RBG-16-179, Summarizes Analysis of Inclusion of Redundant Chlorine & Ammonia Detectors in Control Bldg Ventilation Sys Design. NRC Reconsideration of Requirement Requested.Meeting in Bethesda,Md in Nov Proposed

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Summarizes Analysis of Inclusion of Redundant Chlorine & Ammonia Detectors in Control Bldg Ventilation Sys Design. NRC Reconsideration of Requirement Requested.Meeting in Bethesda,Md in Nov Proposed
ML20085K944
Person / Time
Site: River Bend  Entergy icon.png
Issue date: 10/17/1983
From: Booker J
GULF STATES UTILITIES CO.
To: Schwencer A
Office of Nuclear Reactor Regulation
References
RBG-16-179, NUDOCS 8310210221
Download: ML20085K944 (5)


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GULF STATES ; UTXLITIES COMPANY post OFFICE box 2951

  • BEAUVONT, TEX \S 77704 A R EA CORE 4J9 83a 663
  • October 17, 198$

RBG- 16,179 -

File Code G9.S.6 I

Mr. A. Schwencer, chief Licensing Branch No. 2 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D. C. 20555 7

Dear Mr. Schwencer:

7 RIVER BEND STATION - UNITS 1 & 2 DGCKET NO.30-458 & 50-459 2

This letter responds to your letter dated July 15, 1983, to W. J.

Cahill, Jr., which stated the NRC staff's pc.sition that inclusion of redundant chlorine and ammonia detector; in the design of the River Bend Station centrol building ventfjation system was required. As your letter indicated, the NRC re' acned this pasition as a result of its scoping study, which used the T0XCHM model.

CSU trusts that this letter will provide a foundution for subsequent discussions with e.ognizant NRC staff on this sabject. Accordingly, the remainder of this letter provides a summary of the analysis, in more detail than presented in the Final Safety I.nalysis Report (FSAR).

GSU concluded that the River Bena control room operator's ability to perform his responsibilities adequately throughout the unlikely event of an accidental toxic chemical release and subsequent infiltration into the control room will not be compromised by the lack of chlorine and ammonia detectors. This position was ascertained'from the results of a comprehensive, yet conservative, control room habitability evaluation based, in part, on al. available NRC guidance on this subject. SurPl emental sources o. technical literature were consulted, especially with respect.to human te.ponses to exposure from various toxic cnemicals, in areas where more recent information. was necessary to support the analysis. The following sources of NRC guidance were consulted:

o Regulatory Guides 1.78 and 1.95

'o NUREG-0570 and -0800 (Sectivn 0.2.3)

GFO'used a three-tier approach to evaluate the effects of potential accidental releases of both stationary onsito and stationary and transported offsics toxic chemicals on the habitability of the main 8310210221 831017 PDR ADOCK 05000458 800;i A PDR l l C)

control room. Time-history concentrations in the control room resulting from a hypothetical accidental release of every stationary onsite, stationary offsite, and sufficiently transported offsite toxic chemical was estimated with Stone & Webster Engineering Corporation's (SWEC's) VAPOR computer program. The results were compared with the most recently documented human toxicity limits. The VAPOR program has been qualified according to standard SWEC guidelines, which included manual calculations.

SWEC's VAPOR program quantifies the following three processes that

- need to be addressed in a control room habitability evaluation:

i o Transfer of mass to the atmosphere o Dispersion of the mass in the atmosphere o Buildup of the mass in the control room

The VAPOR model is based on the methodology outlined in NUREG-0570, Toxic Vapor Concentrations in the Control Room Following a Postulated
Accidental Release, and the assumptions described in Regulatory Guide 1.78. Specifically, the following assumptions and approaches were used

o "The entire inventory or cargo in one container is released" (NUREG-0570, page 23).

o "The area of spill is predicted by equation (2.1-1), with a minimum thickness of I cm" (NUREG-0570, page 23),

o "The vapor, in the form of a puff or plume, moves directly toward the air intakes of the control room" (NUREG-0570, page 23).

o The centerline concentrations of the vapor are calculated using the formulas in Section 2.2 of NUREG-0570 (page 23).

o The control room air exchange rate is calculated using the formula in Section 2.3 of NUREG-0570 (page 22).

o Concentrations at the outside air intake and inside the control room at any instant are estimated by the formulas in Seution 2.4 of NUREG-0570 (page 22).

o The transfer of mass into the atmosphere is calculated using the formulas in Section 2.1 of NUREG-0570.

The first tier of the evaluation concluded that all but four toxic chemical scenarios resulted in maximum control room concentrations that remained below the applicable toxicity limits for the entire duration of the postulated toxic chemical release. Further consideration of these chemicals was no longer warranted due to the results of the first tier analysis. The following four cases, which involved just chlorine and ammonia, were then submitted for second tier evaluation:

Case Description

A Barge shipments of anhydrous ammonia B Truck shipments of chlorine on U.S. Highway 61 and State Highway 964 C Railroad tank car, containing chlorine, located at the Crown Ze11erbach Paper Mill D Chlorine stored in a rail car at Big Cajun Na. 2 The second tier analysis focused on the rate of buildup of the chemical of concern in the control room atmosphere, since operator habitability is the overall objective of this evaluation. This phase of the analysis was keyed to guidance set forth in Regulatory Guide 1.78.

