ML18153C657

LER 91-011-00:on 910406,simulated Design Basis Accident Conditions Resulted in Failure of Pumps to Develop Design Flow & Discharge Pressure.Caused by Inadequate Design. Permanent Mod of Radiation Sys evaluated.W/910627 Ltr

ML18153C657
Person / Time
Site:	Surry
Issue date:	06/27/1991
From:	Kansler M VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
91-371, LER-91-011-01, LER-91-11-1, NUDOCS 9107080078
Download: ML18153C657 (6)

Text

... June 27, 1991 e Virginia Electric and Power Company Surry Power Station P. 0. Box315 Surry, Virginia 23883 U. S. Nuclear Regulatory Commission Document Control Desk Serial No.: 91-371 Docket Nos.: 50-280 50-281 License Nos.: DPR-32 DPR-37 Washington, D. C. 20555 Gentlemen:

Pursuant to Surry Power Station Technical Specifications, Virginia Electric and Power Company hereby submits the following Licensee Event Report for Units 1 and 2. REPORT NUMBER 91-011-00 This report has been reviewed by the Station Nuclear Safety and Operating Committee and will be reviewed by the Corporate Management Safety Review Committee.*

ansler Sta ion Manager Enclosure cc: Regional Administrator Suite 2900 101 Marietta Street, NW Atlanta, Georgia 30323 9107080078 910627 PDR ADOCK 05000280 S PDR

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NRCFORM3&i U.S. NUCLEAR REGULATORY COMMISSION 16,89) LICENSEE-ENT REPORT (LER) APPROVED 0MB NO. 3150-0104 EXPIRES: 4/30/92 TIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS FORMATION COLLECTION REQUEST: 50.0 HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS AND REPORTS MANAGEMENT BRANCH IP-530). U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT 13150-0104).

OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503. FACILITY NAME (11 !DOCKET NUMBER 121 I PAGE 131 TITLE (41 Surry Power Station, Unit 1 Service Water Radiation Monitoring Pumps Inoperable to Air Binding as a Result of Inadequate Design 0151010101 21 8 Io , loF o I 5 Due EVENT DATE (51 LER NUMBER 161 REPORT DATE 171 OTHER FACILITIES INVOLVED 181 MONTH DAY YEAR YEAR :,:,::::::

SEQUENTIAL

{::::: REVISION MONTH DAY ::::::::;:

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NUMBER YEAR FACILITY NAMES Surry Unit 2 DOCKET NUMBERISI o I 5 I o I o I o I 2 18 I 1 o 1 s 3 I o 9 1 9 1 1 -o I 11 1 -o 1 o o I 6 2 1 1 OPERATING MODE (81 NAME N THIS REPORT IS SUBMITTED PURSUANT TO THE R~QUIREMENTS OF 10 CFR §: {Chock on* or moro of the following)

(111 20.4051c) 50.73(ol(2J(ivl 73.71(b) -,_ -50.38(cllll 50.731*1121M 73.71 (cl ---50.38(c)(2)

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OTHER (SpBcify in Abstr*ct --b11/ow and in Text, NRC Form 50.73(el(21(i) 50.73(ol(2Jlviiil(AI 366A) --50.73(ol(2J(iil 50.73(ol(2J(vliil(BI

--50.73(ol(2lliiil 50.73l*J121M LICENSEE CONTACT FOR THIS LER (12) TELEPHONE NUMBER M. R. Kansler, Station Manager AREA CODE 8 IO I 4 3 I s 1 7 1-1 3 I 1 1 8 I 4 CAUSE SYSTEM COMPONENT I I I I I I I I COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (131 TURER I I I I I I CAUSE SYSTEM t I COMPONENT MANUFAC* TURER I l I I I I I I I I I I ',', *,', *.*.*.*.*.*.

