NUREG/CR-0215, SECY-78-540: Issuance of NUREG/CR-0215, Estimates of Potential Radiation Doses from Wristwatches Containing Tritium Gas

SECY-78-540: Issuance of NUREG/CR-0215, Estimates of Potential Radiation Doses from Wristwatches Containing Tritium Gas

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Issue date:	10/12/1978
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October 12, 1978 SECY-78-540 UNITID 3'r A T!S For:

From:

Thru:

Purpose:

Discussion:

NUCLEAR REGULATORY COMMISSION INFORMATION REPORT The Commissioners Robert 8. Minogue, Director, ffice o St()ads/evelopment f, Executive Director for Operations l...

.1 --**.j)_ - -

• 1 ISSUANCE OF NUREG/CR-0215, "ESTIMATES OF POTENTIAL RADIATION DOSES FROM WRISTWATCHES CONTAINING TRITIUM GAS11 To inform the Commission of the issance of the subject report.

We plan to issue contractor report NUREG/CR-0215 (Enclosure A) on radia tion doses resulting from exposure to wristwatches containing tritium gas in sealed glass tubes.

The report is the first in a series being prepared by Oak Ridge National Laboratory, under contract to NRC, on radiation doses associated with consumer products containing tadioactive materials.

-:-!"'.c :"csults *.-:ill be consiccrcd by 1'.SS ;1 reviewing iicense applications for the manufacture and distribution of these watches.

The report estimates that the maximum individual dose for persons involved in the distribution, use, repair and disposal of the watches i 0.3 millirem per year under normal conditions.

Accidents such as breaking the tritium gas tube could cause individual doses ranging from 0.5 to 1000 millirems but would probably be closer to the lower value.

We will release the report witH a pulic announcement (Enclosure B) and a Federal Regist r Notice (Enc1osure C) in the next few days.

For completeness on the subject, we are enclosing IAEA-SM-232/57, 1 1Large Scale Distribution of Tritium in a Commercial Product11 (Enclosure D),

which will be presented by NRC staff at an International Symposium on the Behavfour of Tritium in the En.vironment on October 16, 1978.

The paper notes that one million curies (MCi) of tritium activity were distributed last year in liquid crystal display 1vristwatches and estimates that up to one MCi of tritium activity per year may be released to the environment in the future from discarded wristwatches.

Robert B. Minogue, Director Office of Standards Development

Contact:

A.N. Tse, SD 443-5946

Enclosures:

A - NUREG/CR-0215 - for Commissioners, PE, GC & SECY only B

Draft Public Announcement C

Draft Federal Register Notice D

IAEA-SM-232/57

DRAFT PUBLIC ANNOUNCEMENT NRC ISSUES REPORT ON RADIATION DOSES ASSOCIATED WITH WATCHES CONTAINING TRITIUM GAS The Nuclear Regulatory Commission's Office of Standards Development has issued a report on radiation doses resulting from exposure to wrist-watches containing tritium gas in sealed glass tubes.

The publication is the first in a series of reports being prepared by Oak Ridge National Laboratory, under contract to NRC, on radiation doses associated with various consumer products containing radioactive materials.

The report on tritium gas in watches states that the maximum individual radiation dose for persons involved in the distribution, use, repair and disposal of the watches is 0.3 millirem per year under normal conditions.

(As a comparison, the average radiation dose to individuals in the United States from natural background sources is about 100 milli-rems per year.)

Under a highly improbable disposal situation, in which a person remains for one year at 100 meters from a ground-level fire in which 8000 watcnes are destroyed, the individual could receive a dose of 17 millirems.

Accident situations were analyzed in which the glass tubes are broken.

Doses in these cases would depend upon how much of the tritium gas is converted to oxide form, the length of exposure, and the amount of air into which the tritium is dispersed.

Doses could range from 0.5 l

millirem to 1000 millirem (one rem).

However, the Oak Ridge report

notes, the doses received under such conditions would probably be closer to the lower value and the probability of occurrence of accidents is believed to be low.

Tritium combined with a phosphor is used in watches because of the luminescent, glow-in-the-dark properties.

