ML20091K892
| ML20091K892 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Pilgrim |
| Issue date: | 12/15/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17139C189 | List:
|
| References | |
| FOIA-84-105 NUDOCS 8406070236 | |
| Download: ML20091K892 (9) | |
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ENCLOSURE SAFETY EVALUATION REPORT N-1 LO0p OPERATION PILGRIM NUCLEAR POWER STATION - UNIT 1 (PNPS 1)
1.0 INTRODUCTION
The current PNPS-1 Technical Specifications 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 idle recirculation loop cannot be returned to service. The ability to operate at reduced power with a single loop is highly desirable fram availa-bility/cutage planning standpoint in the event that maintenance or component unavailability renders one loop inoperable.
By BECo letter #81-94 dated May 12, 1981. Boston Edison Company (the licensee) re-quested changes to the Technical Specification for Single Loop Operation of PNPS-1.
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The requested changes would permit PNPS-1 to operate at up to 50% of rated power with one recirculation loop out of service. While analyses indicate that it may be safe to operate BWR: on a single loop in the range of 72% of rated power, the experience (reference letter from L. M. Mills, TVA dated March 17, 1980 to H..nenton, NRC) at Browns Ferry Unit 1 has caused concern about flow and power oscillations.
- However, because single loop operation at 50% rated pcwer at several plants, including Browns Ferry, has shown to result in acceptable flow and power characteristics, we will permit the PNPS-1 to operate at power levels up to 50% of rated with one loop out of service during Cycle 6.
If requested, we will consider operation at a higher power level for PNPS-1 with one recirculation loop out of service after staff concerns stemming from Browns Ferry - Ur.it I single loop operation are satisfied.
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'l 2 EVALUATION __
2,1 Accidents (Other than Loss of Coolant Accident (LOCA)) and Transients Affected By One Recirculation Loop Out of Servicq 2.1 1 One Pumo 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 de-termine the impact this accident would have on one recirculation pump operation.
These analyses were parfcrmed using NRC approved models for a hrge core BWR/4 plant. The analyses were conducted from steady-state operation at the following initial conditions, with the added ccedition of one inactive recirculation loop.
Two sets of initial conditions were assumed:
a.
Thermal Power = 75% and core flow = 58% of rated b.
Thermal Pcwir = 82% and core flow = 56% of rated These conditions were chosen because they represent reasonable upper limits of single-loop operation within existing Maximum Ayerage Planar Linear Heat Generation Rate (MAPLHGR) and Minimum Critical Power Ratio (MCPR) limits at the same maximum pump speed.
Pump seizure was simulated by setting the single operating pump speed to zero instantaneously.
The anticipated sequence of events following a recirculation pump seizure which occurs during plant operation with the alternate recirculation loop out of service is as follows:
a.
The recirculation loop flow in the loop in which the pump seizure occurs drops instantaneously to zero, b.
Core voids increase which result in a negative reactivity insertion and a 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 flow all exhibit transient behaviors.
However, it is not anticipated that the increase in water level will cause a turbine trip and result in scram.
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-It is-expected that the transient will terminate at a condition of natural circu-lation and reactor operation will continue.
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 applicable to Pt1PS-1.
2.1.2 Abnormal Transients 2.1.2.1
- a. Idle Loop Startup The idle loop startup-transient was analyzed, in the PflPS-1 FSAR, with an initial power of 70%. The licensee is to operate at no greater than 50% power with one loop out of service.
Additionally, the Technical Specifications are being modi-fied 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 in-creased 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 large inadvertent flow in-crease which could cause the MCPR to decrease below the Safety Limit for a low i
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 f
f t
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' derived assuming both recirculation loop pumps increase speed to the maximum permitted by the scoop:. tube position set screws.
This condition maximizes the power in-crease and hence tne AMCPR for transients initiated from less than rated conditions._
i When operating on one loop the flow and power increase will be less than associated
4 with two pumps increasing speed, therefore, the. K factors derived from the two-f pump assumption are conservative for single-loop operation.
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 per-formed to demonstrate that, even if the operator ignores all instrument indications and the alarm which could cccur 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 ques-tion and lower initia,1 power for single-loop operation assures that the MCPR safety limit is not violated.
