NUREG/CR-1184

SAND79-1787

RV

EVALUATION OF SIMULATOR ADEQUACY FOR THE

RADIATION QUALIFICATION OF SAFETY-RELATED EQUIPMENT

Lloyd L. Bonzon

William H. Buckalew

Manuscript Submitted:

Date Published:

August 1979

May 1980

A

Sandia National Laboratories

Albuquerque, NM 87185

operated by

Sandia Corporation

for the

US Department of Energy

Prepared for

Research Support Branch

Office of Water Reactor Safety Research

US Nuclear Regulatory Commission

Washington, DC 20555

Under Interagency Agreement DOE 40-550-75

NRC FIN No. A-1051-0

3-4
p.
EXECUTIVE-SUMMARY

The qualification of Class 1, safety-related, equipment is of continuing concern to the nuclear power industry. Equipment qualification is

encompassing in scope and concept; that-is, any qualification program must

consider the specific functional signature of the equipment under the combined environments of its aging history, followed by the combined environments of its particular design basis accident. The radiation environment

is just one of several; if strong interactions occur between radiation and

other environments (e.g., temperature), the radiation effects are not

clearly separable. It is not precisely correct, therefore, to speak of

"radiation qualification." Nonetheless, radiation qualification is addressed in this report to evaluate the adequacy of radiation simulators

typically used in qualification testing. Where possible, discussion of

combined environment efiects is made. "Adequacy" need not be based on oneto-one correspondence of the actual radiation signature with a simulator

signature, although that would be sufficient to assure adequacy. Instead,

adequacy is judged on the basis of equivalence of equipment "damage" as a

result of the exposure; under that definition of adequacy, the radiation

signatures may not be identicalbut the damage (and damage mechanisms)

must be quite similar.

Before simulator adequacy could be evaluated, it was necessary to

provide background information and calculations -in three areas. These are

summarized in the report and are detailed in numerous companion topical

reports.

First, it was necessary to accurately define the actual loss-ofcoolant accident (LOCA) radiation signatures. In fact, it is more nearly

correct to describe these LOCA-radiation signatures as "hypothesized".

While they are intended to be conservative estimates of releases during

the LOCA, they more nearly represent unterminated LOCA conditions. The

bases for these reported hypothesized radiation signatures are Regulatory

Guide 1.89 and a newer draft of 1.89. It is also recognized that new data

5
base and new initiatives to describe "best-estimate" LOCA radiation signatures (,based on best-estimates of accident time-sequencing, progression,

and fission-product release fractions) are currently underway. However,

it is generally recognized that these continuing studies will not substantially affect the evaluation of simulator adequacy, because any

signature will have (1) gamma and beta radiations, (2) nearly invariant

spectral-time shape, and (3) time varying, but shape consistent, magnitudes. The differences will then be primarily manifested in magnitude

and in assumptions of "instantaneous" release of the fission products.

Second, from the earliest calculations of accident source signature,

it was recognized that the principal concerns in simulator adequacy would

be associated with the (1) beta component, (2) time-varying gamma and beta

spectra, and (3) time-varying gamma and beta magnitude. Similarly, it was

apparent that exposed organic materials would be most (relatively) sensitive to the differences between simulators' and actual signatures.

Therefore, it was first necessary to make comparative calculations of

exposed organics' .response to the various radiation signatures. In the

report, a modeled electrical cable is used as an example of a typical

Class 1, safety-related, equipment item with significant exposed organic

materials. Its significance is as an exposed organic material, not just

as an electrical cable. Cobalt and cesium are examined as typical examples of simulators; other gamma sources (e.g., spent-fuel elements) are

not expected to strongly influence any judgment of simulator adequacy.

Clearly the closer the spectrum (and particle-type) and magnitude match,

the more "adequate". is the simulator.

The third area to be addressed, preliminary to the evaluation of

simulator adequacy, was the identification of radiation damage mechanisms.

For this evaluation, two separate investigations were conducted: the

first by IRT Corporation staff and the second by Sandia staff. The major

damage mechanisms postulated were

e Electrical changes, charge buildup, electrical

noise spikes

* Temperature changes

6
a Chemical and mechanical changes

o Differential mechanical stress

Each of these is specifically addressed in the report with judgment of its

importance to simulator adequacy concerns made.

The trapped charge in the insulator is largely a consequence of the

nonuniform dose deposited in the cable. The mechanism that applies here

is that the secondary emission leaving a volume element is not balanced by

secondary emission from adjacent points because the adjacent points are

not receiving the same primary radiation. The gamma source simulators do

not show such a strong attenuation as does the true LOCA (particularly,

beta) source so they will not precisely simulate the trapped charge and

any resultant noise spikes. The amplitude of resultant noise pulses,

caused by breakdown in the cable, depends almost completely on the exact

details of the cable termination. If the termination is either a small

resistive load or a large capacitive load, then the noise spikes will not

be large. Because leakage currents are calculated to be small, the noise

spikes are small and the choice of simulator is relatively unimportant;

the LOCA environment is adequately simulated as long as average doses are

"maintained".

Temperature changes in materials may be sufficient to be of concern.

Here the beta radiation can be viewed as a total heat source, since the

depth-dose features are relatively unimportant. In the same regard, the

simulator may be relatively unimportant as long as the heat source is

duplicated (where important). Thus, while the simulator is not a factor,

the simulation of the heat load is a consideration.

Total chemical and mechanical changes in materials are not a strong

function of the radiation source, if the total damage is duplicated as

appropriate. That is because the LOCA and simulator energy losses in

materials are via the same mechanisms. Further, the available data indicate only minor dose-rate effects in elastomeric materials.

7
One feature of radiation damage not generally duplicable by the

common simulators is the differential stress, due to strongdepth-dose

profile dependence, from the LOCA beta source. The mechanism involves

the shrinkage of a material relative to its remaining elongation; if the

surface of an elastomer suffers shrinkage on the order of the remaining

elongation, it is plausible that surface crazing or cracking could occur.

However, available data show only minimal shrinkage (a few percent), even

when the total elongation is reduced to near zero (either thermally or by

radiation). Hence, differential stress is not a practical concern.

It is concluded that the standard gamma-radiation simulators can

adequately duplicate the damage mechanism and damage in safety-related

equipment that result from postulated nuclear plant ambient- and accidentradiation environments. The conclusion can be no stronger than that

because the simulators must be intelligently used in an overall qualification program that implies combinations of environments, magnitudes,

secondary radiations, and other considerations. Other specialized

simulators, which more closely achieve the LOCA-radiation signature, are

equally adequate, with similar provisos. However, there seems to be no

reason to select one simulator over another. One recommendation is to

overstress the equipment/material everywhere to a greater total dose than

expected from the combined LOCA-radiation signature; dose rates should

also approximate the expected (combined) rates. However, other logical

data-based techniques (e.g., averaged dose and rates) may also be acceptable.

In summary, we have seen no evidence of unique damage mechanisms in

exposed organic materials that demand unique radiation-simulation techniques. But neither can radiation be arbitrarily applied to the test item

without consideration of the complete qualification program. Future work

should consider the equivalences of beta/gamma and neutron/gamma ratios in

bulk degradation, charge breakdown transient and permanent effects, secondary emissions, and more complex equipment.

8
CONTENTS

Page

Introduction 15

1.1 Background, Accident-Radiation Signatures 15

1.1.1 General 15

1.1.2 New Initiatives in RadiationSignature Definition 16

1.2 Background, Comparative Calculations 18

1.3 Background, Potential Damage Mechanisms 19

2 LOCA Radiation Signatures 21

2.1 Origin of Signature Bases 21

2.2 Energy-Release Rates -- Source 1 22

2.3 Spectra -- Source 1 26

2.4 Doses and Dose Rates for a Generic Containment 31

2.5 Summary 35

3 Comparative Calculations of Exposed Organics'

Response to Simulator and LOCA Radiation 37

3.1 Depth-Dose and Charge Deposition 37

3.2 Summary 46

4 Damage Mechanisms Identified and Prioritized 47

4.1 Concerns in Adequacy Evaluations 47

4.2 IRT Study Summary 48

4.3 Sandia Study Summary 51

9
CONTENTS (cont)

Page

4.4 Relative Importance of Damage Mechanisms

Relative to Simulator Adequacy 52

4.5 Other Damage Mechanisms 52

5 Radiation-Induced Electrical Signals in Cables 55

5.1 Background 55

5.2 Radiation-Induced Disturbances 63

5.3 Conclusions 64

6 Bulk Temperature Effects 67

6.1 Background 67

6.2 IRT Heat Flow and Temperature Estimates -

LOCA Source 67

6.3 Some Sandia Estimates - Simulator Source 68

6.4 Conclusions 72

7 Bulk Polymer Degradation 73

7.1 Integrated Radiation Dose Effects 73

7.2 Dose-Rate and Oxygen Effects 74

7.3 Conclusions 74

8 Differential Mechanical Stress in Insulating Materials 77

8.1 Background 77

8.2 Energy Deposition and Polymer Degradation 78

8.3 Polymer Degradation - Elongation/Shrinkage

Experiments 78

8.4 Polymer Degradation - Elongation/DensityChange Experiments 79

8.5 Other Considerations 82

8.6 Conclusions 82

10
CONTENTS (cont)

Page

9 Summary and Conclusions

References

85

87

APPENDIX A --

APPENDIX B --

Calculations to Support Evaluation of Test

Sources for Radiation Qualification of Class

1E Equipment, IRT 8167-010(B)

Evaluation of Radiation Damage Mechanisms

in a Reactor Power Cable in a Loss-of-Coolant

Accident, IRT 0056-002A

91

171

ILLUSTRATIONS

F igure

1.1 Temporal Fission Product Release Sequence - Unterminated

LOCA Without Cooling

1.2 Gamma-Ray Energy Release Rate vs Elapsed Time From

LOCA - "Best-Estimate" Source

1.3 Beta Energy Release Rate vs Elapsed Time From LOCA -

"Best-Estimate" Source

2.1 Gamma-Ray and Beta Energy Release Rate vs Elapsed

Time From LOCA - Source 1 (Airborne), 4000 MW

2.2 Beta Energy Release Rate vs Elapsed Time From LOCA -

Source 1 (Airborne) and Several Reactor Operating Times

2.3 Gamma-Ray Energy Release Rate vs Elapsed Time From

LOCA - Source 1 (Airborne), Daughter Product Contributions

2.4 Average Gamma-Ray Energy vs Reactor Cooling Time -

Source 1

2.5 Average Gamma-Ray Energy vs Reactor Cooling Time -

Source I and Several Reactor Operating Times

2.6 Average Beta Energy vs Reactor Cooling Time - Source 1

and Several Reactor Operating Times

17

17

18

22

23

24

27

28

28

11
ILLUSTRATIONS (cont)

Figure P age

2.7 Gamma-Ray Dose/Dose Rate vs Elapsed Time From Release -

Airborne Source 32

2.8 Gamma-Ray Dose/Dose Rate vs Elapsed Time From Release -

Specifically Combined Airborne, Plateout, and

Waterborne Sources 34

2.9 Beta Dose/Dose Rate vs Elapsed Time From Release -

Airborne Source 34

2.10 Beta Dose/Dose Rate vs Elapsed Time From Release -

Specifically Combined Airborne, Plateout, and

Waterborne Sources 35

3.1 Dose vs Penetration Depth - 6 0 Co, 1 3 7 Cs, and Source 1

(Airborne) Gamma Rays Onto Typical Cable Configuration 39

3.2 Dose vs Penetration Depth - 6 0 Co and Source 1 (Airborne) Betas Onto Typical Cable Configuration 40

3.3 Dose vs Penetration Depth - 6 0 Co, 1 3 7 Cs, and Source 1

(Plateout) Gamma Rays Onto Typical Cable Configuration 41

3.4 Dose vs Penetration Depth - 6 0 Co and Source 1 (Plateout) Betas Onto Typical Cable Configuration 42

3.5 Dose vs Penetration Depth - 6 0 Co, 1 3 7 Cs, and Source 2

(Plateout) Gamma-Rays Onto Typical Cable Configuration 43

3.6 Dose vs Penetration Depth - 6 0 Co and Source 2 (Plateout) Betas Onto Typical Cable Configuration 44

4.1 Dose Rate vs Penetration Depth - Combined LOCA Radiation

Enviro.nment, 1-min and 4-d Following LOCA 49

4.2 Material Elongation/Shrinkage Change vs Integrated

Dose - Illustrative Example for an Organic Material 51

5.1 Dose Rate vs Penetration Depth - Combined LOCA Radiation

Environment, 1-min and 4-d Following LOCA 60

5.2 Dose vs Penetration Depth - 6 0 Co Onto Typical Cable

Configuration, With and Without Intervening Iron Liner 61

12
ILLUSTRATIONS (cont)

Figure Page

6.1 Outer Surface Polymer Temperature vs Exposure Dose Rate 71

6.2 Temperature Differential Across Cable Jacket and

Insulation vs Exposure Dose Rate 71

8.1 Polymer Aging vs Aging Time - Aging Thermally Accelerated 80

8.2 Polymer Aging vs Aging Time - Aging Thermally Accelerated 80

8.3 Polymer Aging vs Aging Time - Aging Radiation Accelerated 81

8.4 Polymer Aging vs Aging Time - Aging Radiation Accelerated 81

TABLES

Table

2.1 Source Types and Distribution Categories 21

2.2 Percent Deviation of Selected Irradiation Times

From Equilibrium Irradiations

Energy-Release Rate vs Cooling Time 25

2.3 Average Particle Energy vs Cooling Time - Source 1

and Several Reactor Operating Times 29

3.1 Charge Deposition in the Cable Configuration 45

5.1 LOCA Sources Specification 56

5.2 Source 1 Airborne Spectra Parameters 57

5.3 6 0 Co Spectra - Medium CH2 58

5.4 Charge Deposition in the Cable Configuration 62

5.5 LOCA Conditions Average Dose Rates - rads (mtl)/s 65

6.1 Dose-Rate Deposition Estimates - LOCA and 6 0 Co Sources 68

6.2 Instantaneous Temperature Rates - *C/s 69

13-14

EVALUATION OF SIMULATOR ADEQUACY

FOR THE RADIATION QUALIFICATION OF

SAFETY-RELATED EQUIPMENT

1. Introduction

The qualification of Class 1, safety-related, equipmentI is a continuing concern to the nuclear power industry. Equipment qualification is

encompassing in scope and concept; that is, any qualification program must

consider the specific equipment functional signature under the combined

environments of its aging history, followed by the combined environments

of its particular design basis accident. The radiation environment is

just one of the several environments. Thus, radiation is not clearly or

cleanly separable; to speak of "radiation qualification" is not precisely

correct.

Nonetheless (as a first approximation), radiation qualification will

be addressed in this report in order to evaluate the adequacy of radiation

simulators typically used in qualification test simulations. Where possible, discussion of combined environment effects will be made. "Adequacy" need not be based on one-to-one correspondence of the actual radiation signature with a simulator signature, although that would be sufficient to assure adequacy. Instead, adequacy is to be judged on the

basis of equivalence of equipment "damage" as a result of the exposure;

under that definition of adequacy, the radiation signatures may not be

identical but the damage (and damage mechanisms) must be quite similar.

1.1 Background, Accident-Radiation Signatures

1.1.1 General

Preliminary to the evaluation of simulator adequacy, it is necessary

to accurately define the actual radiation signatures. That has been

previously done and reported2-6 under the Task 2 effort associated with

the overall Qualification Testing Evaluation (QTE) program. 7

15
In fact, it is more nearly correct to describe these loss-of-coolant

accident (LOCA) radiation signatures as "hypothesized". While they are

intended to be conservative estimates of releases during the LOCA, they

more nearly represent unterminated LOCA conditions. The bases for these

reported hypothesized radiation signatures are Regulatory Guide 1.898 and

a newer draft of 1.89.9

Since simulator adequacy is dependent upon the actual radiation

signature, a review of this effort is included as Chapter 2 in this

report.

1.1.2 New Initiatives in Radiation-Signature Definition

It may be appropriate to note that the LOCA radiation signature has

not been finally established. Originally, Regulatory Guide 1.898 recognized only one source term for radiation qualification. More recently a

draft Guide 9 discusses a two-level source term. The larger term, as

originally specified, is to be applied to containment heat-removal and

isolation systems, postaccident monitoring (PAM) equipment, and the like.

The smaller is to be applied to the majority of the safety-related systems. These two sources are logically based in that the larger is nearly

an unterminated LOCA condition, the smaller represents a degraded (not

totally dysfunctional) safety-systems response to a LOCA-initiating event;

thus the two-tiered source recognizes the circular logic and that it is

inappropriate to demand qualification of equipment to environments that

can only occur if that same equipment has already been assumed to have

failed so as to produce the environments.

Much more recently, under the QTE program, 7 effort has been directed

toward a so-called "best-estimate" LOCA-radiation signature incorporating

best-estimates of accident time-sequencing, progression, and fissionproduct release fractions. Full disclosure and distribution of this work

by IRT Corporation1 0,11 has been made in a Sandia report released as

Reference 12. Figures 1.1-1.3 visually summarize some of the key features

of the "best-estimate" signature.

16
INITIATION OF LOCA

BLOWDOWN REMOVAL OF WATER IN CORE (5 to 10 s)

GAP ASSUMED 100% RELEASE TIME

RLEASE I NETIT

-UNCERTAINTY - MELTDOWN RELEASE

VAPORIZATION RELEASE . . .. .. **.*.. . .~.. * .. -. i.

[-- OXIDATION RELEASE E ....

0 11.0 .2.0 3.0 5.0

RT-16934 TIME AFTER ACCIDENT (h)'

Figure 1. 1 Temporal Fission Product Release Sequence -

Unterminated LOCA Without Cooling

(from Reference 12)

1, 0 9

TIME AFTER LOCA (s)

Figure 1. 2 Gamma-Ray Energy Release

Rate vs Elapsed -Time From LOCA -

"Best-Estimate" Source

(from Reference 12)

17
1011

1010 -- S. i• u ......- •. 

>V

.109

108

O-1 L7• o oo O o6 

10- 100 10 1 10 10 04 0 0 10 7 108

TIME AFTER LOCA (s)

Figure 1.3 Beta Energy Release Rate

vs Elapsed Time From LOCA-

"Best-Estimate" Source

(from Reference 12)

While it is important to understand that the ultimate radiation

qualification signature(s) may be modified by these studies and by database programs, 1 3 it should also be realized that they can not substantially affect the evaluation of simulator adequacy. That is, any signature will have (1) gamma and beta radiations; (2) nearly invariant

spectral-time shape; and (3) time varying, but shape consistent, magnitudes. The differences will then be primarily manifested in magnitude

and "instantaneousness". The evaluation of simulator adequacy in this

report will be discussed relative to the larger Regulatory Guide 1.89

source term, also known as Source 1.

1.2 Background, Comparative Calculations

From the earliest calculations (in this series) of accident source

signature,2 it was recognized that the principal concerns in simulator

18
adequacy would be associated with the (1) beta component, (2) time-varying

gamma and beta spectra, and (3) time-varying gamma and beta magnitude.

Similarly, it was apparent that exposed organic materials.would be particularly susceptible to the differences between simulators' and actual

signatures. It was imperative, and preliminarily necessary, to make

comparative calculations of exposed organics' response to the various

extremes of radiation signatures. Some of this effort has been previously

reported in the literature,6,14 but the full and final report15 prepared

by IRT Corporation is included as Appendix A of this report.

In that report, a modeled electrical cable is used as an example of a

typical Class 1, safety-related, equipment item with significant exposed

organic materials. Its significance is as an exposed organic material,

not just as an electrical cable. Cobalt and cesium are examined as

typical examples of simulators; other gamma sources (e.g., spent-fuel

elements) are not expected to strongly influence any judgment of simulator

adequacy. Specialized suurces (e.g., bremsstrahlung, linacs, and the like)

were not examined for two major reasons. First, these are generally smallvolume sources not amenable to long-term, large-volume irradiations.

Second, gamma simulators represent an extreme for the simulator adequacy

concerns, specifically the (actual) beta signature; if adequacy can be

shown for gamma simulators, the specialized sources may then also be

adequate. Besides the simulators examined, the report15 also addresses

unique test conditions (e.g., intervening steel test chambers) and certain

test/actual conditions (e.g., 70-psig steam surrounding the test

specimens).

Since the comparative calculations influence and are bases for the

evaluation of simulator adequacy, a review of this effort is included as

Chapter 3 in this report.

1.3 Background, Potential Damage Mechanisms

The third area to be addressed, preliminary to the evaluation of

simulator adequacy, is the identification of radiation damage mechanisms,

particularly those most influenced by a priori known differences in

19
simulator and actual signatures. For this evaluation, two separate investigations were conducted: the first by IRT Corporation staff1 6 and the

second by Sandia staff. 1 7 The former is included as Appendix B of this

report. The major damage mechanisms postulated were

* Electrical changes, charge buildup, electrical

noise spikes

* Temperature changes

* Chemical and mechanical changes

* Differential mechanical stress

Since these damage mechanisms are the true bases for simulator adequacy

evaluation, they will be discussed and prioritized in Chapter 4 and individually addressed in succedent chapters.

20
2. LOCA Radiation Signatures

2.1 Origin of Signature Bases

The hypothesized LOCA radiation source. for a light-water reactor has

been specified by the US Nuclear Regulatory Commission in its Regulatory

Guide 1.898 for purposes of qualification testing of Class 1, safetyrelated, equipment in commercial power reactors. The approach taken in

the Guide is to specify certain fractions of fission products by categories that are assumed to be released from the reactor core and distributed within the containment structure. More recently a new draft of

the Guide 9 suggested a separation of the qualification source into a twotiered system to be chosen as appropriate to the equipment being qualified

(Table 2.1). That draft Guide then calls for two radiation source terms

(for containment heat-removal systems and similar equipment, and for other

safety-related electrical systems) and three distribution categories for

each source (airborne, waterborne, and plateout).

TABLE 2.1

Source Types and Distribution Categories

(From Reference 9)

Source I Airborne 100% noble gases, 25% iodines

(Containment heat

removal systems, etc) Plateout 25% iodines, 1% solids

Waterborne 50% halogens, 1% solids

Source 2 Airborne 10% gpble gases (except 8 5 Kr),

(Other safety-related 30% 0 Kr, 5% iodines

electrical systems)

Plateout 5% iodines

Waterborne 10% halogens

21
From this specification it remains for the user to translate these

source bases into energy release rates and energy spectra for gamma rays

and beta particles as a function of time afterithe accident. Such calculations involve fol[owing the buildup and decay of the fission produ ts

in the core for some prescribed operating conditions of the reactor. It

is useful to examine the variation in energy release rates and spectra

that result from different operating conditions or other choices of parameters not specific in the Guide. These parametric calculations have been

completed and reported.4,5,6 The work is summarized in Sections 2.2 and

2.3. In that summary, the emphasis is towards Source 1, the currently

required radiation qualification source. 8 In almost every instance, the

conclusions reached about Source 1 pertain equally to Source 2; the

principal difference is in magnitude.

2.2 Energy-Release Rates -- Source 1

Energy-release rates. have been calculated for a wide variety of

reactor-operating parameters including fuel composition, power level,

duration of operation, and treatment of progeny; the results of these

extensive energy-release rate calculations are presented in References 4

and 5. An example of the results is shown in Figure 2.1 where the normalized beta and gamma-ray energy-release rates are plotted as a function of time after LOCA for the case of 200-d continuous operation at

4000 MW(t). Figures 2.2 and 2.3 and Table 2.2 illustrate various

parametric calculations and their effect on energy-release rates.

1011 I I I I I I I I

"- 1010

109

(U 108

~Figure 2.1

l7

0)6Gamma-Ray and Beta Energy Release

P4106 Rate vs Elapsed Time From LOCA --

boSource I (Airborne), 4000 MW

0)1°0 _ - Beta

-- Gamma

:104 _

10"1 100 102 103 104 105 106 107 108

Time After LOCA (s)

22
BETA PAYS- SOURCE I (AIR),i 1JATTPURE U-235

toll

1010

10

LU

I.-

4K

Iix

-j

z

hi

10

10

10

10 5

04 A - Equilibrium X - 5000 days

0 - 500 days

+ - 200 days

10 0

10- 10 0 10 10 2. 10 3 10 4 10 6 10 7 i0

TIME AFTER LOCA (SECONDS)

Figure 2.2 .Beta Energy Release Rate vs Elapsed

Time From LOCA - Source 1 (Airborne)

and Several Reactor Operating Times

(from Reference 5)

23
GAMMA RAYS-SOURCE I (AIR), EQUILIBRIUM, -EFFECTS OF DAUGHTERS

1011

101

U

w

w

z

w~

10

10

10 d I

A - With daughters

X - Without daughters

10 -1

10-1 10 0 1 2 10 10 10 4 10 10 10 "7 10 10

TIME AFTER LOCA (SECONDS)

Figure 2.3 Gamma-Ray Energy Release Rate vs Elapsed

Time From LOCA - Source I (Airborne),

Daughter Product Contributions

(from Reference 5)

24
TABLE 2.2

Percent Deviation of Selected Irradiation Times from Equilibrium Irradiations

Energy-Release Rate vs Cooling Time (from Reference 5)

SOURCE I (Gamma)

Cool ing Air Plate Out Water

Time 5000 d 500 d 200 d 5000 d 500 d 200 d 5000 d 500 d 200 d

-2 -2 -2

1 d 3.2x02 4.8x0- 4.8xi0 1.99 2.76 4.04 1.17 1.64 2.40

4 d <0.1 <0.1 <0.1 4.76 6.63 9.63 3.39 4.70 6.81

10 d 0.12 0.22 0.23 7.48 10.4 14.8 5.62 7.81 11.2

30 d 0.92 1.84 1.93 15.2 21.0 28.6 13.7 19.0 25.8

60 d 12.9 24.6 25.7 23.8 32.7 41.7 23.6 32.3 41.3

1 y 49.1 92.5 96.9 65.1 87.3 91.0 65.2 87.3 91.0

SOURCE I (Beta)

Coo ing Air Plate Out Water

Time 5000 d 500 d 200 d 5000 d 500 d 200 d 5000 d 500 d 200 d

1 d 1.76 3.88 4.09 5.45 9.73 13.0 3.44 6.17 8.21

4 d 4.53 10.0 10.6 12.0 21.3 28.4 9.22 16.5 21.8

10 d 8.56 19.0 20.0 16.0 28.5 37.7 13.6 24.1 31.8

30 d 30.3 67.0 70.6 23.6 41.61 53.9 22.6 39.7 55.9

60 d 40.8 90.1 95.0 29.3 50.7 64.6 29.2 S0.5 64.4

1 y 41.5 91.6 96.5 49.4 76.1 87.0 49.5 76.1 87.0

rQ
Several conclusions can be drawn from the energy-release rate

calculations:

a. The length of irradiation prior to LOCA (in the

range 200 d to equilibrium) does not have a

significant influence on the energy-release rates

until postaccident times greater than about one

day;.after that, differences can be significant.

b. The reactor operating power affects the fission

product inventory by neutron capture transmutation

of the fission products and fuel, and by depletion

of the fissile isotope. For the postaccident time

range of interest here and for realistic power

levels and irradiation histories, these effects

are not significant.

c. Several methods for treating daughters of the

specified fission product types were investigated.

