ML20154H886
| ML20154H886 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 09/14/1988 |
| From: | Mroczka E, Werner R NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| IEB-88-007, IEB-88-7, NUDOCS 8809220166 | |
| Download: ML20154H886 (4) | |
Text
a.
General Offices
- Seiden Street. Beriin, Connecticut I
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- a P.O. BOX 270 T :Ta",'ET.'"'".'.""
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HARTFORO. CONNECTICUT 06141 o27o L
J (2031 665-5000 September 14, 1988 Docket No. 50 245 A07301 Re: NRC Bulletin 88 07 U.S. Nuclear Regulatory Comission Attn: Document Control Desk Washington, D.C.
20555 Gentlemen:
Millstone Nuclear Power Station, Unit No.1 Response to "NRC Bulletin 88-07, Power Oscillations in Boilina Water Reactors (BWRs.)"
II) requested licensees for boiling water reactors NRC Bulletin No. 88 07 (BWRs) to take actions to inform operators regarding the power oscillation event which took place at LaSalle Unit 2 on March 9,1988, and to review the adequacy of procedures, operator licensing programs, and instrumentation in dealing with a power escillation.
Since Northeast Nuclear Energy Company (NNECO) received the bulletin on June 17, 1988, confirmation of completion of the requested action is due by September 15, 1988.
Our response concerning Hillstone Unit No. 1 is provided herein.
Reauested Action Within 15 days of receipt of this bulletin, all BWR licensees should ensure that any licensed reactor operator or shift technical advisor performing shift duties has been thoroughly briefed regarding the March 9,1988 LaSalle Unit 2 event.
Response
All operations personnel documented their review of the event by signing a Document Ack1owledgen.ent sheet.
Most personnel signed the sheet within 15 days of receipt of the bulletin.
For personnel who did not sign the sheet within 15 days of receipt of the bulletin, it was verified that these person-nel were not on :hift during the period prior to signing the sheet, or had attended a prior briefing regarding the event.
l (1)
C. E. Rossi letter to all holders of operating licenses or construction permits for BWRs, "NRC Bulletin No. 88 07. Power Oscillations in Boiler i
l Water Reactors (BWRs)," dated June 15, 1988.
I d
I 8809220166 880914 PDR ADOCK 05000245 g
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O PDC t
i U.S. Nuclear Regulatory Commission A07101/Paga 2 September 14, 1988 Reauested Action Within 60 days of receW ot *nis bulletin, all BWR licensees should verify the adequacy of their pr x edures and operator training programs to ensure that all licensed operators and shift technical advisors are cognizant of:
a) those plant conditions which may result in the initiation of uncontrolled power oscillations, b) actions which can be taken to avoid plant conditions which may result in the initiation of uncontrolled power oscillations, c) how to recognize the onset of uncontrolled power oscillations, and d) actions which can be taken in responst, to uncontrolled power escil-1ations, including the need to scram the reactor if oscillations are not promptly terminated.
Addressees should also verify the adequacy of the instrumentation which is relied upon by operators within their procedures.
It is expected that all BWRs will have procedures and operator training programs to address uncontrolled power oscillations regardless of calculated decay ratios.
Response
Millstone Unit No.1 is a low power density BWR-3, and therefore it has not been as susceptible to thermal hydraulic instabilities as have been the higher power density BWRs.
As such, the BWR 3s have been exemptef2[ rom the calcula-tion of cycle-specific thermal hydraulic decay ratios.
When SIL 380, Revision 1, was issued, the recommendations contained in it were supplied for "information only" to BWR 2 and 3 operators.
Thus, while the information on thermal hydraulic instability contained in SIL-380 was passed on to appro-priate personnel, no specific guidance regarding thermal hydraulic instability was incorporated into Millstone Unit No. l's procedures.
However, in light of the LaSalle incident where thermal hydraulic insta-bilities were experienced even though the calculated decay ratio was relative-ly small, a new procedure, ONP 526 "Uncontrolled Power Oscillations," was prepared and approved by August 17, 1988.
This procedure includes a descrip-tion of plant conditions that could result in initiation of uncontrolled power oscillations, guidance on recognizing uncontrolled power oscillations, and action to be taken in the event that uncontrolled power oscillations occur, including the need to scram the reactor if oscillations are not promptly terminated.
(2) NRC SER from Cecil 0.
Thomas to H.
C.
Pfefferlen, "Acceptance for Referencing of Licensing Topical Report NEDE-240ll, Rev. 6. Amendment 8 Thermal Hydraulic Stability Amendment to GESTAR !!," MFN 061-85, dated April 24, 1985.
I l
' U.S. Nuclear Regulatory Commission A07301/Page 3 September 14, 1988
/>lrection for actions to be taken tc, avoid plant conditions which may result in the initiation of uncontrolled power oscillations is not provided in ONP 526.
