Regulatory Guide 5.27

Special Nuclear Material Doorway Monitors

ML003740050
Person / Time
Issue date:	06/30/1974
From:	Office of Nuclear Regulatory Research
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RG-5.27
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June 1974 U.S. ATOMIC ENERGY COMMISSION

REGULATORY GUIDE

DIRECTORATE OF REGULATORY STANDARDS

REGULATORY GUIDE 5.27 SPECIAL NUCLEAR MATERIAL DOORWAY MONITORS

A. INTRODUCTION

2. General Characteristics Typically, the detectors of a doorway monitor are Paragraph (b), "Exit Requirement," of § 73.60, "Ad NaI(Tl) scintillators or solid or liquid organic scintilla ditional Requirements for the Physical Protection of tors. Geiger-Mueller detectors have also been used in this Special Nuclear Material at Fixed Sites," of 10 CFR Part application, although the lower intrinsic efficiency of

73, "Physical Protection of Plants and Materials,"

these detectors renders them less suitable than scintilla requires that individuals exiting from material access tion detectors.

areas be searched for concealed special nuclear material Detectors are arranged such that a detection area is (SNM). This guide describes means acceptable to the Regulatory staff for employing SNM doorway monitors defined by a plane perpendicular to the line of passage of individuals through the doorway monitor. Various to comply with that requirement.

arrangements of the detectors are possible; however, specific placement of detectors is usually dictated by the

B. DISCUSSION

need to eliminate dead spots.

Special nuclear material doorway monitors provide an Some commercially available doorway monitors are efficient, sensitive, and reasonably unobtrusive means of equipped with an automatic background updating searching individuals exiting from a material access area system. The automatic background updating system for concealed SNM. With proper installation and opera periodically monitors and averages the background. A

tion, gram quantities or less of SNM can be detected doorway monitor equipped with an automatic back with a high level of reliability while maintaining a low ground updating system is also provided with a treadle false alarm rate. pad or beam-break system to indicate that the sensitive area is occupied. When the sensitive area is occupied, the I. Theory of Operation radiation level detected by the doorway monitor is The doorway monitor is composed of a detector compared with the mean background. If the level is unit(s), associated electronics, and alarm logic. The "significantly" greater than the mean background, an detector unit(s) is sensitive to the radiations which alarm condition ensues. Significance is usually deter emanate from the SNM and responds to these radiations mined by comparing the radiation level when the (usually gamma rays) by generating current pulses. These sensitive area is occupied with the mean background plus pulses are amplified, filtered, and fed to alarm logic some multiple of the square root of the mean back v'hich interprets the number (or rate) of pulses in some ground*

period of time, for example, one second. The alarm logic may be either a digital or analog system; in either case, if *The square root of the mean of a Poisson-distributed quantity the number (or rate) of pulses exceeds a set level, an is the unbiased estimate of the standard deviation of that alarm condition ensues. quantity.

USAEC REGULATORY GUIDES Copies of published guides may be obtained by request indicating the divisions desired to the US. Atomic Energy Commission, Washington, D.C. 20545, Regulatory Guides are issued to describe and make available to the public Attention: Director of Regulatory Standards. Comments and suggestions for methods acceptable to the AEC Regulatory staff of implementing sPecific parts of improvements in these guides ae encouraged and should be sent to the Secretary the Commission's regulations, to delineate techniques .ned by the staff in of the Commission, US. Atomic Energy Commission, Washington, D.C. 20545, evaluating specific problems or postulated accidents, or to provide guidance to Attention: Chief, Public Proceedings Staff.

applicants. Regulatory Guides are not substitutes for regulations and compliance with them is not required. Methods and solutions different from those set out in The guides ae issued in the following ten broad divisions:

the guides will be acceptable if they provide a basis for the findings requisite to 6. Products the imuance or ontinuance of a permit or license by the Commissio

1. Power Reactors

2. Reaseerd enidTest Reactors

7. Transportation

3. Fuels and Materials Facilities 8. Occupational Health Published guidas will be revised periodically, asappropriate, to accommodate 4. Environmental and Siting 9. Antitrust Review comments amd to refloct new informeaion or experience. 5. Materials and Plant Protection 1

0. General

Thus the condition for an alarm can be written as Areas, and Material Access Areas,") in such a manner that objects cannot be passed over, around, or under the G > B + n, detection area.

