Information Notice 1997-60, Incorrect Unreviewed Safety Question Determination Related to Emergency Core Cooling System Swapover from the Injection Mode to the Recriculation Mode

Incorrect Unreviewed Safety Question Determination Related to Emergency Core Cooling System Swapover from the Injection Mode to the Recriculation Mode

ML031050207
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, 05000051, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	08/01/1997
From:	Slosson M Office of Nuclear Reactor Regulation
To:
References
IN-97-060, NUDOCS 9707300063
Download: ML031050207 (10)

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UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 August 1, 1997 NRC INFORMATION NOTICE 97-60: INCORRECT UNREVIEWED SAFETY QUESTION

DETERMINATION RELATED TO EMERGENCY

CORE COOLING SYSTEM SWAPOVER FROM THE

INJECTION MODE TO THE RECIRCULATION

MODE

Addressees

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

Purpose

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

addressees to an instance in which a licensee has incorrectly determined that changes to its

emergency core cooling system (ECCS) swapover procedures that resulted in interruption of

flow and a consequent core heatup in the long-term cooling phase of a potential loss-of- coolant accident (LOCA) did not involve an unreviewed safety question (USQ). It is expected

that recipients will review this 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.

DescriDtion of Circumstances

On May 1, 1989, a license amendment was issued approving a semi-automatic ECCS swap- over procedure for Salem Nuclear Unit 2. This procedure provided the plant with the

capability to switch the ECCS suction from the refueling water storage tank (RWST) to the

containment sump (i.e., from the injection mode of operation to the recirculation mode of

operation) without interruption of ECCS flow to the core. It further provided continuous

suction to the high-head safety injection (HHSI) and intermediate-head safety injection (IHSI)

pumps. The semi-automatic swapover design provided this capability by automatically com- pleting the following steps: (1) opening the suction line valves between the residual heat

removal (RHR) pump and the sump; (2) starting component cooling water to the RHR heat

exchangers; (3) opening the suction crosstie valves between the HHSI and IHSI pumps; and

(4) when the sump line valves are fully open, closing the suction line to the RWST. Manual

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IN 97-60

August 1, 1997 operator action was still required to align the suction of the HHSI and IHSI pumps to the

discharge of the RHR pumps (i.e., the piggyback mode of operation) and to trip the con- tainment spray pumps. Subsequently, both the licensee's individual plant examination and

the NRC technical evaluation report on Salem human reliability analysis issued in August

1995 identified ECCS swapover as one of the most risk-significant operator actions for

Salem.

For Salem Unit 2, ECCS swapover is initiated when the level in the RWST reaches the low- level alarm setpoint. In addition, to prevent vortexing in the RWST and to protect the ECCS

pumps, emergency operating procedures (EOPs) direct operators to trip all ECCS pumps

taking suction from the RWST if the RWST low-low level alarm setpoint is reached. There- fore, the maximum time available for successful completion of ECCS swapover is the time

that it would take the RWST to drain from the low-level alarm setpoint to the low-low level

alarm setpoint. In 1995 and 1996 the licensee performed evaluations that consiaered: (1)

uncertainties in specific operator action times, (2) the introduction of "three-point"

communications, (3) higher than previously assumed containment spray pump flow, and (4)

the identification of more limiting single-failure scenarios. The licensee concluded that

under certain accident conditions, the operators may not be able to complete the swapover

before reaching the low-low level alarm setpoint. For such scenarios, the operators would

be directed to trip the ECCS pumps taking suction from the RWST, thereby interrupting

ECCS flow to the core.

The licensee's analyses for the small break loss-of-coolant accident (SBLOCA) and

accumulator line break accidents allotted the operators 11.8 minutes and 12.9 minutes, respectively, for completing the ECCS swapover procedure from the point that the RWST

level reaches the low-level alarm setpoint. Licensee calculations showed that the low-low

level alarm setpoint would be reached at 10 minutes for the SBLOCA and 7.9 minutes for the

accumulator line break. As discussed above, this is the point at which the operators are

directed to stop all ECCS pumps taking suction from the RWST, thereby interrupting ECCS

flow to the core. Therefore, for the balance of the time allotted for completing the swapover

procedure (i.e., 1.8 minutes for the SBLOCA and 5 minutes for the accumulator line break),

core cooling would have to be provided without ECCS flow. The licensee evaluated these

changes to the swapover procedure, including the introduction of interruption of ECCS flow, pursuant to 10 CFR 50.59 and determined that the changes did not involve a USQ. Accord- ingly, the licensee implemented the changes without NRC staff approval.