Substantial differences in energy release rates

can be obtained depending on whether or not

daughters are included.

2.3 Spectra -- Source 1

In addition to energy-release rates, energy spectra of the fission

products were also calculated at selected times after LOCA. The method of

calculation' involved folding the activities of each of the fission-product

isotopes at the time of interest with the individual beta or gamma-ray

spectrum of that nuclide and summing over all nuclides. The results of

the spectra calculations for all sources and distribution categories are

given in References 4 and 5.

An interesting result obtained from the calculations is the behavior

of the average particle energy as a function of cooling time. An example

of these'results (for Source 1) is shown in Figure 2.4. The spectra

"soften" (i.e., average energy decreases) with time, reaching a minimum in

the neighborhood of 1 to 10 d, then "harden" at longer times. This behavior occurs for both gamma-ray and beta spectra. The general variation

in average energy is not unexpected since it is generally true that radioactive emissions from short-lived nuclides are higher in energy than those

26
from long-lived nuclides; the rehardening of the spectra must be a. function of the selected fission product inventory.

Other examples of spectral behavior with variation of parameters are

shown in Table 2.3 and Figures 2.5 and 2.6.

The spectral shape has potential for impact on radiation qualification testing and thus the implication of changing spectrum hardness must

be addressed. This is particularly true when radiation simulators that

have fixed or monoenergetic spectra (like Cobalt-60) are used in qualification testing.

1.0

0.9H

.0.8 -

SOURCE -1

(D

zr

W.

().7 H0.6 r

0.5 -

0.4 ý0.3 -- -------- 0 WATER

C----- PLATE OUT

SAIR 0.2 -- T

0.1 --

0 I

10"4 10-2 10-1 100 101 102 10 3

COOLING TIME (DAYS)

RT- 16054

Figure 2.4 Average Gamma-Ray Energy, vs Reactor Cooling

Time - Source I (from Reference 5)

27
1.0

0.9 SOURCE -1 4000 MW I

'3

0.8 1-

0.7k

0.6 [

0.5 1-

0.41-

O----o WATER (200 d)

0------ . AIR (200 d)

0---C PLATE OUT (200 d)

--- ~~ WATER (EOUILIB.)

0 -0 PLATE OUT (EQUILIB.) 0.3 F- - AIR (EQUILIB.)

0.2 F0.1

101T0 o '20 o .0 110-4 14 10- 3 O

RT-16064

Figure 2.5

10-2 10-1 100

COOLING TIME (DAYS)

Average

Cool ing

Reactor

Gamma-Ray Energy vs Reactor

Time - Source 1 and Several

Operating Times (from Reference 5)

I

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0------0 WATER (200 d) SOURCE -1 4000 MW

-.. 4 AIR (200 d)

0-----0 PLATE OUT (200 d) 7 ~----~WATER (EQUILIB.)

e-o• PLATE OUT (EQUILIB.)

IIR A (EUILI8.)

f I I I Z ia,

0.1

0 I • I I I i i

O0.4 10-3 10- 2 10-1

COOLING TIME (DAYS)

00 101 102 103

RT - 1606 3

Figure 2.6 Average Beta Energy vs Reactor Cooling

Time - Source 1 and Several Reactor

Operating Times (from Reference 5)

28
TABLE 2.3

Average Particle Energy vs Cooling Time - Source I and Several Reactor Operating Times (from Reference 5)

Time After Equilib. 5000 d 500 d 200 d Equilib. 5000 d SOO d 200 d

LOCA Initiation

Source I (Air) Y Source I (Air) p

0,

1

1

12

1

4

10

30

60

i

0

1

1

12

1

4

10

30

60

1

min

h

h

day

days

days

days

days

year

min

h

h

day

days

day-s

days

days

year

0.7095

0.7556

0.6361

0.2864

0.2248

0.1638

0.1640

0.2297

0.3567

0.5252

0.8320

0.8263

0.7776

0. 5367

0.4781

0.5012

0.5282

0.6069

0.6466

0.6551

0.8917

0.8658

0.7876

0.5267

0.4568

0.4552

0.4728

0.5705

0.6408

0.6551

0.17096

0.7556

0.6361

0.2864

0.2247

0.1638

0.1639

0. 2284

0.3428

0.5253

Source 1 (Plate Out) y

0.8323

0.8266

0.7780

0.5357

0.4756

0.4954

0.5201

0.5974

0.6393

0.6222

0.8325

0.8269

0.7783

0.5354

0.4748

0.4937

0.5179

0.5966

0.6425

0.5985

0.7096

0.7556

0.6361

0.2864

0.2247

0.1637

0.1637

0.2268

0.3224

0.5269

0.7096

0.7556

0.6361

0.2864

0.2247

0.1637

0.1637

0.2267

0. 3201

0.5296

0.8327

0.3271

0.7785

0.5343

0.4727

0.4887

0.5110

0.5881

0.6370

0.6398

0.8917

0.8662

0.7881

0.5252

0.4534

0.4452

0. 4 570

0.5460

0.6281

0.6398

1.0066

0.7866

0.5609

0.2652

0.2102

0.1656

0.1678

0.2158

0.2441

0.2456

0.7492

0. 6475

0.4657

0.3719

0.3493

0.3131

0.3307

0.3934

0.4249

0.4631

0.8307

0.7063

0.4628

0.3592

0.3357

0.2825

0.2964

0.3772

0.4230

0.4631

1.0080

0.7879

0.5622

0.2654

0.2098

0.1638

0.1643

0.2014

0.2432

0.2456

Source 1 (Plate Out) B

0.7528

0.6501

0.4663

0.3698

0.3456

0.3025

0.3174

0. 3829

0.4210

0.4922

0.7550

0.6517

-0.4660

0.3670

0.3409

0.2901

0.3002

0.3613

0.4012

0.5568

1.0098

0.7895

0.5638

0.2656

0.2092

0.1615

0.1595

0.1746

0.2325

0.2456

1.0100

0.7897

0.5639

0.2657

0.2092

0.1612

0.1-590

0.1700

0.2217

0.2456

0.7570

0.6530

0.4659

0.3648

0.3373

0.2796

0.2849

0.3375

0.3712

0.5473

0.8357

0.7101

0'.4629

0.3546

0.3278

0.2566

0.2568

0.3181

0.3680

0.5473

Source I (Water) y Source I (Water) B

0

1

1

12

1

4

10

30

60 I'.0

min

h

h

day

days

days

days

days

year

0.8914

0.8660

0.7878

0.5260

0.4552

0.4505

0.4654

0.5585

0.6322

0.6222

0.8915

0.8661

0.7880

0.5258

0.4547

0.4490

0.4630

0.5558

0.6345

0.5985

0.8330

0.7081

0.4631

0.3578

0.3331

0.2736

0.2836

0.3641

0.4185

0.4922

0.8345

0.7092

0.4630

0.3559

0.3301

0.2642

0.2691

0.3415

0.3982

0.5568
LO0 TABLE 2.3 (cont)

Time After

LOTA Initiation Equilib. 5000 d 500 d 200 d Equilib. 5000 d 500 d 200 d

Source 2 (Air) y Source 2 (Air) 8

0

1

1

12

1

4

10

30

60

1

0

1

1

12

1

4

10

30

60

1

0

1

1

12

1

4

10

30

60

1

min

h

h

day

days

days

days

days

year

min

h

h

day

days

days

days

days

year

0.7192

0.7550

0.6502

0. 3369

0.2766

0.2109

0.2099

0.2803

0.3951

0.5251

0.8397

0.8331

0.7870

0.5141

0.4286

0.3716

0.3528

0.3698

0.3801

0.6750

0.9007

0.8727

0.7930

0.5141

0.4286

0.3716

0.3528

0.3698

0.3801

0.6738

0.7192

0.7550

0.6502

0.3369

0.2766

0.2107

0.2095

0.2782

0.3784

0.5251

Source 2 (Plate Out) y

0.8397

0.8331

0.7870

0.5141

0.4286

0.3716

0.3528

0.3698

0.3801

0.6750

0.8397

0.8331

0.7870

0.5141

0.4286

0.3716

0.3528

0.3698

0.3801

0.6750

0.7192

0.7550

0..6502

0.3369

0.2765

0.2105

0.2091

0.2755

0.3513

0.5257

0.7192

0.7550

0.6502

0.3369

0.2765

0.2105

0.2091

0.2753

0.3481

0.5266

0.8397

0.8331

0.7870

0.5141

0.4286

0.3716

0.3528

0.3698

0.3801

0.6750

0.9007

0.8727

0.7930

0.5141

0.4286

0.3716

0.3528

0.3698

0.3801

0.6738

0.9435

0.7408

0.5246

0.2785

0.2296

0. 1781

0.1829

0.2283

0.2449

0.2455

0.6820

0.6049

0.4389

0.3411

0.3146

0.2155

0.1959

0.2025

0.2075

0.1993

0.8165

0.6974

0.4492

0.3411

0.3146

0.2155

0.1959

0.2025

0.2075

0.2576

0.9468

0.7438

0.5273

0.2792

0.2291

0.1743

0.1762

0.2205

0.2444

0.2456

0.9510

0.7474

0.5306

0.2801

0.2285

0.1691

0.1660

0.1895

0.2387

0.2456

0.6820

0.6049

0.4389

0.3411

0.3146

0.2155

0.1959

0.2025

0.2075

0.1993

0.6820

0.6049

0.4389

0.3411

0.3146

0.2155

0.1959

0.2025

0.2075

0.1993

Source 2 (Plate Out) 6

0.9514

0.7478

0.5310

0.2802

0.2284

0.1686

0.1648

0.1816

0.2317

0.2456

0.6820

0.6049

0.4389

0.3411

0.3146

0.2155

0.1959

0.2025

0.2075

0.1993

0.8165

0.6974

0.4492

0.3411

0.3146

0.2155

0. 1959

0. 2025

0. 2075

0.2576

Source 2 (Water) y Source 2 (Water) a

min

h

h

day

days

days

days

days

year

0.9007

0.8727

0.7930

0.5141

0.4286

0.3716

0.3528

0.3698

0.3801

0.6738

0.9007

0.8727

0.7930

0.5141

0.4286

0.3716

0.3528

0.3698

0.3801

0.6738

0.8165

0.6974

0.4492

0.3411

0.3146

0.2155

0.1959

0.2025

0.2075

0.2576

0.8165

0.6974

0.4492

0.3411

0.3146

0.2155

0.1959

0.2025

0.2075

0.2576
2.4 Doses and Dose Rates for a Generic Containment

The conversion of the gamma and beta release signatures to dose and

dose rate must account for the transport of the radiation inside the

containment with its complement of internal structure. Since this calculation is completely plant specific, further simplifying assumptions

were made to complete these scoping estimates. Several are discussed

here; the reader should also review Reference 2.

" The containment structure was modeled as an empty

cylinder with an inside radius of 1768 cm, inside

height of 6355 cm, and concrete walls, 114 cm

-thick; total free volume is approximately 6.25 x

1010 cm3 (2.2 million ft 3 ); the internal structure

was not modeled at all. Certainly for betas, and

to a first approximation for gammas, free volume is

a pertinent scaling factor. While the modeled

structure is most typical of a PWR containment, the

scaling factors should allow approximate application to BWR structures as well.

" An additional factor is the reactor power assumed

prior to the LOCA. While merely a scaling factor

that can be adjusted for a specific plant, the full

impact of these environments is more graphically

illustrated when a "typical" power level is

assumed. The calculations are presented for a 4000-

MW(t) plant, approximately the 1300-MW(e) class of

a nuclear power plant.

" Certain other assumptions are important in the calculation of dose and rate, but do not affect the

energy-release rates and spectra:

31
a. Instantaneous, uniform release or deposition.

b. Engineered safety features are neglected.

c. Containment leakage is neglected.

The first assumption is particularly important in

establishing the initial dose rate; the latter two

may affect the total integrated dose, although

typical containment leak rates are on the order of

0.1 to 0.5 volume percent per day and thus would

change the total dose by 3% to 15% over a 30-d

period.

The gamma dose and rate from the airborne volumetric source is shown

in Figure 2.7 as a function of time after release. The initial centerline

dose rate is about 3.5 Mrad/h and the dose to 30 d is about 28 Mrad. The

edge and midradius dose rates are also shown; because of the penetrability

of the gamma radiation, the edge dose and rate are similar in magnitude

(e.g., about 2.5 Mrad/h initial dose rate).

10 ,.100

=' •CRATE "" ATE,.-

01

1.0 .

o: .

! / ~DAY ",

.011 -20 .1i

10 10- 100 101 1D`II

HOURS AFTER RELEASE

Figure 2.7 Gamma-Ray Dose/Dose Rate

vs Elapsed Time-From

Release - Airborne Source

32
However, the dose and rate to a particular area of the containment is

a combination of the three sources. Clearly, the airborne source and the

plate-out source are additive (spatially). But the waterborne source is

less spatially defined. Figure 2.8 assumes that 1/10 of the waterborne

source is added to the airborne and plate-out sources. The resultant

initial centerline dose rate is about 4.5 Mrad/h and the dose to 30 d is

about 45 Mrad. While the airborne source is the principal dose and rate

contributor everywhere in containment, the plate-out source adds significantly to the edge dose so that dose and rate are almost uniform

throughout the containment in this model. The doses and rates are severe,

but are a result of the assumptions that must be critically examined for

specific plant applicability.

The complementary beta rates and doses are shown in Figures 2.9 and

2.10. For the airborne beta source (Figure 2.9), the initial centerline

rate is greater than 50 Mrad/h (about 75 Mrad/h at 1 s) and the dose to

30 d is about 320 Mrad. The early time decay is very rapid, so that at

1 h the dose rate is about 15 Mrad/h and at 1 d about 1.7 Mrad/h. The

edge dose and rate are also shown; a reasonable assumption is that the

edge dose and rate are about 1/2 the centerline values since a receptor

at the edge is exposed to essentially a semi-infinite volume.

As was done for the gamma sources, Figure 2.10 combines the three

spatial beta sources by assuming 1/10 of the waterborne source is added to

the airborne and plate-out source. The resultant initial centerline dose

rate is greater than 50 Mrad/h and the dose to 30 d is about 370 Mrad.

The edge dose and rate are even more significant because of the plate-out

source; the initial rate exceeds 80 Mrad/h and the dose to 30 d is 5 to 6

times the centerline dose. While these are very significant doses and

rates, the assumptions must be critically examined for specific plant

applicability.

33
0

I.-

0r

(3

C-,

HOURS AFTER RELEASE

Figure 2.8 Gamma-Ray Dose/Dose Rate vs

Elapsed Time From Release -

Specifically Combined

Airborne, Plateout, and

Waterborne Sources

0

4:

0

4:

4:

C,

100

10 " .

1.0

0.1 Z

Figure 2.9

1000

100

10

I , I . .. , g' "I • l o-1 0o 1o o o

0 OUR 100 10 1

HOURS AFTER RELEASE

Beta Dose/Dose Rate

vs Elapsed Time From

Release - Airborne Source

34
-: 10 _ --- EDGE 100 Dc>

C,

'< 1.0 DOE lO 0

0.] ? 4 1

1o0 10-1 10 10 11

HOURS AFTER RELEASE

Figure 2.10 Beta Dose/Dose Rate vs Elapsed Time From

Release - Specifically Combined Airborne,

Plateout, and Waterborne Sources

2.5 Summary

The significant features of the LOCA-radiation signature definition

can be summarized as follows:

* A (formal) definition of expectable magnitudes of

the gamma and beta dose and rate for a typical

containment, using the applicable Regulatory

Guides. These values are further segregated

according to their spatial dependence as waterborne, airborne, and plate-out sources. The

implications of the spatial dependence may be significant in radiation qualification testing, and

should at least be a consideration.

* A formal recognition that the beta dose and rate is

significantly greater than the corresponding gamma

values. Compared to the gamma contribution, betas

have been shown to contribute perhaps seven times

35
more dose (to 30 d) and to have correspondingly

greater dose rates. Both measures of radiation are

very significant in radiation qualification

testing.

A definition of the LOCA-radiation sources energy

spectra as a function of time following the

hypothesized releases. Both the gamma and beta

spectra exhibit a changing energy dependence with

time. For mono- or fixed-energy simulators, the

changing spectra cannot be followed. While not a

clearly important test parameter, this must be a

consideration in testing and will be a consideration in evaluating the adequacy of simulators.

The resolved energy spectra also demonstrate an

apparent sensitivity to the assumed nuclide

fractionation which could be an important feature

if a "new" LOCA source term were hypothesized.

• While sensitive to the assumed nuclide fractionation selected, the energy-release rates and

spectra are not strongly influenced by reactoroperating parameters, such as fuel composition,

power level, duration of operation, and treatment

of progeny.

36
3. Comparative Calculations of Exposed Organics'

Response to Simulator and LOCA Radiation

3.1 Depth-Dose and Charge Deposition

In an effort to evaluate the performance of simulators compared to

the LOCA sources, a series of calculations of energy deposition in a

modeled electric-power cable were carried out; 1 5 the full report is

attached as Appendix A. The model used for the calculations consisted of

a solid copper conductor surrounded by an elastomeric insulator (ethylenepropylene rubber) and jacket (Hypalon). Using a coupled photon-electron

transport technique based on Monte Carlo methods, the energy deposition

(and charge deposition) as a function of radius in the cable was calculated for the LOCA sources, 6 0 Co, and 1 3 7 Cs. The dimensions and materials

selected as the modeled cable may be considered in the range of typical

cables, but not exactly like any one manufacturer's type in particular.

Similarly, the significance is not as an electrical cable, but as an

exposed organic material specimen; slightly different elastomeric materials (but composed basically of CH2 ) would not be expected to have much

effect on the results, nor would small changes in dimensions be expected

to change the conclusions.

The calculations also take advantage of the interesting spectral

features of the LOCA radiation signatures. In order to establish bounds,

the depth-dose calculations were limited to the extremes of the hardest

spectra (1 min) and the softest spectra (4 d) (see Figures 2.4 through

2.6). Included in the various parametric calculations were effects of

water thickness for waterborne beta sources, effects of an intervening

steel test chamber, effects of 70-psig steam versus dry air as a surrounding medium, comparison brute-force calculations of distributed

airborne sources, and the like.

Figures 3.1 through 3.4 illustrate various Source 1 depth-dose

calculations as well as comparison simulator results. For scaling

37
purposes, note that the doses can be expressed per unit incident fluence.

Since the surface area of a 10-m segment of the model cable is 7102.5 cm2 ,

one particle per 10-m segment represents a fluence of 1.480 x 10-4

particles/cm2 . To scale the depth-dose results presented here to a

specified particle fluence (0), one multiplies the doses by 0/1.408 x

10-4. For example, to determine the dose for an incident fluence on the

cable of 10 photons/cm2 , multiply by 10/1.408 x 10-4 = 71,025.

Figures 3.5 and 3.6 show selected depth-dose calculations for Source

2; these can be compared directly with Figures 3.3 and 3.4, respectively.

Another potential damage mechanism is charge buildup, illustrated in

Table 3.1. Net charge deposition is defined as the number of electrons

entering a zone in excess of those leaving a zone. Thus, a positive value

for the net number of electrons deposited produces a net negative charge

in that region. Conversely, a negative value of electrons deposited

results in a positive charge. Charge deposition is to be interpreted as

the instantaneous charge deposited for the various identified fission

product sources. No mechanisms for leakage or other forms of dispersal of

the charges have been included. The gamma-ray sources (including 6 0 C6)

consistently produce a positive charge on the outer layer of the jacket

(Hypalon), but on the interior of the cable no regular pattern is apparent. The beta sources, on the other hand, produce a much larger negative charge on the outermost region of the cable which falls off with

decreasing radius. A much more regular behavior is observed in the copper

regions. For the case of the cable surrounded by water, the charge

buildup is about two orders of magnitude smaller. In a combined betagamma radiation field, there will be some compensation of the oppositesign charge depositions.

38
10-13

10-

RT-1660

CABLE RADIUS, mr

Figure 3.1 Dose vs Penetration Depth - 6 0 CO, 1 3 7 Cs, and

Source 1 (Airborne) Gamma Rays Onto Typical Cable

Configuration. The isotopic source results

have been normalized at the outer zone.

(from Reference 15)

39
7.290 9.474 11.304

12~1

~i13

Lfn

t 0

C-D

0 2 4 6

CABLE RADIUS, nu

RT-16602

8 10 12

Figure 3.2 Dose vs Penetration Depth - 6 0 Co and

Source 1 (Airborne) Betas Onto

Typical Cable Configuration. The

isotopic source results have been

normalized at the outer zone.

(from Reference 15)

40
10-12 7.290 9A474 11.304

-J

L.I

z

0

C

CL~.J

C

0

RT-16607

Figure 3.3

2 4 6 8 10 12

CABLE RADIUS, nm

Dose vs Penetration Depth - 6 0 Co, 1 3 7 Cs,

and Source 1 (Plateout) Gamma Rays

Onto Typical Cable Configuration.

The isotopic source results have

been normalized at the outer zone.

(from Reference 15)

41
cc

C)

0r

Wi 0

w,

0T 79

CABLE RADIUS, mm

Figure 3.4 Dose vs Penetration Depth - 6 0 Co

and Source 1 (Plateout) Betas Onto

Typical Cable Configuration. The

isotopic source results have been

normalized at the outer zone.

(from Reference 15)

42
7.290 9.474 11.304

r0

Ir.

I--

RT- 16616

0 2 4 6 8 10 12

CABLE RADIUS, mm

Figure 3.5 Dose vs Penetration Depth - 6 0 Co, 137Cs,

and Source 2 (Plateout) Gamma Rays Onto

Typical Cable Configuration. The

isotopic source results have been

normalized at the outer zone.

(from Reference 15)

43
7.290 9.474 11.304

LUj

-j

I.-

Lf)

Cr

0 2 4 6 8

CABLE RADIUS, mm

10 12

RT-17890

Figure 3.6 Dose vs Penetration

Source 2 (Plateout)

Cable Configuration

source results have

at the outer zone.

