on halogenated polymer:; :<hriuiJ be avoided becau:re of the corrosive nature of the ga.~e,; fm1111.L /i.ll insulations we rated das~ 03

should be !:.uitable for us~ \\,.;:i::n canisters providing the proper derating factor bu~ed on I he 011,d temperature, thermal drcuit of the cani:ster, and high-teniperac,,r~

physical strengths shown in Fig. l are taken into con,:idcrr,l!n!:.

On the basis of these data, clay-filled EP.\\I anc! EPD:\\I hn*:,} th~

best combination of propc;-ties for canister applicatiom*.

e ATTACHMENT 3

Ston~ & W~bster Engineering P~O.. !1v}I. 232S Boston, Kk.

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Dear Sir:

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