. (2) The detector elements should be designed and where B is the mean background, G is the radiation level positioned so that detection sensitivity is as uniform as with the sensitive area occupied, and n is a multiplier, possible over the detection area; in no case should any usually an integer between 4 and 10.* The value of n areas where SNM is not detectible be permitted.

directly affects the false alarm rate, and the combination (3) Power, sensitivity, and other controls of the of B and n affect the sensitivity. doorway monitor should be tamper-safed when unat tended.

Although the automatic background updating system (4) Signal lines connecting alarm relays to the allows unattended use of the doorway monitor, for alarm monitor should be supervised.

technical reasons, the system may be less effective in (5) Some doorway monitors may require an indi certain situations. Techniques to prevent this are des vidual to occupy the detection area for a specified time, cribed in the Regulatory Position. longer than a normal walking pace would provide. If this is the case, the doorway monitor should be provided Doorway monitors not equipped with an automatic with a treadle pad and a "clock" device to assure that background updating system either must rely on the the detection area is occupied for the requisite time. An inherent sensitivity of the instrument and low back aural and visual indication should be given if an ground variation to ensure that concealed SNM will be individual being searched does not occupy the area detected or must be attended so that a measurement of sufficiently long.

background can be taken immediately prior to use and b. System Specification the alarm level set to maintain the desired sensitivity to (1) Plutonium-239. A doorway monitor used to concealed SNM. As with the doorway monitor equipped detect plutonium should be capable of detecting a with an automatic background updating system, a minimum of 0.5 gram of plutonium-239 encased in a doorway monitor not so equipped compares the activity minimum of 3 mm of brass at a 90% confidence limit.

with the detection area occupied with some set value, The false alarm rate should be less than 0.1% (Appendix usually the measurement of background taken just prior C).

to use. In any case, the expression above can be used as a (2) Uranium-233. A doorway monitor used to condition of alarm by replacing B + nr'Wwith the set detect uranium-233 should be capable of detecting level. within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> of purification* a minimum of 1 gram of uranium-233 containing between 7 and 10 ppm of Whether or not a doorway monitor is equipped with uranium-232 encased in a minimum of 3 mm of brass at an automatic background updating system, high back a 90% confidence limit. The false alarm rate should be ground activity will decrease sensitivity. Measuring activ less than 0.1% (Appendix C).

ity for longer periods will somewhat compensate for (3) Uranium-235. A doorway monitor used to high background; however, longer measurement periods detect uranium-235 should be capable of detecting a will make use of the doorway monitor less convenient. minimum of 3 grams of uranium-235 contained in uranium enriched to 20% or more in the uranium-235

C. REGULATORY POSITION

isotope encased in a minimum of 3 mm of brass at a 50%

confidence limit. The false alarm rate should be less than

1. Minimum Qualifications for SNM Doorway Monitors 0.1% (Appendix C).

a. General

(1) SNM Doorway monitors should be used in 2. Use of Doorway Monitors conjunction with a metal detector and should be In general, doorway monitors should be used in installed in a passageway (see Regulatory Guide 5.7, locations of minimum background and minimum back

"Control of Personnel Access to Protected Areas, Vital ground fluctation. If circumstances dictate use of a doorway monitor in an area of high background,

• Note that, in general, for a count rate system, the condition for sufficient shielding should be provided to maintain afarm should be modified to account for the response time of necessary sensitivity.

the instrument as follows:

a. Attended Doorway Monitor G > B + n1]0l - e-t/7) (1) If the doorway monitor is attended during where t is the counting time and r is the time constant of the use, it need not be equipped with an automatic instrument. If, as should be the case, t/,r > 5 the added factor is essentially unity. *Purification means removal of all decay products.

