Information Notice 1993-89, Potential Problems with BWR Level Instrumentation Backfill Modifications

Potential Problems with BWR Level Instrumentation Backfill Modifications

ML031070176
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:	11/26/1993
From:	Grimes B K Office of Nuclear Reactor Regulation
To:
References
IN-93-089, NUDOCS 9311190454
Download: ML031070176 (8)

UNITED STATES NUCLEAR REGULATORY

COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 November 26, 1993 NRC INFORMATION

NOTICE 93-89: POTENTIAL

PROBLEMS WITH BWR LEVEL INSTRUMENTATION

Addressees

All holders of operating

licenses or construction

permits for boiling water reactors (BWRs).

Purpose

The U.S. Nuclear Regulatory

Commission (NRC) is issuing this information

notice to alert addressees

to potential

problems that have been identified

by licensees

involving

hardware modification

to the reactor vessel water level instrumentation

system. It is expected that recipients

will review the information

for applicability

to their facilities

and consider actions, as appropriate, to avoid similar problems.

However, suggestions

contained

in this information

notice are not NRC requirements;

therefore, no specific action or written response is required.Description

of Circumstances

NRC Bulletin (NRCB) 93-03, "Resolution

of Issues Related to Reactor Vessel Water Level Instrumentation

in BWRs," issued on May 28, 1993, requested

that licensees

implement

hardware modifications

necessary

to ensure the level instrumentation

system design is of high functional

reliability

for long-term operation.

In response to this bulletin, all BWR licensees

with the exception of Big Rock Point, which does not use cold reference

leg instrumentation, have either implemented

modifications

or have committed

to implement

modifications.

The majority of these licensees

have decided to install a reference

leg backfill system to supply a continuous

flow of water from the control rod drive (CRD) hydraulic

system through the reference

legs to preclude migration of dissolved

noncondensible

gases down the legs. In August 1993, a potential problem was found at the Susquehanna

nuclear power plant during the design of this backfill modification.

Discussion

It was postulated

at Susquehanna

that a manual isolation

valve in one of the reference

legs (see Figure 1) could be closed by operator error. Closure of this valve would result in pressurization

of that reference

leg to CRD system pressure and erroneous

indication

of low reactor water level and high reactor pressure on all instrumentation

associated

with that reference

leg. The transient

resulting

from pressurization

of the most limiting reference

leg 9311190454

1 KE-e 93-o 93 Ill

K.,_ IN 93-89 November 26, 1993 includes reactor scram and opening of all safety relief valves (SRVs) due to the false high reactor pressure.

The SRVs would remain open and depressurize

the reactor until the valves are closed by operator action, or actual reactor pressure falls below approximately

446 kPa [50 psig] at which time the valves can no longer stay open. Reactor depressurization

and loss of inventory through the SRVs, in combination

with the false low water level signal on the affected reference

leg, would result in closure of the main steam isolation valves, actuation

of high-pressure

and low-pressure

emergency

core cooling system (ECCS) and containment

isolation.

Low-pressure

ECCS injection

would commence after the low-pressure

permissive

is satisfied.

This permissive

would be satisfied

in this scenario, allowing the low pressure ECCS injection valves to open, because only one of the pressure transmitters

is affected and the logic would still be satisfied.

A single failure could defeat this logic, however, preventing

all low-pressure

ECCS Injection.

The low-pressure

permissive

can be bypassed in the control room to open the injection

valves for all four low pressure core spray (LPCS) pumps. The Susquehanna

licensee has informed the NRC that it has physically

disabled the manual isolation valves to prevent misoperation

of these valves; in addition, the valves are not readily accessible

as they are located 6.1 meters [20 feet] above the floor.This event was recently analyzed for the LaSalle plant by Commonwealth

Edison.The analysis indicates

that the low-pressure

permissive

for opening the low-pressure ECCS injection

valve would be defeated for the LaSalle design due to the false high pressure signal, thus preventing

ECCS injection

from the affected division.

If a single failure is assumed in the relay for the low-pressure permissive

on the other division, no low-pressure

ECCS injection would be available.

Because the induced plant transient

is potentially

so severe, LaSalle has designed its backfill modification

to make the injection point for the backfill system on the reactor side of the manual isolation valve and excess flow check valve, thereby precluding

the potential

for pressurization

of the reference

leg through the backfill system.Commonwealth

Edison took a different

design approach for its Dresden and Quad Cities plants. The backfill system design for Dresden and Quad Cities injects into the reference

leg on the instrument

rack side of the manual isolation

valve and excess flow check valve. Additional

administrative

controls were developed

to ensure that the isolation

valve would not be inadvertently

closed. The licensee analyzed the inadvertent

closure of the manual isolation

valve for the Dresden and Quad Cities plants and concluded that, while multiple SRVs would open, the resultant

plant transient

could be mitigated

by appropriate

operator actions. Without operator actions, the low-pressure ECCS would be available

for event mitigation;

however, a single failure in the instrumentation

system could defeat the low-pressure

permissive

for opening the low-pressure

ECCS Injection

valves and result in no low-pressure ECCS being available

for this transient.

