ML19305E557
| ML19305E557 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 05/06/1980 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19305E551 | List: |
| References | |
| NUDOCS 8005200051 | |
| Download: ML19305E557 (4) | |
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o UNITED STATES o,,
8 NUCLEAR REGULATORY COMMISSION o
E WASHINGTON, D. C. 20555 y
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 60 TO LICENSE NO. DPR-49 IOWA ELECTRIC LIGHT AND POWER COMPANY CENTRAL IOWA POWER COOPERATIVE i
CORN BELT POWER COOPERATIVE DOCKET NO. 50-331 DUANE ARNOLD ENERGY CENTER 1.0 Introduction By letter dated May 2,1980, Iowa Electric Light and Power Company (the licen:ee) requested changes to the Technical Specifications (Appendix A) appended 'to Facility Operating License No. DPR-49 for the Duane Arnold Energy Center (DAEC). The requested changes would pennit the DAEC to operate at up to 50% of rated power with one recir-culation loop out of service.
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On April 30, 1980, the "A" loop recirculatio~n pump motor generator set tripped.
Subsequent investigations indicated that the motor is shorted to ground, thus requiring motor rcpinding before the loop can be returned to service. The licensee estimates a minimum of three weeks is required for motor repair.
2.0 Evaluation 2.1 Accidents (Other than LOCA) and Transients Affected by One Recirculation Loop Out of Service 2.1.1 One Pemp Seizure Accident The licensee has qualitatively compared the consequences of a pump seizure accident during single loop operation with the consequences of c LOCA during full power operation with both loops in service.
Pre-vious analyses have demonstrated that the pump seizure accident is not as severe as a LOCA for two pump operation. The same conclusion can be made for the one pump case by analyzing the two events.
In both events, the recirculation driving loop flow is lost instantaneously, in the seizure because of pump stoppage, in the LOCA because of a line severance.
In the seizure event, natural circulation flow continues, water level is maintained, and the core remains submerged; thus a continuous core cooling mechanism is provided.
However, fo a LOCA complete flow stoppage occurs and the water ? evel decreases, result-ing in core uncovery and subsequent fuel rod cladding overheating.
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J i 1 addition, the reactor pressure does not decrease for a pump seizure Since event, whereas complete depressurization occurs for the LOCA.
the potential effects of a pump seizure accident are bounded by the effects of a LOCA, the licensee has taken the position that specific pump seizure analyses for one loop operation are not necessary.
Although this gives some assurance of acceptability of the pump sei-zure event, the staff notes that the acceptance criteria for pump seizure are more stringent than the criteria for a LOCA. Standard Review Plan 15.3.3 (Reactor Coolant Pump Rotor Seizure, and Reactor i
Coolant Pump Shaft Break) requires that for the pump seizure accident, the release of radioactivity should be a fraction of 10 CFR 100 guide-i Only limited amounts of fuel failures are acceptable for pump lines.
seizures, whereas significantly more failures are acceptable for LOCA.
l The licensee, however, will limit reactor power during single loop operation to 50% of rated power. As indicated on the DAEC power / flow operating map, the natural circulation line intersects the 100% flow Thus, with power limited to 50%, reactor control line at 53% power.
power is at a value where no fuel damage will occur even if pump sei-zure should occur.
i The staff finds the power limit of 50% to be acceptable on the basis that the power limit will assure no significant fuel damage will result should the pump seizure event occur during one loop operation at DAEC.
2.1.2 Abnormal Transients
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2.1.2.1 Idle Loop Startup The idle loop startup transient was analyzed, in the DAEC FSAR, with an initial power of 55%. The licensee has connitted to operate at no greater than 50% power with one loop out of service. Additionally, the Technical Specifications are being modified to require that, during single loop operation, the suction valve in the idle loop be shut and electrically disconnected. These measures are being taken to preclude startup of an idle loop.
2.1.2.2 Flow Increase The Minimum Critical Power Ratios (MCPRs) in the present Technical Specifications for operation at full power have previously been reviewed and found to be acceptable. A large inadvertent flow increase could cause the MCPR to decrease below the Safety Limit Therefore, MCPR for a low initial MCPR at reduced flow conditions.
the required MCPR must be increased at reduced core flow by a flow factor, Kr. The Kf factors are derived assuming both recirculation loops increase speed to the maximum permitted by the scoop tube This condition maximizes the power increase and position set screws.
hence the AMCPR for transients initiated from less than rated con-ditions. When operating on one loop the flow and power increase will be less than with two pumps increasing speed, therefore the Kf factors derived from the two-pump assumption are conservative for one loop operation.
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. 2.1.2.3 Rod Withdrawal Error The rod withdrawal error at rated power analysis indicated that the rod block monitor (RBM) will stop rod withdrawal at a critical power ratio (CPR) which is higher than the safety limit. The minimum critical power ratio (MCPR) requirement for one loop operation will be equal to that for two loop operation because the nuclear character-istics are independent of whether core flow is attained by one or two pump operation, if flow asymmetries are not incurred with one-loop operation. Tests at Quad Cities have shown that flow is uniform across the core for one pump operation with the equalizer valve closed. The results of these tests are considered applicable and acceptable for DAEC.
Onerpump operation results in backflow through 8 of the 16 jet pumps while flow is being supplied to the lower plenum from the active jet pumps. Because of this backflow through the inactive jet pumps the present rod-block equation and APRM settings must be modified.
The licensee has modified the two-pump rod block equation and APRM settings that exist in the Technical Specification, for one-pump operation and the staff has found them acceptable.
The staff finds that one loop transients and accidents other than LOCA, which is discussed below, are bounded by the two loop operation analysis and are therefore acceptable.
2.2 Loss of Coolant Accident (LOCA)
The licensee has contracted General Electric Co. (GE) to perform single loop operation analysis for DAEC LOCA. The licensee states that preliminary evaluation of these calculations (that are per-forned according to the procedure outlined in NED0-20566-2, Rev.1) indicates that a multiplier of 0.86 should be applied to the MAPLHGR limits for single loop operation of the DAEC. The licensee asserts further that GE has performed a large number of single loop analyses for similar plants; and, in no case has a multiplier of less than 0.70 been required. Additionally, because DAEC does not have the LPCI modification and because the limiting LOCA break is a suction line break, the single loop MAPLHGR multiplier is expected to be significantly larger than for most other BWRs.
However, the licensee has proposed that, until the GE calculations can be verified, a multiplier of 0.65 be utilized.
The staff's evaluation finds that value of MAPLHGR reduction factor to be conservative and, therefore, acceptable.
3.0 Summary For the reasons previously discussed, the staff finds acceptable the l
proposed single loop operation during the period necessary to affect repairs to the recirculation pump motor generator.
Power is limited to no greater than 50% of rated power.
e 4.0 Environmental Corciderations We have determined that this amendment does not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact. Having made this determination, we have further concluded that the amendment involves an action which is insignificant from the standpoint of environmental impact and pursuant to 10 CFR Section Sl.5(d)(4) that an environmental impact statement, negative declaration, or environ-mental impact appraisal need not be prepared in connection with the issuance of this amendment.
5.0 Conclusion j
We have concluded, based on the considerations discussed above, that:
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(1) because the amendment does not involve a significant increase in i
the probability or consequences of accidents previously considered and does not involve a significant decrease in a safety margin, the amendment does not involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) such activities will be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.
Dated: May 6,1980
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