ML18046B071
| ML18046B071 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 11/16/1981 |
| From: | Johnson B CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| GL-81-21, NUDOCS 8111200643 | |
| Download: ML18046B071 (2) | |
Text
consumers Power company General Offices: 212 West Michigan Avenue, Jackson, Ml 49201 * (517) 788-0550 November l6, l98l Director, Nuclear Reactor Regulation Att Mr Dennis M Crutchfield, Chief Operating Reactors Branch No 5 US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-255 - LICENSE DPR-20 PALISADES PLANT - RESPONSE TO GENERIC LETTER NO. 81-2l NRC Generic Letter No. 8l-21 dated May 5, 1981 and entitled Natural Circulation Cooldown identified two areas of concern applicable to all pressurized water reactors requiring action.
These areas of concern are 1) The Unacceptability of Vessel Voiding during antic~pated Cooldown Conditions and 2) Failure of the Operator to have prior knowledge and training for this event.
Consumers Power Company was requested per NRC Generic Letter No. Bl-21 to assess the Palisades Plants procedures and training program with respect to the two identified areas of concern.
The assessment was to include the following items:
- 1.
A demonstration (e.g. analysis and/or test) that controlled natural circulation cooldown from operating conditions to cold shutdown conditions, conducted in accordance with Palisades procedure, should not result in reactor vessel voiding.
- 2.
Verification that supplies of condensate-grade auxiliary feedwater are sufficient to support your cooldown method.
- 3.
A description of the Palisades training program and the provisions of the procedures (e.g. limited cooldown rate, response to rapid change in pressurizer level) that deal with prevention or mitegation of reactor vessel voiding.
Consumers Power Company responses to the three identified items for Palisades Plants procedures and training program are as follows:
- 1.
An analysis was performed on a generic 3410 Mwt class C-E plant and reported in CEN-154 to determine the reactor vessel (RV) upper head water temperature during a natural circulation cooldown.
The RV upper head cooling was assumed to be by heat conduction through the coolant and metal mass to the hot leg elevation region which was being cooled by natural circulation through the steam generators (S/G's).
Included in the analysis were both localized natural circulation induced flow and shririkage induced flow into the RV upper head region.
The reactor was assumed to trip from full power with simultaneous loss of primary coolant pumps (PCP's).
After two hours at hot standby a 75° F/hr cooldown was instituted under natural circulation conditions.
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Dennis M Crutchfield, Chief Palisades Plant November 16, 1981 2
The results of the analysis indicate that the cooling in the RV upper head region significantly lags behind the cooling in the RV plenum.
Thus, depressurizing to a shutdown cooling (SDC) pressure of 250 psig when the plenum temperature is at a SDC entry temperature of 3250 F will cause voiding in the upper head region.
By delaying the depressurization until about 23 hours2.662037e-4 days <br />0.00639 hours <br />3.80291e-5 weeks <br />8.7515e-6 months <br /> after the reactor trip the upper vessel temperature will cool to below the saturation temperature at 250 psig and thus preclude voiding.
By using a more rapid cooldown or a lower SDC entry temperature this delay before depressurization can be decreased.
The above analysis for the 3410 MWT class of plant very conservatively bounds Palisades.
The reason for this is that Palisades has cruciform control rods whose guide structure is much more open than that of the 3410 MWT class plant.
As a result, for Palisades there will be greater flow into the upper head region providing for a more rapid cooling of the vessel head.
This would result in shorter delay times for depressurization as well as lower water requirements that those reported below.
- 2. If it is assumed that the natural circulation cooldown is conducted without the availability of the condenser then energy is removed from the S/G's by steaming to the atmosphere.
Analysis shows that 172,000 gallons of water is needed assuming the S/G's are permitted to boil down to about one-third of the tube height.
The present Technical Specifications require a minimum of 100,000 gallons of onsite stored water.
However, Lake Michigan water can be utilized using a fire pump to supply water to the AFW pump suction.
- 3.
Palisades Plant Off-Normal Procedure, ONP-21, Natural Circulation, has been revised to address the analysis discussed in the responses to items 1 and 2 and is presently approved for plant use.
All plant operators will be trained Ofi this revised procedure before Palisades starts up from the present (1981) refueling outage.
Brian D Johnson Senior Licensing Engineer CC JGKeppler, USNRC NRC Resident Inspector - Palisades