ML20213E691
| ML20213E691 | |
| Person / Time | |
|---|---|
| Site: | Columbia  |
| Issue date: | 11/17/1983 |
| From: | Houston R Office of Nuclear Reactor Regulation |
| To: | Novak T Office of Nuclear Reactor Regulation |
| References | |
| CON-WNP-0678, CON-WNP-678 NUDOCS 8312070015 | |
| Download: ML20213E691 (11) | |
Text
RSS Re F RSB P/F: WilP-2 TCollins R/F NOV 17 N AD/RS Rdg.
BSh ron UHodg:s TCollins MEi10RAf! Dull FOR:
Thomas Novak, Assistant Director for Licensing, DL FROM:
R. Wayne Houston, Assistant Director for Reactor Safety, DSI SUBJECT':
SAFETY EVALUATION OF WNP-2, SIllGLE LOOP OPERATION Plant Nare:
WNP-2 Docket ?! umber:
50-397 NSSS Supplier:
General Electric Responsible Branch:
LB-2 Project !!anager:
R. Auluck Review Status:
Complete Enclosed is the Safety Evaluation Report to permit WNP-2 to coerate on a single recirculation loop with power limited to 50% of rated thermal pow r, g : e--:;y-M 27 I' U.rjr.qj:M.a R. Wayne !!ouston, Assistant Director for Reactor Safety, DSI
Enclosure:
As stated cc:
R. flattson L. Phillips G. Schwenk D. B. Vassallo R. Auluck C. Berlinger D. Hoffmann C._Berlinger
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CONTACT:
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.RSB R/F RSB P/F: WNP-2 TCollins R/F AD/RS Rdg.
BSheron WHodges TCollins
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!!EMORANDUf1 FOR:
Thomas Novak, Assistant Director for Licensing, DL FR0ft:
R. Wayne Houston, Assistant Director for Reactor Safety, DSI
SUBJECT:
SAFETY EVALUATION OF h?iP-2, SINGLE' LOOP OPERATI0fl
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Plant Name:
WNP-2
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Docket Number:
S0-397
/
NSSS Supplier:
/
Responsible Branch:
LB-2
/
Project Itanager:
R. Auluck f
Review Status:
Complete
/
f Enclosed is the Saf'ety Evaluation Repo/t to permit WNP-2 to operate on a single recirculation loop with power' limited to 50% of rated thermal power.
R. Wayne Houston, Assistant Director for Reactor Safety, DSI
Enclosure:
As stated cc:
R. (fattson L. Phillips G. Schwer)k D. B. Vassallo R. Aulu'ck C. Berlinger D.
offmann CONTACT:
T. Collins, RSB X24478 l
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ENCLOSURE SAFETY EVALUATION REPORT N-1 LOOP OPERATION WNP-2 1.0 Introduction By letter dated September 8,1983, the Washington Public Power Supply System (the applicant) provided safety analyses and proposed Technical Specifications to allcw Single Loop Operation of WNP-2. The prcposal requests permission to operate with cne recirculation lcap out of l
service for unlimited time.
While analyses indicate that it may be safe to operate BWRs on a single loop in the range higher than 50% of rated power, the experience (reference letter frcm L. M. Mills, TVA, dated March 17, 1980 to H. Denton, NRC) at Browns Ferry Unit i has caused concern about flow and power oscillations. However, because single loop operation at 50% rated power at several plants, including Browns Ferry Unit 1, has shown acceptable flow and power characteristics, we will permit WNP-2 to operate at power levels up to 50% of rated with one loop out of service during its initial fuel cycle.
We will request from the applicant any additional information required for permanent approval for single loop operation.
If requested, we will also consider operation at higher power levels for WNP-2 with one recirculation loop out of service after staff concerns stemming from Browns Ferry Unit 1 single loop operation are satisfied.
[
2 EVALUATION 2.1 ACCIDENTS (OTHER THAN LOSS OF COOLANT ACCIDENT (LOCA)) AND
. TRANSIENTS AFFECTED BY ONE RECIRCULATION LOOP OUT OF SERVICE F
b
2.1.1 ONE PUMP SEIZURE ACCIDENTS.
The applicant states that the one-pump seizure accident is a relatively mild esent during two recirculation pump operation.
Analyses were perfor:ed to determine the impact this accident would have on one recirculation pump operation.
These analyses were performed using NRC approved models.
The analyses were conservatively conducted from a steady-state operating condition of 79% rated thermal power and 64% core fl ow.
