05000245/LER-1996-061, :on 961121,containment Isolation Function in Design Basis Accident Concurrent W/Loss of One Train of Dc Sys Failed.Caused by Inappropriate Exclusion in Past of Operation Conditions.Requirements Documented

:on 961121,containment Isolation Function in Design Basis Accident Concurrent W/Loss of One Train of Dc Sys Failed.Caused by Inappropriate Exclusion in Past of Operation Conditions.Requirements Documented

ML20133A906
Person / Time
Site:	Millstone
Issue date:	12/23/1996
From:	Robert Walpole NORTHEAST NUCLEAR ENERGY CO.
To:
Shared Package
ML20133A898	List: 05000245/LER-1996-061, :on 961121,containment Isolation Function in Design Basis Accident Concurrent W/Loss of One Train of Dc Sys Failed.Caused by Inappropriate Exclusion in Past of Operation Conditions.Requirements Documented
References
LER-96-061, LER-96-61, NUDOCS 9701020160
Download: ML20133A906 (3)

LER-1996-061, on 961121,containment Isolation Function in Design Basis Accident Concurrent W/Loss of One Train of Dc Sys Failed.Caused by Inappropriate Exclusion in Past of Operation Conditions.Requirements Documented

Event date:
Report date:
2451996061R00 - NRC Website

text

.

NRC FORM 366 U.S. NUCLEAR REGULATC,RY COMMISSION APPROYED BY oMB No. 31t>o-0104 (4-95)

ExPtREs 04/30/98

' fof?#"o'a/c'1J'aTJs?& "Us"1AA"o^"iG8,"7s J

n^c"??o'L'"#"P"*MKel'oJSM.* Ja?We'ns LICENSEE EVENT REPORT (LER) l'E'u'! '"u'c%fre*"#&"'caJ "s'o?"#!s";~*!'s* e

!,?Rc'3"M '#J3E!*r'l~^n"se"1' "'a%?r"oi"8fM'"*

u (See reverse for required number of digits / characters for each block)

F ACluTV NAME (1)

DOCKET NUMBER (2)

PAGE (3)

Millstone Nuclear Power Station Unit 1 05000245 1 of 3 TITLE (46 Failure of Containment Isolation Function in a Design Basis Accident Concurrent with a Loss of One Train of DC System EVENT DATE (5)

LER NUMBER (6)

REPOF:T DATE (7)

OTHER FACILITIES INVOLVED (8)

MONTH DAY YEAR YEAR SEQUENilAL REVISION MONTH DAY YEAR FACIUTY NAME DOCKET NUMBER NUMBER 11 2i 96 96 061 00 12 23 96 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 5: (Check one or more) (11)

MODE (9)

N 20.2201(b) 20.2203(a)(2)(v) 50.73(aH2)(i) 50.73(aH2Hviii)

LEVEL (10) 000 20.2203(aH3)(i)

X 60.73(a)(2)(ii) 50.73(a)(2Hx)

POWER 20.2203(a)(1) 20.2203(aH2Hi) 20.2203(a)(3Hii) 50.73(aH2Hiii) 73.71 20.2203(aH2)(ii) 4 20.2203(aH4) 50.73(aH2Hiv)

OTHER 20.2203(aH2Hiii) 50.36(C)(1) 50.73(aH2)(v) specify m Abstract below or in NRC Form 366A 20.2203(aH2)(iv) 50.36(C)(2) 50.73(aH2)(vii)

LICENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER (include Area Codel Robert W. Walpole, MP1 Nuclear Licensing Manager (860)440-2191 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE

CAUsE

SYSTEM COMPONENT MANUFACTUHER REPORTABLE To NPRDs To NPRDS

[

SUPPLEMENTAL REPORT EXPECTED (14)

EXPECTED MONTH DAY YEAR SUBMISSloN YES NO Uf yes, complete EXPECTED SUBMISSION DATE).

ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) (16)

On November 21,1996, with L plant shutdown, the reactor in the cold shutdown condition and the fuel off-loaded, it was found that the function of containment isolation for penetration X-14, Reactor Water Clean-up (RWCU) system, would not have been available postulating a loss of S2 DC train concurrent with a design basis accident consisting of a simultaneous loss of coolant accident (LOCA) with a loss of offsite power (LNP). The loss of containment isolation function under this scenario would occur only during heat-up or cool-down of the reactor with the reactor pressure under 100 psig, when the RWCU system is operating in the auxiliary pump line up. Under this condition, the reactor may be critical but the core power is only a few percent and the turbine is off-line. This event was reported pursuant to 10 CFR 50.72(b)(1)(ii)(B) as a condition that is outside the design basis of the plant. There were no automatic nor manually initiated safety system responses as a result of this event. The cause of this event is the inappropriate exclusion in the past of some operating conditions, such as the auxiliary valve line-ups, from the requirements of the containment isolation function. There were no actual safety consequences. The safety implications of the event are minimal since the event could only take place under a short duration window in the start-up or cool down of the reactor, the probability of the postulated failure to happen simultaneously with the design basis accident is extremely low and the existing procedures in place would mitigate the consequences of such event. The containment isolation design requirements for RWCU system auxiliary pump operation mode will be determined and, if required, a plant modification such as changing the power source to the RWCU system containment isolation valves will be implemented.