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..... * ... SUPPLEMENTAL REPORT EXPECTED 1141 MONTH DAY YEAR EXPECTED SUBMISSION I YES (If yos, comp/ore EXPECTED SUBMISSION DATE) DATE ll51 I ABSTRACT (Limit to 1400 spaces, i.e .. approximately fifteen single-space typewritten Jines) '16) N RC Form 366 16.S91 On April 6, 1991, with Unit 1 at 100% power and Unit 2 in Cold Shutdown, a functional test of the Unit 2 Service Water (SW) radiation monitoring pumps under simulated design basis accident conditions resulted in a failure of the pumps to develop design flow and discharge pressure.

This condition impairs the capability of the radiation monitors to detect radioactive leakage into the SW system from the Recirculation Spray Heat Exchangers; however, alternate means of leakage detection would have been available if a design basis accident had occurred.

This condition was caused by a transient vacuum condition at the pump suction which resulted in air binding of the pumps. The transient vacuum condition in the Circulating Water (CW) discharge tunnel resulted from isolation of the main condenser and prevented normal self-priming of the radiation monitor pumps. The automatic starting of these pumps has been defeated.

Emergency Operating Procedures have been revised to require manually breaking CW discharge tunnel vacuum to permit normal self-priming of these pumps and to provide for manually starting the pumps. Permanent modification of the radiation monitoring system is being evaluated.

This report is required by-10CFR50.73(a)(2)(vii)(C).

I I I,, NRC FORM 366A (6-89) FACILITY NAME (1) U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVA REPORT (LER). TEXT coiffi'NUATION DOCKET NUMBER (2) APPROVED 0MB NO. 3150-0104 EXPIRES: 4/30/92 .. ATED BURDEN PER RESPONSE TO COMPLY WTH THIS MATION COLLECTION REQUEST: 50.0 HRS. FORWARD ENTS REGARDING BURDEN ESTIMATE TO THE RECORDS AND REPORTS MANAGEMENT BRANCH (P-530), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555, AND TO l'HE PAPERWORK REDUCTION PROJECT (3150-0104), OFFICE Of MANAGEMENT AND BUDGET, WASHINGTON, DC 20503. LER NUMBER (6) PAGE (3) Surry Power Station, Unit 1 TEXT (If mom space n,quimd, UIM additional NRC Form 356A 'al (17) 1.0 NRC Form 366A (6-89) DESCRIPTION OF THE EVENT On April 6, 1991, with Unit 1 operating at 100% power and Unit 2 in Cold Shutdown, a* functional test conducted on Unit 2 Service Water Radiation Monitoring Pumps [EIIS-BI,P]

2-SW-P-5B and 2-SW-P-5C resulted in* failure of the pumps to develop sufficient flow and discharge pressure to perform their design function.

These pumps, which take suction at the SW discharge from Recirculation Spray Heat Exchangers (RSHXs) [EIIS-BI,HXJ 2-RS-E-lB and 2-RS-E-lC, were tested as part of a SW flow test of the same RSHXs.

• The SW flow test, which was controlled by Special Test Procedure 2-ST-301, simulated the initiation of SW flow to the RSHXs under design basis accident conditions.

The test admitted SW flow to the RSHXs by opening the associated SW isolation valves while isolating Circulating Water (CW) [EIIS-KEJ flow through the Unit 2 main condenser.

The radiation monitor pumps were started approximately one minute after the initiation of* SW flow through the

• RSHXs, which simulated actual design basis operation of the pumps. Both the 2-SW-P-5B and the 2-SW-P-5C pumps were operated for 37 minutes. Neither pump developed the flow or discharge pressure necessary to perform its design function.

The low flow annunciators for these pumps actuated in accordance with design and did not clear for the duration of the pump run. The failure of* these pumps to achieve design performance during this initial test is attributed to the vacuum created in the SW discharge piping by isolation of CW flow through the main condenser.