The licensee also determined

that this design presented

an unreviewed

safety question because it would increase the probability

of a previously

analyzed accident, and submitted

an application

to amend its license pursuant to 10 CFR 50.90. The NRC is currently

reviewing

the licensee submittal.

IN 93-89 November 26, 1993 Other minor problems with the backfill system have been encountered

when installing

the system and returning

the instrumentation

to service after installation

was complete.

At the Perry plant, a problem occurred when the licensee was in the process of venting one of the instrument

lines following the installation

of the modification.

The job plan directed the operation

of the wrong valve, and instead of opening the vent valve the technician

opened the isolation

valve, allowing air into the reference

leg. As a result, the instrumentation

associated

with the high pressure core spray system (HPCS) was inoperable

until it was re-filled

and vented. Similar events have occurred at other plants due to procedural

inadequacy

or lack of attention

to detail.Related Generic Communications

• NRC Information

Notice 92-54, "Level Instrumentation

Inaccuracies

Caused by Rapid Depressurization," July 24, 1992.* Generic Letter 92-04, "Resolution

of the Issues Related to Reactor Vessel Water Level Instrumentation

in BWRs Pursuant to 10 CFR 50.54(f)," August 19, 1992.* NRC Information

Notice 93-27, 'Level Instrumentation

Inaccuracies

Observed During Normal Plant Depressurization," April 8, 1993.* NRC Bulletin 93-03, Resolution

of Issues Related to Reactor Vessel Water Level Instrumentation

in BWRs,' May 28, 1993.This information

notice requires no specific action or written response.

If you have any questions

regarding

the information

in this notice, please contact the technical

contact listed below or the appropriate

Office of Nuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, Director Division of Operating

Reactor Support Office of Nuclear Reactor Regulation

Technical

contact: Amy Cubbage, NRR (301) 504-2875 Attachments:

1. Simplified

Sketch of Backfill Modification

2. List of Recently Issued NRC Information

Notices

rfl tO CONDENSATE

POT REACTOR VESSEL (QA BOUNDARY U DRYWELL REACTOR BLDG 7 MANUAL L ISOLATION C EXCESS FLOW$ CHECK VALVE REFERENCE

LEG CRD CHARGING WATER HEADER INSTRtUm RACK VARIABLE LEG C FIGURE 1 -SIMPLIFIED

SKETCH OF BACKFILL MODIFICATION

e0 (cI-Ij3 ED w, A4...achment

2 IN 93-89 November 26, 1993 LIST OF RECENTLY ISSUED NRC INFORMATION

NOTICES Information

Date of Notice No. Subject Issuance Issued to 93-88 93-87 93-86 93-85 93-84 Status of Motor-Operated

Valve Performance

Pre-diction Program by the Electric Power Research Institute Fuse Problems with Westinghouse

7300 Printed Circuit Cards Identification

of Iso-topes in the Production

and Shipment of Byproduct Material at Non-power Reactors Problems with X-Relays in DB- and DHB-Type Circuit Breakers Manu-factured by Westinghouse

Determination

of Westing-house Reactor Coolant Pump Seal Failure 11/30/93 11/04/93 10/29/93 10/20/93 10/20/93 All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for test and research reactors.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for pressurized

water reactors (PWRs).93-83 Potential

Loss of Spent Fuel Pool Cooling Following

A Loss of Coolant Accident (LOCA)10/07/93 All holders for boiling (BWRs).of OLs or CPs water reactors 93-82 93-81 Recent Fuel and Core Performance

Problems in Operating

Reactors Implementation

of Engineering

Expertise on Shift 10/12/93 10/12/93 All holders of OLs or CPs for nuclear power reactors and all NRC-approved

fuel suppliers.

All holders of OLs or CPs for nuclear power reactors.OL -Operating

License CP -Construction

Permit

IN 93-89 a-> November 26, 1993 Other minor problems with the backfill system have been encountered

when installing

the system and returning

the instrumentation

to service after installation

was complete.

At the Perry plant, a problem occurred when the licensee was in the process of venting one of the instrument

lines following the installation

of the modification.

