ML17252A271

Transmittal of Reportable Occurrence Report No. 50-249/1977-9

ML17252A271
Person / Time
Site:	Dresden
Issue date:	04/21/1977
From:	Stephenson B B Commonwealth Edison Co
To:	Kappler J G NRC/RGN-III
References
50-249/1977-9
Download: ML17252A271 (3)

See also: IR 05000249/2019077

Text

Commonwe4t

Edison Dresden Nuclear Power Station R.R. #1 Morris, Illinois*

60450 Telephone

815/942-2920

BBS Ltr. # 334 April 21,

Mr. James G. Keppler, Regional Director Directorate

of Regulatory

Operation

-Region JI I U. S. Nuclear Regulatory

Commission

799 Roosevelt

Road Glen Ellyn, 111 inois 60137 Enclosed please find Reportable

Occurrence

report number 50-249/1977-9.

This report is being submitted

to your office in accordance

with the Dresden Nuclear Power Station Technical

Specifications, Section 6.6.B. Stephenson

tation Superintendent . Dresden Nuclear Power Station BBS:skm Enclosure

cc: Director of Inspection

& Enforcement

Director of Management

Information

&

Control Fi 1 e/NRC APR 2 G 1977

L * l1 \ .. *CONTROL BLOCK: l 1 LICENSE.E

EVENT REPORT 91 I I I I * .dASE PRINT ALL REQUIRED INFORMATION)

6 LICENSEE UC EN SE EVENT NAME LICENSE NUMBER TYPE TYPE I I LI 0 1 31 I 0 1 ° 1.:... I 0 I 0 I 0 I 0 I 0 1-1° I 0 I .1 4*1 1 11 I 1 I 1 I I 0 1 11 7 89 14 15 25 26 30 ;31 32 CATEGORY REPORT. REPORT* TYPE SOURCE DOCKET NUMBER EVENT DATE REPORT DATE @TI]coN'T

I I I L!J L!:J I 01 s 1 o o 1 2 1 4 I 9 I I 0 I 4 1 1 I o I 71 7 I I 01 4j 212117 1 7 I 1 * *0 57 58 59 60 61 68 69 74 75 80 EVENT DESCRIPTION

[filfil I During control rod withdrawal

operations

at approximately

44% power, the unit 7 8 9 . lo1 3 1 I 013erato.r

discovered

that Rod Block Monitor (RBM) channels 7 and 8 were automatically

8 1 7 8

lol 4 1 .!;l __

_____ (q{5 j *j!; .

__ :_J_. __ o_t __ h __ e_r._* .;..i _n .... t.e_r _i o __ r_c_o_n_t_r_o_l_r_o_d_s_w_e_re_t_h_e_n_s_e_l,....e_c_t_e_d_t_.o_c_h.,...e_c_k_t_h_e_f:..,.u_n_c_t.:....* 7 8 9 lo __.,..,.o_f.__t_h_,e_R_B_M_.--*

_c_o_n_t_r_o_l

_ro_d_B.;..-_7_w_a_s_t_h_e_o_n_l

_y_o_t h_e_r __ i n_t_e_r_i_o_r_c_o.;..n_t.._r_o_l

_r_od __ t h_a.,..t_w

__ a __ s ____ s_Jl 7 8'9 PRIME. (continued)

80 . SYST.EM CAUSE COMPONENT.

COMPONENT

COOE . . COOE COMPONENT

CODE SUPPUER MANUFACTURER

VDLATlJN (§0 I I I B I LlJ I II N I s I Tl R I u I I G I 0 I 8 I 0 I 7 8 9 10 11 12 17 43 44 47 48 CAUSE DESCRIPTION (olal I Investigation

revealed that a shorted diode in the control rod select circuitry

I 7 8 9 . . 80 lolsl

___

... pu ___

___ 1_1 e_d_g_e_r_o:..,.d

__ s_e_1_e_c_t_e

__ d_11_i_nd-ic_a_t_io_n_f_o_r

____ j 1 ioj

__ c_o_n_t_r_o_l_r_o_d_s_B_-_7_a_n_d_B_-_s_.

__ T_h_e_d_e_f_e_c_t_iv_e_d_io_d_e_._w_a_s_r_e_p_l_a_c_e_d_,_a

__ nd_p_r_o_p_e_r_R_B_M

___ 7 8 9 80 FACIUTY METHOD OF . ('continued)

• . STATUS " POWER . OTHER STATUS DISCOVERY

DISCOVERY

DESCRIPTION

l_Ll I 0 I 4 I 4 I * 1.___N_A ____ -" I See 11 Eve*nt Descr i pt i on 1*1 EE1 7 .a. 9 10 . 12 13 44 45 46 ,,. 80 .FORM OF .ACTIVITY

CONTENT RELEASED OF RELEASE AMOUNT . OF ACTIVITY

9 10 . 11 44 rn 7 8 NA LOCATION OF RELEASE 45 80 PERSONNEL

EXPOSURES

NUMBER TYPE DESCRIPTION

[ill] I. o L ol 01 L.fJ .-=---*-N_A . _________________ 7 8 9 11 12 13. BO . . PERS.ONNEL

• 1NJURIES NUMBER OESCRl°PTION

[ill] I 0 I 01 01.';::-*

-* __

7 a*s 11 12 00 OFFSITE , CONSEQUENCES . NA 7 8 9 80 LOSS OR DAMAGE TO FACILITY TYPE . DESCRIPTION

EID lLl NA 7 8 9

PUBLICITY

[fill NA . 7 8 9 80 ADDITIONAL

FACTORS Eifil 7 8 9 * N ;:; . 60 7

__ .......

ED ..

_,_ __ J_e_f_f_e_r_y....,.R_.

_w_o_J_* n_a_r_o_w""'s_k_i

---

PHONE: __ E_x_t_.

GPO a 111.* a 117

• * EVENT DESCRIPTION (continued)

found to cause :a oypass of the RBM system. Withdrawal

of control rods B-7 and B-8 was suspended

and an investigation

was initiated.

The safety significance

of this event was minimal because the RBM backs up

rod selections.

Although the Tech Specs require the RBM to be * operab 1 e above 30% power, the Tech Spec bases indicate that the RBM function is not necessary

below 70% power. The significance

was further mitigated

by the core location of B-7 and

since both control rods are located one position

the core periphery.

This is not a repetitive

occurrence.

(50-249/1977-9)

CAUSE DESCRIPTION (continued)

operation

was verif1ed before further withdrawals

of control rods B-7 and B-8 were performed.

All other interior control rods have been successfu(ly

checked for similar problems.

This is the first rep0,r_ted

failure of any of these diodes. No further corrective

action was

The Rod Block Monitoring

system. was supplied by the General Electric Company.