ML19256D257
| ML19256D257 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 03/04/1971 |
| From: | Ross D US ATOMIC ENERGY COMMISSION (AEC) |
| To: | Deyoung R US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 7910170769 | |
| Download: ML19256D257 (4) | |
Text
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$11 R. C. DeYoung, Assistant Director for Pressurized Water Reactors DRL THRU: Charles G. Long, Orief, PWR Project Branch No. 2, DRL NPSH REQUIREMENTS FOR THREE MILE ISLAND UNIT 1 (DOCKET 50-289)
At a recent meeting of the Task Force we stated that we intended to require conformance with Safety Guide No.1 regarding NPSH on ESP pumps. At a subsequent meeting with Met-Ed we found out that the EPSH calculations are carried out under the assumption that contain= ant pressure is at equilibrium with the sump water temperature. Thus, when the susp water temperature is above 212*F (for example, it is 220*F 15 minutes after an accident and again at 220*F during recirculation), they assume that containment pressure is approH=mrely 17.2 psia. The increment is 2.5 psi, or about 6 ft H 0.
2 Our recently-released Safety Guide No. 1 states that adequate NPSH should be provided assuming:
a)
H=
expected temperatures of pusped fluids ;
b) no increase in coneminmant pressure from that present prior to the accident.
I reviewed the PSAR to detaraine the extent to which commitments had been made then. In answer to our question 5.7, Met-Ed filed Supplement 1, October 1967 c(nemining a preliminary estimate of NPSH. They assumed an initial partial pressure of 13.75 psia, or 32 feet of H 0.
The friction losses in a 12-inch line carrying 2
6000 gpa (one LP pasp, 2 spray pumps) was estimated at 33 ft H 0.
2 Thus the NPSH available to the LP pumps was 14.5 ft H 0.
The spray 2
pump NPSH available is 15 ft, due to a slightly lower elevation.
In both cases the NPSH available exceeds that required. The last*
sentence of Met-Ed's answer i;o our Q 5.7 was:
"in all of the calculations no credit has been taken for the MBA reactor buildfag pressure, during which time these pumps would be in operation".
In the final design Met-Ed provided 14-inch recirculation lines from the RB samp, instead of 12-luch lines, decreasing the friction AP.
However the LP pump and spray pump flow rates will likely be higher than tia reference design values, increasing the raquired NPSH.
- See questico and answer, enclosed.
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We asked Mat-Ed what the effect would be of requiring conformance to the Safety Guide. They responded by saying that adequate NPSH margin could not be assured; rather, the operator would have to throttle flow, or stop a pump.
Conclusions 1.
It is reasonably clear that at the CP review Met-Ed was not taking credit for RB pressure in calculating NPSH. Thus the change that they made in the interim was at their risk,
_ and there can be no backfitting argument in regard to the Safety Guide.
2.
The Safety Guide is consenatively unrealistic in that it is a violation of somebody's law of thermodynamics to consider the pumping of liquid at 14.7 psia, 220*F.
Further. lit appears that as one travels down the recirculation line from the sump to the pump, one is losing pressure by friction twice as fast as gaini"F by elevation. Banca if we said that the building pressure was such that the sump water was a saturated liquid, there would be two-phase flow at the p op inlet.
3.
Met-Ed has not documented its calculations, nor has it disclosed the plans for regulating (by orifice or otherwise) LP and spray flow rate to their design values. This must be done.
4.
The 14-inch recirculation lines are literally cast in concrete, and nothing can be done about =aking iem larger. Surely the pumps are bought. Perhaps some adjustments can be made in the field in regard to tri==ing the impeller so that the pumps do not overdeliver. If operational measures are eventually approved, such as flow reductico, the operator has ample time (greater than 30 mins.).
Action We are going to:
A.
Emmind Met-Ed of their October 1967 NPSH commitment, and tell them we still require ft.
b.
Ask for the updated calculations to be documented.
c.
Defer the formal consideration of alternatives until Met-Ed has responded.
Denwood F. Ross FWR Project Branch lNo. 2 Livis ten-of--Reactorticensing-sumwr >
Form AEC-lis Rev. 9-53) AECM 0240 or novaseuser nevnes omca : i a a s.-e i r
Jt. C. DeYoung DISTRIBUTION:
S. Hanauer D. Ross (2)
H. Schierling PWR-2 Reading Docket File (50-289) {
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c-,plement No. 1 October 2, 1967 QUESTION What volume of water is necessary (in the sump area) to provide 5.7 the required NPSH of the recirculation pumps? We believe that the sump should retain a high enough column of water to provide the required head without the necessity of a large water inventory in the containment.
ANSWER.
Per Fig. 6-3 in the PSAR,13 25 ft H O NPSH is required for the 2
Decay Heat Removal Pumps at 3000 gym each.
Per Fig. 6-7, 15 ft H O NPSH is required for the Reactor Bldg. Spray Pumps at 1500 2
gpm each.
Preliminary calculations indicate that a maximum friction head loss in the suction piping to these pumps is 33 ft H O when only 2
6 one of the two 12 in, diameter suction lines is carryinn the full 6,000 gpm recuired to maintain one decay heat removal and two R. 3.
spray pumps at full caracity.
Detailed calculations of friction head losses and the NFSH available to each rump will be nerformed when manufacturer 's drawings of the eauinment, to be provided. are avail-able and the final pipine layout has been completed.
Based on an initial partial tressure of air in the containment
':uilding atmoschere of 13.75 sia. 32 ft of H00 head will be c
available to these pumps frcm this source.
Eased on the layout o
drawings, 15.5 ft of static suction head will be available to the Decay Heat Removal Pumps and 16 ft of static suction head vill be available to the Peactor Building Spray Pumps when the water level in the reactor building sumn is 2 ft below the basement ficer level in the reactor building. With this water level in the reactor building sume. the NPSH available to the one Decay Heat Remcval Pump on the line is ( 32.0 + 15. 5 - 33 ) = 14. 5 ft H O and that avail-2 available to the two Peactor Building Spray Pumps on the line is (32 + 16 - 33) = 15 ft H 0.
The NPSH recuired for the Reactor 2
Building Spray Punts is ecual to the NPSH available.
Because of the preliminary nature of the information on which the above calculaticns are based. it is estimated that the NPSH available to both the Decay Heat Removal Pumps and the Reactor Euilding Spray Pumps vill be greater than that required when the water level in the reactor building Sump is full to the floor level.
In all of the calculations no credit has been taken for the :SU(
reactor building tressure. during which time these pumes would be in cperation.
}k)0 125 5.7-1 (Pevised 1-e 68)
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