ML20038A633

Forwards Response to NUREG-0737 Open Items II.B.1, RCS High Point Vents & II.K.3.1, Installation & Testing of Automatic Power-Operated Relief Valve Isolation Sys. Operating Guidelines for High Point Vents... Encl

ML20038A633
Person / Time
Site:	Midland
Issue date:	11/10/1981
From:	Jackie Cook CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Harold Denton Office of Nuclear Reactor Regulation
Shared Package
ML20038A634	List: ML20038A633 ML20038A640
References
RTR-NUREG-0737, RTR-NUREG-737, RTR-NUREG-737., TASK-2.B.1, TASK-2.K.3.01, TASK-TM 14832, NUDOCS 8111160078
Download: ML20038A633 (5)

Text

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i 3 Consumers i

' POW 8f James W Cook gggl5 wuliiyMI Vsce PressJent - Projects, I-ngsneenng and Constnsctson Generet off 6ces- 1945 West Parnell Road, Jackson, MI 49201 * (517) 788 0453 November 10, 1981 e&ogh, t Harold R Denton, Director (

Office of Nuclear Reactor Regulation Division of Licensing

1. $ULl iL 'o, US Nuclear Regulatory Commission , NOV 31991~ -

Washington, DC 20555 t ui [ ', .

MIDLAND PROJECT 1 MIDLAND DOCKET NOS 50-329, 50-330 RESPONSE TO DRAFT SER FOR SELECTED NUREG-0737 ITEMS FILE: 0505.818 SERIAL: 14832 ENCLOSURES: (A) RESPONSE TO SELECTED NUREG-0737 OPEN ITEMS (B) B&W DOCUMENT 86-1122009-02, OPERATING GUIDELINES FOR HIGH POINT VENTS D" RING SMALL BREAK TRANSIENTS We have reviewed the draf t of the NRC Staff Safety Evaluation Report for selected NUREG-0737 items provided by the R L Tedesco letter to J W Cook dated October 21, 1981. Enclosed is our response to the open items contained in the draft.

The response provided by this letter :,upplements information provided to the Staff in a telephone conversation on September 23,1981. We expect that with the information provided the items can be resolved by the Staff prior to issuance of the SER. Responses to NUREG-0737 Items II.K.2.17 and II.K.2.19 were transmitted in a J W Cook letter to H R Denton dated September 17, 1981 and incorporated into Revision 39 of the FSAR to be submitted in November 1981.

SccI JWC/JRW/fms CC RJCook, Midland Resident Inspector DSHood, US NRC W S TPSpeis, US NRC DBMiller, Midland Construction (3) /[

RWHuston, Washington oc1081-0411a131 A K O (([jk PDR

• s SELECTED NUREG-0737 ACTION ITEMS DRAFT SER RESPONSE TO OPEN ISSUES II.B.1 - Reactor Coolant System High Point Vents A. Provide reference to the codes and standards to which the reactor coolant system vents will be designed. Discuss the seismic and environmental qualification and provide appropriate justification.

Response

The reactor coolant system high point vents are part of the reactor coolant pressure boundary and meet the requirements of the ASME Code for Section III Class 1 components. The system is designated quality Group A and seismic Category I. The environmental qualifications for the solenoid valves are discussed in Chapter 2 of the equipment qualification volumes being provided with Revision 39 of the FSAR.

B. Discuss independence of power supplies for the vent line valves

Response

Independence of the power supplies for the reactor coolant system high point vent line valves is discussed in Section 5.4.15 of the FSAR (Rev 37). Applicable drawings are listed in the same section.

C. Provide the procedures that will be used in operational testing of the vents.

Response

Testing of the valves will meet the requirements of Section XI,

Article IWV of the ASME Code for Class B valves. Each vent valve will be cycled individually while the other valve associated with the vent is closed. The cycling will be done under plant conditions that preclude the potential for discharge to the containment atmosphere. Cycling the valves

at normal operating pressure is therefore excluded.

D. Provide the operational procedures for the vents and supporting analysis

( including venting of gas which might be present in the reactor vessel head.

Response

B&W Document 86-1122009-02, " Operating Guidelines for High Point Vents During Small Break Transients," is attached. Specific guidelines for Midland will be developed using the methods of this document as part of our ongoing ATOG program.

Vent guidelines for both small break transients and inadequate core cooling (ICC) situations are developed within the attachment.

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In examining use of the hot leg vents for small break transients, it was found that, for situations where the RC pumps cannot be operated, the vents could be utilized to remove gases trapped in the upper portions of the hot leg and thereby facilitate the system refilling process and reestablishment of natural circulation. The presence of non-condensible gases in the reactor vessel head will not prevent reestablishment of natural circulation. Generic calculations indicate that system refill utilizing the hot leg vents could take several hours. For an ICC event, the hot leg vents are to be opened to aid in minimizing the accumulation of non-condensible gases within the steam generator tubes. Once the core has been recovered, vent usage proceeds as described above for a small break transient.

