ML20217R355

Forwards Further Clarification of Applicability of X/Q for Loss of Coolant Accident to Main Steam Line Break Event

ML20217R355
Person / Time
Site:	Byron
Issue date:	08/28/1997
From:	Hosmer J COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9709050092
Download: ML20217R355 (3)

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n,mnu,nw ratoi renon omquny 1 UM) Opus l*!.K r lh3Wfiork GfoiC, Il. (46 I WOI August 28,1997 i

U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555

Subject:

Additional Information Pertaining to the Tecimical Specifi:ation Amendment for the Reduction in in Dosc Equivalent lodine Byron ' Units I and 2 NEGlo.S et Numbers: 50.454 and 455 k

Reference:

J. Ilormer letter to the Nuclear Regulatory Commission dated August 22,1997, transraitting Dose Consequence Calculation for Exclusion Area Boundary and Low Population Zone The referenced letter transmitted the Commonwealth Edison Company (Comed)'s dose calculation for the control room. Attached is further clarification of the applicability of the X/Q for the Loss of Coolant Accident to the Main Steam Line Break event.

Comed is looking forward to meeting with the Staff on September 4th to further discuss any issues related to the dose calculations.

I If you have any questions, please contact this office, Sincerely,

/./n }l,A n~*~,

[ John B. Ilostrier Engineering Vice President Attaciunent I

cc:

A Beach, Regional Administrator - Rlli G. Dick, Byron Project Manager - NRR S. Burgess, Senior Resident inspector - Byron Office of Nuclear Facility Safety - IDNS 9709050092 970828 ADOCK 050004 4

(; y fDR k:nla b> Ton.082897 doe:1 A Unicom Conque) 1>

Applicability of the LOCA X/Q for the MSLB Scenario For the LOCA's impact on the control loom dose, the assessment described in the Byron UFSAR, Section 6 4 specifies a X/Q based on the site meteorological data and the Murphy-Campe Diffuse Source-Single Receptor Model The Control Room total dose is comprised of four components, three of which are dependent on site meteorology. For purposes of the design basis assessment, leakage of radioactivity from the containment air space is conservatively assumed to reach the emironment through cracks at unspecified locations on the containment surface This leakage is captured and completely mixed in the turbulent wake downwind of the power plant structures The parameter, X/Q,is the relative downwind concentration per unit release and is a measure of atmospheric dispersion.

The atmospheric dispersion of this source of r 4dioactivity, a diffuse source, was compared to the X/Q dispersion models available in the Murphy-Campe paper (Reference 1) referenced by the NRC in Standard Review Plan 6.4. The X/Q model selected for use was Equation 6 lDilTuse Source Point Receptorj of the Murphy Campe paper. This model conservauvel) assumes that the release is a diffuse source [the containment surface] and travcis m an unencumbered straight line path to a receptor of interest.

The two emergency control room air intakes for Dyron are located within the turhine buildmg at cicvation 466'-9" on the common auxiliary building turbine buildmg wall. For reference, the ground level turbine building floor clevation is 401'-0, an intermediate floor is at clevations 426' 0, the main turbine building deck is at clevation 451'-0. The Murphy-Campe, Equation 6 model conservatively assumes that the turbine building structure is not avadable, as the only parameters m Equation 6 a.c the containment cross sectional area, the containment diameter (14T-0), and the plan view distance between the containment surface and the receptor (100' 0). The model basically assumes that the plant building complex is reduced to a smgle containment standing in free space with the point receptor also standing in free space at a distance equal to the plan view distance between the containment and the air intake cited above.

The X/Q value for the first 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> time period was determined from the meteorology data given m UFSAR, scetion 2.3. Specifically the fifth percentile wud speed (that speed exceeded 95% of the time)

(0.67 m/s) was used to determine this initial period X/Q The X/Q values for time periods beyond the initial 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> wcrc determined usir,1 the guidance of Murphy-Camp (Reference 1). Specifically, the guidance of Table i provided the percentile wind speeds to be used to account for temporal variations in wind speed and factors to account for temporal variations in wind direction The values of X/Q used in this analysis are given in Table 6 4-la. The value of X/Q for the 1st 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> of the LOCA was 4.05E 3 s/m'.

4 The MSLB accident assumes that a main steam line ruptures at a location upstream of the main steam isolation vahes (MSIVs), Points A and B of Figure 1. The resultant overpressure is relieved to the environment through blowout panels and doors in one of the safety valve houses located at ground level and at the outer surface of the containment (UFSAR Section 3 0 Attachment A3.6). Two of these valve houses are provided for cach unit.

The scenario (for radiological assessment purposes) proceeds as follows: the steam release from the pipe break enters the environment via the valve house, is captured in the downwind turbulent wake caused by the containment and other plant structures, then is transported to the control room emergency air intake,

. No credit is taken for the buoyant rise of the escaping high temperature steam.

The Murphy-Campe model described for the transport of MSLB cfiluents is the same as that for the LOCA cmuents; therefore the same value of X/Q is conservatively used in radiological dose assessments for both scenarios.

1. Reference 1. K. G. Murphy and K. M. Campe. " Nuclear Power Plant Control Room Ventilation System Design For Meeting General Criterion 19". Paper presented at the 13th AEC Air Cleaning Conference, August 1974.

k:nla. byron 082897 doc 3

LOCA Vs MSLB Leakage Locations s

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s MSlV Rooms

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I 100', Distance used in Steam Line Tunnel /

Control Room Dose Aux. Bldg (Elev. 383')

1I Analysis Turbine Bldg. Floor Elevations:

Control Room Intake in Turbine Turbine Bldg.

40l',426' & 45l' Bldg. (Elev. 466'9")

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