Incorporating tritium gas into a digital watch allows the time display to te illuminated continu-

ously, thus eliminating the need for the manually operated, battery-powered lighting system. used in some other types of digital watches.

Use of tritium gas in such products was authorized by the former Atomic Energy Commission (AEC) in 1969.

Another use of tritium in watches--application of tritium paint to the hands and dials to make them luminescent--was authorized by the AEC in 1961.

It was noted that tritium is a less radioactive substitute for the radium that was used in the first luminescent watches (and is still used in some current-day watches).

Radiation doses resulting from this other use of tritium in watches will be the subject of another report in the series on radiation doses from consumer products.

Other reports in the series will deal with radiation doses associated with incandescent mantles and welding rods containing thorium and doses associated with smoke detectors containing americium.

The availability of these other reports will be announced as they are completed.

The report on watches containing tritium gas in sealed glass

tubes, entitled "Estimates of Potential Radiation Doses from Wristwatches Con-taining Tritium Gas," NUREG/CR-0215, is available for public inspection

at the Commission's Public Document Room, 1717 H Street, NW., Washington, D.C.,

or may be purchased from the National Technical Information Service, Springfield, Virginia 22161, at $4.50 for paper copy and $3.00 for microfiche.

RETESET PRE PSE RISA EG POOPIE MO r

l SRR mae ER eT TFS SEES

7590-01 NUCLEAR REGULATORY COMMISSION TOPICAL REPORT Notice of Issuance and Availability The Nuclear Regulatory Commission staff has released a topical report on potential radiation doses from wristwatches containing tritium gas.

The report was prepared by the Oak Ridge National Laboratory under a contract to NRC.

The report, NUREG/CR-0215, "Estimates of Potential Radiation Doses from Wristwatches Containing Tritium Gas," presents estimates of poten-tial radiation doses to members of the general public, both individually and collectively, from exposure to wristwatches containing tritium gas in sealed glass tubes.

The study considered exposures that could occur during the distribution,

use, repair, and disposal of such wristwatches, as well as under certain postulated accident conditions involving the wristwatches.

NUREG/CR-0215 is available for-public inspection at the Commission's Public Document Room at 1717 H Street NW., Washington, D.C.

Copies may be purchased at current rates from the National Technical Information Service, Springfield, Virginia 22151.

(Paper copy:

$4.50; Microfiche:

$3.00)

(5 U.S.C.

552(a))

Dated at this day of

1978, For the Nuclear Regulatory Comnission Robert B.

Minogue, Director Office uf Standards Development

IAEA-SM-232/57 IAEA/NEA International Symposium on the Behaviour of Tritium in the Environment October 16, 1978 San Francisco, California, U.S.A.

LARGE SCALE DISTRIBUTION OF TRITIUM IN A COMMERCIAL PRODUCT F.

Combs and R.

J.

Doda U.S.

Nuclear Regulatory Commission Washington, D.C.

ABSTRACT Tritium enters the environment from various sources including nuclear reactor operations, weapons

testing, natural production, and from the manufacture, use and ultimate disposal of commercial products containing tYitium.

A recent commercial application of tritium in the United States involves the backlighting of liquid crystal displays (LCD) in digital electronic watches.

These watches are distributed through normal commercial channels to the gen-eral public.

One million curies (MCi) of tritium were distributed last year in this product.

This is a significant quantity of

tritium, when compared to free world power reactor-produced tritium (3 MCi/yr) or to naturally-produced tritium (6 MCi/yr).

This is the single largest commercial appli-cation involving tritium to date.

The final disposition of tritium from large quantities of this product, after its useful

life, must be estimated by considering the means of disposal and the possibility of dispersal 9f tritium concurrent with disposal.

The most likely method of final disposition of this product will be disposal in solid refuse; this includes burial in land fills and incineration.

Burial in land fills will likely contain the tritium for its effective

lifetime, while incine-ration will release all of the tritium gas (as the oxide) to the atmosphere.

The use and disposal of this product will be addressed as a

part of an environ-mental study that is presently being prepared for the U.S.

