ML20070K299

Confirms Commitments Made by Licensee at Meeting W/Licensee & NRC on 940707 Re Control Room Emergency Filter Sys Commitments

ML20070K299
Person / Time
Site:	Cooper
Issue date:	07/20/1994
From:	Horn G NEBRASKA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NLS940002, NUDOCS 9407260173
Download: ML20070K299 (6)

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e m COOPER NUCLEAR STATION . 4 P.O. 80X 98. SHOWNVILLE, NEBRASKA 68321  !

Nebraska Public Power District '"WWi hw  !

NLS940002 July 20, 1994 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555

Subject:

Control Room Emergency Filter System Commitments Cooper Nuclear Station Docket No. 50-298, DPR-46

References:

Meeting Between Nebraska Public Power District and the Nuclear Regulatory Commission on July 7, 1994; Same subject  !

" Control' Room Operator Dose Due to Inleakage to Control Room",

Nuclear Engineering Design Calculation, NEDC 94-071 l

Gentlemen:

The purpose of this letter is to confirm the commitments made by Nebraska Public, Power District (District) at the referenced meeting, provide the basis

l. why 0.03" Water Gauge (wg) positive pressure in the Control Room envelope provides adequate assurance that operator dose will remain within General Design Criteria ' (GDC) limits and to provide our current plan and schedule regarding this issue.

I. Prior to startup, the District will establish the following administrative, operability, and surveillance requirements for the Control Room Emergency Filter System:

1. The Control Room envelope pressurization operability limit will be

= +0.03" wg with respect to the adjacent buildings and atmosphere.

If this pressurization requirement cannot be met, the District will declare the system inoperable and enter.the appropriate Limiting.

Condition for Operation (LCO)

2. The Control Room envelope pressurization administrative operating limit will be a +0.04" wg with respect to the adjacent buildings and atmosphere. If this pressurization requirement cannot be met, the .;

District will initiate an accelerated testing frequericy to ensure l that the operability limit of a +0.03" wg is met. During the' period of accelerated testing,;the District will initiate efforts to restore the pressure to a +0.04" wg.

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3. The normal testing f requency will be once per month - (31 -days) .

4, The accelerated testing frequency will be once every two weeks cI14, days).

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U. S. Nuclear Regulatory Commission e

July 20,_1994 Page 2 ,

5. Accelerated testing may be suspended and the normal frequency resun.wd after two consecutive biweekly tests with results a +0.0'"fwg.

6. The surviillance interval may be extended by a maximum of 25% to allow-for adverse wind conditions.  :

4 II. Following startup, the District will perform the following additional actions:

1. A Technical Specification change will be submitted to allow for increased flow in the system.

2. Modifications and/or adjustments will be made to the Control Room Emergency Filter System to increase the ventilation flow and the pressurization margin. ,

3. Following NRC approval of Item 1 and completion of Item 2, operability and administrative limits for Control Room pressurization will be increased by 0.01" wg to a +0.04" wg and a +0.05" wg respectively.

4. The surveillance frequencies for the operability and administrative limits-will remain as described in Items I.3, I.4, and I.6.above.

5. Accelerated testing may be suspended and the normal frequency resumed after two consecutive biweekly tests with results  ;

a +0.05" wg.

III. The basis for the +0.03" wg operability limit is as follows: 3 No Loss of Offsite Power occurs which results in the ventilation systems in adjoining areas maintaining a negative pressure with respect to ,

atmosphere. This provides the least positive pressure margin for the

! Control Room with respect to atmosphere.

Based upon Nuclear Engineering Design Calculation, NEDC 94-071, the '

District has determined that the following constitutes the worst case

! conditions relative to operator dose:

1. 'The design basis Loss of Coolant Accident ,LOCA), whfab provides the highest source term. ,

2. A 30 minute fumigation period upon accident initiation'followed by  ;

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Stability Class 4 meteorological conditions, which provide the highest source term concentration.

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U. S. Nuclear Regulatory Commission July 20, 1994 Page 3 Given these conditions, the District has determined that a = +0.03" wg operability limit is acceptable for the following reasons:

1. Under the stated conditions, filtered outside air would be brought into the Control Room through the Emergency Filter System. Sources of unfiltered outside air consist of doors, cable and pipe penetrations, building wall openings, and two control Building HVAC ducts which pass through the envelopa. Positive pressurization of the Control Room envelope using filtered outside air ensures that leakage would be out of the envelope through door seals, penetrations, and building wall openings. .

I The Control Building HVAC ducts supply air to and exhaust air from the Emergency Switchgear Rooms. The supply duct is at a higher pressure than the Control Room envelope with the ventilation . system in service. This duct is designed and installed to seismic class I criteria and, therefore, postulating a catastrophic failure is not reymired. The ducts were extensively sealed when originally installed and recent testing has determined them to be leak tight.

2. The Control Room is surrounded on three sides by other buildings.

Wake effects from the adjacent buildings for most wind directions tend to reduce the atmospheric pressure surrounding the Control Building thereby increasing the Control Room's positive pressure margin. The one exception is a northerly wind when the north wall and roof of the Control Room could experience a positive pressure from direct impingement. It is conservatively estimated that a wind speed of 8 mph would result in maximum wind pressures on the exposed wall or roof of 0.024" wg (using a 0.8 pressure coefficient per ASHRAE). However, during this case, the Control Room is upwind of any expected plume release point thus limiting the consequences of any inleakage.

