ML20058N714

Requests Exemption to 10CFR50.44 & 10CFR50,App A,Criterion 41 Per 10CFR50.12 Re Eliminating Requirements Maintaining Operational & Test Hydrogen Recombiners

ML20058N714
Person / Time
Site:	Waterford
Issue date:	10/15/1993
From:	Burski R ENTERGY OPERATIONS, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
W3F1-93-0073, W3F1-93-73, NUDOCS 9310200235
Download: ML20058N714 (16)

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[ Octob'eril5,'1993 U.S. Nuclear: Regulatory Commission Attn:: Document. Control Desk Washington, D.C. 20555:

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Subject:

- -Waterford 3-SES' ,

w. Docket No. 50-382

-License No. NPF-38 Hydrogen..Recombiners, 10CFR50.12 Specific Exemption [

1 to'10CFR50.44:and 10CFR50, Appendix A, Criterion 41 j

Gentlemen:

The purpose of this letter is to. request a specific exemption to

10CFR50.44 and:10CFR50, Appendix-A, Criterion.41 in accordance with

-10CFR50.12. ' The ~ purpose of. the exemption is the elimination of the

[ requirements to maintain operational ~;and test the hydrogen recombiners.

The e'xemption'requestLis provided as attachment one to this letter.

~ On May~4 at the annual Regulatory. Information Confereace,-Dr. Murley announced:a pilot.~ program, Cost Beneficial Licensing Action Initiative ,.

. (CBLA), established by NRR to give special consideration to licensee  :

-requests for changes requiring staff review that' involve high cost and low

. safety benefit. ':In response to Dr. Murley's initiative,l Entergy Operations met with NRR staff on June 8,- 1993, to present an initial list g, _ of._CBLAs.: .As discussed on June 8, 1993, the proposed change to eliminate '

[ 'th'e: requirements' associated with the hydrogen recombiners is being

submitted underithe CBLA_ program.

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--Specifically, the deletion of technical: specification 3.6.4.2 and its associated bases T.S. 3/4.6.4 from the Waterford.3 license is requested. ,

.The hydrogen recombiners will ' remain physically in the. plant, but the ';

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_ , Hydrogen Recombiners, 10CFR50.12 Specific Exemption  !

to'10CFR50.44 and 10CFR50, Appendix A, Criterion 41 W3F1-93-0073 L Page 2- 1 October 15, 1993 '

system will not be maintained operational, nor will it' be tested. This letter provides the detailed justification for the elimination of the hydrogen recombiners, and therefore, this letter also provides the basis

r. for technical specification change request NPF-38-139. The technical specification amendment request and the 10CFR50.92 evaluation have been L submitted to the NRC via letter W3F1-93-0075.

This exemption request is in compliance with sections (a)(2)(ff),

7 -(a)(2)(fv), and (a)(2)(vi) of 10CFR50.12. The exemption request  ;

demonstrates that: the underlying purpose of the regulation is achieved

[(a)(2)(f f)], there is a benefit to the public health and safety

[(a)(2)(iv)], and there is present material circumstances not considered

! when the reg:;1ation was adopted [(a)(2)(vf)].

The_ technical justification is predicated on the following technical bases: ,

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1. Short term post LOCA hydrogen generation is less than 1%, well below p the 4% hydrogen flammability limit.

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2. Long term post LOCA hydrogen generation at 30 days is about 5.7%

which is less than the flame propagation limit of 6%, which

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according to Regulatory Guide 1.7 would not result in adverse ,

effects to containment systems. A time period of 30 days would  ;

provide ample time within which to mobilize resources and to implement long term recovery actions, 'such as containment venting, for. example, by using the Containment Atmosphere Release System, (CARS).