9701020160 961223 PDR ADOCK 05000245 S

PDR

m.

i

'NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (445)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FActLITY NAME 10 DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3)

YEAR SEQUENTIAL REVISION i

Millstone Nuclear Power Station Unit 1 05000245 NUMBER NUMBER 2 of 3 96 061 00 i

TEXT (if more space is required, use additional copies of NRC form 366A) (17)

I.

Description of Event

l l

On November 21, 1996, with the plant in cold shutdown and fuel off-loaded, during re-evaluation of the j

limiting single failure for Emergency Core Cooling Systems (ECCS) and containment isolation function for the auxiliary valve line-ups that was being performed to address Commitment No. B15926-4 per LER 96-050, it was found that the function of containment isolation required when the reactor is critical or the coolant temperature is at or above 212 degree F would not have been available with a single failure of one DC train concurrent with the design basis accident. The design basis accident that is being considered is LOCA simultaneous with an LNP. The penetration involved is X 14 for the RWCU system.

There were no automatic not manually initiated safety system responses as a result of this event. This event was reported on November 21,1996, pursuant to 10 CFR 50.72(b)(1)(ii)(B) as a condition that is outside the design basis of the plant.

11. Cause of Event

The cause of this event is an inappropriate exclusion in the past of some operating conditions, such as auxiliary valve line ups from the requirements of containment isolation function.

Ill. Analysis of Event During the reactor heat-up or cool-down when the reactor pressure is below 100 psig, the RWCU flow is established by placing the auxiliary pump in service. Operation of the auxiliary pump requires opening of a containment isolation motor operated valve (MOV) (1-CU-5) located in the pump suction line in this scenario, the reactor is either subcritical (cool-down) or critical with the power being less than a few percent. In both situations, the turbine is off line.

The two valves providing the containment isolation function in these scenarios are powered from the S2 division of the plant electrical system. The inboard MOV (1-CU 2) is AC powered while the outboard MOV is DC. A postulated failure of the S2 DC system would disable the inboard AC valve only if LNP is postulated coincidentally. The assumed loss of the DC bus would disable the diesel generator, which could provide power to the inboard AC valve.

This issue was brought to the forefront during an evaluation for the corrective action for LER 96-050.

There were no actual safety consequences. The RWCU system operates with 1-CU-5 open when the reactor is starting-up from cold shutdown or cooling-down. The turbine is off-line and the plant electrical loads are energized through the start-up transformer (RSST). Under this condition, the probability of an LNP event is much reduced. The RWCU system piping and the secondary containment also are barriers to any release of radioactive material. Therefore, the safety implication of the failure of containment isolation function at this penetration under the postulated condition is minimal.

IV. Corrective Action

As a result of this event and the subsequent investigation, the following corrective actions are required:

GdRC FORM 366A (4-95)

_. = _ _._.- _.- _ _._._. __. _ ____._.._. _ _____ _._ _.._...-. _. _. _ --.

.U.S. NUCLEAR REGULATORY COMMISSION 14.ts>

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3)

YEAR SEQUENTIAL REVISION I

Millstone Nuclear Power Station Unit 1 05000245 NUMBER NUMBER 3 of 3 96 061 00 TEXT (If more space is required, use additional copies of NRC Form 366A) (11)

I l

Document the containment isolation design requirements for RWCU system auxiliary pump operation e

j mode if required, a plant modification such as changing the power source to the RWCU system l

containment isolation MOVs will be implemented prior to startup for operating cycle 16.

l l

The ongoing 10 CFR 50.54(f) review of the systems will address the containment isolation function requirements prior to startup for cycle 16.

V.

Additional Information

Sitnitar Events LER 96-050-00, "LOCA Concurrent with LNP, and Loss of DC Power Prevents Closure of LPCI Torus Test L

Return Valves." The condition discussed in this LER was discovered during a review that is in progress as a result of Commitment No. B15926-4 from LER 96-050-00.

Manufacturer Data i

None.

?

l r

1 i!

I