05000423/LER-1997-007, :on 970123,non-conservative Assumptions Used in TSs Shutdown Margin Curve Identified.Caused by Lack of Procedures for Generation & Documentation of Reactor Operational Info.Engineering Procedure Will Be Revised

:on 970123,non-conservative Assumptions Used in TSs Shutdown Margin Curve Identified.Caused by Lack of Procedures for Generation & Documentation of Reactor Operational Info.Engineering Procedure Will Be Revised

ML20135B042
Person / Time
Site:	Millstone
Issue date:	02/21/1997
From:	Peschel J NORTHEAST NUCLEAR ENERGY CO.
To:
Shared Package
ML20135B028	List: 05000423/LER-1997-007, :on 970123,non-conservative Assumptions Used in TSs Shutdown Margin Curve Identified.Caused by Lack of Procedures for Generation & Documentation of Reactor Operational Info.Engineering Procedure Will Be Revised
References
LER-97-007, LER-97-7, NUDOCS 9702280057
Download: ML20135B042 (4)

LER-1997-007, on 970123,non-conservative Assumptions Used in TSs Shutdown Margin Curve Identified.Caused by Lack of Procedures for Generation & Documentation of Reactor Operational Info.Engineering Procedure Will Be Revised

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor
4231997007R00 - NRC Website

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NRC FORM 366 U.S. NUCLEAR REGULATORY Commission APPROVED BY OMB NO. 3160-0104 pgg EXP1REs 04/30/98 Eo OoN Ne'c'$oN REQ E$T 50 E

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FACtWTY NAME 113 DOCKET WUMBER (2)

Pact (3)

Millstone Nuclear Power Station Unit 3 05000423 1 of 4 TITLE 44)

Non-Conservative Assumptions Used in Technical Specifications Shutdown Margin Curve EVENT DATE (5)

LER NUMRER (6)

REPORT DATE (7) oTHER FACILITIES INVOLVED (B)

MONTH DAY YEAR YEAR SEQUENT'AL Revision MONTH DAY YEAR FACluTY NAME DOCKET NUMBER NUMBER 01 23 97 97 007 00 02 21 97 OPERATING THis REPORT is SUBMITTED PURSUANT To THE REQUIREMENTS oF 10 CFR 5: (Check one or more) (11)

DE(m 6

4 20.2201(b) 20.2203(a)(2)(v) 50.73(a)(2)(i)

So.73(a)(2)(viii)

POWER 20.2203(a)(1) 20.2203(a)(3)(i)

So.73(a)(2)(ii)

So.73(a)(2)(x)

LEVEL (10) 000 20.2203(a)(2Hi>

20.2203(a)(3)(ii)

So.73(a)(2)(iii) 73.71 20.2203(a)(2)(ii) 20.2203(a)(4)

So.73(a)(2)(iv) oTHER 20.2203(a)(2)(iv)

So.36(c)(2) 50.73(a)(2)(vii)

LICENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER (include Atee Codel J.M. Peschel, MP3 Nuclear Licensing Manager (860)437-5840 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE

SYSTEM COMPONENT MANUFACTUNER REPORTABLE

CAUSE

sYUEM COMPONENT MANUFACTURER REPORTABLE TO NPRDS To NPRDs SUPPLEMENTAL REPORT EXPECTED (141 EXPECTED MONTH DAY YEAR SUBM!ssioN f NO YEs (If yes. complete EXPECTED submission DATE).

ABSTRACT (Limat to 1400 spaces. i.e., approximately 15 single-spaced typewritten lines) {161 On January 14,1997, as the result of an engineering review, it was postulated that an incorrect assumption had been made in determining the degree of error in a Cycle 6 Shutdown Margin Curve which had previously been found to be in error. Subsequent Engineering evaluation concluded that the Cycle 6 Shutdown Margin - Mode 3 curve had been non-conservative. On January 23,1997, with the unit in Mode 5, a prompt event report was made to the Nuclear Regulatory Commission of this historical condition pursuant to 10CFR50.72(b)(2)(iii)(A) as an event or condition that alone could have prevented the fulfillment of the safety function of structures or systems that are needed to shutdown the reactor and maintain it in a safe shutdown condition.