The NRC became aware of the above-described changes to Salem Unit 2's semi-automatic

ECCS swapover procedure during a special NRC inspection conducted between March 24 and April 17, 1997. The inspectors were concerned with the introduction of interruption of

flow into the ECCS swapover procedure as the NRC staff had not reviewed this approach fcr

Salem Unit 2. Additionally, the inspectors were concerned about the potential for such

scenarios to violate the requirement contained in 10 CFR 50.46(b)(5), "Long term cooling."

IN 97-60

August 1, 1997 Discussion

Pursuant to 10 CFR 50.59, a licensee may make changes in its facility and procedures as

described in the safety analysis report (SAR) without prior Commission approval, unless

the proposed change involves a USQ. In part, 10 CFR 50.59 states that changes shall be

deemed to involve a USQ if the probability of occurrence of a malfunction of equipment

important to safety previously evaluated in the SAR may be increased, or if a possibility

for a malfunction of a different type than any evaluated previously in the SAR may be

created.

The changes to the swapover procedure in the Salem case introduced reliance on manual

operator actions, where such actions were not previously required to stop and restart

ECCS pumps, and reliance on ECCS pumps to restart shortly after being stopped during an

accident.

This was contrary to the intent of the 1989 design change, which was to increase the

reliability of ECCS swapover by automating ceirain features, so that the RHR pumps would

not have to be stopped and restarted, and reduce susceptibility to human error in ECCS

swapover. As a result of the inspection findings, the staff evaluated these changes and

found them to have increased the probability of a malfunction of equipment important to

safety in that the changes provide additional opportunities for operator error, especially

considering the conditions and the time constraints under which the operators would be

working. In addition, restarting ECCS pumps shortly after they have been stopped involves

uncertainties as to whether the pumps will restart and is not recommended by pump vendors.

Therefore, an increase in the probability of malfunction of the ECCS pumps was also

introduced. On the basis of the above discussion, the staff concluded in Inspection Report

50-311/97-11 that these changes did involve a USQ.

In addition, the interruption of flow during ECCS swapover could potentially result in another

fuel uncovery following the initial blowdown and reflood phase of a LOCA. Consequently, the

fuel could reheat during that phase of the accident. Therefore, such an interruption of ECCS

flow could violate the long-term cooling requirement of 10 CFR 50.46 (b)(5). Additional

cycling of the fuel (i.e., introduction of heatups in the long-term cooling phase of the accident)

also increases the probability of cladding failure and therefore involves a USQ as defined in

10 CFR 50.59. For the Salem case, the licensee evaluated the effects of the interruption of

flow on the core. The licensee wanted to maximize the time available to the operators to

complete the swapover. The allowable times for flow interruptions as noted above were

calculated on the basis of maintaining the core under water to avoid core heating. The

licensee has since implemented EOP changes to allow operators to complete the swapover

without interruption of flow. In addition, the licensee verified through simulator exercises

that all operating crews could perform the revised EOPs well within the time frame required

to prevent interruption of flow. The NRC found the licensee's actions to resolve these issues

to be acceptable.

KJ

IN 97-60

August 1, 1997 This information notice requires no specific action or written response. If you have any

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

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

ary e . Slosson, Acting Dire r

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Mohammed A. Shuaibi, NRR Thomas Koshy, NRR

301-415-2859 301-415-1176 E-Mail: mas4@nrc.gov E-mail: txk@nrc.gov

Frank R. Orr, NRR Doug Dempsey, RI

301-415-1815 (610) 337-5347 E-Mail: fro@nrc.gov E-mail: dadl@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

L~te /A T

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.

Attachment

IN 97-60

August 1, 1997 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

97-59 Fire Endurance Test 08/01/97 All holders of OLs or CPs

Results of Versawrap for nuclear power reactors

Fire Barriers

97-58 Mechanical Integrity of 07/31/97 Holders of and Applicants

In-Situ Leach Injection for Licenses for In-Situ

Wells and Piping Leach Facilities

97-57 Leak Testing of Packaging 07/30/97 Suppliers and users of

Used in the Transport of packaging for the trans- Radioactive Material portation of radioactive

