Information Notice 1997-25, Dynamic Range Uncertainties in the Reactor Vessel Level Instrumentation

Dynamic Range Uncertainties in the Reactor Vessel Level Instrumentation
	ML031050317
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	05/09/1997
From:	Slosson M; Office of Nuclear Reactor Regulation
To:	;
References
	IN-97-025, NUDOCS 9705070146
	Download: ML031050317 (8)
	v • d • e

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 May 9, 1997 NRC INFORMATION NOTICE 97-25: DYNAMIC RANGE UNCERTAINTIES IN THE

REACTOR VESSEL LEVEL INSTRUMENTATION

Addressees

All holders of operating licenses or construction permits for Westinghouse pressurized-water

reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert

addressees to a recent incident in which a licensee failed to provide adequate periodic

corrections for analytical uncertainties in the reactor vessel level indicating system (RVLIS).

This failure could lead plant operators to take nonconservative actions during an emergency.

It is expected that recipients will review this information for applicability to their facilities and

consider actions, as appropriate. However, suggestions contained in this information notice

are not NRC requirements; therefore, no specific action or written response is required.

Description of Circumstances

On March 3, 1997, the licensee for Diablo Canyon Units 1 and 2 discovered that since initial

installation of the RVLIS, dynamic range indications had not been renormalized as described

in the Westinghouse operations manuals. Because dynamic range uncertainties caused by

changes in the reactor coolant system (RCS) hydraulics were not verified, normalized, or

changed periodically per vendor recommendations, it was initially believed that the RVLIS

dynamic flow range indication readings were 6-8 percent higher than actual values. Later, an

engineering evaluation performed by the licensee showed that RVLIS readings were about

10 percent higher than actual values. These higher-than-actual readings could have caused

plant operators to take non-conservative actions during a loss of RCS inventory event.

Discussion

The Westinghouse RVLIS is a differential pressure (dip) measuring system for determining

the water level in the reactor vessel or the relative void content of the RCS, or both. In

addition to directly indicating of vessel water level, it provides useful information relating to

leaks and small breaks in the RCS. This system employs separate sets of three d/p cells, and the display consists of level indications in three ranges. The narrow range (also called

full range), displays collapsed water levels from 0 to 100 percent between the empty and the

full vessel with none of the reactor coolant pumps (RCPs) running. The upper range displays

vessel levels above hot-leg connections, again with none of the RCPs running. During

69705070146 97 IDZ

IN 97-25 May 9, 1997 normal at-power plant operation with the RCPs running, the displays for these two ranges are

off scale. The wide range or dynamic range is scaled from 0 percent with the vessel empty

and with no RCPs running, to 100 percent with the vessel full and all RCPs running.

After initial installation, instruments for the dynamic range are calibrated using analytical

uncertainties associated with the calculated values of the flow differential pressure head loss.

This calculation is based on head characteristics of the RCPs and various flow resistances of

the RCS. The vendor recommended that all calculated values be verified, confirmed, and

adjusted during subsequent plant startups to correct uncertainties involving system hydraulic

changes for each fuel cycle, such as steam generator tube plugging and change in fuel

assembly flow resistance. This process, known as "normalizing," returns the outputs to an

indication of 100 percent at zero power with all RCPs running. In the event of an accident

during the cycle leading to loss of coolant with continued RCPs operation, the coolant would

be circulated as a void mixture, and the RVLIS dynamic range would indicate the increase in

voids as a decrease in dynamic range output. By renormalizing the dynamic range to

100 percent at the beginning of each cycle, the dynamic range output indicates the

approximate void content relative to a zero void condition.

During an internal review, the Diablo Canyon licensee discovered that, since initial startup, the calculated uncertainty values associated with the RCS flow characteristics for the RVLIS

dynamic head transmitter had never been periodically verified as recommended in the

Westinghouse (vendor) manual. The licensee contacted Westinghouse to discuss the

problem, and implemented corrections for RVLIS indications by recalibrating the instruments

through an online dynamic range normalization. During this process, the licensee discovered

that the RVLIS readings erred by about 10 percent in the nonconservative direction.

This information notice requires no specific action or written response. If you have any

questions about information in this notice, please contact one of the technical contacts listed

below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.

Marylee M. Slosson, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: S.V. Athavale, NRR Tai L. Huang, NRR

(301) 415-2974 (301) 415-2867 E-mail: sval@nrc.gov E-mail: tlhl@nrc.gov

Thomas Koshy, NRR

(301) 415-1176 E-mail: txk@nrc.gov

Attachmept: List of Recently Issued RC Information Notices

4114 fl, J kAlT

. - IF

Attachment

IN 97-25 May 9, 1997 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

97-24 Failure of Packing Nuts 05/08/97 All U.S. Nuclear Regulatory

on One-inch Uranium Commission licensees and

Hexafluoride Cylinder certificatees authorized

Valves to handle uranium hexa- fluoride in 30- and 48-inch

diameter cylinders

97-23 Evaluation and Reporting 05/07/97 All fuel cycle conversion, of Fires and Unplanned enrichment, and fabrication

Chemical Reactor Events facilities

at Fuel Cycle Facilities

97-22 Failure of Welded-Steel 04/25/97 All holders of OLs or

Moment-Resisting Frames CPs for nuclear power

During the Northridge reactors

Earthquake

97-21 Availability of Alternate 04/18/97 All holders of OLs

AC Power Source Designed for nuclear power

for Station Blackout Event reactors

97-20 Identification of 04/17/97 All holders of OLs

Certain Uranium for nuclear power

Hexafluoride Cylinders

that do not comply

with ANSI N14.1 Fabrication

Standards

97-19 Safety Injection 04/18/97 All holders of OLs

System Weld Flaw at or CPs for nuclear

Sequoyah Nuclear power reactors

Power Plant, Unit 2 OL = Operating License

CP = Construction Oermit

IN 97-25 V May 9, 1997 normal at-power plant operation with the RCPs running, the displays for these two ranges are

off scale. The wide range or dynamic range is scaled from 0 percent with the vessel empty

and with no RCPs running, to 100 percent with the vessel full and all RCPs running.