The cause of this event has been determined to be the lack of procedures for the generation and documentation of reactor plant operational information.

This condition was significant in that the use of an incorrect curve in determining the RCS boron concentration required to ensure adequate shutdown margin could have prevented the fulfillment of the safety function of the systems needed to maintain the reactor in a safe shutdown condition.. A comparison between the actual RCS boron concentration values measured during periods of Mode 3 operation and the required shutdown margin RCS boron concentrations for Cycle 5 and Cycle 6 verified that, due to intentional over-boration, there had been no violation of the shutdown margin requirements contained within Technical Specification 3.1.1.1.2. Therefore, the safety consequence Cf this event was minimal.

9702280057 970221 PDR ADOCK 05000423 S

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• U.S. NUCLEAR RE!ULATCY Commission M 95)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (61 PAGE (3)

YEAR SEQUENTIAL REvislON Millstone Nuclear Power Station Unit 3 05000423 NUMBER NUMBEF) 2 of 4 97 007 00 l

TEXT (11more space is required, use additional copies of NRC Form 366A) 117) 1.

Description of Event

On January 14,1997, as the result of an engineering review, it was postulated that an incorrect assumption had been made in determining the degree of error in a Cycle 6 Shutdown Margin Curve which had previously been found to be incorrect. Subsequent engineering evaluation concluded that the Cycle 6 Shutdown Margin - Mode 3 curve had been n:n-conservative. On January 23,1997, with the unit in Mode 5, a prompt event report was made to the Nuclear Regulatory Commission of this historical condition pursuant to 10CFR50.72(b)(2)(iii)(A) as an event or condition that alone could have prevented the fulfillment of the safety function of structures or systems that are needed to shutdown th3 reactor and maintain it in a safe shutdown condition.

Reactor Engineering produced the Cycle 6 Shutdown Margin - Mode 3 curves in May of 1995. These curves were based upon information contained within the vendor-supplied Nuclear Design Report (NDR). On June 14,1996, it was utscavered that one of the curves (Mode 3, All-Rods-In (minus 1), Reactor Coolant System Temperature equal to 557 degrees Fahrenheit) had been developed improper 1y.

A calculation was pt>rtormed to determine the correct data, which were then compared to the data used to plot the inco rect curve. The original data were found to be non-conservative by up to 4 parts per million (ppm) boron over a core bumup range of 2000-4000 Megawatt Days per Metric Ton Uranium (MWD /MTU). This determination was based upon an assumption that a 100 ppm boron addition to the required shutdown margin RCS boron concentration listed in th2 NDR was 'available margin'. Since the plant was not in Mode 3 during this bumup window, and that the curves were not requimd to be used, the event was determined to be not reportable. A review of other Cycle 6 curves which were developed by Reactor Engineering found no additional errors.

On January 14,1997, it was suggested that the assumption that the 100 ppm boron allowance listed in the NDR was

• available margin

• could be incorrect. It was subsequently determined that the 100 ppm boron allowance was an analytical margin that could not be used by plant personnel as "available margin'. Without credit for the boron allowance, the bumup window over which the original curve was non-conservative expanded to a range of 0 to

~14500 MWD /MTU. The unit was operated in Mode 3 three times during this bumup window. A review of plant records was conducted to compare actual RCS boron concentration values which were measured during Mode 3 operations to the corrected required shutdown margin RCS boron concentrations. It was verified that, due to ovor-boratiun for extra margin, no violation of the Technical Specification shutdown margin requirements had occurred.

However use of this curve by operations personnelin determining adequate shutdown margin alone could have prevented the reactor from being maintained in a safe shutdown condition.

