ML15117A260
| ML15117A260 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 10/26/1994 |
| From: | Berkow H Office of Nuclear Reactor Regulation |
| To: | Boger B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| TAC-M88279, TAC-M88280, TAC-M88281, NUDOCS 9411020048 | |
| Download: ML15117A260 (10) | |
Text
Qctober 26, 1994 MEMORANDUM TO:
Bruce A. Boger, Acting Director Division of Reactor Projects, Region II FROM:
Herbert N. Berkow, Director Project Directorate 11-3.
Division of Reactor Projects -
I/II Office of Nuclear Reactor Regulation
SUBJECT:
TIA 93-023 - USE OF NON-SAFETY RELATED SERVICE WATER EQUIPMENT AT OCONEE, UNITS 1, 2, AND 3 (TAC NOS. M88279/M88280/M88281)
By memorandum dated January 5, 1994, Region II submitted Task Interface Agreement (TIA)93-023 for staff resolution. The specific concern related to the use at Oconee of non-safety related equipment to mitigate an accident which had been identified during a review of the Emergency Condenser Circulating Water (ECCW) system. Five specific questions were presented for resolution of the issue.
The Plant Systems Branch (SPLB) reviewed the matter, and a copy of the results of their review is attached. The review addressed each question and, in addition, addressed generic aspects associated with the particular questions.
No specific actions have been recommended by the staff in response to these particular questions. However, you may wish to provide these review findings to the licensee for their action as appropriate.
Please contact Len Wiens at (301) 504-1495 if you have any questions concerning this review. This completes our actions on TAC Nos. M88279, M88280, and M88281.
Docket Nos. 50-269, 50-270 and 50-287
Attachment:
Plant Systems Branch Review of TIA 93-023 DISTRIBUTION:
Central File7 PUBLIC PDII-3 R/F SVarga JZwolinski MSinkule, RII CMcCracken To receive a copy of this document, indicate in the box:
"C"
= Copy without attachment/enclosure "E" = Copy with attachment/enclosure "N" = No copy OFFICE LA:PD23:DRPE E
PM:PD23:DRP E D:PD
- E E
NAME CNorsworthy 6-LWiens jT6ifnn IHB ko l(ir DATE J/2/94 f/
/94 VV 94
/ /94
/ /94 DOCUMENT NAME: G:\\OCONEE\\TIA9323 9411020048 441028 PDR ADOCK 05000269 CH FECENT C0P P
PDR__
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-4001 October 26, 1994 MEMORANDUM TO:
Bruce A. Boger, Acting Director Division of Reactor Projects, Region II FROM:
Herbert N. Berkow, Director Project Directorate 11-3
/
Division of Reactor Projects - I/II(
Office of Nuclear Reactor Regulation
SUBJECT:
TIA 93-023 - USE OF NON-SAFETY RELATED SERVICE WATER EQUIPMENT AT OCONEE, UNITS 1, 2, AND 3 (TAC NOS. M88279/M88280/M88281)
By memorandum dated January 5, 1994, Region II submitted Task Interface Agreement (TIA)93-023 for staff resolution. The specific concern related to the use at Oconee of non-safety related equipment to mitigate an accident which had been identified during a review of the Emergency Condenser Circulating Water (ECCW) system. Five specific questions were presented for.
resolution of the issue.
The Plant Systems Branch (SPLB) reviewed the matter, and a copy of the results of their review is attached. The review addressed each question and, in addition, addressed generic aspects associated with the particular questions.
No specific actions have been recommended by the staff in response to these particular questions. However, you may wish to provide these review findings to the licensee for their action as appropriate.
Please contact Len Wiens at (301) 504-1495 if you have any questions concerning this review. This completes our actions on TAC Nos. M88279, M88280, and M88281.