Nuclear Regulatory Commission.

1.

INTRODUCTION The total inventory of tritium in the environment and the means by which this inventory is increasing is of special interest and importance to the world population because any released tritium is rapidly assimilated into the earth's ecology.

Tritium enters the environment from various primary sources including nuclear reactor operations, weapons

testing, and natural production.

The natural production of tritium occurs predominantly by the fast-neutron irradiation of nitrogen by cosmic rays and by the direct ejection of tritium by stars.[1]

There is yet another pathway for tritium to enter the environment.

Tritium, that has been manufactured for commer-cial uses, may be released during the manufacture, use and ultimate disposal of commercial products containing tritium.

Examples of commercial products which contcin tritium and which are distributed in the United States are electron tubes, tritium-painted time-pieces, exit signs, and other self-luminous products.

A recent commercial application of tritium in a product available to the general public in the United States involves the backlighting of liquid crystal displays (LCD) in digital electronic watches.

Sealed glass tubes containing tritium as the activator and a phosphor as the luminescent material are used to backlight the entire LCD area for nighttime viewing of the digital output.

These watches, in final assembled

form, are distributed through normal commercial channels to the general public.

It is difficult to estimate the number of watches that will be distributed in the future because of the recent introduction of watches with LCDs, the low prices already experienced in the market place for these watches, competition with LCD watches not containing tritium and consumer acceptance of this product.

However, one manufacturer has estimated distribution of 3 million watches in calendar year 1979.

Since each watch contains a maximum of 200 mCi of

tritium,

.6 MCi will be made available for consumer use from this one manufacturer alone.

This product application does represent a significant quantity of

tritium, when compared to free world power reactor-produced tritium (3 MCi/a) or to naturally-produced tritium (6 MCi/a),

and qualifies it as the single largest commercial application involving tritium to date.

2.

BACKGROUND One of the oldest commercial applications of radioactivity in products available to the general public is the use of radioluminescent materials (principally, for use in timepieces).

The original method of timepiece lighting involved painting a mixture of radium and phosphor on the surfaces of the timepiece desired for light-ing.

Even though this method is still being used to some extent, the use of radium is declining rapidly.

The use of radium has been replaced largely by painted mixtures of a tritium compound and phosphor or a promethium-147 compound and phosphor.

These are the methods most used today for mechanical watches.

Consumer products, such as watches containing radioactive material, can only be distributed in the United States under regulations which provide for exempt distribution of the product.

This means that a manufacturer may transfer possession of or distribute the product to persons exempt from licensing and regulatory requirements.

However, the manufacturer must have

a specific license which authorizes this transfer or distribution.

The U.S. Nuclear Regulatory Commission issues specific licenses to individuals to manufacture products containing radioactive material and to distribute these products to persons who are not licensed.

These products must be manufactured in accordance with standards established by the U.S. Nuclear Regulatory Commission.

After such a product is distributed, there is no further regulatory control over the use and disposal of the product.

The use of tritium-activated lighting for timepieces for the general public began in the United States in 1960, when regulations were established which allowed the distribution of timepieces, each containing up to 25 mCi of a painted mixture of tritium, to persons exempt from licensing require-ments.

In 1969, a class exemption from licensing requirements was added to the regulations and provided for the distribution of self-luminous products containing tritium, krypton-85 or promethium-147 and for the use of such products by persons not licensed to possess radioactive material.

In 1975, the first specific license in the United States was granted, under the class exemption for self-luminous products, for the distribution of digital electronic watches, containing approximately 200 mCi of tritium each, to persons exempt from licensing.

The Federal government retains jurisdiction over any specific licenses granted which authorize distribution under this class exemption for self-luminous products.

Se LICENSE REQUIREMENTS Strict product qualification and analysis is required, to insure that the product meets the safety criteria in the regulations, before a specific license to distribute nder the class exemption is granted.

The product must be designed and manufactured so that wear and abuse are unlikely to cause a potential dose to persons in excess of specific guidelines during normal handling and use of the product.