Depth - 6 0Co and

Betas Onto Typical

The isotopic

been normalized

(from Reference 15)

44
TABLE 3.1

Charge Deposition in the Cable Configuration

(from Reference 15)

Net Eiec trons Deposited per 10 Source (;arnma Rays Incident an a 103 cm Length of Cable

Zone Airborne I'late-01mt Wdlerboritt Outer Radius 60 Source I Source 2 jource I Soirc•t 2 Source I Surcc 2 Material (nrn) Co I mrin days I min 4 days I min 4 days I ruil 4 day%. - I mum 4 days I siiru 4 day%

ilypalon 11.304 -5.10 -1.05 -0.30 -1.70 -0.45 -9.15 -8.15 -8.15 -5.00 -0.95 -0.85 -1.60 -0.75

10.847 -2.35 -0.25 0.10 -0.80 0.15 -0.55 0.25 -1.95 -0.80 -0.40 -0.15 0.35 0.05

10.390 0.45 -0.20 -0.05 0.20 -0.05 1.25 0.50 0.15 -0.35 0.60 0.20 -0.15 0.15 9.932 0.70 -0.60 0.30 0.15 0.15 0.25 0.80 -0.90 1.55 -0.30 0.10 0.15 -0.20 EPR 9.474 0.10 A0.25 -0.05 -0.10 0.15 -0.65 -1.20 0.75 -1.25 -0.10 0.10 0.25 0.35 8.928 -0.35 0.05 -0.25 0.15 -0.15 -1.05 0.75 -0.15 0.90 0.50 -0.10 -0.05 -0.25 8.382 -0.30 0.10 0.25 -0.15 -0.20 -1.05 0.25 0.0$ -0.70 -0.20 0.05 -0.25 -0.10 7.836 0 0.30 -0.10 -0.40 0 0.95 -0.60 0.35 -0.35 -0.25 -0.25 -0.20 0.10 Copper 7.290 -0.60 0.10 0.10 0.25 0.20 0.20 0 -0.25 0.45 -0.15 -0.15 0.25 0.05 5.832 -0.25 -0.15 -0.10 -0.10 -0.20 0.55 0.60 0.60 0.30 0.35 0.10 0.10 0.05 4.374 1.50 -0.05 0.05 -0.05 0.05 -0.30 -0.30 0.10 -0.10 -0.25 -0.05 0 -0.05 2.916 -0.30 0.10 -0.05 0.20 -0.05 0 0.15 -0.40 0 0.05 0.0) 0.05 0 1.458 -0.15 0.05 0 -0.05 0.05 0 -0.05 0.25 0 -0.05 0 0 0

Net Electrons Deposited per 10 3 .ource Betas Incident on a 103 cm Length of Cable

Hypilon 11.304 -5.10 60.90 175.80 75.(,0 169.80 350.20 363.20 357.30 535.80 2.94 2.01 2.76 8.09 10.847 -2.35 29.00 10.70 29.10 11.90 114.50 116.70 119.60) 65.50 1.34 0.40 0.88 1.08 10.390 0.45 22.60 0.60 22.70 2.00 60.50 61.33 56.50 11.50 0.84 0.15 0.40 0.27

9.932 0.70 17.30 0 17.10 0.20 34.90 39.00 34.00 3.40 0.46 0.05 0.24 0.02

IPIH 9.474 0.10 14.20 0 14.90 0.10 19.80 17.33 17.90 0.60 0.33 0.06 0.11 0.01

8.928 -0.35 12.30 0 9.80 0 9.70 12.00 9.30 0.20 0.19 -0.01 0.03 0.01

8.182 -0.30 9.10 0 7.20 0 7.10 4.33 7.70 -0.10 0.11 0.02 0.03 0 7.836 0 8.20 0 5.20 0 4.80 3.33 3.20 0.10 0.13 0.02 0.02 0

Copper 7.290 -0.60 26.40 0 16.10 0 9.10 10.33 8.20 0 0.26 0 0.01 0. 5.832 -0.25 0.50 0 0 0 0.10 0 0.10 0 0 0 0 0 4.374 1.50 0 0 0 0 0.10 0 0 0 0 0 0 0 2.916 -0.30 0 0 0 0 -0.10 0 0 0 0 0 0 0 1.458 -0.15 0 0 0 0 0 0 0 0 0 0 0 0

4- "In
3.2 Summary

The interpretation of the depth-dose calculations in terms of establishing simulator adequacy is not straightforward. Reasonable matching of

the dose profile in the cable by the simulator source would be sufficient

to guarantee its adequacy. However, a failure to produce equivalent depth

versus dose does not necessarily mean that the simulator is inadequate; it

is necessary to determine the mechanism of failure of the cable in the

LOCA radiation field, and then ascertain whether or not this damage mechanism is sufficiently stressed by the simulator. A plausible argument is

that the 60Co or 1 3 7Cs sources produce a more conservative situation

since, if they are normalized at the surface, they always produce more

dose in the inner regions of the cable than do the LOCA sources. Thus,

according to this argument, if the cable survives the 6 0 Co irradiation

test, it will survive the LOCA radiation environment since the latter will

deposit a smaller dose in the interior. In order for this argument to be

valid it is necessary that the degradation of the cable be directly related to total dose. It is not clear that the problem is as simple as

that. For example, charge buildup and dielectric breakdown are dependent

upon the dose gradient in the cable. Other failures such as heating and

gas evolution from the breakdown of polymeric materials and differential

mechanical stress could also depend upon the dose gradient.

46
4. Damage Mechanisms Identified and Prioritized

4.1 Concerns in Adequacy Evaluations

As indicated previously, simulator adequacy is assured if its

radiation signature adequately matches the LOCA-radiation signature.

However, the previous discussion in Chapters 2 and 3 indicates, in general, that is not the case. Finally, the true indicator of adequacy is

that the damage mechanisms and damage be duplicated in the test item.

To identify these radiation damage mechanisms, the staff of the IRT

Corporation was asked to consider the possible mechanisms and to discuss

their relative importance; their full report16 is attached as Appendix B.

Concurrently, Sandia staff, expert in radiation effects in polymers, separately evaluated the possible mechanisms and critiqued the IRT report.

Before proceeding to the discussion of damage mechanisms, it is

important to narrow attention to the pertinent features of radiation

qualification and simulator adequacy.

First, it will be a priori concluded that gamma simulators are

inherently adequate (dose rate will be discussed later) to simulate the

gamma accident and the ambient-radiation signature, when taken as a

separate entity. The various figures in Chapter 3 illustrate the nearly

identical relative depth-dose profiles on which this conclusion is based.

Thus, for the ambient (i.e., aging) environments when only gammas are

present,18'19 gamma simulators are adequate; aging environments will not

be further discussed in this report. Similarly, the gamma-accident

signature is adequately addressed using gamma simulators.

Second, just because gamma simulators are adequate for the gamma

accident-radiation signature taken as a separate environment, that does

47
not endorse or justify the typical sequential qualification program where

the radiation (accident and ambient) profile is separately applied. Discussion of possible combined-environments effects will be included in

succeeding sections; an example may be radiation heating added to the

already elevated temperature from the direct LOCA heat releases.

Third, even when taken singly, adequate gamma-profile simulation must

include both a spectral and a magnitude consideration. The data, shown in

Chapter 3, indicates that spectra are reasonably accommodated. Some other

data 2 0 demonstrate dose-rate effects in certain elastomeric materials, but

these would seem to be relatively insignificant so long as the simulator

rate is within an order of magnitude or so of the rate to be simulated.

(With justifying data, the range of dose rate may be significantly extendable, which is imperative for accelerated aging techniques.)

Fourth, concern for adequate beta simulation can be reduced to concern for induced heating (and/or heating rate) if beta penetrability is

not a concern. That is to say, for "shielded" equipment, beta radiation

is adequately simulated by adequate heating of the "shielded" equipment by

any radiation simulator (or other heating-simulator device). (But consideration should be given to secondary radiations, bremsstrahlung, from

beta interactions with materials.)

Very simplistically then, the adequacy of a radiation simulator

hinges on the beta-radiation damage-simulation adequacy.

4.2 iRT Study Summary" 6

The IRT study identified three major damage mechanisms which are

generally related to radiation damage:

" Charge buildup, discharge and electrical changes

" Temperature changes due to dose rate

" Mechanical/chemical change due to total dose.

In discussing the effects of these mechanisms, the information in Figure

4.1 served as bases. Further, it was assumed that the surrounding

environment was at an elevated temperature (143°C, approximately 60 psia)

48
somewhat typical of the LOCA condition. The summary discussion is presented here; additional detail is supplied in the subsequent chapters.

2 x 104

10 4

2 x 103

U) 0

an

_j

0

103

10 2

10 2

101

10 0 10,

2 x 10O 2 x 10-1

DISTANCE FROM CABLE CENTER, cm

RT-17025

Figure 4.1. Dose Rate vs Penetration Depth - Combined LOCA

Radiation Environment, 1-min and 4-d Following LOCA

49
"The trapped charge in the insulator is largely a consequence of the

nonuniform dose deposited in the cable. The mechanism that applies here

is that the secondary emission leaving a volume element is not balanced by

secondary emission from adjacent points because the adjacent points are

not receiving the same primary radiation. The gamma-source simulators do

not show such a strong attenuation as does the true LOCA source so they

will not properly simulate the trapped charge and any'resultant noise

spikes. The amplitude of noise pulses built up by breakdown in the cable

depends almost completely on the exact details of the cable termination.

If the termination is either a small resistive load or a large capacitive

load, then the noise spikes will not be large. However, because radiationinduced leakage currents are judged to be inconsequential, we suggest that

the LOCA environment is adequately simulated by 6 0 Co as long as average

doses are matched.

"The 6 0Co and 1 3 7 Cs simulation-radiation sources do not reproduce the

true LOCA attenuation into the cable so that the temperature profiles

established by these simulators will not accurately reproduce the true

LOCA profiles. In particular, the simulation fields are not attenuated in

the cable as is the true LOCA spectrum. Thus, the simulator will deposit

too much power in the copper and inner portions of the Hypalon compared

with the power deposited into the outer surface. If the simulation is

performed so that the total doses are equivalent, then the simulator will

exaggerate the heating of the inner insulator region. This is the inverse

of the case of electrical effects generated by trapped charges where the

simulator understresses the effect.

"The most serious problems that will occur with the cable are chemical and mechanical deterioration which are expected to occur after a

few hours to a day in LOCA environment. Impact strength and elongation

changes by 50% within 10 h. In order to properly evaluate these effects,

the expected vibrational and bending stresses should be included *in the

specification of the LOCA environment."

50
4.3 Sandia Study Summary 1 7

The work of Harrah 1 7 identified one other potential damage (or failure) mechanism that is a result of the strong radial dependence of the

depth-dose profile. The mechanism involves the shrinkage of a material

relative to its remaining elongation and is illustrated in Figure 4.2. If

the surface of an elastomer suffers shrinkage on the order of the remaining elongation, it is plausible that surface crazing or cracking could

occur. If the dose (ahd elongation and shrinkage) are nearly equal across

the material, it is unlikely that cracking would occur because of the.

absence of a differential stress; hence, the mechanism is a direct result

of a steep depth-dose profile in the material. (Further complications

could occur as illustrated by the temperature dependence in the figure.)

Dose -*

Figure 4.2 Material Elongation/Shrinkage Change vs Integrated

Dose - Illustrative Example for an Organic Material

51
4.4 Relative Importance of Damage Mechanisms Relative to Simulator

Adequacy

All four mechanisms will be discussed in Chapters 5 through 8, but

they can be immediately assessed as to their relative importance.

Charged particle distribution is a direct function of depth-dose

profiles and beta radiation. Charge breakdown and noise pulses depend

specifically on the elastomeric material and/or the cable terminations.

Generalized conclusions may be difficult to obtain.

Temperature changes in material may be sufficient to be a concern.

Here the beta radiation can be viewed as a total heat source, since the

depth-dose features are relatively unimportant. In the same regard, the

simulator may be relatively unimportant as long as the heat source is

duplicated (where important).

Total chemical and mechanical changes in materials are not a strong

function of the radiation source as long as the total damage is duplicated

as appropriate.

The singularly important mechanism may be the differential stress

caused by the actual radiation environments that can not, in general, be

duplicated by existing gamma-radiation simulators. Chapter 8 will examine

the available supporting data and estimate the importance of the damage

mechanism and of its accurate simulation.

4.5 Other Damage Mechanisms

It is impossible to be inclusive of all possible damage mechanisms

or to suggest adequate simulation techniques for all occasions. Some of

these mechanisms are a result of the specific functioning and design of

the equipment. For example, electronic assemblies may be more or less

susceptible to the radiation signatures by their design or choice of components. It is not possibleto examine all specifics in this study.

52
Other potential damage mechanisms have also been suggested. Secondary emissions induced by beta interactions may be an important

consideration even when the primary betas do not penetrate. Here an

example might be the bremsstrahlung superimposed on the internal sensing/transmitting elements of a transmitter when the primary betas are

stopped by the metal case of the housing., Certainly this added contribution (theoretical energy conversion can range to 10 percent or more)

must be accounted for, but it might be logical to account for this by

summing with the gamma-accident rate and dose.

Surface (and bulk) conductivity changes might also be important in

some practical application. But again, the location of such sensitive

equipment would be internal to a housing (in general) and not exposed to

primary beta radiation. Thus while the effect may be real, simulation is

not first-order dependent on the beta component.

The purpose of this section is to recognize that other unique or

specific damage mechanisms or simulation considerations exist. Others,

not specifically identified in this report, probably exist as well. That

is just one reason that it is impossible to endorse any simulator for

every application. Simulators must be intelligently used in an overall

qualification program.

53-54

5. Radiation-Induced Electrical Signals in Cables

5.1 Background

Radiation-induced signals in cables are primarily the result of

ionization-induced conductivity changes in the cable insulation and the

ultimate release of trapped charge in the insulation material. Ionization

of atoms in the insulation will occur when one or more orbital electrons

is removed, leaving a positively charged ion and one or more free electrons. Ionization may be produced in the case of a LOCA-radiation environment through either source-electron/target-electron collisions or

photon-electron collisions and subsequent secondary-electron/targetelectron interactions. In the simulator environment, ionization most

likely will occur through the source-photon/target-electron, secondaryelectron/target-electron, processes. Significant charge trapping is the

result, generally, of nonuniform energy dissipation (either photon or

electron) in an insulating material.

Simulation of the LOCA-radiation environment is complicated by the

presence of a large electron component not usually present in typical

isotopic irradiation facilities. It is generally accurate to state that

the presence of a large electron component in the radiation field can

result in charge-/energy-deposition profiles in materials whose magnitude

is extremely dependent on penetrationdepth into the material. Herein,

apparently, lies the main concern about the adequacy of isotopic simulators to reproduce the electrical effects of a LOCA-radiation exposure.

The typical LOCA sources expected, presented in Table 2.1 and based

on conditions set forth in Reference 9, are given again in Table 5.1.

Composition and quantity of radiation emitters potentially available for

release is dependent on the reactor-operating history and elapsed time

from the hypothesized excursion. Regardless of the nature of the excursion, once the reactor primary system has been breached, fission

55
products available for release are considered to be instantaneously released and uniformly dispersed. A consequence of uniform material dispersion is that any source "self-absorption" is minimized. This means that

the preponderence of electrons emitted in fission-product decay and

normally absorbed in the fuel and cladding must be added to the decayproduct gamma-source term for purposes of estimating damage to safety

systems and components.

TABLE 5.1

LOCA Sources Specification (Reference 9)

Source 1 Airborne 100% noble gases, 25% iodines

(Containment heatremoval systems, Plateout 25% iodines, 1% solids

etc)

Waterborne 50% halogens, 1% solids

Source 2 Airborne 10% ggble gases (except 85Kr)

(Other safety- 30% Kr, 5% iodines

related electrical

systems) Plateout 5% iodines

Waterborne 10% halogens

The LOCA electron and photon spectra are varying functions with time;

however, it was demonstrated in Chapter 2 that spectra existing at about

1 min and 4 d reasonably bracket the hardest and softest spectra associated with a LOCA source. In Table 5.2 are listed average and peak

energies for both electron and photon spectra at both 1 min and 4 d

following a postulated LOCA. 5 Depending on the elapsed time from the

onset of a LOCA, electron to photon dose ratio (rad/rad) is on the order

of 10/1 to 100/1.

Many gamma-irradiation facilities doing materials testing, instrument calibration, basic research, and the like, use 6 0 Co. Therefore, for

purposes of comparison, we will assume a typical (LOCA) simulator would be

6 0 Co configured in the conventional fashion; i.e., some sort of an array

56
of source 6 0 Co pencils. As is well known, 6 0 Co decays by beta emission

which is in coincidence with a cascade of photons at- 1.17 and 1.33 MeV.

End-point energy of the decay-beta particle is about 0.3 MeV and, thus,

will not contribute to the radiation field external to the source pencils.

TABLE 5.2

Source 1 Airborne Spectra Parameters

(Reference 5)

Gamma Spectra

Elapsed Time E (MeV) Emax (MeV)

1 min 0.72 5.0

4 d 0.16 0.75

Beta Spectra

1 min 0.75 3.4

4 d 0.17 0.60

The electron spectrum generated by scattering of photons in a medium

may be estimated on the basis of photon cross-sections for the medium

(Reference 21). In Table 5.3 are tabulated electron and photon spectra

for 6 0 Co and a medium of CH2 composition. The photon data are uncollided

values; the rationale is that scattering in the source and medium would

have little effect on line broadening of the two cobalt (gamma) lines.

Examination of Tables 5.2 and 5.3 shows that the 6 0 Co spectra, in

CH2 , are comparable to the LOCA 1-min spectra but are considerably

harder than the LOCA 4-d spectra. In the range of energies listed in

Tables 5.2 and 5.3, energy loss by electrons will be through ionization

and excitation; hence, energy-deposition mechanism by both LOCA and the

isotopic simulators are identical. In the case of the isotopic simulator,

once a state of electron equilibrium in the scattering/absorbing.medium is

established, energy loss by recoil electrons through ionization and excitation processes will be compensated for by photon energy loss to electrons

57
by Compton scattering. The range22 of a maximum energy 6 0 Co recoil electron in CH2 is about 0.465 g/cm2, approximately equal to the distance required to establish electron equilibrium in the CH2 . The thickness of

insulation and jacket on a typical power cable (of interest here) just

happens to be approximately 0.450 g/cm2 which is about equal to the range

of maximum energy recoil electron in CH2 and also is the thickness of

material necessary to establish a characteristic electron spectrum. At

this penetration depth, free electron density and electron trapping become

somewhat constant with deeper penetration. As material thickness is increased, energy deposition also increases until a state of electron equilibrium is achieved. At this point energy deposition/density/trapping

versus depth of penetration should remain constant provided the incident

photon beam remains essentially unattenuated. Thus, the energy/charge

profile in the typical cable insulation and sheath exposed to the 6 0Co

isotopic source should be a monotone, increasing function with

penetration.

TABLE 5.3

6 0 Co Spectra - Medium CH2

Gamma Spectrum

E (MeV) Emax (MeV)

1.25 1.33

Electron Spectrum

0.58 MeV 1.12 MeV

The LOCA source energy/charge depositions differ from the isotope

deposition profiles in that a state of electronic equilibrium is never

achieved. For the 1-min source, maximum electron energy is about 5 MeV

and the ratio of electron to photon power is in the range of (10-100)/i.

Since the range of the electrons approaches 2.4 g/cm2 , this means primary

58
(source) electrons dominate energy/charge deposition and, since no internal (material) source of high energy secondaries is available, charge/

energy deposition is expected to decrease monotonically with increasing

penetration. The 4-d source is characterized by both lower energy photon

and electron spectra. The range 2 2 of the maximum energy electron is about

0.21 g/cm2 ; hence, the primary electron component should be dissipated in

the outermost cable sheath. The relatively soft primary photon spectrum

assures that attentuation of the photon beam will occur with penetration

into the cable materials. Attenuation of the primary photon (recoil

electron) beam along with complete removal of the primary electron beam

(in the outer sheath) assures that the general shape of the 4-d deposition profile is similar to but lower in magnitude than the 1-min spectrum.

In summary it may be stated that as far as basic energy transfer

mechanisms are concerned, the LOCA spectrum and the 6 0 Co spectrum transfer

energy to the test material via the same processes: ionization and excitation. The LOCA sources are always rapidly attentuated with penetration

into materials, whereas 6 0 Co exposures will result in minimum attentuation

of primary source particles.

To this point we have inferred, inductively, the general shape of the

trapped charge and free electron distributions existing in insulating materials exposed to both LOCA and 6 0 Co radiation environments. However, in

order to evaluate the severity of radiation-induced signals in cables,

accurate estimates of absolute charge deposition along with energy deposition profiles (induced conductivity change is proportional to dose rate)

are required. Deposition/charge profiles were calculated 1 5 using sources

listed in Table 5.1 for 1-min and 4-d postrelease times. Additional

calculations based on 6 0 Co and 1 3 7 Cs source terms were also made. The

energy/charge deposition profiles were calculated in all instances, using

the coupled electron-photon Monte Carlo transport code SANDYL. 2 3

Deposition calculation results are presented in Figures 5.1 and 5.2.

The results in Figure 5.1 have been normalized on the basis of LOCA electron and photon dose rate calculated by Bonzon. 2 Deposition profile data

for 6 0 Co are given in Figure 5.2 for two conditions. In the first

59
instance, the calculation considers the deposition in a cable configuration under free field conditions and, in the second, deposition in a cable

shielded by 1/4-in. steel as might occur during testing in an autoclave

chamber. In Table 5.4 the respective charge deposition results are

tabulated.

2 x104

L)

_I

-a

w

Ucc

W

oIU)

0

0

2 x 103

103

10 2

101

100

2 x 10-1 2 x 0.5 1.0

DISTANCE FROM CABLE CENTER, cm

RT-17025

Figure 5.1 Dose Rate vs Penetration Depth - Combined LOCA

Radiation Environment, 1-min and 4-d Following

LOCA (from Reference 15)

60
7.290 9.474 11.304

CU

$4

0

-1

~10

0

0

10-1

6 8

Cable Radius, mm

! 12

RT-16599

Figure 5.2 Dose'vs Penetration Depth - 6 0 Co

Onto-Typical Cable Configuration,

With and Without Intervening Iron

Liner (from Reference 15)

61
TABLE 5.4

Charge Deposition in the Cable Configuration

(from Reference 15)

Net Electrons r•"epsited per 103 Source (arnma flays Incident on a 103 cm Length of Cable

Zone Airborne W'ltte-OiL Waterbore, Outer Radius Source I - Source 2 Souirce 2 .iouet. 2 - otwce S.urru 2 Material (FmI) Co I irin 4 days I min 4 days I mtin 4 day% 1 n(i11 4 days I litin 4 days I ihur 4 days

Hlypalon 11.304 -5.10 -1.05 -0.30 -1.70 -0.45 -9.15 -3.15 -3.15 -5.00 -0.95 -0.85 -1.60 -0.75 10.847 -2.35 -0.25 0.t0 -0.30 0.15 -0.55 0.25 -1.95 -0.80 -0.40 -0.15 0.)5 0.05 " I0.390 0.45 -0.20 -0.05 0.20 -0.05 1.25 0.50 0.15 -0.35 0.60 0.20 -0.t5 0.1) 9.932 0.70 -0.60 0.30 0.35 0.15 0.25 0.30 -0.90 1.55 -0.30 0.20 0.15 -0.20 EPR 9.474 0.20 -0.25 -0.05 -0.10 0.15 -0.65 -1.20 0.75 -1.25 -0.10 0.20 0.25 0.3) 3.923 -0.35 0.05 -0.25 0.15 -0.15 -2.05 0.75 -0.35 0.90 0.50 -0.10 -0.05 -0.25 8.382 -0.30 0.10 0.25 -0.15 -0.20 -2.05 0.25 0.05 -0.70 -0.20 0.05 -0.25 -0:20 7.836 0 0.30 -0.20 -0.40 0 0.95 -0.60 0.35 -0.35 -0.25 -0.25 -0.20 0.20 Copper 7.290 -0.60 0.20 0.20 0.25 0.20 0.20 0 -0.25 0.45 -0.15 -0.15 0.25 0.05 5.132 -0.25 -0.15 -0.10 -0.20 -0.20 0.55 0.60 0.60 0.30 0.35 0.20 0.10 0.05 4.374 1.50 -0.05 0.05 -0.05 0.05 -0.30 -0.30 0.10 -0.20 -0.25 -0.05 0 -0.05 2.916 -0.30 0.20 -0.05 0.20 -0.05 0 0.15 -0.40 0 0.05 0.05 0.05 0 1.458 -0.15 0.05 0 -0.05 0.05 0 -0.05 0.25 0 -0.05 0 0 0

Net Electrons Deposited per to3 Sowce Betas Incident on a 103 cm Length of Cable

Hypalon 11.304 -5.20 60.90 175.30 75.t,0 169.30 350.20 363.20 357.30 535.80 2.94 2.01 2.76 8.09 10.847 

10.390 

-2.35 

0.45 

29.00 10.70 29.30 11.90 214.50 226.70 119.60 65.50 1.34 0.40 0.33 2.0x 22.60 0.60 22.70 2.00 60.50 61.33 56.50 11.50 0.34 0.15 0.40 0.27

9.932 0.70 17.30 0 17.10 0.20 34.90 39.00 34.00 3.40 0.46 0.05 0.24 0.02 EPI? 9.474 0.10 24.20 0 14.90 0.20 19.80 17.33 17.90 0.60 0.33 0.06 0.11 0.01 8.928 -0.35 12.30 0 9.80 0 9.70 12.00 9.30 0.20 0.19 -0.01 0.03 0.01 8.382 -0.30 9.10 0 7.20 0 7.10 4.33 7.70 -0.20 0.21 0.02 0.03 0 7.836 0 8.20 0 5.20 0 4.80 3.33 3.20 0.10 0.13 0.02 0.02 0 Copper 7.290 -0.60 26.40 0 16.20 0 9.10 10.33 8.20 0 0.26 0 0.01 0 5.382 -0.25 0.50 0 0 0 0.20 0 0.20 0 0 0 0 0 4.374 1.50 0 0 0 0 0.10 0 0 0 0 0 0 0 2.916 -0.30 0 0 0 0 -0.10 0 0 0 0 0 0 0 1.458 -0.15 0 0 0 0 0 0 0 0 0 0 0 0
5.2 Radiation-Induced Disturbances

The problem of radiation-induced disturbances in cables. was analyzed

by IRT. 1 6 The IRT analyses estimated (a) cable conductivity changes

resulting from a LOCA radiation and temperature environment, (b) the

consequences of the conductivity change, and (c) the effects of charge

trapping in cable insulation.

Dielectric and conductivity calculations were based on the dose rates

estimated to be present in the cable as a result of the "I min" LOCAradiation environment (Figure 5.1 and Table 5.5). Effects of such

conductivity changes were analyzed on the basis of a shunt resistance.

The effects of charge trapping (Table 5.4) that were considered were

(a) electric field enhancement, (b) possible 12 R dielectric heating,

and (c) noise spikes resulting from instantaneous charge release.