Docket Nos. 50-269, 50-270 and 50-287
Attachment:
Plant Systems Branch Review of TIA 93-023
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 4E September 15, 1994 MEMORANDUM TO:
Loren R. Plisco, Director Project Directorate 11-3 Division of Reactor Projects I/II FROM:
Conrad E. McCracken, Chie Plant Systems Branch A
Division of Systems Safety and Analysis
SUBJECT:
TIA ON USE OF NON-SAFETY RELATED SERVICE WATER EQUIPMENT AT OCONEE 1, 2, AND 3 (TIA 93-023, TAC NOS.
M88279/M88280/M88281)
Plant Name:
Oconee Nuclear Power Station, Units 1, 2, and 3 Licensee:
Duke Power Company (Duke)
Review S+itus:
Complete By letter dated January 05, 1994, Region II requested technical assistance from NRR related to the use of non-safety equipment to mitigate an accident at Oconee Nuclear Station, Units 1, 2, and 3. The concern was identified during a review of the emergency condenser cooling water (ECCW) system. The ECCW system functions to provide flow from Lake Keowee to the suction of the low pressure service water (LPSW) pumps and through the main condenser when the condenser cooling water (CCW) pumps are not available. The concern as identified by the Region involves reliance on non-safety related equipment which is susceptible to single failures to provide a suction supply to the LPSW pumps which are required to mitigate the consequences of an accident.
The concern also involves reliance on other equipment to support the use of the ECCW system in.the condenser cooling mode.
In identifying their concerns, the Region asked the following specific questions related to this issue:
- 1.
Can the licensee take credit for non-safety related, non-Technical Specification CCW pumps to mitigate a design basis event (LOOP/LOCA)?
- 2.
Can the licensee take credit for non-safety related, non-seismic support systems (such as the HPSW system) to mitigate a design basis event?
CONTACT: W. LeFave, NRR 301-504-3285
R. Borchardt
-2
- 3.
Should CCW pump combinations and applicable Keowee lake levels be addressed in the Technical Specifications if they are required to be operating prior to an event to ensure that ECCW flow can be established? Should a Technical Specification be established for Keowee lake level that incorporates operation of the LPSW system?
- 4.
Is the condenser cooling mode required for other than a total loss of AC power scenario? Should the condenser cooling mode equipment/system be considered safety related? Should the condenser cooling mode be single failure proof? Is the water inventory available to the emergency feedwater system adequate to eliminate requirements for the condenser cooling mode?
- 5.
Does the licensing basis of Oconee include consideration for the loss of (.fsite power coincident with the accident/transient for other than the large break LOCA (such as steam generator tube rupture)?
Bec::se of the amount of detail required to respond to the Region's concerns we are providing our evaluation/response as an attachment to this letter.
We should also point out that our evaluation of the licensee's request to eliminate the ECCW system from the TSs (transmitted to you by letter dated July 7, 1994) directly addresses some of these concerns as we concluded that the ECCW system is not required to mitigate any design basis events at Oconee.
However, for clarity we have again addressed these issues in this response.
To the extent practical, our responses have also addressed any generic aspects associated with a particular question in order to clarify our acceptance criteria for certain licensing requirements. This may help to avert future TIA's involving similar requests.
We consider our efforts on TAC Nos. M88589/M88590/M88591 to be complete. If you have any questions regarding this response, please contact Bill LeFave of my staff on 504-3285.
Docket Nos. 50-269 50-270, and 50-287
Attachment:
As stated DISTRIBUTION Docket File Plant File SWest GHubbard JLyons GHolahan
[G:\\SECTIONA\\LEFAVE\\TIA93-23]
SPLB:DSS SK5LB:DSSA SPLB:DSSA WLe"e GHubbard CMcCracken 9/,; /94 9/ '94 1979 OFFICIAL RECORD COPY
.1.
R. Borchardt
-2
- 3.
Should CCW pump combinations and applicable Keowee lake levels be addressed in the Technical Specifications if they are required to be operating prior to an event to ensure that ECCW flow can be established? Should a Technical Specification be established for Keowee lake level that incorporates operation of the LPSW system?
- 4.
