ML19317D498
| ML19317D498 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 05/17/1976 |
| From: | Parker W DUKE POWER CO. |
| To: | Rusche R Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7912060758 | |
| Download: ML19317D498 (2) | |
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DuxE POWER COMPA.NY Powra Bun. nmo 422 SocTn Curacu STnezT, CHAEWTTE, N. C. 28242 wlLLI AM o PA R M E R, J R.
/8C E PRESILEN' TgLgmesoasg; Anga 704 5'ta s. Paco ct ro~
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g' g,egulatoty Docket
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- Mr. Benard C. Rusche, Director C
Nuclear Reactor Regulation
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6 U. S. Nuclear Regulatory Commission
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Mr. R. A. Purple, Chief s
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Operating Reactors Branch No. 1 f
Re: Oconee Units 1 and 2 Docket Nos. 50-269 and -270
Dear Sir:
The following information is submitted to clarify certain aspects of the calculational procedure previously utilized to establish the flux / flow trip setpoints for Oconee 1 (Cycle 3) and Oconee 2 (Cycle 2) and now revised to include an additional allowance for the accuracy of the reactor protection system flow instrumentation string.
The flux / flow trip setpoints for Oconee 1 and Oconee 2 were determined utilizing a calculational procedure which consisted of various conservative assumptions and allowances including (1) a steady-state power level of 108%
(indicated power level of 102% plus 6% uncertainty in power level measurement),
(2) design power peaking factors and hot channel factors, (3) a conservative value for the trip delay time, (4) maximum effect of fuel densification on DNBR, (5) an allowance for errors in the coolant inlet temperature and system pressure, (6) a 5% reduction in hot assembly flow to account for flow maldistribution, (7) a reactor coolant system flow rate of 107.6 percent of the original design flow rate (as compared to the measured flow values of l
108.6% for Oconee 1 and 111.5% for Oconee 2), (8) a conservative allowance l
for core bypass flow through control rod and instrument guide tube, core shroud, etc., (9) the effective core flow further reduced by 4.6% for an assumed stuck open vent valve, and (10) the flow measurement errors associated with the RPS flow instrument string assumed to be calibrated out of the system.
The flux / flow ratio resulting from this calculation was further reduced by 1.5% for flow signal noise to yield a flux / flow trip setpoint of 1.055 for l
Oconee 1 and 1.07 for Oconee 2.
The flux / flow trip setpoint analysis, however, did not explicitly include an allowance for possible errors in the RPS flow instrument string, as has been previously indicated in discussions with the staff.
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Ruoche May 17, 1976 Page 2 Detailed analysis of the precision and reliability of the various components of the RPS flow instrument string - AP transmitter, summer amplifier, function generator, and bistable comparator - indicates that the errors in the RPS flow instrument string could amount to a 1.2% reduction in the flux / flow ratio.
However, the 4.6% additional core flow available from the consideration that the vent valves remain closed more than adequately compensates for this reduction.
A re-analysis of the Oconee 1 flux / flow ratio without including the effect of an assumed stuck open vent valve yielded a flux / flow trip setpoint of 1.08 after including an allowance of 1.2% for errors in the RPS flow instrument string and 1.5% for noise in the flow signal. Thus, the existing 1.055 flux /
flow trip setpoint is conservative compared to that which could be allowed and still provides a flow margin in excess of 3%.
In the case of Oconee 2 also the proposed flux / flow trip setpoint of 1.07 for Cycle 2 continues to be conservative, and the fact that the measured flow is 111.5 percent of the original design is indicative of the considerable flow margin that exists in the flux / flow trip setpoint.
I Ve truly yours, i a.nk~.
WilliamO. Parker,Jr.f)
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