ML20079M701

Application for Amend to License NPF-3, Deleting Requirement for Containment Recirculating Fans.Ser Encl

ML20079M701
Person / Time
Site:	Davis Besse
Issue date:	01/14/1984
From:	Crouse R TOLEDO EDISON CO.
To:
Shared Package
ML20079M679	List: ML20079M677 ML20079M701
References
NUDOCS 8401270394
Download: ML20079M701 (6)

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APPL 0ATION FOR AMENDMENT TO FACILITY OPERATING LICENSE NO. NPF-3 FOR DAVIS-BESSE NUCLEAR POWER STATION UNIT NO. 1 Enclosed are forty-three (43) copies of the requested changes to the Davis-Besse Nuclear Power Station Unit No. 1 Facility Operating License No. NPF-3, together with the Safety Evaluation for the requested change.

The proposed changes include Section 3.6.4.2, 4.6.4.2 and Bases.

By -

Vice President, Nuclear

,/1LL Sworn and subscribed before me this/ Fday of January, 1984 1Es hr A . h s /K.LL Notary Public (Ji 'd ) .

LAURIE A. BRUDZINSKI Notary Public. State d Ohio My Commissa Egiros May 16.1986 P

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i Docket No. 50-346 License No. NPF-3 Serial No. 1020 '

Attachment '

1. Changes to 8) avis-llesse ' uelear Power Station Unit 1, Appendix A Technical Specifications Section 3.6.4.2, 4.6.4.2 and Bases.

A. Time required to Implement. This change is to be effective upon NRC approval.

B. Reason for Change (Facility Change Request 84-011).

The containment recirculating fans were required by the original plant design to ensure mixing of hydrogen in the containment following a LOCA. Reviews of other PWR license applications (NTOLs) and analysis of hydrogen mixing following a LOCA shows that the containment recirculating fans are not required.

C. Safety Evaluation (See Attached)

D. Significant flazard Consideration (See Attached)

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4 SAFETY EVALUATION This amendment requeet is for the deletion of Technical Specification 3.6.4.2, 4.6.4.2 and its basis for the containment recirculation system.

3 The original safety function of the containment recirculation system was to assure proper mixing of hydrogen in the containment dome so that localized hydrogen burns in the top of the containment would be prevented

- following a LOCA. During the early 1970's, when Davis-Desse was designed, there had been only limited research performed on the diffusion and/or mixing of hydrogen. Additional research has now been performed that now shows that cantainment dome recirculation systems are no longer required, and that they now provide no safety function.

The concern that prompted the original design of the containment recircul-ation system was originated from the thought that hydrogen, being a light density gas, may rise up and concentrate in the containment dome area creating a stratified hydrogen distribution. In this case, the average 4

hydrogen concentration may be lower than the threshold for hydrogen burn initiation but, a stratified distribution, as described, may cause a localized burn in the containment dome. The containment recirculation system, consisting of two independent trains of duct works and fans, was designed to- recirculate the air from the top of the containment dome to Lhe-lower elevations in the conLainment.

A U.S. Department of Energy sponsored study was conducted in 1978 to investigate the " Mixing of radiolytic hydrogen generated within a contain-ment compartment following a LOCA NUREG/CR-0304". It was performed by Los Alamos National Lab for the NRC. The report has provided detailed

. mathematical and experimental proof that the molecular diffusion process and the turbulent mixing caused by small temperature difference between the floor and the ceiling of the containment will be sufficient to ensure proper mixing of hydrogen in containment.

, , Consumer's Power, Midland Unit I and 2, does not have a Technical Specifications requirement for the containment recirculation system by taking credit for their containment air coolers and containment spray systems. The NRCs. evaluation of the Midland design is in NUREG-0793 on page 6-17. Davis-Besse also has these systems as part of the units design.

At Davis-Besse, low reactor coolant system pressure or high containment pressure will automatically initiate the containment air coolers and high containment pressure will automatically initiate the containment spray to

, condense the steam and depressurize the containment following a LOCA.