5.27-2

(d) Activate the electronics and alarm logic background updating system, although such capability is when an individual is within the detection area and preferred. initiate operation of the doorway monitor.

(2) Prior to each use* of a doorway monitor not (3) An alarm should sound in the central alarm equipped with an automatic background updating station if, when occupied, the activity in the detection system, a measurement of background should be taken, area exceeds the internally set threshold level (the mean and the alarm threshold should be set to the proper background plus some multiple times the square root of value listed in Table I for the measured background and the mean background), as such a situation would the proper n value as determined in Appendix B. Each indicate the presence of SNM upon the individual being individual to be checked should, in turn, enter the checked.

detection area and be required to remain sufficiently (4) The doorway monitor should be equipped long for the device to operate properly. During use, the with a high-background alarm which will sound if the background should be checked and the alarm threshold average background at the location of the doorway reset at least each 15 minutes. monitor exceeds the appropriate maximum permissible

(3) With the individual being checked in the background level listed in Table II as determined in detection area, an alarm should sound if the activity in Appendix C. The doorway monitor should not be used the detection area exceeds the alarm threshold T, as such during such periods of high background. Other moni a situation would indicate the presence of SNM. tored exits should be used.

(4) The doorway monitor should be equipped with a high-background alarm which will sound if the 3. Testing and Calibration measurement of background exceeds the appropriate a. Testing maximum permissible background level listed in Table II Doorway monitors should be tested by passing an as determined in Appendix C. The doorway monitor appropriate source of the amount and isotope specified should not be used during such periods of high back in Regulatory Position C.l.b. through the doorway ground. monitor no less frequently than once per day.* In b. Unattended Doorway Monitor addition, a functional performance test should be carried

(1) If the doorway monitor is unattended, an out at least once per week. An acceptable functional automatic background update system should be incor performance test procedure is discussed in Appendix A

porated into the doorway monitor electronics and alarm of this guide logic. The control circuitry, if possible, should be located b. Calibration at the central alarm station (or other monitoring point). Doorway monitors should be calibrated with a

(2) Door interlocks and closed-circuit TV in source of the amount, configuration, and variety of SNM

combination with beam breaks, motion detectors, and/ to be detected (e.g., 0.5 gram Pu in 3 mm of brass).

or treadle pads, should be employed to: Calibration should be carried out according to a proce (a) Indicate to the person manning the central dure such as that in Appendix B.

alarm station that an individual has entered the secure c. Operating Instructions access passageway and/or is approaching the doorway Operating instructions should be posted near the monitor, doorway monitor,* if attended, or at the monitoring (b) Allow observation of the individual ap point if the doorway monitor is unattended. The proaching the doorway monitor, instructions should clearly indicate the procedure for use (c) Preclude a slow approach to the sensitive of the doorway monitor and the procedure for setting area of the doorway monitor, and thresholds, if appropriate. In addition, the operating instructions should indicate what corrective action is to

• By use is meant an individual or several individuals, each, in be taken and who is to be notified in the event of a turn, being checked for SNM by the doorway monitor. The malfunction.

maximum period between threshold sets while the doorway monitor is in use is determined by the stability of local *Doorway monitors used to search for concealed U-233 should background and may necessarily be more frequent than every be tested according to §6 of Appendix A.

15 minutes.