When natural circulation has been reestablished, the operator can proceed to depressurize the plant. In order to assure that natural circuiation is not interrupted during the depressurization due to expansion of any gases which may be present in the RV head, calculations were performed to determine the maximum allowable depressurization rate. This maximum depressurization rate assures that the amount of gases expanded into the hot leg from the RV head is not greater than the release rate of the hot leg vents, thereby preventing the accumulation of gases in the hot leg and maintaining natural circulation. This calculated depressurization rate is not a limiting factor in our ability to cool down the plant.

Removal of any gases in the reactor vessel head by the coolant is expected to occur gradually and would be enhanced by reactor coolant pump operation, pressurizer degasification, or both. The presence or removal of gas in the RV head is immaterial based on the information provided since it would neither impede natural circulation or plant recovery.

E. Since the vents exhaust directly into containment atmosphere provide information showing that the proper mixing will be obtained.

Response

The reactor coolant system high point vents exhaust into the region above the operating floor. Four safety grade reactor building cooling units provide sufficient forced convective mixing for any hydrogen released through these vents. These cooling units are located at el 685', above and outside the perimeter of the s3.condary shield wall. Each cooling unit fan takes a suction from the region above the operating floor and dis-charges down to the region outside the secondary shield wall. The capacity of each f an is 36,000 cfm at slow speed and 73,000 cfm at fast speed. Therefore, the containment atmosphere is turned over at least every 24 minutes assuming only two coolers at slow speed. The containment atmosphere turnover, combined with the restricted flow from the vents, ensure adequate mixing.

F. Demonstrate that LOCA analyses already performed for Midland bound the cases of inadvertent vent operation or vent line severence or provide new analyses.

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Response

The vent orifice (0.25 inch diameter) is sized so that potential flow is less than normal makeup capacity. Therefore, inadvertent vent operation would not result in a LOCA. The vent is a one inch line which is equivalent to a 0.005 square ft break if severed. The plant response in this case is bounded by the small break LOCA analysis submitted in the letter from J H Taylor (B&W) to S A Varga (NRC) dated July 18, 1978.

II.K.3.1 - Installation and Testing of Automatic Power-Operated Relief Valve Isolation System A. Provide and justify the values chosen for block valve closure setpoints.

Response

The low pressure setpoint is 2100 psig. This is 60 psi below nominal

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primary system pressure and 135 psi below the expected reseating pressure of the PORV (2235 psig). This setpoint will ensure that the block valve will close and prevent a low pressure reactor trip at 1900 psig and an ECCAS signal at 1500 psig. Normal steady state pressure is controlled within a band of 20 to 25 psi, thus this pressure setpoint should not be reached unless the plant is in an transient condition. The block valves will remain open unless coincidence exists with improper PORV position.

B. Justify that the signals and power supplies to the redundant block valves are independent.

Response

The independence of the signals and power supplies to the redundant block valves is discussed in Section 7.6.1.7 of the FSAR (Rev 37). Applicable drawings are listed in the same section.

C. Discuss the testing program needed to demonstrate operability of the system including justification that the block valves can close under full flow conditions to isolate a stuck open PORV.

Response

l Each Midland Unit has two block valves upstream of the PORV, one manufactured by Target Rock, the other by Anchor Darling. Preop testing will involve checkout and calibration of the instrumentation and controls for these valves as well as valve operation with simulated signals.

Operability of the Anchor Darling block valves under normal conditions has been established through the EPRI PORV/ safety valve qualification program.

i A 3" Anchor Darling double disc gate valve of the sm + basic design as the Midland valves was satisfactorily tested during the portion of the EPRI program conducted at Duke Power Company's Marshall Station. The 3" valve I. equipped with a Rotorque operator initially experienced dif ficulty closing against full flow and also had excessive leakage when it did close.

i Modifications to the valve seat and the Rotorque operator corrected these mi1181-0424a131

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problems and the valve was successfully retested. Based on the Marshall experience, Anchor Darling has modified the seats of the Midland valves to improve the disc / seat bearing area and leakage characteristics. The Midland valves are equipped with a Limitorque operator, SMB00-25 rated at 14,000 lbs thrust. The torque switch setting for the Midland system will be set at 191 ft-lb which will provide more than sufficient thrust (9550 lbs) to close the valves against full flow. Anchor Darling has performed conservative calculations to show this. Since no Target Rock block valve was tested by EPRI, Consumers Power is conducting a study to determine if the Marshall testing bounds the Target Rock design. Based on the outcome of this study, Consumers Power will inform the NRC of any actions necessary to ensure that the Target Rock valve will close against full flow.

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