ML20058L262

Environ Impact Statement Comments, Jul 1972

ML20058L262
Person / Time
Site:	Monticello
Issue date:	07/31/1972
From:	ENVIRONMENTAL PROTECTION AGENCY
To:
Shared Package
ML20058L261	List: ML20058L256 ML20058L262
References
D-AEC-00056-30, D-AEC-56-30, NUDOCS 9105130422
Download: ML20058L262 (25)

Text

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i EPA #D-AEC-00056-30 E!NIR0101CNTAL PROTECTION AGENCY i

Washington, D.C. 20460 July 1972

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ENVIRONMENTAL IMPACT STATDIENT CO3NENTS Monticello Nucient Generating Plant TABLE OF CONTENTS PAGE

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INTRODUCTION AND CONCLUSIONS 1

i R/QIOLOGICAL ASPECTS l

Radioactive Waste Management 3

i Dose Assessment 7

Effluent Monitoring 8

Transportation and Reactor Accidents 9

NON-RAD 10 LOGICAL ASPEC'iS

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Tnermal Ef fects 11 i

Temperature Standards 13 j

Cooling Requirements 15 Biological Effects 16 Chemical Impact 18 Monitoring and Surveillance 20 Air Quality 21 Additional Comnents 23 I

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INTRODUCTION AND CONCLUSIONS

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The Environmental Protection Agency (EPA) has reviewed the draft environmental statement for the Monticello Nuclear Generating f

Plant prepared by the U.S. Atomic Energy Commission (AEC) and issued I

on May 26, 1972. Following are our major conclusions:

1.

Operation of the Monticello Nuclear Generating Plant during i

1971 resulted in the discharge of radioactive gases at levels f

I that were small percentages of 10 CFR Part 20 limits. Based on r

1971 experience, continued operation until the modified off-gas l

system becomes operational can be expected to have only a minor l

environmental impact. However, current operating data should be examined and presented in the final statement to see if they 7

i corroborate this conclusion.

4 2.

The iodine discharge from the turbine building should be reduced i

to meet proposed Appendix I, 10 CFR Part 50 guidelines and to ensure that the radiation dose to the child's thyroid is maintained at

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i levels comparable to those suggested in Appendix 1.

(The potential

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dose estimated by the AEC [67 mrem] would be excessive.)

f 3.

Several modes of operation of the liquid waste management system i

have been discussed in the FSAR, environmental report, and draft l

statement.

Since each mode would result in different environmental j

i impacts, the final statement should describe how the liquid waste treatment equipment will be operated.

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The capability of the plant vaste treatment systems to adequately process large volumes of contaminated liquids should be discussed in

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I the final statement.

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l 5.

The analyses regarding dose assessment and liquid effluent discharge f

i concentrations assume a condenser cooling water dilution flow of 645 cfs. Since the applicant has agreed to operate in the closed-cycle mode as much as practicable, these analyses should be made for a 36 cfs dilution flow.

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The dose assessment should include the contribution f rom leakage I

t of off-gases from the decay tanks and from direct shine from facility i

structures and components (e.g., turbine, tanks, and stack),

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7.

Dose assessments for routine releases and accidents should be k

evaluated using as much operational data as possible (e.g., on-site meteorology, equipment performance, leakage, and partition factors).

The results should then be compared with those calculated with the f

i standard models.

8.

The proposed operation of.the plart does not assure that j

water quality standards will be met at all times. Thus,a r

I specific operational plan should be developed to meet water j

quality criteria on a continuous basis. This plan should be addressed in the final statement.

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Serious consideration should be given to operating the l

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cooling towers aII year unless it can be shown that limited opera-r tion will not be significantly detrimental to aquatic life.

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10. In order to comply with the recommendations of the National f

i Technical Advisory Committee to the Secretary of Interior and to protect aquatic organisms, the mixing zonc ;Sould be limited to

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25% of the river's width and tr paratures should be maintained below 80*F.

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RADIOLOGICAL ASPECTS Radioactive Uaste Manarcnent l

The off-gas system modification, scheduled to be operational by l

i December, 1972, will have the capability for reducing the condenser j

off-gas effluent discharges to levels below those proposed in Appendix I to 10 CFR Part 50.