.3. Waterford 3 analyses establish that a hydrogen burn at 8.1% hydrogen concentration, following a design basis LOCA without long term hydrogen control. would produce a peak pressure of 31.0 psig which is below the containment design pressure of 44 psig. A hydrogen concentration of 8.1% envelops the TMI burn which occurred at about 7 to 8% hydrogen concentration, reference seven (7), and produced a peak pressure of 28 psig. The pressure resulting from the hydrogen

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l Hydrogen Recombiners, 10CFR50.12 Specific Exemption to 10CFR50.44 and 10CFR50, Appendix A, Criterion 41  ;

W3F1-93-0073'  ;

Page 3 October 15, 1993 J r

burn, 31.0 psig, is also below the Waterford 3 limiting design basis accident -(MSLB) peak pressure of 43.6 psig. The actual containment failure pressure for Waterford 3 is expected to be in the range of 2.5 to 3.0 times the containment design pressure based on

. containment failure pressures for containment designs similar to

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Waterford 3.

4. Recombiners have a negligible impact on reducing hydrogen generation from severe accidents. Accordingly, removing the. hydrogen recombiners has a negligible-impact on severe accident risks.

1 The request meets the eligibility. criteria for categorical exclusion of an environmental impact statement or environmental assessment as set forth in 10CFR51.22(c)(9). ,

.The NUMARC letter of June 22, 1993 to the NRC stated that the NRC staff and NUMARC concluded that elimination of combustible gas control

, . requirements was technically feasible. While the NRC and NUMARC concluded that significant resources would be required to address this issue from a L

! rulemaking and generic' industry perspective, this request is expected to

. require minimal resources to evaluate on a plant specific and regulation exemption basis. Thus, we believe this request represents an appropriate balance between resources and benefits.

In summary, we believe this exemption request is an excellent case of a requirement marginal to safety. The provisions of 10CFR50.12 are satisfied,- the exemption is technically justified, and there is a benefit to the public health and safety.

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F Hydrogen Recombiners, 10CFR50.12 Specific Exemption to 10CFR50.44 and 10CFR50, Appendix A, Criterion 41 W3F1-93-0073 Page 4 October 15, 1993 b

Please contact me or Robert J. Murillo should there be any questions regarding this matter.

Very truly yours,

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R.F. Burski Director Nuclear Safety RFB/RJM/dc Attachment cc: J.L. Milhoan, NRC Region IV, D.L. Wigginton, NRC-NRR, R.B. McGehee, N.S. Reynolds, NRC Resident Inspectors Office, Administrator Radiation Protection Division, (State of Louisiana), American Nuclear Insurers r

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y Attachment One.

10CFR50.12 Soecific Exemotion To 10CFR50.44 and 10CFR50. Accendix A.

Criterion 41: Hydroaen Recombiners

- 1.0 Puroose The purpose of this document is to request a specific exemption to 10CFR50.44 and 10CFR50, Appendix A, Criterion 41 in accordance with.

10CFR50.12. The purpose of the specific exemption is the elimination of 7

the requirements to maintain operational and test the hydrogen recombiners at Waterford 3.

2.0 Definition of Specific Exemotion p This specific exemption requests that technical specification 3.6.4.2 and its associated bases T.S. 3/4.6.4 be deleted from the Waterford 3  :

license. The hydrogen recombiners will remain physically in the plant, but the system will not be maintained operational, nor will it be tested. ,

e 3.0 Reaulatory Basis for Snecific Exemotion The exemption request is in compliance with sections (a)(2)(ff),

. (a)(2)(f v),- and (a)(2)(vi) of 10CFR50.12. The exemption request demonstrates that: the underlying purpose of the regulation is achieved

[(a)(2)(f f)], there is a benefit to the public health and safety

[(a)(2)(fv)], and there are present material circumstances not L considered when the regulation was adopted [(a)(2)(vi)].  !

)

4.0 Backaround l

The hydrogen recombiners were provided in accordance with 10CFR50.44 )

and 10CFR50, Appendix A, criterion 41 to be available to maintain the o hydrogen concentration within containment below its flammable limit

during. post-LOCA conditions. Either recombiner unit is capable of L controlling the hypothetical hydrogen generation during a DBA associated l

.with (1) zirconium water reactions, (2) radiolytic decomposition of water, and (3) corrosion. The hydrogen control systems'are consistent with the recommendations of Regulatory Guide 1.7, March 1971. The l

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- 10CFR50.12 Specific Exemotion To 10CFR50,44 and 10CFR50. Aooendix A.  ;

' Criterion 41: Hydrocen Recombiners- l l

licensing basis for the hydrogen recombiners is described in FSAR section 6.2.5. The exemption request is submitted in accordance with and in the spirit of the NRC Program for Elimination of Requirements Marginal to Safety.