material required to per- form packaging leak tests

97-56 Possession Limits for 07/28/97 All licensees authorized

Special Nuclear Material to possess special nuclear

at the Environcare of material

Utah Low-Level Radioactive

Waste Disposal Facility

97-55 Calculation of Surface 07/23/97 All Uranium Recovery

Activity for Contaminated Licensees

Equipment and Materials

97-54 NRC Licensed Operators 07/18/97 All holders of OLs or CPs

at Six Non-Power Reactor for test and research

Facilities Allow their reactors and all licensed

Operator Licenses to operators at test and

Expire research reactor facilities

97-53 Circuit Breakers 07/18/97 All holders of OLs or CPs

Left Racked Out in for nuclear power reactors

Non-Seismically

Qualified Positions

OL = Operating License

CP = Construction Permit

. . S

IN 97-60

August 1, 1997 This information notice requires no specific action or written response. If you have any

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

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

original signed by S.H. Weiss for

Marylee M. Slosson, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Mohammed A. Shuaibi, NRR Thomas Koshy, NRR

301-415-2859 301-415-1176 E-Mail: mas4@nrc.gov E-mail: txk@nrc.gov

Frank R. Orr, NRR Doug Dempsey, RI

301-415-1815 (610) 337-5347 E-Mail: fro@nrc.gov E-mail: dadl@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

Tech Editor has reviewed and concurred on 06/19/97

• SEE PREVIOUS CONCURRENCE

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OFFICE -TEC -C:OGCC:PECB

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-t K>

IN 97-xx

July xx, 1997 This information notice requires no specific action or written response. If you have any

questions about the 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: Mohammed A. Shuaibi, NRR Thomas Koshy, NRR

301-415-2859 301-415-1176 E-Mail: mas4@nrc.gov E-mail: txkenrc.gov

Frank R. Orr, NRR Doug Dempsey, Region I

301-415-1815 (610) 337-5347 E-Mail: froenrc.gov E-mail: dadl@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

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IN 97-xx

July xx, 1997 This information notice requires no specific action or written response. If you have any

questions about the 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 L. Slosson, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Mohammed A. Shuaibi, NRR Thomas Koshy, NRR

301-415-2859 301-415-1176 E-Mail: mas4@nrc.gov E-mail: txk@nrc.gov

Frank R. Orr, NRR Doug Dempsey, Region 1

301415-1815 610-337-5347 E-Mail: fro@nrc.gov E-mail: dadl@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

• SEE PREVIOUS CONCURRENCE

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CONTACT

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NAME MShuaibi* JLyons* MRafky* AChaffee MSlosson

FOrr*

GGalleti*

EMcKenna*

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DATE 7/97* 7/15/97 07/22/97 07/ A97 07/ /97

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UII-ILIAL KtUWKU LUY'T

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IN 97-xx

July xx, 1997 This information notice requires no specific action or written response. If you have any

questions about the information in this notice, please contact one of the tp6ihnical contacts

listed below or the appropriate Office of Nuclear Reactor Regulation (N R) project

manager.

Marylee L. Slosson, A ng Director

Division of Reactor P gram Management

Office of Nuclear actor Regulation

Technical contacts: Mohammed A. Shuaibi, NRR / Thomas Koshy, NRR

301-415-2859 / 301-415-1176 E-Mail mas4@nrc.gov txk@nrc.gov

Frank R. Orr, NRR Doug Dempsey, Region 1

301-415-1815 610-337-5347 E-Mail fro@nrc.gov dad1 @nrc.gov

Attachment: List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:\TXK\FLOWINT.IN

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OFFICE TECH (A)C D

CONTACT

S I __

NAME MShuaibi* JLyon

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EMcKenna*

TKoshy

O70

IN 97-xx

July xx, 1997 ,

This information notice requires no specific action or written response. If )u,nave any

questions about the information in this notice, please contact one of the tE Jiinical contacts

listed below or the appropriate Office of Nuclear Reactor Regulation (NRF project manager.

Marylee)Slosson, A ng Director

Division of Reactor ogram Management

Office of Nuclear O actor Regulation

Technical contacts: Mohammed A. Shuaibi, NRR Thomas Koshy, NRR

301-415-2859 301-415-1176 E-Mail mas4@nrc.gov txk@nrc.gov

Frank R. Orr, NRR Doug Dempsey, Region 1

301-415-1815 610-337-5347 E-Mail fro@nrc.gov dadi @nrc.gov

Attachment: List of Recently Issued NRC Notices

DOCUMENT NAME: G:=TXKFLOVMNT.IN

To receive a copy of fths document, Indicate In the box: with enclosures "N"a No