Section A of Regulatory Guide 1.78 states, in part that:

"This guide describes assumptions acceptable to the Regulatory Staff to be used in assessing the habitability of the control room during and after a postulated external release of hazardous chemicals and describes criteria that are generally acceptable to the Regulatory Staff for the protection of the control room operators."

Table C-1 of Regulatory Guide 1.78 lists both chlorine and ammonia as hazardous chemicals for which this guide is considered applicable.

Section C.7 of Regulatory Guide 1.78 states, in part, the following:

The detection mechanism for each hazardous chemical should be considered. Human detection may be appropriate if the build-up of the hazardous chemical in the control room is at a slow rate due to slow air turnover. The air flows for infiltration, makeup, and recirculation should be considered for both normal and accident conditions. The volume of the control room and all other rooms that share the same ventilating air, during both normal conditions and accident conditions, should be considered. The time required for buildup of a hazardous chemical from the detection concentration to the toxicity limit should be considered (footnote: the time from detection to incapacitation should be greater than two minutes. Two minutes is considered sufficient time for a trained operator to put a self-contained breathing apparatus into operation, if these are to be used). (Emphases added)

Section B, Paragraph 5 of Regulatory Guide 1.95 also addresses the two minute concentration limit, by in part stating:

This concentration the toxicity limit.. 15 ppm by volume (45 mg/cu. m.)..., is the maximum concentration that can be tolerated for two minutes without physical incapacitation of an average i human (i.e., severe coughing, eye burn, or severe skin l irritation).

These statements formed the basis for the second tier assessment. The objective of this analysis was to determine, for each of the four i

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cases, whether the control room concentration increased from a human detection odor threshold concentration to the toxicity limit concentration within 2 minutes under a spectrum of meteorological conditions. If this did not occur, then the habitability of the control room would not be jeopardized as the operator would have sufficient time to don his breathing apparatus after smelling the toxic chemical. Accordingly, VAPOR was run for various wind speed / stability combinations, recognizing that the control room concentration buildup rate is a function of chemical puff and/or plume transport (e.g., the faster the wind speed, the more rapidly the toxic cloud moves past the intake, thus reducing the amount of material infiltration into the control room).

This evaluation concluded that for Case B,_ buildup from detection did not exceed the toxicity limit within 120 seconds for all meteorological conditions. For the other three cases, under certain meteorological conditions the buildup did exceed the toxicity limit within 120 seconds. Accordingly, Cases A, C, and D were submitted for a third and final tier of analysis.

It should be noted here that conservatisms were applied to che second tier of analysis in the areas of odor detection by the human nose and human toxicity levels. The "120-second clock" was started with odor detection concentration values that were above the lower human perception levels and was stopped with human toxicity concentration values below levels that could be withstood. This approach resulted in shorter elapsed times and consequently yielded a higher frequency of problem meteorological scenarios than if more realistic perception levels had been used.

The third tier of the evaluation assessed the frequencies of occurrence of the few wind speed / stability combinations that led to unacceptable builaup times from the wind stability summaries (30-ft winds) presented in the RBS FSAR. The relevant wind direction sectors considered for each case and the frequencies of occurrence of unacceptable buildup meteorological conditions were:

Frequency of Unacceptable Case Wind Direction Sectors Buildup Conditions A South through (clockwise) 0.44%

West C South-Southeast 0.00%

D Southwest 0.04%

Only two cases (Cases A and D) have the potential, under a very small frequency of climatological conditions, of resulting in an unacceptable buildup of toxic chemicals in the control room environment. GSU perceives that since the analytical techniques employed are highly conservative (e.g., NUREG-0570 and Regulatory Guide 1.78 assume that crosswind dispersion is absent, since the wind direction always directly transports the spilled chemical to the control room intake) and the remaining events are of such low frequency, the actual possibility of jeopardizing the control room operator's capacity to perform his required tasks is remote. It is GSU's opinion that such a remote possibility does not warrant the use

of detectors, since the mitigative value of such detectors, in light 1 of the above analysis, is imperceptible. l l

Consideration should be given that the concentrations determined above j are those that concern the operator, i.e. those concentrations in the

control room. The Staff's scoping study identified in your July 15, 1983 letter did not address this concentration but that at the control t l room air intake. These concentration's are expected to be quite different due to air volume of the control room and other rooms that ,

share this ventilating equipment.

Further, GSU requests that the Staff consider the use of human detection and self-contained breathing apparatus as allowed by '

Regulatory Guide 1.78 for buildup of concentrations at a slow rate.

i GSU believes this appropriate for our application because of the insignificant frequency of unacceptable meteorological conditions.

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, Gulf States Utilities requests that the Staff review the methodology and conservatisms described above and reconsider its requirement from the July 15, 1983 letter for ammonia and chloride detectors. GSU i

further proposes that a meeting be established in Bethesda during November, 1983 to discuss this issue. GSU will contact the NRC t Project Mannger to establish the meeting date.

Sincerely,

p. 2. W J. E. Booker Manager-Engineering Nuclear Fuels & Licensing River Bend Nuclear Group ERG /JWL/kt L

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