ML20214J291

Safety Evaluation Re Preliminary Design for safety-grade Anticipatory Reactor Trips on Loss of Main Feedwater &/Or Turbine Trip

ML20214J291
Person / Time
Site:	Oconee, Arkansas Nuclear, Crystal River, Rancho Seco, 05000000
Issue date:	12/20/1979
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20213D074	List: ML20213D072 ML20214J291
References
TASK-2.K.2.10, TASK-TM TAC-45188, NUDOCS 8705270746
Download: ML20214J291 (7)

Text

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1. 'o,, UNITED STATES 8' '

c. NUCLEAR REGULATORY COMMISSION

'f E WASHINGTON, D. C. 20655

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR RFACTOR REGULATION OF PRELIMINARY DESIGN FOR SAFETY-GRADE ANTICIPATORY REACTOR TRIPS (ARTS) ON LOSS OF MAIN FEEDWATER AND/OR TURBINE TRIP FOR _,

DUKE POWER COMPANY OCONEE NUCLEAR STATION, UNITS NOS. 1, 2 AND 3 ,

DOCKETS NOS. 50-269, 270 AND 287 )

SACRAMENTO MUNICIPAL UTILITY DISTRICT RANCHO SEC0 NUCLEAR GENERATING STATION .- )

DOCKET NO. 50-312.

l ARKANSAS POWER & LIGHT COMPANY ARKANSAS NUCLEAR OllE, UNIT 1 DOCKET NO. 50-313 FLORIDA POWER CORPORATION l

CRYSTAL RIVER NUCLEAR GENERATING STATION UNIT NO. 3 DOCKET NO. 50-302 I. BACKGROUND Following the accident at Three Mile Island Unit 2, an assessment of feedwater transients in the Babcock and Wilcox (B&ti) designed pressurized water reactors was performed. The results of that review were reported in NUREG-0560 This i report highlighted a concern regarding the challenges to the power-operated l relief valves (PORV) in the B&W design. In response to I&E Bulletin 79-05B, i

the licensees lowered the existing setpoint for the high pressure reactor trip and raised the setpoint of the PORV. By inverting these setpoints the challenge rate to the PORY and thus the chance of it not reseating following actuation was reduced.

To provide additional margin to the automatic opening setpoint, the licensees pmposed design provisions for direct reactor trip on loss of main feedwater or turbine trip. This design modification was approved and incorporated as part of the required actions of the Commission's Confirmatory Shutdown Orders issued in May 1979. In order to achieve a timely implementation it was deter-mined that a " control-grade" design was sufficient for the short-term. In the short-term the licensees implemented hardwired, control-grade trips inde- ,

pendent of the reactor protection system (RPS). For the long-term, the trips were to be upgraded to safety-grade and become part of the RPS.

As part of the long-term requirements, each licensee submitted their proposed designs for safety-grade reactor trips to be incorporated in the existing RPS.

8705270746 791220 ~

PDR P ADOCK 05000269 ppg,

These submittals are listed as References 1 through 8 of Attachment 2 to this evaluation. The following evaluation is applicable to Oconee Units 1, 2 and 3; Arkansas Nuclear One, Unit 1, Rancho Seco and Crystal River Unit 3.

II. EXISTING RPS The existing plant RPS includes four redundant and independent channels.

Each channel has its own independent input sensors that are physically and electrically separated from the sensors of the other channels. The present trip conditions that are monitored by these sensors and channels include:

1. Nuclear power / flux (high)

2. Nuclear power based on flow (high)

3. Nuclear power based on reactor coolant

4. Reactor coolant system pressure (high) pump status (high)*

5. Reactor coolant system pressure (low)

6. Reactor coolant system pressure based on temperature (low)

7. Reactor coolant temperature (high)

8. Reactor building (containment) pressure (high)

Within the RPS cabinets each of the four channels contain a logic string of the above inputs. Any individual actuation will cause the logic string to trip and actuate a trip relay. The trip relays of the four channels form a two-out-of-four coincident logic to open the reactor trip breakers.

III. DESCRIPTION OF PROPOSED DESIGN The licensees have proposed ARTS which will actuate on turbine trip and/nr main feedwater pump trip. These anticipatory trips provide additional protection and conservatism beyond that provided by the existing RPS.