Is the condenser cooling mode required for other than a total loss of AC power scenario? Should the condenser cooling mode equipment/system be considered safety related? Should the condenser cooling mode be single failure proof? Is the water inventory available to the emergency feedwater system adequate to eliminate requirements for the condenser cooling mode?
- 5.
Does the licensing basis of Oconee include consideration for the loss of offsite power coincident with the accident/transient for other than the large break LOCA (such as steam generator tube rupture)?
Because of the amount of detail required to respond to the Region's concerns we are providing our evaluation/response as an attachment to this letter.
We should also point out that our evaluation of the licensee's request to eliminate the ECCW system from the TSs (transmitted to you by letter dated July 7, 1994) directly addresses some of these concerns as we concluded that the ECCW system is not required to mitigate any design basis events at Oconee.
However, for clarity we have again addressed these issues in this response.
To the extent practical, our responses have also addressed any generic aspects associated with a particular question in order to clarify our acceptance criteria for certain licensing requirements. This may help to avert future TIA's involving similar requests.
We consider our efforts on TAC Nos. M88589/M88590/M88591 to be complete. If you have any questions regarding this response, please contact Bill LeFave of my staff on 504-3285.
Docket Nos. 50-269 50-270, and 50-287
Attachment:
As stated
RESPONSE TO REGION II TIA 93-023 RELATED TO USE OF NONSAFETY EQUIPMENT TO MITIGATE THE CONSEQUENCES OF AN ACCIDENT AT OCONEE PLANT SYSTEMS BRANCH DIVISION OF SYSTEMS SAFETY AND ANALYSIS BACKGROUND By letter dated January 5, 1994, Region II requested technical assistance (TIA 93-023) to address concerns related to the use of non-safety equipment to mitigate the consequences of an accident at the Oconee Nuclear Station, Units 1, 2,. and 3. These concerns resulted from a routine Resident Inspection conducted between March 28 and May 1, 1993, and documented in NRC Inspection Report Nos. 269, 270, 287/93-13. The TIA first describes the concerns in general and then follows up with specific questions. We had some problems with the general description/identification of the concerns because we did not agree with the specified premises used to describe certain system functions which we will try to clarify during this response.
RESPONSE TO GENERAL DESCRIPTION OF CONCERNS The conc rns were identified during a review of the emergency condenser circulating water (ECCW) system. The TIA identificJ 'he ELCu system as the ultimate heat sink for the Oconee units. We do not agree with this assessment and it may be a little misleading. In Section 9.2.4 of the Oconee FSAR Duke identifies only the condenser circulating water (CCW) system as the UHS and does not include the ECCW mode. This also is a little misleading because it deviates somewhat from how the staff normally defines the UHS. The staff's usual definition of the UHS for a plant would only include the body of water which serves (supply and return) a safety related cooling water system that removes heat from the plant via a heat exchanger. At Oconee the CCW system becomes part of the UHS because it is a source of water to the low pressure service water (LPSW) system which removes heat from the plant via a heat exchanger. We, therefore, consider the CCW system (including the pumps) as a safety related system because of its function as a source of water to the LPSW system. The CCW system also functions to remove heat from the main condenser; however, this function is not considered safety related.
In the ECCW mode, the CCW system is designed to provide water to the LPSW system and flow through the main condenser from the Keowee Lake via a siphon arrangement (actually two siphons, one for the LPSW supply and one for the condenser) that does not rely on the CCW pumps once initiated: however, the CCW pump(s) must be running initially if the lake is below a certain level to ensure the siphon path initiates flow upon loss of the CCW pumps. If siphon flow does not initiate upon loss of the CCW pumps because the CCW path is not water solid, it cannot be started without starting the CCW pumps. As described in our safety evaluation related to removal of the ECCW system from the TSs, the "siphon system" is the ECCW system and is divided into two distinct parts. The "first siphon" supplies water to the suction of the LPSW Attachment
-2 pumps, while the "second siphon" provides flow through the main condenser.
The operation of the first siphon is unaffected by the operation of the second siphon; however, the second siphon relies in part on the operation of the first siphon. We consider the first siphon to be a safety related function as it is sometimes relied upon to provide water to the LPSW pumps.