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 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 exists in the Technical Specification for one-pump cperation 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 opera-tion analysis for PNPS-1 LOCA. Single loop analysis for the ECCS limits was performed
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with no credit for the core spray heat transfer system.
The licensee states.that evaluation of these' calculations (that are performed according to the procedure e
outlined in NED0-20566-2, Rev.1) indicates that a multiplier of 0.84 (8x8 fuel) and 0.'84 (8xBR fuel) (Ref: - NEDE 24268 June 1980) should be applied to the MAPLHGR limits for single loop operation of the PNPS-1.
i-We find the use of these MAPLHGR multipliers to-be acceptable.
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3.
Thermal Hydraulics The licensee has confirmed that analysis uncertainties are independent of whether flow is provided by two loops or single loop.
The only exceptions to this are core total flow and TIP reading. The effect of these uncertainties is an in-crease in the t1CPR by.01, which is more than offset by the K factor required f
-at low ficws. The steady state operating MCPR with single-loop operation will be
- conservatively established by multiplying the K factor to the rated flow MCPR f
limit.
4.
Stability Analysis As indicated in the applicant's submittal NED0-24268, operating along the i
minimum forced recirculation line with one pump running at minimum speed is more stable ~ than operating with natural circulation flow only, but is less stable than operating with both pumps operating at minimum speed.
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.The licensee will be required to operate in master manual to reduce the effects of instabilities due to controller feedback.
The staff has accepted previous stability analyses results as evidence that the core can be operated safely while our generic. evaluation of BWR stability characteristics and analysis methods con-tinues. The previous-stability analysis results include natural circulation con-ditions and 'thus ' bound the single loop ' operation.
We conclude that with appropriate limitaticns to recognize and avoid: operating instabilities, the reactor can be operated safely in the single loop mode.
Our evaluation,of the flow / power oscillations evidenced in Browns Ferry will continue and any conclusions resulting from'this. study Will be applied to PNPS-1.
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SUMMARY
Ort SINGLE LOOP OPERATION 1.
Steady State Thermal Power Level will not exceed 50%
Operating at 50% power with appropriate T-S changes was approved on a long term basis for the Duane Arnold Plant, Peach Bottom Units 2 and 3 and Cooper Nuclear Station (Safety Evaluation Reports (SER) dated November 19, 1981, May 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 cot be exceeded for these plants.
2.
Minimum Critical Power Ratio (MCPR) Safety Limit will be Increased by 0.01 to 1.08
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The MCPR Safety Limit will be increased by 0.01 to account for increased uncertain-ties in core flow and Traversing Incore Probe (TIP) readings.
The licensee has re-ported that this increase in the MCPR Safety Limit was addressed in GE reports specifically for PNPS-1 for one loop operation.
On the basis of previous staff reviews for Duane Arnold, Cooper and Peach Bottom and on our review of plant comoarisons we find this analysis acceptable for PNPS-1.
3.
Minimum Critical Power Ratio (MCPR) Limiting Condition for Operation (LCO) will be Increased by 0.01 (Tech. Spec. Table 3.11-1)for 8x8,P8x8R Fuel Respectively The staff require that the operating limit MCPR be increased by 0.01 and multiplied by the appropriate two loop X factors that are in the PNPS-1 T-S.
This will preclude f
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 Average Planar Linear Heat Generation Rate (MAPLHGR) Limits will
'be Reduced by Appropriate Multipliers The _ licensee proposed reducing the T-S MAPLHGR by 0.84 (8x8 fuel); and 0.84 (P8x8R)
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for single loop operation. These reductions were based on analyses by General 8
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. Electric (GE) in reports NEDE 24011-P-A-1 and NED0 24268.
The Peach Bottom units were allowed to operate with their MAPLHGR values reduced by factors of 0.83 and 0.81 for an unlimited period of time for the two types of fuel listed above.
5.
The APRM Scram and Rod Block Setooints and RBM Setpoints will be Reduced The licensee proposed to modify the two loop APRM Scram, Rod Block and Rod Block Monitor (RBM) setpoints to account for back flow through half the jet pumps.
The changes were based on plant specific analyses by GE.
These setpoints equations will be changed in the PNPS-1 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 recirculation 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 ficw through the recirculation loop degrading the intended LPCI per-formance.
The removal of power also helps to preclude a start up of an idle loop transient.
7.
