NLS8600287, Application for Amend to License DPR-46,revising Tech Specs to Reflect Permanent Removal of RHR Reactor Pressure Vessel Head Spray Line Piping & Associated Primary Containment Isolation Valves.Fee Paid

Application for Amend to License DPR-46,revising Tech Specs to Reflect Permanent Removal of RHR Reactor Pressure Vessel Head Spray Line Piping & Associated Primary Containment Isolation Valves.Fee Paid

ML20209G676
Person / Time
Site:	Cooper
Issue date:	09/05/1986
From:	Kuncl L NEBRASKA PUBLIC POWER DISTRICT
To:	Muller D Office of Nuclear Reactor Regulation
Shared Package
ML20209G682	List: ML20209G696 NLS8600287, Application for Amend to License DPR-46,revising Tech Specs to Reflect Permanent Removal of RHR Reactor Pressure Vessel Head Spray Line Piping & Associated Primary Containment Isolation Valves.Fee Paid
References
NLS8600287, NUDOCS 8609150053
Download: ML20209G676 (7)

Text

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Nebraska Public Power District "~"""d$kS5fhSat****"

NLS8600287 September 5,1986 Office of Nuclear Reactor Regulation BWR Project Directorate No. 2 Division of BWR Licensing U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attention: Mr. Daniel R. Muller

Attachment:

1) Evaluation of Technical Specification Change with Respect to 10CFR50.92

Subject:

Proposed Change No. 24 to Technical Specifications Reactor Pressure Vessel IIcad Spray Cooper Nuclear Station NRC Docket No. 50-298, DPR-46 In accordance with the applicable provisions specified in 10CFR50, Nebraska Public Power District requests that the Technical Specifications for Cooper Nuclear Station (CNS) be revised to reflect the permanent removal of the RIIR reactor pressure vessel head spray line piping and associated primary containment isolation valves (RIIR-MOV-32 and RilR-MOV-33) .

The proposed change will: 1) delete the operability and test requirements for the two indicated containment isolation valves,

2) remove said valves from Tab!c 3.7.1 listing primary containment isolation valves , 3) remove said valves from Table 3.7.4 referencing penetration and valve numbers, and

4) delete the vessel head spray function from Group 2, Containment Isolation. An evaluation of the proposed change j with respect to the requirements of 10CFR50.92 and the l applicable revised Technical Specification pages are contained in j the attachment.

i By copy of this letter and the attachment, the appropriate State of Nebraska Official is being notified in accordance with 10C FR50.91(b) . This proposed change incorporates all amendments to the CNS Facility Operating License through Amendment 100 dated May 20, 1986.

This change has been reviewed by the necessary Safety Review Committees and payment of $150 is submitted in accordance with 10 C FR 170.12.

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Mr. Dani:Il R. MuHer  :

Page 2 September 5,1986 l In addition to three signed originals, 40 copies are also submitted for your use. Should you have any questions or require additional information, please contact me.

Sincerely,

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d , /614 L. G. Kunci Vice-President, Nuclear LGK/Irb:lk18/9 Attachment ec: H. R. Borchert Department of Health State of Nebreaka ,

Mr. Deni:1 R. Mullar Paga 3 September 5,1986 STATE OF NEBRASKA)

)ss PLATTE COUNTY )

L. G. Kuncl, being first duly sworn, deposes and says that he is an authorized representative of the Nebraska Public Power District; a public corporation and political subdivision of the State of Nebraska; that he is duly authorized to submit this request on behalf of Nebraska Public Power District; and that the statements contained herein are true to the best of his knowledge and belief.

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L. G.) Kuncl Subscribed ence and sworn to before me this d day MA) .