Current technical specifications and operational requirements minimize operations which could result in uncontrolled power oscillations.
Operation without forced circulation is not permitted (Technical Specification 3.6.H.4).
Single loop operation for an extended period of time is currently prohibited (Technical Specification 3.6 H.2). Operation in the high power / low flow area of the power / flow map, where oscillations may occur is limited to brief periods during reactor start up and shutdown evolutions and minor maintenance activities.
These evolutions are conducted under the direction of Reactor Engineering personnel.
Subsequently, a "caution" statement has been added to appropriate procedures, stating that BWR power oscillations have occurred during high power / low flow operating conditions, and referencing ONP 526 for additienal information.
The average power range monitoring (APRM) system recorders serve as the primary indication that an oscillation is occurring.
A review of these recorders concluded that they are adequate to monitor a power oscillation.
It has been verified that no modifications to the neutron monitoring system have been made that could impair the abliity to detect and adequately display neutron flux oscillations with a frequency of 0.'.i hz. Plant operating proce-dures presently in place require control room operators to monitor this instrumentation.
It should also be noted that there are differences between the APRM/ local power range monitoring (LPRN) systams at Millstone Unit No. I and at LaSalle County Station that make detection and mitigation of oscillations at Millstone Unit No. I easier:
1.
The flow biased APRM scram circuitry at LaSalle contains an RC filter that simulates core thermal power rather t with a time constant As discussed in the Augmented Inspection Team Report,g neutron flux.
while the neutron flux during the LaSalle event had relatively large fluctuations, core thermal power remained relatively constant.
Conse-quently, no APRM flow biased scram resulted.
At Millstone Unit No.1, the APRM flow blased scram circuitry has no RC filter installed, i.e., neutron flux is directly monitored.
At the 100%
rod line, natural circulation point, which is the condition of the plant following a trip of both recirculation pumps from rated conditions, core power would be approximately 50% with a flow blased flux scram setpoint of much less than the 120% flux trip setpoint at LaSalle.
Thus, an automatic scram would be generated at relatively low neutron flux oscil-lation values.
Although Millstone Unit No. I's Technical Specifications do not allow power operation without forced circulation, the above stated logic holds for operation at all reduced flows.
2.
Filters were placed on the LPRM high alarms at LaSalle.
No such filters exist on the Millstone Unit No. I circuitry. Thus, regional oscillations (3) Augmented Inspection Team Report concerning the LaSalle incident, Report No. 50 373/88008' 50-374/88008, dated May 16, 1988.
i 5 U.S. Nuclear Regulatory Connission
'A07301/Page 4 September 14, 1988 would be alarmed even if the APRM circuitry does not fully respond due to I
J the "cancelling" effect of regional APRM oscillations.
)
l An operator training program revision will be made to include appropriate information regarding power oscillations and associated procedures.
This change will be completed by the Nuclear Training Department, based on a job task analysis of DNP 526 and other procedural changes.
The NRC bulletin has been routed to all Millstone Unit No. I licensed personnel and will be presented in the 1988 Requalification Training Program by October 31, 1988.
This information will also be presented to the 1988 Licensed Operator Initial Training and the 1988 Licensed Operator Upgrade Training Program.
NNECO recognizes the significance of the power oscillation event at LaSalle Unit 2 and we will continue to address related concerns at Millstone Unit No. 1.
We are actively participating in the BWR Owners' Group Thermal Hydrau-lic Stability Committee, whose workscope has been reviewed by the NRC Staff to
)
j assure responsiveness to NRC concerns.
NNEC0 believes that existing operating procedures and instrumentation and e
4 ongoing operator training address the occurrence of uncontrolled power oscil-1ations during all modes of operation at Millstone Unit No. 1.
i Should you have any further questions on this issue, please contact us.
L Very truly yours, j
NORTHEAST NUCLEAR ENERGY COMPANY i
u.<.
E. J. Mroczka
[
Senior Vice President N' Q l
nk l
" By:
R. P. Werner r
j Vice President l
4 cc:
W. T. Russell, Region ! Administrator
[
]
M. L. Boyle, NRC Project Manager, Millstone Unit No. I j
W. J. Raymond, Senior Resident inspector, Millstone Unit Nos. 1, 2, and 3 t
j L. Kolownauski, Resident inspector, Millstone Unit No. 1 STATE OF CONNECTICUT
(
i ss. Berlin COUNTY OF HARTFORD Then personally appeared before me, R. P. Wernor, who being duly sworn, did i
state that he is Senior Vice President of Northeast Nuclear Energy Company, a Licensee herein, that he is authorized to execute and file the foregoing information in the name and on behalf of the Licensee herein, and that the i
statements contained in said informattor, are true and correct to the best of his knowledge aM belief.
i sh,% XJ AM,0tL6-l Notary Public '
yy c p n n W W O i 31. W L 4
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