Using the conductivity value, based on the "l min" LOCA, the IRT

calculations estimate a shunt resistance in the range of 70 to 7 megohms

would result depending, of course, on the value of cable length used in

the calculation.

Charge trapping calculations estimate an initial electric field

enhancement on the order of 10-8 V/cm. Release of trapped charge is based

on the assumption that charge buildup proceeds until dielectric breakdown

occurs. Based on the above assumption, it is estimated that currents on

the order of I A/cm of failed cable could be induced.

The assumption that charge buildup proceeds until instantaneous

insulation breakdown occurs allows for estimating the absolute maximum

radiation induced noise spike that may be expected. An additional, more

realistic estimate of the effect of charge trapping has been obtained

wherein charge mobility was considered to be a function of cable conductance and the charge induced voltage gradient occurring in the cable

insulation. Charge distribution within the cable insulation was based on

the one minute (LOCA) beta dose rate and its companion electron distribution within the cable.

63
Using these assumptions it is calculated that the charge distribution

associated with the maximum anticipated dose rate would result in a maximum voltage gradient across the cable of about 1200 volts per centimeter.

Since typical cable dielectric strength is on the order of 106 volts per

centimeter, it is highly unlikely that noise pulses on the order of those

.predicted above or that insulation breakdown could occur in cables exposed

to LOCA radiation environments.

5.3 Conclusions

Based on the IRT calculation, LOCA radiation-conductivity changes

and electric-field buildup should have negligible effect on an electric

cable's function. In the case of noise-spike generation due to charge

release, currents on the order of 1 A/cm may be induced. Currents of this

magnitude would have little effect on power cables. In the case of signal

leads, however, cable termination would need to be specified; e.g., high

impedence terminations result in a large induced-voltage pulse. However,

based on the continuous charge drain calculations described in Section

5.2, it is not likely that a charge necessary to generate a one ampere

current would be trapped in the exposed cable. In general, then a LOCAradiation environment would not significantly alter electric signals or

power transmission in exposed insulated electric cables.

In order to assess the adequacy of an isotopic simulator, the average dose rates calculated for the LOCA-radiation environment and those

estimated for a 6 0 Co simulator are shown in Table 5.5. The simulator

results are based on the results in Figure 5.2 and the assumption of a

60Co source strength capable of delivering a dose rate of 5 Mrad/h.

It may be observed that such a source would be capable of delivering

(at an extended time) any specified LOCA integrated-absorbed dose to any

region that may be considered particularly susceptible to radiation induced damage. Note that the simulator dose rate in the dielectric components is less than those LOCA one-minute dose rates. Since the IRT1 6

analyses of radiation induced electrical disturbances in cables were based

64
in part on the LOCA one-minute values of absorbed dose rates and were

demonstrated to be of negligible consequence, it may be concluded that

simulator induced electrical disturbances/damage in cables would also be

of little consequence.

TABLE 5.5

LOCA Conditions

Average Dose Rates - rads(mtl)/s

Elapsed Time

From LOCA

1 min

4 d

Copper

5.9 + 2

1.9

Cable Regions

EPR

6.4 + 3

2.6 + 1

Hypalon

1.1 + 4

1.0 + 2

60Co Capabilities - rads(mtl)/s - (5 Mrad/h source)

3.8 + 3 4.5 + 3 3.0 + 3

NOTE: 5.9 + 2, read as 5.9 x 102

65-66

6. Bulk Temperature Effects

6.1 Background

In Section 5.1 both LOCA and hypothetical isotopic (simulator)

radiation sources were defined on the basis of phenomenology and calculations. Since the source description necessary for cable degradation

analysis will suffice for material bulk temperature effects as well, only

the appropriate data are presented again here.

Table 6.1 lists averaged values of energy deposition16 in the three

zones of a typical cable configuration. Also in the table are comparable

dose rates for two isotopic simulators - a 60Co source delivering 1 rad/s

and another delivering 5 Mrad/h (1400 rad/s). Normalization discussed

earlier is based on the averaged dose distribution across the Hypalon

region.

6.2 IRT Heat Flow and Temperature Estimates - LOCA Source

Heat flow and temperature (changes) resulting from LOCA radiationenergy deposition were estimated by IRT1 6 for the generic cable. The

source terms used were the 1-min values given in Table 6.1. Heat flow

across the insulator and sheath were estimated using the one-dimensional

conduction equation. Using these approximations it was estimated that a

total temperature difference of about 8*C would be required to conduct the

deposited energy from the cable to the atmosphere. In the event of poor

transfer at the cable/air interface, conduction was assumed to proceed

inward and then through the copper conductor. In this instance a temperature rise between 100 and 100°C was predicted. Since these predictions approach the maximum allowable temperature (above a superimposed

LOCA thermal temperature) for certain insulation materials, the study

argued that alternate heat-flow paths would probably restrict the

insulator temperature to acceptable limits by heat transfer to the

67
atmosphere in addition to circulation along the central conductor.

Reference 16 presents no numerical results for isotope simulation.

TABLE 6.1

Dose-Rate Deposition Estimate - LOCA and 6 0 Co Sources

LOCA Dose Depositions - rads(mtl)/s

Elapsed Time Cable Regions

From LOCA Copper EPR Hypalon

1 min 5.9 + 2 6.4 + 3 1.1 + 4

4 d 1.9 2.6 + 1 1.0 + 2

6 0 Co Dose Depositions - rads(mtl)/s - 1 rad/s Source

2.75 3.20 2.20

60Co Dose Deposition - rads(mtl)/s - 5 Mrad/h Source

3.80 + 3 4.5 + 3 3.00 + 3

NOTE: In the case of the LOCA tabulation, primary electron

and photon contributions have been summed.

NOTE: The 5 Mrad/h isotope source choice is arbitrary but

not unrpqsonable. Typical planar (one directional

field) OCo sources are capable of producing

exposures on the order of 2 to 3 Mrad/h.

6.3 Some Sandia Estimates - Simulator Source

Since the iRT 1 6 analysis included no calculation of the' thermal effects of a simulator exposure, the following simulator heating estimates

are included for the purpose of comparison.

Instantaneous temperature rises were estimated for the three-region

cable assuming the LOCA radiation field for the 1-min and 4-d intensities

and for a hypothetical 60Co irradiator configured for a 5 Mrad/h maximum

dose rate. Instantaneous temperature rise, based on room temperature heat

capacities24 are given in Table 6.2.

68
TABLE 6.2

Instantaneous Temperature Rates - °C/s

Cable Regions

Source Copper EPR Hypalon

6 0 Co - 5 Mrad/h 9.7 - 2 2.2 - 2 1.4 - 2

LOCA - 1 min 1.5 - 2 3.1 - 2 5.3 - 2

LOCA - 4 d 5.0 -5 1.2 - 4 4.8 - 4

It is observed from Table 6.2 (and assuming that the cable is in

equilibrium with its external environment) that heat flow for the cobalt

exposure would be, initially at least, in the reverse direction to that

for cable exposed to.LOCA environments. Temperature differences necessary

for energy transport by conduction across the several cable boundaries

were estimated in a manner similar to that used in Reference 16.

Using the conduction equation for concentric cylinders and the values

of thermal conductivity listed in the reference, it is estimated that a

temperature difference of 70 C and 90 C, across the EPR and Hypalon, respectively, would be required to balance the energy input from the 6 0 Co configured for a 5 Mrad/h dose rate. Transfer of this energy to the surroundings is accomplished by convection and radiation. Energy transfer from

the outer cable sheath to the surrounding environment is estimated by an

expression of the form: j

q = (hc + hr) x A x (Ts - T )

where hc and hr are, respectively, convective and radiative heat-transfer

coefficients, A is a unit of surface area, Ts is the cable surface temperature, and T is the ambient temperature. hc was estimated using methods

presented in Reference 25, while hr was obtained using Reference 26.

Under conditions of maximum simulator energy input (5 Mrad/h), an

equilibrium value of (Ts - T ) 65 0 C is obtained. Working backwards

through the cable, a temperature of 81°C above ambient would be required

in the EPR if an equilibrium energy-transfer condition were to exist.

69
Ultimate temperatures achieved in the various cable regions will depend

upon specification of the ambient environment. Obviously, thermal damage

to the cable insulation and sheath will occur should that ambient specification be too large. Reduction of the simulator dose rate by an appropriate value (an option usually available on well-designed simulators)

would reduce the cable temperature to within acceptable temperature

limits.

We observe that although temperature gradients resulting from 60Co

exposures probably do not simulate those due to a LOCA exposure (assuming

the temperature profile tracks with the energy-deposition profiles), adjustment of the 6 0Co dose rate will allow for maintaining cable temperatures below maximum rating during any simulator-radiation exposure -- a

result in accordance with IRT predictions 1 6 for a LOCA exposure.

In Figures 6.1 and 6.2 polymer temperatures as a function of simulator dose rate have been plotted. Figure 6.1 is a plot of outer surface

•(Hypalon) temperature as a function of dose rate; temperature plotted is

Hypalon surface temperature versus environment temperature. As may be

observed (and was discussed earlier), reduction in dose rate is an effective method of lowering surface-environment temperature differential.

Figure 6.2 plots temperature differential across the EPR and Hypalon

regions as a function of simulator dose rate; temperature behavior is as

would be expected. Although these calculations were specifically for a

6 0 Co simulator, the character of the plotted data should be comparable

for other isotopic source environments -- lowering of surface-environment

temperature lowers the temperature differentials in the sample interior.

70
100

0

Outer Surface Polymer

Temperatures •S (T - T uu ) as

a Function of Exposure

Dose Rate

T = Cable Surface

s Temperature

Tco= Environment

Temperature

50

0 0 5 0 Exposure Dose 5 Rate Mrad/h 10

Figure 6.1

201

Outer Surface Polymer Temperature

vs Exposure Dose Rate

10

Temperature Differential

as a. Function of Exposure

Dose Rate, Across the

Jacket and Insulator

Solid = Drop Across

iHypalon

11 • Dashed Drop Across

EPRQ

0

H

1~

U '

0

Figure 6.2

5

Exposure Dose Rate - Mrad/h

10

Temperature Differential Across Cable Jacket

and Insulation vs Exposure Dose Rate

71
6.4 Conclusions

Radiation-induced temperature rise in polymeric materials were considered for two radiation sources -- a LOCA-radiation environment and a

hypothetical 6 0 Co simulator. The one minute LOCA studies were performed

by IRT1 6 for two cases. In both studies it was assumed that thermal

equilibrium had been established in the cable. .Considered first was the

case where the cable was in good thermal contact with its environment. In

this instance thermal equilibrium could be maintained, by radial conduction to the environment, with a thermal gradient of but a few degrees. In

the case of poor. thermal contact it was estimated that gradients on the

order of 100 0 C might be required to maintain thermal equilibrium. The IRT

report concluded that actual conditions would bridge these two extremes

and that service temperatures of the insulating and sheathing components

would not be exceeded.

Sandia calculations were based on a 6 simulator capable of rates

on the order of 5 Mrad/h - a rate between the LOCA 1-min and 4-d rates.

The results predict that because of ,differences in energy deposition, heat

flow would (initially at least) be in opposite directions for the exposures. These calculations predict that simulator-radiation-induced heating of cable configurations can be held to tolerable operating temperatures and simultaneously deliver a dose to materials on the order of a

LOCA-radiation deposited dose.

In summary we conclude that one-minute LOCA radiation environments

probably will not result in cable temperatures in excess of specified

service temperatures. Similarly it may be stated, that a suitably designed

60Co simulator will deliver prescribed radiation absorbed doses to cable

components while not exceeding the service temperatures of the various

cable materials.

72
7. Bulk Polymer Degradation

7.1 Integrated Radiation Dose Effects

Bulk polymer degradation is, primarily, the result of radiation in-

*duced ionization. Effects to polymers exposed to ionizing radiation may

be:

a. Radical (or ion) production

b. Molecular chain cleavage

c. Molecular chain cross linkage, and

d. Gas evolution

LOCA radiation effects to bulk polymeric materials were investigated by

IRT (analytically) on the basis of total integrated absorbed dose.16 The

IRT analysis is based, primarily, on polymer degradation resulting from

chain cross linking and unsaturation. Yield parameters (G-values) required for the analysis were based on those given in the literature.

The IRT calculations for Hypalon and ethylene-propylene may be

summarized as follows:

a. Hypalon

(1) 90 Mrads (10 h) - onset of deterioration

(2) 300 Mrads (I to 2 d) - serious loss of stability

b. Ethylene Propylene Rubber

(1) 100 Mrads (1 to 2 d) - 20% loss in tensile strength

(2) 500 Mrads (5 to 10 d) - 50% loss in tensile strength

The above estimates are based on a combination of the 1-min and 4-d LOCA

source estimates.

73
7.2 Dose-Rate and Oxygen Effects

Although the dose-rate and oxygen effects reported here are the results of an investigation into the feasibility of accelerated polymer

aging tests, the results can well have a bearing on the simulation of a

LOCA environment.

The results of this study2 7 are both experimental and theoretical .in

nature. In essence, the premise of this study was that radiation damage

to a polymeric material, polyethylene in the study, was due primarily to

the interactions of radiation produced radicals, in the polymer, with

oxygen present in the materials. The rationale,.here, being that the

presence of oxygen in the neighborhood of the active species (radicals)

enhanced molecular chain cleavage with resultant suppression of the crosslinking reaction. For the particular applications of this study molecular

cleavage was considered to be more detrimental than cross-linking.

While holding total integrated dose constant, this study examined

polymer degradation as a function of dose rate, oxygen pressure, and

polymer sample thickness. Polymer degradation was based on reduced gel

formation (inhibited cross-linking) with variation of the above

parameters.

The theory predicted and experiments confirmed that polymer degradation (inhibited gel formation) varied directly with the square root of

environment oxygen pressure and in an inverse manner with the square root

of the dose rate for a given polymer thickness and integrated radiation

dose. Since integrated dose was held constant, dose rate dependence of

polymer damage was a function of oxygen diffusion time into the interior

of the polymer sample.

7.3 Conclusions

We have reported the results of two studies on the radiation induced

degradation of polymeric materials. The first, by IRT1 6 , was theoretical

in nature and examined the effects of a LOCA radiation environment on

74
polymer performance. The second study was concerned with simulating the

long term aging effects of polymers; this study was both experimental and

theoretical.

The IRT study demonstrated that significant polymer degradation, in

a LOCA environment, would occur for exposure times between 10 hours and

8 days. The second study demonstrated that a correlation between radiation dose rate, oxygen concentration, etc., and a polymer damage parameter could be established.

Based on the first study, typical LOCA dose rates, to Hypalon for example, would range somewhere between 104 and 102 rads/sec (see Table 5.5).

Reference to Table 5.5 indicates that the typical simulator is, on the

average, able to deliver a dose rate comparable to the LOCA dose rate.

The results in Section 7.2 show that under certain conditions and for

a specific material that a predictable relationship between polymer damage

and the polymer environment exists. The specific results of the study

cannot be generalized to all polymer materials and environments. The

study does indicate that given a specific polymer and environment, that

environment and its effects could be adequately simulated by an appropriately designed simulator experiment.

To sum up, it is considered that, based on these studies, the effects

of a LOCA environment on bulk polymer materials could be reasonably well

simulated with judiciously designed simulator experiments.

75-76

8. Differential Mechanical Stress in Insulating Materials

8.1 Background

In Sections 7.1 and 7.2, effects to bulk polymers were discussed.

In those sections, neither deposition profile nor methods of monitoring

polymer degradation were considered. In considering differential stress

effects, energy deposition distributions are of basic importance. In view

of that importance, some aspects of energy-deposition distributions will

be reviewed (e.g., effects of source energy distribution and particle

makeup).

Methods of monitoring polymer degradation become important in considering possible stress effects since the parameter used to monitor

degradation may proceed at a much more rapid rate (with dose/dose rate)

then the parameter responsible for internal stress generation.

Polymer degradation, as a result of exposure to a simulated LOCA

environment, has been based on changes in the polymer elasticity. 2 0

Elasticity change has proved to be a particularly sensitive and easily

measurable parameter. Much degradation data, in the form of change in

ultimate elongation, has been accumulated for several polymers exposed

to a variety of environments.

Stress generation has been attributed to differential shrinkage in

elastomeric material as a result of nonuniform energy deposition in the

sample. It now becomes clear that if loss in elasticity proceeds at a

more rapid rate than shrinkage, then (due to loss in elasticity) the

polymer material may for all intents and purposes become useless as an

insulating material well before appreciable shrinkage has occurred.

77
8.2 Energy Deposition and Polymer Degradation

Isotopic-source irradiation of polymeric materials will deliver a

relatively uniform energy deposition into the polymer. On the other hand,

a LOCA exposure delivers a nonuniform temperature distribution that correlates with the dose distribution. The result of a LOCA exposure on a

macroscopic scale is a nonuniform material-degradation profile that is a

decreasing function with penetration in any material layer of a sample.

The difference in cable energy deposition profiles for cables irradiated under LOCA and simulator conditions are presented in Figures 5.1

and 5.2 respectively. From the figures it is apparent that a cable

configuration exposed to a LOCA environment will exhibit a deposition

pattern that is highly spatially dependent. By comparison simulator

irradiated cable samples will exhibit almost negligible spatial dose

dependence. Hence simulation dose based on the surface dose to a LOCA

irradiated specimen would certainly overstress most regions of the sample.

Initially, such a procedure to greatly overstress most zones in the cable

configuration, when compared to a LOCA exposure, would appear to be a

conservative approach to testing. However, if it is postulated that

polymer degradation is accompanied by material dimensional change, then

the above statement about conservative simulator overtesting is probably

not true.

A uniformly irradiated cable would undergo uniform dimensional

change. On the other hand, a LOCA or nonuniformly irradiated cable

would contain regions of unequal dimensional change. Hence nonuniformity

in dimensional changes could give rise to circumferential and/or radial

stresses with resultant mechanical damage. Thus, if the above postulation concerning dimensional changes is true and the change is appreciable

compared to other effects, then uniform overstress of the cable sample

would not represent a conservative or valid test.

8.3 Polymer Degradation - Elongation/Shrinkage Experiments

Elongation/shrinkage experiments were performed by Gillen, 2 8 using

several typical safety-related cable samples. The elongation/shrinkage

78
changes were induced in all cases by an accelerated aging technique at

elevated temperatures. Multiple samples were used in all experiments.

The results for these thermally aged cable polymers 2 8 are given in

Figures 8.1 and 8.2. The results plotted are fractions of initial elongation versus aging time for the various materials aged at several temperatures. In most tests aging was continued until the samples were almost

totally degraded. Also, plotted in Figures 8.1 and 8.2 are shrinkage data

for each sample.' Data presented in this instance are fractions of initial

length versus aging time. In all instances, open symbols represent elongation data while matching closed symbols are representative of shrinkage

data. As may be seen from the data, shrinkage of most samples was insignificant -- the maximum observed shrinkage was about 5%. It is also

interesting that the preponderance of cable shrinkage occurred early (in

time) in the aging experiments. From the thermal-aging data of Gillen it

may be observed that changes in sample dimension remain slight up to the

point where severe degradaLion occurs.

8.4 Polymer Degradation - Elongation/Density-Change Experiments

The elongation/density-changeexperiments investigated the effects to

polymers similar in composition to those used in the thermal-aging experiments reported in Section 8.3. The elongation/density-change effects

were radiation-induced with a 6 0 Co irradiator. The irradiations were

performed under ambient conditions (i.e., at room temperature and in an

air atmosphere).

Data from these experiments include changes in elongation versus

radiation (integrated) exposure and shrinkage data in the form of density

changes versus dose. In Figures 8.3 and 8.4 are presented the radiation

elongation and shrinkage data. 2 9 ' 3 0 Presented in the figures are fractional parameter changes versus exposure dose. Again the open symbols

represent elongation data and the respective closed symbols represent

density data.

79
O

0

0

0

Hypalon @

Hypalon @

Hypalon @

Hypalon @

EPR @ 150

EPR @ 150

139.5 ± 0.5 0 C - Manufacturer A C/C0

139.5 ± 0.5 0C - Manufacturer A L/L°

140.9 ± 0.5 0 C - Manufacturer B E/I 0

140.9 ± 0.5 0 C - Manufacturer B L/L0

±0.50C - Manufacturer A C/C 0

± 0.5 0 C - Manufacturer A L/LE

v CLPO @ 140 ± 0.5°C - Manufacturer C /Co0

v CLPO @ 140 ± 0.5 0 C - Manufacturer C L/L0

o Hypalon @ 141.2 ± 0.5 0 C - Manufacturer B E/Ie

0

0 Hypalon @ 141.2 ± 0.5 0

C - Manufacturer B L/L 0

0

0

0

o

60

Cd

0

0

. 1.

$4

0

M

w

0

0

Aging Time (h) 100 A$

Aging Time (h)

Figure 8.1 Polymer Aging vs Aging Time -

Aging Thermally Accelerated

Figure 8.2 Polymer Aging vs Aging Time - Aging Thermally Accelerated
A Hypalon @ RT /C0 Ref 0

A Hypalon @ RT P/P Ref 0

v Hypalon @ RT CIE Ref 0

Y Hypalon @ RT PIp Ref

0

29

29

30

30

A

0

0

EPR

EPR

EPR

EPR

EPR

EPR

A@ RT C/E Ref 29 0

A @ RI P/Po Ref 29

B @ RT EIE Ref 29 0

B @ RT P/P Ref 29 0

RT €E/ Ref 30 0

RT P/P Ref 30 0

0

I.

w(-X

0

I'

0

J-J

1.04

0 QL

1.0

d •0 .

0

.rd

0

0.51-

! I I I - L

15 40 .100

Exposure Dose (Mrad)

300

Exposure Dose (Mrad)

Figure 8.3 Polymer Aging vs Aging Time -

Aging Radiation Accelerated

Figure 8.4 Polymer Aging vs Aging Time - Aging Radiation Accelerated
As may be observed, the polymer densities were little affected by the

radiation aging even to the point of complete loss of sample elasticity.

Lack of density change may be interpreted as absence of significant sample

dimensional change.

8.5 Other Considerations

One further item of interest in the realm of simulator adequacy is

that of radiation-induced temperature rise of simulator versus LOCAexposed samples. All other things being equal, the ultimate temperature

rise in a given irradiated sample will be dependent on the energy deposition rate. Simulator capability to achieve early time LOCA rates does not

exist. It is just possible that early time LOCA exposures could result in

a combined temperature-radiation aging condition not normally present in a

simulator-irradiation test. Although the combined effects may be small,

such effects could probably be compensated for. Gillen2 7 has demonstrated that a functional relationship between thermal- and radiationinduced aging exists for several polymeric materials. This relationship

shows that over a certain range the effect of temperature fluctuations on

aging could be accounted for by adjustment of dose rate and vice versa.

Establishing such relationships for cable polymers would then allow

compensation to be made for any elevated temperatures occurring during a

LOCA exposure and not present during a simulator exposure.

8.6 Conclusions

Polymer tensile elongation is an easily measured parameter that is

extremely sensitive to radiation or thermally-induced stress. Since loss

of tensile elongation is a major cause of polymer failure, monitoring of

tensile elongation changes of radiation or thermally-stressed material

represents a particularly sensitive measure of polymer performance; there

is concern that other physical changes in stressed polymeric materials

(dimensional/density or material shrinkage) would be particularly sensitive to the LOCA environment. Major contributors to polymer failure were

considered in Figures 8.3 and 8.4. The results of the studies summarized

in Figures 8.3 and 8.4 show that, in materials stressed both thermally and

82
by radiation, failures due to loss in elasticity could be expected before

any appreciable material dimensional changes. In the case of combined

•radiation/thermal stress of polymers, recent studies strongly suggest that

simulator environments could be adequately compensated for so that the

proper LOCA effect could be reasonably duplicated.

It is concluded that:

a. Polymer tensile elongation change is a valid monitor for material

performance

b. Loss of elasticity is a major contributor to mechanical failure

of polymeric materials - dimensional change contributing little, if any,

to that failure. Hence, differential-mechanical stress failure is not a

practical failure mechanism

c. Exact simulation of a LOCA radiation/thermal stress is not

required to reproduce the LOCA radiation/thermal-stress-induced changes.

83-84

9. Summary and Conclusions

The standard gamma-radiation simulators can adequately duplicate the

damage mechanisms and damage in safety-related equipment that result from

the postulated nuclear-plant ambient and accident radiation environments.

The conclusion can be no stronger than that because the simulators must be

intelligently used in an overall qualification program that implies combinations of environments, magnitudes, secondary radiations (e.g.,

bremsstrahlung), functioning, and other considerations.

Other specialized simulators, which strive to more closely achieve

the LOCA-radiation signature, are equally adequate with similar provisos.

However, there seems to be no reason to select one simulator over another.

One recommendation is to overstress the equipment/material everywhere

to greater total dose than expected from the combined LOCA-radiation

signature; dose rates should also approximate the expected (combined)

rates. However, other logical data-based techniques (e.g., averaged dose

and rates) may also be acceptable.

In summary, we have seen no evidence of unique damage mechanisms in

exposed organic materials that demand unique radiation-simulation techniques; neither can-radiation be arbitrarily applied to the test item

without consideration of the complete qualification program.

Nevertheless, this study should not terminate because not all aspects

of simulator adequacy evaluation are complete. A few areas requiring

additional attention can be suggested:

* Equivalence of beta/gamma and or neutron/gamma (for aging

environments) ratios in bulk degradation. That is, are peak

doses/rates appropriate, or are averaged values acceptable?

