ML19338E404

Forwards Evaluation of Modified Off Gas (Mog) Treatment Sys. Sys Cabable of Reducing Gaseous Radioactive Matls Release

ML19338E404
Person / Time
Site:	Dresden
Issue date:	06/07/1974
From:	Tedesco R US ATOMIC ENERGY COMMISSION (AEC)
To:	Goller K US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 8009290527
Download: ML19338E404 (7)

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in JUN 7 1974

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R sc K. Goller, Assistant Director for Operating Reactors, L

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TAR-879, REVIEW OF HODIFIED OFICAS TREATMENT SYSTEMS FOR DRESDEN-1 Plant Name: Dresden Unit I h.

Docket No: 50-10 L.1 Licent.ing Stage:.0L ireued Project Imader:

R. D. Silver h

Requested Completion Date: June 7, 1974 Description of Response: Review of Modified Offgas Treatment System L

for Dresden-1 F

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We have reviewed the Modified Offgas (MOG) Treatment System for Dresden-1. Our evaluation of the proposed system is enclosed.

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We find the system capable of reducing the release of radioactive materials in gaseous effluents during normal operation, including anticipated operational occurrences, to "as 10# as practicable" levels, in accordance with 10 CFR Part 20 and 10 CFR Part 50.34a.

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However, due to the potential for hydrogen explosions during

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periods when the recombiners are not operating, the design should include liquid seals downstream of rupture disks, and provisions

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to prevent permanent loss of liquid seals in the event of an explosion.

j-Original signed by:

Robert L. Tedeseo Robert L. Tedesco, Assistant Director for Containment Safety Directorate of Licensing Encic ure:

Review of M0G Treatment System for Dresden-1 cc: w/o enclosure A. Giambusso V. Mcdonald P

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System Description-q=;n The Modifie'd Offgas (MOG) Treatment,Sys' tem includes equipment and instrumentation to control the releases of radioactive materials in

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gaseous effluents from the Dresden Unit 1 main condenser air ejectors.

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The system will consist of redundant preheaters, catalytic recombiners, kb..

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moisture nacators, an existing holdup pipe, four 6.5 ton charcoal beds, and associated instrumentation and cooling equipment.

Prior to entering the charcoal beds, the gas will be dried to a dew point of A-

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40 F.

The charcoal beds will be maintained at a temperature of 70 F.

_ mE Upon exiting the charcoal beds, the remaining gases will be released

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to the atmosphere via a 300 f t stack.

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System Evaluation Dresden Unit I has a single shell condenser; therefore, we have employed

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a value of 10 scfm air inleakage in our evaluation.

Based on the para-meters given in Appendix B to WASH-1258, we calculate holdup times in the delay beds of I day for krypton and 18 days for xenon. With the addition of the catalytic recombiner, the existing 10 minute holdup

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pipe will provide a delay of one hour.

Using these parameters and the modified versica of the STEFFEG computer code given in Appendix C to WAsu-1258, we calculate a noble gas release rate from the M0G of 5300 Ci/yr, and we expect that almost all of the iodine from this source will be held in the charcoal.

The licensee has calculated a noble gas k

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release rate frem the M0G of 25,000 Ci/yr. The licensee's higher value is due to the n=":mption a higher air inleakage rate,(12 scfm)

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and a higher of f-gas rate (100,000 uCi/sec at 30 minutes decay) used

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in their evaluation.

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Dresden-l. shares a site with Dresden Units 2 and 3.

The releases i

j-havr; been calculated in the FES for Units 2/3 to be 48,000 Ci/yr/ unit.

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n of noble gases and 0.34 Ci/yr/ unit of I-131.

Unit I will release an

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_ additional 1900 Ci/yr of noble gases and 0.35 Ci/yr of I-131 from

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Based on our evaluation, the releases of radioactive materials' in gaseous effluents from Dresden Units 1, 2 and 3 will not result in an annual air dose, at or beyond the site j,

boundary, in excess of 10 mrad for gamma radiation and 20 mrad for beta radiation, the annual thyroid dose to an individual will not

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III, System Desian

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The proposed M0G system is designed to Quality Group D and non-Sef ;mic Category I criteria.

The system includes redundant preheaters, recombiners, desuperheaters, condensers, moisture separators, reheaters and particulate filters, and we therefore. consider that the e

design includes sufficient redundancy to perform its function during periods of maintenance and equipment downtime.

The design hac the i

capability to maintain concentrations'of radioactive materials in gaseous effluents at and beyond the site boundary within the limits of Table 11 Column 1 of Appendix B to 10 CFR Part 20 during periods s

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when the of fgas rate at 30 minutes decay is 70,000 uCi/sec,.which we

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consider the appropriate design value for a reactor of this size.

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3-In the design, dilution with steam is employed to maintain hydrogen

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concentrations below the lower explosive limit.

A hydrogen analyzer f:)

is provided to ensure that the recombiner is operating properly.

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The system is designed to 350 psig or higher to maintain its integrity in the event of a hydrogen explosion. However, the system is equipped r

with rupture disks which relieve to the building atmosphere in the event of an explosion.

Gases escaping by this pathway will be released, undecayed, via the 300 ft stack, to the environment.

Operating experience has shown that hydrogen explosions are expected to occur in BWR offgas systems, and that as long as one hour may be required to

' terminate the release following an explosion.

Because of the potential for a hydrogen explosion during periods when the recombiner is not operating, the design should include liquid seals downstream of rupture disks, and provisions to prevent permanent loss of seals following an explosion.

The design includes provisions to automatically terminate releases from s

the M0G in the event the concentrations of radioactive material in the i

gas entering the holdup pipe exceeds a predetermined level.

A radiation monitor is provided at the outlet of :he charcoal beds that will automatically alarm in the event concentrations of radioactive materials in the effluent exceed a predetermined value.

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Evaluation Pindings

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We have reviewed the sys'.em's capability to reduce releases of radio-

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active materials in gaseous effluents to "as low as practicable" levels I-in accordance with 10 CFR Parts 20 and 50.36a considering normal operation

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f and anticipated operational occurrences, the design provisions incorporated l

to preclude hydrogen explosions and to control releases of radioactive

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l materials in gaseous effluents in accordance with General Design Criteria 60 of Appendix A to 10 CFR Part 50, and the quality group i

and seismic design classification of the M0G system. We have reviewed l

the applicant's system descriptions, process flow diagrams, design i

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objectives, and design criteria for the components of the M0G system.

We have performed an independent calculation of the releases of radio-l active materials in gaseous effluents based on the method, of WASH-1258.

The basis for acceptance in our review has been conformance of the appli-

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cant's designs, design criteria, and design bases for the gaseous waste system to the applicable Commission Regulations referenced above, as well as to staff technical positions and industry i

standards.

Based on our evaluation, we find the proposed gaseous l

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waste system acceptable.

l However, due to the potential for hydrogen explosions during startups and other periods when the recombiner is bypassed, the design should i

l include liquid seals downstream of rupture disks, and provisions to iG prevent permanent loss of seals following an explosion.

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References *

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Appendix B to 10 CFR Part 20 - Published December 31, 1970.

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Appendix A to 10 CFR Part 50 - Published July 15, 1971.

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10 CFR Part 50 Section 50.34a - Published March 16, 1971.

4. -WASH-1258_" Final Environmental Statement Concerning Proposed Rule

• ""F Making Action: Numerical Guide.for Design Objectives and Limiting Conditions for Operation to Meet the Criterion "As Low As Practicable" for Radioactive Material in Light-Water-Cooled Nuclear Power Reactor 9::.

Efiluents" Vol. 2, July 1973.

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