No credit is taken for these trips in the FSAR Chapter 15 analyses. Pre-viously existing and diverse parameters will cause a reactor trip should these proposed trips fail to function.

The proposed trips are to be incorporated into the existing RPS. They each contain four redundant and independent inputs to interface with the four i RPS channels.

l The turbine trip is to be sensed by four independent pressure switches.

The feedwater pump trip is similarly sensed (for each pump) by four inde-pendent pressure switches. The logic is arranged such that both main feedwater pumps must be tripped to cause reactor trip.

• The trip system in Crystal River 3 does not monitor for this condition.

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A reactor flux level premissive (bypass) is provided to facilitate startup and shutdown of the plant. This pemissive automatically blocks the reactor trip upon turbine trip or main feedwater pump trip when reactor power is decreased below 20% power. During power, escalation, as reactor power increases to above 20%, the bypass is automatically removed and the reactor trips are reinstated. This flux signal is part of the existing RPS and therefore, is-implemented in the RPS four channel arrangement.

The pressure switch inputs are routed to the RPS cabinets for interface in the present logic trip strings through added RPS modules. The flux bypass is also implemented through a new RPS module. The RPS modules will contain contact buffers, bistables, and auxiliary relays as required. All additional equip-ment will be designed in accordance with the design bases of the existing RPS and will conform with the acceptance criteria and design requirements of the RPS.

The licensees have stated that the cabinet mounted equipment to be supplied by B&W will be fully testable from the RPS cabinets. The equipment will have l provisions for simulating input signals and verifying the proper response of the RPS channel. This testing will be similar to that presently performed on the RPS and will be integrated into the periodic testing of the cabinets.

With respect to environmental qualification, all equipment associated with the ARTS is located outside containment. In addition, the licensees have i stated that the new RPS modules to be used have been qualified for use in i B&W safety systems. Also, the pressure switch sensors will be equivalent to switches presently used in other plant safety applications. 3 i

With respect to seismic qualification, the licensees have stated that all equipment will be seismically qualified (with the exception of some equipment located in non-seismic Category I areas - See Section IV).

Existing RPS power supplies, flux signals, interlock circuits, and indicators l will be used as required by the added equipment.

IV. EVALUATION In perfoming our evaluation of the licensees' proposed designs, we utilized information provided by the licensees listed as References 1 though 8 of this evaluation.

The infomation presented in these submittals addressed only the preliminary design for the safety-grade ARTS. Included in the information is a brief description of the system and simplified logic and schematic diagrams. i We have concluded that the licensees have identified the design bases and criteria for this additional equipment, as well as provided a preliminary design description; however, the design details are not sufficiently complete to make a determination that the design satisfies the identified criteria. -

Therefore, as additional design details are developed and prior to operation $

of the new equipment, we will require that the licensees submit the final

design for our review and approval. The final design shall include final logic diagrams, electrical schematic diagrams, piping and instrumentation diagrams and location layout drawings.

In our evaluation of the ARTS, we concentrated on the adequacy of the design approach as it pertains to the existing RPS. That is, we detennined whether the trip would meet the requirements of a safety-grade system and whether its addition would in any way degrade the existing RPS.

The " Design Basis" and " Requirements" of the ARTS as required by IEEE 279-1971 are to be equivalent to those of the existing RPS with the exception that the input sensors will not conform to seismic requirements. We conclude that this is acceptable based on the anticipatory nature of these trips and that other fully qualified trips serve as back up protection. There is a related concern with the location of these inputs, which needs to be addressed in more detail by the licensees. Specifically, for those sensors located in non-seismic areas which have previously not contained RPS inputs, we will require that their installation (including circuit routing) be analyzed to demonstrate that the effects of credible faults (i.e., grounding, shorting, application of high voltage, or electromagnetic interference) or failures in these areas will not be propagated back to the RPS and degrade the RPS performance or oper-ability. This will require that specific provisions (e.g., conduit) be -

utilized to keep the circuits sufficiently separated. Therefore, we will require that the licensees submit such an analysis, along with the final design, prior to the operation of the ARTS.

With respect to equipment qualification, the licensees have supplied " Seismic and Environmental Qualification Sumary Reports" for the equipment to be supplied by B&W. The balance of the qualification information is not yet available. Therefore, we require that the information for the remaining equipment be submitted when available. In addition, as part of the final design package, we require information which demonstrates that the envion-mental test conditions bound the actual worst case accident conditions expected at the installed locations. The detailed test procedures and test data will be examined as part of the review of the final design.

