ML20091K531
| ML20091K531 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Browns Ferry |
| Issue date: | 08/16/1982 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17139C189 | List:
|
| References | |
| FOIA-84-105 NUDOCS 8406070125 | |
| Download: ML20091K531 (11) | |
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ENCLOSURE SAFETY EVALUATION REPORT N-1 LOOP OPERATION BROWNS FERRY NUCLEAR PLANT UNITS 1, 2, AND 3 (BFNP-1, 2, 3)
1.0 INTRODUCTION
The current BFNP-1, 2, and 3 Technical Specification do not allow plant operation beyond 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> if an i'dle recirculation loop cannot be returnea to service.
The ability to operate at reduced power with a single loop is highly desirable fr'om availability / outage planning standpoint in the event that maintenance or component unavailability-rendered one loop inoperable.
l By letter dated March 4, 1982, Tennessee Valley Authority (the license 2) requested changes to the Technical Specification for Single Loop Operation of BFNP-1, 2, and 3. 'The requested changes would permit BFNP-1, 2 and 3 to operate at up to 50% of rated power with one recirculation 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 toH.Denton,NRC)atBrowns 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 Plant Unit-1, has shown to result in acceptable flow and power characteristics, we will permit TVA to operate at power levels up to 50% of rated with one loop out of service during Cycle 5.
t g 6 g 25 840319 BELL 84-105 PDR
If requested, we will reconsider operation at a higher power level for BFNP-1, 2 & 3 with one recirculation loop out of service after staff concerns stemming from Browns Ferry - Unit I 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 2.1.1 One Pump Seizure Accident The licensee states that the one-pump seizure accident is a relatively mild event during two recirculation pump operation.
Similar analyses were performed to determine the impac+, th'is accident would have on one recirculation pump operation. These analyses were performed using flRC approved models for BFNP-1.
The analyses were conducted from steady-state operation at the following initial conditions, with the added condition of one inactive recirculation loop. Tvm sets of initial conditions were assumed:
a.
Thermal Power = 75% and core flow = 58% of rated b.
Thermal Power = 821 and core flow = 56% of rated These conditions were chosen because they represent reasonable upper limit; of single-loop operation within existing Maximum Average Linear Heat Generation Rate (MAPLHGR) and Minimum Critical Power Ratio (MCPR)
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limits at the same maximum pump speed.
Pump seizure was simulated by setting the single cperating pump speed to zero instantaneously.
3 The anticipated sequence of events following a recirculation pump seizure which occurs during plant operation with the af ternate recirculation loop out of service is as follows:
a.
The recirculation 1 bop flow in the loop in which the pump d
seizure occurs drops instantanecusly to zero.
b.
Core voids increase which resuits in a negative reactivity insertion and sharp decrease in neutron 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 fics all exhibit transient behaviors.
However, it is not anticipated that the increase in water level will cause a turbine trip and result in scram.
It is expected that the transient will teminate at a condition of natural circulation and reactor operation will continue. There will also be a small decrease in system pressure, j
The licensee concludes that the MCPR for the pump seizure accident for BFNP-1 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 applicable to Browns 4
Ferry Nuclear Plant Units 2 and 3.
2.1.2 Abnomal Transients 2.1.2.1 a.
Idle Loop Startup The idle loop startup transient was anlayzed, in the. BFNP-1, 2 & 3 FSAR, with an initial power of 68%. The licensee is to operate at no greater
4 than 50% power with one loop out of service.
Additionally, the Technical Specifications ate 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.
l 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 l
total flow and Traversing In-core Probe (TIP) readings. The MCPR will l
vary deanding 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 j
recirculation Icop pumps increase speed to the maximum permitted by the scoop, tube position set screws. These conditions maximize the power increcse and hence maximum MCPR for transients initiated from less j
than rated conditions. When operating on one loop the flow and power increase will be less than associated with two pumps incrcasing speed, therefore, the K factors derived from the two-pa,np assumption are g
conserwtive for single-loop operation.
c.
Rod Withdrawal Error The rod withdrawal error at rated power is given in the FSAR for the inital core and in cycle Apendent reload supplemental submittals.
These analyses are performed to demonstrate that, even if the operator G
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ignores all instrument indications and the alarm which could occur 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 safe'ty limit.
Cderection of the rod bicek i
equation and lower initial power for single-loop operation assures that the MCPR safety limit is not violated.
j i
i One-pump operation results in backflow through 10 of the 20 jet' pumps
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while flow is being supplied to the lower plenum from the active jet f
4 pumps. Because of this backflow through the inactive jet pumps the l
t present rod-block equation and ApMM settings must be modified.
The l
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licensee has modified the two-pump rod block equation and ApRM settings j
s f
l that exist in the Technical Specification for one-pump operation and the i
staff has found them acceptable.
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l The staff finds that one loop transients and accidents other than LOCA, f
f
, which is discussed below, are bounded by the two loop operation analysis l
and are therefore acceptable.
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2.2 Loss of Coolant Accident (LOCA)
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The licensee has contracted General Electric Co. (GE) to perform single loop operation analysis for SFNp-1, t & 3 LOCA. The licensee states that evaluation of these calculations (that are perfnewed according to i
theprocedureoutlinedinNED0-805442,Rev.1)indicatesthata L
muli,plierof0.70(7x7 fuel),'0.83(Satfuel),0.42(4x44 Fuel)0.82 (ptm8R fuel) (Ref t - NEDE 24236 May 1M1) should be applied to the f
MAptH8R. limits for single loop operation of SFNp 1, t & 3.