5.27-3

TABLE I

ALARM THRESHOLD

T

B n= 4 5 6 7 8 9 10

100 140 150 160 170 180 190 200

120 164 175 186 197 208 219 230

140 .187 199 211 223 235 246 258

160 211 223 236 249 261 274 286

180 234 247 260 274 287 301 314

200 257 271 285 299 313 327 341

220 279 294 309 324 339 353 368

240 302 317 333 348 364 379 395

260 324 341 357 373 389 405 421

280 347 364 380 397 414 431 447

300 369 387 404 421 439 456 473

320 392 409 427 445 463 481 499

340 414 432 451 469 488 506 524

360 436 455 474 493 512 531 550

380 458 477 497 516 536 555 575

400 480 500 520 540 560 580 600

420 502 522 543 563 584 604 625

440 524 545 566 587 608 629 650

460 546 567 589 610 632 653 674

480 568 590 611 633 655 677 699

500 589 612 634 657 679 701 724

520 611 634 657 680 702 725 748

540 633 656 679 703 726 749 772

560 655 678 702 726 749 773 797

580 676 700 724 749 773 797 821

600 698 722 747 771 796 820 845

620 720 744 769 794 819 844 869

640 741 766 792 817 842 868 893

660 763 788 814 840 866 891 917

680 784 810 836 863 889 915 941

700 806 832 859 885 912 938 965

720 827 854 881 908 935 961 988

740 849 876 903 930 958 985 1012

760 870 898 925 953 981 1008 1036

780 892 920 948 975 1003 1031 1059

800 913 941 970 998 1026 1055 1083

820 935 963 992 1020 1049 1078 1106

840 956 985 1014 1043 1072 1101 1130

860 977 1007 1036 1065 1095 1124 1153

880 999 1028 1058 1088 1117 1147 1177

900 1020 1050 1080 1110 1140 1170 1200

920 1041 1072 1102 1132 1163 1193 1223

940 1063 1093 1124 1155 1185 1216 1247

960 1084 1115 1146 1177 1208 1239 1270

980 1105 1137 1168 1199 1230 1262 1293

5.27-4

TABLE I (Cont'd)