5.0 ' Technical Justification

' The technical justification is predicated on the following technical ,

p bases:

1. Short term post LOCA hydrogen generation is less than 1%, well below the 4% hydrogen flammability limit.

2. Long term post LOCA hydrogen generation at 30 days is about 5.7% which is less than the flame propagation limit of 6%, which according to Regulatory Guide 1.7 would not result in adverse b effects to containment systems. 'A time period of 30 days would provide ample time within t:hich to mobilize resources and to implement long term recovery actions, such as containment venting, for example,. by using .the Containment Atmosphere Release _ System, (CARS).

-3. Waterford 3 analyses establish that a hydrogen burn at 8.1%

hydrogen concentration, following'a design basis LOCA without long

term hydrogen control would produce a peak pressure of 31.0 psig which is below the containmer.t design pressure of 44 psig. A hydrogen concentration of 8.i% envelops the TMI burn which occurred at about 7 to 8% hydrogen concentration, reference seven (7), and produced _a peak pressure of 28 psig. The pressure resulting. from the hydrogen burn, 31.0 psig, is also below the Waterford 3 limiting design basis accident (MSLB) peak pressure of 43.6 psig. The actual containment failure pressure for Waterford 3 is expected to be in the range of 2.5 to 3.0 times the containment' design pressure based on containment failure pressures for containment designs similar to Waterford 3.

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~4.- Recombiners have a negligible impact on reducing hydrogen generation from severe accidents. Accordingly, removing the hydrogen recombiners has a negligible impact on

. severe accident risks. ,

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10CFR50.12 Specific Exemotion

'To 10CFR50.44 and 10CFR50. Accendix A.

Criterion 41: Hydrocen Recombiners. ,

Each of .these. technical bases is herein discussed.

Short Term Post LOCA Hydroaen Generation Is Less Than 1%

1mmediately following a design basis LOCA, in the first minutes, hydrogen would be' generated by oxidation of zircaloy fuel cladding. The p resulting hydrogen concentration in containment would be less than 1%,

reference FSAR Figure 6.2-54, attached, which is well below the 4%

hydrogen flammability limit. Therefore, the hydrogen recombiners are  :

not needed in the.short-term following a design-basis LOCA.

e Lona Term Post LOCA Hydrocen Generation Is less Than Flame Procacation .

Limit. Which Accordina to Reaulatory Guide 1.7. Would Not Result In Adverse Effects to Containment Systems.

b In the' days following a design-basis LOCA, hydrogen will slowly build g up in containment from radiolysis of water and corrosion of metallic L aluminum and zine and zinc-based paints. Figure 6.2-54 of the FSAR shows hydrogen concentrations in containment post-LOCA. Waterford 3 uses a non-zinc protective coating to prevent corrosion of zinc-based paint', so the hydrogen produced from oxidation of zinc-based paint would be significantly less than-shown in FSAR Figure 6.2-54. Also, the hydrogen produced from oxidation of zirconium was increased by a factor of 5 for conservatism over the hydrogen production calculated in the L ECCS performance analysis. The hydrogen concentrations are shown in FSAR Figure'6.2-54. Realistically, the hydrogen from zinc-paint corrosion is negligible, and the hydrogen from zircaloy oxidation 1.;

c - one-fifth the value shown in FSAR Figure 6.2-54.- Figure 1, attached, shows these hydrogen concentrations. In Figure 1, zinc-based paint corrosion was neglected, and the FSAR Figure 6.2-54 zirconium o concentration was divided by 5. The other hydrogen concentrations were

taken directly from FSAR Figure 6.2-54. The total hydrogen shown in-

[ Figure I was calculated by adding the curves for the hydrogen sources L

shown in the figure. Using these total hydrogen values, the hydrogen concentration, without recombiners, will reach the 4% concentration E flammability limit at'17 days and be about 5.7% at 30 days which is less

than the 6% flame propagation limit. Regulatory Guide 1.7 establishes that for hydrogen concentrations between 4%-and 6%, only partial burning will occur, which will_not result in effects that would be adverse to p

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10CFR50.12 Specific Exemotion k

To 10CFR50.44 and 10CFR50. Anoendix A.