Pump seizure was simulated by setting the single operating pump speed to zero instantaneously.
Results of the analyses indicate that neither pressure nor cladding thermal limits are exceeded during the event.
Peak vessel pressure is calculated to be 1055 psig (ASME code limit is 1375 psig) and MCPR is 1.10 (safety limit is 1.07).
2.1.2.
Abnormal Operational Transients The applicant discussed the effects of single loop operation on the course of abnormal operational transients.
Pressurization and cold water increase events, as well as rod withdrawal error were addressed.
Flow decrease is covered by the pump seizure accident already described.
The results of calculations for the limiting event for each category were presented.
Initial operating conditions were conservatively assumed to be 79% rated thermal power and 64% core flow.
2.1.2.1 a)
Pressurization Events The limiting pressurization event is the generator load rejection without bypass transient.
For single loop operation, the licensee has calculated that the maximum vessel pressure is 1158 psig and the MCPR is 1.29.
Each of the values satisfies its respective safety limit, b)
Cold Water Increase The limiting cold water increase event is the feedwater controller failure to maximum demand transient. The reactor is assumed to be in single loop operation when failure of the feedwater control system instantaneously increases the feedwater flow to runout capacity (173% of initial flow).
The peak pressure is calculated to be 1124 psig and the MCPR is 1.25, each satisfying its respective safety limit.
c)
Rod Withdrawal Error The rod withdrawal error at rated power is given in the FSAR for the initial core and in cycle dependent reload supplemental submittals.
These analyses are performed to demonstrate that, even if the operator ignores all instrument indications and alarms which could occur during the course of the transient, the rod block system will stop rod withdrawal at a minimum critical power ratio which is higher than the fuel cladding integrity safety limit.
Correction of the rod block equation and lower initial power for single-loop operation assures that the MLPR safety limit is not violated.
One-pump operation results in backflow through 10 of'the 20 jet pumps while flow is being supplied to the lower plenum from the active jet pumps.
Because of this backflow through the ir. active jet pumps, the present rod-block equation and APRM settings must be modified.
The applicant has proposed modifications to the two-pump rod block equation and APRM settings to allow for one-pump operation.
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 analyses and are therefore acceptable.
2.1.3 MCPR Uncertainties For single-loop operation, the rated condition steady-state MCPR limit is increased by 0.01 to account for increased uncertainties in the core total flow and Traversing In-core Probe (TIP) readings.
The MCPR will vary depending on flow conditions.
This leads to the possibility of a j
large inadvertent flow increase which would cause the MCPR to decrease
~below the Sefety Limit for a low initial MCPR at reduced flow l
l conditions. Therefore, the required MCPR must be increased at reduced l
l core flow by a flow factor K. The K factors for two loop operation f
f are derived assuming both recirculation loop controllers fail. This condition maximizes the pover increase and hence maximun a MCPR for transients initiated from less than rated conditions. When operating on one loop, the flow and power increase will be less than that associated with two loops at full flow.
The K factors derived from the two-loop f
P
(
assumptions are therefore conservative for single loop operation.
2.2 Loss of Coolant Accident (LOCA)
The a'pplicant has performed analyses of a spectrum of recirculation suction line breaks under single loop operation conditions.
The licensee states that evaluation of these calculations has been performed in accordance with the procedure cutlined in NEDO-20566-2, Rev., 1.
The results indicate that for P8x8R fuel a multiplier of 0.84 must be applied to the MAPLHGR limits for single loop operation at WNP-2.
3.
Thermal Hydraulig The applicant has confirmed that analys-is uncertainties are generally independent of whether flow is provided by two loops or a single loop.
The only exceptions to this are uncertainties in core total flow and TIP reading.
The effect of these uncertainties is accounted for by increasing the safety limit MCPR by.01 tc 1.07. The steady state operating MCpR with single-icop operaticn will be conservatively established by multiplying the rated flew MCPR limit by the Kf factor.
4.
Stability Analysis As indicated in. the applicant's submittal, operating along the ninimum forced recirculation line with the one pump running at minimum speed is more stable than cperating with both pumps running at minimum speed, The applicant is required to operate in master manual to reduce the effects cf instabilities due to controller feedback.
The staff has accepted previous stability ar.alysis results as evidence that the core can' be operated safely while our generic evaluation of BWR stability characteristics and analysis methods continues.
The previous stability analysis results include natural circulation conditions and thus bound the single loop operation.
In addition, the decay ratio (.70) predicted for the initial cycle for Unit 1 shows margin relative to Browns Ferry
- 1 (observed stability margin of.83) which had the flow noise oscillations during SLO.
