ML17252A271

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

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

Text

Commonwe4t Edison Dresden Nuclear Power Station R.R. #1 Morris, Illinois* 60450 Telephone 815/942-2920 BBS Ltr. # 334 April 21, 1~77 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 & P~ogram Control Fi 1e/NRC APR 2 G1977

L

• l1 \

LICENSE.E EVENT REPORT

.. *CONTROL BLOCK: l 1

91 I I I I 6

• .dASE PRINT ALL REQUIRED INFORMATION)

LICENSEE UC EN SE EVENT NAME LICENSE NUMBER TYPE TYPE

~I I I LI 0 1'-~1 1135 1 14 31 I 01° 1.:... I 0 I 0 I 0 I 0 I 0 1-1° I 0 I .1 4 *1 15 1 11 I 1I 1I I 0

1 11 7 89 25 26 30 ;31 32 REPORT. REPORT*

CATEGORY TYPE SOURCE DOCKET NUMBER EVENT DATE REPORT DATE

@TI]coN'T I I I L!J L!:J I 01 s 1 o 1~1 o 1 2 1 4 I 9 I I 0 I 4 1 1 I o I 71 7 I I7501 4j 212117 17 I 1 * *0 57 58 59 60 61 68 69 74 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 7 89!:-'.---------------------------------~....;._----------__.J*

. 8 1

11 8 lol 4 1 .!;l__.b_y.;..p_a~s_s_e~d=-a_n_d_i_n_d_i_c_a_te_d__e_d_g_e__,r_o_d_s_e_l_e_c_t_ed___w_h_e_n_i_n_t_e_r_i_o_r_c_o_n_t_r_o_1_ro_d_B_-_s_w_a_s_____~l 11 (q{5j *j!;.._ @.; ;:~;.; ; ~" )'" *~:; ; ;*c" 't-"e. ___~:_J_.__o_t__h__e_r._*.;..i_n....t.e_r_io__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.:....*i-'o_n_i_n_g--~1 8

7 8 9 lo Isl~ ~I__.,..,.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_th_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 sI Tl R I u I ~ I G I 0 I8 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 1~*--w_a_s___t_h_e....,....c_a_u_s_e_.~o-f_t_h_e_._s...pu___r_ro_u~s--R_B_M_b_y_p_a_s_~_a_n_d___ e_d_g_e_r_o:..,.d__s_e_1_e_c_t_e__d__i_nd-ic_a_t_io_n_f_o_r____~I 11 11 j ioj j~_b_.~_*t_h__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___~l 1

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

• . STATUS " POWER . OTHER STATUS DISCOVERY DISCOVERY DESCRIPTION EE1 l_Ll I 0 I 4 I 4 I *1.___N_A_ _ _ _-" ~ I See 11 Eve*nt Descr i pt i on 1*1 7 .a. 9 10 . 12 13 44 45 46 ,,. 80

.FORM OF

.ACTIVITY CONTENT rn RELEASED OF RELEASE AMOUNT . OF ACTIVITY LOCATION OF RELEASE

~ ~ l~_NA-.,,.;-----....J' NA 7 8 9 10 . 11 44 45 80 PERSONNEL EXPOSURES NUMBER TYPE DESCRIPTION

[ill] I. o L ol 01 L.fJ .-=---*-N_A._ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___;.....;...__~--_J 7 8 9 11 .12 .

13. BO PERS.ONNEL *1NJURIES NUMBER OESCRl°PTION

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

7 a*s 11 12 00 OFFSITE , CONSEQUENCES

.E~L 7 8 9 NA 80 LOSS OR DAMAGE TO FACILITY TYPE . DESCRIPTION 7EID8 9lLl NA 10!::--------------------'--....--....;._--------------......:.--------8~0 PUBLICITY

[fill NA

. 7 8 9 80 ADDITIONAL FACTORS Eifil 7 8 9

• N 60 7~B.9~.----,.-----------.--.------~~----------------....:...------_..:.....:...__......."--~ ~ ED

.. NA-'\1E~.~._,___J_e_f_f_e_r_y....,.R_._w_o_J_*n_a_r_o_w""'s_k_i- - - - - - - - PHONE: _ _E_x_t_._\..;;;~23);;;;;2;;;.___

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 p~ocedural rod selections. Although the Tech Specs require the RBM to be

• operab 1e 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 B~8, since both control rods are located one position i~side 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 deem~d~)warranted. The Rod Block Monitoring system. was supplied by the General Electric Company.