ML20150D768

Safety Evaluation Approving Util Inadequate Core Cooling Instrumentation Sys Contingent on Completion of Emergency Procedures & Operator Training & Submittal of Applicable Tech Specs

ML20150D768
Person / Time
Site:	Maine Yankee
Issue date:	07/07/1988
From:	Office of Nuclear Reactor Regulation
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ML20150D761	List: ML20150D768
References
CON-FIN-B-0779, CON-FIN-B-779 NUDOCS 8807140130
Download: ML20150D768 (10)

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1. pum UNITED STATES 8 g NUCLEAR REGULATORY COMMISSION 3 j WASHINGTON, D. C. 20555

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ENCLOSURE 1 SAFETY EVALVATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PELATING TO INADEQUATE CORE COOLING INSTRUMENTATION MAINE YANKEE ATOMIC POWER COMPANY MAINE YANKEE ATOMIC POWER STATION DOCKET N0. 50-309

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1.0 INTRODUCTION

A meeting was held on August 25, 1986 (Ref. 1) with the Maine Yankee Atomic Power Company (NYAPC0) to discuss the Inadequate Core Cooling Instrumentation (ICCI) for the Maine Yankee Atomic Power Station (Maine Yankee). As a result of this meeting, MYAPC0 proposed several changes in its ICCI systems Ly letter dated October 31, 1986 (Ref. 2). The staff, in conjunction with its Technical Assistance ceasultant at Oak Ridge National Laboratory (ORNL), reviewed the October 31, 1986 submittal and prepared a request for additional information (Ref. 3). By letter dated January 23, 1987 (Ref. 4) MYAPC0 provided a partial response to the staff's request for additional information. MYAPC0 stated that some information would require completion of the detailed design of the ICCI systems. By letter dated March 28, 1988 (Ref. 5), MYAPC0 submitted its final report on the design and accuracy evaluation of the ICCI system.

The staff has reviewed the information presented by MYAPC0 in its submittals of October 31, 1986 (Ref. 2), January 23, 1987 (Ref. 4), and March 28, 1988 (Ref. 5). This staff review includes significant technical input prepared by its cc1sultants at ORNL under technical assistance contract FIN B-0799.

The staffs' evaluation of the design and accuracy evaluation of MYAPC0's ICCI system follows.

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4 2.0 EVALUATION ,

2.1 Saturation Margin Monitor (SMM) System A Saturatior. Margin Monitor System, meeting the requirements of NUREG-0737 Item II.F.2, has been proposed for Maine Yankee. The system consists of two independent channels with displays located on the main control board that indicate subcooling margin between 200*F subcooled to 50*F superheated.

Inputs to each channel consist of eight CETs (two from each core quadrant) and

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one pressurizer (RCS) pressure input. An additional temperature input from separate RTDs at the reactor nead is also available to each SMM channel for monitoring the margin to saturation in the head region. The SMM provides digital readout and recording on the main control board and isolated analog inputs to the plant computer for use in the Safety Parameter Display System (SPDS). Appropriate alarms are initiated from the S'ai channels and from the equivalent SPDS information.

Each SMM is a Safety Class 1E, Seismic Class 1 instrument designed by Combustion Engineering for use as a post-accident monitoring instrument. The design meets IEEE Standards 344-1975 and 323 A974 for seismic and environmental qualification of electrical compoaents. Each channel is powered from independent Class IE power supplies and the two channels are physically separated from each others.

Based upon calculations performed for the temperature and pressure input channels and the calculator modules, the overall temperature margin uncertainty for the SMM channels is 13.7'F under normal conditions and 137.0'F under accident conditions (degraded containment).

2.2 Core Exit Thermocouple (CET) System The Core Exit Thermocouple system consists of a total of 52 CETs distributed throughout the core at the fuel alignment plate elevation. The primary display consists of two different core map 3; one available on demand via

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l) printers located in the Control Room, and the second via the SPDS. The SPDS is a CRT display which shows all CET locations and temperatures. CETs for the two SMM trains are color-coded for .asy identification. Average core teraperature, highest core temperature and trending of CET temperatures are also displayed on the SPDS.

