ML20214P475

Responds to 860919 Request That Filter Be Installed on Condenser Offgas Sys Line at TMI-1 to Reduce Possible Radioactive Releases to Environ.Nrc Does Not Believe Placing Filter on Sys Will Provide Measurable Improvement in Safety

ML20214P475
Person / Time
Site:	Three Mile Island
Issue date:	11/26/1986
From:	Harold Denton Office of Nuclear Reactor Regulation
To:	Davenport D CONCERNED MOTHERS & WOMEN ON TMI
References
NUDOCS 8612040230
Download: ML20214P475 (3)

Text

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O% og NOV 2 61986 Distribution: Docket File NRC & L PDRs HDenton RVollmer DCrutchfield FMiraglia/MSchaaf JStolz RIngram Ms. Deborah Davenport PPAS DMossburg JThoma/TRoss Concerned Mothers and Women PBD#6 Yellow Ticket File: 86906 RWeller 1802 Market Street Of6 tao Camp Hill, Pennsylvania 17011

Dear Ms. Davenport:

In your letter of September 19, 1986, you requested that a filter be installed on the condenser off-gas system exhaust line at Three Mile Island Unit 1 (TMI-1) to reduce possible radioactive releases to the environment via this pathway that could result from steam generator primary-to-secondary leakage during accidents or normal operating conditions.

The presence of radioactive materials (i.e., noble gases, iodines and particulates) in the secondary coolant system of a pressurized water reactor (PWR) such as TMI-1 results primarily from primary (i.e., reactor coolant system) to secondary leakage of radioactive materials present in the reactor coolant. Small quantities of radioactive materials are normally present in reactor coolant as a result of corrosion product activation and fission i product escape from fuel rod assemblies. Both primary-to-secondary leakage and the fission product activity (e.g., I-131) in the reactor coolant s are closely monitored and controlled within appropriate limits in the plant Technical Specifications. As a result, the secondary systems in pressurized water reactors are generally free from significant levels of contamination.

Historically, releases from PWR secondary systems to the environment have not been a sionificant contributor to offsite doses. With respect to TMI-1, plant airborne releases (including condenser off-gas exhaust) for the most recently documented semi-annual period (January 1, 1986 - June 30, 1986) were less than 1% of the annual dose objectives in NRC regulations (Appendix I to 10 CFP Part 50). The Appendix I regulations are intended to ensure that releases of radioactive materials in liquid and gaseous plant effluents are kept "as low as is reasonably achievable" during normal reactor operations, including anticipated operational occurrences. (Appendix I does not apply to accidentconditions). The dose objectives of Appendix I are incorporated in the TMI-1 Technical Specifications to provide reasonable assurance that the annual dose to any individual from atmospheric releases of radioiodines and particulates will not be in excess of 15 mrem to any organ. TMI-1 operational history has demonstrated that existing plant design provisions for controlling releases of radioactive materials to the environment during normal operation are adequate to ensure that Appendix I objectives are met.

Notwithstanding the adequacy of plant design to ensure compliance with Appendix I, the NRC staff raised concerns in early 1983 with General Public Utilities Nuclear Corporation (GPUN, the TMI-1 licensee) about the j condenser off-gas radionuclide monitoring system used during normal J operations. The TMI-1 condenser off-gas monitoring system, as originally installed, was capable of continuously monitoring only the noble gases.

To measure the levels of radiciodines and particulates in the off-gas,

" grab" samples had to be taken periodically. The NRC staff's concerns were 861204C230 DR 861126 ADOCK 05000289 PDR

NOV 2 61986 specifically related to the licensee's inability to continuously sample condenser off-gas for radioiodine during normal plant operations. In response to this concern, GPUN committed in 1984 to modify the condenser off-gas monitoring system to provide the capability for continuous sampling of radiciodine. This modification will be completed during the present refueling outage (i.e., by March 1987). Design provisions for monitoring and samplina of condenser off-gas during accident conditions have already been installed as a result of requirements imposed on the licensee prior to the restart of TMI-1.