Isolation of CW flow through the main condenser has been shown to create a transient vacuum condition in the CW discharge tunnel. This is due to the gravity flow design of the CW system. The dry layup condition of the RSHX SW discharge piping combined with the vacuum produced by main condenser isolation prevented the filling of the suction lines to the 2-SW-P-5B and 2-SW-P-5C pumps, causing the pumps to become air bound. A second test of the radiation monitor pumps was conducted after the CW discharge tunnel vacuum transient had dissipated.

The CW discharge tunnel vacuum breaker valve, 2-CW-117, was opened to assure that the CW discharge tunnel was at atmospheric pressure.

In this test, both the 2-SW-P-5B and 2-SW-P-5C pumps achieved design flow and discharge pressure immediately after being started. The low flow annunciators did not actuate for either pump, confirming that the pumps were

.. NRC FORM 366A (6-89) FACILITY NAME (1) U.S. NUCLEAR REGULATORY COMMISSION LICENSEE E"8J-REPORT (LER) TEXT CO~NUATION DOCKET NUMBER (2) APPROVED 0MB NO. 3150-0104 EXPIRES: 4/30/92 *ATED BURDEN PEA RESPONSE TO COMPLY WTH THIS AMATION COLLECTION REQUEST: 50.0 HAS. FORWARD ENTS REGARDING BURDEN ESTIMATE TO THE RECORDS AND REPORTS MANAGEMENT BRANCH (P-530), U.S. NUCLEAR REGULATORY COMMISSION.

WASHINGTON, DC 20555, AND TO 1HE PAPERWORK REDUCTION PROJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON.

DC 20503. LER NUMBER (6) PAGE (3) Surry Power Station, Unit 1 0 15 IO IO IO , 2 I s, 0 91 1 -0, 1 I 1 -0 I O O t3 OF O I 5 TEXT /ff more 0/)IJce is mquin,d, us,, additional NRC Form ~'8) (17) NRC Form 366A (6-89) operating properly.

The results of the second test confirmed that the initial deficiencies in the operation of the radiation monitor pumps were caused by the initial vacuum condition in the SW discharge piping and the resulting air binding of the pumps.

• Following the completion of engineering evaluations on May 30, 1991 regarding the design basis requirements of the radiation monitor pumps, it was determined that a reportable condition existed in accordance with 10CFR50.73(a)(2)(vii)(C), since the delayed operation of the sample pumps temporarily caused multiple channels to become inoperable in a single system designed to control the release of radioactive material.

2. O SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS The RSHX SW outlet radiation-monitors are provided to detect a passive failure involving loss of structural integrity of a RSHX tube during the recirculation heat removal phase of a design basis loss of coolant accident (LOCA). The SW outlet from each of the four RSHXs per unit is monitored.

A sample is drawn from each SW outlet by a sample pump, passed through a liquid sampler, and returned to the SW line. Operators would be alerted to a high radiation condition by an alarm in the control room. SW flow through a leaking RSHX would be isolated by closing the RSHX SW motor operated isolation valves from the main control room (MCR). Air binding of the radiation monitor pumps impairs the capability of the radiation monitors to identify leakage of radioactive liquid into the SW system. During the short term (injection) period following a design basis LOCA, passive failures such as heat exchanger tube leaks are not considered credible (

Reference:

ANSI/ANS-58.9-1981), hence ity of the radiation monitors is not required.

In the long term (recirculation phase), passive failures must be considered.

Based on operation of full engineered safeguards, which results m the most rapid depletion of the refueling water storage tank, recirculation mode transfer can occur as early as 29 minutes after onset of a LOCA. While air binding could render the RSHX SW outlet radiation monitors inoperable, the CW discharge tunnel radiation monitor [EIIS-KE-RM], which is located downstream of the RSHX SW discharge piping, would be available.

Although this monitor has less sensitivity than the RSHX SW outlet monitors, it is not affected by a vacuum in the CW discharge tunnel and could be used to detect gross RSHX leakage.

