ML20237B870

Responds to Request for Addl Info Re GL 96-06, Assurance of Equipment Operability & Containment Integrity During Design- Basis Accident Conditions

ML20237B870
Person / Time
Site:	Monticello
Issue date:	08/05/1998
From:	Hammer M NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-96-06, GL-96-6, TAC-M96835, NUDOCS 9808200036
Download: ML20237B870 (4)

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I l Northern States Power Company

• , , 2807 W. Highway 75 Monticello, MN 55362 Telephone (612) 295-1317 August 5,1998 GL 96-06 US Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 MONTICELLO NUCLEAR GENERATING PLAN Docket No. 50-263 License No. DPR-22 ,

Response to Request for Additional Information Dated June 8,1998 Related to the Monticello Response to Generic Letter 96-06 (TAC NO. M96835)

Ref.1 NRC Generic Letter 96-06, " Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions," September 30,1996 Ref. 2 Letter from William J Hill, NSP, to US NRC Document Control Desk, " Thirty Day Response to NRC Generic Letter 96-06 Assurance of Equipment l Operability and Containment Integrity During Design-Basis Accident Conditions," October 25,1996 Ref. 3 Letter from William J Hill, NSP, to US NRC Document Control Desk, "120 Day i Response to NRC Generic Letter 96-06 Assurance of Equipment Operability I and Containment integrity During Design-Basis Accident Conditions," January / l 28,1997 (

Ref. 4 Letter from Tae Kim, NRC, to Roger O. Anderson, NSP, "Monticello Nuclear 7Jy Generating Plant - Request for Additional Information to Northern States / s Power Company's Response to Generic Letter 96-06 (TAC No. M96835),"

June 8,1998 l By Ref. 2 and 3, Monticello provided the required responses to Ref.1, Generic Letter l 96-06 " Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditi,o,ns."

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o ,u J By letter dated June 8,1998 (Ref. 4), the NRC staff requested additional information (RAI) in order to complete review of Northern States Power's response to the Generic 9808200036 980805 PDR ADOCK 05000263 P PDR

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Page 2, GL 96-06 NSP Response to RAI Dated 6/8/98 l- Letter iNcludin'g assurance damaging water hammer would not occur. This letter responds to that request.

Regarding RAI item 6, no modifications are planned, however, NSP commits to the I

. following:

l By December 31,1998, NSP will revise applicable procedures to define Reactor Building Closed Cooling Water (RBCCW) flow conditions under abnormal and l accident conditions. These procedures willprevent RBCCWDrywell flow unless: 1) primary containment integnty is not required, or 2) the drywell bulk atmospheric '

temperature is less than the RBCCWatmospheric vaporpoint, or 3) Drywell RBCCWfans are not operating. Further, lf the drywellbulk atmospheric l

temperature has exceeded the atmospheric vaporpoint of the RBCCW water, the procedures willprevent reestablishing flow to the drywell until the system has been refilled.

Attachment A discusses control of the RBCCW system under abnormal and accident operating conditions. '

in regard to item 1 of the RAI, NSP considered void formation, slug acceleration and j void collapse descriptions of NUREG/CR-5220 " Diagnosis of Condensation-Induced j l

Waterhammer,"_to prohibit possible RBCCW water hammer or two phase flow when primary containment is needed. This is the basis for the above commitment. Since no water hammer or two phase flow will occur, items 2,3, and 4 of the RAI are not applicable,to Monticello. For RAI item 5, RBCCW fabrication drawings NX-13142-29, NX-13142-38 and NX-13142-45 are submitted as Attachment B to this response.

P&lD drawings NH-36042 and NH-36042-2 are also attached. i Please contact Sam Shirey, Sr. Licensing Engineer, at 612-295-1449 if you require additional information related to this request.

k Michael F. Hammer rdet44D Plant Mar,ager Monticello Nuclear Generating Plant c: Regional Administrator - Ill, NRC NRR Project Manager, NRC l Sr Resident inspector, NRC i State of Minnesota Attn: Kris Sanda J Silberg Affidavit to the US Nuclear Regulatory Commission j Attachment A: Abnormal and Accident Operating Conditions for Controlling RBCCW Attachment B: NRC Requested Drawings.