In the event of accident or upset conditions, such as major primary-to-secondary leakage from a postulated steam generator tube rupture, an immediate indication of radioactivity in the condenser would be detected by the condenser off-gas exhaust line radiation monitor and an automatic alarm would be sounded in the control room. The operator would then monitor the effluent release and, in accordance with procedures, isolate the leaking steam generator by closing the main steam isolation valve to ensure projected doses are within the regulatory limits for normal operation (10 CFR Part 20) (i.e., less than 1500 mrem to any organ from radiciodines and particulates). Thus, offsite doses would be controlled to a low level. For the rupture of a single steam generator tube and assuming no action is taken by the operator to isolate the affected steam generator (which is an event postulated in the safety review of the plant),

total offsite doses would be well below regulatory limits for accident conditions (10 CFR Part 100). This event is addressed by approved accident analyses described in the TMI-1 Final Safety Analysis Report (FSAR).

Based on the projected impact of releases to the atmosphere via the condenser off-gas exhaust during normal or accident conditions (as discussed above), the NRC staff concludes that existing design provisions are adequate to protect public health and safety, and there is no justification for requiring GPUN to place a filter on the condenser off-gas exhaust. The condenser off-gas exhaust is not a major pathway for release and, as you mention in your letter, this conclusion is also applicable to the THI-2 accident experience. I should point out that a filter was placed on the TMI-2 condenser off-nas exhaust, following the accident, primarily to reduce contamination of auxiliary building internal areas. This filter, and filtration added to the radwaste chemical lab trailer exhaust, were also installed by the licensee to reduce further any offsite releases, regardless of the minimal benefit to be derived.

Although the filter served to reduce some of the lingering effluent releases from the condenser exhaust to the environment, this source posed no significant risk to the public health and safety.

In summary, the NRC staff does not believe placing a filter on the TMI-1 condenser off-gas system will provide a measurable improvement in safety.

I trust this letter is responsive to your concerns.

Sincerely.

Original Signed By:

Rickd H. .#xr Harold R. Denton, Director Office of Nuclear Reactor Pegulation PBE *See previous white for concurrences 4

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NOV 2 6 G86 specifically related to the licensee's inability to continuously sample condenser off-gas for radiciodine during normal plant operations. In response to this concern, GPUN committed in 1984 to modify the condenser off-gas monitoring system to provide the capability for continuous sampling of radiciodine. This modification will be completed during the present refueling outage (i.e., by March 1987). Design provisions for monitoring and sampling of condenser off-gas during accident conditions have already been installed as a result of requirements imposed on the licensee prior to the restart of TMI-1.

In the event of accident or upset conditions, such as major primary-to-secondary leakage from a postulated steam generator tube rupture, an immediate indication of radioactivity in the condenser would be detected by the condenser off-gas exhaust line radiation monitor and an automatic alarm would be sounded in the control room. The operator would then monitor the effluent release and, in accordance with procedures, isolate the leaking steam generator by closing the main steam isolation valve to ensure projected doses are within the regulatory limits for normal operation (10 CFR Part 20) (i.e., less than 1500 mrem to any organ from radiciodines and particulates). Thus, offsite doses would be controlled to a low level. For the rupture of a single steam generator tube and assuming no action is taken by the operator to isolate the affected steam generator (which is an event postulated in the safety review of the plant),

total offsite doses would be well below regulatory limits for accident conditions (10 CFR Part 100). This event is addressed by approved accident analyses described in the TMI-1 Final Safety Analysis Report (FSAR).

Based on the projected impact of releases to the atmosphere via the condenser off-gas exhaust during normal or accident conditions (as discussed above), the NRC staff concludes that existing design provisions are adequate to protect public health and safety, and there is no justification for requiring GPUN to place a filter on the condenser off-gas exhaust. The condenser off-gas exhaust is not a major pathway for release and, as you mention in your letter, this conclusion is also applicable to the TMI-2 accident experience. I should point out that a filter was placed on the THI-2 condenser off-gas exhaust, following the accident, primarily to reduce contamination of auxiliary building internal areas. This filter, and filtration added to the radwaste chemical lab trailer exhaust, were also installed by the licensee to further reduce any offsite releases, regardless of the minimal benefit to be derived.

Although the filter served to reduce some of the lingering effluent releases from the condenser exhaust to the environment, this source posed no significant risk to the public health and safety.

In summary, the NRC rtaff does not believe placing a filter on the TMI-1 condenser off-gas system will provide a measurable improvement in safety.

I trust this letter is responsive to your concerns.

Sincerely, Harold R. Denton, Director Office of Nuclear Reactor Regulation PBE VNP i

E.,JWermeil 4

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