ML20128E877

Informs That Util Proposed Corrective Actions to re-establish Operability of Control Room Emergency Ventilation Sys May Not Be Acceptable for Listed Reasons

ML20128E877
Person / Time
Site:	Browns Ferry
Issue date:	01/29/1993
From:	Hebdon F Office of Nuclear Reactor Regulation
To:	Medford M TENNESSEE VALLEY AUTHORITY
References
TAC-M83348, TAC-M83349, TAC-M83350, NUDOCS 9302110127
Download: ML20128E877 (9)

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k p, UNITED $TATES NUCLEAR REGULATORY COMMISSION j- j WAsHINoTON. D, C. 70555

% + January 29, 1993 Docket Nos, 50-259, 50-260 and 50-296 Tennessee Valley Authority ATTN: Dr. Mark 0. Medford, Vice President Nuclear Assurance, Licensing and fuels 3B Lookout Place 1101 Market Street Chattanooga, Tennessee 37402-2801

Dear Dr. Medford:

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SUBJECT:

CONTROL ROOM EMERGENCY VENTILATION SYSTEM CORRECTIVE ACTIONS -

BROWNS FERRY NUCLEAR PLANT (TAC N05. M83348, M83349, AND M83350)

By letter dated July 31, 1992, the Tennessee Valley Authority (TVA) submitted a description of their proposed corrective actions to resolve previously, identified deficiencies with the Control Room Emergency Ventilation System (CREVS) at the Browns Ferry Nuclear Plant (BFN), Units 1, 2 and 3. In this letter, TVA stated that once these corrective actions were implemented, BFN would be in full compliance with General Design Criterion (GDC) 19 of Appendix A to 10 CFR Part 50. In addition, TVA-submitted an application dated September 10, 1992, that would amend the BFN Technical Specifications (TS) to re-establish operability requirements for CREVS.

As part of our review of the aforementioned submittals, the staff conducted an onsite audit during the week of December 8, 1992, The purpose of this audit and the staff's preliminary conclusions are summarized in Enclnsure 1. During the course of the audit, the staff raised a number of specific questions, identified the need for certain additional information, and made some general observations that are also documented in. Enclosure 1. The substance of this enclosure was previously provided to TVA during an exit meeting by the staff on December 11, 1992.

As of this date, we have completed enough of our review to conclude that TVA's proposed corrective actions to re-establish operability of CREVS may not be acceptable for the following reasons:

1. It does not appear that TVA has adequately quantified the unfiltered in-leakage into the control room envelope. In our judgement, an inappropriate test was utilized, in addition, it appears that neither the leakage past various dampers nor leakage from ductwork which penetrates the control bay habitability zone (CBHZ) were quantified. Therefore, the unfiltered in-leakage of 3717 cfm may be.

an underestimation. The actual quantity of unfiltered in-leakage s into the CBHZ is a critical assumption in TVA's control room operator dose calculations for establishing compliance with GDC 19, 9302110127 930129 PDR ADOCK 05000259 _ . _ _

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Dr. Marie 0, Medford January 29, 1993 2 .- TVA did not include as part of its TS amendment application a surveillance requirement to quantify ;BHZ in-leakage as stated in the staff's safety evaluation associated with the issuance of License Amendment 173 to DPR-52, c' justify why such a surveillance requirement is unnecessary.

As noted above, TVA conducted a test to quan* 4 fy unfiltered in-leakage into the CBHZ, Our technical concerns with the adequacy of TVA's special test procedure are detailed in Enclosure 2.

The control room habitability issue at BFN must be resolved prior to Unit 2 -

Cycle 7 restart. Recognizing the limited time available between now and then, we suggest a meeting as soon as possible to discuss the staff's initial conclusions described above, furthermore, in order to support ongohg staff review efforts, TVA is requested to formally respond to the questions. .

additional information, observations, and concerns identified in Enclosures 1 and 2 within the next 30 days.

This requirement affects 9 or fewer respondents and, therefore, is not subject to the Office of Management and Budget review under P.L.96-511.

If there are any questions regarding this letter or its enclosures, please contact Thierry M. Ross at (301) 504-1474.