ALARM THRESHOLD

T

B n = 4 5 6 7 8 9

1000 1126 1158 1190 1221 1253 1285 1316

1200 1339 1373 1408 1442 1477 1512 1546

1400 1550 1587 1624 1662 1699 1737 1774

1600 1760 1800 1840 1880 1920 1960 2000

1800 1970 2012 2055 2097 2139 2182 2224

2000 2179 2224 2268 2313 2358 2402 2447

2200 2388 2435 2481 2528 2575 2622 2669

2400 2596 2645 2694 2743 2792 2841 289C

2600 2804 2855 2906 2957 3008 3059 3110

2800 3012 3065 3117 3170 3223 3276 3329

3000 3219 3274 3329 3383 3438 3493 3548

3200 3426 3483 3539 3596 3653 3709 3766

3400 3633 3692 3750 3808 3866 3925 3983

3600 3840 3900 3960 4020 4080 4140 4200

3800 4047 4108 4170 4232 4293 4355 4416

4000 4253 4316 4379 4443 4506 4569 4632

4200 4459 4524 4589 4654 4718 4783 4848

4400 4665 4732 4798 4864 4931 4997 5063

4600 4871 4939 5007 5075 5143 5210 5278

4800 5077 5146 5216 5285 5354 5424 5493

5000 5283 5354 5424 5495 5566 5636 5707

5200 5483 5561 5633 5705 5777 5849 5921

5400 5694 5767 5841 5914 5988 6061 6135

5600 5899 5974 6049 6124 6199 6273 6348

5800 6105 6181 6257 6333 6409 6485 6562

6000 6310 6387 6465 6542 6620 6697 6775

6200 6515 6594 6672 6751 6830 6909 6987

6400 6720 6800 6880 6960 7040 7120 7200

6600 6925 7006 7087 7169 7250 7331 7412

6800 7130 7212 7295 7377 7460 7542 7625

7000 7335 7418 7502 7586 7669 7753 7837

7200 7539 7624 7709 7794 7879 7964 8049

7400 7744 7830 7916 8002 8088 8174 8260

7600 7949 8036 8123 8210 8297 8385 8472

7800 8153 8242 8330 8418 8507 8595 8683

8000 8358 8447 8537 8626 8716 8805 8894

8200 8562 8653 8743 8834 8924 9015 9106

8400 8767 8858 8950 9042 9133 9225 9317

8600 8971 9064 9156 9249 9342 9435 9527

8800 9175 9269 9363 9457 9550 9644 9738

9000 9379 9474 9569 9664 9759 9854 9949

9200 9584 9680 9775 9871 9967 10063 10159

9400 9788 9885 9932 10079 10176 10273 10370

9600 9992 10090 10188 10286 10384 10482 10580

9800 10196 10295 10394 10493 10592 10691 10790

5.27-5

TABLE II

MAXIMUM PERMISSIBL

E. BACKGROUND

a = 0, Pa = 50%

B

G n= 4 5 6 7 8 10

9

100 67 61 55 50 46 42 38

120 83 76 70 64 59 54 50

140 100 92 85 78 72 67 62

160 117 108 100 93 86 80 74

180. 134 124 116 107 100 93 87

200 151 141 131 123 114 107 100

220 168 157 147 138 129 121 113

240 186 174 163 153 144 135 127

260 203 191 180 169 159 150 141

280 221 208 196 185 174 165 155

300 238 225 213 201 190 179 170

320 256 242 229 217 205 194 184

340 274 259 246 233 221 210 199

360 292 277 263 249 237 225 214

380 310 294 280 266 253 240 229

400 328 312 297 282 269 256 244

420 346 329 314 299 285 272 259

440 364 347 331 316 301 287 274

460 382 365 348 332 317 303 290

480 400 382 365 349 334 319 305

500 418 400 383 366 350 335 321

520 436 418 400 383 367 351 337

540 455 436 417 400 383 367 352

560 473 454 435 417 400 384 368

580 491 471 452 434 417 400 384

600 510 489 470 451 433 416 400

620 528 507 488 468 450 433 416

640 546 525 505 486 467 449 432

660 565 543 523 503 484 466 448

680 583 562 541 520 501 482 464

700 602 580 558 538 518 499 481

720 620 598 576 555 535 516 497

740 639 616 594 573 552 532 513

760 657 634 612 590 569 549 530

780 676 652 629 607 586 566 546

800 695 671 647 625 603 583 563

820 713 689 665 643 621 600 579

840 732 707 683 660 638 617 596

860 750 725 701 678 655 633 613

880 769 744 719 695 673 650 629

900 788 762 737 713 690 667 646

920 806 780 755 731 707 685 663

940 825 799 773 748 725 702 679

960 844 817 791 766 742 719 696

980 863 835 809 784 760 736 713

5.27-6

TABLE II (Cont'd)