Criterion 41: Hydroaen Recombiners e  ;

containment systems. A time period of 30 days would provide ample time within which to mobilize resources and to implement long term recovery actions, such as. containment venting, for example, by using the ,

Containment Atmosphere Release System, (CARS).

A Desian Basis LOCA Without Lona Term Hydroaen Control Would Produce Pressures Below the Containment Desian Pressure.

If a hydrogen burn were to occur following the long term buildup of i hydrogen, the containment integrity would be maintained. NUREG/CR-4330 (Vol. 3, p. 4.7) describes the hydrogen deflagration at Three Mile Island 2, with.an initial hydrogen concentration of 7 to 8%, which produced no ' containment breach and minimal damage to equipment.

Plastics and other low-melting point materials, such as telephone cases and the crane operator's seat were damaged. Both Waterford 3 and THI-2 are large dry containments. Waterford 3 analyses using the MAAP code, reference 8, establish that for a 8.1% hydrogen concentration, the containment peak pressure resulting from a hydrogen burn would be 31.0 psig which is below the containment design pressure of 44 psig. A hydrogen concentration of 8.1% envelops the TMI burn which occurred at about 7 to 8% hydrogen concentration, reference seven (7), and produced a peak pressure of 28 psig. The pressure resulting from the hydrogen burn,-31.0 psig, is also below the Waterford 3 limiting design basis accident (MSLB) peak pressure of 43.6 psig. The actual containment failure pressure for Waterford 3 is expected to be in the range of 2.5 to 3.0 times the containment design pressure based on containment failure pressures for containment designs similar to Waterford 3.

Thus, a design-basis LOCA without long-term hydrogen control would not challenge containment integrity.  ;

Removina Hydroaen Recombiners Has Nealiaible Imnact On Severe Accident Riik For severe accidents that are beyond the design basis, for example, a LOCA with failure of all safety irdection, major core damage and melting occurs. The rate of hydrogen generation for these events is so large that_ the recombiners would have a negligible impact on reducing hydrogen concentrations. ~The Waterford 3 IPE, Reference 6, was performed without

110CFR50.12 Soecific Exemotion To 10CFR50.44 and 10CFR50. Accendix A.

Criterion 41: Hydroaen Recombiners taking any credit for the hydrogen recombiners reducing the containment hydrogen concentration. The IPE established that containment performance under severe accident conditions was acceptable even without the recombiners. The hydrogen recombiners are designed to heat the ambient air to a temperature range of 1150 F to 1400 F, which is within the temperature range at which hydrogen auto ignition will occur. Thus, as the hydrogen concentration increases, the recombiners may be an ignition source and thereby increase the likelihood of a hydrogen burn for severe accidents.

6.0 Compliance With 10CFR50.12

.The following information demonstrates compliance with 10CFR50.12.

Section fa)(2)(if): IThe underivino purpose of the reaulation is achieved 1 The underlying purpose of 10CFR50.44 and 10CFR50, Appendix A, Criterion 41, is achieved. 10CFR50.44(c)(1)(f) and (c)(1)(if) state that it shall be shown that following a postulated LOCA either an ,

uncontrolled hydrogen-oxygen recombination would not take place in containment; or the plant could withstand the consequences of an uncontrolled hydrogen-oxygen recombination without loss of safety function. 10CFR50, Appendix A, criterion 41 states that a hydrogen control system shall be provided as necessary to control hydrogen following postulated accidents to assure that containment integrity is maintained. Thus, the underlying purpose is that an uncontrolled hydrogen-oxygen recombination would not take place, or that given an uncontrolled hydrogen oxygen recombination, containment integrity is assured.

