ML20091K546
| ML20091K546 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Monticello |
| Issue date: | 09/10/1982 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17139C189 | List:
|
| References | |
| FOIA-84-105 NUDOCS 8406070130 | |
| Download: ML20091K546 (12) | |
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ENCLOSURE SAFETY EVALUATION REPORT N-1 LOOP OPERATION MONTICELLO NUCLEAR GENERATING PLANT
1.0 INTRODUCTION
The current Fanticello Technical Specifications do not allow plant I
operation beyond 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> if an idle recirculation loop can not be returned to service.
The ability to operate at reduced power with a single loop is highly desirable from an availability / outage planning standpoint in the event that maintenance or component unavailability renders ene loop inoperable.
By letter dated July 2,1982, Northern States Power Company (NSP) (the licensee) requested changes to the Technical Specification for Single f
Loop Operation of Monticello.
The requested changes would permit Monticelle to operate at up to 50% of rated power with one recirc'.:lation loop out of 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 from 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 l
Browns Ferry Plant Unit-1, has shown to resul't-in acceptable flow and I
l power characteristics, we will permit NSP to operate at power levels up l
to 50% of rated with one looli out of service, during Cycle 10.
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If requested, we wP1 re:onsider operation at a higher power level for Monticello with one recirculation loop out of service after staff concerns stemmine from Browns Ferry - Unit I single loop operation are satis fied.
-2 EVALUATION 2.1 Accidents (Other than Loss of Coolant Accident (LOCA)) and Transients Affected by One Recirculation Loop Out of Service 2.1.1 One Pumo Seizure Accident The licensee states that the or,e-oump seizure 3.ccident is a relatively mild event during two recirculation pump operation.
Similar analyses were performed to detemine the impact this accident would have on one recirculation pump operation. These analyses were performed using NRC approved models for a large core BWR/4 plant.
The analyses were conducted from steady-state operation at the following initial conditions, with the added condition of one inactive recirculation loop.
Two sets of initial conditions were assumed:
a.
Thermal Power = 75% and core flow = 58% of rated b.
Themal Power = 82% and core flow = 56% of rated These conditions were chosen because they represent reasonable upper limits of single-loop operation within existing Maximum Average Linear Heat Generation Rate (MAPLHGR) and Minimun Critical Power Ratio (MCPR) limits at the same maximum pumo speed.
Pump seizure was simulated by
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setting the single operating pump speed = to zero instantaneously.
L
g The anticipated sequence of events following a recirculation pump seizure which occurs during plcnt operation with the alternate recirculation loop out of service is as follows:
a.
The recirculation loop flow in the locp in which the pump seizure occurs drops instantaneously to zero.
b.
Core voids increase which resu.lts in a negative reactivity insertion and sharp decrease in neutrcn flux, c.
Heat flux drops more slowly because of the fuel time constant.
d.
Neutron flux, heat flux, reactor water level, steam flow, and feedwater flow all exhibit transient behaviors.
However, it is not anticipated that the increase in water level will cause a turbine trip ar.d rcsult in scram.
It is expected that the transient will terminate at a condition of natural circul tion and an orderly reactor shutdown will be accomplished. There will also be a small decrease in system pressure.
The licensee concludes that the MCPR for the pump seizure accident for the large core BWR/4 plant was determined to be greater than the fuel cladding integrity safety limit; therefore, no fuel failures were postulated to occur as a result of this analyzed event.
These results are apolicable to Monticello.
2.1.2 Abnormal Transients-2.1.2.1 a..
Idle Loop Startup
.The idle loop startup transient was anlayzed, in the Monticello FSAR, with an-initial power of 60%.
The licensee is to operate at no greater n
r a
_4, 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.
b.
Flow Increase 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 11CPR will vary depending on flow conditions.
This leads to the possibility of a large inadvertent flow increase which could cause the MCPR to decrease below the Safety Limit for a low initial MCPR at reduced flow conditions. Therefore, the required MCPR must be increased at reduced core flow by a flow factor K The K factors are derived assuming both f,
f recirculation loop pumps increase speed to the' maximum permitted by the scoop tube position set screws. This condition maximizes the power increase and hence maximum A MCPR for transients initiated from less than rated conditions. When operating on one loop the flow and power increase will be less than associated with two pumps increasing speed, therefore, the K factors derived from the two-pump assumption are
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f cor,se. vative for single-loop operation.
c.