MAXIMUM PERMISSIBL

E. BACKGROUND

a -'0, Pa = 50Z

B

G n = 4 5 6 7 8 9 10

1000 881 854 827 802 777 753 730

1200 1069 1039 1009 981 953 926 900

1400 1258 1225 1193 1161 1131 1101 1073

1600 1448 1412 1377 1343 1310 1278 1247

1000 1638 1600 1563 1527 1491 1457 1423

2000 1829 1789 1749 1710 1673 1636 1600

2200 2020 1978 1936 1895 1855 1816 1778

2400 2212 2167 2124 2081 2039 199D 1958

2600 2404 2357 2312 2267 2223 2180 2138

2800 2596 2548 2500 2453 2407 2363 2318

3000 2789 2738 2689 2640 2593 2546 2500

3200 29S2 2929 2878 2828 2778 2730 2682

3400 3175 3121 3068 3016 2964 2914 2865

3600 3368 3312 3258 3204 3151 3099 3048

3800 3561 3504 3448 3392 3338 3284 3232

4000 3755 3696 3638 3581 3525 3470 3416

4200 3949 3888 3829 3770 3713 3656 3600

4400 4143 4081 4020 3960 3900 3842 3785

4600 4337 4273 4211 4149 4088 4029 3970

4800 4531 4466 4402 4339 4277 4216 4155

5000 4725 4659 4593 4529 4465 4403 4341

5200 4919 4852 4785 4719 4654 4590 4527

5400 5114 5045 4977 4910 4843 4778 4713

5600 5309 5238 5169 5100 5032 4966 4900

5800 5503 5432 5361 5291 5222 5154 5087

6000 5698 5625' 5553 5482 5411 5342 5274

6200 5893 5819 5745 5673 5601 5531 5461

6400 6088 6012 5938 5864 5791 5719 5648

6600 6283 6206 6130 6055 5981 5908 5836

6800 6478 6400 6323 6247 6172 60'97 6024

7000 6673 6594 6516 6438 6362 6286 6212

7200 6868 6788 6709 6630 6552 6476 6400

7400 7064 6982 6902 6822 6743 6665 6588

7600 7259 7176 7095 7014 6934 6855 6777

7800 7455 7371 7288 7206 7125 7045 6965

8000 7650 7565 7481 7398 7316 7234 7154

8200 7846 7760 7674 7590 7507 7425 7343

8400 8041 7954 7868 7782 7698 7615 7532

8600 8237 8149 8061 7975 7889 7805 7721

8800 8433 8343 8255 8167 8081 7995 7911

9000 8628 8538 8449 8360 8272 8186 8100

9200 8824 8733 8642 8553 8464 8376 8290

9400 9020 8928 8836 8745 8656 8567 8479

9600 9216 9122 9030 8938 8348 8758 8669

9800 9412 9317 9224 9131 9039 8949 8859

5.27-7

TABLE II (Cont'd)

MAXIMUM PERMISSIBL

E. BACKGROUND

S= 1.3, Pa = 90%

B

G n 4 5 6 7 8 9 10

100 57 51 46 42 38 34 31

120 72 65 59 54 49 45 41

140 87 80 73 67 62 57 52

160 103 95 87 81 75 69 64

180 119 110 102 95 88 81 76

200 135 126 117 109 101 94 FS

220 151 141 132 123 115 107 100

240 168 157 147 138 129 121 113

260 185 173 163 153 143 135 127

280 201 189 178 168 158 149 1L0

300 218 206 194 183 172 163 154

320 235 222 210 198 187 177 167

340 252 239 226 214 202 191 181

360 270 255 242 229 217 206 196

380 287 272 258 245 233 221 210

400 304 289 275 261 248 236 224

420 322 306 291 277 263 251 22S

440 339 323 308 293 279 266 254

460 357 340 324 309 295 281 268

480 374 357 341 325 311 297 283

500 392 374 357 342 326 312 298

520 409 391 374 358 342 327 313

540 427 409 391 374 358 343 329

560 445 426 408 391 374 359 344

580 463 443 425 407 391 375 359

600 480 461 442 424 407 390 375

620 498 478 459 441 423 406 390

640 516 496 476 457 439 422 406

660 534 513 493 474 456 438 421

680 552 531 511 491 472 454 437

700 570 549 528 508 489 470 453

720 588 566 545 525 505 487 469

740 606 584 562 542 522 503 485

760 624 602 580 559 539 519 500

780 642 619 597 576 555 535 516

800 660 637 614 593 572 552 532

820 679 655 632 610 589 568 549

840 697 673 649 627 605 585 565

860 715 690 667 644 622 601 581

880 733 708 684 661 639 618 597

900 751 726 702 679 656 634 613

920 770 744 720 696 673 651 630

940 788 762 737 713 690 668 646

960 806 780 755 731 707 684 662

980 824 798 773 748 724 701 679

5.27-8

TABLE II (Cont'd)