These systems can also accomplish the function of providing proper mixing

, of hydrogen during the initial phase of hydrogen generation from metal-water reaction. The hydrogen generated from radiolytic decomposition of water in the containment sump and on the floor will be mixed uniformly with the rest of the containuent atmosphere by the molecular diffusion l

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i process, and by the turbulent mixing due to temperature variations and the containment air coolers. These coolers mix the hydrogen and air in the lower part of the containment. Containment spray or containment dome recirculation is not needed during this phase of hydrogen generation to provide mixing. This will assure that a hydrogen buildup will not occur in the. containment dome and that the hydrogen monitoring system will obtain representative samples of the. containment atmosphere.

These containment recirculation fans are used during normal operation to prevent temperature stratification of the air. This temperature stratification has caused the grease to melt off from the polar crane.

This is an operational problem that has no safety significance. No other equipment requiring low temperatures is located in the top of containment.

The temperature stratification process is a different mechanism from the diffusion process that allows the hydrogen to uniformly mix within the containment.

Pursuant to the above evaluation, it is concluded that the proper mixing of hydrogen following a LOCA can be accomplished without the containment recirculation system and therefore, the Technical Specification require-ment should be deleted. The proposed change does not constitute'any unreviewed safety question.

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i SIGNIFICANT HAZARD CONSIDERATION The amendment request to delete the requirement for the Containment Recirculating System does not contain a Significant Hazard Consideration.

The Containment Recirculating System was part of the original plant design i for prevention of hydrogen concentration in the containment dome. Since

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the issuance of the Davis-Besse Unit No. I license other reviews have been performed and additional analysis to show that the fans are not needed to prevent stratification of hydrogen.

The attached amendment request would delete the requirement for the Limiting Conditions for Operating Sections 3.6.4.2, Surveillance Requirements 4.6.4.2 and the associated Bases for the Containment Recirculating Fans from the Technical Specification (Davis-Besse is a B&W Standard Technical Specification Plant). The specifications for the recirculating fans were required as part of the original plant design to assure proper mixing of hydrogen in the containment dome to prevent localized hydrogen burn following a LOCA. The concern that prompted the design for the containment recirculating system was originated from the thought that hydrogen, being a light density gas, may rise up and concentrate in the containment dome area creating a stratified hydrogen distribution.

The containment recirculation system, consisting of two independent trains of duct works and fans, is designed to recirculate the air from the top of the~ containment dome to the lower elevations in the containment. This is

! the only safety function performed by these fans.

The provision to have containment recirculating fans are not required at certain other PWR plants. The reviewers have seen fit not to require these plants to have fans for the dedicated purpose of containment recirculation to prevent hydrogen et, ratification in a post LOCA condition. In addition to the reviews, there have also been analysis performed on the behavior of hydrogen following a LOCA.

A U.S. Department of Energy study was conducted in 1978 to investigate the

" Mixing of radiolytic hydrogen generated within a containment compartment following a LOCA (NUREG/CR-0304)". It was performed by Los Alamos National Laboratory for the NRC. The report has provided detailed mathematical and experimental proof that the molecular diffusion process and the turbulent

. mixing ' caused by small temperature difference between the floor and the ceiling of the containment will be sufficient to ensure proper mixing of hydrogen in containment.

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i The Commission has provided guidance concerning the appl.. cation of the standards in 10 CFR 50.92 by providing certain examples (48 FR 14870).

One of the examples of actions involving no significant hazards -

considerations relates to a relief granted upon demonstration of acceptable operation from an operating restriction that was imposed because acceptable operatien was not yet demonstrated. This assumes that the operating restriction and the criteria to be appiled to a request for relief have been established in a prior review and that it is justified in a satisfactory way that the criteria have been met.

Davis-Besse Unit No. 1 Technical Specifications include the containment recirculating system. Since the issuance of our license, reviews and data have shown that the Technical Specification related function performed by these fans is no longer required.

Therefore, based on the above and the attached Safety Evaluation, this is not a Significant Hazard.

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