Rod Withdrawal Error The rod withdrawal error at r~ated power is given in the FSAR for the inital core and in cycle depandent reload supplemental submittals.
These analyses are performed to demonstrate that, even if the operator
s ignores all instrument indications and the alarm which could occur-4 during the course of the transients, 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 MCPR safety limit is not violated.
4 One-pump operation results in backficw 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 inactive jet punps 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 ar,d 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. (dE) to perform single loop operation analysis for Monticello LOCA.
The licensee states that evaluation of these calculations (thut are performed according to the procedure outlined in IEDD-20556-2, Rev.1) indicates that a muliolier of 0.85 (8x8 fuel), 0.85 (8x8R Fuel) 0.85 (P8x8R fuel) (Ref: - NEDE 24271 June 1980) should be applied to the IMPLhGR limits for single loop l
operation of Monticello.
f
a a.
We find the use of these MAPLHGR multipliers to be, acceptab THERMALHYD_f;ULICS_
R 3.
The' licensee has confirmed that analysis uncertainties are i
l independent of whether flow is provided by two loops or s ng The only exceptions to this,are core total flow and TIP
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loop.
The effect of these uncertainties is an increas reading.
factor required at MCPR by.01, which is more than offset by the K f
The steady state operating MCPR with single-loop low flows.
i the X operation will be conservatively established by multiply ng f
factor to the rated flow MCPR limit.
STABILITY A!!ALYSIS 4.
operating As indicated in the applicant's submittal NED0-24271_,
ing along the minimum forced recirculation line with one pump ru l
at minimum speed is more stable t. han operating with natura h both cir'culation flow only, but is less stable than operating wit pumps operating at minimum speed.
d The licensee will be reouired to operate in master manual k
The staff the effects of instabilities due to contro1,1er feedbac.
ht has accepted previous stability analyses results as eviden l ation of BWR the cors can be operated safely while_our generic eva u The stability characteristics and analysis methods continues.
l ion previcus stability 2nalysis results include natural circu a In addition, conditions and thus bound the single loop operation.
i llo shews the decay ratio (.62) predicted for cycle 10 of Mont ce
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margin relative to Browns Ferry #1 (.83) which had the flow noise oscillations during SLO. We conclude that with appropriate limitations to recognize and avoid operating instabilities, that the reactor can be operated safely in the single loop mode.
Our evaluation of the flow / power oscillations evidenced in Browns Ferry 4
will continue and any-pertinent conclusions resulting from this study will be applied to Monticello.
5.
E MMARY ON SINGLE LOOP OPERATION 1.
Steady State Thermal Power Level will no't exceed 50%
Operating at 50% power with appropriate T-S changes was approved on a long term basis for the Duane Arnold Plant, Feach Botton Units 2 and 3, Pilgrim-1 and Cooper Nuclear Station (Safety Evaluation Reports (SER) dated November 19,1981, May 15,1981, December 15, 1981, and December 10, 1981 respectively).. Authorization for single loop operation for extended periods was also given to Dresden Unit 2 and 3 and Quad Cities Units 1 and 2 (SER July 9, 1981).
It was concluded that for operation at 50%, power transient and accident bounds would not he exceeded for these plants.
2.
Minimum Critical Power Ratio (MCPR) Safet Limit will be Increased by 0.01 to 1.08 The MCPR Safety Limit will be increased by 0.01 to account for increased uncertainties in core flow.and Traversing Incore Probe (TIP) readings. The licensee has repor,ted -that this increase in the MCPR Safety Limit was addressed in GE reports specifically for Monticello for one loop operation.
On the basis of previous staff
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reviews for Pilgrim-1, Cooper, Duane Arnold ~and Peach Bottom and our review of plant comparisons we find this analysis acceptable for Monticello.
3.
Minimum Critical Power Ratio (MCPR) Limitino Condition for
'_0,oeration (LCO) will be Increased by 0.01.
The staff require that the operating limit MCPR be increased by 0.01 and multiplied by the appropriate two loop K factors that are f
in the Monticello T-S.
