Information Notice 1985-76, Recent Water Hammer Events

Recent Water Hammer Events

ML031180351
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, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Skagit, Marble Hill
Issue date:	09/19/1985
From:	Jordan E NRC/IE
To:
References
IN-85-076, NUDOCS 8509170373
Download: ML031180351 (6)

SSINS No.: 6835 IN 85-76 UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF INSPECTION AND ENFORCEMENT

WASHINGTON, D.C. 20555 September 19, 1985 IE INFORMATION NOTICE NO. 85-76: RECENT WATER HAMMER EVENTS

Addressees

All nuclear power reactor facilities holding an operating license (OL) or a

construction permit (CP).

Purpose

This notice is to inform recipients of recent water hammer events in steam

supply lines to auxiliary feedwater (AFW) pump turbines, a steam exhaust line

from a high pressure coolant injection (HPCI) pump turbine, and discharge lines

from feedwater pumps (involving pump start logic). It is expected that recipi- ents will review the information for applicability to their facilities and

consider actions, if appropriate, to preclude a similar problem occurring at

their facilities. However, suggestions contained in this information notice do

not constitute NRC requirements; therefore, no specific action or written

response is required.

Description of Circumstances

In the past, the NRC has studied water hammer events in its Unresolved Safety

Issue (USI) A-1. Most of these events involved either the feedwater or steam

generator systems in pressurized water reactors (PWRs). In publishing its

technical findings relevant to this issue (Reference 1), the NRC realized that

total elimination of water hammer is not feasible, because of the possible

coexistence of steam, water, and voids in various nuclear plant systems. The

frequency of events forming the subject of USI A-1 peaked in the mid-70's but

then decreased as corrective equipment designs and procedures came into use.

Recently, additional events have been reported indicating an increased

frequency.

AFW Pump Turbine Steam Supply Lines

Water hammer events have been previously reported in the steam supply lines to

HPCI and reactor core isolation cooling (RCIC) turbioes in boiling water

reactors (BWRs), as discussed in Reference 1, but have not been previously

reported with any frequency in steam supply lines to AFW (or equivalent system)

turbines in PWRs.

8509170373

If

IN 85-76 September 19, 1985 On May 8, 1985, at Waterford 3, an event occurred during an AFW surveillance

test that damaged 7 struts and 1 snubber supporting the steam supply line to

the turbine driven pump. The system passed the surveillance test satisfactorily.

These steam supply lines at Waterford employ heat tracing circuits to keep the

empty portions of pipe above 280'F to prevent water collection. The licensee

observed that two heat tracing circuits on a long run of empty pipe had.not

been operating properly and identified two low points as possible'sources of

water slugs.

While not all, of the licensee's investigations have been completed, the most

likely explanation of the event is water hammer..from a steam driven water slug

produced by condensed weepage past the closed isolation valve into the normally

empty pipe. The licensee's corrective actions include assuring the heat. '

tracing circuitry is keeping the pipe above 280'F and adding drains to the low

points.

.Similar- events have been reported at Diablo Canyon 1, on June 6, 1985, and at

..San.Onofre 3, on April 16, 1985.- Jo both these events, damage was restricted

to pipe support snubbers and both systems passed the surveillance tests satis- factori-ly. At Diabl.o Canyon,. steam traps on the supply line had been inadver- tently left isolated. At San Onofre, the cause could not be'established, but

.~the licensee has decided to replace the. existing steam traps with orifices to

reduce the possibility of collecting-condensation in the pipe..

Before March 21, 1985, at Davis-Besse, damage was found to pipe hangar supports

on long, unheated, approximately horizontal sections of the crossover supply

lines to the turbine driven pumps. This damage is likely due to acceleration

of water slugs formed from condensation, of steam in these.lines. While not

definitely concluding so, the licensee suspects that the formation might also.

have contributed to overspeed trips of both.turbines'on June 9, 1985, and other

• irregularities in turbine speed characteristics before that date. (Information

Notice No. 85-50 provides further information about'the Davis-Besse.event of

• June 9, 1985.)

HPCI Pump Turbine Steam Exhaust Line

Water hammer events in the steam exhaust lines of HPCI and RCIC turbines in

BWRs have been discussed in References 1 and 2. The following events, while

similar in some respects, introduce new information relating the events to the

operation of the turbine.

On April 2,.1985, at Pilgrim, the licensee found a failed inner rupture disk on

the HPCI turbine exhaust line and a damaged snubber near the torus penetration

• -.of the line. Believing that a water hammer had occurred from trapped conden- sate because the exhaust line had not been purged with nitrogen before a prompt

manual restart after a turbine trip, the licensee decided to purge the exhaust

line for a longer time after system operation and to inspect the line supports

following system operation.