Short term post-LOCA hydrogen generation is less than 1%, well below the 4% hydrogen flammability limit. Long term post-LOCA hydrogen generation at 30 days would be about 5.7% which is less than the flame propagation limit of 6%, which according to Regulatory Guide 1.7 would not result in adverse effects to containment systems. A time period of 30 days would provide ample time within which to mobilize resources and to implement long term recovery actions, such as containment venting, for example, by using the Containment Atmosphere Release System, (CARS).

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IOCFR50.12SpecificExemotion To 10CFR50.44 and 10CFR50. Accendix A.

Criterion 41: Hydrocen Recombiners Waterford 3 analyses establish that for a design basis LOCA without long ,

term hydrogen control, a hydrogen burn with 8.1% hydrogen concentration will produce a peak pressure of 31.0 psig which is below the containment design pressure of 44 psig. A hydrogen concentration of 8.1% envelops the TMI burn which occurred at about 7 to 8% hydrogen concentration, reference seven-(7), and produced a peak pressure of 28 psig. The pressure resulting from the hydrogen burn, 31.0 psig, is also below the Waterford 3 limiting design basis accident (MSLB) peak pressure of 43.6 psig. The actual containment failure pressure for Waterford 3 is expected to be in the range of 2.5 to 3.0 times the containment design pressure based on containment failure pressures for containment designs similar to Waterford 3. Thus, there is significant assurance the underlying purpose of the regulations will be achieved.

Section (a)(2)(fv): IThere is a safety benefit to the oublicl

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The implementation of the exemption would achieve a safety benefit for the public. Technical specification surveillance requirement 4.6.4.2 requires the implementation of various resource intensive tests and operations, and these resources could be transferred to more safety significant activities. Technical specification surveillance requirements require a functional test of the recombiner, a channel calibration of all recombiner instrumentation and control circuits, ,

visual examination of the recombiner enclosure, and a resistance to ground test of the heater electrical circuits. These requirements collectively translate to about 400 man-hours or $20,000 annually over

.the. life of.the plant. These resources could be transferred to more safety significant activities which would be a safety benefit to the ,

public. l 1

Section (a)(2)(vi) IThere are cresent material circumstances not considered when the reculation was adoptedl j i

The benefit of time has provided experience and information which provide a better perspective about hydrogen generation. Two important material circumstances are the effects and the risks of hydrogen generation.

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IOCFR50.12SpecificExemotion l

} To 10CFR50.44 and 10CFR50. Anoendix A.

Criterion 41: Hydrocen Recombiners Traditionally, technical and regulatory evaluation perspectives have held that hydrogen burn is to be avoided due to the uncertainties of containment failure. The THI-2 hydrogen deflagration provided an important benchmark for the effects of a hydrogen deflagration. THI-2, which involved about a 45% core claddiq water reaction, and a mixture of about 7% to 8% hydrogen, produced no containment breach and minimal damage to equipment. Containment damage was essentially limited to plastics and other low melting point materials like telephone cases and the crane operator's seat. The TMI-2 deflagration thus provides actual experience which establishes a significantly lower effects threshold which was not considered when the regulations were promulgated.

Many PRA evaluations and tools have been developed which provide a L 'better insight about the risks of hydrogen generation. Waterford 3

" analyses establish that a hydrogen burn with 8.1% hydrogen concentration following a design basis LOCA without long term hydrogen control would produce a peak pressure of 31.0 psig which is below the containment design pressure of 44 psig. A hydrogen concentration of 8.1% envelops the THI burn which occurred at about 7 to 8% hydrogen concentration, reference seven (7), and produced a peak pressure of 28 psig. The peak pressure resulting from the hydrogen burn, 31.0 psig, is also below the Waterford 3 limiting design basis accident (MSLB) peak pressure of 43.6 psig. The actual containment failure pressure for Waterford 3 is expected to be in the range of 2.5 to 3.0 times the containment design pressure based on containment failure pressures for containment designs

_ similar to Waterford 3. The Waterford 3 IPE also establishes that the hydrogen recombiners have a negligible impact on severe accident risks.

7.0 Environmental Conside*ations This exemption request involves the use of facility components L located within the restricted area, as defined in 10 CFR part 20, and changes a surveillance requirement. Entergy Operations Incorporated, L has determined that this request does not involve:

'10CFR50.12 Specific Exemotion To 10CFR50.44 and 10CFR50. Appendix A.