85
" Charge breakdown resulting in transient noise and/or permanent

damage may be important in selected equipment.

" Secondary emissions, magnitudes and effects, may be a

consideration.

" Simulator adequacy evaluations should be extended to more complex

and specific equipment items.

86
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1. IEEE Standard for Qualifying Class 1E Equipment for Nuclear Power

Generating Stations, IEEE Std. 323-1974., the Institute of Electrical

and Electronics Engineers, Inc., 1974.

2. L. L. Bonzon, Radiation Signature Following the Hypothesized LOCA,

SAND76-0740 (NUREG76-6521), (Albuquerque: Sandia Laboratories,

revised October 1977).

3. L. L. Bonzon, "In-Containment Radiation Environments Following the

Hypothesized LOCA (LWR)", Transactions of the American Nuclear

Society, pp 601-602, TANSAO, 23, 1976.

4. L. L. Bonzon, N. A. Lurie, D. H. Houston, and J. A. Naber, Definition

of Loss-of-Coolant Accident Radiation Source, SAND78-0090

(Albuquerque: Sandia Laboratories, February 1978).

5. L. L. Bonzon, N. A. Lurie, D. H. Houston, and J. A. Naber, Definition

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May 1978).

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87
12. L. L. Bonzon and N. A. Lurie, Best-Estimate LOCA Radiation Signature,

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1978 (Albuquerque: Sandia Laboratories, 1978).

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1976.,

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(New York: Academic Press, 1968).

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88
24. K. C. Weast, ed., Handbook of Chemistry and Physics - 50th Edition

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26. W. H. Giedt, Principles of Engineering Heat Transfer (New York:

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27. Seguchi, T., Hashimoto, S., Kawakami, W., and Kurijama, E., Radiation

Damage of Polymer Materials I. Simulation Studies on Distribution of

Oxygen Concentration in Polymer Film Under Irradiation in Oxygen,

JAERI-M7315, October 1977.

28. Private communication, K. T. Gillen, April 1979.

29. Fujita, H., Obuchi, H., Okade, M., Mio, K., and Terasaki, I., "Radiation Resistance of Rubber and Plastic Cables", Dainichi Nippon Densen

Johio, #48, 1971.

30. Kakuta, T., Wakayama, N., and Kawakami, T., Gamma Irradiation Test of

Wire and Cable Insulations and Electronic Materials, JAPFNR-172,

August 1974.

89-90

APPENDIX A

Calculations to Support Evaluation of Test Sources for

Radiation Qualification of Class 1E Equipment

IRT 8167-010(B)

April 9, 1979

91-92

f

IRT 8167-010(B)

CALCULATIONS TO SUPPORT

EVALUATION OF TEST SOURCES

FOR RADIATION QUALIFICATION OF CLASS

I E EQUIPMENT

IRT

Corporation

FINAL REPORT - Phases 5 and 6

N. A. Lurie

This report documents part of the Qualification Testing Evaluation

(QTE) Program (A 1051-8) being conducted by Sandia Laboratories

for the United States Nuclear Regulatory Commission under DOE

Contract AT(29-l)-789.

Prepared for

SANDIA LABORATORIES

Albuquerque, New Mexico

Under

Contract 07-3272

April 9, 1979

Instrumentation

Research

Technology

7650 Convoy Court • P.O. Box 80817

San Diego, California 92138

714 / 565-7171

Telex: 69-5412

93
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TABLE OF CONTENTS

1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

2. PHYSICAL PROPERTIES ........

2.1 Physical Properties ........

2.2 Damage Mechanisms ............

2.3 Source-Cable Configuration .......

3. METHODS OF CALCULATION .........

3.1 Transport Methods ..............

3.2 Source Distributions ............

3.2.1 Spatial Distributions ....

3.2.2 Energy Distributions ....

3.3 Dose Enhancement ............. 3.4 Uncertainties . . . .. . . . . . .

4. RESULTS FOR LOCA SOURCES . ....

4.1 Source Selection ........... . ..

4.2 Depth-Dose Calculations .........

4.3 Charge Deposition Results .....

5. SIMULATOR SOURCES .... .........

5.1 6 0Co Source ... ... . .. ..

5.2 137Cs Source ...............

5.3 Depth-Dose Results .... ........

6. COMPARISONS OF RESULTS, DISCUSSION

6.1 LOCA Versus Simulator Results . . .

6.2 Discussion and Conclusions .......

6.2.1 Model Sensitivity ...... .

. . . . . .

. . . . . .

. . . . . .

. . . . . .

. . .. . . . .

AND CONCLUSIONS-. .

. . . . . .

K .e . o o. l. . o. o o.

. . . . . .

. ~ ~ o ..

. . .. o. . . .

. . . . . .

. . . . . .

101

101

101

103

, 105

105

. . 106

• 107

. 111

113..

, 115

117

117

* 117

, . 134

137

, 137

* , 138

139

143

. 143

. 143

143

, •157

. 161

, 161

162

, 162

162

163

6.2.2 Comparison Criteria . . . .

7. RECOMMENDATIONS FOR FURTHER WOR

7.1 Consideration of Damage Mechanisms

7.2 Other Source Calculations . ....

7.3 - Model Sensitivity .........

7.4 Other Components and Simulators .

REFERENCES ..... ...............

APPENDIX: TABULATED DEPTH VERSUS DOSE IN CABLE ........... .. 165

95
LIST OF FIGURES

Figure

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

Model of the reactor power cable .................... ..... 102

Source-cable geometry ..... ........................ . •.108

Distribution of incident angles (with respect to surface normal)

on cables .............. .............. ............ ... 109

Relationship between distributions with respect to surface normal and

with respect to a point source ........ . .... .......... ... 110

Original and perturbed gamma-ray spectra at various radii (1000 cm,

500 cm and 200 cm) ......... ...................... ... 112

Original and perturbed waterborne gamma ray spectra (Source I

at I minute) at various radii ............ .................. 114

Original and perturbed airborne beta spectra (Source I at I minute)

at various radii ................ ........................ 115

Depth-dose calculations for airborne gamma rays on the cable

(Source I at 1 minute and at 4 days) ...... ................ .. 121

Depth-dose calculations for airborne gamma rays on the cable

(Source 2) . ....... ......... ............ ........ 122

Depth-dose calculations for airborne betas on cable (Source 1) . . . . 123

Depth-dose calculations for airborne betas on cable (Source 2) . . . . 124

Depth-dose calculations for plate-out gamma-ray sources on cable

(Source 1) ............... ........................... .. 125

Depth-dose calculations for plate-out gamma-ray sources on cable

(Source 2) ......................... .............. .. 126

Depth-dose calculations for plate-out beta sources on cable

(Source 1) .......... ................................ 127

Depth-dose calculations for plate-out beta sources on cable

(Source 2) ............. ........ ................. .. 128

Depth-dose calculations for waterborne gamma-ray sources

(Source 1) ........... ......................... . . . 129

Depth-dose calculations for waterborne gamma-ray sources

(Source 2) ............. ........................... .. 130

Comparison of two thicknesses of water layer on depth-dose results

for waterborne beta spectrum at I minute (Source 1) ......... .... 131

Depth-dose calculations for waterborne beta sources (Source 1) . . . . 132

Depth-dose calculations for waterborne beta sources (Source 2) . . . . 133

600

6Co source irradiation configuration .. . .... .. .. .. . .. 138

Degraded 60Co energy spectrum at the cable surface with V"

iron liner ................... .......................... 139

96
23 Depth-dose in cable due to 60Co gamma rays with and without iron

liner (test chamber) ................................... 140

24 Depth-dose in cable for 137 Cs gamma rays ................. .. 141

25 Comparison of depth-dose for 60Co and 137Cs with airborne gamma rays(Suce).........................14 ra s(Source 1) . . . . . * * * * * * ' * ' * * * * * * * * * *144

26 Comparison of depth-dose for 60Co and 137Cs with airborne gamma

rays (Source 2) ........... ..... ...... .. ........... 145

27 Comparison of depth dose for 60Co with airborne betas (Source I) . . . 146

28 Comparison of depth dose of 60Co with airborne betas (Source 2) . . . 147

29 Comparison of depth dose for 60Co with plate-out gamma rays

(Source I) ...... ....... ....... *..........................148

30 Comparison of depth dose for 60Co and 137Cs with plate-out gamma

rays (Source 2) .... ....... ....... ............ ........ 149

31 Comparison of depth dose for 6 0Co (normalized at average dose in

surface zone) with plate-out betas (Source 1) ..... ............ 150

32 Comparison of depth dose for 60Co (normalized at average dose in

surface zone) with plate-out betas (Source 2) ................ .. 151

33 Comparison of depth dose for 60Co (normalized to average dose in.

surface zone) with waterborne gamma rays (Source 1) ........... .. 152

34 Comparison of depth dose for 60Co (normalized to average dose in

surface zone) with waterborne gamma rays (Source 2) ......... . .153

60 35 Comparison of depth dose for Co (normalized to average dose in

surface zone) with waterborne betas (Source 1) .............. .. 154

36 Comparison of depth dose for 60Co (normalized at surface) with

waterborne betas (Source 2) ........ ... ................ .. 155

37 Influence of steam on the gamma ray source spectra

(Source 1 at I hour) ......... ............. .... ..... 156

38 Depth-dose profile for Source I gamma rays at I hour with and

without steam in the surrounding medium ...... ............. 158

39 Comparison of airborne gamma ray energy deposition (Source I at

I minute) for approximate, perturbed source and for "brute-force"

model .......... ........... ........... 159

97-98

1. INTRODUCTION

Phases 5 and 6 of the present program are devoted to consideration of energy

deposition in a model reactor component. The objective of this work is to establish the

basic data required to assess the validity of various radiation simulators for duplicating

the damage in reactor Class IE equipment resulting from a loss-of-coolant accident

(LOCA). The definition of the LOCA source terms as specified by U.S.N.R.C.

Regulatory Guide 1.89 (Ref 1) was considered in Phases 2 and 3 of the program (Ref 2).

Those energy spectra were used as starting points in the present calculations.

The reactor component considered for this initial comparison was a power cable.

Energy deposited by the beta and gamma-ray fields as defined in Phases 2 and 3 are to

serve as benchmarks for comparison with the simulator results. Simulators used for

qualification testing come in man), forms including 60Co and 137Cs isotope sources,

bremsstrahlung and electrons from linear accelerators (Linacs), and spent fuel assemblies. By far the most common testing is by 60Co irradiation. The energy deposition in

60

terms of dose versus depth for the LOCA sources and for Co will provide part of the

data necessary to formulate judgments as to the validity of 60Co as a test source.

Previous work on this problem (Ref[s 3,4) was preliminary and qualitative in

nature. The present work was intended as a careful quantitative study to provide the

calculational data necessary to allow meaningful conclusions to be drawn about the

adequacy of simulator sources.

In the sections that follow a description is given of the mathematical model used

for the cable including the approximations and assumptions made. Discussion is also

given of the source-cable geometry. Proper configuration of the source is a very

important aspect of proper modeling. Section 3 discusses the methods employed for

carrying out the calculations and the inherent approximations; some special treatments

of the sources were required to make the calculations tractable. In Section 4 the

sources selected for study are summarized, from the many previously calculated. This

is followed by the results for the LOCA sources. Section 5 includes the same

information for the simulator sources. Finally, some comparisons and discussion are

presented in Section 6 along with our conclusions and recommendations for additional

work in Section 7.

99
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100
2. CABLE MODEL

2.1 PHYSICAL PROPERTIES

There are many types and manufacturers of cable used in nuclear power plants.

The type selected for study here is a 600%' power cable consisting of a copper core with

elastomer insulator and jacket. Discussions with several manufacturers were held to

collect data on their "typical" 600V cables. Not surprisingly, it was found that the

dimensions and material compositions varied widely. Thus, the model selected may be

considered in the range of typical cables, but not exactly like any one manufacturer's

type in particular. Other, slightly different elastomeric materials (but composed

basicallyoof CH 2 ) would not be expected to have much effect on the results, nor would

small changes in dimensions be expected to change the conclusions. It is difficult,

however, to generalize without doing model sensitivity calculations wherein these

model parameters are varied systematically. In the discussion of results (Section 6) a

few comments are given about the expected sensitivity of the model.

The dimensions and material properties of the model are shown in Figure 1. Only

an unshielded cable was studied. Each region of the cable was subdivided into annular

zones of uniform thickness for calculations of depth versus dose. For most cases four

or five zones were used for each region.

2.2 DAMAGE MECHANISMS

The question of ultimate interest is to what extent a given radiation field will

affect the properties or operating characteristics of a material or component. In many

instances, experience has shown that the degradation is directly related to the total

energy deposited or absorbed dose. Thus, the usual analysis of radiation effects

involves determination of the (nonequilibrium) dose to the critical regions of the

component. In many complex systems such as electrical or electronic equipment this

simple approach may not be adequate. The controlling damage mechanisms may involve

phenomena that are not simply related to the energy deposition. Therefore, any

measure of simulator performance must use as a basis the best estimate of the

101
HYPALON: C

ETHYLENE-PR(

RUBBER (EPR

HYPALON

85 H157CE 13so2 (P = 1.55 g/cm3 )

ETCHL2 R (P 1.27 g/cmU 3

•ETHYLENE-PROPYLENE RUBBER

COPPER

RT-16620

Figure 1. Model of the reactor power cable

controlling damage mechanism, whether it is energy deposited or some other quantity

appropriate to the component of interest."

A detailed evaluation of the damage mechanisms for reactor components is a

complex analysis problem that is beyond the scope of this project. Even for the case of

a reactor power cable there are many physical interaction phenomena that must be

considered (Ref 5). The type of calculations presented here that will support such an

assessment are the energy deposition profiles, that is, the dose versus radial depth in

the cable. We also attempted to calculate net charge deposition as a function of radial

depth.

102
2.3 SOURCE-CABLE CONFIGURATION

Regulatory Guide 1.89 (Ref 1) calls for three distribution categories (airborne,

plate-out, waterborne) for each of two LOCA sources. For purposes of studying their

interactions in the cable, each of the three distribution categories require.s a different

source configuration. The airborne source was taken to consist of a uniform

distribution of point sources in air plus 70 psig saturated steam. A few calculations

were also done with dry air (i.e., no steam) to evaluate the sensitivity of this

parameter. The waterborne source was assumed to consist of sources uniformly

distributed in the water. The plate-out source was uniformly distributed on the surface

of the cable.

The latter geometry presents no calculational difficulty. The spatially extended

source distributions, however, are not efficiently treated by direct Monte Carlo

transport methods. The reason for this is that the cable subtends a very small solid

angle; in other words, the probability that a source particle sampled from the air will

hit the cable is too small to get statistically meaningful results in a reasonable time.

Consequently, an approximate technique was used to map the distributed airborne and

waterborne sources into a practical configuration. The details of this procedure are

described in subsection 3.2.

103
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104
3. METHODS OF CALCULATION

Detailed descriptions of the calculational methods employed in this work to calculate the energy deposition are given in the subsections that follow. Treatment of the

distributed source problem is also described.

3.1 TRANSPORT METHODS

All of the calculations of depth versus dose reported here were carried out using

the code SANDYL (Ref 6). It is the most general and widely recognized coupled

photon-electron transport code presently available. It.has served as the industry standard for several years. Extensive experience with this code has demonstrated its capabilities for a wide variety of transport problems (Ref 7).

SANDYL is a FORTRAN code for computing photon-electron transport and

deposition in complex systems by the Monte Carlo method. The code was developed at

Sandia Livermore Laboratories (Ref 6). It. is based on a photon transport code from

Lawrence Livermore Laboratory (SORS) (Ref 8), and the electron transport codes of

Berger (Refs 9,10). Like many transport codes, SANDYL uses the physical approach

which consists of random sampling and simulation of individual histories which are used

to construct the solution to the physical problem. A transport equation is never

explicitly written and solved. The only information needed to simulate a history is the

probabilistic description of all events which may occur at each point in the history. The

random, probabilistic nature of particle/radiation interaction with matter renders

Monte Carlo methods particularly well suited to problems of particle/radiation transport. The necessary information in this case includes a description of the geometrical

boundaries of the different regions through which transport occurs, the material composition of each region, and the cross sections (differential in energy and direction) of the

constituent isotopes.

A simulation consists of generating a large number of particle histories one at a

time, with primary particles starting at the source, and secondaries starting at their

generation points along the trajectories. As the particles traverse the different regions

105
of the system, the contributions to the quantities of interest are tallied following each

collision to generate the desired information. The average of these quantities for a

number of primary, and their induced secondary, particle histories represents a statistical approximation of the solution.

Photon histories are generated by tracing their trajectories from collision to

collision. At each point of photon-medium interaction the type of interactions, secondaries and the new photon energy, direction, and distance to the next collision are

determined on the basis of probability distributions characteristic of the medium

composition. Photon collisions can result in photoelectric absorption, Compton

scattering, or pair production. Secondary photons include bremsstrahlung, fluorescence,

and annihilation radiation.

Electrons are treated in a slightly different manner because, as a result of being

electrically charged, they suffer a much larger number of collisions. The method used

for electron transport is known as condensed-history Monte Carlo (Ref 10). Accordingly, an electron history is generated by following the trajectory in spatial steps of

pre-computed length, so that the electron energy and direction at each point may

depend on a number of different collisions which may have occurred in the previous

step. Therefore, electron energies and directions are determined on the basis of

multiple scattering distributions. Within a step, secondary photons and electrons are

generated according to the corresponding probability distributions. Electron interactions include electron-electron collisions, bremsstrahlung radiation, and medium

polarization. Secondary electrons which are followed include knock-on, pair, Auger,

Compton, and photoelectric electrons.

Three-dimensional geometries with a high degree of complexity can be treated.

,The problem geometry is divided into zones of homogeneous atomic composition

bounded by planes and quadrics. Options are available for splitting or biasing to

improve the statistical uncertainty in certain problems. The code calculates flux or

energy deposition (dose or spectrum) in any desired zones as well as net charge

deposited. Photon and electron transport are followed in an energy range from 1 keV to

I GeV or higher.

3.2 SOURCE DISTRIBUTIONS

The source configurations specified for the airborne and waterborne cases are

spatially distributed, isotropic sources surrounding the cable. As noted earlier, spatially

106
extended sources present a problem for Monte-Carlo-type calculations because the

region of interest is small compared to the dimensions of the source. In this problem

the cable radius is about 1 cm whereas the source consists of point sources uniformly

distributed in the containment with dimensions of the order of 25 m (radius). For

gamma rays in air there is little attenuation, and sources at distant points can

contribute to the energy deposition in the cable. The attenuation in water is

considerably greater and thus smaller source regions can be considered. The most

energetic betas in this work (-6 MeV) have a range in air of -25 m; their range in

water, however, is only about 3 cm.

In this study we have used an approximate method to obtain the distributions of

radiation, both in energy and angle, incident on the surface of the cable. This permits

conventional Monte Carlo methods to be used with maximum efficiency to calculate the

depth-dose profiles of interest. We have assumed that the energy and annular

distributions are not coupled so that each may be approximated independently.

3.2.1 Spatial Distibutions

The sources are taken to be uniformly distributed in an annular region surrounding

the cable (see Figure 2). The high symmetry of the problem means that only sources in

a sector of the annulus need be considered. Furthermore, if the cable is taken to be

infinitely long so that end effects can be ignored, the polar angles are uniformly

distributed between ±7r/2, and the problem may be reduced to a two dimensional

problem. Symmetry further allows us to collapse the two dimensional sector to a line

AB where the density of points on the line increases with radius like. the area of the

sector, that is, like (r2 -R 2 ).

A Monte Carlo technique was utilized to calculate the angular distribution of

particles striking the surface of the cable. The method may be described as follows:

The source position was randomly selected along the line AB where the density of

sources increases with radius. The probability that a particle emitted at the chosen

distance from the cable strikes the cable (ignoring attenuation and scattering in the

medium) was calculated in' the following way. Only particles emitted into a cone

defined by the cable can hit it. A particle from within the cone was selected at random

and its angle of incidence on the surface of the cable (with respect to the surface

normal) was computed. The computed angle was stored with a weight equal to the solid

angle, (the probability of a hit) and the whole process was repeated. In this way a

107
SOURCE REGION

CABLE

AREA - (r 2-R2)

TWO-DIMENSIONAL GEOMETRY i

RT-16619

Figure 2. Source-cable geometry

108
distribution of normal angles was generated which corresponds to the case of the

spatially distributed source with no attenuation or scattering in the medium.

The results of such calculations for the cases where the source annulus is 2.5 rn

radius and 25 rn radius are shown in Figure 3. The 25 m dimension corresponds roughly

to the radius of the containment of a commercial light water power plant, and also the

range of a 6 MeV beta particle in air. The 2.5 m dimension is taken as an effective

thickness of the gamma-ray source in water. Less than 0.1 percent of all gamma rays

beyond 2.5 m would reach the cable for the waterborne sources used here.

IU-

.-,

SOURCE RADIUS

2.5 M

-- SOURCE _

-- RADIUS -

25 -

I - i

0 10 20 30

ANGLE OF

40 50 60 70 80

INCIDENCE (DEGREES)

90

RT- 16603

Figure 3. Distribution of incident angles (with respect to surface normal) on cables

109
The shapes of the angular distributions are virtually identical for these two cases

and correspond to a cosine distribution. It was found that for any size of annular source

region large compared to the cable radius, the incident angular distribution of particles

has the cosine shape. When the thickness of the source region is of the order of the

cable radius or less, a departure from the cosine shape was observed (the distribution

becomes flatter).

Although it is not necessary, it was convenient for the subsequent depth-dose

calculations, to transform the calculated distribution of incident angles into a distribution from a fixed point source at a specified distance from the cable, Figure 4 defines

the angles. We call N(c) the calculated distribution of normal angles, a, from the

distributed source. We desire to express this in terms of the angles 0 measured with

respect to a point source at a specified distance. The transformation is given by

d+R cos a

N(w) e N() ags cosrad

where the angles are related by

sin al d+RR sin 0.

SOURCE

RT-16618

Figure 4. Relationship between distributions with respect to surface normal and

with respect to a point source

110
If N(ce) is a cosine distribution, as was apparently determined by the Monte Carlo

calculations,

N(oa) = Ccos a

where C is a constant which depends on the size of the source region. Thus,

N(o) = c+R Cos0

where 0 can assume values from 0 to sin- I Thus, the source azimuthal angles

at distance d from the cable may be selected according to the distribution N(O), and the

resulting particles which strike the cable will do so with an angular distribution

identical to that which is obtained from an extended spatial distribution of isotropic

point sources. For the three dimensional problem, the azimuthal angle is combined with

the polar angle (sampled from a uniform distribution between ±r/2) to yield the

direction cosines of a source particle.

3.2.2 Energy Distributions

The energy spectrum of particles incident on the cable from a spatially extended

source will differ from the fission product source spectrum because of energy loss due

to scattering and attenuation in the surrounding medium. The extent to which the

source spectrum is perturbed depends, upon the nature of the medium (especially the

density) and the size of the region considered. To account for such spectral changes the

following calculations were made. Each fission product source was uniformly distributed in a simple model of the reactor containment consisting of a large cylinder of air

plus steam or water surrounded by concrete. The flux energy spectra at various radii in

the containment were calculated to determine the radial variation of the spectra. For

this purpose only the spectral shapes are of interest.

The calculational procedure used was to distribute the source throughout the

containment volume and sample the particle spectrum crossing successively smaller,

imaginary, concentric cylinders. The radii were reduced until the statistical uncertainty became -unacceptably large. For the case of gamma rays in air, computations

were done at 9 radii between 200 cm and 25 m.

It was found that the airborne source spectrum is somewhat perturbed by the

interactions in the air-steam mixture and with the concrete wall. However, the radial

variation of the spectrum is very slight. In general, the structure of the original source

ill
spectra are smoothed. A few examples of the results are shown in Figure 5 for the case

of Source I gamma rays at - minute (see Section 4.1 for a description of the sources

used in this study). The slow radial variation of the shape of the perturbed spectra

shown in Figure 5 suggests that the energy spectrum at the cable would not be very

different wherever the cable is located in the containment (ignoring internal structure),

except perhaps near the wall. Thus, the perturbed spectrum at the radius of 200 cm

(the smallest feasible for these calculations) was used as the source term for the depthdose calculations in the cable. Similar results obtained for the other gamma-ray

sources in air.

bk

z

R7-16612 ENERGY (MeV)

Figure 5. Original and perturbed gamma-ray spectra at various radii (1000 cm,

500 cm and 200 cm). The starting spectrum (labeled "fission product

source") corresponds to airborne gamma rays at I minute. Only the

shapes of spectra are significant for the present purposes.

112
The same type of procedure was used for the beta sources in air and for the

gamma ray sources in water. Of course, the limited ranges of the, latter sources

permitted much smaller cylindrical regions to be used. At the same time, the

perturbations to the original spectra are significantly greater.. Figure 6 shows the

original and perturbed spectra for waterborne gamma rays at several radii including the

radius corresponding to the outer surface of the cable. Note that there is a much more

significant softening of the spectrum due to interactions in the water.

An example of the air and steam attenuation on the beta system is displayed in

Figure 7. As with the gamma rays, the shape of the spectrum is not rapidly varying

with radial position in the containment. The perturbed spectra at the surface of the

cable were used for subsequent depth-dose calculations.

For the case of beta particles in water, the range is sufficiently small for the

most energetic betas (-3 cm) that normal Monte Carlo procedures can be utilized

without approximation.