An application for a license must include a description of the product and its use; a description of the byproduct material including quantity, chemical

form, physical form and solubility; details of construction and design; safety features under normal and severe conditions of handling; quantities involved in distrib-ution and storage; method of labeling and marking; procedures and results of prototype testing; estimated dose commitments using a strict set of cri-teria; detailed quality control procedures; and other specific information.

The analysis, required prior to acceptance of this product application for distribution to exempt persons, considers breakage and accident incidents for single units in use, distribution and storage, and multiple or bulk units in manufacture, distribution, storage and disposal.

The safety criteria in the regulations limit the average dose, or dose commitment, to members of the group expected to receive the highest dose from normal use and disposal of a single exempt unit to 1 millirem per year, and limit the

dose, or dose commitment, received by persons engaged in marketing, distrib-

uting, and servicing of exempt products, as a result of exposure to the quantities of exempt units likely to accumulate in one location to 10 millirem per year.

In addition, prototype test criteria which are required by the U.S.

Nuclear Regulatory Commission include a detectable tritium leakage limit of

.1 uCi/d per watch, after all other tests (vibration, temperature, thermal

shock, pressure,

impact, and immersion) have been performed.

The analysis and evaluation of the use of tritium for backlight-ing LCD digital watches satisfied all of the safety criteria in the regu-lations and approximately 12 licenses have been granted since 1975 to

manufacture and distribute these watches, under the class exemption for self-luminous products.

4.

PRODUCT CHARACTERISTICS Digital electronic watches which use hybrid integrated circuits are a

fairly recent development, with the first watches of this type coming on the market about 1973.

These watches can utilize either light-emitting diodes (LED) or a liquid crystal display (LCD) for the digital readout.

Tritium backlighting is used for the LCD digital watch only, i.e.,

the method used provides for backlighting the entire area behind the opaque numerics of the display.

The self-luminous module contains sealed glass tubes which contain tritium gas and a phosphor coating on the internal surface of the tube.

The tritium tubes are normally sealed automatically by laser and have very low leakage rates of tritium gas

- usually less than

.01 uCi/d for each unit([3].

This would represent a tritium leakage of less than 3.6 Ci/a from 1 million watches.

Automatic laser sealing produces extremely uniform and controlled seal areas due to the precise manipulation of a focused laser beam.

In the construction of the watch, the tritium tubes are shock-mounted in a metal pan and the LCD with a diffuser is placed over the pan.

The LCD-source-pan assembly, along with electrical connectors and electronics, is assembled into a single package called a watch module.

The module is then mounted in a watch case.

The watch is extremely shock-resistant with respect to damage to the tritium tubes and can withstand severe handling, such as, drops onto a steel plate from heights of 2 meters.

Access to the light sources may be accomplished only by disassembly of the watch which requires some destruction of the components that were used to assemble the watch.

Any repair and maintenance which involves removal of the module must be performed under a specific license, granted by the U.S. Nuclear Regulatory Commission, which authorizes redistribution.

Dose estimates provided by the manufacturers show whole body dose commitments of the order of 2.5 microrem per year to individuals using the watch and 1.0 microrem per year to individuals engaged in the distribution and marketing of the product.

A recent report([2]

estimates doses of 3

to 20 microrem per year to individuals using the watch and

.4 to 100 microrem per year to individ-vals engaged in distribution and marketing.

Customer acceptance, low market price, and product uniqueness have all contributed to the early distribution of large numbers of tritium backlighted digital watches.

Quantities of

tritium, contained in backlighted digital watches distributed in the United States, are as follows:

Fiscal Year Ending:

June 30, 1977

.013 MCi tritium June 30, 1978 1.00 MCi tritium June 30, 1979 4.00 MCi tritium (estimated)

For comparison purposes, there are approximately

.3 MCi tritium distributed in all other commercial products each year in the United States, and approxi-mately

.7 MCi tritium produced by power reactors in the United States each year (see Figure 1).

TRITIUM MEGACURIES PER YEAR (MCi/a)

J OTHER COMMERCIAL PRODUCTS POWER REACTOR PRODUCED DIGITAL WATCH LIGHTING 1978 FISCAL YEAR (ENDING JUNE 30th)

Figure 1. Annual Tritium Quantities in U.S.