The instrumentation currently utilized for measuring Control Room positive pressurization is an inclined manometer graduated in 0.01" wg increments (i.e. ~ 0.005" wg accuracy). Combining the 0.005" wg accuracy with the 0.024" wg wind effect, assuming up to an 8 mph wind, shows that a reading of 0.03" wg or greater ensures positive pressure at wind speeds up to 8 mph.

The CNS testing program was reviewed against the potential for wind wake effects, wind speed, and direction which could adversely affect testing. The results of the review, and confirmed by testing, determined that the wind wake effect would be insignificant'for wind speeds less than 4 mph. Testing will be performed with wind speeds of 0-4 mph to prevent masking of potentially degraded conditions.

Per the " Handbook of Chemical Analysis Procedures," FEMA, the worct case meteorological conditions (Sta3111ty Class A) would occur ~at wind speeds of s 6.7 mph. The source term concentration in the vicinity of the Coatrol Room is inversely proportional to wind speed

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ti. S. Nuclear Regulatory Commission j July 20, 1994 Page 4 due to the dispersal effects of the higher winds. At wind speeds.

> 6 7 mph, the operator thyroid dose becomes insignificant regardless of the positive pressure in the Control Room.

Based upon the negligible dose effects at wind speeds > 6.7 mph and that 0.03" wg provides positive pressure up to wind speeds of 8 mph, maintaining a positive pressure in the Control Room envelope is not required at wind speeds a 8 mph.

3. Nuclear Engineering Department Calculation, NEDC 94-971, was performed to determine the worst case doses for desigit basis ,

conditions. If the actions described above are taken eo ensure that the control Room envelope remains at a positive pressura during the worst case bounding condition, the limits of 10 CFR 50, Appendix A, GDC 19 are met with significant margin. However, even_ assuming the ,

minimum Technical Specification allowable filter flow rate of 305 cfm and unfiltered inleakage of as much as 2000 cfm, the GDC 19 limits are still met (see Attachment A). ,

The District believes that the test pressure acceptance criteria and test frequencies described above will ensure that Control Room habitability will be maintained under all postulated accident conditions.

IV. A modification to the Control Room Emergency Filter System is being developed for installation during the 1995 refueling outage. This modification will significantly increase the filtered flow rate and increase the envelope pressure. More restrictive operability criteria will be developed as part of the modification.

If you have any questions, or need any additional information, please contact me.

Sincerely,

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G( R Horn VI. President - Nuclear Attachment

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cc: Regional Administrator USNRC - Region IV Arlington, Texas NRC Resident Inspector

-Cooper Nuclear Station cc: NPG Distribution ,

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flLS 94 0002

, July 20, 1994 Attachment ATTACHMENT A Control Room Operator Radiological Accident Dose The radiological dose to the Control Room operators following a design basis accident has been calculated per the methodology outlined in Reference 1.

Overall worst case operator dose has been determined to occur due to a design basis LOCA. This dose is shown as Case A in the table below. A sensitivity analysis has shown that using the maximum filtered flow rate as specified by Technical Specifications 3.12.A.2.c (341 cfm +10%) is the worst case for the dose analysis. The unfiltered flow rate is 10 cfm based upon the assumption that the Control Room envelope is positively pressurized and the only unfiltered inleakage is due to the opening and closing of doors. Some of the conservative assumptions utilized in the dose calculations are as follows:

1) Charcoal adsorber filter efficiencies of 95% and 90% are utilized for the Standby Gas Treatment and Control Room Emergency Filter Systems respectively.

2) No mixing in Secondary Containment and instantaneous mixing in Primary Containment and the Control Room are assumed.

3) Instantaneous release of fission products occurs with no time delay and with maximum allowable MSIV leakage added to containment leakage.

4) Worst case fumigation conditions occur for the first 30 minutes, followed by Stability Class A meteorological conditions. Site specific wind conditions are utilized to determine plume effects (X/0).

5) Source terms available for immediate release from containment include 100% of the noble gases and 25% of the halogens, in accordance with the Updated Safety Analysis Report and Regulatory Guide 1.3.

Cases B and C show the results of a sensitivity analysis for unfiltered flow rates. The unfiltered flow rate used for Case C (2000 cfm) is conservatively determined from Reference 2 assuming no positive pressurization'. For Cases B and C, the filtered flow is 305 cfm since, at the higher unfiltered flow rate, the minimum filtered flow rate (341 cfm -10%) is more conservative. For all cases, the Control Room operator doses are within 10CFR50, Appendix A, GDC 19 limits of 5 Rem whole body (and 30 Rem thyroid) per Reference 2.

Case Filtered Flow Unfiltered Thyroid Whole Body Rate (cfm) Flow Rate Dose (Rem) Dose (Rem)

(cfm)

A 375 10 11.39 1,74 B 305 1000 27.08 1.77 C 305 2000 29.75 1.78

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, fiLS94 0002

, July 20, 1994 Attachment

References:

i) " Nuclear Power Plant Control Room Ventilation System Design for Meeting General Criterion 19", K. G. Murphy and Dr. K. M. Campe, 13th AEC Air Cleaning Conference, 1974.

2) US NRC Standard Review Plan, Section 6.4, " Control Room Habitability i System", Rev. 2-July 1981.

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