Sixteen qualified CETs, two per quadrant per channel, are connected to the SMM trains and indicators on the main control board for backup display. A selettor switch on each channel allows rapid checking of each CET. The two ,

channels are redundant, independent trains energized from separate Class 1E power supplies. The backup display is available at all times during operation and has been incorporated into the plant emergency procedures.

Calculations were performed predicting normal and accident uncertainty of the CETs to be 10.7*F. This uncertainty contributes also to the SMM and PITS uncertainties.

2.3 Primary Inventory Trend System (PITS)

The PITS uses differential pressure measurement to indicate collapsed liquid level in the reactor vessel when the coolant pumps are r:ot operating. The system consists of redundant, independently powered channels using environmentally-qualified differential pressure transmitters to measure hydrostatic head between the top and bottom of the reactor vessel. A common impulse line is used for both channels. Thetopportionoftheline(reference leg) is connected to a reactor head flange and the bottom portion of the line (variable leg) is connected to an incore instrument guide tube below the vessel in the instrument sump. The measurement height from top to bottom of the vessel is 41.25 ft. A seal pot at the top of the reference leg provides a reservoir for thennal expansion and contraction of the reference leg water and for displacement of dissolved gases. Density compensation for fluid in the vessel and in the impulse line is provided by CET temperature measurements, pressurizer pressure, and RTDs on the vertical runs of impulse line.

4 The differential pressure transmitters, which input directly to their' associated channel microprocessors, are located in the outer annulus of the containment building at an elevation above the worst case containment flood level. The Rosemount 1154D dp transmitters are seismically and environmentally qualified to IEEE Standards 344-1975 and 323-1974.

The vessel level computed by the microprocessors is displayed on Leeds and Northrup strip chart recorders on the main control board vertical section C for each PITS channel. Each recorder is scaled to read from 0 to 100% reactor, vessal static level without reactor coolant pumps on. The recorders provide imediate status indication ano inventory trend. In addition, isolated signals are provided to the SPDS which displays level and twelve minutes of trend. Historical data beyond twelve minutes can be provided via high speed h printers in the Control Room and Technical Support Center. l The worst case instrument accuracies were derived by comparing levels calculated with the use of steam tables and no instrument error, to levels calculated by the compensation modules with the maximum instrument error.

The accuracies were determined assuming conservative combinations of vessel temperature and pressure involving subcooled, saturated, and superheated conditions. The accuracy values were then root-sum-squared with the accuracy of the microprocessor and displays to determine the final system accuracies.

The resulting uncertainties ranged from +17.8%/-11.1% (at 100% level, subcooled) to +7.7%/-13.1% (at 33% level, superheated).

An analytical assessment of the adequacy of the PITS indications was made by simulating the system response for two small break transients. The simulated response of the PITS was compared to the calculated collapsed liquid level in the same region, for a 3-in. cold leg break and for a stuck-open PORV. The comparisons, which did not include instrument uncertainties, showed good agreement for all parts of the transients.

, 5 2.4 Procedures, Training, and Technical Specifications Emergency procedures and training in the use of Inadequate Core Cooling Instrumentation have not been reviewed. Revised Technical Specifications for the instrumentation have not been submitted.

2.5 Summary of Evaluation of Maine Yankee's ICCI System The staff concludes that the revised design of Maine Yankee's ICCI system ,

meets the requirements of NUREG-0737 Item II.F.2 and resolves the concerns raised in the review of a previous design. Adequate redundancy is provided so that at least one channel of the SMM, CET and PITS should remain functional after a single active failure. Sufficient information is available to the operators from other primary indications to determino which subsystem channel is more correct, in the event of total or partial failure in a channel. The common impulse line for the otherwise redundant channels represents a practical compromise which recognizes the difficulty of retrofitting lines and penetrations in an existing plant. The staff concludes that this arrangement is acceptable and has been approved at other plants.

