ML19256D273
| ML19256D273 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 12/29/1970 |
| From: | Danielle Sullivan US ATOMIC ENERGY COMMISSION (AEC) |
| To: | US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 7910170786 | |
| Download: ML19256D273 (6) | |
Text
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Files V. A. Moore, Chief Electrical Systcas Branch, 073 SC' EL\\ TIC DIAGP&! REVIrJ, T11REE MILE ISLA'iD Iit: CLEAR STATIO:1 U::IT IO 1.
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DOCK 7.T NC.Cif-M We met with the applicant and his consultants en Deceirber 15 and 16 to review the schematic diagra:aa of the followint; system :
(1) Offsite A.C. Power (Switchyard)
(2) Onsite A.C. Power (3)
D.C. (Station Batteries)
(4) Reactor Scram (5) Rod control (6) liigh Pressure Injection (7) Low Pressure Injection (8) Containment Spray (9)
Fan Coolers (10) Containment Isolation In attendence were:
Metropolitan Edison Cowany John L. Bachofer, Jr.
Peter P. Karish Donald II. Reppert
'illliam T. Schnauss Gilb ert AssocLates Willian F. Sailer
'Jillian Z. Meek Victor H. Wallems 3E1 J. E. 11111 R. F. Ryan Fennell R. Thomasson R. W. Crain Diarond Power Specialitv.Co.
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SUMMARY
We completed our review of the schematic dia;; rams.
The follovicr ite=
are outstanding:
(a) Individual instrument channels can be 1 ypassed by means of "dt-~
modules" which are substituted for the channel's histabic w:it.
There is no indication in the contro'. roon when the bypass 1.: in effect as required by Para. 4.13 of IEEE-279.
(b) The sys te= which automatically ter.inctes 'cor:, dil :th sidered by the applicant to be a protection svate.
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ate their proposal tilat it be placed in the catenery of a contrni systen.
(c) A single annunciator vindov indicates the bv assint of cna or'x diesel generators. This kind of indication is a-bi;un..
The results of our review are as follows:
(1) Offsite A.C. Power Power is brought to the switchyard over two di"crzcat ri at.-of- -
The switchyard breakers are arranged in a breaker-ar-d-s
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- statica transformers are respectively fed from one of the tuo busn at the switchyard.
We observed no eefteteneW.
(2) Onsite A.C. Power The syste:n, with the exception of one sving bus at the 480 volt level, is split throughout. n e diesels are individually started by loss of voltage at their respective buses. The feeders to each emergency bus are opened by control circuits energi:cd from t'le D.C.
subsystem assigned to that bus.
Under accident conditions, the sequencing of loads at a bus is initiated by the instrument logic train (A or E) ansigned to that bus. The starting of a diesel is not conditioned by the operation of the other.
The swing bus circuitry is mechanically interlocked, and fused, to prevent sier.titaneous closure and also to prevent a fault at the casunon bus from being propagated back to the diesels. The interlock systers satisfiss the single failure criterion and is acceptable.
In view of the potential for conuson mode failures, however, we asked the applicant to consider deletion of this automatic swing feature as a means of improving system reliability. He will con-sider ita deletion.
(3)
D.C. (Station Batteries)
There are two independent d.c. systems power from station batteries located in separate, adjacent rooms. With the exception of one sering bus, which is acceptably interlocked, the system is split thro ughout.
Bere is a common-duct ventilation syste= with two vent and two exhaust fans redundantly powered from the emergency busca.
The applicant vill consider deletion of the automatic swing feature as a means of improving system reliability.
We observed no deficiencies.
(4) Reactor Scram Reactor Scram logic is two-out-of-four.
Each set of four instru ent channels monitoring a parameter is energized from one of four inverter power supplies. The instruments fail to the " trip" modo upon loss of power.
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. Each instrument in a set (e.g., pressure) is assigned to one of four logie channels with one instrument f rom each of the other ce:3.
This is a general coincidenea arranzenent such that the tris in~ of any one instr ment in a logic channel trios a corresponding :;rcuo of relays assigned to that channel. Those relays form the sever:1 two-out-of-four logic arrays which interrupt power to the scran breakers at the rods. The instrument channela are mounted in cabinets such that redundant channels are p'.ysically independcat.
We scra:n system is redundant and independent, and is testabic dor.
to the tripping of individual scram breakers during reactor opera-tion.
We observed ona deficiency; specifically, each instrument channel c.sn be bypassed by the substitution of a "dtramy a:odule" for the associated histable. h ese bypasses are not indicated in the c:a-trol room as required by Para. 4.13 of IEEE-279. The applicant agreed to consider a design codification. We vill resolve this matter prior to completing our review.