Operation of the plant at discharge levels which f

are small fractions of 10 CFR Part 20 limits until the modified system f

i becomes operational is acceptable. Operating data for 1971 are presented

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in the draft statement and indicate that the planz operated at small I

fractions of 10 CFR Part 20 limits.

Continued operation at these discharge Icvels until such time as the modified system becomes operational would i

appear to have a minimal environmental impact. There is a question i

whether the 1971 data are representative of current operating conditien'.

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Thus, the nost recent data (since Decamber,1971) should be used as a bases j

l for evaluating the environmental impact of temporary operation without the i

modified off-gas systen.

These data should be presented in the final statement.

The draft statement indicates that essentially all liquid wastes i

I are being treated by pewdex filter-demineralizers and deep-bed l'

demineralizers and that most of the waste is to be recycled.

If the vaste equipment is operated as described in combination with maximum possible j

l recycle, the waste effluents can be considered "as low as practicable" t

I within the capabilities of the existing equipment and should be within j

the guidelines of the proposed Appendix 1 to 10 CPR Part 50.

In addition, the described operation would seem to be consistent with the " require-4 ments" provided in the State of IUnnesota Waste Disposal Permit. No I

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assurance is given that the systmo will be operated as described. Further, the treatment of liquid waste as described in the draft statement is j

inconsistent with the rpplicant's description in the environment al i

4 report and FSAR.

r A recent Supreme Court decision regarding some provisions of the

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state permit to the effect that states cannot pre-empt the effluent standards setting authority of the AEC, raises the questien whether the portion of the permit requ. ring demineralization of all liquid radio-active waste is binding. As a consequence, the validity of the AEC i'

analyses concerning operation of the waste treatment system is not i

evident since there may be no requirements on the applicant to operate j

l the equipment in the manner described. The final statement should I

clarify these aspects. In addition, the applicant's criteria for i

i providing additional treatment or to initiate discharge to the t

environment should be detailed.

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The statement does not consider the environmental effects of efflu-ents resulting from maintenance operations, such as draining of the torus (which has already been necessary) and condenser maintenance,

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l or the ability of the liquid waste treatment system to process these

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Iarge volumes of contaminated liquids. These analyses should be included

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in the final strtement, including presentation of relevant details such j

t (1) the expected or potential maintenance operations resulting in

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as:

i very large volumes of contarinated liquids, (') the concentration of t

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radionuclides, (3) the ability of the plant vaste system to receive and t

treat these liquids, (4) che resulting environmental impact, and (5)

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l the frequency of the events.

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A The AEC evaluation of the radioactive liquid discharges was based I

i on 645 cfs dilution flow using once-through condenser cooling. The applicant, however, as a result of the request of the Minnesota Pollution f

I Control Agency, has agreed to utilize the closed-cycle mode of cooling l

i tower operation to the maximum extent practicable. The capability of i

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attaining the proposed Appendix I discharge concentrations with a cooling f

tower blowdown fIrr of 36 cfs should tre included in the final statement.

Our evaluation indicates that the allowabic annual discharge, as limited l

by Appendix 1 concentration limits, would be considerably less than the 5 Ci provided by Appendix I (and assumed in the statement) when operating in the closed-cycle mode.

i The method of processing radioactive checical wastes should be more

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clearly defined because of inconsistencies between the draft statement and the environner cal report. For example, as described in the draf t l

l statement, radioactive chemical wastes are blended with other liquid i

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vastes and de=ineralized or " solidified" by using them as vetting agents l

for the cement in the solid waste system. The applicant indicates, however, the wastes are filtered before being released to the ensironment, t

j if the radioactivity Icvels are acceptable. Otherwise, the chemical wastes I

are solidified. Apparently, the AEC expects some radioactive chemical l

i vastes will be piutessed as described by the applicant since, in dis-

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cussing the ultimate disposal of chemical waste sludged from the twin I

20,000 gallon retention basins, the environmental statement (page V-19) l indicates that "... settled materials are removed and disposed of as solid f

t radwaste."

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6 The environmental report indicates that steam is available for use in deicing the water intake structure.

the source of this steam is not described in either the TSAR or the environmental report; the draft statement did not address this.

If process steam is to be used for this purpose, the radiological consequences should be evaluated and presented I

in the final statement.

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Finally, the draf t statement did not address alternatives to the present liquid waste management system. Alternatives, such as addition j

of evaporators, should be included.