Maine Yankee has not provided a dynamic level indication to indicate void fraction when the primary coolant pumps are operating. The basis for not providing a dynamic level indication is because the pumps are shut off before margin to saturation is completely lost. Relief from the requirement for pumps-on level indication was agreed upon by the NRC.

The measurement uncertainty of the PITS, while significat.ly larger than claimed for sealed dp systems with transmitters outside containment, provides sufficient resolution for unambiguous determination of action points and is equivalent to other plants using transmitters inside containment.

Qualification, redundancy, and display features of the revised system have been significantly improved over previous Maine Yankee designs and the ICCI system now meet the intent of NUREG-0737, Item II.F.2.

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3.0 CONCLUSION

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1 The staff concludes that Maine Yankee Atomic Power Company's ICCI system for Maine Yankee consisting of (1) a vessel inventory system based on a differential pressure (dp) system, (2) a saturation margin monitor, and (3) a core exit thermocouple system is acceptable since it meets the requirements of Item II.F.2 of NUREG-0737. The staff acceptance, however, is contingent on '

the resolution of the following open items.

1. Emergency procedures and operator training in the use of the ICCI system have not been reviewed by the staff.

2. Technical Specifications for the ICCI system have not been submitted and reviewed by the staff. l

3. An implementation letter report as required by Item II.F.2 of NUREG-0737 must be submitted by MYAPC0 (see attachment to this safety evaluation report).

4.0 REFERENCES

1. NRC memorandum from Patrick M. Sears to Ashok C. Thadani, dated September 11, 1986.

2. Letter (GDW-86-256) from G. D. Whittier (MYAPCO) to Ashok C. Thadani ,

l (NRC),datedOctober 31, 1986.

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3. Letter from Patrick M. Sears (NRC) to J. B. Randazza (MYAPCO), dated  !

November 26, 1986. l

4. Letter (GDW-87-15) from G. D. Whittier (MYAPCO) to Ashok C. Thadani (NRC),datedJanuary 23, 1987.

5. Letter (GDW-88-69) from G. D. Wnittier (MYAPC0) to Richard Wessman (NRC),

dated March 28, 1988.

4-ATTACHMENT MILESTONES FOR IMPLEMENTATION OF INADEQUATE CORE COOLING INSTRUMENTATION

1. Submit final design description (by licensee) (complete the documentation requirements of NUREG-0737, Item II.F.2, including all plant-specific information items identified in applicable NRC evaluation reports for generic approved systems).

2. Approval of emergency operating procedure (E0P) technical guidelines - (by NRC).

NOTE: This E0P technical guideline which incorporates the selected system must be based on the intended uses of that system as described in approved generic E0P technical guidelines relevant'to the selected system.

3. Inventory Tracking Systems (ITS) installation complete (by licensee).

4. ITS functional testing and calibration complete (by licensee).

5. Prepare revisions to plant operating procedures and emergency procedures based on approved E0P guidelines (by licensee).

6. Implementation letter

• report to NRC (by licensee).

7. Perform procedure walk-through to complete task analysis portion of ICC system design (by licensee).

C. Turn on system for operator training and familiarization.

9. Approval of plant-specific installation (by NRC).

10. Implement modified operating procedures and emergency procedures (by licensee).

- System Fully Operational -

• Implementation Letter Report Content l (1) Notification that the system installation, functional testing, and calibration ir, complete and test results are available for inspection.

(2) Summary of lii:ensee conclusions based on test results, e.g.:

(a) the system performs in accordance with design expectations and within design error tolerances; or

p-2 (b) description-of deviations from design performance specifications and basis for concluding that the deviations are acceptable.

(3) : Description of any deviations of the as-built system from previous design descriptions with any appropriate explanation.

(4) Request for modification of Technical Specifications to include all ICC instrumentation for accident monitoring.

(5) Request for NPC approval of _the plant-specific installation.

(6) ill conform to the Confirm that theofE0Ps technical content used forE0P NRC approved operator training w(generic or plant guidelines i specific). I I

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