The Eoualizer line between the loops will be Isolated The licensee will close appropriate valves in the cross-tie (equalizer) line be-tween 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 need for control system analyses and to reduce the effects of potential flow instabilities.
This was also required of Peach Bottom.
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9.
' Surveillance Requirements The staff requires that the licensee 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%.
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) 3.
The MCPR Limiting Condition for Operation (LCO) will be increased by 0.01 (Tech. Spec. Table 3.ll-1)for 8x8 and P8x8R fuel respectively, i
4.
The Maximum Average Planar Linear Heat Generation Rate (MAPLHGR) limits will be reduced by multiplying 0.84, and 0.84 for 8x8, P8x8R' fuel respectively (T.S. reference 3-12-1) 5.
The APRM Scram and Rod Block Setpoints and the RBM Setpoints, shall be reduced to read as follows:
~T.S. 2.1.A.1 S _ (.65W + 51.7% )
T.S. 2.1.A.1*
S _ (.65W + 51.7%) FRP/MFLPD T.S. 2.1.A.3 S _,(.65W + 38.7%)-
T.S. 2.1.A.3*
S _ (.65W + 38.7% ) - FRP/MFLPD T.S. 3.2.C.
APRM Upscale _(.65W + 38.7%) FRP/MFLPD RBM Upscale _(.65W + 38.7%) FRP/MFLPD 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 lwill 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 the recirculation pump speed will be reduced if the noise exceeds 1 psi peak to peak.
1 L*In the event that MFLPD exceeds FRP.
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... - Therefore, based upon the above evaluation and a history of successful operation of other BWRs of the same type as PNPS-1 we conclude that single-loop operation of FNPS-1 up tospawer level of 50% and in accordani:e 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 6 only.
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SEP201982 MEMORANDUM FOR:
Themis P. Speis, Assistant Director for Reactor Safety Division of Systems Integration FROM:
Brian W. Sheron, Chief, Reactor Systems Branch, DSI
SUBJECT:
BWR SIHGLE LOOP OPERATION - STATUS REPORT #2 Under multiplant action item E-04, there are 15 plants which involve single locp operation (SLO) the status of each plant is given below.
SER Licensing Plant Issued for 50%
Amendment Name Operation Issued Notes
- 1. Dresden-2 July 9, 1981 Yes
- 2. Dresden-3 July 9, 1981 Yes
- 3. Quad Cities-1 July 9, 1981 Yes
- 4. Quad Cities-2 July 9, 1981 Yes
- 5. Peach Bottom-1 May 15, 1981 Yes
- 6. Peach Bottom-2 May 15, 1981 Yes
- 7. Duane Arnold November 19, 1981 No 1
- 8. Cooper December 10, 1981 No 1
- 9. Filgrin-1 December 15, 1981 No 1
- 10. Browns Ferry-1 August 16, 1982 No 1,2
- 11. Brcwns Ferry-2 August 16, 1982 No 1,2
- 12. Browns Ferry-3 August 16, 1982 No 1,2
- 13. Monticello September 10, 1982 No 1
- 14. Brunswick-1 Being Reviewed, SER Due on November 1,1982
- 15. Brunswick-2 Being Reviewed, SER Due on November 1, 1982 Notes 1.
Instrumention & Control review by EG&G, San Ramon Operations, CA is not completed.
Licensing amendment will be issued after we get an acceptable TER frca EG&G.
2.
CPB sections en thermal hydraulics and stability analysis are not included in the SER submitted for Browns Ferry Units 1,2,&3.
As a follow up to the Browns Ferry-1 meeting with GE on single loop operation, questions were forwarded to T. Novak by memo dated January 15, 1982 from T. Speis for sending to GE and the utility group.
-Recently, approval was granted by GA0 for sending the questions to the licensees.
Questions are expected to be sent to the individual
, !As o_y 21 Y
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SEP 2 01952 licensees during first week of October 1982.
Approval for single loop operation at a power greater than 50'.' can be granted only after staff concerns stemming frca Browns Ferry-IJnit 1 single loop operation are satisfied.
Brian W. Sheron, Chief Reactor Systems Branch, DSI cc:
R. Mattson D. Vassalo t
R. Clark K. Eccelston B. Sigel J. VanVliet H. Nicolaras C. Berlinger RSB Section Leaders L. Phillips G. Schwink t
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