ML20059J286

Safety Evaluation Supporting Amend 85 to License NPF-62

ML20059J286
Person / Time
Site:	Clinton
Issue date:	11/05/1993
From:	Office of Nuclear Reactor Regulation
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ML20059J284	List: ML20059J282 ML20059J286
References
NUDOCS 9311120151
Download: ML20059J286 (6)

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UNITED STATES i*

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NUCLEAR REGULATORY COMMISSION WASHINGTON. D.C. 20555-0CC1 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 85 TO FACILITY OPERATING LICENSE NO. NPF-62 ILLINOIS POWER COMPANY. ET AL.

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CLINTON POWER STATION. UNIT NO. 1 DOCKET N0. 50-461

1.0 INTRODUCTION

By letter dated December 15, 1992, the Illinois Power Company (IP, the licensee) requested an amendment to facility Operating License No. NPF-62, to change the technical specifications (TS) for the Clinton Power Station (CPS).

The proposed change would increase the allowed outage time for differential temperature instruments associated with the containment and reactor vessel isolation control system (CRVICS) as described in the TS Table 3.3.2-1, CRVICS INSTRUMENTATION.

2.0 EVALUATION The purpose of the differential temperature instruments associated with CRVICS is to monitor leakage from the reactor coolant pressure boundary and initiate alarms and/or an isolation function before predetermined limits are exceeded.

Pursuant to this purpose, this instrumentation is designed to detect and effect an automatic isolation in response to a 25-gallon-per minute (gpm) equivalent steam leak in the particular area being monitored. The differential temperature is measured by comparing the area air handling unit's cooling water supply line temperature to the cooling water return line temperature.

The proposed change was prompted by a loss of 'B' (East) reactor water cleanup (RWCU) heat exchanger room air handling unit, which occurred at CPS on December 12, 1991.

During this event the Shift Supervisor (SS) noted an increasing ambient temperature trend in the 'B' RWCU heat exchanger room, as indicated by the equipment area ambient temperature recorder. The SS immediately checked the differential temperature indication for the associated heat exchanger room, and it was indicating zero.

In response to this indication, the status of the air handling unit fan was checked locally, and was determined to have failed.

By analyzing the area differential temperature recorder, it was determined that the air handling unit had been failed for approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> and 25 minutes. The existing TS requires the affected system isolation valves be closed within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. Therefore, this event resulted in operation prohibited by the plant's TS, and was documented in CPS Licensee Event Report (LER)91-007.

9311120151 931105 DR ADDCK 05000461 PDR l

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. In response to this event, IP proposed to increase the' allowed outage' time for_

the CRVICS differential-temperature isolation instrumentation to allow-j sufficient time to identify and correct inoperable air. handling units that support the operation of these instruments.. The proposed change would be i

applicable to those instruments that isolate one'or more of the following systems:

(1) main steam lines, (2) RWCU, (3) reactor core-isolation cooling (RCIC), and (4) residual heat removal (RHR). The CPS TS currently require a 1

CHANNEL CHECK to be performed on these instruments at least once every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.

In addition, the TS currently require the main steam system to be isolated within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> for a failure of 3 of the 4 differential temperature-channels.

Furthermore, it requires the RWCU, RCIC, and RHR systems to be i

isolated and the associated system declared inoperable within I hour for a i

failure of both differential temperature channels for each of the respective systems. Therefore, IP proposes an increase in the allowed outage' time to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, to provide a reasonable period of time to detect and correct inoperabilities of these instruments caused by air handling unit failures.

Main Steam Line Isolation

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The main steam line break leak detection subsystem consists of three types of monitoring circuits:

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(1) ambient and differential area temperature is monitored and an alarm and main steam line isolation valve logic are initiated when the monitored temperature rises above a preset maximum, i

i (2) volumetric flow rate through the main steam lines provide comparative n

information to initiate an alarm and main steam line isolation closure when the monitored flow rate exceeds a preset maximum,'and i

(3) low water level in the reactor vessel is detected and a trip signal is sent to the isolation logic when the level ~ decreases below a' preselected set point.

i Other main steam isolations are accomplished by main steam line high pressure, main steam line area high radiation, and low condenser vacuum.