IN 85-76 September 19, 1985 On May 18,. 1985, the Pilgrim licensee found'two damaged snubbers'on the HPCI

steam exhaust line after another surveillance test. The licensee believes that

the snubber damage may have occurred when the HPCI turbine tripped, slowed, and

automatically restarted after only a few seconds during the test. The damage

occurred on the exhaust line near the torus penetration downstream of the

vacuum breaker and stop check-valve.

To lessen the severity of transients caused by quick starts of the turbine, the

licensee revised HPCI procedures to manually control the speed on starting and

installed a bypass line around the governor's actuator assembly to increase

hydraulic pressure downstream of the actuator's internal pump. On testing, the

licensee found the initial spike in turbine speed to be lessened considerably.

These changes were designed to decrease the likelihood of overspeed tripping on

starting.

The water hammers likely were caused by water being siphoned into the exhaust

line from the suppression pool as steam in the exhaust line condensed. The

operation of the drain and vacuum breaker subsystems on the line may not have

been adequate for the short operating cycles experienced. For example, the

vacuum breaker is only of 1-inch size for a 20-inch exhaust line. The licensee

now is considering installing a bigger vacuum breaker on the line near the

torus penetration. This type of problem, which could be expected to occur in

an actual demand under accident conditions, might not be noticed on surveil- lance testing if fast-start testing were not employed.

Logic Problems With Main Feedwater Pump Restart

On August 21, 1984, the licensee at McGuire 1 experienced a loss of offsite

power, which with the manual closing of the main steam isolation valves

-required by the event resulted in a loss of all condensate and feedwater pumps.

The loss of power also caused the feedwater pump recirculation valves to the

condenser to fail open as designed. This partially drained the feed system.

When power was restored and the feed pumps manually restarted, water hammer

occurred.

Inspection revealed that the water hammer caused only minor damage to conden- sate booster pump discharge pressure gauges. The licensee is modifying proce- dures to minimize the possibility of water hammer on pump restart following a

loss of offsite power. This is an example of a system being designed to drain

on loss of power, creating the conditions for subsequent water hammer. Similar

conditions also have been reported for the auxiliary saltwater systems at

Diablo Canyon Units 1 and 2.

IN 85-76 September 19, 1985 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.

dward . Jordan, Director

Divis n of Emergency Preparedness

an Engineering Response

Office of Inspection and Enforcement

V. Hodge, IE

(301)492-7275 Attachments:

1. References

2. List of Recently Issued IE Information Notices

Attachment 1 IN 85-76 September 19, 1985 References

1. "Evaluation of Water Hammer Occurrence in Nuclear Power Plants,"

NUREG-0927, Revision 1, Office of Nuclear Reactor Regulation, U.S. Nuclear Regulatory Commission, March 1984.

2. "Water Hammer in Boiling Water Reactor High Pressure Coolant Injection

Systems," Engineering Evaluation Report No. AEOD/E402, Office of Analyti- cal Evaluation of Operational Data, U.S. Nuclear Regulatory Commission, January 10, 1984.

Attachment 2 IN 85-76 September 19, 1985 LIST OF RECENTLY ISSUED

IE INFORMATION NOTICES

Information Date of -

Notice No. Subject Issue Issued to

85-75 .Improperly Installed Instru- 8/30/85 All power reactor

mentation, Inadequate Quality facilities holding

Control And Inadequate Post- an OL or CP

modification Testing

85-74 Station Battery Problems 8/29/85 All power reactor

facilities holding

an OL or CP

84-70 Reliance On Water Level 8/26/85 All power reactor

Sup. 1 Instrumentation With A facilities holding

Common Reference Leg an OL or CP

85-73 Emergency Diesel Generator 8/23/85 All power reactor

Control Circuit Logic Design facilities holding

Error an OL or CP

85-72 Uncontrolled Leakage Of 8/22/85 All power reactor

Reactor Coolant Outside facilities holding

Containment an OL or CP

85-71 Containment Integrated Leak 8/22/85 All power reactor

Rate Tests facilities holding

an OL or CP

85-70 Teletherapy Unit Full 8/15/85 All material

Calibration And Qualified licensees

Expert Requirements (10 CFR

35.23 And 10 CFR 35.24)

85-69 Recent Felony Conviction For 8/15/85 All power reactor

Cheating On Reactor Operator facilities holding

Requalification Tests an OL or CP

85-68 Diesel Generator Failure At 8/14/85 All power reactor

Calvert Cliffs Nuclear facilities holding

Station Unit 1 an OL or CP

OL = Operating License

CP = Construction Permit