3.3 DOSE ENHANCEMENT

Several years ago it was observed that photon energy deposition profiles near the

interface of materials of different atomic number showed significant enhancement

(Ref 11). The physical explanation of this phenomenon is that secondary electrons

originating in the high atomic number material are deposited in the adjacent low atomic

number material producing a dose that far' exceeds the energy deposited by direct

photon interactions. The effect is sensitive to many parameters including direction and

energy of the incident photon beam and the atomic numbers of the materials. The

importance of the phenomenon lies in the fact that dose enhancements of two orders of

magnitude or more can be obtained.

Since its discovery there has been extensive study of dose enhancement effects

particularly as they relate to electronic devices. Much study has been devoted to

developing methods to accurately predict the doses near interfaces (Ref 12). By and

large this has been successful, with both analytical and Monte Carlo codes shown to be

satisfactory for most purposes. The key to properly accounting for dose enhancement is

proper treatment of all secondary radiation transport and energy deposition processes.

The code that has proved to be the most effective, and thus used as a benchmark for

comparisons with other simpler codes, is SANDYL. Thus, for the work reported here,

carried out exclusively with SANDYL, the phenomenon of dose enhancement is

correctly included in the energy deposition results.

113
I

LAJ

z

I-

&

0 05 1.0 1.5

ENERGY (MeV)

RT-16611

2.0 2.5 3.0

Figure 6. Original and perturbed waterborne gamma ray spectra (Source I

at 1 minute) at various radii.

114
10-1

Li

--'- L. . L

~rr

-4

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 ,4.0 4.5

ELECTRON ENERGY, Me%

R7-16610

Figure 7. Original and perturbed airborne beta spectra (Source I at I minute)

at various radii

3.4 UNCERTAINTIES

There are several types of uncertainty associated with the calculations of energy

and charge deposition reported here. The easiest to understand is the statistical

uncertainty associated with the Monte Carlo sampling processes. It is obtained by

repeating the calculations with identical numbers of histories, and computing the

standard deviation of the mean of the distribution of values of the quantity tallied. For

the calculations reported here ten samples were used to determine the mean and

standard deviation.

115
Error bars representing the one standard deviation uncertainties are shown on all

depth-dose calculations. For nearly all the calculations with gamma ray sources the

uncertainties are less than 10 percent with most regions being less than 5 percent. The

exceptions are the few innermost regions of the copper where uncertainties become as

high as 30 percent in some cases. For the beta sources the large attenuation in the

outer region means that very little energy reaches the interior of the cable. Consequently, for the beta calculations the uncertainties in the energy deposition in the

copper, where the fluence has dropped by three orders of magnitude or more, are sometimes ±50 percent or more. It is possible that biasing techniques could be used to

improve this situation, but they were not utilized in this study. However, it is very

unlikely that any of the conclusions reached would be altered by improvements in the

accuracy of the dose at the interior of the cable.

A more vaporous contribution to the uncertainty of the results has to do with the

modeling and computational methods employed. These are very difficult to estimate.

Sometimes, a rough idea of the magnitude of this error can be obtained by sensitivity

analysis, the procedure by which one determines how sensitive a calculated result is to

alterations of the model or changes in an approximation., A serious limitation to this

approach is that often the most significant approximations are the result of inherent

limitations of the calculational tools and cannot be eliminated. In a few cases model

sensitivity was investigated in this study. For example, the use of approximate methods

to handle the spatially extended sources resulted from the inability of the calculational

procedures to handle this type of source efficiently. An effort to understand

qualitatively the uncertainty introduced by this approximation was made by performing

a "brute-force" calculation. This consisted of a dose versus depth calculation for the

cable with an exact treatment of the airborne (i.e., a uniform spatial distribution of

isotropic point sources) rather than using the perturbed sources developed here.

In order to get any results with the "brute-force" model it was necessary to

reduce the size of the air-steam region surrounding the cable from a thickness of 25 m

to 2 m. For thicknesses larger than 2 m the solid angle subtended by the cable is too

small to get useful information without excessive use of computer time. This, of

course, introduces an additional approximation and complicates the interpretation of

the results. A discussion of these results is given in subsection 6.2.

Suggestions for additional work along these lines are described in subsection 7.3.

However, no quantitative assessment of the magnitude of the modeling errors has been

included, and the error bars shown on the figures represent only the statistical part of

the uncertainty.

116
4. RESULTS FOR LOCA SOURCES

4.1 SOURCE SELECTION

Selections from the source spectra calculated in Phase 3 were made for the

depth-dose studies in the model cable. The low power (Q watt) results for an

equilibrium irradiation for Sources I and 2 which included all daughters but did not

include capture and depletion effects were used. Cooling times which produced the

hardest (i.e., highest average energy) and softest spectra were selected in order to

study the bounding conditions. The hardest spectrum occurs at the shortest cooling

time. As a matter of practicality, the very short cooling times are not expected to be

accurate since a significant number of nuclides which contribute to the energy release

at short times do not have spectral data in the library. Therefore, the one-minute

cooling time data were selected for the hard spectrum. The softest spectrum (i.e.,

lowest average energy) occurs between I and 10 days depending on the type of source;

the 4-day results were selected. Thus, for each source and each distribution category

depth-dose calculations were carried out at two times for betas and gammas. For

convenience, the spectra used for the calculations reported in the next section are

reproduced from Reference 2 in Tables I through 3.

4.2 DEPTH-DOSE CALCULATIONS

Results of the depth-dose calculations in the model cable are given in Figures 8

through 20 for the airborne, plate-out, and waterborne sources at I minute and 4 days

cooling. The results are expressed in rads (0 rad = 10-2 Gy) per source particle incident

on a ten-meter length of cable, where the source particles have been sampled from the

input (perturbed) spectral distributions. For. most of the calculations 2 x 10 histories

were tracked for each source. For scaling purposes note that the doses can be

expressed per unit incident fluence. Since the surface area of a ten-meter segment of

the model cable is 7102.5 cm 2 , one particle per ten-meter segment represents a fluence

of 1.408 x 10-4 particles/cm2 . To scale the depth-dose results presented here to a

specified particle fluence, 0, one multiplies the doses by 0/1.408 x 10-4. For example,

117
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"U T 4 DAYS

r-- J i

10 -1

LO

_r -T

C-' I

o10 I

0 2 4 6 8 10 12

RT-16608CABLE RADIUS, mm

RT-660

Figure S. Depth-dose calculations f or airborne gamma rays on the cable (Source I

at I minute and at 4 days)

to determine the dose for an incident fluence -on the cable of 10 photons/cm 2, multiply

by 10/1.408 x 10-4 = 71025.

It may be seen that the largest dose is in the jacket and insulation materials.. For

the gamma ray sources the dose in the conductor is 5 to 10 times smaller than in the

insulator and jacket. For the beta sources the dose is two or more orders of magnitude

less in the conductor than at the surface. The airborne gamma-ray source calculations

121
CL

k.)

16-

I.

O" i "

.4 DAYS

10- 151 - III

0 2 6 8 10 12

CABLE RADIUS, mm

RT-16335

Figure 9. Depth-dose calculations for airborne gamma rays on the cable (Source 2)

.I

122
7.290 9.474 11.304

10 "11

I-.

6n

z

10 3

10'1 4

0 2 4 6 8 10 12

CABLE RADIUS, mm

RT-15638

Figure 10. Depth-dose calculations for airborne betas on cable (Source 1)

123
10-11

7.290 9.474 11.304

-0J1

c10- 1

2ý.

C-)

w i

r•J

CABLE RADIUS, mm

RT-16609

Figure 11. Depth-dose calculations for airborne betas on cable (Source 2)

124
-W

_-

C

It

L:-

I,,

10-13

10- 14

CABLE RADIUS, rm

RT-16954

Figure 12. Depth-dose calculations for plate-out gamma-ray sources on cable

(Source 1)

125
7,240 9:474 11304

-• l~~ MINUTE -••• .-S

ou,' 1O13 4 DAYS _- -_

I--

10

9-

C

10- 14 __jII

0246 8 10 1.2

CABLE RADIUS, nin

RT- 16593

Figure 13. Depth-dose calculations for plate-out gamma-ray sources on cable

(Source 2)

126
I-i

-I

L)

L.J

I~)

0

I0

L..J

Li

10-12

10- 1

CABLE RADIUS, mm RT-17891 -2

Figure 14. Depth-dose calculations for plate-out beta sources on cable (Source 1)

127
7.290 9.474 11.304

ms

-lo100 2.-

LUJ

100

lo 10.

10-1

- 1 0-2

RT-780-

0 2 4 6 8 10 12

CABLE RADIUS, mm

Figure 15. Depth-dose calculations for plate-out beta sources on cable (Source 2)

128
lO0 3

LnJ

C

C

i0-15

0 2 4. 6 8

CABLE RADIUS, mm

RT-16636

10 12

Figure 16. Depth-dose calculations for waterborne gamma-ray sources (Source 1)

129
10-1

10-1

LDJ

10-151

0 2 4 6 8 10 12

CABLE RADIUS, mm

RT- 166 34

Figure 17. Depth-dose calculations for waterborne gamma-ray sources (Source 2)

130
10-13

10-14

21.

C3

10o s

10-1 6

17-i

R7-1 6597 CABLE RADIUS, mm

Figure 18. Comparison of two thicknesses of water layer on depth-dose results for

waterborne beta spectrum at I minute (Source 1)

131
-AJ

LL)J

0

,r)

LLJ

z

,-

0

0 2 4 6

CABLE RADIUS, mm

RT-16596

8 10 12

Figure 19. Depth-dose calculations for waterborne beta sources (Source 1)

132
1O-13 7.290 9.474 11.304

10"14 i

-14

1 MINUTE

L0" "

C 4 DAYS

lo1--"0 

r-J

I~ j* 10"18 -- L. l i I

0 2 4 6 8 10 12

CABLE RADIUS, mm

RT-16595

Figure 20. Depth-dose calculations for waterborne beta sources (Source 2)

shown in Figures 8 and 9 display little difference in the jacket and insulator for I

minute and 4 days cooling in spite of the fact that the spectra are quite different.

There is a large difference, however, in the energy deposited in the conductor between

these two cases.

The results for the airborne beta sources, shown in Figures 10 and. 11, are

dramatically different for the two cooling times. The very soft betas at 4 days do not

penetrate the insulator, depositing most of their dose in the surface layer of Hypalon.

133
For the case of the plate-out sources, the sources were assumed to be deposited

on the surface of the cable. The results are shown in Figures 12 and 13 for the two

gamma ray sources, and in Figures 14 and 15 for the beta sources. Again we find a

dramatically different shape for the depth-dose profile for gamma rays and beta

particles. The betas lose most of their energy in the first few layers of the jacket,

whereas the gamma rays produce fairly uniform dose in both the jacket and insulator.

The results for waterborne gamma ray sources are shown in Figures 16 and 17.

The observed profile is similar to the airborne and plate-out cases.

For beta particle sources distributed in water the range is relatively small which

means that straightforward Monte Carlo calculations are feasible. Using the range of a

6 MeV beta particle as a limiting dimension, the thickness of the water layer surrounding the cable was taken to be 3 cm. This is a very conservative overestimate

since there are very few betas at 6 MeV or higher in the source spectra. For the worst

case - that is, the case where the spectra have the most high energy beta particles

(Source I at I minute) - nearly 99 percent of the beta energy is lost in the water. As a

further test, the thickness of the water layer was increased to 4 cm to determine if the

depth-dose profile was affected. The results, shown in Figure 18, indicate that the

thicker water layer has a negligible effect on the depth-dose profile within the

statistical accuracy (1o) of the calculations. Because the results were computed per

source particle born in the water, the histograms shown in Figure 18 have been

normalized at the outer zone of Hypalon.

Figures 19 and 20 show the depth-dose profiles in the cable from beta sources

distributed in a 3 cm thick layer of water surrounding the cable.

4.3 CHARGE DEPOSITION RESULTS

A radiation damage mechanism that in certain cases could limit operation is

charge buildup. Radiation induced nonuniform charge distributions in a dielectric could

build to levels sufficient to cause breakdown of the dielectric. Although we have not

made a detailed analysis of mechanisms for radiation damage in a reactor power cable,

we attempted to investigate charge deposition in the model cable along with energy

deposition. In fact, the SANDYL code automatically tallies net charge in each zone

where energy is deposited. Net charge deposition for this purpose is defined as a

number of electrons entering a zone in excess of those leaving a zone. Thus, a-positive

value for the net number of electrons deposited produces a net negative charge in that

region. Conversely, a negative value of electrons deposited results in a positive charge.

134
The code does not provide information on the standard deviation of the charge

deposition, but from repetitive runs it appears that the uncertainties are much greater

than the uncertainties associated with the energy deposition.

The choices of zone sizes and number of histories run were optimized entirely on

the basis of the energy deposition calculations. It is possible that different (thinner)

regions and longer running times would be useful for studying the behavior of charge

deposition in the cable.

The results of the calculations are summarized in Table 4. Net charge deposition

in each layer is shown for 60Co and for each of the sources investigated in this work.

Charge deposition is to be interpreted as the instantaneous charge deposited for the

various identified fission product sources. No mechanisms for leakage or other forms of

dispersal of the charges have been included. The gamma-ray sources (including 60Co)

consistently produce a positive charge on the outer layer of the jacket (Hypalon), but on

the interior of the cable no regular pattern is apparent. The beta sources, onthe other

hand, produce much larger negative charge on the outermost region of the cable which

falls off with decreasing radius. A much more regular behavior is observed. For the

case of the cable surrounded by water, the charge buildup is about two orders of

magnitude smaller. Of course, in a combined beta-gamma radiation field, there will be

some compensation of the opposite signed charge depositions.

Interpretation of these results and their importance insofar as failure of the cable

is concerned must await on analysis of the mechanisms of damage.in the cable. We

present the results of our charge deposition calculations without further analysis.

135
Net Electrons Deposited per 103 Source Gamma Rays Incident on a 103 cm Length of Cable

Zone Airbor-e - Plate-O,,t Wat bo... --

Outer Radius 60 Source I Source 2 Source I Sou rc. 2 Source 2 Iurc.v_ - Material (mm) Co I mn 4 days I min 4 days I min 4 days I 1i11 4 days I "v'm 4 days I miin 4 days rl

Hypalon 11.304 -5.10 -1.05 -0.30 -1.70 -0.45 -9.15 -8.15 -8.15 -5.00 -0.95 -0.85 -1.60 -0.75

10.847 -2.35 -0.25 0.10 -0.80 0.15 -0.55 0.25 -1.95 -0.80 -0.40 -0.15 0.55 0.05

10.190 0.45 -0.20 -0.05 0.20 -0.05 1.25 0.50 0.15 -0.35 0.60 0.20 -0.15 0.15

9.932 0.70 -0.60 0.30 0.35 0.15 0.25 0.80 -0.90 1.55 -0.30 0.10 0.15 -0.20

EPR 9.474 0.10 -0.25 -0.05 -0.10 0.15 -0.65 -1.20 0.75 -1.25 -0.10 0.10 0.25 0.35

8.928 -0.35 0.05 -0.25 0.15 -0.15 -1.05 0.75 -0.15 0.90 0.50 -0.10 -0.05 -0.25

8.382 -0.30 0.10 0.25 -0.15 -0.20 -1.05 0.25 0.05 -0.70 -0.20 0.05 -0.25 -0.40

7.836 0 0.30 -0.10 -0.40 0 0.95 -0.60 0.35 -0.35 -0.25 -0.25 -0.20 0.10

Copper 7.290 -0.60 0.10 0.10 0.25 0.20 0.20 0 -0.25 0.45 -0.15 -0.15 0.25 0.05

5.832 -0.25 -0.15 -0.10 -0.10 -0.20 0.55 0.60 0.60 0.30 0.35 0.10 0.10 0.05

4.374 1.50 -0.05 0.05 -0.05 0.05 -0.30 -0.30 0.10 -0.10 -0.25 -0.05 0 -0.05

2.916 -0.30 0.10 -0.05 0.20 -0.05 0 0.15 -0.40 0 0.05 0.05 0.05 0 1.458 -0.15 0.05 0 -0.05 0.05 0 -0.05 0.25 0 -0.05 0 0 0

Net Electrons Deposited per 10 Source Betas Incident on a 103 cm Length of Cable

0 Hypalon 11.304 -5.10 60.90 175.80 75.60 169.80 350.20 363.20 357.30 535.80 2.94 2.01 2.76 8.09

10.847 -2.35 29.00 10.70 29.30 11.90 114.50 116.70 119.60 65.50 1.34 0.40 0.88 1.08

10.390 0.45 22.60 0.60 22.70 2.00 60.50 61.33 56.50 11.50 0.84 0.15 0.40 0.27

9.932 0.70 17.30 0 17.10 0.20 34.90 39.00 34.00 3.40 0.46 0.05 0.24 0.02

EPR 9.474 0.10 14.20 0 14.90 0.10 19.80 17.33 17.90 0.60 0.33 0.06 0.11 0.01

8.928 -0.35 12.30 0 9.80 0 9.70 12.00 9.30 0.20 0.19 -0.01 0.03 0.01

8.382 -0.30 9.10 0 7.20 0 7.10 4.33 7.70 -0.10 0.11 0.02 0.03 0

7.836 0 8.20 0 5.20 0 4.80 3.33 3.20 0.10 0.13 0.02 0.02 0 0

Copper 7.290 -0.60 26.40 0 16.10 0 9.10 10.33 8.20 0 0.26 0 0.01 0

5.832 -0.25 0.50 0 0 0 0.10 0 0.20 0 0 0 0 0 >

4.374 1.50 0 0 0 0 0.20 0 0 0 0 0 0 0

2.916 -0.30 0 0 0 0 -0.20 0 0 0 0 .0 0 0 !fl

1.458 -0.15 0 0 0 0 0 0 0 0 0 0 0 0
5. SIMULATOR SOURCES

There are several types of radiation sources either presently being used or

proposed for use as simulators of the LOCA radiation sources for the purpose of

qualification. These include 6 0 Co, 13 7 Cs, bremsstrahlung spectra, electrons from a

linear accelerator and spent fuel elements. By far the most common testing source

used today is 60Co. It is inexpensive, readily. available and requires relatively. little

labor. In this section we examine the energy deposition resulting from two of these

sources using the same model for the cable that was used previously. The source

configuration was selected as typical of the high power sources used in industry.

Comparison of various simulator source results with the LOCA results will provide a

basis for determining the suitability (and perhaps ranking) of the simulators for testing.

5.1 60Co SOURCE

The geometry adopted for the 60Co source configuration is shown in Figure 21.

The source was assumed to be bienergetic (1.173 and 1.332 MeV) on the surface of a

cylinder of radius 12 in (30.48 cm), coaxial with the cable. Air at standard temperature

and pressure (STP) with a density of 0.001293 g/cm3 filled the space between source

and cable.

Typically a test chamber is used to contain the test piece and its environment.

The effect of a 1/4-inch (0.64 cm) steel test chamber with an inside radius of 10 inches

(25.4 cm), also coaxial with the cable, was examined. Figure 22 shows the spectrum of

photons at the cable surface after penetrating or backscattering from the steel. There

is some degradation of the 60Co photons, but nearly 82 percent are still in the

broadened photopeak. The remaining photons are approximately uniformly distributed

over the low energy portion of the spectrum. The average photon energy penetrating

the test chamber is 1.156 MeV compared to 1.253 MeV without the chamber.

137
'4L'

ISOTROPIC 6 0 Co

SOURCES

ON SURFACE

lo-1"

CABLE

RT- 16621

Figure 21. 6 0 Co source irradiation configuration

5.2 13 7 Cs SOURCE

Another long-lived isotopic source suggested for use in qualification testing is

137Cs. This isotope produces monoenergetic gamma rays of 0.662 MeV. For this study

the same model was used for the source as was used for 60Co. However, no steel test

chamber was included, and no other processes were considered which- degraded the

source gamma rays before they impinged on the cable.

.1

138
10-3 I I I I I I !

I

C.-

El .7.

0

* .* 0 0 S

0 .- e~o * %*,~ m 0 .0 *be*

-. **? 00. ,.~ 00* 0 0

* 0 0

- 00. .0 0 0' 0 mOO

0 0 0 - 0 *e 00 * 6 0 '0

60Cc LINES -

(UNDEGRADED)-

i I I

J

10- 

.0.35

1~ I 

0.55 

I L .

0.75 

I

0.95 ~: ~r

PHOTON ENERGY

1,15

(i•eV)

1.35

RT-16604

Figure 22. Degraded 60Co energy spectrum at the cable surface with K" iron liner.

5.3 DEPTH-DOSE RESULTS

Insofar as energy deposition in the model cable is concerned, the. degradation of

the 6 0 Co spectrum by the test chamber walls is negligible as may be seen from the

depth-dose calculations in Figure 23. Calculations with and without the chamber are

within the statistical uncertainties. The error bars represent one standard deviation

(see subsection 3.4). Additional degradation of the source. spectrum resulting from the

source itself was not considered here. This may be important depending on the design

of the source and the irradiation geometry (Ref 13).

The depth-dose results for C37Cs are given in Figure 24. The softer gamma rays

produce only a slightly different profile in the cable than 6 0 Co. The principal

difference is in the dose in the conductor; the profile in the insulator and jacket are

virtually identical for the two isotopes.

139
7.290 9.474 11.304

C)

10,

C3

10- 14

6 8

CABLE RADIUS, mm,

RT-16599

Figure 23. Depth-dose in cable due to 60Co gamma rays with and without iron liner

(test chamber)

140
7; 290O 9. 474 11-304

C_

C,

0 2 6 6 10 12

CABLE RADIUS, m'

RT-1659S

Figure 24. Depth-dose in cable for 137Cs gamma rays

141
(This page intentionally left blank)

142
6. COMPARISONS OF RESULTS, DISCUSSION AND CONCLUSIONS

6.1, LOCA VERSUS SIMULATOR RESULTS

Depth-dose profiles for each of the sources studied are compared with the 60Co

results in Figure's 25 through 36. Since there is so little difference between 60Co and

13 7Cs, we include the 13 7Cs results in only a few cases. Since only the shapes of the

depth-dose profiles are of consequence here, the simulator results were normalized to

the LOCA.calculations to give the same average dose in the outer layer of the jacket.

Although this is an arbitrary choice, other normalizations would produce no different

conclusions; for example, renormalizing the Co result to give roughly equal dose in

the EPR for the airborne gamma rays from Source I would result in seriously

underestimating the dose in the jacket.

As is very clear from the comparisons shown, the 6 0 Co and 13 7Cs sources do not

produce depth-dose profiles in the cable that resemble the LOCA sources for any of the

cases examined. If equivalence of these profiles is to be used as the only basis for

judging simulator adequacy, then we must conclude that these isotopic sources are

inadequate. It is also clear that the most serious discrepancy is with the beta sources,

as expected. The penetrability and energy loss characteristics of beta particles are

very different from gamma rays, and thus it is not surprising that monoenergetic

gamma sources provide a poor simulation of the response to betas.

6.2 DISCUSSION AND CONCLUSIONS

6.2.1 Model Sensitivity

The importance or sensitivity that the model and assumptions have on the results

and on the uncertainities associated with the results are not always transparent. One

way that insight might be gained regarding model effects is to vary parameters of the

model and repeat the calculations. Although resources did not permit extensive studies

of model parameters such as cable diameter, insulator thickness, or material compositions, a few such calculations were made. In particular, a calculation with slightly

143
10- __/ 13 7Cs

10

02 4 6 8 I0 1

RT-16605 CABLE RADIUS, m

Figure 25. Comparison of depth-dose for 0Co and 13Cs with airborne gamma rays

(Source I). The isotopic source results have been normalized at the outer

zone (surface) of hypalon.

144
L.)

0--

14

00

PT- 16601

6 E

CABLE RADIUS, mm

Figure 26. Comparison of depth-dose for 6 0Co and 13 7Cs with airborne gamma rays

(Source 2). The 6 0Co and 13 7Cs results have been normalized to the

average dose at the surface.

145
7.290 9.474 11.304

10-11

i012

-4

I--

CLx 1-13

~ 14 L.ý 10

10-16

0 6

CABLE RADNIS, m"r,

12

RT-16602

Figure 27. Comparison of depth-dose for 6 0Co with airborne betas (Source 1).

6 0Co result normalized to the average dose at the surface.

w

146.
7.290 9.474 11.304

10-II

10-12

10-

C-

(S<

CC-.,

CCA EL E R A ý':jS , M.-

60 Figure 28. Comparison of depth-dose of Co with airborne betas (Source 2);

6 0Co result normalized at the average surface dose.

147
L.J

S10

zý

E

10 " 1

0 2 4 6

CABLE RADIUS, mm RT-16607

8 10 12

Figure 29. Comparison of depth-dose for 60Co and 137Cs with plate-out gamma

rays (Source 1). Both the 6 0Co and 13 7Cs results have been normalized

to the average surface dose.

148
.u ~137s L

m I MINUTE

L

• O-13m 4 DAYS •

C)

I.-

*10-

0 2 4 6 8 10 12

RT- 16616 CABLE RADIUS, mm

Fig ure 30. Comparison of depth-dose for 60 Co and 137Cs with plate-out gamma

rays (Source 2). 'Both 60Co and 137Cs have been normalized at the

average surface dose.