In addition, there is a manual isolation initiation capability.

For the main steam line and main steam line drain isolation valve control, four instrument channels are provided for each measured variable'. The instrument channel trips are combined into a 2-out-of-4 logic using. isolation modules to assure that no single failure _in a channel can prevent the safety action by disenabling another channel'nor can a single failure of one division logic prevent isolation by the remainder of the system. 'This is accomplished by combining the output trip signals of the logic divisions in a 2-out-of-2 logic. Divisions 1 and 4 or divisions 2 and 3 are required to transmit.a signal to the CRVICS. The purpose of this 2-out-of-2 logic is to ensure that a failure of any one division does not result in inadvertent action-In response to this signal, the CRVICS initiates the closure of all main steam

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. t line isolation valves and drain valves, the RWCU system isolation valves, and the RCIC system suction and steam supply line isolation valves.

The existing TS require the plant be in at least STARTUP with the associated i

isolation valves closed within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> or be in at least hot shutdown within -

12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and cold shutdown within the next 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for a condition with three of the four main steam line tunnel differential temperature channels inoperable. The proposed TS will require the plant be in at.least STARTUP with the associated isolation valves closed within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or be in at least hot shutdown within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and cold shutdown within the next 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for a condition with 3 or 4 main steam line tunnel differential temperature channels inoperable, provided at least 2 main steam line tunnel ambient temperature channels remain operable.

Reactor Water Cleanun System Isolation 1

The RWCU leak detection subsystem consists of the following two types of monitoring circuits:

(1) comparison of RWCU system water inlet and outlet flow rate, and (2) ambient and differential temperature monitoring.

Ten ambient temperature and ten differential temperature instrument channels monitor the RWCU system area temperatures.

Five area and five differential temperature switches are associated with each logic channel. Two ambient temperature elements are located in each of the following locations: Pump Room 1, Pump Room 2, Pump Room 3, Heat Exchanger Room East, and Heat Exchanger Room West. Two pairs of differential temperature elements are located in the ventilation chilled water inlets and exhausts of the above locations.

Additionally, one ambient or differential temperature monitoring circuit in each of two divisions, monitoring main steam line tunnel temperature, will cause an isolation of the RWCU system. These monitors are the same units that effect isolation of the main steam lines. A trip of any one of these temperature switches will result in the activation of an annunciator and an automatic isolation of the RWCU system.

For a failure of both differential temperature channels associated with the RWCU system isolation trip function, the existing TS requires that the affected system isolation valves be closed within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and the affected system declared inoperable. The proposed TS would allow this time limit to be increased to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> provided that the minimum OPERABLE channels per trip system requirement for the ambient temperature-high trip function for the associated area is met for both trip systems.

Reactor Core Isolation Coolino System Isolation The RCIC leak detection subsystem consists of the following two types of monitoring and control circuits:

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I (1) steam flow rate in RCIC steamlines, and l

(2) ambient and differential temperature monitoring.

Additionally, leak detection is provided by alarm circuits that monitor the RCIC equipment area's sump level, sump pump run time, and sump pump running frequency.

Two ambient temperature elements are located in the RCIC equipment room.

Also, two pairs of differential temperature elements are located in the RCIC equipment room's ventilation chilled water inlet and exhaust. Additionally, one ambient or differential temperature monitoring circuit in each of two divisions, monitoring main steam line tunnel temperature, will cause an isolation of the RCIC system. A trip of any one of these temperature switches will result in the activation of an annunciator and an automatic closure of the RCIC pump suction line. Furthermore, this signal will also trip the RCIC turbine.

It should be noted, however, that there is a time delay associated i

with the RCIC system isolation signal from main steam line tunnel i

l temperatures. The purpose of this time delay is to allow main steam and RWCU j

to be isolated before RCIC, thereby preserving the operation of the RCIC i

system for reactor vessel water makeup and core cooling.

for a failure of both differential temperature channels associated with the i

RCIC system isolation trip function, the existing TS requires that the affected system isolation valves be closed within I hour and the affected system declared inoperable. The proposed TS would allow this time limit to be increased to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> provided that the minimum OPERABLE channels per trip l

system requirement for the ambient temperature-high trip function ~ for the associated area is met for both trip systems.