Criterion 41: Hydrocen Recombiners

a. A significant hazard consideration, as described in our amendment application Technical Specification Change Request NPF-38-139, reference letter W3F1-93-0073.

b. A significant change in the types or significant increase in the amounts of any effluents that may be released offsite.

c. A significant increase in individual or cumulative occupational radiation exposure.

Accordingly, this request meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b),

no environmental impact statement or environmental assessment need be prepared in connection with this exemption request.

8.0 References

1) 10CFR50, Appendix A, Criterion 41.

2) 10CFR50.44.

3) Regulatory Guide 1.7.

4) FSAR section 6.2.5.

5) Technical Specification 3.6.4.2 and TS 3/4.6.4.

6) Letter, R.F. Burski (Waterford 3) to U.S. Nuclear Regulatory Commission, "Waterford 3 SES, Docket No. 50-382, License No. NPF-L 38, Response to Generic Letter 88-20, ' Individual Plant Examination for Severe Accident Vulnerabilities - 10CFR50.54(f),'"

W3F192-0311.

7) NUREG/CR-4330, Vol. 3, May 1987.

8) EPRI NP-7071-CCML, "MAAP 3.0B--Modular Accident Analysis Program for LWR Power Plants," November 1990.

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,3F1-93-0073' W

Attachment Two '

The Modular Accident Analysis Program (MAAP) computer code has been used to evaluate _ the impact of a hydrogen burn on the Waterford 3 containment  ;

pressure. The containment conditions at which the hydrogen burn was initiated  !

were similar to the conditions expected to exist post-large break LOCA, low containment pressure and 8.1% hydrogen concentration in the containment. The l

. results show that. the containment pressure spike due to complete hydrogen burn is 31.0 psig which is below the containment design pressure of 44 psig.  ;

MAAP incorporates fully integrated models for the major severe accident phenomena and system mitigating effects that can affect containment response.

MAAP code is used throughout the industry to simulate LWR behavior under severe accident conditions. MAAP analyses were used to determine the accident i progression including the. timing of events, the magnitude of the potential pressure loads that could cause containment failure, and the effect of plant ,

specific design features on severe accident phenomena as part of Waterford 3 IPE effort. A plant specific model was developed for MAAP 3B Version 17.02 that incorporated the Waterford 3 design features. This model was used to simulate a hydrogen burn and its impact on Waterford 3 containment pressure.

The hydrogen burn was initiated at a containment condition similar to post LOCA conditions.

, .The scenario considered is a large break LOCA with one train of containment cooling two containment fan coolers and one containment spray, available. To

. generate the desired amount of hydrogen, it is also assumed that no safety

. injection-is available throughout the accident. This scenario was selected to

.. achieve the desired containment conditions, pressure and hydrogen concentration. This accident condition resulted in a hydrogen mass equivalent to' 8.1% hydrogen concentration for containment dry conditions long term post i

LOCA. This condit" conservatively bounds the 30 days post design basis LOCA

' conditions which is expected to be at about atmospheric pressure and 5.7%

hydrogan concentration. A complete hydrogen burn was-simulated at the above i conditions, 23.9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> into the accident.

i h-The following lists the containment conditions before and after the hydrogen  ;

burn: l l

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ev-W3F1-93-0073 Attachment Two Page 2 Containment pressure'before initiating 8.1 psig

' hydrogen' burn Hydrogen Concentration before burn 8.1%

Containment' peak pressure after the burn 39.1 psig Containment pressure rise (AP) due to burn 31 psi

-The above results show that the pressure spike in the containment due to a complete hydrogen burn initiated at conditions more conservative than expected at 30 days after a design basis' large break LOCA,. is below the containment-design pressure, 44 psig. This pressure is also below the Waterford 3 limiting design basis accident (MSLB) peak pressures of.43.6 psig. The containment initial pressure in the MAAP calculational case is based on severe accident conditions at 23.9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> after the accident. The peak containment

-pressure was established by substracting 8.1 psi from the MAAP 39.1 psig value to account for long term post LOCA containment dry conditions.

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