The Job plan directed the operation

of the wrong valve, and instead of opening the vent valve the technician

opened the isolation

valve, allowing air into the reference

leg. As a result, the instrumentation

associated

with the high pressure core spray system (HPCS) was inoperable

until it was re-filled

and vented. Similar events have occurred at other plants due to procedural

inadequacy

or lack of attention

to detail.Related Generic Communications

• NRC Information

Notice 92-54, "Level Instrumentation

Inaccuracies

Caused by Rapid Depressurization," July 24, 1992.* Generic Letter 92-04, "Resolution

of the Issues Related to Reactor Vessel Water Level Instrumentation

in BWRs Pursuant to 10 CFR 50.54(f)," August 19, 1992.* NRC Information

Notice 93-27, 'Level Instrumentation

Inaccuracies

Observed During Normal Plant Depressurization," April 8, 1993.* NRC Bulletin 93-03, 'Resolution

of Issues Related to Reactor Vessel Water Level Instrumentation

in BWRs," May 28, 1993.This information

notice requires no specific action or written response.

If you have any questions

regarding

the information

in this notice, please contact the technical

contact listed below or the appropriate

Office of Nuclear Reactor Regulation (NRR) project manager.orig /s/'d by BKGrimes Brian K. Grimes, Director Division of Operating

Reactor Support Office of Nuclear Reactor Regulation

Technical

contact: Amy Cubbage, NRR (301) 504-2875 Attachments:

1. Simplified

Sketch of Backfill Modification

2. List of Recently Issued NRC Information

Notices* SEE PREVIOUS CONCURRENCE

SRXB:DSSA*

OGCB:DORS*

TECH ED.* SRXB:DSSA*

SRXB:DSSA*

D:DSSA* OGCB:DORS*

ACUBBAGE PWEN RSANDERS WLYON RJONES ATHADANI GMARCUS 1 11/16/93 11/15/93 11/16/93 11/18/93 11/20/93 11/23/93 11/2.493 DOCUMENT NAME: 93-89.IN

IN 93-xx November xx, 1993 This information

notice requires no specific action or written response.

If you have any questions

regarding

the information

in this notice, please contact the technical

contact listed below or the appropriate

Office of Nuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, Director Division of Operating

Reactor Support Office of Nuclear Reactor Regulation

Technical

Contact: Amy Cubbage, NRR (301) 504-2875 Attachments:

1. Simplified

Sketch of Backfill Modification

2. List of Recently Issued NRC Information

Notices* SEE PREVIOUS CONCURRENCE

SRXB:DSSA*

OGCB:DORS*

TECH ED.*ACUBBAGE PWEN RSANDERS 11/15/93 11/16/93 11/15/93 SRXB:DSSA*

WLYON 11/16/93 SRXB:DSSA*

RJONES 11/18/93 D: DSSA*ATHADANI 11/20/93 OGCB:DORS GMARCUS At'i 11/23/93 D: DORS BGRIMES 11/ /93 DOCUMENT NAME: BWRWTLVL.WEN

instrumentation

associated

with the high pressure core spray system (HPCS) was inoperable

until it was re-filled

and vented. Similar events have occurred at other plants due to procedural

inadequacy

or lack of attention

to detail.Related Generic Communications

• NRC Information

Notice 92-54, "Level Instrumentation

Inaccuracies

Caused by Rapid Depressurization," July 24, 1992.* Generic Letter 92-04, "Resolution

of the Issues Related to Reactor Vessel Water Level Instrumentation

in BWRs Pursuant to 10 CFR 50.54(f)," August 19, 1992.* NRC Information

Notice 93-27, "Level Instrumentation

Inaccuracies

Observed During Normal Plant Depressurization," April 8, 1993.* NRC Bulletin 93-03, "Resolution

of Issues Related to Reactor Vessel Water Level Instrumentation

in BWRs," May 28, 1993.This information

notice requires no specific action or written response.

If you have any questions

regarding

the information

in this notice, please contact the technical

contact listed below or the appropriate

Office of Nuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, Director Division of Operating

Reactor Support Office of Nuclear Reactor Regulation

Technical

Contact: Amy Cubbage, NRR (301) 504-2875 Attachments:

1. Simplified

Sketch of Backfill Modification

2. List of Recently Issued NRC Information

Notices EDITED BY: R. Sanders DATED: 11/15/93 SRXB:DSSA*

OGCB:DORS*

SRXB:DSSA*

SRXB:DSSA*

D:DSSA OGCB:DORS

D:DORS ACUBBAGE PWEN WLYON RJONES ATHAqkNI GMARCUS BGRIMES 11/15/93 11/16/93 11/16/93 11/18/93 11/?V/93 11/ /93 11/ /93* SEE PREVIOUS CONCURRENCE