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UNITED STATES NUCLEAR REGULATORY COMMISSION NORTHERN STATES POWER COMPANY MONTICELLO NUCLEAR GENERATING PLANT DOCKET NO. 50-263 RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION ON GENERIC LETTER 96-06 (TAC NO. M96835)

Northern States Power Company, a Minnesota corporation, by letter dated August 5,1998, provides the requested response to NRC Request for Additional Information on Generic Letter 96-06 dated June 8,1998. This letter contains no restricted or other defense information.

NORTHERN STATES POWER COMPANY By EMt/1 ~

Michael F." Hammer Plant Manager Monticello Nuclear Generating Plant On this5 b day of[ % (AsT MSB before me a notary public in and for said County, personally appea@d Michael F. Hammer Plant Manager, Monticello Nuclear Generating Plant, and being first duly sworn acknowledged that he is authorized to execute this document on behalf of Northern States Power Compa ',y, that he knows the contents thereof, and that to the best of his knowledge, information, and belief the statements made in it are true and that it is not interposed for delay.

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Samuel I. Shirey  : SAMUEL 1. SHIREY ,

Notary Public - Minnesota 4 em eueuc MINNESOTA :

Sherburne County ,

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My Commission Expires January 31,2000 l

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ATTACHMENT A ABNDRMA'L AND ACCIDENT OPERATING CONDITIONS FOR CONTROLLING RBCCW The following abnormal and accident conditions involving RBCCW were considered:

1. USAR Chapter 5, Containment System, Section 5.2.3.9, Drywell Temperature Analysis for Small Break Accidents, or Section 5.2.3.2, Containment Response to a Loss of Coolant Accident with Offsite Power.

At the beginning of a LOCA, the RBCCW Drywell Cooling Fans (fans) get a trip signal at 2 psig drywell pressure associated with an Emergency Core Cooling t System (ECCS) initiation. With the fans tripped, heat transfer from the DW coolers to the RBCCW water is minimized. The RBCCW pumps would be running, circulating cool water through the RBCCW piping keeping its vapor

pressure elevated. Under these conditions, RBCCW water will not boil and l water hammer will not occur since voids are not present. The fans can r

automatically restart only after the ECCS signal clears. This can only occur if drywell pressure is below 2 psig at which point the drywell bulk atmospheric temperature would be below the RBCCW system vapor pressure.

2. USAR Chapter 5, Containment System, Section 5.2.3.9, Drywell Temperature Analysis for Small Break Accidents, or Section 5.2.3.2, Containment Response to a Loss of Coolant Accident with Loss Of Offsite Power (LOOP).

At the beginning of a LOCA, the RBCCW Drywell Cooling Fans (fans) get a trip signal at 2 psig drywell pressure associated with an (ECCS) initiation. With the fans tripped, heat transfer from the DW coolers to the RBCCW water is minimized. Also, the RBCCW pumps lose power due to an ECCS load shed signal. Loss of fans and pumps assures no water hammer will occur. This is because it is unlikely voids would be present at the time the pumps lose power since the elevated RBCCW water vapor pressure still exists and the large heat transfer mechanism of the fans does not exist. If voids should exist, no mechanism exists to accelerate a water slug since the pumps have lost power.

As stated in the commitment, applicable procedures will be revised to prevent manually restarting the pumps thus preventing void collapse. The pump control logic has no automatic restart.

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! ATTACHMENT A ABNURMA'L AND ACCIDENT OPERATING CONDITIONS FOR CONTROLLING RBCCW

3. Abnormal Conditions, RBCCW System Pressure Failure or Station Black Out (SBO).

The RBCCW pumps will stop before drywell bulk atmospheric temperature reaches the RBCCW atmospheric vapor pr9ssure. After the pumps have stopped, even if drywell temperatures reach the RBCCW atmospheric vapor pressure, no water hammer will occur since no drive mechanism exists to accelerate a water slug.

If drywell temperature has exceeded the RBCCW atmospheric vapor pressure, procedures will prevent the possibility of void collapse by prohibiting restart of the RBCCW pumps until the system is properly fillel l

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