ML20065J708
| ML20065J708 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 04/14/1994 |
| From: | Rithert W BOSTON EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 94-042, 94-42, IEB-93-002, IEB-93-2, NUDOCS 9404180397 | |
| Download: ML20065J708 (4) | |
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90$1DN ED60N NRCB 93-02, Supplement 1 Pilgrim Nuclear Power Station Rocky Hi!! Road Plymouth Massac ;setts 02360 April 14, 1994 s'
BECo Ltr. 94 042 W. C. Rothert General Manager Technical U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C.
20555 Docket No. 50-293 License No. DPR-35 Response to NRC Bulletin 93-02, Supplement 1
" Debris Plugging of Emergency Core Cooling Suction Strainers" NRC Bulletin 93-02, Supplement 1, requested owner's of Boiling Water Reactors (BWRs) to take interim actions to enhance the capability to prevent or mitigate loss of Emergency Core Cooling System (ECCS) following a Loss of Coolant Accident (LOCA) due to suppression pool strainer clogging. The requested actions along with Boston Edison Company's response are discussed below.
REQUESTED ACTION Provide training and briefings to apprise operators and other appropriate emergency response personnel of the information contained in NRC Bulletin 93-02, Supplement 1, and in the referenced NRC Information Notices regarding the potential for suppression pool strainer clogging.
RESPONSE
The information contained in Bulletin 93-02, Supplement 1 and in the referenced NRC Information Notices regarding the potential for suppression pool strainer clogging was incorporated into the Operator Requalification Training Program.
Training is in progress and the estimated completion date for training of Operations personnel is May 14, 1994.
Training for appropriate Emergency Response Personnel is scheduled for completion by April 20, 1994.
Included in this group are the Emergency Directors and Emergency Plant Managers.
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REQUEST'ED ACTION Assure that the Emergency Operating Procedures (EOPs) make the operator aware of possible indications of ECCS strainer clogging and provide guidance on mitigation.
RESPONSE
The Pilgrim Station symptom-based Emergency Operating Procedures (E0Ps)
(flow / logic diagrams) are based on the BWROG Emergency Procedure Guidelines Rev. 4.
On loss of the ECCS Pumps (regardless of reason),
the E0Ps direct the operators to lineup alternate sources of water for reactor cooling / fill if ECCS pumps are not capable of maintaining reactor water level.
REQUESTED ACTION Institute procedures and other measures to provide compensatory actions to prevent, delay, or mitigate a loss of available Net Positive Suction Head (NPSH) margin under LOCA conditions.
Such measures should be consistent with providing the design basis emergency system functions for core and containment cooling.
RESPONSE
Pilgrim Station Procedures 2.2.19, " Core Spray", and 2.2.20, " Residual Heat Removal", will be revised to provide guidance on identifying the symptoms of strainer clogging and measures to provide compensatory actions to prevent, delay, or mitigate a loss of available NPSH margin under LOCA conditions.
The procedures will be revised and are scheduled for issuance by May 13, 1994.
BACKGROUND in 1984, Boston Edison Company requested General Electric Company to-perform an. analysis to evaluate containment emergency sump (suppression pool)-
performance in accordance with Regulatory Guide (RG) 1.82.
The primary concern was potential clogging of the Residual Heat Removal (RHR) and Core Spray (CS) Systems suction strainers in the torus (suppression pool);
by insulation debris during a design basis LOCA.
The evaluation was performed in accordance with the methods in the August 25, 1983 draft of.RG 1,82 Rev. 1.
The analysis concluded the area of the RHR and CS suction strainers had 'to be enlarged based on the maximum calculated insulation debris loading.
In'1984,
.six new suction strainers (2 for CS and 4 for RHR) were installed having an open strainer area three times greater than-the six strainers removed. The 0
NPSH was evaluated, at 175 F, maximum debris loading on the strainers, and no overpressure condition in torus. This temperature is greater than the maximum bulk pool temperature for the worst case transient (160 F) or post accident l
condition (166 F).
The above actions provided reasonable assurance the NPSH' for RHR and CS pump would be appropriate for all conditions.
During this same time frame, the insulation on the piping systems located in the drywell was removed and replaced with the blanket type NUCON insulation.
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r Although some degree of shredding of the NUCON blanket insulation is expected during a design basis LOCA, much of the displaced insulation would consist of complete blanket sections or portions of blanket sections and would not degrade due to alkaline conditions because of thL neutral pH of the Pilgrim Station suppression pool.
Unlike the Barseback and Perry Plant design, Pilgrim Station has an enclosed suppression pool (torus). The insulation displaced from the drywell piping during a Design Basis Accident would have to travel a torturous path to reach the water in the suppression pool.
Calculations indicate the amount of debris reaching the pool would not be sufficient to result in simultaneous clogging of the six ECCS strainers.
As stated in BEC0's response to Bulletin 93-02, unlike the open suppression pool of the Mark III Containment, the torus is closed except for vent pipes connecting the torus to the drywell. Procedural controls are in place to provide inventory control when the torus is open.
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This design in conjunction with the procedural controls minimizes the entry of dust, dirt, and other foreign material into the suppression chamber.
Cleanliness of the torus at Pilgrim Station has been satisfactory. The torus was partially drained and inspected during Refueling Outage (RF0) No. 7 (1986-1988). During RF0 No. 8 (1991) the torus was cleaned and inspected utilizing underwater divers and a vacuum pump to remove minor amounts of accumulated sediment and one respirator face mask. The divers were inspecting the condition of the torus in conjunction with NRC Information Notice (IN) 88-82.
Ten of the sixteen bays were painted.
The remaining 6 bays are scheduled to be cleaned and painted during RF0 No. 10.
Due to the cleanliness of the suppression pool, further clogging of suction strainers by filtration of pre-existing debris following a design basis LOCA is not considered to be significant for Pilgrim Station.
Based on the above discussion, Pilgrim Station's design, procedural and administrative controls are in place to preclude events similar to those referenced in Bulletin 93-02, Supplement 1.
W. C. Roth rt Commonwealth of Massachusetts) i County of Plymouth)
Then personally appeared before me, W. C. Rothert, who is duly sworn, did state that he is General Manager Technical of Boston Edison Company and that he is duly authorized to execute and file the submittal contained herein in the name and on behalf of Boston Edison Company and that the statements in said submittal are true to the best on his knowledge and belief.
My commission expires: Inmrq T7,2 coo 5
L DATE NOTA {POBLIC
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Mr'. Thomas T. Martin Regional Administrator, Region I 475 Allendale Road King of Prussia, PA 19406 Mr. R. B. Eaton Div. of Reactor Projects 1/11 Office of NRR - USNRC One White Flint North - Mail Stop 1401 11555 Rockville Pike Rockville, MD 20852 Sr. NRC Resident Inspector Pilgrim ~ Nuclear Power Station
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