The additien of the off-gas recombiner, the pressurized gas decay t

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tanks, and charcoal filters should reduce the discharges of radioactive A

off-gases from the condenser to small fractions of 10 CFR Part 20 limits I

and within the guidelines of the proposed Appendix I to 10 CFR Part SC.

j This pressurized system, however, does have greater potential for leakage l

of off-gas than other currently proposed systers which are to be operated at ambient pressures. While the draft statement addresses radiogas discharges resulting from steam leakage, it does not consider leakage f

i from the pressurized tank system. Since any releases from this system vill result in ground level discharges rather than releases through the j

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elevated plant stack, the dose consequences of the potential leakage may l

4 be significant relative to Appendix I dose limits. This leakage is not 131 expected to significantly increase anticipated discharges of 1,

t' since there are two charcoal filters upstream from the decay tanks.

The decay tank system is designed to provide 50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br /> decay rt a condenser air in-leakage of 20 cfm.

Since the decay time proyided by the pressurized holdup tanks is a function of condenser air in-leakage l

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rates, the effluent discharges may be considerably different than the l

1evels presented in the draft statement. It would be helpful if the

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t experience at Monticello and other comparable Ek'Rs relative to condenser i

air in-Icakage rates could be detailed in the final statement.

In addition, a discussion of.the applicant's criteria for condenser repair and/or l

operating requirements which would limit operation at in-leakage rates exceeding the assumed 20 cfm value should be presented in the statement.

131 According to the draf t statement, the release of I from the tur-bine building vents will result in effluent discharges substantially l

in excess of the proposed Appendix I levcis. Also, according to the 131 envire mental ?. port, these estimates are consistent with I

discharges ext-icnced at operating Ek'R plants. The final statement 131 s'

address potential means of reducing the I concentrations I

released from the turbine building, giving particular attention to i

charcoal filters for the turbine building vents, a clean steam system for

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the turbine gland scal, and/or release of the turbine building ventilation j

air through the elevated stack.

Dose Assessment I

5 The potentisi dose (67 nrem) to a child's thyrs1d at the nearest f arm would be excessive and necessary measures should be taken to reduce the dose to levels suggested by the proposed Appendix I to 10 CFR I

Part 50.

The other AEC projected dose consequences are well within j

i the proposed guidelines. The statement, however, did not consider j

t potential doses from off-gas leakage from the pressurized decay l

tanks nor the direct shine doses from (1) the turhine, (2) outside condensate storage tanks, C3) radwaste building equipment, and (4) the i

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clevated stack. Furthermore, the assumptions and/or their bases used in j

i the doce evaluations should be better defined. For instance, (1) the

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statement indicat the expected releases are bas ion an annual average-l t

stack discharge rate of 44,000 pCi/see while Table III - 3 indicates 100,000 pCi/sec, (2) the bases for the atmospheric dispersion factors are not included, and (3) the bases for the assumed steam leakage, iodine Since partition factors, and coolant leakage rates are not presented.

this is an operating plant, actual operating data would provide the best I

bases for making estimates of plant performance, and we encourage the AEC to obtain pertinent measurements, to compare the measurements with the t

assumptions used in the standard AEC models, and to use the measured parameters in evaluating the radiological impact of the plant.

The AEC has estimated that operation of Monticello during 1971 resulted in maximum doses of (1) S mrem to a child's thyroid and (2) 11 man-rem to the population within 50 miles. No estimate was made of the l

maximum dose to the hypothetical individual at the critical site boundary j

i or the nearest farm. In addition, these doses were based on release data l

from the first 6 months of operation, even though release data for the j

l' entire year are contained in the draft statement. The final statement 1

should provide evaluation of the doses based on the entire year of j

i operation and should be based on on-site meteorological data, if available.

Effluent Monitoring I

Neither the draft statement nor the applicant's environmental report E

l indicate that the turbine building vents are monitored for radioactivity.

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l Since ground level discharges of radionuclides from the turbine building and the future recombiner building vill contribute significant releases j

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(particularly for 1), these vents should be monitored for gross I

i radioactivity and iodine discharges. Since Safety Guide 21 requires

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I such monit ring for plants currently undergoing licensing review, EPA strongly encourages that these guidelines be applied at Monticello.