The ARTS testability, particularly with respect to the sensors (paragraph 4.9 of IEEE 279-1971), is not sufficiently addressed for us to conclude that adequate provisions are being incorporated to accomplish the RPS channel tests.

Therefore, we will require that the licensees include provisions to perform channel functional tests at power on a periodic basis (i.e., during RPS monthly surveillance tests).

As part of the final design submittal, we will require that the licensees provide the RPS check-out procedure which will demonstrate both the opera-bility of the new trips and the continued operability of the previous RPS.

V. CONCLUSION The licensees have identified the design bases and design requirements for the

" Anticipatory Reactor Trips". They have also provided a preliminary design description. We have concluded that this identification along with the preliminary design description provides sufficient bases for approval of the preliminary design.

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4 In order to approve the final design, as soon as possible, we shall require

' the licensee to submit the above identified information as soon as it is available. .In addition, a site visit may be required and would be coordinate with our Office of Inspection and Enforcement.

Attachments:

1. Summary.of Infonnation Needed for Final Design Approval

2. References o

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py,A Su#'^ Attachment 1 ASOL

, SUMARY OF INFORMATION NEEDED FOR FINAL DESIGN APPROVAL i

Page nunber in SER Requiremebt 5- 7

3/ 4. The final design submittal should include the final logic i diagrams, electrical schematic diagrams, piping and instru-mentation diagrams and location layout drawings.

4. For sensors located in non-seismic areas which have not

! previously contained RPS inputs, perfom and submit an analysis which shows that the installation (including circuit routing) is designed such that the effects of 1 credible faults (i.e., grounding, shorting, ,

application of high voltage, or electromagnetic inter-ference) or failures in these areas could not be propa-gated back to the RPS and degrade the RPS performance or operability, t 4. Submit " Seismic and Environmental Qualification Summary Reports" for the equipment which has not been previously y' submitted. In addition, we require that you demonstrate that the environmental test conditions bound the actual +

. worst case accident conditions expected at the installed

! locations.

4. Assure that the ARTS testability includes provisions to

i. perfom channel functional tests at power. Testing of this

' circuitry is to be included in the RPS monthly surveillance tests.  ;

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5. Include in the final design submittal the RPS check-out j procedure which will demonstrate both the operability of >

the new trip circuitry and the continued operability of 5

the previous RPS.

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a-~ c Attachment 2 REFERENCES - ANTICIPATORY REACTOR TRIP t

OCONEE Units 1, 2 and 3 (NRC), dated May 21, 1979

1. Letter from W. O. Parker (DUKE) to H. R. Denton

Subject:

Response to IE Bulletin 79-05B.

2. Letter from W. O. Parker (DUKE) to H. R. Denton (NRC), dated October 5,1979

Subject:

Response to NRC letter dat.ed September 7,1979 (Request for Additional 2 Information).

ARKANSAS NUCLEAR ONE, Unit 1 2

3. Letter from D. C. Trimble (AP&L) to K. V. Seyfrit (NRC), dated May 21,1979

Subject:

Response to IE Bulletin 79-05B.

4. Letter from D. C. Trimble (AP&L) to R. W. Reid (NRC), dated October 8,1979

Subject:

Response to NRC letter dated September 7,1979 (Request for Additional Information).

RANCHO SECO

5. Letter from W. C. Walbridge (SMUD) to R. H. Engelken (NRC), dated May 21, 1979

Subject:

Response to IE Bulletin 79-05B.

6. Letter from J. J. Mattimoe (SMUD) to R. W. Reid (NRC), dated October 5,1979

Subject:

Response to NRC letter dated September 7,1979 (Request for Additional

, Information).

CRYSTAL RIVER, Unit 3

7. Letter from W. P. Stewart (FPC) to J. P. O'Reilly (NRC), dated May 21,1979

Subject:

Response to IE Bulletin 79-05B.

8. Letter from W. P. Stewart (FPC) to R. W. Reid (NRC), dated October 2, 1979

Subject:

Response to NRC letter dated September 7,1979 (Request for Additional

. In formation) .

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