ML17334A994

Requests Exemption from Design Basis for Main Steam Noble Gas Effluent Radiation Monitors Located Downstream of Porv. Range Reported in 851015 Ltr Clarified.Fee Paid

ML17334A994
Person / Time
Site:	Cook
Issue date:	09/08/1986
From:	Alexich M INDIANA MICHIGAN POWER CO. (FORMERLY INDIANA & MICHIG
To:	Harold Denton Office of Nuclear Reactor Regulation
References
AEP:NRC:0678Z, AEP:NRC:678Z, NUDOCS 8609150300
Download: ML17334A994 (6)

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ACCESSION NBR: 8609150300 DOC. DATE: 86/O'P/08 NOTARIZED: NO DOCKET FACIL."50-315 Donald C. Cook Nuclear Power Planti Unit ii Indiana 5 05000315 50-316. Donald C. Cook Nuclear Power Planti Unit 2. Indiana 5 05000316 AUTH. NAhfE AUTHOR AFFILIATION ALEXICHif'. P. Indiana Zc Michigan Electric Co.

RECIP. NANE REC IP IENT AFFILIATION DENTONi H. R. Office of Nuclear Reactor Regulationi Director (post 851125

SUBJECT:

Requests exemption from design basis for main steam noble gas effluent radiation monitors located downstream of PORU.

Range reported in 851015 ltr clarified. Fee paid.

DISTRIBUTION CODE: A0010 COPIES RECEIVED: LTR Submittal: General Distribution Q ENCL Q SI ZE:

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INDIANA 8 MICHIGAN ELECTRIC COMPANY P.O. BOX 16631 COLUMBUS, OHIO 43216 September 8, 1986 AEP:NRC:0678Z Donald C. Cook Nuclear Plant Unit Nos. 1 and 2 Docket Nos. 50-315 and 50-316 License Nos. DPR-58 and DPR-74 MAIN STEAM NOBLE GAS EFFLUENT RADIATION MONITORS REQUEST FOR EXEMPTION Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Dear Mr. Denton:

The purpose of this letter is Lo request an exemption from the design-basis range for the main steam noble gas effluent radiation monitors located downstream of the power-operated relief valves (PORVs) and to clarify the range reported in a previous letter dated October 15, 1985.

In our letter to you dated October 15, 1985 (AEP:NRC:07730),

reported that the range of the main steam noble gas monitors was 3 uCi/cc it was (microcuries per cubic centimeter) to 20 x 10 uCi/cc. The range reported was based solely upon the monitors'esponse to Xe-133, not a Xe-133 equivalent mixture.

The Xe-133 equivalent mixture is determined by the steam generator tube rupture (SGTR) accident scenario, which results in a release of radioactivity. In the attachment to our letter AEP:NRC:0678W, dated June 23, 1986, we indicated that the only credible accident scenario for determining the main steam radioactivity concentration was a steam generator tube rupture. The noble gas monitors'esponse to this mixture and therefore the monitors'ange are dependent on the geometry of the system and the relative quantities of the various radionuclides released.

In this case the geometry is a thick-walled carbon steel pipe surrounding the steam effluent which is several inches from the monitor itself. This geometry leads to a high degree of attenuation of low-energy gamma rays (Xe-133) in the pipe walls, which are essentially overshadowed by the dose contribution from the high-energy gamma rays seen by the monitor.

Therefore, the monitor must be calibrated to account for these low-energy gamma rays. The calibration constant calculated for a given accident scenario directly limits the range capability of the monitor.

Based upon the referenced accident scenario, the maximum radioactivity concentration expected in the main steam effluent released from the PORV is 0.263 uCi/cc Xe-133 equivalent. This value corresponds to a total count rate of 323 cpm, taking shielding of the pipe into account.

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Mr. Harold R. Denton AEP:NRC:0678Z Studies of mockups of the PORVs by our consultant show that the maximum count rate remains essentially linear up to 200,000 cpm for these monitors. Based upon this maximum count rate and shielding from the pipe, the monitors'esponse at 200,000 cpm would correspond to 162 uCi/cc Xe-133 equivalent. In practice, however, we believe it imprudent to require that these monitors operate beyond the linear region of their response cuges.

Therefore we request an exemption from the design-range maximum of 10 uCi/cc listed in NUREG-0737 Table II.F.1-1, wi(h respect to these monitors.

In place of the above value, we wish to use 10 uCi/cc Xe-133 equivalent activity. As discussed above we believe this value will adequately cover any credible accident release, since our calculated release from an SGTR is only 0.263 uCi/cc.

Pursuant to the requi ement" of 10 C"R 170.12(c), we have enclosed an application fee of $ 150.00 for review of this exemption request.

This document has been prepared following Corporate procedures which incorporate a reasonable set of controls to insure its accuracy and completeness prior to signature by the undersigned.

Very truly yours, M. P. Alexich Q@~q C~

Vice President cm Enclosure cc: John E. Dolan W. G. Smith, Jr. - Bridgman R. C. Callen G. Bruchmann G. Charnoff NRC Resident Inspector - Bridgman

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