Information Notice 1991-54, Foreign Experience Regarding Boron Dilution

Foreign Experience Regarding Boron Dilution
	ML031190351
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, Atlantic Nuclear Power Plant
Issue date:	09/06/1991
From:	Rossi C; Office of Nuclear Reactor Regulation
To:	;
References
	IN-91-054, NUDOCS 9108300203
	Download: ML031190351 (5)
	v • d • e

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 September 6, 1991 NRC INFORMATION NOTICE 91-54: FOREIGN EXPERIENCE REGARDING BORON DILUTION

Addressees

All holders of operating licenses or construction permits for pressurized

water reactors (PWRs).

Purpose

The U.S. Nuclear Regulatory-Commission (NRC) is issuing this information

notice'to alert addressees.to a potential sequence of events that may result

in a rapid injection of unborated reactor coolant water into the reactorcore.

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 require- ments; therefore, no specific action or written response is required.

Description of Circumstances

The NRC has learned of analyses, performed by a foreign program, of certain

events and event sequences which indicate that there is a potential for a

rapid injection into a PWR reactor core of unborated reactor coolant whose

effects would be more severe than similar events considered in the safety

analyses of most U.S. plants.

The adverse events involve the accumulation of a significant volume of

unborated water in a part of the primary coolant system during plant shutdown.

Various actions performed during plant shutdown could result in such an

accumulation. Once the unborated water is accumulated, the startup of an idle

reactor coolant pump could send the unborated water into the reactor core causing

a significant and unplanned reactivity insertion.

The following sequence of events is evaluated in the foreign study.

The sequence is initiated by the loss of one of two offsite electrical power

sources. This loss of power, occurs while the reactor coolant water is being

diluted for reactor startup. At this time, decay heat is insufficient to

cause natural circulation of the reactor coolant. It is assumed that the

operating reactor coolant pump(s) are powered from the failed offsite power

source and cease running. However, the charging pumps, powered from the

alternate power source, continue to operate and a significant volume of

unborated water is accumulated in the reactor coolant system. If,at this

9108300203 E4q LD (Oia'2

002098 mI: i s stI

IN 91-54 September 6, 1991 point, an idle reactor coolant pump is started, the accumulated volume of

weakly borated or unborated water would be injected into the reactor core.

Discussion of Safety Significance

The safety analyses for most U.S. nuclear plants do not address this explicit

sequence of events. However, the staff is aware of one representative analysis

of a similar sequence for a U.S. PWR. In that analysis, the results indicate

that such an accident could cause some core damage but that breach of the

reactor coolant system would be unlikely. The NRC is continuing to study other

possible sequences that could cause a similar unplanned injection of unborated

water. The above postulated sequence of events would occur as a result of

actions performed during plant restart from a shutdown condition and as such is

being considered as part of the NRC's review of shutdown risk.

This accident sequence 'involves several assumptions regarding plant conditions

and equipment configuration and, therefore, may not apply to a particular U.S.

plant. Training and procedures that emphasize the need to ensure uniform

boron concentration in the reactor coolant system at all times and the imple- mentation of-appropriate caution in starting an idle reactor coolant loop can

reduce the probability of occurrence of such an event.

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

youhave any quesions abottt the Information-4n this notiepklease_.contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation project manager.

CRoOe &W

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical contacts: N. Prasad Kadambi, NRR

(301) 492-0841 M. Caruso, NRR

(301) 492-3235 Attachment: List of Recently Issued NRC Information Notices

r , .

Attachment

IN 91-54 September 6, 1991 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

89-90, Pressurizer Safety Valve 09/05/91 All holders of OLs or CPs

Supp. 2 Lift Setpoint Shift for nuclear power reactors.

91-53 Failure of Remote Shutdown 09/04/91 - All holders of OLs or CPs

System Instrumentation for nuclear power reactors.

Because of Incorrectly

Installed Components

91-52 Nonconservative Errors 08/29/91 All holders of OLs or CPs

In Overtemperature Delta- for Westinghouse (W)-designed

Temperature (OTAT) Set- nuclear power reactors.

point Caused by Improper

Gain Settings

86-14, Overspeed Trips of AFW, 08/26/91 All holders of OLs or CPs

-Supp-. 2 HPC0-6nd;RCIC Turbiiies for nuclear power reactors.

91-51 Inadequate Fuse Control 08/20/91 All holders of OLs or CPs

Programs for nuclear power reactors.

91-50 A Review of Water Hammer 08/20/91 All holders of OLs or CPs

Events After 1985 for nuclear power reactors.

91-49 Enforcement of Safety 08/15/91 All Nuclear Regulatory Com- Requirements for Radiog- mission (NRC) licensees

raphers authorized to use sealed

sources for industrial

radiography.

91-48 False Certificates of Con- 08/09/91 All holders of OLs or CPs

formance Provided by West- for nuclear power reactors.

inghouse Electric Supply

Company for Refurbished Com- mercial-Grade Circuit

Breakers

91-47 Failure of Thermo-Lag 08/06/91 All holders of OLs or CPs

Fire Barrier Material to for nuclear power reactors.

Pass Fire Endurance Test

OL = Operating License

CP = Construction Permit

- t.IN - 91-54 September 6, 1991 point, an idle reactor coolant pump is started, the accumulated volume of

weakly borated or unborated water would be injected into the reactor core, Discussion of Safety Significance