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We find the use of these MAPLHGR multipliers to be acceptable.
3.
SUMMARY
ON SINGLE LOOP OPrRATION 1.
Steady State Thermal Power level will not exceed 50%
Several BWRs have previously been authorized to operate for a short period of time with one recirculation loop.
In all but one case, power level has been limited to 50 percent; the one exception was Browns Ferry Unit No. 1.
On September 29, 1978, based on analyses perfortned for TVA by the General Electric Company (GE), we -
authorized TVA to operate Browns Ferry 1 for about two months at power levels up to 82 percent of full rated power.
During power ascension with Browns Ferry 1 in single loop operation, jet pump
' low variations were noted in the active loop above a pump speed of 65percentofratedflow(about59percentofratedpower).
Whenever TVA tried to increase the power level above this point, they noted variations in jet pump flow, neutron flur, and related parameters. Accordingly TVA administrative 1y limited Browns Ferry Unit 1 operation to less than 60, percent for the approximately two months the unit operated on a single loop.
While analyses indicate that it should be safe to sperate BWRs on a single loop in the range of 85 percent of rated power, the experience at Leowns Ferry Unit I has raised concerns about authorizing single loop operation for SWRs above 50 percent rated power until there is a better understanding of what may have causec the variations in this facility.
r.
- Operating at 50% power with appropriate T-S changes was approved on a long term basis for the Cooper Nuclear Station, Duane Arnold Plant and Peach Bottom Unit: 2 and 3 (Safety Evaluation Reports (SER) dated December 10, 1981, November 19, 1981 and May 15, 1981 respectively).
Authorization of single 1 cop 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 be exceeded for these plants.
2.
Minimum Critical Power Ratio (MCPR) Safety 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 reported that this increase in the MCPR Safety Limit tras addressed in GE reports specifically for BFNP-1, 2 & 3 for one loop operation. On the basis of previous staff reviews for. Cooper, Duane Arnold and Peach Bottom and our review of plant comparisons we find this analysis acceptable for BFNP-1, 2 & 3.
3.
Minimum Critical Power Ratio (MCPR) Limitino Condition for Operation (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 BFNP-1, 2 & 3 T-S.
This will preclude an inadvertent flow 4
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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 Average-Planar Linear Heat Generation Rate (MAPLHGR) Limits will be Reduced by Aporooriate Multioliers The licensee proposed reducing the T-S MAPLHGR by 0.70 (7x7 fuel);
O.83 (8x8 fuel); 0.82 (8x8R) and 0.82 (P8x8R) for single loop operation.
These reductions were based on analyses by General Electric (GE) in reports NEDE 24011-P-A-1 and NEDO 24236.
The Peach Bcttom units were allowed to operate with their MAPLHGR values reduced by factors of 0.71, 0.83, and 0.81 for an unlimited period of time for the first three types of fuel listed above.
5.
The APRM Scram and Rod Block Setpoints will be Reduced The licensee proposed to modify the two loop APRM Scram, Rod Block and Rod Block Monitor (RBM) setpoints tc account for back flow 1
through half the jet pumps. The changes were based on plant specific anlayses by GE. These setpoints equations will be changed in the BFNP-01, 2 & 3 T-S.
The above changes are timilar to the Peach Bottom T-S changas and are acceptable to the staff.
6.
The Suction Valve in the Idle Loop is Closed and Elec'.rically
, Isolated i
The licensee will close the recirculaticn pump suction valve 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
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9-removal of power also helps to preclude a start up of an idle loop l
7.
The Ecualizer line between the loopc will be Isolated lhe licensee will close appropriate valves in the cross-tie (cqualizer) line between the loops.
The previously discussed i
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 need for control system analyses and to reduce the effects of potential ficev instabilities.
This was also required of Peach Bottom.
9.
Surveillance Requirements The staff requires that the licensee perform daily surveillance on the jet pumps to ensure that the pressure drcp for one jet pump in a loop does not vary from the mean of all jet pumps in that loop by more than 5%.
- 10. Provisions to Allow Operation with One Recirculation Loop 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. 1.1A)
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10-3.
The MCPR Limiting Condition for Operation (LCO) will be increased by 0.01 4.
The Maximum Average Planar Linear Heat Generation Rate (MAPLHGR) limits will be reduced by multiplying 0.70, 0.83, 0.82, and 0.82 for 7x7, 8x8, 8x8R, P8x8R fuel respectively (T.S. reference Table 3.51) 5.
The APRM Scram and Rod Block Setpoints and the RBM Setpoints, shall te reduced to read as follows:
T.S. 2.1.A.1 S __ (.66W + 54% -0.66a W)
T.S. 2.1.A.1*
S _ (.66W + 54% -0.66 AW) FRP/MFLPD T.S. 2.1.A.3 S _,(.66W + 42%
.66aW)
T.S. 2.1.A.3*
S _ (.66W + 42% -0.664 W)
APRMUPscale_(.66+42%-0.66AW)
RBM Upscale _(.66W +40%)
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 noise be measured once per shift and I
(
the recirculation. pump speed will be reduced if the noise i
exceeds 1 psi peak to peak.
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+:., ', Therefore, based upon the above evaluation and a history of successful operation of other BWRs of the same type as BFNP-1, 2 &
3 we conclude that single-loop operation of BFNP-1,2,& 3 up to a power level of 50% and in accordance with the proposed TSs, will not exceed the accident and transient bound; 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 cuthorized during cyclo 5 'nly.
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