Information Notice 1985-13, Consequences of Using Soluble Dams

Consequences of Using Soluble Dams

ML031180619
Person / Time
Site:	Beaver Valley, Millstone, Hatch, 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, 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, 05000000, 05000262, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Skagit, Marble Hill, Crane
Issue date:	02/21/1985
From:	Jordan E NRC/IE
To:
References
IN-85-013, NUDOCS 8502190137
Download: ML031180619 (4)

SSINS No. 6835 IN 85-13

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF INSPECTION AND ENFORCEMENT

WASHINGTON, D. C. 20555

Addressees

All boiling water reactor (BWR) and pressurized water reactor (PWR) facilities

holding an operating license (OL) or construction permit (CP).

Purpose

This-notice is provided to alert licensees and applicants of the potential for

introducing insoluble fibers into the reactor coolant system as a result of the

use of soluble dams during pipe replacement. Recipients are expected to review

the information for applicability to their facilities and consider actions, if

appropriate, to preclude similar problems occurring at their facilities.

However, suggestions contained in this notice do not constitute NRC requirements;

therefore, no specific action or written response is required.

Description of Circumstances

Following an extended outage to replace major portions ofthe recirculation

system piping, the Monticello plant experienced excessive scram times during

surveillance testing of the control rod system. The excessive scram times were

caused by clogged inner filters in the control rod drive mechanisms (CRDMs).

The filters were clogged by fibers from soluble dams used to contain an inert

gas for welding during the pipe replacement.

During hydrostatic testing following the pipe replacement, the licensee found

scram times approaching 10 seconds on several control rods. Technical

Specifications require the rods to be 90% inserted within 3.8 seconds.

Investigation by the licensee, including friction testing, verified that there

was no mechanical binding of the rods. Additional investigation involved the

examination of the filters in the hydraulic flow path on the CRDMs.

These

examinations revealed that the inner filters in the flow path were plugged, thus increasing the scram insertion time.

Discussion:

There are three aspects of this event worth noting. The first is the impact of

foreign material in the reactor coolant system on BWR scram times.

The second

is the more general implications to both PWRs and BWRs regarding insoluble

material from soluble dams. The third is the importance of ensuring the

cleanliness of reactor coolant system water following major maintenance on

system piping components.

8502190137

IN 85-13

February 21, 1985 BWR CRDM INNER FILTER

In a BWR, a scram is slowed by a clogged movable inner filter because water

must pass through the filter during a scram and fill the volume beneath the

spud and over the top of the stop piston. If water does not pass through the

movable inner filter and the reactor is at full pressure, a large differential

pressure develops across the filter during a scram that retards rod motion.

The purpose of the inner filter is to remove particulates from the reactor

coolant system entering the CRDMs, thus reducing wear to the seals of the stop

piston. A clogged movable inner filter will affect scram times only while the

reactor is at pressure. If the reactor is not at pressure, the differential

pressure across a clogged filter is not sufficient to significantly retard rod

motion. A clogged inner filter will not prevent a scram; it can only slow the

scram because there is a small amount of bypass flow around a movable inner

filter. Neither will a clogged inner filter affect normal rod movement.

Before the recirculation pipe was replaced, all but two of the CRDMs at Monticello

had movable inner filters mounted beneath the spud.

Some plants of a more

recent design havema fixed inner filter mounted to the top of the stop piston.

The fixed filter will not inhibit scram insertion if it becomes clogged.

All

but a few licensees of older plants have modified their CRDMs with a fixed

filter using kits supplied by General Electric.

As-a'corrective-measu-re-at Monticello,- the liceinee-is-- replacing all ofthe

CRDM inner filters. Of the 121 CRDMs, 64 have now been modified to accept

the fixed inner filter. Movable inner filters were used for the remaining 57 CRDMs.

Changing the filters in the CRDMs (6 to 8 rods per day) resulted in

significant radiation exposure, approximately 3.0 man-rem per day.

After replacing some of the movable filters, the licensee discovered that the

replacement filters had an incorrect mesh size (2-mil), even though the

filters came from General Electric in boxes marked as the correct replacement

movable inner filter which should have a 10-mil mesh. As a consequence, the

CRDMs with these filters were removed a second time and replaced with filters

of the proper mesh size.