In the TIA, Region II also stated that the CCW pumps are not considered safety related and are load shed during a design basis event (LOCA/LOOP). We disagree that the CCW pumps are not safety related although they are.
automatically load shed in the event of a LOOP. The CCW pumps are relied upon via operator action within about an hour to maintain safe plant shutdown following most design basis accidents/events including a (LOCA/LOOP). We believe Duke also considers them to be safety related based on FSAR Table 3-2 "System Component Classification," and Table 8-1 "Loads to be Supplied from the Emergency Power Sources."
RESPONSE TO SPECIFIC ISSUES
- 1.
Ca;: the licehsee take credit for non-safety related, nci technical specification CCW pumps to mitigate a design basis event (LOCA/LOOP)?
In general, licensees' cannot take credit for non-safety related equipment to mitigate the consequences of a design basis LOCA. However, for other design basis events, credit for equipment can vary depending on what design basis event is being considered. Generally, for a plant being licensed today, if the design basis accident/event can be caused by a seismic event (such as a break in nonseismic piping) then the staff usually requires that only safety related equipment can be relied upon to mitigate the effects. Otherwise, we give credit for any equipment which is not directly failed as a result of the accident/event. This is usually the case for operating plants also but it could vary from plant to plant depending on the licensing basis.
However, all equipment necessary to mitigate a design basis event does not have to be covered by the technical specifications. Failure of safety related equipment not covered by the TSs may place the plant outside its design basis without requiring a TS action statement to be entered. In other cases where the non-TS equipment supports equipment covered by the TSs, a failure of the supporting equipment may cause entry into the action statement for the piece of equipment that is being supported.
Therefore, at Oconee, the licensee can (and needs to) take credit for the CCW pumps which we believe are safety related. However, it would be considered a backfit to require them to be in the TSs.
- 2.
Can the license take credit for non-safety related, nonseismic support systems (such as the HPSW system) to mitigate a design basis event?
As we stated in response to Question No. 1, whether credit can be taken depends upon the design basis event being considered. Each event is evaluated separatL' a-redit ded 'ads on what can initiate the event. With regar
- o the HPSW system, credit should not be given as a supporting system in response to a LOCA if the HPSW system is required to function for operation of the CCW
-3 system or the "first siphon" associated with ECCW operation. However, the HPSW system role following a LOCA is not clear. The TIA states that it cools the CCW pumps and provides seal water to the CCW pumps (both of these functions would require HPSW to be safety related and seismic. According to the FSAR it cools the turbine-driven EFW pump (not required to be safety related or seismic) but no mention is made regarding cooling to the CCW pumps.
The FSAR states that the LPSW system provides CCW pump seal water via a 100,000 gallon elevated water storage tank (presumably gravity flow).
This function could be safety related if it is required to maintain siphon flow from the CCW system to the LPSW pump suctions. In this case, the integrity of the HPSW system would have to be maintained following a seismic event. This cannot be done via a SQUG walkdown (as noted in the TIA) because the SQUG criteria is only applicable to supports and specifically excludes piping.
If indeed, the CCW pumps rely on the HPSW system for cooling, then this function of the HPSW is also safety related.
- 3.
Should CCW pump combinations and applicable Keowoe lake level be adressed in the TSs if they are required to be operating prior to an event to ensure that ECCW flow can be established? Should a TS be established for Keowee lake level that incorporates operation of the LPSW system?
Using the criteria of the Commission's Final Policy Statement on Improved Technical Specifications, the answer is yes, the CCW pumps/lake level are initial condition assumptions that would be required to be included in the TSs. However, as we noted in our evaluation of the proposed elimination of the ECCW system from the TS, FSAR Section 16.9.7 identifies these initial conditions as licensee commitments and also would declare the LPSW systems inoperable if they are not met, thus placing the plant into a TS action statement for the LPSW system. We also concluded that the administrative controls specified in FSAR Section 16.9.7 (same wording and format as the TSs) provide adequate assurance of LPSW operability. What the Region's question basically asks is should we move FSAR Section 16.9.7 to the TSs. We do not believe this is necessary nor justified since such a requirement would be considered a backfit. It is also clear that some of these issues were discussed previously with the licensee and the staff agreed that the administrative controls were adequate in lieu of a TS. However, the adequacy of the detailed evaluations (calculations and tests) used to arrive at the specific requirements identified in FSAR Section 16.9.7 have not been reviewed by the staff.
