ML19290C267

Forwards Evaluations Required Per 790906 Fire Protection Safety Evaluation Items 3.2.3 & 3.2.7.Addl Info Re Items 3.2.5 & 3.2.6 Will Be Provided When Available.Nrc Comments Re Mods Should Be Sent by 800301

ML19290C267
Person / Time
Site:	Prairie Island
Issue date:	12/31/1979
From:	Mayer L NORTHERN STATES POWER CO.
To:	Office of Nuclear Reactor Regulation
References
TAC-11094, TAC-11095, NUDOCS 8001100448
Download: ML19290C267 (4)

Text

de NSF NORTHERN STATES POWER COMPANY M I N N E A PO L.l e , M I N N E S OTA 5 5 401 December 31, 1979 Director of Nuclear Reactor Regulation U S Nuclear Regulatory Commission Washington, DC PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket No. 50-282 License No. DPR-42 50-306 DPR-60 Evaluations Required by the Fire Protection Safety Evaluation Report Sections 3.2.3, 3.2.5, 3.2.6, and 3.2.7 of the Prairie Island Fire Protection Safety Evaluation Report issued by the NRC Staff on September 6, 1979 require the completion of evaluations of the following items:

3.2.3 Hydrogen Seal Oil Units 3.2.5 Fire Dampers 3.2.6 Fire Pump Barrier 3.2.7 Hydrogen Hazard-Auxiliary Building The requested evaluations for items 3.2.3 and 3.2.7 have been completed and are attached. Preliminary evaluations are provided for items 3.2.5 and 3.2.6. Additional information related to items 3.2.5 and 3.2.6 will be provided when available. As noted in the attachment, certain modifications are proposed to resolve NRC Staf f concerns in these areas. Comments or questions relating to the modifications we have described should be sent to us by March 1,1980 to permit us to revise our plans to the satisf action of the NRC Staff and complete all work by October 31, 1980.

Please contact us if you have any questions related to the attached evaluations.

M ss M ,

L 0 Mayer, PE \

Manager of Nuclear Support Services j gj gg-l Li LJD LOM/DMM/ak cc: J G Keppler G Charnoff Attachment 8001100 .

i At t achment Director of Nuclear Reactor Regulation U S Nuclear Regulatory Commission December 31, 1979 3.2.3 Hydrogen Seal 0.1 Units The Hydrogen Seal Oil Unit trenches we propose to ir.3 tall were described in detail in our letter dated December 26, 1979. Refer to item 3.1.4(1) and Figures 3, 4, and 5 of the attachment to that letter.

The Hydrogen Seal Oil Units are located in the basement area of the Turbine Building. Sections 4.5 and 5.23.1 of the fire Protection Safery Evaluation Report for Prairie Island state that a considerable number of safety related systems, including those required for safe shutdown, are contained in this area of the turbine building. This is in error. There is safeguards cabling and equipmeat in the safeguard corridor (auxiliary feedwater, battery, and switchgear rooms) through the center of the turbine building enclosed in a seismic walled sect ion. There is no safety related equipment outside the corridor. The nearest safety related equipment is 150 feet from a seal oil unit and is protected by an 18-inch concrete wall. Refer to our safe shutdown reanalysis submitted for NRC Staff review on October 22, 1979 for specific equipment and cable locations.

We conclude, therefore, that an oil fire ir the vicinity of a seal oil unit cannot endanger safety related equipment. Any oil fire will be confined to the immediate vicinity of the unit by the proposed trenches.

3.2.5 Fire Dampers We have committed to install fire dampers at a number of locations in the plant (refer to item PF-30 in Attachment (2) to our letter dated March 9, 1979). The scope of this NRC Staff concern has now expanded to include all fire zones containing safety related equipment (taken to mean equipment necessary for safe plant sh u td own ) .

Portions of the Prairie Island Fire Hazards Analysis describing ventilation system fire damper locations are in error. We are now in the process of updating this Analysis and correcting these errors. If ventilation paths which could endanger areas containing safe shutdown equipment are found to be unprotected in addition to those identified in PF-30, we will provide the necessary protection.

Prctection of a rating commensurate with the fire loading will be provided. Three-hour protection vil1 be provided in those paths communicating with the Turbine Building.

A list of specific new damper locations and ratings will be provided for NRC Staf f review when our investigation is completed. This information should be available by May 1,1980.

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3.2.6 Fire Pump Barrier The power supply cable for the motor-driven fire pump will be relocated or protected. No relocation of the control cable is necessary since it is routed on the opposite side of the room.

The NSP Plant Engineering and Construction Department is reviewing the feasibility of installing an enclosure around the motor-driven pump. The pump is now located directly over No. 11 circulating water pump intake bay on the thinnest portion of the floor. If our review shows the floor capable of supporting a structure of this type, and if materials are available that meet applicable standards, an enclosure will be installed.

The results of the floor evaluation and the enclosure design (if feasible) will be submitted for NRC Staff review. This information should be available by May 1, 1980.

3.2.7 Hydrogen Hazard-Auxiliary Building We have previously shown that existing high flow protection for hydrogen piping is sufficient to limit concentrations of the gas below 4% in all areas of the Auxiliary building wheie a line break could occur. High flow protection causes an automatic isolation of the hydrogen lines which must be manually reset at the auto-shutoff valve. Refer to item PF-27 in Attachment (2) to our letter dated March 9,19 79. Item 3.2.7 of the Fire Protection Safety Evaluation requires an evaluation of the effects of hydro-gen pockets of explosive concentrations or flaring at the line failure location on safety related equipment and cables. A leakage rate less than the auto-shutof f valve setpoint must be postulated for this to occur.

In a letter dated October 22, 1979 we submitted for NRC Staff review a reanalysis of fire areas containing equipment and cable required to safely shut down both reactors. This reanalysis was required by item 3.2.1 of the NRC Fire Protection Safety Evaluation Report.

The potential for a hydrogen line break exists in the following fire areas: 58, 59, 73, 74, and 84.

As noted in the safe shutdown reanalysis, equipment or cables for redundant hot or cold shutdown functions is located in fire areas 58, 59, 73, and 74. The line is normally isolated to fire areas 59 and 74 where it is only used for volume control tank makeup (a manual operation). Cable and equipment for redundant safe shutdown functions is well separated in all four areas with the exception of a number of cable tray crossover nodes. These nodes are listed in Table 3.1-1 of our safe shutdown reanalysis dated October 22, 1979. We proposed the installation of flame retardant blankets in open cable trays passing less than 3 feet below another tray at these nodes.

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A review of the hydrogen line routing in fire areas 58 and 73 in relation to the nodes identified in Table 3.1-1 of the safe shutdown reanalysis has been completed. A minium horizontal separation of 9 feet was found to be maintained at all locations from the nearest hydrogen piping.

Local pockets of explosive concentrations of hydrogen are not likely in the area of the tray crossings because of the separation distance from the piping and the fact that such tray crossings cannot physically occur in isolated small regions where pockets would be found. Fire damage to redundant cable due to flaring of leaking hydrogen gas is also not likely due to the physical separation noted above.

Preplanned strategies in areas 58, 59, 73, 74 and 84 will require isolation of the hydrogen line in the event of fire.

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