MAXIMUM PERMISSIBL

E. BACKGROUND

a = 1.3, P= = 90%

G n= 4 5 6 7 8 9 10

1000 843 816 790 765 741 718 695

1200 1027 997 968 940 913 887 861

1400 1212 1180 1148 1117 1088 1059 1030

1600 1398 1363 1329 1296 1264 1232 1201

1800 1536 it48 1512 1476 1441 1407 1374

2000 1773 1734 1695 1657 1620 1584 1548

2200 1962 1920 1879 1839 1800 1761 1724

2400 2151 2107 2064 2022 1980 1940 1900

2600 2340 2294 2249 2205 2162 2119 2078

2800 2530 2482 2435 2389 2344 2300 2256

3000 2720 2670 2622 2574 2527 2481 2435

3200 2911 2859 2808 2759 2710 2662 2615

3400 3101 3048 2996 2944 2894 2844 2795

3600 3292 3238 3183 3130 3078 3027 2976

3800 3484 3427 3371 3317 3263 3210 3158

4000 3675 3617 3560 3503 3448 3393 3340

4200 3867 3807 3748 3691 3634 3577 3522

4400 4059 3998 3937 3878 3319 3762 3705

4600 4251 4188 4126 4066 4006 3946 3888

4800 4443 4379 4316 4253 4192 4131 4072

5000 4636 4570 4505 4442 4379 4317 4256

5200 4828 4761 4695 4630 4566 4502 4440

5400 5021 4953 4885 4819 4753 4688 4624

5600 5214 5144 5075 5007 4940 4874 4809:

5S00 5407 5336 5266 5196 5128 5061 4994

6000 5600 5528 5456 5386 5316 5247 5180

6200 5793 5720 5647 5575 5504 5434 5365

6400 5987 5912 5S38 5765 5692 5621 5551

6600 6180 6104 6029 5954 5831 580G 5737

6800 6373 6296 6220 6144 6070 5996 5923

7000 6567 6488 6411 6334 6258 6184 6110

7200 6761 6681 6602 6524 6447 6371 6296

7400 r9955 6874 6794 6715 6636 6559 6483

7600 7148 7066 6985 6905 6826 6747 6670

7800 7342 7259 7177 7096 7015 6936 6857

8000 7536 7452 7369 7286 7205 7124 7044

8200 7731 7645 7561 7477 7394 7313 7232

8400 7925 7838 7753 7668 7584 7501 7419

8600 8119 8031 7945 7859 7774 7690 7607

8800 3313 8225 8137 8050 7964 7879 7795

9000 8508 8418 8329 8241 8154 8063 7983

9200 8702 8611 8521 8433 8345 8257 8171

9400 8897 8805 8714 8624 8535 8447 8360

9600 9091 8998 8906 8815 8725 8636 8548

98-00 9286 9192 9099 9007 8916 8826 8737

5.27-9

APPENDIX A

PROCEDURE FOR TESTING SNM DOORWAY MONITORS

FOR

FUNCTIONAL PERFORMANCE

Doorway monitors should be tested by employing a background taken immediately after the test varies by test source of the same isotope of SNM the doorway more than 2vN from the background taken before the monitor is used to detect as follows: test, the test should be repeated, for such a difference indicates nonrandom fluctuations of the background or

1. With the detection area unoccupied, measure and equipment malfunction. The probability of such an record background. occurrence due to the randomness of the background is less than 8%.

2. Determine alarm threshold T from Table I (see Appendix B). 5. A calibration source (Appendix B) should be carried repeatedly to various places within the detection area of

3. Place a test source in the detection area of the the doorway monitor in simulation of actual use to doorway monitor. The test source should be such that verify that the SNM can be detected everywhere within the activity in the detection area slightly exceeds the T the detection area and to assure proper operation of level.* The doorway monitor should go into an alarm treadle pads, beam-break, or similar devices if the condition if operating properly. doorway monitor is so equipped.

4. Remove test source to its original location and 6. Doorway monitors used to search for concealed measure background once again. If the measurement of uranium-233 should be tested with each uranium purification run, but no more frequently than daily. The

• The test source may be improvised by partially shielding the test source should be freshly purified uranium-233 calibration source. (within four hours of removal of decay products).