We conclude that with appropriate limitations to recognize and avoid operating instabilities, the reactor can be operated safely in the single loop mode.
Our evaluation of the flow / power escillations evidenced in Browns Ferry will continue and any pertinent conclusions resulting from this study will be applied to WNP-2.
5.
Summary of Single Loop Ooeration
- 1. Steady State Thermal Power Level will not exceed 50%
Rated Power Operating at 50% power with appropriate TS changes has been approved on a cycle basis for several operating plants.
It is concluded that operation of WNP-2 at 50% power, consistent with the provisions of item 7 below, will not result in transient or accident bounds being exceeded.
- 2. Minimum Critical Power Ratio (MCPR) Safety Limit will be Increased by 0.01 to 1.07 The MCPR Safety Limit will be increased by 0.01 to account for increased uncertainties in (TIP) readings.
The applicant has determined that the change conservatively bounds the uncertainties introduced by single loop operation.
- 3. The Maximum Average Planar Linear Heat Generation Rate (MAPLHGR) Limits will be Reduced by Aporopriate Multipliers The applicant proposed. reducing the TS MAPLHGR to 84 percent of its two loop value for Single Loop Operation.
These reductions were based on an analysis method proposed by General Electric in NEDE-20566-2 and are intended to provide additional conservatism for LOCA events.
A reduction factor of 0.84 is consistent with that approved for other plants similar to WNP-2.
- 4. The APRM Scram and Rod Block Setooints will be Reduced The applicant proposed to modify the two loop APRM Scram, Rod Block and Rod Block Monitor (RBM) setpoints to account for back flow through half of the jet pumps.
These setpoint equations will be included in the WNP-2 TS.
- 5. The Recirculation System will be in Master Manual Control The staff requires that the applicant operate the recirculation system in the manual master mode to eliminate the need for control system analyses and to reduce the effects of potential flow instabilities.
- 6. Surveillance Requirements The staff requires that the applicant perform daily surveillance on the jet pumps to ensure that the pressure drop for one jet. pump in a loop does not vary from the mean of all jet pumps in that loop by more than 5%.
- 7. Provisions to Allow Doeration with One Recirculation Looo Out of Service 1.
The steady-state thermal power level will not exceed 50% of rated.
2.
The Minimum Critical Power Ratio (MCPR) Safety Limit will be increased by.01 to 1.07, 3.
The Maximum Average Planar Linear Heat Generation Rate (MAPLHGR) Limit will be reduced to a value of 0.84 times the two-loop value.
4.
T.S. 2.2.1 S f 0.66W + 47.7 (Trip Setpoint)
S & 0.66W + 50.7 (Allowable)
T.S. 3.2.2 S 1 (0.66W + 47.7)T* (Trip Setpoint)
S & (0.66W + 50.7)T* (Allowable)
S
& (0.66W + 38.7)T* (Trip Setpoint)
RB S
6,(0.66W + 41.7)T (Allowable)
RB T.S. 3.3.6 APRM Upscale 4 0.66W + 38.7 (Trip Setpoint) 60.66W+41.7(Allowable)
RBM Upscale 6 0.66W + 36.7 (Trip Setpoint) 1 0.66W + 39.7 (Allowable)
- T as defined in T.S. 3.2.2.
a
_g.
5.
APRM flux noise will be measured once per shift and the recirculation pump speed will be reduced if the flux noise exceeds the maximum allowable level.
'6.
The core plate AP noise will be measured once per shift and the recirculation pump speed will bc reduced if the noise exceeds the maximum allowable level.
7.
The maximum allowable level for APRM flux noise and core plate AP shall be determined as follows:
The APRM flux noise and core plate AP will be monitored at 40 percent of rated power for i to I hour to establish a baseline noise level.
This baseline noise level (peak to peak oscillation) will be increased by 50 percent to establish a maximum allowable limit.
8.
The recirculation flow control system must be in the master manual mode.
9.
Individual jet pump AP will be shown on a daily basis not to vary by more than 5% from the mean for all jet pumps in the i
same loop.
Conclusions Based upon the above evaluation and a history of successful operation of other BWRs, we conclude that single-loop operation of WNP-2, up to a power level of 50% and in accordance with the proposed TSs, will not exceed the accident and transient bounds previously found acceptable by the NRC staff.
l Single loop operation up to a power level of 50% is therefore, acceptable and authorized for WNP-2 during cycle 1.
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