This will preclude an inadvertent flow increase from causing the MCPR to drop below the safety limit MCPR.
This was also approved by the staff for Peach Bottom 2 and 3.
4 The Maximum Averaae Planar Linear Heat Generation Rate (MAPLHGR) Limits will be Reduced by Aooropriate Multipliers The licensee proposed reducing the T-S MAPLHGR by 0.85 (8x8 fuel);
0.85 (8x8R) and 0.85 (P8x8R) for single loop operation.
These reductions were based on analyses by General Electric (GE) in reports NEDE 24011-P-A-1 and NEDO 24271.
The Peach Bottom units were allowed to operate with their MAPLHGR values reduced by factors of 0.71, 0.83, and 0.81 for un unlimited period of time for the fi.st three types cf fuel listed above.
5.
The APRM Scram and Rod Block Setoofnts will be Reduced The licensee proposed to modify the two loop APRM Scram, Rad Block and Rod Block Monitor (RBM) setpoints to, account for back flow through hal.f the. jet pumps. The changes were based on plant specific anlayses by GE. These setpoints equations will be changed
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-9 in the Monticello T-S.
The above changes are similar to the Peach Bottom T-S changes and are acceptable to the staff.
6.
The Suction Valve in the Idle Loop is Closed and Electrically Isolated The licensee will close the recircularti-on pump suctica vaive and remove power from the valve.
In the event of a loss of coolant accident this would preclude partial loss of LPCI flow through the recirculation loop degrading the intended LPCI performance.
The removal of power also helps to preclude a start up of an idle loop transient.
7.
The Ecualizer line between the locos will be Isolated The licensee will close appropriate valves in the cross-tie (equalizer) line between the loops.
The previously discussed analysis assumed the two loops were isolated.
Therefore, it is required that the cross-tie valve be closed.
8.
The Recirculation Control will be in Manual Control The staff requires that the licensee operate the recirculation system in the manual mode to eliminate the neeff for control system analyses and to reduce the effects of potential flow instabilities.
This was also required of Peach Bottom.
l 9.
Surveillance Reauirements The staff requires that the licensee perform daily surveillance on l
the jet pumps to ensure that the pressure drop for one jet pump in i
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a a loop does not' vary from the mean of all j5t pumps in that loop by more than 5%.
- 10. Provisions to Allow Ooeration 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 1.08 (T.S. 3.11C) 3.
The MCPR Liniting Condition for Operation (LCO) will be increased by 0.01 4.
The Maximun Average Planar Linear Heat Generation Rate (MAPLHGR) limits will be reduced by multiplying 0.35 for 8x8, 8x8R, P8x8R fuel respectively (T.S. reference Table 3.11.1) 5.
The APRM Scram and Rod Block Setpoints and the RBM Setpoints, shall be reduced to read as follows:
T.S. 2.3.A.1 S j (.65W + 55% -0.65A W)
T.S. 2.3.A.1*
S j (.65W + 55% -0.65a W) FRP/MFLPD T.S. 2.3.B S j (.65W + 43%
.654W)
T.S. 2.3.B*
S 3 (.65W + 43% -0.65a W)*
APRM Upscale j(.65 + 43% -0.65A W)
RBM Upscalet_(.65W +43% - 0.656 W)
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6.
The suction valve in the idle loop is closed and electrically isolated until the idle loop is being prepared for return to service.
7.
APRM flux noise will be measured once per shift and the recirculation pump-speed will be -reduced if the flux noise exceeds 5-percent peak to peak.
8.
The core plate delta noiss be measured once per shift and the recirculation pump speed will be reduced if the noise exceeds 1 psi peak to peak.
Therefore, based upon the above evaluation and a history of successful operation of other BWRs of the same type as Monticello we conclude that single-loop operation of Monticello 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 and is therefore acceptable.
The approval for single loop operation up to a power level of 50%
is authorized during cycle 10 only.
We have. concluded, based on the considerations discussed above,
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that: (1) because the anendment does not involve a sicnificant j
increase in the prcbability or conse:;uen,ces of accidents previously considered or create the possibility of an accident of a type different from.any evaluated previously,'and does not involve a
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... - significant decrease in a safety margin, thh 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 Comission't 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.
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