ML19261F064
| ML19261F064 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 08/25/1972 |
| From: | US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML19261F061 | List: |
| References | |
| NUDOCS 7910180678 | |
| Download: ML19261F064 (3) | |
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THREE MILE ISLAND - SAFETY EVALUATION - NUCLEAR Design Section 4.0 REACTOR DESIGN 4.1 General The design of the Babcock and Wilcox Company (B&W) reactor for the Three Mile Island Unit 1 f acility is similar, in mos t respec*.s, to the dcsign of other pressurized water reactors that we have recently approved for operation, and is in particular nearly identical to that of the Duke Power Company Oconee Unit 1 reactor. These designs employ full and part length control rods and dissolved boron for control, and Zir:aloy fuel cladding.
4.2 Nuclear Design The computer programs, calculational techniques and experimental validations used by B&W to predict the nuclear characteristics of reactor designs were found suitable in the Oconee Unit 1 eva.iation, and are therefore suitable for Three Mile Island.
Our general conclusions for Oconee Unit I regarding adequacy of the reactor physics in areas such as control rod provisions and withdrawal rates, use of a control rod bank in the : ore for xenon ovetride control, use of soluble boron, expected range of the Doppler, moderator and power reactivity coefficients, and power decay curves apply also to Three Mile Island. Three Mile Island has slightly higher fuel 1486 180 7S 9910180
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enrichment (2.62% average) than Oconee Unit 1 (2.1% average) for a longer first cycle life. To hold down the excess reactivity resulting from this loading, fixed B4C burnable poison rods have been provided.
Three are used rather than increased soluble poison because increased soluble. poison concentration would increase the beginning of life positive moderator temperature coefficient.
In fact, the 1088 burnable poison rods, worth 4% ap, more than compensate for the increased load-ing and result in a reduction in the predicted maximum positive
-5 moderator temperature coefficient for Three Mile Island L' +5 x 10
-5 ap/*F, compared to the value oft 9 x 10 ap/*F for Oconee Unit 1.
The reduction is in the direction of increased safety.
There are no core exit thermoccuples ' or special incore detector cali-bration tubes in the core instrument thimbles in Three Mile Island, as there were in Oconee Unit 1.
These were included in Oconee Unit 1 to provide extra information early in life in the "first of a kind" reactor, but are not deemed necessary in those that follow. Since Oconee Unit 1 operation will precede that of Three Mile Island, we find this situation satisf actory.
The basic instrumentation for monitoring the nuclear power level and distribution in Three Mile Island is the same in principle as for all PWR plants recently licensed for operation. Primary reliance is placed on four axially split, out-of-core detectors that are spaced 1486 181
approximately 90* apart around the reactor pressure vessel. These generate power level infarmation, and provide power distribution tilt indication in the axial direction and the horizontal plane.
Also 52 assemblies of self-powered incore neutron detectors are available for incore mapping. Each assembly can measure local neutron flux at seven elevations '.n the core. 'Normally output of these de-tectors will be readout through the plant computer. However, a backup readout system independent of the computer is provided for 36 selected detectors. The applicant has provided for availability of these detectors for monthly calibration of the out-of-core detector tilt factor in the Technical Specifications. He has also provided for a reactor scram is the event of excessive axial tilt.
Both of the latter items were issues in the Oconee Unit 1 review.
In view of the considerations above and the similarity to preceding reactors, we find the Three Mile Island nuclear design acceptable.
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