- 4.
Is the condenser cooling mode required for other than a total loss of AC power scenario? Should the condenser cooling mode equipment/system be considered safety related? Should the condenser cooling mode be single failure proof? Is the water inventory available to the emergency feedwater (EFW) system adequate to eliminate requirement for the condenser cooling mode?
-4 The original licensing basis for the ECCW system was for a total loss of AC power only. When the Region refers to the condenser cooling mode in this question we assume they are talking about the ECCW mode since they refer to a complete loss of AC power. Because the condenser cooling mode is not required to mitigate any design basis events, it does not need to be safety related or single failure proof. (Refer to next response regarding the steam generator tube rupture event.)
With regard to the last question, we do not believe the water inventory available for the EFW system is relevant to the elimination of the requirements for the ECCW system because the ECCW system is not relied upon for any design basis events. The standby shutdown facility (SSF) is the system currently relied on in the event of a complete loss of AC power, albeit the ECCW and EFW systems would be the preferred and most likely method of coping with an actual event. The only design basis event that relies upon heat removal via the main condenser is the steam generator tube rupture event.
The dose analysis for this event assumes a cooldown rate of 100 degrees per hour, which implies the main condenser and reactor coolant pumps are available. The EFW system and the available inventory of water from the upper surge tanks and the condenser hotwell was deemed as acceptable at the time of licensing. That inventory was evaluated for a loss of main feedwater without a loss of offsite power. With offsite power available, the EFW inventory is depleted faster since the reactor coolant pumps remain operating. The licensee assumed a plant cooldown under these conditions and showed that the inventory was adequate. It should be noted that we do not require the plant to be brought to cold shutdown following each and every event. For a new plant the licensee would have to show that the plant could be brought to safe cold shutdown using only safety grade equipment and assuming any single failure. However, no such requirements were in place at the time of Oconee's licensing. Subsequent detailed reviews during the peost-TMI era did not result in any substantial improvements in the area of EFW water supplies. Also, since the addition of the SSF with its long term capability, we believe the inventory issue is less important now than at the time of licensing. Any additional requirements would constitute a backfit.
- 5.
Does the licensing basis for Oconee include consideration for the loss of offsite power coincident with the accident/transient for other than the large break LOCA (such as steam generator tube rupture)?
To answer this question one would have to look at each and every event since the LOOP assumption could vary depending upon the event (see response to Q1).
For instance, the steam generator tube rupture event at Oconee did not assume a LOOP. This is obvious because the FSAR Chapter 15 analysis assumes a 100 degree per hour cooldown rate; hence, the reactor coolant pumps (ergo offsite power) must be available. A loss of offsite power would have to be assumed by today's standards. However, this condition was not backfit to operating plants and the analysis is plant specific. For other events the complete analysis assuming a loss of offsite power may not have been completed because it was assumed the accident or transient was more severe if offsite power was not lost. An example of this is the steam line break accident in FSAR Section 15.13. In that analysis the licensee states that without loss of offsite power is the worst case scenario because it is a cooldown event. Thus, a scenario involving a LOOP may not have been completely analyzed. If it can be
-5 shown that the LOOP following a main steam line break is more limiting, then the plant may be shown to be outside its design basis. A good rule of thumb to determine whether or not a LOOP should be assumed following a particular event or accident is whether the event causes a plant trip. If a plant trip results from the event/accident then a LOOP should be assumed (See SRP Section 3.6.1).
However, this is not a regulation or specified requirement and each operating plant's analyses must be reviewed on a case by case basis to determine the licensing basis for a particular plant.