1979 (EST.)

5, ULTIMATE DISPOSAL The analysis required prior to licensing this product for distribution to exempt persons, evaluates breakage and accident scenarios for single units in

use, distribution and

storage, and for multiple or bulk units in manufac-

sure, distribution, storage and disposal.

However, the long term disposi-

tion, that is, the final or ultimate disposition of tritium from large quantities of this product after its useful

life, must be estimated by con-sidering the means of disposal and the possibility of dispersal of tritium concurrent with disposal.

The most likely method of the final or ultimate disposition of this product will be disposal in solid refuse; this includes burial in land fills and incineration.

Burial in land

fill, in all probability, will contain the tritium in the product for its effective lifetime because of the lack of stress.

However, incineration will release all of the tritium gas (imme-diately converted to the oxide) to the atmosphere.

After some period of time (the digital electronic watch may have an average lifetime of 6

to 10 years),

the yearly production rate of the product will approximate the yearly dis-posal rate.

After the product's disposal rate approaches some equilibrium value in the

future, it is possible by considering the factors of production

rate, lifetime, radioactive decay, and disposal

rate, to estimate that an approximate quantity of 2

MCi of tritium contained in this product may be disposed of per year as solid refuse.

This would only occur about 10 years in the future and only if present trends in acceptance and use of this prod-uct continue.

The fraction of this disposal quantity of tritium that will ultimately be released to the atmosphere will depend on a number of unknown

factors, the principal one being the fraction of solid refuse that is dis-posed of by incineration.

The quantity of tritium released to the environment at a future date could be up to 1 MCi/a and, thus, would represent a signifi-cant addition of tritium to the environment when compared to the free world power reactor-produced tritium of 3 MCi/a or to naturally-produced tritium of 6 MCi/a.

The U.S.

Nuclear Regulatory Commission, as part of a continuing program of licensing and regulatory review, has undertaken a study which will evaluate the environmental effects of the use and disposal of a number of commercial products containing radioactive materials; and this will include digital electronic watches containing tritium.

The results are expected within two years and will serve as the basis for a generic environmental impact statement to be prepared by the U.S.

Nuclear Regulatory Commission.

Tritium does not bioaccumulate in the environment, in food chains or in man

[4].

However, tritium does accumulate physically in the environment;

and, therefore, the environmental impact statement will investigate both the effects of the use of this product and the effects of the fraction of tritium released to the environment during the disposal of this product.

6.

SUMMARY

A large scale commercial application of tritium is the use of sealed glass tubes containing tritium and a phosphor to backlight liquid crystal displays in digital electronic watches.

Projections indicate that large quantities of this product will be disposed of or discarded sometime in the

future, after the product's useful life is over.

The total quantity of tritium contained in the discarded

items, after considering radioactive

decay, may be on the order of 2 MCi/a, approximately 10 years in the future.

6

The fraction of this disposal quantity of tritium that will be released to the environment (for example.

by incineration) will depend on a number of unknown factors.

The quautity of tritium that is actually released to the environment in the future could be up to 1 MCi/a.

[1]

[2]

[3]

[4]

REFERENCES

Jacobs, D.

G.,

Sources of Tritium and Its Behavior Upon Release to the Environment, TID-24635, National Technical Information Service, Spring-

field, Virginia, 1968.

McDowell-Boyer, L.

M.

and O'Donnell, F.

R.,

Estimates of Potential Radiation Doses from Wrist Watches Containing Tritium Gas, NUREG/CR-0215, ORNL/NUREG/TM-225, National Technical Information Service, Springfield,

Virginia, August, 1978.

Ristagno, C.

V.,

"The Use of Tritium Luminous Sources for Lighting Digital Wrist Watches," Symposium on the Public Health Aspects of Radioactivity in Consumer Products, February 2,

1977.

Rohwer, P.

S.

and Wilcox, W.

H.,

Nuclear Safety, "Radiological Aspects of Environmental Tritium," 17 2

(1976) 216.