Residual Heat Removal System Isolation I

The RHR leak detection subsystem consists of the following two types of monitoring and control circuits:

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(1) steam flow rate in common RCIC/RHR steamlines, and 1

(2) ambient and differential temperature monitoring, i

Additionally, leak detection is provided by alarm circuits that monitor the RHR areas' sump level, sump pump run time, and sump pump running frequency.

Two ambient temperature elements are located in each of the RHR heat exchanger rooms. Also, each RHR heat exchanger room's ventilation chilled water inlet i

and exhaust contains two pairs of differential temperature elements. A trip of any one of these temperature switches will result in the activation of an annunciator and an automatic closure of the RCIC suction and steam supply containment isolation valves, and the RHR return-to-feedwater, shutdown l

cooling suction, fuel pool cooling assist, and reactor vessel head spray line l

containment isolation valves.

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for a failure of both differential temperature channels associated with the RHR system isolation trip function, the existing TS requires that the affected system isolation valves be locked closed within I hour and the affected system declared inoperable. The proposed TS would allow this time limit to be increased to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> provided that the minimum OPERABLE channels per trip i

system requirement for the ambient temperature-high trip function for the

. associated area is met for both trip systems.

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SUMMARY

For all the above systems, there are two or more leakage detection systems available for each system or area that is a potential source of leakage.

In addition, accessible areas are inspected periodically, and the temperature and i

l flow indications are monitored regularly. Any abnormal instrument indication is investigated.

The setpoints for the ambient temperature instruments were calculated assuming the air handling units were in service during winter conditions. As. a result, an isolation signal will be generated in response to high ambient temperature i

indication in the event of a 25-gpm equivalent steam leak under all cooling

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conditions.

In addition, because redundant ambient temperature switches are required to be operable for each of the affected areas during the extended out of service period, the isolation signal would be generated even in the event l

of a single failure. Furthermore, with the associated air handling unit out i

l of service, the ambient temperature would increase at a faster rate and, therefore, isolation would occur sooner than assumed in the ambient temperature setpoint calculation.

The CPS design requires the operation of the air handling units associated with the main steam tunnel, the RWCU heat exchanger and pump rooms, the RCIC equipment room, and the RHR pump rooms to support the operation of the CRVICS differential temperature instruments provided to-detect leakage from these systems. The staff verified that the differential temperature isolation functions for the main steam system, RWCU system, RCIC system, and the RHR system associated with containment and reactor vessel isolation control system are adequately backed-up by the ambient temperature trip functions, and other diverse functions to justify an increase in the allowed outage time in order to repair an inoperable air handling unit. Therefore, the staff finds the proposed TS changes acceptable.

4.0 STATE CONSULTATION

In accordance with the Commission's regulations, the Illinois State official was notified of the proposed issuance of the amendment. The State official had no comments.

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5.0 ENVIRONMENTAL CONSIDERATION

.fl This amendment changes a requirement with respect to installation or use of a d

facility component located within the restricted area as defined in 10 CFR-Part 20. The NRC staff has determined that the amendment involves no il r

significant increase in the amounts, and no significant change'in the types, j

of any effluents that may be released offsite, and -that there is no significant increase in individual or cumulative occupational radiation exposure.

The Commission has previously issued a proposed finding that the:

amendment involves no significant hazards consideration and there has been'no j

public comment on such finding (58 FR 6999). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).

Pursuant to 10 CFR 51.22(b), no environmental impact statement.

i or environmental assessment need be prepared in connection with the: issuance j'3 of the amendment.

6.0. CONCLUSION The staff has concluded, based on the considerations discussed above, that:

-i (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common -

defense and security or to the health and safety of the public.

]j Principal Contributor: Richard A. Skokowski Date:

November 5, 1993 I

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