martin.kreativermoment on "Strip Shortcodes from RSS"

Hi, I'm not sure if this is the right section.
If not not, please move.

I got this template to create my rss, but all shortcodes are shown in plaintext.

<?php
/*
Template Name: Custom Feed
*/

$numposts = 10;

function yoast_rss_date( $timestamp = null ) {
  $timestamp = ($timestamp==null) ? time() : $timestamp;
  echo date(DATE_RSS, $timestamp);
}

function yoast_rss_text_limit($string, $length, $replacer = '...') {
  $string = strip_tags($string);
  if(strlen($string) > $length)
    return (preg_match('/^(.*)\W.*$/', substr($string, 0, $length+1), $matches) ? $matches[1] : substr($string, 0, $length)) . $replacer;
  return $string;
}

$posts = query_posts('showposts=5');

$lastpost = $numposts -1;

header("Content-Type: application/rss+xml; charset=UTF-8");
echo '<?xml version="1.0"?>';
?><rss version="2.0">
<channel>
  <title></title>
  <link></link>
  <description></description>
  <language>de_DE</language>

<?php foreach ($posts as $post) { ?>

  <item>

    <title><?php echo get_the_title($post->ID); ?></title>
	    <link><?php echo get_permalink($post->ID); ?></link>
	<description><![CDATA[ <br /> ]]><?php echo '<![CDATA[' .get_the_post_thumbnail($post->ID, 'thumbnail') .']]>' ?><![CDATA[ <br /> ]]><?php echo '<![CDATA['.yoast_rss_text_limit($post->post_content, 500).'<br/><br/>Weiterlesen: <a href="'.get_permalink($post->ID).'">'.get_the_title($post->ID).'</a>'.']]>';  ?></description>
    <pubDate><?php yoast_rss_date( strtotime($post->post_date_gmt) ); ?></pubDate>
    <guid><?php echo get_permalink($post->ID); ?></guid>
  </item>

 <?php } ?>
</channel>
</rss>

Tried to use strip_shortcodes but I don't know where to place this. It dives me an empty page, or (on another position) it changes nothing.

Please help me out

Thanks