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Transportation and Reactor Accidents As has been indicated in previous reviews. EPA has identified a need for additional information on two types of accidents associated f

with nuclear power plants which could result in radiation exposure to i

the public:

(1) those involving transportation of spent fuel and radioactive vastes and (2) in-plant accidents. Since these accidents i

are common to all nuclear power plants, the environmental risk for l

each type of accident is amenable to a general analysis. Although the AEC has done considerable work for a number of years on the safety aspects of such accidents, we believe that a thorough analysis of the I

probabilitics of occurrence and the expected consequences of such ac-cidents would result in a better understanding of the environmental l

risks than a less-detailed examination of the questions on a case-by-case basis. For this reason, we have reached an understanding with the

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AEC that they will conduct such analyses with EPA participation concurrent

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with review of impact statements for indiv,idual facilities and will make 4

the results availabic in the near future. We are taking this opproach

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i primarily because we believe that any changes in equipment or operating procedures for individual plants required as a result of the investigations could be included without appreciable change in the overall plant design.

If major redesign of the plants to include engineering changes were ex-pected or if an immediate public or environmental risk were being taken l

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while these two issues were being resolved, we would, of course, make j

our concerns known.

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The statement concludes "..'.that the environmental risks due to

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' postulated radiological accidents at the Monticello Nuclear Gener'ating i

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Plant are exceedingly small and need not be considered further." This l

conclusion is based on the standard accident assumptions and guidance l

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I issued by the AEC for light-water-cooled reactors as a proposed amendment to Appendix D of 10 CFR Part 50 on December 1, 1971. EPA commented on l

this proposed amendment in a letter to the Commission on January 13, 1972.

These comments essentially raised the necessity for a detailed discussion of

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the technical bases of the assumptions involved in determining the various classes of accidents and expected consequences. We believe that j

the general analysis mentioned above will be adequate to resolve these points and that the AEC will apply the results to all licensed facilities.

i Since on-site meteorological measurements may have been made for j

s several years, the dose consequences of postulated accidents should be i

evaluated based on the on-site data rather than the standard assu=ptions

.i given in the accident guide. While this may have been done for the analyses i

in the draft statement, the information provided only refers in general l

i to the proposed annex to Appendix D of 10 CFR Part 50. We encourage the AEC to utilize the on-site meteorological data to evaluate the accident consequences.

At least one operational transient has occurred at Monticello f

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I which resulted in unplanned release of gaseous radioactivity to the i

environment.

In additien, because of damage to baffles in the plant

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I containment system, a controlled discharge of high volumes of radioactive liquid waste was necessary.

It would be helpful in evaluating the significance of potential accidents if the abnormal occurrences experienced at Monticello could be related to the nine classes of accidents given in the draft state-j i

ment.

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i NON-RADIOLOGICAL' ASPECTS f

Thermal Effects In our opinion, the model employed by the applicant is not

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i adequate for analyzing the behavior of the thermal plume.

Throughout I

the statement there are various discussions which involve the low flow figures.

However, the value of the 7-day once in 10-year low t

flow is not given.

The 38 and 40 year records of flow below and i

t above the plant site should be adequate to predict a design low flow 7

i at the. site without relying completely on the six years of record.

In addition, analysis of the thermal plume, withdrawal of. river f

e water for condenser use, and biological effects should be discussed

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for the 7-day once in 10-year low flow.

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Temperature predictions for low flow are not particularly representative of low flow conditions.

Similar projcctions should

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q be made for the months of September and December when low flows i

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below 1,000 cfs are common.

f Calculations are given for the downstream distance affected by l

t plume temperature rises greater than 5"F for the month of August.

i It would be appropriate to expand these calculations to include low l

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flows during winter months.

Such calculations would give some idea i

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of the size of the mixing zone at those times, and indicate the area l

of potential impact on aquatic life.

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l The draft statement indicates that summer maximum water tem-i perature in the cooling system will be about 98'F and will'last s

1 about three minutes.

This seems inconsistent with the fact that

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t the July daily maximum river temperature is around 85'F and with an anticipated delta T of 26.8*,

the maximum would then approach i

112*F.

In addition, it is implied that the helper mode will be l

i used, but does not mention the use of closed-cycle during this thermally critical period.

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1 13 N

i Temperature Standards The AEC recommends to the Northern States Power Company that the plant not exceed a maximum temperature of 90*F over one-half the river width at any time.