5.27-10

APPENDIX B

PROCEDURE FOR DETERMINING MAXIMUM PERMISSIBL

E. BACKGROUND

Background should be measured over several work found from Table II, the sensitivity of the doorway shifts to determine the setpoints for alarm threshold monitor will generally be below that specified as (with or without automatic background updating) to minimum in Regulatory Position C.l.b of this guide.

assure that normal operation will be minimally affected by alarms due to high background. The parameter n is a function of the background variation and the permissible false alarm rate and is The doorway monitor should be calibrated with the calculated from amount of the appropriate isotope specified in Regula tory Positions C.l.b(1), (2), or (3) of this guide (e.g., 0.5 1 /2 gram plutonium-239 in 3 mm of brass). n >3.1 (var B) (2)

The calibration procedure described below is essen tially a means of determining maximum permissible Generally, n is taken as an integer. If n satisfies the background for effective operation of the doorway above expression, the expected false alarm rate (Appen monitor. dix C) due to background fluctuations should be less than 0.1%. Larger values of n will decrease the expected

1. Place a calibration source variously about the detec false alarm rate; however, the maximum allowable tion area and take readings to determine the least background for a given G will also decrease.

sensitive point. This location of minimum sensitivity should be maintained as the calibration point. 4. For doorway monitors equipped with automatic background updating systems, the alarm threshold is

2. Measure background over several workshifts to deter mine the periods of high background and the range of Counts > B + nVii, (3)

background. A minimum of 20 measurements should be taken. The variance of the background is given by where n should be derived from expression (2), and the instrument set accordingly.

N

Var B 1 N*- (Bi-B)2 (1) 5. The high-background alarm should be set at the B

value given in Table II for the measured G and calculated n values.

where N is the number of measurements, B is the mean ith of the background measurements, and Bi is the 6. For doorway monitors not equipped with an auto background measurement. matic background update, the value of n determined above should be employed in the use of the doorway

3. With the calibration source at the calibration point, monitor according to Regulatory Position C.2.a.

the mean gross counts G should be determined during a *The false alarm rate is estimated by the probability that an period of high background to establish the upper observation of a quantity distributed normally about some operating range of the doorway monitor. Table II lists value X will exceed X by n(Std. deviation of X). The factor 3.1 various maximum permissible background levels for a limits the false alarm rate to 0.1%, while the factor given value of G for values of the parameters n and a. (Var B/B) 1 /2 compensates for observed deviations in the During periods when the background exceeds the value background distribution from Poisson.

5.27-11

APPENDIX C

DETECTION CONFIDENCE LIMITS, THRESHOLDS,

AND MAXIMUM PERMISSIBL

E. BACKGROUND

With a calibration source at the calibration point, the The condition for a false alarm* is written as condition for an alarm is, in general, b= B +j a-'"B> T (4)

g> T = B + m/Va' B (1) where b is a single measurement without the source and

0 is a number corresponding to a false alarm probability Pp. For P = 0.1%, 0 = 3.1. Hence the necessary where g is a single measurement of G (the mean condition for maintaining a false alarm rate below Pp is radiation level with the source), B is the mean back ground, and m is some multiplier. The detection b= B+ -"B < B+ m ar. (5)

confidence limit is the probability that with the calibra However, the doorway monitor actually compares b iton source at the calibration point, any single determin with B + ni, hence the condition on n becomes ation of G will exceed a threshold T, i.e., the above inequality will be satisfied. For any given probability Pa., orV < rn'VaTr = nvff (6)

there exists a value a such that or g > G- (2) n>0 ( Va B ) 1/2 (7)

In Table I threshold values of T were determined by with a probability of Pa, where g is any single measure substituting equation (6) into equation (3):

ment of the quantity G. Hence the condition for a detection confidence limit of Pais T = B + nv'r The values of B in Table II were then calculated for G- & _-r*-G > T = B + m,,/'r B. (3) a = 1.3 and a = 0 from equation (3) assuming that, for the determination of G, the background should be reasonably stable and therefore \/Var G -\

For a given value of G, solving (3) gives the maximum permissible B at which the doorway monitor will detect *False alarm means an alarm condition generated by statistical the source with a confidence Pr-For Pa = 90%, a = 1.3, fluctuations in the background radiation or by instabilities of the electronics which appear as background fluctuations when and for Pa = 50%, a = 0. the detection area is occupied.

5.27-12