ML17252A271

Dresden, Units 2 and 3, 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 01 31 I 01 ° 1.:... I 0 I 0 I 0 I 0 I 0 1-1° I 0 I .14*1 1 11 I 1 I 1 I I 01 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 12 14 I 9 I I 0 I 41 1 I o I 71 7 I I 01 4j 212117 17 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 . lo131 I 013erato.r discovered that Rod Block Monitor (RBM) channels 7 and 8 were automatically81 7 8 lol41 .!;l __ _____ (q{5j *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_1e_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 ____ j1ioj __ 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 11Eve*nt Descr i pt i on1*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.