Water quality for this particular i

section of the Mississippi River (Fort Ripley to Anoka) is classified l

f as adequate for purposes of drit. ling water, fish and wildlife, recreation, and industry.

Drinking water use does not include a i

temperature maximum, but fish and wildlife, recreation, and industrial uses provide a maximum of 86*F.

Under these conditions, we believe that the plant will exceed the temperature standard by 4*F, particu-

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larly during the warmer months of the year.

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It is anticipated that in the near future Minnesota's thermal t

standards will be revised to conform with temperature maximums I

recommended by EPA at a joint meeting of Federal and state agencies l

B held in St. Louis, Missouri, on March 3, 1971.

These recommendations i

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are:

Temperature (*F)

January 37 l

February 37 t'

March 43 April 55 May 67 i

June 80 l

July 80 August 80 September 80

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October 67 November 55 December 43 i

Minnesota also has indicated that it will follow the mixing zone recommendations of the National Technical Advisory Committee i

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s (Water Qualitv Criteria, Report of the National Technical Advisory i

Committee to the Secretary of the Interior, April 1,

1968, Washington, i

t D.C.).

The committee recommends that a zone of passage for squatic organisms, "should contain preferably 75 percent of the cross-f sectional area and/or volume of flow of the stream..."

This requirement conflicts with the plants current use of a mixing

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zone which includes 50 percent of the width of the river.

l There is no description given of methods used in predicting temperature patterns.

Temperature patterns are based on monthly average conditions of flow and temperature.

We believe this approach i

will not give an acceptable analysis for potentially damaging i

t critical periods.

One statement cites average summer river tempera-e tures for July, August, and September as 71*F (page 111-10) and l

i then cites the average summer effluent temperatures under helper

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mode operation.

i Cooling towers were not designed for winter operations (page i

i 111-6, 7); hence, load curtailment may be necessary to meet standards.

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t This approach, however, will mean that the river will be thermally I

stressed to the maximum during critica] low flow periods.

This

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should be avoided.

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Coo 3 inn Requirements I

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To assure that the cooling system components will be operated 5

to maximize environmental protection we recommend that the license l

require continuous closed-cycle operation until:

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a mixing zone is delineated satisfactory to the State and l

EPA 2.

an operational plan for the helper system is fully documented 3.

the efficacy of this plan has-been checked against several i

years of-stream temperature and discharge data j

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full and reliable monitoring and gauging instrumentation is i

installed.

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1 Biolonical Effects.

The draft statement discusses the effects of the intake

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structure and iclocity on fish and concludes that some impingement I

or entrainment of small fish entering the intake canal will probably i

occur.

These effects may become most significant during the winter j

wh'n warm water is recirculated to the intake canal to prevent ice e

formation.

Further evidence is presented showing that survival of entrained larval fish will be low.

Based-on the discussions in the i

statement, it would appear necessary to redesign the intake structure to reduce fish entrainment.

Year-round closed-cycle operation would significantly reduce this problem.

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i The withdrawal of 75 percent of the river water during low flow appears excessive.

What will the effect on aquatic life be during this period due to entrainment an the temperature increase?-

l Closed-cycle operation by use of cooling towers during these times, t

or reduction in power output should be considered.

As a result of the high temperature rise during open-cycle l

j operation the chance of winter kill in case of a plant shutdown is I

greatly increased.

A 27*F instantaneous drop in temperature could 1

f be lethal to most fish attracted to the discharge area.

i Since the pre-operational studies did not identify spawning i

areas in the vicinity of the plant, a study should be made to I

identify and quantify such areas.

Since walleye are one of the most numerous sport fish in the area, it would be appropriate to discuss their apparent need for a winter chill period and the effects of 1

l the heated water on this chill period.

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t 17 The aquatic sampling frequency should list the days samples were taken.

Sampling, to be more representative, should have been extended l

over the summer months, particularly during hot days and low flow

periods, f

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i Chemical Impact

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With the exception of chlorine, the chemical and sanitary wastes should cause no problems.

Peak concentrations of chlorine are above recommended levels.

Average concentrations of chlorine within the discharge channel are not adequately described.

When i

major portions of the river water are routed through the plant, l

there is a significantly diminished supply of dilution water remaining I

in the stream.

The discussion of the treatment of chemical wastes and blowdown 4

water in the settling basin should be expanded in the final statement.