This condition is therefore being reported pursuant to 10CFR50.73(a)(2)(v)(A), as an event or condition that alone could have prevented the fulfillment of the safety function of structures or systems that are needed to shutdown the re:ctor and maintain it in a safe shutdown condition.

11.

Cause of Event

The cause of this event has been determined to be the lack of procedures for the generation and documentation of re:ctor plant operational information.

l i.

NRC ToRM 366A U.s. NUCLEAR EEGuLAToRY CoMM!ssioN LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3)

YEAR SEQUENTIAL REVISloN Millstone Nuclear Power Station Unit 3 05000423 NUMBER NUMBER 3 of 4 97 007 00 TEXT Ut more space is required use additional copies of NRC form 366A) l11) lil. Analysis of Event This condition was significant in that the use of an incorrect curve in determining the RCS boron concentration required to ensure adequate shutdown margin could have prevented the fulfillment of the safety function of the systems needed to maintain the reactor in a safe shutdown condition.

A comparison between the actual RCS boron concentration values measured during period of Mode 3 operation and the required shutdown margin RCS boron concentration for Cycle 6 was conducted following determination of the condition being reported. There were no adverse safety consequence in that during this cycle, it was verified that, due to intentional over boration, there had been no violation of the shutdown margin requirements contained within Tcchnical Specification 3.1.1.1.2.

IV. Corrective Action

The following corrective action will be taken:

1.

The Reactor Engineering procedure will be revised to provide for the generation and documentation of reactor plant operational information provided to the operating shift by September 1,1997.

2.

A supplement to LER 96-009-00 will be submitted by March 1,1997 to correct the statement related to additional conservatism.

V.

Additional Information

During the preparation of this report, LER 96-009-00 was reviewed as a potentially similar event. It was determined that the 100 ppm RCS boron allowance listed in the NDR was considered to be "available margin".

Similar Events

LER 96-009-00 Inoperable Shutdown Margin Monitors from Low Count Rate, Due to inadequate Design Control On April 23,1996, with the plant in Mode 5, at 0-percent power, Engineering personnel discovered that both channels of Shutdown Margin Monitors were inoperable due to the instrument count rate being below a minimum count rate for operability. A review of previous outages indicates the condition may have existed three times within the last two years during Mode 5 operation. The condition is prohibited by Technical Specification 3.3.1. Table 3.3-1, item 21, which requires two Shutdown Margin Monitor (SMM) channels to be OPERABLE.

Upon discovery an immediate notification was made pursuant to 10CFR50.72(b)(1)(ii)(B). A subsequent review determined that there was no safety significance associated with the shutdown margin monitors being inoperable. The Reactor Coolant System (RCS) was borated significantiy higher than the boron concentration assumed in the analysis of a dilution event for the shutdown condition. The SMM alarms at a setpoint above the neutron count rate,15 minutes prior to tJaC FORM 366A 44-95)

'U.S. NUCLEAR REIULATORY C MMISSION 1

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3)

YEAR SEQUENT 4AL REVISION Millstone Nuclear Power Station Unit 3 05000423 NUMBER NUMBER 4Of4

)

97 007 00 TEXT lif more space is required, use additional copies of NRC Form 3SSA) (17) criticality, to provide time for operator action to mitigate an unintended dilution. A review of this event and the historical events indicated that the actual, higher than required, RCS boron 1

concentrations provided reasonable assurance of meeting the required 15-minute alarm time to J

criticality for a postulated dilution event.

As immediate action the plant complied with the app'icable Technical Specification Action Statement. The action taken to prevent recurrence was to reduce the SMM setpoint. During a corrective action review of the vendor's boron dilution analysis, a potential non-conservative assumption on subcritical multiplication was identified, and an immediate notification was made on May 13,1996, pursuant to 10CFR50.72(b)(1)(ll)(B). A subsequent review determined that the analysis was acceptable, and the plant was not in a condition that was outside the design basis.

Manufacturer Data None 1

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