Sincerely, Signed By Vic Nerses Frederick J. Hebdon, Director Project Directorate 11-4 Division of ReactLr Projects - I/11-Office of Nuclear Reactor Regulation

Enclosures:

1. Exit Meeting Summary

2. Comments un Special Test i

cc e/ enclosures:

See next page OFC PDil-4/LA PDil-4/PMN PDll-4/PM/U PD_ll-4/Do NAME kvvMY$'n5r\ TRoss:ab JWillia[ Nbd'ork DATE  % 1/M/93 1/n/93 1/M /93 1/ Mf 93

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9 Tennessee Valley Authority Browns Ferry Nuclear Plant ATIN: Dr. Mark O. Medford cc:

Mr. John B. Waters, Chairman Claude Earl Fox, M.D.

Tennessee Valley Authority State Health Officer ET 12A State Dept. of Public Health 400 West Summit Hill Drive State Office Building Knoxville, Tennessee 37902 Montgomery, Alabama 36130 Mr. J. R, Bynum, Vice President Regional Administrator Nuclear Oparations U.S.N.R.C. Region 11 3B Lookout Place 101 Marietta Street, N.W.

1101 Market Street Suite 2900 Chattanooga, Tennessee 37402-2801 Atlanta, Georgia 30323 Mr. Charles Patterson Site Licensing Manager Senior Resident Inspector Browns Ferry Nuclear Plant Browns Ferry Nuclear Plant Tennessee Valley Authority U.S.N.R.C.

P.O. Box 2000 Route 12, Box 637 Decatur, Alabama 35602 Athens, Alabama 35611 Mr. O. J. Zeringue, Vice President Site Quality Manager Browns Ferry Nuclear Plant Browns Ferry Nuclear Plant Tennessee Valley Authority Tennessee Valley Authority P.O. Box 2000 P. O. Box 2000 Decatur, Alabama 35602 Decatur, Alabama 35602 Mr. M. J. Burzynski, Manager Nuclear Licensing and Regulatory Affairs SB Lookout Place Chattanooga, Tennessee 37402-2801 TVA Representative Tennessee Valley Authority 11921 Rockville Pike Suite 402 Rockville, Maryland 20852 General Counsel Tennessee Valley Authority ET llH 400 West Summit Hill Drive Knoxville, Tennessee 37902 Chairman, Limestone County Commission P.O. Box 188 Athens, Alabama 35611

,. v Enclosure 1 Dim BL 0EDLLEty Ca 1 i

The purpose of thes NRC's n I9LBo2ELllah1DA1111Yiturdina_

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a clearer 1. understanding o owing: of the f llto the Browns Ferry \

2 the problems associated with r Plant was to obtain habitability; operation of the ventilation the control room habi y zone; 3

the proposed modification systems associated with o contr l room 4 and the habitability zone;s to the control roo 5.

the accident assumptions; m ventilation systems 6.

the plans to maintain and t toxic gas challenges as est for habitability zone int egrity;

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7 habitability zone conditiona result; and o

of the existing j

the Technical Specificati room ons.

The intent of addressing th result of evaluation safety t reflected th conclusions:his visit, e above the NRCitems staff haswas dra to ensure the Bro 1.

wn the following ormance. As a preliminary TVA has taken some rather problems associated with the conformance requirements of significant the Browns actions Fer insaddres ng the i

of GDC 19ry of Nuclear Power Plant to thecont include:

Appendix A to 10and CfR the a.

Part 50. -These modification intake; of the supply d

b. ucting for the control room replacement of the existin c.

increased capacity CREVS; g CREVS systems with a.new identificattun of the d.

the event of an accident; stack n the as a potential so the control oaroom habitabilittesting to d anticipated from the

e. y zone and the leakage rateunfilter non-safety exhausts in the sst a revised dose evaluation to d ack; and GDC 19 emonstrate conformance with

f3 Enclosure IL --  :

3 December 11. 1992 Exit Meetilig Aeaardina -

Browns Ferry Control Room Habitability .

The purpose of the_NRC's visit to the-Brcens Ferry Nuclear Plant was to obtain i a clearer understanding of the follosinc:- "

1. the problems associated witn the control room habitability zone;-  :

2. cperation of the ventiluion systems associated with control room >

habitability;

3. the proposed modifications to the control room ventilation systems "

and the habitability zone; ,

4. the accident assumptions;

5. the plans to maintain and test for habitabil'ity zone) integrity;_

6. toxic gas challenges as a result of the-existing control room - -

habitability zone condition; and

7. the Technical Specifications.