It should be noted, however, that a fixed inner

filter should have a 2-mil mesh.

SOLUBLE DAMS

The clogging of the inner filters at Monticello was caused by soluble dams that

did not fully dissolve.

The soluble dams, called DISSOLVO paper, have a starch

binder that is soluble and fibers of cotton and rayon that are not soluble but

deteriorate to soluble products at elevated system temperatures.

One gram

of this paper produces about 1 million fibers i inch in length and 5 microns in

diameter.

The fibers became trapped on the inner filter and effectively caused

the 10-mil filter to act as a much finer filter, which trapped oxides and

particulates that accumulated during the long outage. The manufacturer's

current recommendation is to dissolve the dams and remove the water used for

flushing.

Tests show that the soluble dams require temperatures greater than about 4001F

for a period of 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> for the fibers to deteriorate and change to carbon

IN 85-13 February 21, 1985 dioxide. This explains why the fibers did not deteriorate because the reactor

coolant system was never hotter than about 1850F during the hydrostatic testing

prior to the scram time surveillance testing.

Although not a problem at Monticello, another potential problem with the use of

soluble dams is associated with the glue used to attach them.

If the dams are

installed too close to the weld, the heat of welding can cause the normally

soluble glue to become insoluble. Attempts to remove the product have been

only partially successful.

The NRC has previously issued IE Information Notice No. 81-07: "Potential

Problem With Water-Soluble Purge Dam Materials Used During Inert Gas Welding"

on March 12, 1981. That information notice described other problems with a

different type of soluble dam material.

CLEAN UP OF REACTOR WATER

At Monticello, during the outage to replace the recirculation piping, the

licensee took measures to keep foreign material out of the control rod drive

mechanisms. These measures included keeping a flow of at least 10 gpm through

the drives, except during the time the vessel was drained.

After the pipe replacement, but before refueling and performing scram time

surveillance, the-licensee took measures to remove foreign material from the

reactor coolant system.

For example, the licensee vacuumed portions of the

reactor coolant system including the control rod guide tubes.

Despite these

measures, the licensee found it necessary to operate the reactor water cleanup

system (RWCUS) for about 2 days before refueling in order to restore water

clarity.

Subsequent to the filter clogging problem and to prevent recurrence of the

clogged filters, the licensee has operated the recirculation pumps to sweep

foreign material in the piping into the reactor coolant system and operated the

condensate system with its filter demineralizers.

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact the Regional

Administrator of the appropriate regional office or this office.

7dwar

. Jordan, Director

Divi

n of Emergency Preparedness

and Engineering Response

Eric Weiss, IE

(301) 492-9005 Attachment:

Attachment 1

IN 85-13

February 21, 1985

LIST OF RECENTLY ISSUED

IE INFORMATION NOTICES

Information

Date of

Notice No.

Subject

Issue

Issued to

85-12

85-11

85-10

85-09

85-08 Recent Fuel Handling Events

02/11/85 Licensee Programs For

2/11/85

Inspection Of Electrical

Raceway And Cable Installation

Posttensioned Containment

2/6/85

Tendon Anchor Head Failure

Isolation Transfer Switches

1/31/85 And Post-Fire Shutdown

Capability

Industry Experience On

1/30/85

Certain Materials Used In

Safety-Related Equipment

Contaminated Radiography

1/29/85

Source Shipments

Contamination of Breathing

1/23/85 Air Systems

Pipe Whip Restraints

1/23/85 Inadequate Management Of

1/17/85

Security Response Drills

85-07

All power reactor

facilities holding

a CP

All power reactor

facilities holding

a CP

All power reactor

facilities holding

an OL or CP

All power reactor

facilities holding

an OL or CP

All power reactor

facilities holding

an OL or CP

All NRC licensees

authorized to

possess industrial

radiography sources

All power reactor

facilities holding

an OL or CP

All power reactor

facilities holding

an OL or CP

All power reactor

facilities holding

an OL or CP, & fuel

fabrication & pro- cessing facilities

All pressurized water

power reactor

facilities holding an

OL or CP

85-06

85-05

85-04

85-03 Separation Of Primary Reactor 1/15/85

Coolant Pump Shaft And

Impeller

OL = Operating License

CP = Construction Permit