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Revised Technical Specifications for RHR Reactor Pressure Vessel Head Spray Revised Pages: 52a 168 Table 3.7.1 (Page 1) 173 Table 3.7.4 (Page 1)

The following discussion presents the results of an evaluation of the technical acceptability of removal of the head spray function at CNS relative to plant safety and power generation. Since initial preoperational testing, Cooper Nuclear Station (CNS) has not utilized the reactor pressure vessel head spray function of the residual heat removal system (RHRS). The power generation design basis for the installation of the head spray function at CNS was to improve plant availability by reducing the time required for a refueling outage. The head spray system was designed to supply 625 GPM to the vessel steam dome through the head spray nozzle for use during shutdown cooling to increase vessel head cooldown rate. It was anticipated in the design phase that vessel cooldown and head removal would be critical path activities and that rapid head cooldown would reduce outage time. Head spray operation will, in fact, promote rapid head cooldown. However, at CNS head cooldown is not on the critical path since the critical path is devoted to parallel activities such as shield block removal and MSIV leak rate testing.

Consequently, although the system provides the intended function, the incentive for its inclusion in the design is not realized at CNS and therefore, is not used.

Design documentation for the CNS RHR system does not indicate any safety-related functions for the head spray. In addition, no credit is taken for head spray operation in the safety analysis presented in the CNS Updated -

Safety Analysis Report (USAR). The general Emergency Procedure Guidelines (EPG's) prepared for the BWR Owner's Group and the CNS Emergency Operating Procedures (EOP's) based upon the EPG's neither require nor disallow use of head spray in emergencies.

The use of head spray for emergency makeup to the reactor vessel is possible although unrealistic. Specifically, those accident scenarios where only head spray is available while the other lower pressure makeup systems are inoperable are too improbable to realistically consider. This conclusion is based upon the following considerations:

A. Head Spray as a Low Flow-Low Pressure Makeup System Other low pressure makeup systems such as LPCI and Core Spray provide much greater flow rates. The condensate system can also be used to provide low pressure makeup. Consequently, the contribution that head spray could provide would be insignificant in contrast to any of the other low pressure makeup systams.

B. Head Spray Diverts Flow from LPCI Opening the head spray line will increase overall makeup flow to the reactor vessel but will decrease LPCI flow which is more effective for core cooling since it is directed to the lower vessel plenum rather than the vessel head.

C. Head Spray Requires Manual Operation Manual operator action is required in order to open the head spray injection valves. The low pressure emergency makeup systems (LPCI, CS) are automatically initiated.

D. Head Spray is Isoitted The head spray injection valves are closed when containment isolation occurs. In any severe accident, the containment will isolate automatically and it would be necessary to bypass this isolation in order to open the valves and inject water through the head spray line. ,

E. LPCI is the Preferred Flow Path Head spray can only be used if the RHR pumps are operable. If the RHR pumps are operable, the preferred flow path is via the LPCI injection valves versus head spray since LPCI flow rate to the reactor vessel is much greater than the head spray flow rate. In the instance where core spray is inoperable but the RHR pumps are operable with LPCI injection valves inoperable, head spray could be used. However, it would still be preferable to initiate action to re-establish core flooding by opening the LPCI injection valves rather than expending critical time attempting to bypass the head spray isolation signal.

The head spray line piping section from the reactor vessel to the isolation valves is a potential location for a line break. Removal of the line will then reduce the probability of a small break Loss of Coolant Accident (LOCA).

However, the effect of this reduction on the probability of a small break LOCA would be small since the head spray line represents a small fraction of the primary system piping at CNS.

In summary, head spray has no safety function and no credit has been taken for its use in the safety design basis or emergency operating procedures. Due to its low flow rate and its lack of independence from the LPCI function, the emergency conditions where it may be needed are very improbable. Removal of the head spray line is beneficial in that it deletes a potential location for a primary system pipe break. On balance, the improbable need for head spray and its usefulness and the reduction in line break probability have little effect on overall risk as would be determined from a Probabilistic Risk Assessment (PRA). Consequently, the District has concluded that head spray removal has no significant impact on plant safety.

Removal of head spray would neither increase nor decrease RHR system reliability since it has no impact on the other operating modes of the system.

Use of head spray can promote rapid cooling of regions in the head area.

