ML20106H197
| ML20106H197 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 03/11/1996 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20106H191 | List: |
| References | |
| NUDOCS 9603200302 | |
| Download: ML20106H197 (4) | |
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4 UNITED STATES
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NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 3066 & 4001
.....,f SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.103 TO FACILITY OPERATING LICENSE NO. NPF-62 ILLINOIS POWER COMPANY. ET AL.
CLINTON POWER STATION. UNIT NO. 1 DOCKET NO. 50-461
1.0 INTRODUCTION
By letter dated December 14, 1995, Illinois Power Company, the licensee, submitted proposed changes to the technical specifications (TSs) of the Clinton Power Station (CPS). The licensee proposed modifying TS 3.4.2, " Flow Control Valves (FCVs)," by deleting Surveillance Requirement (SR) 3.4.2.2.
SR 3.4.2.2 requires periodic verification that the average rate of each reactor recirculation system FCV is limited to less than or equal to 11% per second in the opening and closing directions.
The SR was originally included in the TSs because it was an assumption of the transient analyses for recirculation loop control failures that resulted in both recirculation loop FCVs either opening or closing simultaneously.
However, during the fifth refueling outage (Spring 1995), the FCV control system was modified such that failure modes which could result in both FCVs opening or closing simultaneously were eliminated from the CPS plant design.
As a result of this modification, the licensee has determined that SR 3.4.2.2 i
is no longer applicable and has proposed deleting it.
2.0 EVALUATION The reactor recirculation system is used to control reactivity over a wide span of reactor power by varying the recirculation flow rate to control the void content of the moderator. The two loop reactor recirculation system controls flow rate through a two-speed reactor recirculation pump and a flow control valve.
Each of the FCVs has an individual controller that can be operated manually or placed in the automatic mode. When in the automatic mode, both FCVs can be operated jointly using a master controller.
Operation of the FCVs can have a major impact on loss of coolant accident (LOCA) and plant transient analyses.
FCVs are designed to fail "as is" when LOCA conditions are present. SR 3.4.2.1 requires periodic verification that the FCVs will fail "as is."
Upon receipt of a high drywell )ressure signal, electronic circuits will inhibit motion of the FCV so that tie valves maintain i
their preexisting position.
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Transient analyses included in the Updater' infety Analyses Report (USAR) i assumed failures of the recirculation flow controllers. The single failure of i
an individual FCV controller could result in a single FCV suddenly opening or closing at power.
In addition, the single failure of the master controller j
could result.in simultaneous opening or closing of both FCVs. The CPS has i
been designed to handle these transients as described in USAR Section 15.3.2 (inadvertent closure of the FCVs) and Section 15.4.5 (inadvertent opening of i
the FCVs).
3 The transient analyses is dependent upon the rate of FCV opening or closing.
j The FCVs are physically capable of opening or closing very rapidly. USAR Section 15.3.2 assumes that a single FCV closes at a rate of 60% per second.
This speed is the rate at which the FCV would close when limited solely by valve hydraulics. Similarly, USAR Section 15.4.5 assumes that a single FCV opens at a rate of 30% per second. This speed is also the. rate at which the l
FCV would open when limited solely by valve hydraulics. While these numbers are considered theoretical values, the hydraulic limitation of FCV velocity was yerified during initial plant startup as part of the Initial Startup Testing program. This testing found that the velocity of the FCVs varied from 21.7% to 23% per second in the opening direction and from 19.6% to 21.5% per l
second in the closing direction.
l Failure of the master flow controller could result in the simultaneous opening or closing of both FCVs.
For this transient, the USAR analyses relied upon j
the FCV movement to be less than or equal to 11% of stroke per second in both the opening and closing directions. This limit is controlled by an electronic j
limiter of the electrical demand signal sent to the FCV actuator. This was a j
valid assumption for the original FCV control system design since multiple failures involving the master flow controller as well as each FCV's individual controller would have to occur for both FCVs to close at the' faster rates described above. Therefore, Technical Specification SR 3.4.2.2 was imposed to periodically verify that the average rate of simultaneous FCV movement is within the USAR assumptions, i.e., less than or equal to 11% of stroke per second in both the opening and closing directions.
The original design of the Clinton Power Station allowed for three modes of i
automatic control and one mode of manual control of the recirculation loops.
The two highest levels of automatic control modulated both FCVs together while the lowest level of automatic control and the manual control mode utilize
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individual controllers for each FCV. However, control room operators at the j
CPS have historically not used automatic modes of operation and relied upon t
manual control. Therefore, during the fifth refueling outage (Spring 1995),
I the automatic modes of control were eliminated. This modification eliminated I
use of the master flow controller such that flow in each reactor recirculation j
loop is now controlled by use of individual FCV controllers.
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Elimination of the master flow controller only impacts the single failure assumptions of the transient analyses. Elimination of the master flow controller prevents simultaneous opening or closing of the FCVs as a result of a single active failure. Accordingly, the licensee has revised the USAR j
transient analyses by removing this single failure from consideration.
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addition, since SR 3.4.2.2 is specifically associated with the single active failure of the master flow controller, the licensee has proposed to eliminate it because it is no longer applicable to the CPS design.
The licensee also cited operational considerations in their desire to eliminate SR 3.4.2.2.
A limited amount of preventive and corrective maintenance work can be performed on components of the reactor recirculation loops with the plant at power. However, any work that can potentially affect i
the o>erability of the FCVs will require performance of SR 3.4.2.2 which can only >e performed with the plant shut down. Licensee Event Report (LER) 95-06 l
describes a situation when maintenance was performed at power and the l
appropriate post maintenance testing could not be performed. Part of the l
licensee's corrective actions in response to LER 95-06 was to eliminate or revise SR 3.4.2.2 so that the TS surveillance requirements more closely l
reflect plant design.
l The staff has reviewed the licensee's proposal and finds that with the
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l elimination of the master ficw controller, a single active failure can no longer result in the simultaneous opening or closing of both FCVs. The staff also concludes that SR 3.4.2.2 is no longer applicable to the CPS design and 1
may be eliminated. The single failure analyses of a single FCV opening or l
closing is unaffected by this modification and there is no need to impose t
additional requirements.
Therefore, the staff finds the licensee's proposal l
acceptable.
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3.0 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 l
had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
This amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 or changes a surveillance requirement. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no i
significant change in the types, 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 i
proposed finding that the amendment involves no significant hazards 1
-consideration and there has been no public comment on such finding (61 l-FR 1630). Accordingly, the amendment meets the eligibility criteria for i
i categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need l
l be prepared in connection with the issuance of the amendment.
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5.0 CONCLUSION
The staff has concluded, based on'the considerations discussed above, that:
(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.
Principal Contributor: Douglas Pickett Date:
March 11, 1996 l
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