149
__, 0_ 12 - L.J

-J

(A 

ri

01 MINUTE

10 1 3o- r-"

rIr

C)

10 -1

io15 I

-- J

10_i15

0 2 4 6 812

RT-17891 CABLE RADIUS, mm

Figure 31. Comparison of depth-dose for 60Co (normalized at average dose in

surface zone) with plate-out betas (Source 1)

150
7.290 9.474 11.304

LU

-J

I0~

LU

U,

U,

0

IU,

0

0~

LU

0

LU

LU

0 2 4 6 8

CABLE RADIUS, mmn

10 12

RT-17890

Figure 32. Comparison of depth-dose for 0 Co (normalized at average dose Iin

surface zone) with plate-out betas (Source 2)

151
7.290 9.474 11.304

10- 13

-j

CI.'.

0

0 0 1

10-15

j

RT-1 6615

2 4 6 8 10 12

CABLE RADIUS, mm

Figure 33. Comparison of depth-dose for 60oC (normalized to average dose in

surface zone) with waterborne gamma rays (Source 1)

152
IC

0-.

C

C-.

10 "I

0 2

RT-1 6614

4 6

CABLE RADIUS, mm

8 10 12

Figure 34. Comparison of depth-dose for 60Co (normalized to average dose in

surface zone) with waterborne gamma-rays (Source 2)

153
7.290 9,474 11,304

. .......... •/# .,----J "-"--% ."

6 C/o

I MINUTEcz DAYS

LWJ

10"16 0-15

Li,

CABLE RADIUS, IM~

RT-16613

Figure 35.. Comparison of depth-dose for 60 Co (normalized to average dose in

surface zone) with waterborne betas (Source 1)

154
10-13

7.290 9.474 11.304

1 MINUTE --

10

L

C

0~4 DAY

~i0_16 - ~T1o-17

I III Io I

0 2 4 6 8 10 1?

RT-16600 CABLE RADIUS, "fT,

Figure 36. Comparison of depth-dose for 6 0 Co (normalized at surface) with

waterborne betas (Source 2)

different compositon of elastomeric materials typical of the types used in power cables

showed that slight changes in elemental composition of the jacket and insulator have no

effect on the depth-dose results.

Another type of sensitivity calculation that was made has to do with the

importance of steam in the containment atmosphere. For the airborne sources it was

assumed that air plus 70 psig saturated steam filled the containment. The effects of

155
.the steam were examined by repeating the calculations with only dry air as the medium

surrounding the cable. The result of the fission product gamma ray source perturbation

is illustrated in Figure 37. The absence of steam results in less perturbation of the

source spectrum shape. The case shown in the figure is Source I at one hour.

IT

IRT-17510

GAMMA RAY ENERGY (MeV)

Figure 37. Influence of steam on the gamma ray source spectra

(Source I at I hour)

156
The depth-dose profiles in the cable resulting from the two perturbed spectra

given in Figure 37 are displayed in Figure 38. Within the statistical precision of the

calculations there is no significant difference between the two cases. In other words,

for this source the presence of steam in the medium surrounding the cable is of no

consequence insofar as energy deposition in the cable is concerned.

An attempt was made to validate the approximate procedures used to treat the

spatially extended sources. As discussed earlier, a "brute-force" calculation was made,

but with a smaller region of air-steam surrounding the cable. The relative energy

deposition results for the airborne gamma-ray source at one-minute are shown in

Figure 39 (normalized at the outer zone of the jacket). The fact that two different size

source regions were used complicates the interpretation of these results. In addition,

the statistical uncertainties on the "brute-force" results are very large. One observes

that the dose profiles in the jacket and insulator have approximately the same shape,

whereas the dose in the conductor is about twice as large for the "brute-force" case. It

is difficult to say if the latter difference is a result of the perturbation technique or the

limited source thickness used for the exact calculation. However, since the cable

performance is thought to be limited by the energy deposited in the dielectric, the

difference in the deposition in the conductor is probably not significant.

6.2.2 Comparison Criteria

In this work the depth-dose profile in the cable has been used as a basis for

comparing the various LOCA gamma-ray and beta sources with 60Co and 137Cs.

Although depth-dose is probably the most sensitive test, and a sufficient-'condition to

ensure adequacy of the simulation, it may not be a necessary condition. A proper basis

for comparison depends on the radiation damage mechanism important for the particular piece of equipment of interest. If an evaluation of the damage mechanisms

indicates that the depth-dose profile is the proper basis for evaluation, then other

simulator sources should be considered. It is possible that the spectrally distributed

sources will do a better job of simulating the LOCA dose profile.

In analyzing the results of the depth-dose comparisons it is tempting to argue that

the 60Co or 137Cs sources produce a more conseravative situation since, if they are

normalized at the surface, they always produce more dose in the inner regions of the

cable than do the LOCA sources. Thus, according to this argument, if the cable

survives the 60Co irradiation test it will survive the LOCA radiation environment since

the latter will deposit a smaller dose in the interior. In order for this argument to be

157
7.290 9.474 11.304

10-

0)

C-

-eRT 150

CABLE RADIUS, mm

Figure 38. Depth-dose profile for Source I gamma rays at 1 hour with and without

steam in the surrounding medium

158.
r( 1 1 Jr7V'

0

APPROXIMATE, PERTURBED

SOURCE

IT

I I . I -

0 2 4 6 8 10 12

RT-17508 CABLE RADIUS, mm

Figure 39. Comparison of airborne gamma ray energy deposition (Source 1

at I minute) for approximate, perturbed source and for "brute-

*force" model

valid it is necessary that the degradation of the cable be directly related to total dose.

It is not "clear that the problem is as simple as that. For example, charge buildup and

dielectric breakdown are dependent upon the dose gradient in the cable. Other failures

such as heating and gas evolution from the breakdown of polymeric materials and its

subsequent migration and buildup could also depend upon the dose gradient.

159
Another argument against the "conservative" approach is that it could result in

over-testing; that is, it could mean that the testing procedures are unnecessarily or

overly conservative, which results in an unnecessarily high cost of testing or producing

radiation hard cables. It is possible that laboratory testing and/or analysis of the

details of damage in cables could answer this question.

The results for the charge deposition in the cable provide data for further

analysis. It is clear that the 6 0Co source does not reproduce the charge distribution

produced by a beta spectrum. Further interpretation of these results are left for future

consideration as the simulator adequacy evaluation evolves.

160
7. RECOMMENDATIONS FOR FURTHER WORK

During the course of this study a number of fertile areas of investigation were

identified that were beyond the scope of this program, but nonetheless should be

considered as possible areas for future study. We briefly describe each of the subject

areas and suggest directions those topics might take.

7.1 CONSIDERATION OF DAMAGE MECHANISMS

The goals of the present work have been to provide comparative depth-dose

calculations for simulator sources and for the calculated LOCA sources. Interpreation

and evaluation of these comparisons remain to be done as part of the overall program

effort to judge the adequacy of the test sources. Consideration of the mechanisms for

failure should be a part of the interpretation of these results.

As discussed in subsection 2.2, the ultimate concern of the qualification program

is to assure the operation of certain equipment in the reactor during both routine and

accident conditions. For some such equipment or components it can be argued that the

.degradation is related to the total dose or dose profile. For other equipment dose may

not be the controlling variable. Thus, the measure of -adequacy of a testing program

that simulates the expected radiation fields must be based upon the controlling damage

mechanism.

Obviously, the evaluation of failure mechanisms for reactor equipment is complex

and highly specific. That is, each piece of equipment must be examined with a

knowledge of the details of its construction and operation. An example of the

complexity of the analysis is given in Reference 5 for a cable.

One possible approach is for the major generic types of Class IE electrical

equipment subject to radiation qualification to be anlayzed for their radiation vulnerability. For each piece of equipment the controlling damage mechanisms might be

identified so that a meaningful evaluation of qualification testing procedures can

proceed. In the event that the dominant damage is not proportional to dose in the

component, suitable analysis procedures will need to be developed.

161
7.2 OTHER SOURCE CALCULATIONS

The expense and time required to carry out depth-dose calculations necessarily

limited the investigations to a few selected sources. The rationale for the choices was

discussed in subsection 4.1; generally, bounding conditions were selected in order to see

the extent of the variation that resulted in the depth-dose calculations. All the sources

were derived from the low power, equilibrium operation results. It may be useful in the

future to examine some of the more realistic cases, in other words, the higher power,

shorter operation cases which include the effects of capture and depletion. Such

spectra are available in Reference 2.

7.3 MODEL SENSITIVITY

The sensitivity of the cable model to the depth-dose calculations was only briefly

studied. Sensitivity studies simply demonstrate how sensitive a result is to the

assumptions used in the model. Parameters such as cable size, materials, inclusion of

an electrical shield and others can be varied to determine their effect on the results.

Calculations can also be extended to other types of cable used in nuclear power plants.

It may also be interesting to compare the LOCA and simulator results in very

small regions around material interfaces where dose enhancement phenomena are

important. The choices of zone thicknesses in the present work tended to average out

dose enhancement. Previous experience has shown that one might expect very high

local doses in regions near the conductor-insulator interface. Charge buildup at the

interface could also be significant. The extent to which simulators reproduce interface

effects should be investigated.

7.4 OTHER COMPONENTS AND SIMULATORS

The present study was restricted to cables. It may be useful to apply these

methods to other Class IE electrical equipment which must be qualified for use in

nuclear power plants. Prior to doing the type of calculation reported here, it would be

helpful to first assess the mechanisms for failure due to radiation in each component or

piece of equipment. It would also be imformative to extend the calculations to other

simulators such as bremsstrahllung sources, electron machines, and spent fuel assemblies which are spectrally distributed and can be tailored somewhat to produce, variable

spectra.

162
REFERENCES

1. "Qualification of Safety-Related Electric Equipment for Nuclear Power Plants,"

U.S. Nuclear Regulatory Commission Regulatory Guide 1.89, Revision I (Draft,

November 1976).

2. N. A. Lurie, D. H. Houston and 3. A. Naber, "Definition of Loss-of-Coolant

Accident Radiation Source," IRT 8167-002/SAND 78-0090, IRT Corporation,

prepared for Sandia Laboratories (February 1978).

3. L. L. Bonzon, "RadiationTSignature Following the Hypothesized LOCA," SAND76-

0740 (NUREG 76-6521), Sandia Laboratories (Sept. 1977, Rev. Oct. 1977).

4. 3. A. Naber and N. A. Lurie, Nucl. Technology 36, 40-47 (1977).

5. R. E. Leadon, "Radiation Damage Mechanisms in Reactor Components," IRT

Corporation (1977), unpublished.

6. H. Mi. Colbert, "SANDYL: A Computer Program for Calculating Combined

Photon-Electron Transport in Complex Systems," SLL-74-0012, Sandia

Laboratories (1974).

7. N. Vagelatos, N. A. Lurie, and 3. P. Wondra, Proc. ERDA Symp. X-Ray and

Gamma-Ray Sources and Detectors, Ann Arbor, Ml, 1976 (CONF 760539) p. 51.

8. 3. Kimlinger, E. F. Plechaty, and J. R. Terrall, "SORS Monte Carlo Photon

Transport Code," UCRL-50358, Lawrence Livermore Laboratories.

9. M. 3. Berger and S. M. Seltzer, "Electron and Photon Transport Programs," (I) NBS

Report 9836, (II) NBS Report 9837.

10. Ni. 3. Berger, in Methods in Computational Physics, (Academic Press, New York,

1963), Vol. I, p. 135.

11. 3. A. Wall and E. A. Burke, IEEE Trans. Nucl. Sci. NS-17, (No. 6) 305 (1970).

12. E. A. Burke and 3. C. Garth, "An Algorithm for Energy Deposition at Interfaces,"

IEEE Trans. Nucl. Sci. NS-23 (No. 6) 1938 (1976).

13. 3. H. Aitken and W. H. Henry, Int. 3. Appl. Radiation and Isotopes 15_, 713-724

(1964).

163
(This page intentionally left blank)

164
APPENDIX

TABULATED DEPTH VERSUS DOSE IN CABLE

165
Table A-I. Calculated Depth-Dose in Model Cable

Airborne Sources

Gamma-Ray Dose (rads/source particle)a

Radius

(mm)

Source I Source I Source 2

at I m at 4 d at 1 rn Source 2

at 4 d

0

1.458

L 2.916

e0 4. 374

5.832

7.290

7.836

•' 8.382 0.

Im 8.928

9.474

z 9.932

. 10.390

8.629-15

1.407-14

1.999-14

2.789-14

2.981-14

6.763-14

9.019-14

8.832-14

8.927-14

7.044-14

7.707-14

8.247-14

8.585-14

2.064-15-

2.724-15

4.562-15

7.194-15

1.125-14

5.514-14

6.952-14

7.558-14

8.708-14

5.365-14

6.660-14

6.591-14

8.586-14

8.194-15

1.262-14

2.114-14

2.722-14

3.133-14

6.234-14

7.972-14

8.574-14

9.911-14

8.539-14

7.637-14

7.628-14

7.543-14

4.403-15

4.662-15

6.603-15

8.344-15

1.256-14

5.480-14

6.961-14

7.278-14

9.556-14

6.637-14

6.288-14

7.215-14

9.470-14

Beta Dose (rads/source particle)a

Radius

(mm)

Source 1 Source I

at I m at 4 d

Source 2

at 1 m Source 2

at 4 d

Uj

C.

CLi

0

0.

0

1.458

2.916

4.374

5.832

7.290

7.836

8.382

8.928

9.474

9.932

10. 390

10.847

11. 304

2.127-15

1.735-15

1.867-15

3.786-15

1.930-13

7.799-13

8.589-13

1.067-12

1.209-12

1.399-12

1.683-12

2.011-12

2.759-12

1.417-16

7.351-16

6.185-16

5.039-16

8.221-14

4.534-13

5.573-13

6.764-13

9.388-13

1.170-12

1.350-12

1.678-12

2.634-12

5.145-15

1.054-13

1.542-12

1.743-15

2.954-15

3.085-14

1.380-13

1.553-12

Properly expressed as rads per single source particle on a ten-meter

segment of cable, or rads/1.408 x 10-3 particles/cm 2

166
Table A-2. Calculated Depth-Dose in Model Cable

Plate-Out Sources

Gamma-Ray Dose (rads/source particle)a

Radius Source 1 Source I Source 2 Source 2

(mm) at I m at4d at I m at4d

0

1.458 1.020-13 7.545-14 1.226-13 6.547-14

a,, 2.916 1. 166-13 8.033-14 .1.373-13 6.841-14

(. 4.374 1.270-13 .8.096-14 1.380-13 6.838-14

0

U 5.832 1.367-13 9.059-14 1.397-13 7.866-14

7.290 1.467-13 1.037-13 1.514-14 8.342-14

7.836 2.535-13 1.992-13 2.347-13 2.035-13

8.382 2.578-13 2.245-13 2.371-13 2.060-13

,,' 8.928 2.653-13 2.480-13 2.515-13 2.189-13

9.474 2.688-13 2.397-13 2.601-13 2.344-13

z 9.932 2.543-13 2.054-13 2.423-13 1.909-13

0

1 10.390 2.672-13 2.213-13 2.544-13 1.824-13

C. 10.847 2.978-13 2.374-13 2.693-13 2.191-13

" 11.304 2.357-13 2.504-13 2.662-13 2.466-13

Beta Dose (rads/source partlcle)a

Radius Source I Source I Source 2 Source 2

(mm) at I m at 4 d at I m at 4 d

0

1.458 7.268-16

LU 2.916 5.375-16 3.828-16 2.024-15 2.086-16 CL

0 4.374 1.530-15 4.472-16 1.598-15 7.216-17

5.832 1.626-15 3.418-16 2.123-15 4.456-17

7.290 4.851-14 3.844-15 4.757-14 2.584-16

7.836 3.200-13 3.429-14 2.820-13 1.057-15

w 8.382 4.451-13 6.672-14 3.632-13 5.406-16 C. Uj 8.928 5.877-13 1.066-13 4.707-13 3.041-15

9.474 8.900-13 2.102-13 7.157-13 1.305-14

z 9.932 1.322-12 3.600-13 1.185-12 5.210-14

0

-.. 10.390 1.985-12 6.066-13 1.876-12 1.647-13

a. 10.847 3.491-12 1.441-12 3.339-12 8.695-13

11.304 7.865-12 6.117-12 7.819-12 5.766-12

aproperly expressed as rads per single source particle on a ten-meter

segment of cable, or rads/1.408 x 10-3 particles/crm2

167
Table A-3. Calculated Depth-Dose in Model Cable

Waterborne Sources

Gamma-Ray Dose (rads/source particle)a

Radius Source I Source I Source 2 Source 2

(mm) at I m at 4 d at I m at 4 d

ul

0

U

0

1.458

2.916

4.374

5.832

7.290

7.836

8.382

8.928

9.474

9.932

10.390

10.847

11.304

4.788-15

1.103-14

1.092-14

2.051-14

2.166-14

6.900-14

7.483-14

7.771-14

8.796-14

6.322-14

6.140-14

7.581-14

8.092-14

3.432-15

7.030-15

7.527-15

1.138-14

1.578-14

5.524-14

6.889-14

7.410-14

8.129-14

6.137-14

7.768-14

7.381-14

8.703-14

4.115-15

9.129-15

1. 207-14

1.720-14

2.247-14

5.213-14

7.342-14

9.130-14

9.092-14

5.988-14

6.405-14

7.164-14

7.641-14

2.562-15

5.229-15

7.778-15

9.229-15

1.397-14

5.709-14

6.698-14

7.070-14

7.985-14

6.489-14

6.497-14

7.242-14

8.761-14

z

0

C- aBeta Dose (rads/source particle)a

Radius Source I Source I Source 2 Source 2

(mm) at I m at4d at I m at4d

0

U

0

1.458

2.916

4.374

5.832

7.290

7.836

8.382

8.928

9.474

9.932

10.390

10.847

11. 304

5.650-17

1.783-17

4.735-17

8.785-187

1.575-15

8.751-15

9.840-15

1.175-14

1.696-14

2.446-14

3.293-14

4.937-14

8.537-14

5.799-17

9.340-17

2.684-18

1.421-17

6.890-16

3.492-16

1.031-15

1.506-15

1.668-15

3.256-15

7.401-15

2.749-14

7.541-18

2.005-17

4.084-17

6.618-16

8.267-16

1.251-15

2.704-15

6.582-15

1.041-14

1.990-14

4.987-14

4.081-18

2.289-18

4.342-18

1.256-17

4.307-17

7.988-17

9.297-17

7.466-15

3.070-15

1.807-14

z

0

a.

aproperly expressed as rads per single source particle on a ten-meter

segment of cable, or rads/1.408 x 10-3 particles/cm 2

168
Table A-4. Calculated Depth-Dose in Model Cable

Simulator Sources

Dose (rads/source particle)a

Radius 60 6 0 Co 137

(mm) Co (no test chamber) CS

0

1.458

Le 2.916

I. 4.374

0

U 5.832

7.290

7.836

S 8.382

ua 8.925

9.474

z 9.932

0

,.• 10.390

(. 10.847

2 11.304

2.365-13

2.278-13

2.381-13

2.413-13

2.251-13

3.025-13

2.751-13

2.820-13

2.538-13

2.270-13

2.123-13

1.977-13

1.339-13

2.632-13

2.660-13

2.581-13.

2.331-13

2.374-13

3.006-13

2.9,14-13

2.725-13

2.660-13

2.603-13

2.102-13

1.934-13

1.305-13

1.762-13

1.619-13

1.522-13

1.512-13

1.458-13

2. 299-13

2.170-13

2.163-13

2.125-13

1.746-13

1.720-13

1.555-13

1.090-13

aproperly expressed as rads per single source particle on a tenmeter segment of cable, or rads/1.408 x 10-3 particles/cm2

169-170
I
APPENDIX B

Evaluation of Radiation Damage Mechanisms

in a Reactor Power Cable in a Loss-of-Coolant Accident

IRT 0056-002A

August, 1978

171-172
, 't
IRT 0056-002A

,EVALUATION OF RADIATION DAMAGE

MECHANISMS IN A REACTOR

POWER CABLE IN A

LOSS-OF-COOLANT ACCIDENT

Prepared by

3. F. Colwell, B. C. Passenheim, and N. A. Lurie

This report documents part. of the Qualification Testing Evaluation

(QTE) Program (A 1051-8) being conducted by Sandia Laboratories for

the United States Nuclear Regulatory Commission under -DOE

Contract AT(29-1)-789.

Prepared for

SANDIA LABORATORIES

Albuquerque, New Mexico

Under

Contract 07-8944

August 1978

IRT

Corporation

Instrumentation

Research

Technology

7650 Convoy Court - P.O. Box 80817

San Diego, California 92138

714 / 565-7171

Telex: 69-5412

173-174

ABSTRACT AND CONCLUSIONS

This analysis of the response of a reactor power cable to a loss-of-coolant

accident (LOCA) discusses several different possible failure mechanisms.

In the first few fractions of a minute the electrical leakage currents flow and

trapped electrons may discharge, inducing noise pulses into the cable. Quantitative

analysis shows these effects are not serious for a power cable.

If the cable has poor heat contact with the external environment, within a few

minutes radiation energy (dose) will raise the temperature from an already elevated

temperature to approach the maximum service temperature for the insulators.

After a few days the accumulated dose is enough to deteriorate the cable

insulation. This chemical and mechanical deterioration thus represents the ultimate

failure mode of the cable.

It is noted that gamma ray simulators may understress the electrical effects and

overstress the temperature effects. It is also noted that several parameters used in this

study were extrapolated from the values for roughly similar materials in roughly similar

environments. A final, definitive study might have to include a program to measure

these parameters in the materials of interest.

175
TABLE OF CONTENTS

ABSTRACT AND CONCLUSIONS ......... .................... .. 175

1. INTRODUCTION ....... . ............ .................... ... 177

2. CABLE ENVIRONMENT.. ................ ......... ....... 180

3. ELECTRICAL CHANGES IN THE CABLE ............. ............. 186

3.1 Summary of the Electrical Problem ........... .... ......... 186

3.2 Derivation of the Conductivity ..... ..... ............. ... 186

3.3 Derivation of the Electric Field ........ .................. .. 187

3.4 Shunt Resistance Representation of Leakage Current ........... ... 191

3.5 The Noise Pulse Generated by Release of Trapped Charge ........... 192

3.6 Possible Errors in Simulation of LOCA Cable Failure ............ .. 192

4. TEMPERATURE CHANGES IN THE CABLE ........ ............. .. 194

5. CHEMICAL AND MECHANICAL CHANGES IN THE CABLE ........ . . .. 196

6. SUMMARY AND CONCLUSIONS .............................. 199

REFERENCES ......................... .................... 200

176
1. INTRODUCTION

The present work explores the expected failure modes of a power cable subjected

to a loss-of-coolant accident (LOCA) environment in a nuclear power plant. The work

is a more detailed numerical analysis of many of the effects outlined by Leadon in his

preliminary analysis of the problem (Ref 1). An important source of input data for our

present work is the energy deposition study carried out by Lurie, et al. (Refs 2,3).

The model for the .cable which we use is identical to the one for which Lurie did

the irradiation calculation. It is a copper conductor with an ethylene-propylene rubber

(EPR) insulator covered by a chloro-sulfonated polyethylene (trade-name Hypalon)

jacket. It is shown in Figure 1. The material properties for the various regions of the

cable are listed in Table 1.

Table 1. Material Properties of the Cable

Region Within the Cable

Parameter, Symbol, Units

Outer Radius, r, cm

Electrical Cond.,u, (ohm-cm)-

Dielectric Strength, volt/cm

Dielectric Const., k, pure number

Dielectric Relaxation Time, sec

Density,p, gm/cm3

Thermal Cond.,K, watt/cm0 C

Tensile Strength, 1000 psi

Service Temperature, max. °C

for continued use

Copper

0.729

5.7 x 105

N/A

N/A

1.6 x 0

8.94

4.19

EPR

0.947

6.4 x 10-10

1.8 x 10-7

2.3

9 2.2 x10-

0.92

3.47x 10-3

<1

Hypalon

1.1304

1.1 x 10-8

1.0 x 10-5

6.0

4.8 x 10-5

1.25

.9x 10 -3

4.0

177 163

In this task it is first necessary to define the environment to which the cable Is

expected to be subjected and then to calculate how this environment will influence the

177
I 2.2608 cm

HYPALON: C8 5 H1 5 7CE13S02

ETHYLENE-PROPLYENE

RUBBER (EPR): CH2

HYPALON'

(p = 1.25 g/cm3 )

(p = 0.92 g/cm3 )

VYLENE RUBBER

RT- 16620

Figure 1. Model of the reactor power cable

operation of the cable. The definition of the assumed LOCA environment will be found

in Section 2 of this report. The bulk of Section 2 is devoted to adapting the dose

calculations of References 2 and 3 to the specified usage needed here. Section 3 is

devoted to a calculation of the changes in electrical conditions. These changes include

leakage current through the insulation because of its radiation and temperature

enhanced conductivity, induced voltages from trapped charge, and the possibility of

breakdown due to fields generated by this charge.

Section 4 briefly discusses temperature conditions. It should be remarked that

both the electrical and temperature conditions depend on whether or not the cable is in

178
good enough contact with some external sink to exchange charge and thermal energy

respectively. There will undoubtedly be some regions in poor contact with any ground

plane where the fields and temperature can rise because there is no electrical or heat

current flowing through the jacket. Sections 3 and 4 consider cases of both good and

poor ground contact.

The mechanical and chemical deterioration which will occur are treated in,

Section 5. It turns out that disintegration or temperature and radiation enhanced

deformation are the most likely failure modes of the cable.