The intent of addressing the above items was to ensure that'the NRC. staff's~

safety evaluation reflected the Browns Ferry design and' performance. : As: a result of this visit, the NRC staff has drawn the. following preliminary 1 conclusions: ~

1. TVA has taken some rather significant actions in addressing:thee.

problems associated with the control room 1 habitab_ility zone and the?  :

conformance of the Browns Ferry Nuclear Power Plantito the  ;

requirements of GDC 19 of Appendix A to.10 CFR.Part: 50. These-~

include: _

a. modification of the supply ducting for the controliroom' intake; b; replacement of the existing CREVS systems with a:new= _

increased capacity ~CREVS; t-

c. identification of the non-safety _ exhaust locations in the t

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stack as -a. potential source for a ground -level releasecin

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the event =of an accident; >

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d. testing to determine the total unfiltered 1n-leakage-intol g -

the control- room habitability zone and 'the leakage rates: 1 anticipated from the non-safety exhausts _in the stack;: andL a revised dose evaluation to demonstrate conformance withe e,

GDC 19.

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2. The NRC has raised questions about the assumptions in TVA's revised GDC 19 accident analysis. Some of these questions are associated with:

a. whether E01s reflect the accident analysis assumptions made with respect to the timing of operator actions involving dampers in the non-safety stack exhausts and FC0 150B;

b. assumed MS' leakage;

c. assumed adsorber efficiency;

d. exclusion of the dose contribution from leakage associated with the operation of RHR during accident recovery operations;

e. exclusion of 36 mph wind speed event as an incredible event without a demonstration that it meets the exclusionary criteria in SRP 6.5.3;

f. justification for new Chi /Q values;

g. need to address leakage through stack sumps;

h. seismic nature of ducts supplying exhaust to the stack;

i. new control room intakes r.ot designed to include tornado missile protection in accordance with the discussion in SRP 6.4;

j. leakage performance capability of Ruskin and Press dampers in non-safety exhaust lines in stack; and

k. demonstration that the LOCA is the limiting accident with respect to control room operator doses.

3. Based upon the questions raised in Item 2 above, the possibility exists that the NRC's assessment of the capability of the Browns Ferry control room to meet GDC 19 could result in a different conclusion than that drawn by TVA. With that potential existing, TVA may want to identify specific leakage sources, quantify the volume associated with those sources and initiate corrective actions to ensure restart in accordance with the schedule. Some of the sources of in-leakage which the staff believes need to be quantified include the leakage past damper FC0 1508, infiltration via the contaminated ductwork which penetrates the control room habitability zone, and the spread of contaminated air throughout the habitability zone due to the lack of integrity of the relay room and control room air handling units.

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4. Amendment-173 of Unit 2 included in the SE a requirement that TVA-provide a TS surveillance requirement for the demonstration of in-leakage values as a part of the redesign of the CREVS. TVA has not provided such a surveillance requirement in their TS submittal. The staff still believes that such a requirement is applicable. The staff believes that such a test must definitively demonstrate system integrity, must have an established baseline which is related to the accident assumptions, and must confirm acce)tability-with respect to the accident assumption. It is important t1at the baseline test and subsequent tests all reflect the anticipated configuration of the ventilation systems including those associated with adjacent areas.

5. Additional information needs to be provided on the docket to enable the NRC staff to document the basis for concluding that the control room is capable of meeting GDC 19. Some of the information necessary for the docket includes:

a. a summary of the assumptions and the results of the revised dose evaluation;

b. whether the new CREVS design meets the recommendation of RG 1.52, ASME Code AG-1 or ASME N509 and will be tested in accordance with ASME N510;

c. data on special tests conducted to determine unfiltered in-leakage into the control room habitability zone and backflow through the non-safety exhaust ducts;

d. seismic nature of piping and dampers of ductwork in exhausts to the stack;

f. demonstration as to why the new supply ductwork for the control room is not required to have tornado missile protection;

g. type of test.to demonstrate leakage associated with Press dampers;

h. background information for the generation of site-specific-Chi /Q values for the accident evaluations; and

i. demonstration that the LOCA is the limiting accident for the

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determination of the conformance to GDC 19.