(5) Rod Control _
Each rM is driven by a stepping motor energized by a six-phase star-connected povar supply whose phases are energized in the proper i
sequence to effect motor rotation. Each power supply is controlled by a gating circuit which receives coded optical impulses from a system driven by a s: mall, reversible synchronous motor. These motors are powered from line voltage.
The rods are normally operated in groups. We observed that a single failure could per.it an extra group to be withdrau:.
Analysis shows that this accident will be terminated by the pro-tection system prior to the onset of fuel darage.
The rod control wiring between the console and the re mechanisrc is not "hard vired", and individual rods can be pate' ' into dif-ferent control circuits. A patching error is not dete 451e at the control console itself since the "vrong" rod vill give c.: em readout information at the console indica, tor as would the correct rod. We vern informed, however, that the lever linit svitches are hard-wired to specific indicators. Thus, an error can be detected by cross-checking the console "Ir:.rer limit' indication against these indicators. We believe this arrangement is satisfacecry.
he possibility of excessive rod withdrawal speeds is rendered sufficiently low by operating the synchronous motors from line vol-nd. t f a.. i_. crt cra
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. We observed no deficiencies in the red control system.
(6)
Hi,h Pressure Injection The High Pressure Injection system, as are all en;;ineered safety features, is initiated by two-out-of-three instru= eat logic. Each instrument channel controls two relays which are respectively assigned to the A and B logic tr ains.
(Either train initiates the High Pressure Infeet6ea subsystem with which it is associated.)
The contacts from the relays them form the two-out-of-three logic at each train.
The d.c. power for each train is derived from the assigned station battery consistent with the split-bus concept.
Each bistable triit can be individually tripped at power for testing purpos es. Further, each set of relays can be tripped in pairs (two-out-of-three) to initiate the pumps, but not the valves. A sinilar arrangement permits the valves to be tested but not the pumps.
The "Iow Reactor Pressure" initiating circuits can be bypassed below a preset reactor pressure. The syste:n which removes the bypass above a preset pressure satisfies the requirersents of IEEE-279.
The system is redisadant, independent and testable and satisfies lEEE-279. We observed no deficiencies.
(7) Low Pressure Injection The logic and general design of the Low Pressure Injection system are similar to those of the :113h Pressure Injection Systen.
Tac logic is two-out-of-three and comprises two trains which respectively initiats one of the two pumps. The discharge valves are check valves. The system is testable and can be tested down to the initiation of each pump during power operatien.
We observed no deficiencies.
(8)
Contal:rnent Spray The Containment Spray system is initiated by two sets of three pressure switches set at 4 psi and 30 psi.
The switches actuated at 4 psi open the valves throups radtridant logic trains. The 30 psi switches operate a permissive interlock which permits manual initia-tion of the two pn:::ps. We also reviewed the associated service water cooling system and verified that it is also a split and 2 0 $. ffd a.. I sy i w - u ca. 2.r a 6 w a wa w.. c ses s; af a b-.
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s The logic is testable at power. Also, each puro can be operated via a recirculation Icep.
'a'e observed no deficiencies.
(9) Fan Coolers There are three fan coolers initiated by two logic trains.
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train initiates one cooler system and the " swing" system. The remaining portions of the system, including the river water pu::p systen, are redtmdant and arranged as a split bus.
The design is such that one vent fan must be swung. The valves are not swung since the third heat exchanger has two parallel-connected inlet valves operated from the respective logic trains. The swing bus circuitry is mechanically and electrically ir eerloc*r.ed such that no single failure should permit the automatic interconnecting of redsudant a.c. buses, on the cascading of a fault fron the swing bus to the redundant a.c. power sources.
We believe the design of the Fan Cooler system is acceptable. The applicant will, however, consider deletica of the automatic swing feature as a means of improving system reliability.
(10) Containment Isolation The valves are operated from the logic trains which initiate core cooling.
For our review we selected three pairs of redundant isolation valves:
(a) purge inlet, (b) purge outlet and (c) containnent stnp drain.
In all cases, the redundant valves were respectively operated from the redundant logic trains. We observed no deficiencies.
d 5 52-ES3-91 D. F. Sullivan DRS :ES3 :BFS Electrical Systems Branch Division of Reactor Standards ec:
S. Hanauer D. Ross Distr:
E. Casc V. P. core Suppl R. DeYoung J. O"teilly Da ?J R. Boyd D. Himnicutt (CO:I)
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