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The final statement should present a'more thorough analysis of volume and concentration of the various waste chemicals entering the settling the constituents in the blowdown water, and the volume and pt a,

frequency of the blowdown water process.

The removal (fficiencies 1

of the pond and the volume and concentration of pollutants in the pond effluent before dilution with cooling water should be discussed.

I EPA has recommended in the past that the concentration of j

t chlorine in recei ving waters should be limited to the following:

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t Recommendation for Type of Criteria Residual Chlorine Continuous 0.002 mg/ liter r

Intermittent A.

0.1 mg/ liter not to exceed 30 minutes per i

day B.

0.05 mg/ liter not to j

exceed 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> per day i

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Procedures should be discussed for disposal of sludges from the chemical retention basin and from the sanitary wastes treatment system.

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MONITORING AND SURVEILLANCE The monitoring and gauging instrumentation system for water flow and temperature in the vicinity of the plant should be installed, operated, I

and maintained to assure complete representation of plant operation and l

river conditions. Operctional changes that are made to meet all water i

i quality standards on a continuous basis should be made in sufficient l

time to assure no detrimental environmental effects.

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21 Air Quality and Meteorology i

The local area is classified in the state's impicmentation plan as priority 11 with respect to particulate matter and priority Ill to i

carbon monoxide, nitrogen dioxide, hydrocarbons, and photochemical oxident f

i Icvels. The draft statement does not address any non-radiological air

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i quality effects associated with the operation of Monticello Nuclear

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l Generating Plant, even though the applicant presented some limited details

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in the environmental report.

The draft statement should include consider-I ation of the air quality effects of disposal of combustibic solids, if by incineration, and from operation of auxiliary boilers and diesel generators. ;

Relevant information such as number and types of sources, f requency of operation, fuel consumption rates, and type and chemical composition of y

fuel should be presented so that an independent evaluation may be made.

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Furthermore, the statement should clearly define the assumptions and I

bases for the quantities presented. For example, the AEC provided numerical j

values for air emissions from an " alternative" fossil fuel plant which 6

are significantly different than those provided by the applicant.

Without the bases ano assumptions used by the AEC and because of the l

Jack of information regarding fuel characteristics, it is not possibic j

t to resolve the differences nor to make an independent assessment.

There is no mention of the potential for accidents that could

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ii release non-radiuactive air contaminants. Included in the discussion

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t should be the types and quantities of volatile or hazardous materials that could be released, the probabilities of various types of accidents, and the environmental impact of each type of accidental release..

l The source of the meteorological data presented in the environmental

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statement should be defined.

In addition, in order to allow an independent j

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T evaluation of the local micro-meteorological diffusion characteristics, I

the environmental statement should include appropriate joint frequency l

analyses of uind speed, vind direction, and stability conditions supple-I mented with relevant monthly temperature and humidity data.

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23 Additional Comments During our review, ve noted that in certain instances the statement does not present sufficient information to substantiate the conclusions

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presented, k'hile much of the individual details may not be of cajor importance in evaluating the environmental impact of Monticello, the i

cumulative effect could be significant.

Therefore, it would be useful l

i in determining the impact of the plant if the following information I

were included in the final statement:

1.

The possibility of interaction of the cooling tower plume l

with gaseous pollutants, particularly from the Sherburne County power i

generating plants located 7 miles northwest of Monticello.

2.

Available information on the production rates, dispersion, and I

environmental effects of ozone generation by the power transmission lines

{

t and transformers.

t 3.

The effects of noise on the operating personnel and offsite, including the results of noise survey (dBA levels and octave band analyses).

4.

Additional details of the environmental radiation monitoring program, such as the location of sample points and frequency of sampling.

5.

The ultimate disposal of " solid wastes," including procedures to l

dispose of debris removed by the intake screens which will prohibit l

fi backwashing the debris to the river, j

6.

Additional information regarding the handling and disposal of r

dru==ed solid waste e.g., (1) how the drums will be decontaminated, (2) l the shielding provided in the.onsite storage area, and (3) the location of ti the onsite storage area.

+

1 F

l l

t I

fl

24 7.

Criteria for the utilization of the standby gas treatment system for controlling the iodine discharges during purging of the containment.

8.

An evaluation of the quantities of radionuclides which may be released undetected because of limitations of effluent monitor sensitivities.

I