This report follows the temporal development of effects in the cable after the

LOCA environment is established. First the high dose rate will change the electrical

conditions in seconds to fractions of a minute. *The cable survives this challenge.

Within a few minutes the radiation heat input will raise the insulator temperature near

or above its normal service limit. The radiation and mechanical deteriorations induced

by the radiation become serious only after many hours to a few days when the total

accumulated dose has had a chance to build up to high levels.

179
2. CABLE ENVIRONMENT

For simplicity in discussing the attenuation of energy deposition from the cable

edge into the cable interior, we have specialized our analysis to a single case: the

airborne source case shown in Figures 8 and 10 of Reference 3. All sources discussed in

Reference 3 attenuate in roughly the same manner as the airborne sources. An average

over all sources will give substantially the same relative results as found for this one

case. We also limit our analysis to a reactor power of 4,000 megawatts. All doses and

dose rates are proportional to the reactor power so the final results presented here can

be scaled up or down to fit a different particular case.

It is convenient to normalize the depth-dose profile to unity at the cable surface.

The normalized doses per source particle are shown in Figure 2 for gamma radiation,

and in Figure 3 for beta radiation. To get absolute dose deposition profiles, these

energy loss curves must be multiplied by the total number of source particles at the

cable surface.

Of course, not all of the fission product radiation impinges on the cable, so that

an estimate of the local dose rate is also necessary. This has already been carried out

by Bonzon (Ref 4); his results are shown in Figures 4 and 5. Note that these doses are

due to combined environments from airborne, plate-out and waterborne sources. Values

read from Figures 4 and 5 and converted to rads(Hypalon) are given in Table 2. These

surface dose rates are then multiplied by the normalized dose-depth profiles shown in

Figures 2 and 3 to obtain the total dose rates within the cable. The results of this

procedure is exhibited in Figure 6. The leveling off a the EPR-Hypalon boundary is

caused by backscatter into the Hypalon. The very rapid attenuation into the copper is

caused by the rapid attenuation of betas, leaving only gammas which penetrate this far.

The total gamma deposition is down from the total beta deposition by a factor of ten,

so that the removal of betas drops the dose rate by a large factor.

180
IUN

-... 4 DAY COOLING ILO

CM0.

0.0

0.5 l.0

DISTANCE FROM CENTER r (cm)

RT-17027

Figure 2. Normalized dose deposition profiles in a cable by gamma radiation

in the LOCA radiation environment

181
1.0

-J

LO

CD 4 DAY

COOLING

-j

U.'

1 MINUTE COOLING

0. OOr _

0 0.5 1.0

DISTANCE FROM CENTER, cm

RT-17026

Figure 3. Normalized dose deposition profiles in a cable by beta radiation

in a LOCA radiation environment

182
.0

~1.0

o. f

RT0.01

RT-16855

Ln

Cý

CX

-Cc M

cc-cc

Lo

w

M

HOURS AFTER RELEASE

Figure 4. Typical dose rate and dose to air from the combined gamma- sources; airborne source uniformly distributed in the containment volume, plate-out

source uniformly distributed on the containment sidewall surface, /O10

of the waterborne source assumed to be uniformly distributed in the containment volume.

Cj

x.

100

10

0.1

1000

100

10

HOURS AFTER RELEASE

RT- 16854

Figure 5. Typical dose rate and dose to air from the combined beta sources; airborne

source uniformly distributed in the containment volume, plate-out source

uniformly distributed on the containment sidewall surface, 1/10 of the

waterborne source assumed to be uniformly distributed in the containment

volume.

183
Table 2. Radiation Dose Rate in Rad (Hypalon)/Sec at Surface of Cables

Radiation Source

Time After Accident Gamma Beta Total

I minute 1.9 x 102 1.4 x 104 1.5 x 104

4 days 33 310 343

Other important environments include the external temperature which is taken to

be steam at 60 psig. This results in a temperature of 143 0 C, which is rather high but

still below the maximum service temperature shown in Table I. The current expected

is about 20 amps and the voltage is presumed to be a nominal 220V rms (i.e., 310V

peak). The above data are summarized in Table 3. As a convenience in later

discussions, the average dose rate in the different materials, as taken from Figure 6, is

appended to Table 3.

Table 3. Worst Case Environment of the Cable

Reactor Power 4,000 Mwatt

External Temperature 140 0C Peak

Potential of Inner Conductor 310 Volts Peak

Current Carried by Conductor 20 amps

Average Radiation Dose Rate Within the Given Region

in Rad(Material)/Sec

Time After Accident Copper EPR Hypalon

I minute 585.0 6.4 x 103 1.1 x 1O4

4 days 1.9 26.0 100.0

184
2 x 104 2 x 10O3

104

LU'

-cc

10 3

10 2

102

101

101 10 0

2 x 100 2 x 10-1

DISTANCE FROM CABLE CENTER, cm

RT-17025

Figure 6. Total dose rate deposition profile, in a cable due to the combined LOCA

radiation environment.

185
3. ELECTRICAL CHANGES IN THE CABLE

3.1 SUMMARY OF THE ELECTRICAL PROBLEM

The dose rate, which is established soon after the accident will have several

electrical consequences. The radiation induced conductivity, u, will turn the pure

insulator into a shunt resistor (albeit, still a very large one). This effect must be

calculated from the value of conductivity of EPR at the radiation level and at the

temperature listed in Table 3. Such data for EPR could not be found, but had to be

estimated by comparison with data at the correct temperature for similar materials and

for data at lower temperature for the same material. This procedure is acceptable

since the electrical deviations remain small, although measurements on the material of

interest in the environment of interest would be more satisfying. This work is described

in subsection 3.2. The leakage current is the product ofcatimes the electric field, E.

The field is derived in subsection 3.3, and a and E are combined into an effective lumped

shunt resistor in subsection 3.4. Noise pulses caused by release of trapped charge are

discussed in subsection 3.5. Subsection 3.6 mentions differences between the LOCA

radiation and gamma simulators.

3.2 DERIVATION OF THE CONDUCTIVITY

Several workers (Refs 5,7) have determined the electrical conductivity of a

plastic insulator in a radiation environment. They all agree that the radiation induces a

conductivity of the form

a= A-6 , (1)

where • is the dose rate, A is of order 10-15 to 10-20 (ohm-cm rad/sec)- and 6 is

approximately 1.0. Assuming that 6 equals 1 is accurate enough for'our purpose.

186
The conductivity at an elevated temperature must also be found. Theoretically,

the conductivity should be the product of the charge per carrier, e, the mobility, ;A, and

the numbers of carriers,n.

o=nep . (2)

The carriers are generated thermally as well as by the radiation

u=nep(nth +n) , (3)

where nth• no exp(-E/kT).

The data of Harrison and Proulx (Ref 6) are plotted in Figure 7 as a function of

inverse temperature (1000/T). This plot indicates that A has a temperature independent

background plus an exponential variation. This is what would be expected from

Equation 3 if IA is not a strong function of temperature. However, an analysis by

Adamee and Calderwood (Ref 8) indicates that pi itself is an exponential function of T.

Thus, it is safest to assume that the temperature dependence of A is parallel to the

temperature dependence of d. As an aid to .this end, data from an NBS Monograph

(Ref 9) are also plotted in Figure 5. It appears that at 143 0 C (1000/T = 2.40), A will be

of the order of 10- 13 for EPR. Hypalon is a better conductor than EPR so that, under

the same temperature conditions the parameter for Hypalon (A) will be larger. We take

A to be 10-1 2 for Hypalon. The values of aquoted in Table I are found using the above

values of A along with the 1 minute values of j in the appropriate regions presented in

Table 3. In Section 4 of this report, it is concluded that the temperature of the EPR

may rise by as much as 150C which could increase uby a factor of 4. Nevertheless, as

we are about to show, the conductivity does not appear to be large enough to cause any

problem.

3.3 DERIVATION OF THE ELECTRIC FIELD

The electric field is the superposition of the field set up by any potential applied

to the conductor and a field set up by charges trapped in the insqlator. We will show

that the field generated by trapped charge is insignificant compared to the normally

applied voltage.

The trapped charge is the charge deposited per unit time, as calculated in Ref 3,

times the charging time. The charging time is taken to be the dielectric relaxation

187
T°C

10-13 200 175 150 125 100 50 32

143

10-14

0

I0"15. POLYETHELENE A -

MYLAR,

a FROM REF 9

DATA FROM

REF. 6

lO-16 _

-A, POLYSTYRENE ------. 0-0-0--

--- 0-0-0--

A, EPOXY

10-15I

2t0 2.5 3.0

1000

T

RT-17024

Figure 7. Electrical conductivity or, and A as a function of temperature, T.

188
time presented in Table 1. Rather than treat each region separately, an average of

10- 4sec is used. For longer times, the field will be large enough to sweep most of the

charges out of the cable. The total charge deposited within the copper is assumed-to

leak off immediately. This current represents a possible noise signal which has not been

analyzed here because this is a power cable rather than a signal cable. Figure 8 shows

the total charge per unit length QT(r), in the dielectric from the copper out to radius, r.

The charge starts at zero at r = 0.729 and goes negative because it is the accumulated

electronic charge. The displacement, D, is found from the total charge by Gauss' Law

applied to a unit length of the cable

2 n7rDr =QT +Qc ' (4)

where Qc is added to include image charges on the copper. The electric field is

E = Dr/ Eo = (QT+ Qc)/2rEEo (5)

where E is the dielectric constant of the medium and E =8.84 x 10-1 F/cm is the 0 permittivity of free space. The dielectric relaxation. time is calculated from EEo0/0.

The constant Qc in Equation 4 must be found from the voltage, V, across the cable. It

is not a simple problem to decide what this voltage should be. In some places the outer

jacket will make good contact with ground and will be at zero potential. Most places, it

will charge up to an unknown voltage and then sweep the charge out. We shall examine

both cases.

The relation between E and V is

E =-dV/dr . (6)

The solution to Equation 6 is written in terms of integrals over QT" To simplify

notation we use r with subscripts C, E, and H to signify the outer radius of the three

regions. Also subscripts E and H are added to E to signify dielectric constants in these

two regions. The final result is

V=Vc- 1 Tdr/r + Qcn (r/rc)1. (7)

rc.

189
0

E

0

0

U

L.J

0-

0

*'-l I. I I I

1 MINUTE COOLING

4 DAY COOLING

\Ji.I I I

_ý0

-1 x 10"20 -ý -1 x 10-22

-2 x 2C -2 x 10-22

r 1. 0 7 0.8 0.9 1.0 1 .1

r, DISTANCE FROM CABLE CENTER, cm

RT- 17029

Figure 8. Total charge trapped in the cable insulation, QT' from the copper out to

radius r.

The voltage at the Hypalon surface is

VHV-(7 ) 1fr C QT dr/r + QC1n. (rE/rC)

I - r

E

QT dr/r + QcTn (rH/r E)1 (8)

190
The solution for Qc is

Qc= (27EE) (VH - V) + Tdr/r

r

+ 0.38 H QT dr/r 1/1.1

rE

where numerical values of the radii have been inserted into Equation 8.

This value of Q c is inserted into Equation 5 to find the electric field,

E =V = + 6Vc 1-2- /,.l = 266 + 2.6 x 10-8 V/cm.

The second term in E, caused by the trapped charge, is much less than the first

term, caused by the applied voltage. The insulator is in no danger of breaking down if

leakage current can drain off trapped charge as we assume here. The case where

trapped charge builds up is discussed in subsection 3.5. E2

Also, this field will create a Joule heating of uE which is about 5 x 10-5

watt/cm3 . This is much less than the power deposited by the radiation so there is no

danger of "hot spots" driven by the positive feedback between increased a with

temperature and increased Joule heating with increased a.

3.4 SHUNT RESISTANCE REPRESENTATION OF LEAKAGE CURRENT

The leakage current found above can be represented by a lumped shunt resistor,

RS, across the line:

RS= (VH - VC)/lrrLuE = I/7rrLa;0.44/La (9)

where L is the length of the cable. The numerical value of Rs is about 70 MQ2 if L is

10 cm, and it is 7 Mn if L is 100 cm. If a is increased because of increased insulator

temperature then RS will decrease by the same factor. All of these shunt resistances

are high enough to be of no concern for the power cable considered here. It is possible,

however, that they could represent an unacceptable loss in a high impedance measuring

circuit.

191
3.5 THE NOISE PULSE GENERATED BY RELEASE OF TRAPPED CHARGE

We recognize that noise pulses from trapped charge discharges are probably not

important to a power cable but would be for a signal cable. For completeness, we

consider this topic. An estimate of this effect can be found by supposing that the field

builds up to its breakdown limit, EB, in some section of the cable which is not in good

enough contact with a ground plane to allow ordinary leakage current to dispose of the

trapped charge. The total charge built up per unit length, QB' under this circumstance

can be found by inverting Equation 5 with Er = EB 10 6 V/cm

QB = 2lrroEE EB l1.3 x 10-6 C/cm . (10)

When the cable breaks down, the charge QB is transferred from the insulation to

the copper where it neutralizes an equal image charge. In principle, the current flow

during breakdown is perpendicular to the cable and it will not tend to induce an emf

around the circuit to which the cable is connected. The exact magnitude of any induced

emf depends on the geometry of the termination of the cable. If the charge transit

time for the discharge is of order 10-6 sec, and the cable is a meter or more long, then

it is unlikely that the. induced emf would exceed a volt. The main noise will thus be a

return current to establish a new image charge after the discharge. This current will

flow over the period of about 10-6 sec so the 10-6 C/cm will be replaced by a current

which is about one amp per cm of cable which failed. This current can be supplied from

ground through the resistive load termination of the cable. If this load is very big then

a large voltage has to be developed across the load. The charge can also be supplied

from stray capacitance of the load termination. If this load capacitance is as big as the

cable capacity of a few pf/cm, then it can supply the charge without changing its

voltage by too much.

in summary, the amplitude of noise pulses built up by breakdown in the cable

depends almost completely on the exact details of the cable termination. If the

termination is either a small resistive load or a large capacitive load, then the noise

spikes will not be large.

3.6 POSSIBLE ERRORS IN SIMULATION OF LOCA CABLE FAILURE

The trapped charge in the insulator is largely a consequence of the nonuiform dose

deposited in the cable. The mechanism that applies here is that the secondary emission

192
leaving a volume element is not balanced by secondary emission from adjacent points

because the adjacent points are not receiving the same primary radiation. The gamma

source simulators do not show such a strong attenuation as does the true LOCA source

so they will not properly simulate the trapped charge and any resultant noise spikes.

However, because radiation induced leakage currents are judged to be inconsequential

we suggest that the LOCA environment is adequately simulated by Co 6 0 , as long as

average doses are matched.

193
4. TEMPERATURE CHANGES IN THE CABLE

The total energy deposited inside any region of the cable is found by taking the

dose rate within the region from Table 3 and converting the rad/sec to erg/gm-sec.

This is then multiplied by density and converted to watts. The net result for copper is

about 0.052 watt/cm 3. There is also a Joule heat generation from Y2 12 R losses in the

copper. This is only about 10-3 watt/cm3 when I is the nominal maximum of 20 amps;

it is safely ignored compared with the radiation energy.

Two regions of the cable should be considered. The region considered first is in

the middle where heat flow is radially through the insulator. The region near the ends

is considered in the next paragraph.

Select a section of cable L cm long so the total power deposited into the cable is

2 (r QL) 0.052 watt. At equilibrium there will be a temperature gradient, AT, across the

EPR which is big enough to conduct this heat to the external environment. In other

words AT must satisfy

AT (27rrL)KE = 0.052 Tr 2L (12)

The radius r is 0.729 cm and the thickness, Ar, is 0.18 cm which yields a value of AT of

AT = 0.052 x 0.729 x 0.18 1.0 0C (13)

2x3.47x 10-3

3

The radiation energy deposited in the Hypalon is 0.14 watt/cm . If this much heat

flows radially out through the Hypalon itself, then i temperature change of about 7°C

must exist within the Hypalon region. Such a rise above an ambient of 143 degrees is

still safely below the service temperature of both EPR and Hypalon.

If the cable is in poor thermal contact at its outer radius, then the heat must flow

into the copper and the heating problem becomes more serious. The heat must then

flow out lengthwise to the ends of the cable or to regions where radial flow is again

194
permitted. For the case of linear flow in the copper, Equation 12 is recast as

AT 2 2

EL- jrr "c 0.04irr L

AT = 0.04(LAL)/4.19 . (14)

As an illustration, take L AL = 10 cm and AT is about a degree. If L were a meter

and if this were the only heat current allowed, then T could rise by ten to one hundred

degrees, which does approach the temperature limit of the insulators.

On the other hand, the temperature rise may not be quite as large as indicated

above since the two transport mechanisms will operate in pa:allel and allow the

temperature to reach some lower temperature than, that calculated by either mechanism by itself. In any event, however, some sections of the cable may approach the

maximum service temperature of the insulators.

The 60Co and 137Cs simulation radiation sources do not reproduce the true LOCA

attenuation into the cable so that the temperature profiles established by these

simulators will not accurately reproduce the true LOCA profiles. In particular, the

simulation fields are not attenuated in the cable as the true LOCA spectrum. Thus, the

simulator will deposit too much power in the copper and inner portions of the Hypalon

compared with the power deposited into the outer surface. If the simulation is

performed so that the total doses are equivalent, then the simulator will exaggerate the

heating of the inner insulator region. This is the inverse of the case of electrical

effects generated by trapped charges where the simulator understresses the effect.

195
5. CHEMICAL AND MECHANICAL CHANGES IN THE CABLE

Several different chemical changes occur in a polymer or an elastomer (cf. Refs I

1, 10-12) upon exposure to radiation: evolution of gases, crosslirnking, and scission of

bonds (also called unsaturation). The magnitudes of the effects are usually given by a G

factor which gives the number of such events produced by 100 eV of absorbed radiation.

The number of events per rad can be found by multiplying G/eV by 6.24 x 10 eV/erg if

desired. The values of G that are used here are given in Table 4. Some analysis, as

discussed next, was done to obtain these numbers.

Table 4. G, the Number of Chemical Changes per Absorbed 100 eV at 1400C

Process Polyethylene Polypropylene

Crosslinking 3.3 1.0

Hydrogen Evolved 6.0 I.X to 2.0

Unsaturation 3.0 0.8 to 1.0

The values for G for crosslinking and hydrogen evolution in polyethylene are given

by Bolt and Carroll (Ref 10) as a function of temperature. We have used these values in

Table 4. Reference 9 also contains G unsaturation for polyethylene, G crosslinking, and

0 G unsaturation for polypropylene at 20 C. The increase in G with temperature will be

similar to polyethylene so we have scaled these values up similar to the increase of

polyethylene. Kircher and Bowman (Ref 11) indicate that an uns:Iturated hydrocarbon

(polypropylene) evolves hydrogen at one-half to one-sixth the rate of a saturated

hydrocarbon (polyethylene). This allows filling in the final entry in Table 4.

Bolt and Carroll's data indicate that the largest increase in C, is already achieved

by 140 C; a further increase to 200 C raises G by only five percent. There will not be

a large synergistic effect between radiation and temperature above the steam temperature.

This analysis requires the total dose rather than the dose rate used heretofore.

There are two factors to consider in integrating the dose rate over time to obtain dose.

196
The first factor is that the dose rate is steadily decreasing with time. This has already

been accounted for by Bonzon (Ref 4) who presents total dose at the cable surface as a

function of time. This can be used directly for total dose in the '-ypalon region. The

second factor is the energy degradation of the LOCA spectrum so that there is greater

attenuation into the cable with increasing time. This factor was accounted for in the

EPR layer by simply interpolating the attenuation factor between the one-minute and

four-day cases. For later times the original data from Reference 2 is used to

extrapolate the attenuation factor. The total dose so determined is shown in Figure 9.

10 I I I I I

1 2 4 8 16 32

HYPALON REGION DAYS

-0, EPR REGION

103

UJ

10 1

101

100.01 0.1 1.0 10 101(

TIME (HOURS)

RT-17028

Figure 9. Total dose (material) deposited in the cable jacketing

as a function of time for the LOCA radiation

environment

To evaluate the effect of these doses, it is useful to consult Kircher and Bowman

who derive the dose, y (in rads), necessary to create on"! crosslink per mole in material

with molecular weight, M:

=4.8 x 1011P/AGc G (15)

197
Gc, will be between 1.0 and 3.3. For this example a G of 2.0 was selected. The

value of -y to produce a crosslink per monomer (small molecule) w~th molecular weight

M midway between polyethylene 14 and polypropylenc 28, is a out 104 Mrad. The

unsaturation G is about the same as the crosslinking G, while the H2 evolved is much

4 larger. Thus by 10 Mrad (on the average), every monomer in the organic material has

suffered a scission, or a crosslink. By the time this dose has accumulated, the polymer

will be nearly disintegrated. It may be arbitrarily assumed that the material will retain

some semblence of its structure if only one out of twenty monomers is decoupled or

crosslinked. In this case, the acceptable dose is about 300 Mrad. This dose is reached

in the.Hypalon after approximately ten days in a LOCA. environment, and may not be

attained in the EPR region at all.

The mechanical evaluation in References 10 ancl II is als3 of interest in this

regard. It essentially tells the same story as above. I-'ypalon starts to deteriorate at

90 Mrad (about ten hours) and loses stability seriously at 300 Mrad (eight days). The

tensile strength of polyethylene and polypropalene will maintain up to 80 percent of

their original value through 100 Mrad (one to two days) and will drop to 50 percent or

less after 500 Mrad. The elongation and impact strength will deteriorate by 90 percent

or more after 50 Mrad (which is accumulated after ten hours in a LOCA radiation

environment). These later properties will determine the cable's re:;istance to vibration,

which radiation environment should be specified in a LOCA.

We note that there is some uncertainty in the literature concerning the dose level

at which Hypalon becomes seriously deteriorated. The values reported by Bolt and

Carroll (Ref 10) are about a factor of 100 less than those given by Kircher and Bowman

(Ref 11). The latter values are more consistent with fai.lure levels in similar materials,

and therefore they have been adopted here.

198
6. SUMMARY AND CONCLUSIONS

The most serious problems that will occur with the cable are chemical and

mechanical deterioration which are expected to occur after a few hours to a day in

LOCA environment. Impact strength and elongation changes by 50 percent within ten

hours. In order to properly evaluate these effects the expected vo'brational and bending

stresses should be included in the specification of the LOCA environment.

The temperature rise in the insulation layers can approach the recommended

service limit of Hypalon because of the energy deposited in the Hypalon and in the

copper by the radiation field.

It is not expected that leakage resistance will be less than. a megohm. Whether

this impedance is a problem or not depends on what sort of circuits the cable connects.

Voltage noise spikes will probably be of short duration. The amplitude of these spikes

depends on the cable load impedance.

The gradient of dose rate into the cable, which is not simulated by standard

gamma sources, has two consequences. The first is to allow the radiation to deposit

charge into the insulator because the back and forward flow of secondary emission is

not equal. The main role of this trapped charge is to create voltage noise spikes. These

spikes may not be reproduced by a simulator. The second consequence of the i gradient

is that more energy is deposited in the interior by the nonattenu.-ited simulator than is

deposited by the LOCA radiation field. The simulator may e,:aggerate the interior

temperature compared with the actual situation.

Several material parameters such as electrical conductivity and the radiation G

values had to bý interpolated from similar materials or from adjacent temperatures. If

more accurate estimates than are presented here are ever needed, then a measurement

program would be required.

199
REFERENCES

1. R. E. Leadon, "Radiation Damage Mechanisms in Reactor Components," IRT 4311-

011, IRT Corporation (May 11, 1978).

2. N. A. Lurie, D. H. Houston, and J. A. Naber, "Definitior- of Loss-of-Coolant

Accident Radiation Source," IRT 8167-004/SAND78-0091, I'T Corporation, prepared for Sandia Lal)oratories (May 1978).

3. N. A. Lurie, "Evaluation of Test Sources for Radiation Component Qualification,"

IRT 8167-010, Draft (March 1978).

4. L. L. Bonzon, "Radiation Signature Following the Hypothesized LOCA," SAND76-

0740 (NUREG76-652I), Sandia Laboratories, Rev. October 1977.

5. C. Mallon and 3. Wilkenfeld, "Measurement of Electrical Conductivity and Charge

Storage of Insulating Materials," IRT 8172-002, IRT Corporat;on (March 1978).

6. S. E. Harrison and P. F. Proulx, "Measured Behavior of Gamrna-Ray Photoconductivity in Organic Dielectrics," SCR-526 (June 1962).

7. T. 3. Abrens and F. Wooten, "Electrical Conductivity Induced in Insulators by

Pulsed Radiation," Trans. Nucl. Sci. NS-23, 1268 (June 1976).

8. V. Adamee and J. H. Calderwood, "Electrical Conductivity of Dielectrics at High

Fields," J. Appl. Phys. 8, 551 (1975).

9. R. E. Schromm, A. F. Clark, and R. P. Reed, "A Compilation and Evaluation of

Mechanical, Thermal, and Electrical Properties of Selected Polymers," NBS

Monograph 132 (September 1973).

10. R. 0. '3olt and J. G. Carroll (Eds.), Radiation Effects on Organic Materials,

Academic Press (1963).

11. F. Kircher and E. Bowman (Eds.), Effects of Radiation on Materials and Components, Reinhold Publishing Company (1964).

12. A. Charlesby, Atomic Radiation and Polymers, Vol. I (Pergamon Press, 1960).

200
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