Since the loads on the vessel head flange and studs depend on the cooldown rate of the reactor vessel flange and head, use of head spray may increase the thermal duty on the vessel due to the rapid cooldown rate when head spray is initiated. Use of head spray was considered in vessel design; however, removal of head spray may reduce thermal duty.

Since reactor pressure vessel head cooldown is not on the critical path for an outage at CNS, removal of the head spray function will reduce critical path l

outage time by eliminsting the time routinely expended to remove and replace the spool piece between the vessel head and the refueling bulkhead.

Removal of the head spray line also decreases the possibility of a leak at the flange faces of the spool piece or damage due to installation errors, both of which can increase outage time for repairs.

Removal of head spray components will decrease system maintenance requirements and eliminate surveillance and equipment qualification requirements now imposed by valves RHR-MOV-32 and RHR-MOV-33. Plant maintainability will be improved since removal of equipment, particularly in the drywell, will enhance the maintainability of other components in the immediate vicinity.

Removal of the head spray line will reduce radiation exposure, since personnel will no longer be required to remove and reinstall the head spray spool piece.

Due to the above evaluation, the District has determined that the removal of the RPV head spray system is both technically acceptable and advantageous and that this modification will have no adverse impact upon either the CNS safety or powet generation basis. Consequently, the District has elected to permanently remove the head spray line piping located between the RPV head spray nozzle and the refueling bulkhead. The spray nozzle will also be removed from the RPV. Blind flanges will be installed on the RPV head and the head spray refueling bulkhead penetration flanges. Valves RHR-MOV-32 and RHR-MOV-33 will be permanently removed, with RHR-MOV-33 replaced by a welded-in pipe cap.

Accordingly, Nebraska Public Power District requests a revision to the CNS Technical Specifications to reflect the modifications to the RPV head spray system described above. The proposed Technical Specification change will delete the operability and test requirements for Valves RHR-MOV-32 and RHR-MOV-33 and delete reference to these valves from Tables 3.7.1 and 3.7.4.

The change will also delete the vessel head spray isolation on page 52a under Group 2. Isolations.

Evaluation of this Revision with Respect to 10CFR50.92 A. The enclosed Technical Specification change is judged to involve no significant hazards based upon the following:

1. Does the proposed license amendment involve a significant increase in the probability or consequences of an accident previously j evaluated?

Evaluation:

No. The proposed change will decrease the probability of a leak from the reactor coolant system and reduce the potential for a small break LOCA. Also, since blind flanges and welded-in pipe caps are less subject to leakage and not subject to failure-to-close as are

! motor-operated valves, primary containment integrity is enhanced.

Since no credit is given to reactor head spray in the CNS USAR's l safety design basis for, accident mitigation, the modification does not impact the consequences of a previously evaluated accident.

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2. Does the proposed license amendment create the ponsibility for a new or different kind of accident from any accident previously evaluated?

Evaluation:

'Jo . The capped-off piping outside the drywell will not be physically or functionally connected to any other system, component or equipment in a manner which could create a new or different kind of accident. Due to the welded-in cap, the piping will be dead-ended to flow. Primary containment integrity will be insured by performing the appropriate 10CFR50 Appendix J 1eakage tests.

3. Does the proposed amendment involve a significant reduction in the margin of safety?

Evaluation:

The head spray piping penetration at X-17 will continue to be testable as a spare penetration and subject to the appropriate 10CFR50 Appendix J 1eakage tests. As previously described, the head spray system has no safety function and is given no credit in the USAR safety design basis. The proposed modification will, in fact, improve p7 ant safety by slightly reducing LOCA potential and improving primary containment integrity as described above.

Therefore, the proposed amendment involves no significant reduction in the margin of safety.

B. Additional basis for proposed no significant hazards consideration determination:

The District refers the staff to a similar license amendment request granted to the TVA, Docket No. 50-296, Browns Ferry Nuclear Plant Unit 3 described in 49FR38410 where the assessment of the staff was that the application involved no significant hazards consideration, f

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