6. NRC staff believes that TVA should ensure that the TS associated-with the CREVS and the SGTS reflect system design. Potential review items include:

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a. performance of in-place D0P and freon tests at systems rated flow rate;-

b. laboratory test performed utilizing ASTM 03803-1989 test method at a test temperature of 30*C and a relative humidity of 70%;

c. demonstration of an acceptable positive pressure with respect to all adjacent areas of the control room habitability zone at the rated flow; and

d. demonstration of a negative pressure in the reactor building of.0.25 inches water gauge.

7. Some issues that the NRC will be reviewing are:

a. the toxic gas challenge to the control room operators;

b. the seismic nature ~f he exhaust ductwork and dampers in the stack;

c. the requirement for tornado missile protection in the supply ductwork to the control rcom;

d. implementation of TMI Action item Ill.D.3.4 at Browns Ferry, including TS; and

e. requirement for NRC safety evaluation addressing accident doses for operation with reactor building equipment hatches open.

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3 Enclosure 2 Comments on Special Test to Determine Unfiltered In-leakage The staff is concerned that TVA may not _have taken appropriate corrective actions to solve the problem of control room habitability at the Browns Ferry Nuclear Plant. This concern is ba::ed on the fact that-TVA may not have adequately quantified the amount of unfiltered in-leakage into the control room. This preliminary conclusion by the statf is based upon the following.

three points, and subsequent rationale:

1. The staff considers the test methodology utilized by TVA in special test procedure 0-ST-91-07 ir, appropriate for quantifying the absolute ,

infiltration rate.  !

2. TVA neglected to quantify the in-leakage associated with the I ductwork which penetrates the control bay habitability zone (CBHZ);

and

3. The special test procedure was not performed in a configuration consistent with the expected alignment of affected systems during an accident.

TVA's special test procedure employed the standard ASTM E 779. During our review of TVA's special test procedure, the staff referred to ASTM E 779-87.

This standard states the following:

1. Section 1.4 states that the test method cannot be interpreted as a direct measurement of air change rates that would occur under natural conditions.

2. Section 5.6 states, "It is better to use the fan-pressurization method for diagnostic purposes and measure the absolute infiltration rate with the tracer dilution method". ASTM E 741 is the tracer dilution method standard.

3. Section 5.6 also states, "When the absolute infiltration rate is needed, the tracer dilution method should be used over a wide range of wind speeds and directions and indoor-outdoor temperature differences".

Based upon ASTM E _779-87, stated above, the staff would conclude that the test.

method employed by TVA was an inappropriate test and would not have adequately quantified the absolute infiltration rate.

Sources of unfiltered in-leakage into the CBHZ are from the leakage past damper FC0 1508, the ductwork which penetrates the control room envelope and the floor, ceiling and side walls of the control room envelope itself.

Special test procedure 0-ST-91-07 only measured the in-leakage associated with-the latter. In the special test's " Background" section, it. clearly states that the ductwork which penetrates the CBHZ contributes to the unfiltered in-leakage to the CBHZ. However, it goes on to state that the test is limited to the walls and the ceiling and the floors, in that " Isolating these ducts from

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the outside air will ensure that only leakage from the CBHZ is measured. . This

- will more accurately reflect the- system configuration after the duct leakage issue 1.5 resolved". Therefore, it is the staf f's position that the test.

- which was performed by TVA,~may have underestimated.the unfiltered in-leakage.

TVA's special test was not performed in a manner consistent with the operating alignment expected to exist in the event of an accident. There was no flow in ductwork which would ordinarily have flow during and following an accident.

Furthermore, CREVS itself was not operating. These conditions are-inconsistent with the-manner that one would expect the control room envelope-

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to be configured in the event of an accident.

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DISTRIBUTION Docket File NRC and Local'PDRs BFN Rdgs:Juine S. Varga 14-E-4 G. Lainas 14-H-1 F. Hebdon T. Ross J. Williams T. Ross M. Sanders OGC 15-B-18 ACR5(10)

B. Wilson Ril E. Merschoff RII 040039}