NRC FORM 366A (6-89) FACILITY NAME (1) U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EeT REPORT (LER) TEXT CONTINUATION DOCKET NUMBER (2) APPROVED 0MB NO, 3150-0104

• EXPIRES: 4/30/92 MATED BURDEN PER RESPONSE TO COMPLY WTH THIS ORMATION COLLECTION REQUEST: 50.0 HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS AND REPORTS MANAGEMENT BRANCH (P-530). U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (3150-0104).

OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503. LER NUMBER (6) PAGE (3) Surry Power Station, Unit 1 TEXT /ff mom apac,, is requiffJd, ustJ additional NRC Form '*I (17) NRC Form 366A (6-89) The vacuum condition in the CW discharge tunnel would naturally dissipate approximately 2.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after main condenser isolation, as demonstrated in RSHX SW flow tests. After this time, RSHX SW outlet radiation monitor pumps would be capable of priming and delivering design flow and discharge pressure.

Based on the above considerations, this condition did not result in any adverse consequences to public health and safety. 3. O CAUSE OF THE EVENT 4.0 The event was caused by inadequate design. The radiation monitor sample pumps take suction at points where SW pressure is insufficient to allow for self-priming of the pumps in the early stages of RS system operation.

This resulted in the pumps becoming air bound and not developing sufficient flow or discharge pressure.

This deficiency was not detected earlier because the pumps were not previously tested under design basis accident conditions.

IMMEDIATE CORRECTIVE ACTION<S}

In order to ensure that the Unit 1 SW radiation monitor pumps would operate as designed in the event of a design basis LOCA, a Justification for Continued Operation (JCO) was prepared.

This JCO required an operator to be stationed at the Unit 1 CW discharge tunnel vacuum breaker valve, l-CW-117.

The operator was to open the valve, thereby breaking discharge tunnel vacuum, upon notification of a High-High Consequence Limiting Safeguards (CLS) signal. This would ensure sufficient suction pressure to the radiation monitor pumps. Unit 2 remained m Cold Shutdown, thus immediate actions were not necessary.

5. 0 ADDITIONAL CORRECTIVE ACTION{S)

An evaluation of the design basis of the RSHX SW outlet radiation . monitors was performed.

This evaluation resulted in the conclusion that operability of the monitors was not required until the recirculation heat removal phase of a design basis LOCA. This occurs 29 minutes or more following onset of the LOCA. Based on this evaluation, the JCO compensatory actions were modified.

The automatic start of the radiation monitoring pumps which occurred one minute following a High-High CLS signal was defeated by means of a Temporary FACILITY NAME (1) U.S. NUCLEAR REGULATORY COMMISSION LICENSEE E-T REPORT (LER) TEXT CdWINUATION DOCKET NUMBER (21 APPROVED 0MB NO. 3150-0104 EXPIRES: 4/30/92 -MATED BURDEN PER RESPONSE TO COMPLY WT.H THIS RMATION COLLECTION REQUEST: 50.0 HRS. FORWARD MENTS REGARDING BURDEN ESTIMATE TO THE RECORDS AND REPORTS MANAGEMENT BRANCH (P,530), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (3150-0104), OFFICE OF MANAGEMENT AND BUDGET, WASHINGTON, DC 20503. LER NUMBER (61 PAGE (3) Surry Power Station, Unit 1 TEXT /ff man -ce i& n,qui-1, UStl additional NRC Form 366A'&) (171 NRC Form 366A (6-89) Modification which lifted the appropriate leads. Immediate Action steps were added to Procedure E-0, "Reactor Trip or Safety Injection" to require manual opening of the CW discharge tunnel vacuum breaker valve and manual starting of the radiation monitor pumps. These actions ensure that the pumps would be functioning within the required time while eliminating the need to dedicate an operator to the CW discharge tunnel vacuum breaker valve. 6. O ACTIONS TO PREVENT RECURRENCE An engineering evaluation is being conducted in the design of the RSHX SW outlet radiation modifications or changes will be made as completion of this evaluation.

7. 0 SIMILAR EVENTS None. 8.0 ADDITIONAL INFORMATION None. an effort to improve monitors.

Permanent n~cessary following

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